부산대학교 도서관

Kinorhyncha is a phylum of microscopic, benthic marine invertebrates found throughout the world, from the Arctic to Antarctica and from the intertidal zone to the deep sea. Within the most species-rich genus, Echinoderes , we find a putatively monophyletic species group, the so-called Echinoderes coulli -group. The remarkable morphological similarities of the E. coulli -group species and the fact that the group has a global distribution even though most of the species are restricted to intertidal habitats, has led to the hypothesis that dispersal and speciation within the group has been driven by the process of continental drift. However, this has never been confirmed empirically. With morphology and two molecular loci, COI and 18S, we calculated phylogenetic trees by analysing datasets separately and in combination using Maximum Parsimony, Maximum Likelihood and Bayesian Inference. Using different models of evolution in combination with different statistical approaches, we show that two major clade divergences were consistent with historic drifting of continents, suggesting that vicariance has played an important role for the speciation within the E. coulli -group. Furthermore, we found that reconstructions of past tectonic drifting since the Devonian (416–359 million years ago) were able to explain present species distributions, and suggest that the group originated in a supposedly vast shallow marine environment in north-eastern Gondwana by the mid-late Silurian, 426–416 million years ago. A big, and yet unresolved question in meiofauna ecology, is why numerous microinvertebrates show a nearly cosmopolitan distribution, even though they lack pelagic life stages and do not possess special dispersal capabilities. In order to understand the dispersal mechanisms behind these species – do they spread with continental drift or do they have hidden dispersal capabilities? – the phylogeography of an intertidal species group of kinorhynchs was analysed. The results showed that their phylogeny follows present days' geography, suggesting that meiofaunal organisms without dispersal stages possess greater dispersal potential than previously assumed. [ABSTRACT FROM AUTHOR]