Masters Degrees (Zoology)

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Intersex in four South African racial groups in Durban.
(1970) Grace, Hatherley James.; Bain, Peter G.
Chapter I The ontogeny of sex development is introduced and a definition of the intersexual state is given. A resume of intersexes recorded in South Africa is presented together with figures showing the increased demand for cytogenetic services in the country. The motivation for this study is discussed. Chapter II The biological concept of sex is outlined together with notes on the evolution of the dioecious state in animals. Thereafter a brief account of the normal and abnormal intersex states in invertebrates and vertebrates is given. Chapter III Examples of some of the abundant references to ambisexual individuals found in the classical literature, history and mythology are listed and the status of intersexes in modern society is discussed: it does not vary much from the times of ancient Greece and Rome. Chapter IV A summary of the events which led to the establishment of cytogenetics as an independent discipline is given. The discovery of nuclear sex dimorphism is noted and methods of investigation of intersexual patients are described. A detailed description is given of cytogenetic technical. "methods, ; and leads to a diagrammatic explanation of the differential diagnosis of intersexes. This is used as a basis for the classification and accordingly a simplified, unambiguous system is proposed and defended. The sources and numbers of pat~ ients recorded in this thesis are explained. Chapter V The sex chromatin is described in detail? with a description of the methods used for its demonstration and evaluation. A pilot study of normal women of the four races established that there is no inter-racial variation in chromatin frequency. Reasons are given for disregarding nuclear appendages as an accurate indication of 'sex '. Chapter VI Embryological stage s i n the development of the human urogenital tracts are recounted after considering the mechanisms of sex determination. Pathogenesis of intersexuality is considered briefly. Chapter VII Gonadal dysgenesis of the female, including Turner's syndrome and phenotypes of both male and female are presented. The classification, pathology, aetiological and cytogenetic factors are described. Illustrative case reports and extensive discussion of the syndrome are presented. Chapter VIII The Klinefelter syndrome occurs in males with supernumerary X chromosomes; a number of chromatin negative, hypogonadal conditions mimic the syndrome: they are described, with notes on the classification, pathology, aetiology and the cytogenetic features. A series of case reports demonstrate both chromatin positive and negative types. Special reference is made to the dermatoglyphic profiles which were discovered to differentiate the XY males into two groups. Chapter IX Three syndromes, the XXX, XYY and agonadism, were not encountered in this study and are consequently not discussed. Chapter X The adrenogenital syndrome has several distinctive signs which are mimicked by induced virilization; these are described and a number of case reports are presented to illustrate the syndromes. Chapter XI Male intersexes occur in several different forms: the classification of the group is explained and a distinction is made between intersexes and those with simple, or 'pseudo-intersexual', defects. The signs of the different syndromes are detailed, together with data concerning the aetiology and cytogenetics. A series of patients' case histories is used to illustrate the various syndromes. Chapter XII Idiopathic female intersexuality is defined and a short explanation of the classification is given. The signs found in this syndrome are detailed and a single case report, which is of exceptional interest because of severe masculinization and the formation of a phallic urethra, is presented. Chapter XIII Hermaphroditism is defined and the subgroups are explained. The variability of signs is discussed and details of anatomy and histology of the genital tract are given . A single hermaphrodite was encountered during the survey and the case is described. Three other patients, all infants, were suspected of being hermaphroditic but because gonadal biopsy was not undertaken they were discharged from hospital without a diagnosis having been made. Discussion of the aetiological mechanisms is presented and the need for early diagnosis and treatment is emphasized. Chapter XIV Some of the simple genital anomalies and somatic defects which resemble intersex are mentioned and are illustrated by attenuated case reports. Chapter XV The incidence of those intersexual conditions recognizable at birth by anatomical deformity is calculated from a total population of 21,000 live births recorded during the calendar year, 1969. The incidence was very low (1:7000) and does not permit analysis of inter-racial distribution. Prevalence is calculated from the number of new patients seen by the author during 1969 in Durban. Some interesting observations were made but the primary objective, to determine whether or not intersexuality is more prevalent in the Bantu than any other race, could not be answered with certainty because of the small number of patients. Hermaphroditism was shown not to be the most common type of intersex syndrome in the Bantu. Chapter XVI An outline is given of the normal dermatoglyphic features of the finger prints and palms. Some references of the patterns in Turner's and Klinefelter's syndromes are available from the literature and are compared with the profiles of patients from this series. A distinct dimorphism was found in chromatin negative hypogonadal males and was thought to distinguish between those with congenital or acquired pathology. Normal values for South Africans have not been established satisfactorily and the urgent need for this information is stressed. Chapter XVII A general discussion of the highlights of this study of the epidemiology, clinical presentation and cytogenetics of intersexuality is given and a number of conclusions are drawn .
Warning vocalisations and predator information transfer in social birds.
(2008) Seoraj-Pillai, Nimmi.; Malan, Gerard.; Slotow, Robert Hugh.
Alarm or warning vocalizations are produced by many animals when they detect a potential predator. However little is known about the information contained in these vocalizations. This study investigated the warning vocalisations of three passerine species, viz. the Buff-streaked Chat Oenanthe bifasciata, the Stonechat Saxicola torquata and the Bronze Mannikin Spermestes cucullatus. The study investigated whether the alarm calls for terrestrial predators differ in their acoustic structure from alarm calls emitted for aerial predators. Birds were exposed to latex terrestrial snakes and mounted aerial raptors, while changes in six acoustic parameters of alarm calls were measured. Bronze Mannikins were investigated for differences in intra-specific alarm calls between familiar and unfamiliar group members by capturing wild groups of mannikins and randomly mixing these to form assorted groups. Bronze Mannikins emitting warning calls were able to discriminate differences in predator size, and increased their calling rate and decreased the end frequency of the alarm call in response to larger predators. This may be the caller’s response to increased threat or variation in frequency may obscure cues to the caller’s whereabouts. Assorted group members were less aggressive to predator models than original members and panicked more during confrontations. Hence the unfamiliarity of the caller may have disrupted group cohesion. The alarm call acoustics of the social Buff-streaked Chats and the solitary Stonechat were compared to examine the effect of group-living on alarm behaviour. Snakes elicited louder calls from both the chat species than raptors. Louder and collectively more vocal social groups might be more successful in discouraging attacks than an asocial species. Variation in amplitude and call frequencies by the Stonechat provided some evidence that they are equally adapted to identifying predator type. Although Buff-streaked Chats increased their call rate in response to nearby predator models, Stonechats produced shorter calls in response to terrestrial predation particularly when the predators were in close proximity. Knowledge gained through direct encounters with predators or the ease with which raptors and snakes can gain access to nests may have played a part in discrimination of predator threat. Overall this study indicated strong correlations between some alarm acoustic parameters and predator size as well as the degree of threat.
Patterns of distribution, diversity and endemism of terrestrial molluscs in South Africa.
(2007) Govender, Vanashrie.; Slotow, Robert Hugh.; Herbert, David Guy.
