Biogeographic considerations on Coenagrion hylas freyi (Bilek, 1954), based mainly on the karyotype features of a population from North Tyrol, Austria (Zygoptera: Coenagrionidae)

The chromosome cytology of the sp. (n<5 = 14, no m; R1 $ = 26) is compared with that prevailing in odon. pioneer spp., in spp. in the process of expanding their range (which is coupled with infraspeciation), and in those considered to represent Pleistocene ("glacial”) faunal relics. While in h. freyi the chromosome number and the recombination index (Rl) are stabilized at the modal adaptive level of the genus, this is not the case in the taxa referable to any of the 3 said groups. On the other hand, the karyotypic features of h. freyi do agree with those so far known in odon. spp. of trans-eurasiatic or holarctic distribution. The hitherto available information on its habitat requirements and behaviour is also taken into consideration, and it is preliminarily concluded that h.freyi 'is neither a pioneer sp,, nora recent introduction into the European fauna, but rather a trans-eurasiatic taxon, whose post-Pleistocene disjunction is the result of its specialized microhabitat requirements, associated with shallow, essentially stenothermic (sections of) subalpine lakes and ponds, characterized by a rather complex biotic community and by a climax odon. association. The paucity of the hitherto known localities in Europe is tentatively ascribed to the peculiar adult diurnal activity rhythm (which was hitherto unknown and, therefore, greatly reduced the chances of detection of a resident population), and to the rarity of the required type of habitats. — An annotated bibliography on the taxon is appended.