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 (<i>Dysmicohermesdisjunctus</i> (Walker, 1866), <i>Dysmicohermesingens</i> Chandler, 1954, and <i>Orohermescrepusculus</i> (Chandler, 1954)), and another one from eastern North America (<i>Nigroniaserricornis</i> (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 <i>N.serricornis</i> from Michigan was n = 10 (9 autosomal bivalents + Xy_p in the male). The sex chromosomes of <i>N.serricornis</i> formed parachute-type bivalents synchronously with the autosomes. The parachute-type bivalent Xy_p 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).