Molluscs are an important component of South Africa’s biodiversity. The assessment of distribution patterns and factors influencing the biogeographic distribution are an integral part of assessing the conservation status of molluscs and their conservation management needs. The existing terrestrial mollusc data from South Africa were assessed in terms of their value to biodiversity conversation planning and management. Although the data on terrestrial molluscs are incomplete and would be misleading in terms of identifying specific areas for protection, the data do illustrate significant patterns and trends of mollusc endemism and diversity, which can be used to improve biodiversity conservation and management efforts. The distribution of molluscs across the South African landscape illustrated ten broad biogeographical patterns. Two of these patterns reflected ancient distribution patterns of molluscs and consisted of molluscs of the Gondwanaland/southern relict and Laurasian origins. Three biogeographic patterns occurred across the eastern regions. These patterns were defined as the tropical/subtropical east African, subtropical east of southern Africa and east African afromontane patterns. The biogeographic patterns in the west consisted of the characteristic temperate ‘Mediterranean’ Cape centre and the arid regions of northwestern Cape, Namibia and parts of Botswana. An additional biogeographic pattern identified as the nama karoo/central west was recognised. The final two biogeographical patterns described taxa that were widely distributed and taxa that exhibited disjunct distributions. Twenty-six families and forty-three genera were associated with more than one biogeographical pattern. The dominant biogeographic pattern was the tropical/subtropical east African component. Twenty-one families and forty-eight genera were associated with this biogeographical pattern. The east African Afromontane pattern was also a conspicuous biogeographic element in South Africa. Fewer families and genera were distributed in the western and central regions. The distributions of terrestrial molluscs were influenced by a combination of various factors, which included the presence of rivers, the escarpment, altitude, humidity, precipitation, temperature and biomes. Rivers could possibly restrict the distribution of certain mollusc taxa but did not appear to be the dominant factor that influenced the distribution of molluscs across the landscape. In terms of the effect of temperature on the distribution of molluscs, the mean daily and mean annual temperatures appeared to have more of an influence on the distribution patterns than the mean daily maximum and minimum temperatures. Mean annual temperatures influenced the distribution of all families and genera. The mean daily maximum temperature appeared to have little or no effect on the distribution of mollusc taxa. Humidity and biomes also appeared to influence the distribution of taxa. The least inhabited biome was the succulent biome. Many mollusc taxa occurred in the wetter, warmer areas with high humidity levels. Areas of high species richness and high endemic species richness in South Africa were identified using two systems of endemism, one based on distinctive gaps in the frequency distribution of terrestrial molluscs in South Africa and the other based on an existing classification of invertebrate endemism (Hamer & Slotow, 2002). Areas of high mollusc species richness and endemism were also compared to areas of high millipede species richness and endemism. The total number of South African mollusc endemics was 370 (83 % of 447 indigenous species). The dominant mollusc families in South Africa were Achatinidae, Charopidae, Streptaxidae, Subulinidae and Urocyclidae. The first system of endemism identified 56 site endemics (species with only one locality), 50 local endemics (0 < maximum distance < 60 km) and 145 regional endemics (60 km < maximum distance < 330 km). The Hamer & Slotow (2002) classification of endemism classed 67 species as site endemics (maximum distance between localities < 10 km), 47 as local (11 km < maximum distance < 70 km) endemics and 59 as regional endemics (71 km < maximum distance < 150 km). The analysis of mollusc data, with both systems of endemism, showed similar areas of high species and endemic species richness. Quarter-degree grid cells with highest species richness overlapped with grid cells with the highest number of endemic species. However these grid cells coincide with areas that have been intensively sampled and this bias limits the application of the data in conservation planning. The patterns of endemism for molluscs and millipedes within the provinces differed, indicating that the inclusion of a single taxon in conservation planning would inadequately reflect the diversity of invertebrates in South Africa. A preliminary list of specific priority endemic sites for terrestrial mollusc conservation was identified. It is essential that the existing data on invertebrates be evaluated and used to identify key patterns and trends in invertebrate diversity as this will allow for the inclusion of invertebrates in biodiversity conservation planning and management. The analysis of the existing mollusc data identified bio geographical patterns that are important to conservation planning both at the local and national level as well as commonalities and differences between molluscs and millipede distributions. The analysis also highlighted the importance of municipal areas for conservation of hotspots of diversity, particularly in the eastern coastal areas of South Africa.
Conservation of the great white pelican (Pelecanus onocrotalus) and the pink-backed pelican (P. rufescens) in south eastern Africa.
(2006) Bowker, Meyrick Brabbin.; Downs, Colleen Thelma.
Of the seven pelican species found world wide, only the Great White Pelican (Pelecanus onocrotalus) and the Pink-backed Pelican (P. rufescens) are found in Africa. The KwaZulu-Natal province of South Africa supports only one breeding site for each of these species, and both sites represent the southern most breeding colonies for the two species in the eastern region of Africa. These nesting sites fall within the Greater St Lucia Wetland Park, and are afforded a degree of protection, but the same is not true for their foraging and dispersal ranges, and this is a cause for concern. Considerable amounts of data have been collected relating to the status, distribution and breeding efforts of these two species in north eastern KwaZulu-Natal. These data have been collected in a variety of ways by a large number of people. Part of this work represents an attempt to collate and summarise these data to produce an estimation of the status, distribution and breeding success of these species, and to evaluate any trends in their demography. For this south eastern region of Africa I estimated the population for the Great White Pelican to range between 6000 and 9000 individuals, and the Pink-backed Pelican to range between 600 and 900 individuals. Pelicans are highly mobile birds, and this allows them to move considerable distances when they forage, disperse or migrate. They are also long-lived birds with few natural predators. The two pelican species in south eastern Africa have been poorly studied and little is known about their movements, population dynamics and causes of mortality. Habitat change poses a potential threat to pelicans in north eastern KwaZulu-Natal, and habitat loss could drive these species out this region to areas north of South Africa. Much of this north eastern region of KwaZulu-Natal is under threat, mainly through the actions of man. Many areas are naturally unsuitable for pelican foraging, while others are vital to the survival of both species. This study includes an attempt to assess the movements of these two species in south eastern Africa, and to assess the relative importance and condition of the potential pelican habitat in the north eastern KwaZulu-Natal region, focusing particularly on Lake St Lucia and the Pongolo River floodplain. All this is necessary to produce a baseline from which long term predictions of potential pelican species survival can be made. In the absence of documented life tables and environmental variability data, a range of parameters was modelled to generate population viability analyses to simulate possible scenarios. These extinction models show the outcomes of both the deterministic and the stochastic processes. An attempt was also made to identify the factors that impact most severely on the persistence of these two species. The models were most sensitive to variation in survivorship in the first year of life and to the frequency of catastrophes. Changes in these parameters had the greatest effect on extinction risk. In January 2004 Lake St Lucia was reduced to a fraction of its normal capacity as a result of a severe drought in this region of KwaZulu-Natal. After rains in the area the lake level rose and then fluctuated considerably over the next 24 months. During this time the mouth of the estuary into the sea was closed. Great White Pelican numbers and lake levels were monitored throughout this period. This part of the study relates the changes in population numbers to the lake conditions, and highlights the importance of the lake to this avian species. It uses lake levels as a proxy for the conditions of wetlands in the Lake St Lucia region. It also addresses the implications of these relationships to the management strategy of the lake and the conservation of some avifauna. To identify conservation concerns for the Great White and Pink-backed Pelicans it was necessary to generate these baseline estimations. Although much of this information is uncertain for these two species, an attempt has been made here to predict the persistence of these species in north eastern KwaZulu-Natal and to highlight the conservation issues related to their future.
