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

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We analyzed chromosomes of four species of fishflies (Megaloptera: Chauliodinae). Three species were from western North America (Dysmicohermesdisjunctus (Walker, 1866), Dysmicohermesingens Chandler, 1954, and Orohermescrepusculus (Chandler, 1954)), and another one from eastern North America (Nigroniaserricornis (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 N.serricornis from Michigan was n = 10 (9 autosomal bivalents + Xyp in the male). The sex chromosomes of N.serricornis formed parachute-type bivalents synchronously with the autosomes. The parachute-type bivalent Xyp 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).