Patterns of evolutionary change in Baikalian gammarids inferred from DNA sequences (Crustacea, Amphipoda)

The Baikalian gammarids (Crustacea, Amphipoda) are the most widely known an d most spectacular example of an adaptive radiation among contemporary fres hwater invertebrates. To study the phylogeny of the Baikalian gammarids we sequenced a 622-bp-long fragment of the nuclear gene coding for 18S rRNA fr om species of 18 endemic Baikalian genera and Gammarus pulex-a non-Baikalia n taxon. Some important morphological characters appear independently in bo th lineages and suggest parallelism in the development of gigantism and bod y armament. The first lineage comprises benthic, mostly unarmed taxa. The s econd lineage contains predominantly armed taxa, most of which are detrivor ous or carnivorous. (C) 1998 Academic Press.