Wildlife rehabilitation in South Africa.
(2009) Wimberger, Kirsten.
Wildlife rehabilitation, defined as “providing temporary care to injured, ill and orphaned wild animals with the goal of releasing them back into their natural habitat”, developed in response to the increase in human population and urbanisation. Widllife rehabilitation centres developed to deal with casualties from man-made hazards; and because rehabilitation involves human emotions of empathy and compassion, the activity has not tended to be the domain of wildlife specialists, but of concerned members of the public. This has caused concerns for wildlife specialists over the welfare of animals being rehabilitated, because making decisions based on emotions may result in an animal being kept alive under unethical conditions, instead of being euthansed. Furthermore, there may be negative impacts on conservation, as it could divert money away from habitat protection and may place wild populations at risk from disease and genetic pollution. This dichotomy in opinion is most often seen between rehabilitators, who focus on the individual animal, and government wildlife officials, who grant them permits, and who focus on the security of entire communities. Although the value of wildlife rehabilitation cannot be underestimated, in terms of its service to wildlife and the public, there is a need to evaluate whether wildlife rehabilitation may result in more rather than less animal suffering and have a detrimental impact on the existing wild populations. I thus set out to determine the efficacy of wildlife rehabilitation, particularly in South Africa. In the first assessment of rehabilitation centres in South Africa, 65% known centres (n = 63) from all nine provinces returned questionnaires. Several thousand injured, diseased and orphaned animals pass through these centres each year, clearly showing the need for rehabilitation centres in South Africa. However, due to lack of scientific research on the efficacy of rehabilitation methods of care and release, and minimal post-release monitoring, I found that experience and intuition drove most rehabilitation practices. Additionally, because personnel from most centres cited lack of finance as a main impediment to the goal of rehabilitation, the result of rehabilitation may include negative affects on individual animal welfare and survival, as well as on conservation efforts for wildlife communities. Thus, I suggested wildlife rehabilitation be centralised to a provincial or national government. Furthermore, I suggested that guidelines of minimum standards should be developed in consultation with experienced rehabilitators, veterinarians and conservation scientists; to be enforced by trained and dedicated conservation officials. To gain further insight into the need for wildlife rehabilitation in a community in South Africa, I decided to examine four-years of intake records from a large rehabilitation centre in the KwaZulu-Natal Province for trends. Animal intake rate was high (2701 ± 94 per annum). Most of the intake (90%) was birds, with few mammals (8%) and reptiles (2%), and most of these were of locally common species (eg doves, pigeons). This reflects the findings of other studies, namely that species living in close association with humans are the most frequently admitted to rehabilitation centres. In total, most of the animals admitted (43%) were juveniles, which were assumed to be abandoned or orphaned. The implications of then rehabilitating these juveniles, which were largely uninjured, is whether humans should be interfering with nature if the cause was not human-related; can each juvenile (especially in these large numbers) be adequately prepared to survive and thrive when released into the wild; and is there space in the environment for them, without causing harm to others already in the environment. I suggest that the large numbers of animals currently being admitted to the centre may be reduced, possibly through increased public education particularly to leave uninjured juveniles in the wild. Furthermore, improvements in the centre’s recording system may allow for use in funding requests and for various research opportunities. There is a general lack of post-release monitoring in wildlife rehabilitation, and the IUCN advises that confiscated and orphaned animals should be euthanased or placed in life-time captivity. I thus decided to document the post-release fate of rehabilitated vervet monkeys and leopard tortoises, two species commonly admitted to a rehabilitation centre, and rock hyrax (Procavia capensis), as a further case study, even though individuals were not from a rehabilitation centre. Success of releasing rehabilitated animals cannot be judged on whether it results in a self-sustaining population, as in reintroductions, as it is to improve the welfare of that particular animal, independent of its species’ status. Survival is thus the most basic indicator of a successful rehabilitation release. Other aspects, such as behaving similarly to a wild animal, are additional success factors, as they likely influence survival. Although after one year post-release, the two troops (T1 = 35, T2 = 24) of vervet monkeys (including an infant) survived, were independent of human food provision and companionship, had established in an area, and had births in the breeding season following release; low known survival (T1 = 11%, T2 = 50%) make it difficult to designate these releases as successful. However, it was clear that the two groups of rock hyrax released were not successful. The group of rock hyrax that had previously been in captivity for 16 months (n = 17) did not have site fidelity after release, and after three months could not be found. All wild rock hyrax (n = 9), except one whose fate is unknown, were found dead, mostly predated, within 18 days. The release likely failed due to predation. For both vervet monkeys and rock hyrax, a lack of social cohesion was suggested as causing the group to dissolve or split upon release, which in turn would increase their vulnerability to predation. Recommendations are provided for considerations in future releases of captive vervet monkeys and rock hyrax. Movements of two groups of tortoises (ten and seven individuals) released at two different sites were monitored over a year, using radio-telemetry. In total, one tortoise was returned to captivity because of disease, four were killed intentionally or accidentally by humans, three others died due to a combination of disease, starvation and/or dehydration, and the fate of six were unknown. Since only two out of seven tortoises survived 13 months after release and only one out of ten tortoises were known to have survived 25 months after release, rehabilitated leopard tortoises were not successfully released into the wild. Recommendations to improve the success of future releases are provided. The occurrence of disease in the tortoise release was a worrying result, and must be addressed before any further releases are allowed. To summarise, there is a dichotomy between wildlife rehabilitation and conservation throughout the world, but this study highlighted the situation in South Africa. The IUCN guidelines for the reintroduction, introduction and supplementation of animals make it clear that there are many threats to the individual animal, to the release environment and to the conservation of species when transporting and releasing animals, especially if they had been in captivity. I believe that I have presented enough evidence in the thesis to suggest that wildlife rehabilitation may result in negative consequences to the welfare of the individual being rehabilitated and to the wild conspecifics or to other species in the release site. I suggest that wildlife rehabilitation needs to move away from being an emotional-based “animal-rights” organisation, to being objectively managed, such that no harm is caused to conservation by these efforts. This may require them to change their constitution so they are aligned with the IUCN guidelines, where more consideration is given to the possible risks involved in releasing animals. However, the applicability of the IUCN guidelines will vary slightly according to the species and situation, and they require input from the local conservation authorities (as was the case in the studies documented in this thesis). I suggest that the public be educated as to the risks that wildlife rehabilitated animals can pose to the safety of the environment as a whole, and that rehabilitated animals do not necessarily survive or thrive in the wild when released, and thus they have to understand that rehabilitation centres will sometimes have to prioritise casualties for treatment, and euthanase exotic species. In conclusion, implementing further research in ensuring long-term post-release survival of rehabilitated animals; developing and enforcing practical guidelines/minimum standards by dedicated and qualified governmental wildlife conservation officials; and having examinations in order to qualify as a wildlife rehabilitator, will ensure humans are “making amends” instead of having an additional negative impact on conservation and animal welfare.
