Male chromosomes of three Sialis species of alderfly (Megaloptera: Sialidae) in Japan

抄録

We have analyzed the chromosomes of three species of alderfly (Family Sialidae) from Japan. Two species from Hokkaido (Sialis sibirica and S. longidens) showed similar karyotypes with a chromosome number of 2n=30 consisting of 14 pairs of autosomes plus an X and a Y sex chromosome in males. The chromosome number of another species, from Hyogo Prefecture (S. yamatoensis), was 2n=28, with a karyotype composed of 13 pairs of autosomes plus an X and a Y sex chromosome in males. The X chromosomes of these three species were metacentric, while the Y chromosomes appeared as tiny dots that were too small to determine the exact morphology. The sex chromosomes of the first meiotic metaphase (MI) spermatocytes in S. longidens invariably formed a “parachute-like” bivalent synchronously with the autosomes, similar to what is seen in the closely related Family Corydalidae. The three species of Sialidae examined in this paper had higher numbers of chromosomes (2n=28, 30) than corydalid species (2n=20, 22, 24).