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).

We analyzed morphological variation in a hybrid zone between 2n = 16 and 2n = 22 chromosomal races of a Japanese harvestman, Gagrellopsis nodulifera (Arachnida: Opiliones; Sclerosomatidae). We found negative correlations between the sizes of four metric traits and altitude in all populations analyzed. Morphological variation was positively correlated with chromosomal heterozygosity. A karyotypically conspicuous population with an intermediate karyotype 2n = 20, was also morphologically unique in that individuals from this population were much smaller than those from other populations. Besides, in this population the profile of the correlation for the four metric traits analyzed was different from those in the other populations. In one of the hybrid populations, the body size of the chromosomal heterozygotes was significantly smaller than that of homozygotes. Hybrid populations and parental races did not differ in level of fluctuating asymmetry. Possible mechanisms of the karyotype-phenotype associations in the chromosomal hybrid zone are discussed.