Bird community ecology and composition in afrotemperate forests of the Drakensberg Mountains, South Africa.
(2009) Brocklehurst, Zoë Ann.
Recent research has emphasized the importance of understanding the consequences of species loss, not just for biodiversity per se, but also for ecosystem resilience and functioning. Firstly, a baseline analysis of the effects of a naturally patchy landscape on avian community composition and resilience in a high altitude Afrotemperate forest landscape in South Africa is presented. Bird data from a point count survey of 706 counts at 31 forest sites was used to test whether taxonomic species diversity, functional species richness and density of birds provide insight into community resilience in this historically patchy ecosystem. Bird species richness of forest patches ranged from 17 to 38, with a total species richness of 50. Density was slightly but negatively related to both area and species richness. That density compensation is occurring in these Afrotemperate forests suggests a level of resilience in this system. Following on from this, cumulative species-area and function-area graphs were derived to quantify the loss of forest area or taxonomic bird species richness that this landscape may potentially sustain before ecosystem functioning is negatively affected. The concept that species’ patterns of distribution, abundance and coexistence are the result of local ecological processes has recently been challenged by evidence that regionalscale processes are equally instrumental in shaping local community composition. The historically and naturally fragmented Afrotemperate forests of the uKhahlamba– Drakensberg Park, South Africa, offer an interesting test case. In this study the relative effects of local and regional-scale processes on species assemblages in a naturally patchy forest system were investigated. By employing species-area and species-isolation relationships, and nested subset analyses, we showed that isolation (regional-scale process) had a greater effect on bird species richness and composition than area (local-scale process), though the species-area relationship was significant. Using generalized linear models and an information-theoretic approach to model selection, patch area, the size of the regional species pool as well as the distance to the nearest Eastern Mistbelt forest were all influential in determining local bird species richness in these montane forests. Thus, localities are regionally enriched within the constraints on species occupancy provided by the available habitat.
Metabolic physiology of Colubrid dietary specialists, Dasypeltis scabra and Dasypeltis inornata.
(2009) Greene, Sara Nicole.; Perrin, Michael Richard.; McConnachie, Suzanne.
Metabolic rate (MR) and digestive duration are thermally dependant, and energy usage changes as body temperature (Tb) changes. Increased Tb during digestion causes a rapid increase in VO2 and a shorter postprandial metabolic response known as specific dynamic action (SDA). SDA is the additional energy expended above standard metabolic rate (SMR) to carry out functions associated with meal digestion and assimilation. SDA is affected by prey size, prey type and body mass (Mb). Liquid meals require less energy to digest and assimilate than intact prey items resulting in a lower metabolic scope and reduced postprandial metabolic response. Digestive efficiency and metabolism are also affected by the level of dietary specialization which can lead to increased digestive efficiency in terms of duration and energy used for digesting preferred prey items. Here, I investigated the effects of Mb, Tb and ontogeny on standard and digestive MR of two dietary specialists, Dasypeltis scabra and D. inornata. Dasypeltis scabra, found throughout South Africa, and D. inornata, endemic to the eastern parts of South Africa and western part of Swaziland, digest only the liquid contents of freshly laid bird eggs and should have a lower energy cost of digestion and assimilation than other snake species consuming intact prey containing bones, fur or chitinous carapace. To test the effect of changes in Tb on the metabolic response of Dasypeltis, pre- and postprandial metabolic responses of adult D. inornata and adult and neonate D. scabra were compared. SMR and SDA were quantified at five ambient temperatures 20, 25, 27, 30, 32°C using closed system respirometry. SMR was measured for 3 days twice a day at 08h00 and 20h00. Thereafter, snakes were fed a meal of chicken egg equivalent to 20% of Mb and oxygen uptake (VO2) was measured for an additional 5 days at 08h00 and 20h00, and then once a day at 08h00 for an additional 7 – 10 days. Increased Tb resulted in increases in metabolic response variables for all groups. Variation in Tb significantly affected SDA (kJ kg-1) of D. scabra adults and neonates and D. inornata adults. There were few significant interspecific and ontogenetic differences across all temperature trials. Within five days after meal consumption for all groups at 32°C, postprandial VO2 rates peaked at 3.16 - 3.73 times preprandial rates (scope), lower than most other snake species. The optimal digestion temperature appears to be around 32°C in terms of duration, but may be higher to optimize digestion. Across the range of temperatures (20 - 32°C) and masses (3.98 – 71.33g), the duration of significantly elevated VO2 was on average 1.5 - 2 days longer for D. scabra adults and neonates than D. inornata. Digestion duration ranged from 6.5 - 13.5 days for D. inornata and from 7.5 - 16.5 days for D. scabra adults and neonates. Digestive duration was longer for D. scabra than other snake species that consume meals of intact prey of similar size, at the same temperature. Dasypeltis species expended less total energy for digestion and used a smaller proportion of total energy consumed for digestion than other snake species at similar temperatures. Lower maintenance and digestive costs suggest that energy is conserved for allocation to other functions during periods of low prey availability. In addition, Dasypeltis species may rely on thermoregulation to capitalize on reduction in energy output and to increase energy savings between meals.
The effect of intercropping beans on Eldana saccharina Walker (Lepidoptera: Pyralidae) arthropod predator populations in sugarcane.
(1998) Beje, Sibongile.; Baker, C.; Conlong, Desmond Edward.
