Meeting Abstract
Guppies (Poecilia reticulata) from the Northern Range 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 upstream localities live in communities with a far lower risk of predation. A consequence of facing less pressure from predators is that these fish are able to reach large population sizes with high densities. This high density creates strong competition between individuals for food resources, which forces a diet shift from a preference for invertebrates in high predation communities towards the consumption of more algae and detritus in low predation communities. The guppy is a member of Cyprinodontiformes, the most basal members of which are generalist suction feeders. This 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 high and low predation sites within two paired streams using geometric morphometrics to test if differences in diet are associated with differences in jaw and head shape. I predict that guppies from high predation localities will be better adapted for picking high quality prey from environmental surfaces or the water column while those from low predation localities will instead be adapted for the non-selective scraping of environmental surfaces. These predictions in turn suggest the following expected differences in the structure of the jaw and shape of the head: a. an anterior shift in the position of the intramandibular joint; b. a wider dentary and premaxilla; and c. asymmetry between the size and shape of the dentary and premaxilla. Specimens were cleared and stained, then photographed through a microscope from various angles. Analysis was done using the tps software series.
