The origin of species is a fundamental problem in biology. An enduring controversy concerns the relevant importance of geographic isolation versus ecological specialization in promoting speciation. Sponge-dwelling shrimps (Synalpheus) are highly diverse (100 species) and abundant on coral reefs worldwide; several characteristics make them ideal candidates for testing whether niche shifts can initiate speciation in sympatric populations. These include high host specificity, low mobility, and mating in association with the host. Recent studies have revealed significant host-associated differentiation in demography and allozyme frequencies within Synalpheus species, as well as high frequency of undescribed host-specific cryptic species. This research will develop 1) a critical analysis of genetic (allomyze) and host use differentiation among sympatric versus geographically distant demes of the widespread host- generalist S. brooksi; 2) analyze genetic, behavioral, and morphometric characteristics of several currently unrecognized cryptic species of Synalpheus and their host associations; 3) construct a phylogenetic tree for Caribbean Synalpheus, including newly defined species, onto which host use data and life history characters can be mapped to test rigorously for association between the sponge-dwelling habit and the radiation of this group.