Commercial sugarcane in South Africa is a monoculture, and therefore lacks vegetation diversity, which is instrumental in increasing associated faunal diversity. Diverse habitats tend to support more stable populations of herbivorous and predacious animals. It is hypothesised that lack of this diversity in sugarcane was partially responsible for the existence of Eldana saccharina infestation levels that are higher than is commercially acceptable. Amongst the available E. saccharina control strategies, is habitat management. This has been developed with the view of increasing and enhancing predator foraging activity. Through increasing arthropod predator abundance and activity, it is believed that E. saccharina control may be enhanced. In this study, habitat diversity was increased through intercropping beans within sugarcane. Arthropod populations were monitored throughout the sugarcane-growing period, to determine what effect this intercropping had on known potential arthropod predator populations of E. saccharina. The study site was divided into two plots: the intercrop (beans planted within sugarcane rows: sugarcane-bean intercrop) and sole sugarcane: control plot. At monthly intervals, epigeal arthropods were sampled with pitfall traps, while foliage associated arthropods were sampled with a suction trap. Predator activity at the base of the sugarcane stalk, where E. saccharina lays its eggs was monitored with sticky traps. Sampling took place in the sugarcane-bean intercrop and control plots as well as in the roadway bordering the study site. Epigeal predator habitat preference was assessed by randomly placing pitfall traps in the sugarcane rows, bean rows, interrows between sugarcane rows, interrows between sugarcane and bean rows and the roadway. Corresponding with monthly trapping, an E. saccharina infestation and damage survey was conducted. Environmental factors such as weather, light intensity, plant (beans and sugarcane) phenology and weed density were measured, and their effect on E. saccharina potential arthropod predators examined. At harvest, sugarcane stalks were sampled for sucrose yield analysis. Potential E. saccharina predators that were captured included species of the orders and/or families Acarina, Blattidae, Formicidae (Pheidole megacephala and Dorylus helvolus) and Araneida (Lycosidae, Oxyopidae, Thomisidae and Salticidae). P. megacephala and species of Acarina were the only predators caught with all three trapping techniques, thus indicating that they occurred both on the ground and foliage. D. helvolus and Acarina were the only predators caught in significantly higher numbers in the intercrop, suggesting that increased habitat management had positively affected their population sizes. D. helvolus were captured both on the ground and length of sugarcane stalk, while species of Acarina were captured on the ground, foliage and at the base of sugarcane stalk, indicating that they forage at the base of the stalk, where E. saccharina activity is concentrated. Specific ground habitats preferred by D. helvolus included the sugarcane rows and bean rows, while Acarina preferred the interrows between sugarcane and bean rows. Despite the generally low E. saccharina infestation levels during this study, significantly higher levels of infestation occurred in the intercrop when compared to sole sugarcane. As expected with high infestation, higher (although not statistically significant) damage occurred in the intercrop. Surprisingly, sucrose yield and sugarcane stalk mass were slightly higher in the intercrop. The implications of the observations made during this study are discussed in the context E. saccharina management.
Aplexa marmorata (Guilding, 1828)(Basommatophora : Physidae) : an invasive freshwater snail in South Africa.
(2000) Dana, Pelisa.; Appleton, Christopher Charles.
Invasions of ecosystems by alien species is a worldwide problem. Man, with his constant travelling, introduces organisms to places they have never occurred in before. The introductions may be accidental or deliberate. Some of the introduced organisms become invasive and some of these also become pests. Two aquatic pulmonate snails, Physa acuta (Physidae) and Lymnaea columella (Lymnaeidae), were introduced to South Africa probably through the aquarium industry in the 1940s and have now spread to most of the country's freshwater systems. A third invasive pulmonate, and second physid provisionally called Aplexa cf. marmorata, has recently been found in South African freshwaters. Comparison between A.. cf. marmorata found in Durban and P. acuta from Pietermaritzburg as an example of the genus Physa, confirmed that they belong to different genera and are therefore different species. Features compared were the shell, radula, foot, mantle, male genitalia and sperm morphology. Aplexa cf. marmorata is characterized by its foot having a pointed posterior end with a dark mid-dorsal stripe while that of P. acuta does not have these features. The mantle edge ofA.cf. marmorata has short triangular dentations while that of P. acuta has long finger-like projections. Aplexa cf. marmorata does not have an externally visible preputial gland whereas P. acuta does. The penis of A.cf. marmorata has a lateral opening while that of P. acuta has a sub-terminal outlet. TEM sections of the spermatozoon of A.cf. marmorata showed that it has a maximum of two glycogen helices around the mid-piece while P. acuta is known to have three. A study of the population dynamics of A.cf. marmorata in Durban showed it to produce three overlapping generations within a 14 month period whereas P. acuta has been shown to produce as many as eight over a similar time period. Further comparisons between South African A. cf. marmorata and similar material from the West Indies, Nigeria and St Lucia (KwaZulu-Natal) showed that they shared the same features with the specimens collected in Durban and are therefore considered to belong to the same species , Aplexa marmorata (Guilding, 1828). This species is indigenous to the Caribbean and northern parts of South America. The picture is however complicated by the fact that Dr L Paraense, doyen of the Brazilian school of freshwater malacology, does not recognize the genus Aplexa and redescribed this species under the name Physa marmorata in 1986.
Ecological factors influencing the reproductive ecology, territoriality and foraging behaviour of fiscal shrikes.
(1998) Devereux, Claire Louise.; Slotow, Robert Hugh.; Perrin, Michael Richard.
This thesis describes the behavioural ecology of South African fiscal shrikes through detailed field observations and experimental manipulations, and discusses these in the context of reproductive ecology, life history strategies, territoriality, and foraging theory. A population of fiscal shrikes was observed during the period October 1995-0ctober 1997 in a 336 Ha area of grazed bushveld near Pietermaritzburg, South Africa. Fiscal shrike reproduction coincided with the onset of the rainy season. Nests were placed in the centre or north-west regions of tree canopies and contained three or four eggs. Incubation and brooding were performed by females, and shading behaviour was observed in hot weather. Hatching and fledging success averaged 48%. High, exposed nests were less successful than other nests as they were prone to damage during inclement weather. There was a trend in life history strategies between equatorial and South African fiscal shrikes (an increase in clutch size, incubation and brooding durations, and territory size and a decrease in breeding season length), and between northern hemisphere Laniinae (increased intensity in the northern hemisphere), that could be explained by variability in precipitation and temperature, and clutch survival. Fiscal shrikes maintained individual or pair-held territories throughout the year using visual and vocal signalling. Territories averaged 2.2 Ha in area and almost all contained man-made structures. Territory size was inversely proportional to tall tree density, as trees were used for foraging. Fiscal shrikes resided in areas with few natural perch sites by utilising fence lines and overhead cables. When perch density was manipulated fiscal shrikes decreased and increased territory size accordingly. Fiscal shrikes were sit-and-wait foragers and primarily used perch-to-ground forays. The diet of breeding birds consisted of large invertebrates. Small items were consumed and larger items were cached or fed to offspring or females. Fiscal shrikes were central place foragers. Prey size increased in patches over 35 m from the nest. Perch height affected search area, which in turn affected foraging methods, search duration and subsequent movements. Perches may be the limiting resource for other sit-and-wait foragers and the manipulation of perch density could act as a conservation strategy for declining populations.
The evolution of the house sparrow (Passer domesticus) in southern Africa.
(2001) Msimanga, Audrey Ottilia.; Slotow, Robert Hugh.
