Meeting Abstract
Ray-finned fishes have repeatedly colonized both marine and freshwater habitats. Several clades have experienced increased diversification rates following marine to freshwater transitions, yet it remains to be seen if these transitions also consistently lead to higher rates and changes in the direction of morphological evolution. To investigate this hypothesis, we measured eight ecologically and functionally relevant size and shape variables, combining length, depth and width measurements, on 5000+ museum specimens from 2735 teleostean species. We explored a binary and a more complex habitat categorization scheme and analyzed the evolutionary history of habitat use through stochastic character mapping. The fit of single and multi-rate Brownian models of trait evolution was then compared to identify possible rate differences among habitat categories. We found that although marine and freshwater taxa largely overlap in their morphospace occupation, size is an important component of the total variation and delimits a cluster of predominantly freshwater species of smaller body sizes. However, when size is removed, marine species occupy a considerably larger region of morphospace compared to freshwater taxa. The greatest rate differentials among habitat categories were obtained for depth and width variables, which evolved at the fastest rates in marine fishes. Our results highlight differences in body depth/width ratio as an important component of the disparity patterns in marine species, which may have functional consequences as these traits are linked to maneuverability. One possible explanation is that marine habitats have a greater range in structural complexity, leading to a wider array of optimal forms.
