Phenetic analysis, trophic specialization and habitat partitioning in the Baikal amphipod genus Eulimnogammarus (Crustacea)

The pattern of adaptive radiation in the Baikal amphipod genus Eulimnogammarus was investigated through phenetic studies, gut contents analysis and a distributional survey. Eight species of Eulimnogammarus, together with representatives of related genera from Baikal or other regions, were phenetically analysed. This genus exhibited the highest affinity to Baikal-endemic Philolimnogammarus among six genera studied, but not to European “Eulimnogammarus”. Of the eight members of the Baikal genus Eulimnogammarus investigated, seven species were closely affiliated to one another, but one, E. grandimanus, showed a weak affinity not only to other congeners but also to other genera. Detailed studies of mouthpart morphology revealed interspecific differences in the structure of the mandibles and maxillae I. Among the taxa examined, Eurybiogammarus violaceus and Corophiomorphus kietlinskii had the most specialized mouthparts. Nine species of Eulimnogammarus and Philolimnogammarus were found in the littoral zone and were distributed in one of three habitat zones. Gut contents analysis of these taxa demonstrated that E. violaceus is a sponge feeder, but the other species examined were all generalist omnivores. Despite differences in mouthpart morphologies, high trophic overlap was evident between species, and the foods taken reflected the availability of local fauna and flora rather than mouthpart morphology. Possible mechanisms which permit the observed species overlap are considered