The house sparrow, Passer domesticus, is one of the most successful invading bird species in the world. It was introduced to southern Africa around 1900 and has since spread through the region. Its dispersal was characterised by an initial slow phase followed by a rapid increase in the rate of spread. Following 50 years of slow spread, the rate of dispersal accelerated to over 80 km/year. The initial slow rate can be attributed to an Allee effect, defined as "a disproportionate reduction in reproduction below a threshold population density due to reduced probability of finding a mate". The rapid phase involved a combination of long-range jumps (leap-frogging dispersal) and diffusive movement over short distances. Dispersal was significantly faster along railway lines. Introduction of the house sparrow, Passer domesticus, to southern Africa involved unknown numbers of both the domesticus race of Europe and indicus of Asia, resulting in the establishment of a genetically diverse founder population along coastal South Africa. The birds have undergone significant differentiation since introduction about 100 years ago. Significant sexual size dimorphism was detected among southern African house sparrows, especially in flight structures. Males were larger than females in all characters except tarsus and claw length. Overall body size variation was clinaly ordered with a general increase in size with latitude in conformity with Bergmann's rule. Tarsus length also increased southwards, with the longest tarsi in birds of coastal sites in South Africa and the shortest in Zimbabwe. Patterns of variation in morphological characters paralleled climatic trends, especially minimum temperature and humidity. Beak size and shape of Zimbabwean birds appeared to be under the greatest influence of climatic factors. Shorter and more conicaly shaped beaks were selected for in females in Zimbabwe. Natural selection was modifying the morphological characters resulting in adaptive radiation in morphology of southern African populations. Few studies of microevolution (change in morphology over a short period) have been conducted in birds and none in invading bird species in the tropics. A founding population comprising both the Asian and the European races of the house sparrow, P. d. domesticus and P. d. indicus first arrived in Zimbabwe 30 years ago. Because of its recent introduction to Zimbabwe and because of its known potential for rapid adaptation and differentiation elsewhere in its new range, the house sparrow provided the ideal case study in microevolution in tropical Africa. Morphological differentiation in Zimbabwean populations of the house sparrow was analysed to determine temporal variation in local samples and the extent of variation from parent populations of Asia and Europe. Samples collected since arrival in Zimbabwe up to 1980 were compared with those collected from current populations in 1998/1999 to determine local changes over time. The Zimbabwean samples were then contrasted with samples from Asian and European populations to determine the extent of differentiation in the introduced birds of Zimbabwe. Zimbabwean populations had differentiated from their Asian parents in six of the seven morphological characters examined. The greatest differentiation was in beak size and shape for both males and females. Males developed larger beaks and shorter wings than the Asian birds and female beaks became more conical. A large proportion of the potential phenetic diversity of the founding population of both domesticus and indicus genes had been realised in Zimbabwe.
Aspects of the biology of the caracal (Felis caracal Schreber, 1776) in the Cape Province, South Africa.
(1982) Stuart, Christopher Trevor.; Hickman, G.
Felis caracal, despite heavy hunting pressure, is common and widespread throughout the Cape Province. Caracal are considered to be the principal wild predator of domestic livestock (goats and sheep) by most farmers and hunt clubs. Scat and stomach content analysis, as well as observations, indicate that F. caracal prey primarily on small to medium-sized mammals. The feeding habits of caracal-in different areas varied, according to abundance and occurrence of prey species. Captive animals required an average of 586g of meat each day. Killing techniques varied for different sized prey items. Physical and behavioural ontogeny are described for captive born animals. A technique for determining age of F. caracal was developed from study of known-age captive caracal. Examination of females killed in the wild, captive births, and births which were back-dated indicated that although young were born throughout the year, there was a definite birth peak between October and February with the lowest point being in May/June. Caracal were distinctly sexually dimorphic in size. Six F. caracal (four females and two males) were trapped, fitted with radio-transmitters, and released at the capture sites. Animals were cumulatively tracked for a total of 164 weeks. The mean range was 24,16km². A young adult male covered approximately 138km before settling in a 48km² area. Recommendations are presented for reducing losses of domestic stock by the caracal, based on the principal of removing the problem individual rather than blanket control.
Diet, home range and movement patterns of serval on farmland in Natal.
(1990) Bowland, Jane Mary.; Perrin, Michael Richard.; Lawson, D.
Servals (Felis serval) are rare cats occurring in the Natal midlands farmland, Drakensberg mountains and in game reserves in Zululand. They are thought to be extremely uncommon on farmland, yet are sometimes caught and killed in predator control programmes. The objectives of this study were to determine home range, habitat requirements, population density and diet of servals and thereby propose management recommendations for their conservation on farmland in the Natal midlands. Radio-telemetry was used to determine home range and habitat requirements, while diet was determined using scat analysis. Prey availability and vegetation changes in the habitat were monitored seasonally. Servals range over areas of 15-30km², but concentrate their activity in wetland areas where their preferred prey, Otomys irroratus, are most abundant. Over 90% of serval prey comprises small mammals, which occur at high density in the wetlands, but low density elsewhere in the study area. The results of this project have highlighted the importance of wetlands to farmland ecosystems.
Feeding ecology and carrying capacity of a reintroduced pack of African wild dogs in a relatively small, fenced reserve.
(2010) Niemann, Sophie Mary.; Slotow, Robert Hugh.
Reintroduction has been used successfully as a tool to restore declining populations of many threatened species. However, the lack of detailed evaluations of past reintroduction attempts has hindered a priori planning of management actions to achieve conservation goals. The metapopulation approach resulted in the most extensive and successful reintroduction efforts of the African wild dog (Lycaon pictus) in South Africa, but the approach was only recently evaluated by Gusset et al. (2008). For future reintroduction attempts to be successful on relatively small reserves, extensive evaluations are needed. Particular focus on feeding behaviour and impact on prey populations is essential to predict sustainability and carrying capacities in these areas for the African wild dog. A small reintroduced population of African wild dogs (pack number varying from 3 to 13 during the study period) were studied in the Karongwe Game reserve (79 km2) between January 2002 and January 2004. Fourteen prey species were identified: impala (Aepyceros melampus, 60 %) was the most dominant prey followed in descending order by bushbuck (Tragelaphus scriptus, 7.4 %), waterbuck (Kobus ellipsiprymnus, 4.9 %), warthog (Phacochoerus aethiopicus, 4.7 %), kudu (Tragelaphus strepsiceros, 4.4 %), and grey duiker (Sylvicapra grimmia, 4.4 %). Generally, prey were included in the diet in relation to abundance, and the dogs were not rate maximizing foragers but, unlike the findings of previous studies, were opportunistic feeders. The fences and angles in the fence, were used to assist hunting, but only for medium sized prey, impala and bushbuck, which were killed significantly more than expected along the fence line. A predictive prey preference model was then tested, but the model did not account for possible differences in feeding behaviours and prey preferences found in this, nor another study from the small Shambala Game Reserve. The model had limited accuracy as a predictive tool for proposed reintroductions into relatively small reserves. Models which can predict carrying capacity and minimum area requirements were also tested. Large variation and low numbers were predicted, which conflicted with social requirements needed for the survival of the population; further the models did not account for interspecific competition nor simultaneous depletion of prey by other guild predator. If the metapopulation approach is to continue to be successful and sustainable, more detailed evaluations of reintroductions of African wild dog on relatively small, fenced reserves are needed to determine the impact of these dogs on prey populations, and to determine if African wild dog feeding behaviour does differ for these areas in comparison to previously described open systems. With this information, more appropriate protocols regarding reintroduction and management can then be developed, thereby meeting one goal of management and conservation for the African wild dogs and their coexisting prey populations, and which can be used as a model for managing other large predators.
