Evidence for three major clades within the snapping shrimp genus Alpheus inferred from nuclear and mitochondrial gene sequence data

The snapping shrimp genus Alpheus is among the most diverse of caridean shr imps, and analyses of taxa separated by the Isthmus of Panama have been use d to estimate rates of molecular evolution. Although seven morphological gr oups have been informally suggested, no formal phylogenetic analysis of the genus has been previously attempted. Here we infer the phylogenetic relati onships within Alpheus using sequence data from two nuclear genes, glucose- 6-phosphate isomerase and elongation factor-la, and from the mitochondrial gene cytochrome oxidase I. Three major clades corresponding to previously n oted morphological features were identified. Discrepancies between earlier informal morphological groupings and molecular analyses largely consisted o f species whose morphologies were not entirely typical of the group to whic h they had been assigned. The traditional placements of shrimp with highly sessile lifestyles and consequently simplified morphologies were also not s upported by molecular analyses. Phylogenies for Alpheus suggest that specia lized ecological requirements (e.g., symbiotic associations and estuarine h abitats) and modified claw morphologies have evolved independently several times. These new analyses also support the sister species status of transis thmian pairs analyzed previously, although very similar pairs were not alwa ys resolved with the more slowly evolving nuclear loci. In addition, six ne w cryptic species were identified in the course of these studies plus a sev enth whose status remains to be determined. (C) 2001 Academic Press.