c- Morphological variation between populations of the freshwater crab Zilchiopsis collastinensis at different moments of the hydrological cycle

TORRES V,; GIRI F.; COLLINS P.

San José

Congreso; Summer Meeting THe Crustacean Society; 2014

Universidad de Costa Rica; The Crustacean Society

Rivers with floodplain have a high diversity of environments characterized by the hydrological cycle. These present different degrees of connection, both spatially and temporally, affecting the population dynamics, being the individuals adapted to the variations of the flood regimen. Zilchiopsis collastinensis is a burrowing crab that spends most of its life cycle on the banks. It is distributed throughout Paraguay, Bolivia and Argentina. We studied the morphological variations among four populations of Z. collastinensis at two intermediate phases of the hydrological regimen (rising and falling water phases). Crabs were collected by hand in different sites of a floodplain system of the La Plata Basin. Morphological measurements were used to evaluate the shape variation. Sixteen landmarks were placed on the carapace from digital images of crabs. The configurations were superimposed using GPA with object symmetry processed. The CVA test showed statistical differences in shape variation patterns among the population at the two moments. In the rising phase populations of crabs were more different in shape among themselves. Nevertheless in the falling water phase, populations presented small differences, being the crabs of the downstream population the more similar with the others upstream populations. During the high water phase, probably the crabs disperse to the downstream and tend to be more similar, but in low water some populations can be isolated showing more differences among them. Periods of high water would tend to homogenize populations among water bodies decreasing the differences between the populations of nearby sites.