Biodiversity of spiders (Araneae) in a savanna ecosystem and the processes that influence their distribution.
(2000) Whitmore, Cheryl.; Slotow, Robert Hugh.; Crouch, Tanza.
I describe the spider biodiversity for a savanna ecosystem, assess sampling techniques, investigate surrogate measures of species richness and measure the biotic and abiotic processes affecting spider diversity. Spiders were sampled at Makalali Game Reserve, Northern Province, South Africa from February to December 1999 using pitfall traps, sweep netting, beating and active searching. A total of 4832 individuals from 268 species (14 potentially new), 147 genera (8 endemic and 2 new records for South Africa) and 37 families (1 new record for South Africa) were recorded. There was no overall significant difference in spider diversity among different physiognomic habitat types. However, analysing the results at a functional group level revealed that the web builders were significantly affected by the habitat type. Mopane woodland habitat type had the greatest number of web builders and general bushveld the least. Sweeping and active searching sampled the greatest number of individuals and species respectively. I recommend a combination of at least beating and active searching, which together sampled the highest number of unique species, for efficient and cost effective surveys. There was a significant relationship between the spider species richness and other invertebrate richness. However, the relationship is not significant when functional groups are considered separately. There was also a significant relationship between the number of species and families and species and genera. However, species level identifications remain ideal for conservation purposes. Inexperienced participants significantly overestimate the number of species. The use of surrogates is not supported by the work conducted in this study. It is still unclear what biotic and abiotic processes or combination of processes influence spider diversity patterns at the local scale. Different spider functional groups are significantly influenced by different factors. However, habitat diversity (branches and vegetation density) was the most common factor influencing spider diversity . Predicted diversity (modelled using GIS and beta-coefficients from multiple regression analyses) was higher than measured diversity values. While further research into the role of other environmental variables is clearly required, current reserve management should aim to maximise microhabitat structural diversity.
Comparative aspects of the thermal biology of African and Australian parrots.
(2006) Burton, Stephen Leslie.; Perrin, Michael Richard.; Downs, Colleen Thelma.
Deserticolous birds inhabit an environment characterised by high ambient temperatures and low rainfall that has low primary productivity. The combination of these factors may lead to the evolution of adaptations that minimise food and water requirements. One physiological adaptation that has been found in many deserticolous birds is the reduction of basal metabolic rate (BMR). I measured metabolic rate in the laboratory using four species of African lovebirds (Agapornis) , and four species of Australian grass parakeets (one Neopsephotus and three Neophema), all similar in body mass. Tests for differences between groups were carried out using both conventional and phylogenetically independent methods. The BMRs of the lovebird and grass parakeet species were not statistically correlated with habitat type. These results confirm the findings of previous studies on the effect of desert conditions on the BMR of parrots. I also found no significant differences in BMR between the species assemblages from different continents. The lack of significant differences in BMR between deserticolous and nondeserticolous parrots supports the idea that birds are "ex-adapted" to living in desert environments. I suggest that the results may have been affected by phenotypic plasticity in BMR, as recent evidence has shown that the scaling exponent of BMR differs between captive-raised and wild-caught birds. To elucidate the effect of origin (captive-raised vs. wild-caught) on the BMR of birds used in this study a large scale analysis of bird BMR data was undertaken. BMR and body mass data for 242 species of birds were obtained from the literature, this study, and unpublished data from various sources. A phylogeny was constructed using molecular and morphological phylogenies from the literature, and analysed using conventional and phylogenetically independent methods. The conventional analysis found significant differences in the scaling exponents of BMR of captive-raised and wild-caught birds. However the phylogenetically independent method showed non-significant differences between these two groups. Conventional analysis of differences between parrots and all other birds yielded significant differences between these two groups, with parrots having significantly higher BMRs than other birds. Again the phylogenetically independent analysis found non-significant differences between these VII two groups. A test of homogeneity of variance between these two groups found significant differences between the variances ofthe two groups, probably due to disparity in sample size and range of body sizes. The conventional and phylogenetically independent tests for differences between captive-raised and wild-caught parrots yielded non-significant results, suggesting that the parrots are not subject to the phenotypic adjustments postulated for all other birds. The lack of significant differences between captive-raised and wild-caught parrots suggests that the analyses of differing habitat type for African and Australian parrots is indeed valid.
Host suitability in the Diderik cuckoo Chrysococcyx caprius - ploceid brood parasitism breeding system.
(2003) Lemos, Sharon A. C.; Lawes, Michael John.; Henzi, S. Peter.
Host suitability is critically important to the success of brood parasitism. Parasites must select a host that not only accepts its egg but also is capable of successfully rearing the parasite to fledging. Nearly all brood-parasites appear to avoid low-quality hosts that are likely to reject their eggs, that are of inappropriate size, or that feed their nestlings nutritionally inadequate or insufficient food. The diderik cuckoo, (Chrysococcyx caprius), is an obligate brood parasite known to parasitise a wide spectrum of ploceids, including the yellow weaver (Ploceus subaureus) and the southern red bishop (Euplectes orix). Theory predicts that brood parasites should exploit insectivorous passerines of similar adult size to themselves that provision large quantities of high protein food to their young. However, the relatively smaller granivorous red bishop is the most heavily parasitised host species of the diderik cuckoo in southern Africa. To investigate why an apparently unsuitable host species was so heavily parasitized several populations of parasitised red bishops and yellow weavers (omnivores) were studied in the Pietermaritzburg region, KwaZulu-Natal, South Africa. Host suitability was assessed by examining diet quality, host-provisioning rates, cuckoo nestling growth and cuckoo fledging success. Diderik cuckoo nestlings were provisioned the same diet as the host nestlings in red bishop and yellow weaver nests. However, cuckoos in bishop nests received a protein-deficient seed diet from as early as six days following hatching. In contrast, weaver-cuckoo faeces contained 1~ times more insect than their bishop counterparts throughout their nestling period. Provisioning rates by bishop females were significantly slower than by yellow weavers, and neither bishop nor weaver hosts showed any 'supernormal' effort when feeding a young cuckoo. Both host species provisioned cuckoo nestlings at a similar rate and with a similar food mass as their own nestlings. Diderik cuckoos in bishop nests grew at a slower rate and fledged in a poorer condition than their yellow weaver counterparts. Red bishops are likely the most exploited host of the diderik cuckoo because i) cuckoo eggs are more readily accepted by the less discriminating bishop and ii) the bishop-breeding season coincides more closely with that ofthe diderik cuckoo than the yellow weaver. Thus, diderik cuckoos may preferentially exploit bishop hosts because of the low frequency of cuckoo egg rejection, which ultimately results in many cuckoos fledging from bishop nests despite the lowquality diet provisioned and 53% (n = 53) fledging success in nests of this species. In the yellow weaver system, the protein-rich diet and the greater probability of cuckoo nestling survival (80%, n = 5) may compensate for the high rejection rate of cuckoo eggs by this host. Thus, both host systems seem to represent evolutionary compromises for the diderik cuckoo, with neither red bishops nor yellow weavers being entirely ideal as host species.
