Horizontal distribution of chironomid larvae and genetic structure of Chironomus plumosus population offshore in Lake Suwa, Central Japan

In the shallow and eutrophic Lake Suwa of Central Japan, water quality has been markedly restored since the end of 1990s, and the chironomid larval community in the lake may have changed accordingly. The objectives of this study were twofold: to clarify (1) the current horizontal distribution of two chironomids, Propsilocerus akamusi and Chironomus plumosus, in Lake Suwa and (2) the genetic structure of C. plumosus in the lake. The average larval densities of P. akamusi and C. plumosus offshore in the lake were 900 and 600 individuals per m, respectively. Relative to the findings of a 2001 survey, C. plumosus larvae increased. Eight haplotypes were recognized in the cytochrome c oxidase subunit I (COI) sequences of C. plumosus larvae offshore in Lake Suwa, while more were found near the lake center. The phylogenetic tree based on the COI sequences suggests that C. plumosus specimens in Lake Suwa were of the same single lineage as those in several other Japanese lakes, while they diverged from the lineages of Russian specimens.