Chromosomes of four fishfly species (Megaloptera, Corydalidae, Chauliodinae) from North America.

We analyzed chromosomes of four species of fishflies (Megaloptera: Chauliodinae). Three species were from western North America ( (Walker, 1866), Chandler, 1954, and (Chandler, 1954)), and another one from eastern North America ( (Say, 1824)). The chromosome number of the three western species was 2n = 22, with the karyotype consisting of 10 pairs of autosomes plus XY in males. The X chromosomes of these three species are subtelocentric, while the Y chromosomes are small and dot-like. Of the ten pairs of autosomes, the last pair is substantially smaller than the others. The chromosome number in the first meiotic metaphase in spermatocytes of from Michigan was n = 10 (9 autosomal bivalents + Xy in the male). The sex chromosomes of formed parachute-type bivalents synchronously with the autosomes. The parachute-type bivalent Xy has also been found in four fishflies and four dobsonflies (Megaloptera: Corydalinae) from East Asia, as well as in a fishfly and a dobsonfly from North America. These data suggest that the two subfamilies of Corydalidae share a common sex-bivalent mechanism, along with many beetles (Coleoptera).