Radula diversification promotes ecomorph divergence in an adaptive radiation of freshwater snails

Abstract

Adaptive diversification of complex traits plays a pivotal role for the evolution of organismal diversity. However, the underlying molecular mechanisms remain largely elusive. In the freshwater snail genus Tylomelania, adaptive radiations were likely promoted by trophic specialization via diversification of their key foraging organ, the radula. To investigate the molecular basis of radula diversification and its contribution to lineage divergence, we use pooled tissue-specific transcriptomes of two sympatric Tylomelania sarasinorum ecomorphs. We show that divergence in both gene expression and coding sequences is stronger between radula transcriptomes compared to mantle and foot transcriptomes. These findings support the hypothesis that diversifying selection on the radula is driving speciation in Tylomelania radiations. We also identify several candidate genes for radula divergence. Putative homologs of some candidates (hh, arx, gbb) also contributed to trophic specialization in cichlids and Darwins finches, indicating that some molecular pathways may be especially prone to adaptive diversification.