The true chromosome number of Aka-Tombo, Sympetrum frequens (Sel.) of Japan, with a note on the karyotype of S. depressiusculum (Sel.) (Anisoptera: Libellulidae)

Inspired by the little note of S. ASAH1NA (1983, Abslr. Pap. Vlllh ini. Symp. Odonalol., Calgary, pp. 1-3), indicating some "biological puzzles "of the famous Japanese "Aka-tombo” and its continental vicariant S. depressiusculum, we have examined the karyotypic morphology of the two taxa. It was our objective to investigate whether or not the cytotaxonomic approach could provide any evidence towards a tentative solution of the problems concerning their taxonomic status and phylogenetic relationships. The karyotype of the Japanese S. frequens was originally described and figured by K. OGUMA (1915. Dobulsugaku Zasshi 22: 241- -250), based on material from Sapporo, The karyogram No. 11, shown in his figure on p. 245, is referable to this species. At primary spermatocyte metaphase there are clearly 13 elements, representing 11 "normal" bivalents, a very minute m-bivalent, and an X. OGUMA dealt with the same species in his subsequent, English paper (1930. J. Far. Sci. Hokkaido Univ., VI, I: 1-32), in which he revised his earlier views, giving the male haploid number as n = 12 (shown also in fig. 2 d), and stated explicitly that "the smallest chromosome in the chromosome garniture of the primary spermatocyte is the X-chromosome.. ."and suggested "the fading away of [the original m\... through diminution of chromatin”. This publication was referred to by all subsequent workers, listing the chromosome number of S. frequens as n = 12, without examination of any fresh material.