ABSTRACT
Freshwater crabs constitute a common faunal component of tropical and subtropical river systems. They have a worldwide occurrence in these warmer regions, being represented by different taxonomic lineages on different continents or even within continents. Due to their mostly direct development and assumed dependency on fresh water, freshwater crabs are considered reliable model organisms to genetically reconstruct the hydrographical history of a region. However, very few studies have been carried out to directly document within-river dispersal or overland dispersal of these crabs. Thus the questions remain, in how far the restriction to river systems is comparable throughout the different taxa of freshwater crabs, and if all of the taxa can be used similarly well to reconstruct the history of watersheds, orogeny, island formation, and continental drift. In the current study, we analyze the phylogeographic structure of Epilobocera sinuatifrons (Decapoda: Brachyura: Pseudothelphusidae), a freshwater crab species endemic to the Caribbean island of Puerto Rico. Results show limited morphometric and genetic (mitochondrial and nuclear DNA) differentiation among metapopulations along a west-east gradient, paralleling the direction of the main mountain chain. The north-south comparison, in turn, does not show any differentiation, suggesting that the crabs must be able to migrate between headwaters of unconnected river systems. These results are compared to recently published ones on phylogeographic structure within species of Sesarma (Decapoda: Brachyura: Sesarmidae) from Jamaican rivers. The Jamaican freshwater crabs are endemic to a much smaller geographic area and show a pronounced genetic-geographical structure with restricted gene flow among many of the studied rivers systems. These results are unexpected, because the colonization of Jamaica occurred much more recently according to geological history and because the Jamaican crabs still have an abbreviated larval development (Gonza´lez-Gordillo et al. 2010) which should favor distribution within a drainage system and possibly among rivers, if able to survive in coastal areas. This comparison gives evidence for different distribution potential in freshwater crabs and cautions about the assumption that these crabs do not migrate between rivers and are thus infallible biogeographic model systems.
