Ecological speciation in anemone-associated snapping shrimps (Alpheus armatus species complex)

Divergent natural selection driven by competition for limited resources can promote speciation, even in the presence of gene flow. Reproductive isolation is more likely to result from divergent selection when the partitioned resource is closely linked to mating. Obligate symbiosis and host fidelity (mating on or near the host) can provide this link, creating ideal conditions for speciation in the absence of physical barriers to dispersal. Symbiotic organisms often experience competition for hosts, and host fidelity ensures that divergent selection for a specific host or host habitat can lead to speciation and strengthen pre-existing reproductive barriers. Here, we present evidence that diversification of a sympatric species complex occurred despite the potential for gene flow and that partitioning of host resources (both by species and by host habitat) has contributed to this diversification. Four species of snapping shrimps (Alpheus armatus, A. immaculatus, A. polystictus and A. roquen...