Evolutionary Perspectives on Naidinae (Annelida, Clitellata, Naididae): Molecular and Morphological Revelations

Abstract: Naidinae is a group of tiny oligochaetous clitellates, common all over the world, primarily in freshwater. The taxon includes about 180 nominal species. In this thesis it is shown (using molecular data) that Naidinae (sensu Erséus and Gustavsson, 2002) is non-monophyletic, since one genus, Pristina, formerly regarded as part of Naidinae, is well-separated from the remaining naidines by some genera of another clitellate subfamily, Rhyacodrilinae. The ultrastructure of coelomocytes from several naidine and rhyacodriline species are described and compared with each other and with coelomocytes previously studied, from other clitellate taxa. The naidine and rhyacodriline coelomocytes are similar, differing from those of other groups, which corroborates the hypothesis of a close relationship between Rhyacodrilinae and Naidinae.Features of the chaetae are important taxonomic characters of Naidinae. However, the significance of chaetotaxy has been questioned. The correlation between genetic variation and chaetal morphology within the genus Nais is investigated. Principally, chaetal character patterns are congruent with the evolutionary lineages revealed by genetic data, but at least nine lineages correspond to at most six nominal species. The species complex Nais communis/variabilis appears to be a gathering of at least five separately evolving lineages. That is, cryptic speciation is revealed.Finally, six molecular markers are used to elucidate the phylogenetic relationships within the group, and the resulting tree is used to track the evolution of morphological characters commonly used in naidine taxonomy. The tropical genera Dero, Branchiodrilus, and Allonais branch off from the base of the naidine tree of life, suggesting that Naidinae originally evolved in the tropics. Chaetal characters are shown to be homoplastic to a great extent within the group, most certainly contributing to the overall confusion in naidine systematics.