A phylogeny of South African east coast intertidal rocky-shore Polychaete worms (Annelida) and the genetic structure and demographic history of an example, Marphysa corallina.

Abstract

The Annelida is an evolutionarily ancient invertebrate taxon. Recent studies have found that the formerly described sister taxon of the Polychaeta, Clitellata, is a derived Polychaete group thus making Polychaeta a paraphyletic group. Polychaete worms represent one of the most diverse invertebrate groups and are well represented in a variety of environments such as temporary freshwater puddles, rocky intertidal shores, estuaries and the abyssal plain. Polychaetes are fundamentally important in their environments as many are regarded as ecosystem engineers. Phylogenetic relationships within the Polychaeta are poorly understood and some species level classifications are uncertain due to the large number of polychaete worms present. In Chapter two, the phylogenetic relationships within the commonly found polychaete families (Nereididae and Eunicidae) were analysed using the universal mitochondrial cytochrome oxidase subunit 1 (COI). Within Eunicidae, analyses supported a polyphyletic Marphysa and Eunice which is consistent with previous results as individuals from both genera are nested among one another. Within Nereididae, relationships between genera and species were poorly supported and complex. Genera did not form exclusive clades but instead grouped with one another. A large degree of homoplasy has been recorded for the family which could have attributed to the convoluted groupings. Thus it has been suggested that genera from both Eunicidae and Nereididae be revised. Marphysa corallina is a poorly studied Eunicid polychaete which has a tropical indo-west distribution. It was observed to be a common worm among others on the intertidal rocky shores of KwaZulu-Natal and the Eastern Cape. In Chapter three, the population genetic structure and demographic history of M. corallina was investigated using two genes: universal mitochondrial cytochrome oxidase subunit 1 (COI) and the nuclear intron spacer region (ITS1). Diagnostic taxonomic characters were used to identify and validate the specimens as Marphysa corallina. The COI marker revealed that populations were highly connected to one another and formed a large panmictic population whereas ITS1 showed shallow genetic structuring of populations. Family Eunicidae individuals are known to lack a long lived planktonic larval stage which could not have contributed to panmixia as demostrated by the COI marker. Demographic results indicated that populations had recently undergone sudden expansions which could have falsely resembled highly connected populations. Estimation of divergence times places the expansions in the mid to late Pleistocene. Populations had not reached migration-drift equilibrium thus contemporary population distributions of Marphysa corallina along the east coast of South Africa are largely shaped by past climatic events such as in the Pleistocene.