The distribution and abundance of the humpback dolphin (Sousa chinensis) along the Natal coast, South Africa.
(1994) Durham, Ben.; Cockcroft, Victor Gavin.; Forbes, Anthony Tonks.
Populations of the humpback dolphin in Natal, South Africa, are subject to increasing pressures including capture in the shark nets and habitat degradation, and concern has been raised about the status of the population. A minimum of 95 humpback dolphins were caught in the shark nets during the period from 1980 to 1992. Capture and sighting records of the Natal Sharks Board revealed a relatively high occurrence of humpback dolphins at Richards Bay. Elsewhere, in southern Natal, the infrequent sightings and captures were attributed to a seasonal occurrence of dolphins, possibly due to temporary movements away from resident areas. Sighting rates reported by the Natal Sharks Board has decreased by 55%from 1984-86 to 1990-92 and may reflect a decrease in the population. In a photo-identification study, searches took place in ten search areas in Natal. The sighting rates in the different areas revealed a relatively high density of humpback dolphins occurring in north central Natal, from the Tugela River to the St. Lucia estuary (including Richards Bay). This distribution correlated significantly with the turbidity of the water and the width of the inshore continental shelf, and was inversely related to the density of bottlenose dolphins. Within the northern Tugela Bank region, higher densities of dolphins were found surrounding the five river mouths and estuaries. The Natal population was estimated to be between 161 to 166 animals (95% confidence limits 134 to 229). The annual mortality due to shark net captures approximates 4,5%of the population. Various evidence, including a high mortality rate and a decrease in the annual sighting per unit effort reported by the Natal Sharks Board suggest that the humpback dolphin population in Natal is vulnerable and may be decreasing in size. A proposal is made to reduce the capture rate by relocating shark nets away from the Richards Bay harbour.
An investigation of the ichthyofaunal by-catch of the Tugela Bank prawn trawlers.
(1993) Fennessy, Sean Thomas.; De Freitas, A. J.; Van der Elst, Rudy P.
The by-catch of penaeid prawn trawlers operating on the Tugela Bank of Natal was analysed at irregular intervals for a period of three years, from May 1989 to June 1992. This was primarily in response to claims by Iinefishermen that trawlers were catching and discarding juvenile Iinefish species. Catch and effort data were recorded from 159 trawls, and catch composition data from 110 trawls, over a depth range of 20 to 45 meters. A total of 108 teleost species were identified in the by-catch, six of which comprised 80 percent of overall teleost abundance by number. Many of these fish were small-sized shoaling species, which increased their vulnerability to trawlers, and the majority were considered to be estuarine-associated. Multivariate analysis of samples showed there to be significant differences in relative abundance of species by season and depth. Annual average by-catch and discarded quantities were estimated at 400 and 315 tonnes respectively. Discard:retained catch ratios' ranged from 4.25 (± 1.19) : 1 to 15.48 (± 3.86) : 1 for shallow (20-33 meters) and deep (33-45 meters) trawls respectively. Only one important Iinefish, the squaretail kob, Argyrosomus thorpei, occurred in prawn trawl catches. These fish were spawned four to six months prior to being caught and appeared to use the Tugela Bank as a nursery area. They were seasonally abundant, occurring mostly from January to March. During these months trawling effort was generally low, as the prawns had not yet migrated offshore in quantity. Per-recruit analyses showed that the removal of these age 0 fish by trawlers reduced yield-per-recruit and spawning biomass-per-recruit values for the A. thorpei fishery. Aspects of the biology of three common sciaenids occurring in trawl catches, Johnius dussumieri, J. amblycephalus and Otolithes ruber, were investigated. Most of the fish examined were juveniles which utilised the Tugela Bank as a nursery area, owing to the existence of suitable food, and the turbid waters afforded them protection from predators. Standard biological data, such as length frequencies, lengthweight relationships and size at 50% maturity are presented. Based on the data collected and the analyses presented here, management recommendations are presented, which include the improvement of the collection of catch and effort data for the Tugela Bank prawn trawlers; communication of the results of this study to prawn trawler operators in order to encourage the reduction of trawling effort early in the year; consideration to be given to the re-surveying of Tugela Bank ichthyofaunal by-catch in the future in order to assess potential long-term effects of trawling in the area.
Restriction patterns of mitochondrial DNA in natural populations of the murid species Otomys irroratus.
(1994) Rimmer, Alison.; Lamb, Jennifer Margaret.; Contrafatto, Giancarlo.
Mitochondrial DNA (mtDNA) was isolated from 8 different natural populations of the rodent species Otomys irroratus (Muridae: Otomyinae) and from one population of the species 0. angoniensis occurring in South Africa. MtDNA samples were cleaved with five different restriction endonucleases, end-labelled with phosphorous-32, separated by electrophoresis on horizontal 1 % agarose gels and the resulting fragment bands were detected by autoradiography. The individual-specific fragment banding patterns were analysed and compared among the various populations. The percent sequence divergence among and between the populations was calculated using the formula of Nei (1979). A matrix of sequence divergence values for all intergenomic pairwise comparisons was subjected to a clustering analysis by the unweighted pair group method with arithmetic means (UPGMA, Sneath and Sokal, 1973), using the computer programme NTSYS (Rohlf: 1988). The results of these analyses allowed for a preliminary identification of phenetic groupings in the data set. A matrix generated by scoring the restriction endonuclease fragments as present or absent was used to generate a phylogenetic dendogram using the BIOSYS (Swofford and Selander, 1989) programme. The overall restriction fragment variation uncovered in this study revealed 15 different mtDNA haplotypes within the 20 individuals examined. This corresponded to a high degree of polymorphism in the populations where more than one specimen was available, as well as within the species 0. irroratus. There were no clones that were shared between any of the populations sampled. The intrapopulation sequence divergence values uncovered in this study were high (range 0.35 % to 5.08 %), but also consistent with some other reports in the literature for intrapopulation variation. The outgroup, 0. angoniensis revealed the highest divergence values when compared to the mtDNA clones found in 0. irroratus. The phenetic and cladistic cluster diagrams revealed overall similarity with one another. There appeared to be little correlation between the topology of the mtDNA haplotype phenograms and the geographic distance of the sample localities. There was, however, a marked congruence between the distribution of mtDNA haplotypes and the distribution of three distinct cytotypes occurring over the species range. A possible polyphyletic evolution of populations of 0. irroratus was inferred from the cladistic analysis.

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