The karyotypes of Aeshna subarctica elisabethae Djak. and Somatochlora alpestris (Sel.) from Switzerland (Anisoptera: Aeshnidae, Corduliidae)

A. suharctica etisabethae. I <J, Schwarzsee, Seebenalp, Flumserberg, St. Gallen, 1630 m; Sept. 15, 1980; 33 complements photographed. — n = 14, m. — (Fig. 1). — The chromosome morphology of Finnish material (Jyvàskylà and Tvàrminne) was reported by T. OKSALA (1943, Ann. Acad. Sci.fenn. (A) 4 (4): 1-54, 1 pi. excl.; — 1952, Hereditas 38: 449-480). From his 1943 metaphase-l description (p. 13) and figure 2, and from his 1952 figures 1-2 and 13 (micrograph) it is apparent that the Swiss individual is distinct in having, in most metaphase-I figures, a considerably smaller X, which is often but little inferior in size to the relatively small m-bivalent. In Finnish material the latter is too large to be readily discerned from other bivalents at this stage. In view of a certain amount of structural variation (colour pattern) in individuals from Nordic and Alpine populations on one hand, and those from the lowlands of northern Central Europe on the other, a systematic examination of the karyotypic variation throughout the subspecies range is likely to be rewarding. It would be likewise interesting to compare the chromosome morphology of elisabethae to that of the nearctic nominate form. S. alpestris: 5 d, GroBsee, Seebenalp, Flumserberg, St. Gallen, 1630 m; Sept. 15-21, 1980; 55 complements photographed. — n = 13; 13/14, m. — (Figs. 2-3). —-Only in two individuals was the haploid chromosome number invariably 13, while in the other three specimens the n = 14 complements prevailed. There is no m in the n = 13 karyotype and, at metaphase I, the X is the smallest of the set. A clearly structured m-bivalent occurs in the n = 14 complements; it seems to originate in fragmentation of one of the medium-sized pairs. The size of the other elements (bivalents) appears approximately identic in both complements. This is the first member of the genus (out of six studied; cf. B. KIAUTA, 1972, Odonatologica I: 73-102) in which the chromosome number deviates from the n = 13 pattern. The possibility of the existence of a correlation between the peculiar biogeographic character of the species and its recombination potential (i.e. increased genetic flexibility of the genome) cannot be argued on the basis of this incidental evidence.