Growth and reproduction in the fruit bat Epomophorus wahlbergi.
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Date
1983
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Abstract
This study was carried out on the Natal South Coast between 30° 12' S and
30° 19' S, where 1085 Epomophorous wahlbergii were caught by mist-netting, and a
captive breeding colony was kept between June 1977 and February 1982.
Age determination techniques were developed using three criteria; linear
growth measurements to obtain the age of animals prior to the attainment of the
growth asymptote, tooth eruption to determine the age of animals prior to the
attainment of a full permanent dentition, and tooth wear in combination with
birth-pulse timing to obtain the age of animals after the growth asymptote and
full permanent dentition had been reached. Stevens asymptotic growth curve,
performed on forearm length, eye-nose distance and zygomatic width,
observations of tooth eruption in cage born bats and linear regression of tooth
height data provided the basis for age predictions. Age structure of the
population indicated that the greatest percentage of losses occurred between
the 5-10 and 10-15 month age group in both sexes. A maximum ecological
longevity of nine years is suggested.
A killed sample of 81 males and one live caged male provided the basis for the
male reproductive study. Puberty onset occurred at eight months and sexual
maturity attainment at 13-17 months. Sperm was present throughout the year
and no seasonal variations in testicular or gonadial parameters occurred.
However, seasonality was shown in body mass, blood testosterone levels,
epaulette hair length, calling and testes position. The unusual and constant
presence of spermatocytes/spemlatids in the epididymis cauda was observed and meiotic abnormality suggested as an explanation. Epaulettes have an attractive
function for females during the mating period, and calling probably acts as a
means of year-round territory maintenance. Lek mating is considered possible
and a seasonal change in behaviour during the mating season from male groups to
individual callers may occur.
Five hundred and fifty three captured and released females and a killed sample
of 111 females provided the basis for the female reproductive investigation.
Puberty commenced at 2,5 months and sexual maturity was attained at six months.
The first proestrus onset took place at a mean age of 5,6 months and first
conception at 6,2 months. The species exhibits a seasonally polyoestrous
pattern with an extended season. Conceptions occur from May to December, the peak months being May, June and July. Births occur from October to June with
the peak birth season in November and December. The majority of females
undergo one pregnancy per year terminating in November/December with a small
percentage terminating around April.
Primordial, primary, secondary and early vesicular follicles were present in
the ovary year round. The presence of intermediate and late vesicular
follicles however followed a seasonal pattern covering April to November.
Increased uterine epithelial height and endometrial gland numbers followed a
bimodal pattern.
Oestrus can occur in the absence of a male and conception peaks coincided with
shortest daylength, lowest rainfall, temperature and humidity. Fruiting and
rainfall are suggested as ultimate causes of breeding as the peak in lactation
coincided with rainfall and fruiting maxima.
A series of timetables showing variations in the timing of the annual
reproductive cycle with one and two pregnancies is presented. A precaution
against abortion and preparation for a postpartum pregnancy were used to
explain the presence of intermediate and late vesicular follicles in the non-luteal
ovary at the beginning and end of pregnancy.
Ovaries and uterine horns showed a functional dextral dominance although
anatomically left and right appear symmetrical. Alternation of ovarian
function between left and right may occur in those animals undergoing two
annual pregnancies. A localized endometrial reaction may occur but was not
confirmed. No transovular migration takes place. The corpus luteum reached
maximum size at the beginning of pregnancy and was absent at the end.
E. wahlbergi was found not to fit into the usual pattern of autumn conceptions
and spring births. The species showed a high fecundity rate for a monotocous
species and the gestation period was long for its body size.
Parturition, lactation, maternal care and juvenile behaviour were observed in
the captive colony. A method for inducing birth, using Prostaglandin E(2) and
Oxytocin was applied. Births took place during daylight hours. The labour
posture was head down and delivery occurred after three hours of labour. Fetal
presentation was head first and placental delivery was delayed until
approximately two hours after birth. Placentophagia was observed. The infant
is born dorsally furred, with eyes closed and large muzzle, weighing up to 20,3
% of the mother's postpartum mass.
Mother/infant behaviour and juvenile behaviour up to flight initiation is
described. Competent flight takes place at a mean age of 81,1 days. Milk is
higher in carbohydrate content and lower in protein content than previously
studied insectivorous bat milk. A correlation is suggested between head first
delivery presentation, delay in placental delivery, appearance of the infant at
birth and those species which carry their young in flight instead of leaving
than behind in a nursery.
Description
Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1983.
Keywords
Bats--KwaZulu-Natal., Pteropodidae., Bats--Reproduction., Bats--Growth., Theses--Zoology.