Meeting Abstract
Guppies from the mountains of Trinidad co-occur with a diversity of predators in the lower portions of all rivers. Waterfalls limit the upstream distribution of predators, so guppies from these upstream localities live in communities with far lower risk of predation. This lowered risk allows them to grow to large population sizes with high densities. This high density creates strong competition between individuals for food resources, which forces a diet shift in the population from a preference for invertebrates in high predation communities towards the consumption of more algae and detritus in low predation communities. Guppies are a part of the Cyprinodontiform group, the most basal members of which are generalized suction feeders. The clade also contains more recently diverged specialized “pickers,” some of which have in turn evolved a scraping feeding mode. I compared the jaw bones and head shape of guppies from three pairs of high predation and low predation streams from three different Trinidadian drainages to see if differences in diet are associated with differences in jaw and head shape. The dietary shift in the low predation guppies is expected to be accompanied by a shift from the more gracile jaw morphology of a picker towards the more robust and asymmetrical morphology of a scraper. Specimens were cleared and stained, photographed through a microscope from various angles, landmarked and analyzed using canonical variate analysis and discriminant function analysis. Jaw shape was largely influenced by drainage of origin, with low predation populations showing a varied evolutionary response that was consistently significantly different from their high predation counterparts.
