Autosomal fragmentations and fusions in odonata and their evolutionary implications

The fragmentation of autosomes in the karyotypes ofEnallagma cyathigerum (Charp.) (n=1415),Mecistogaster sp. (n=15),Hetaerina rosea Sel. (n=14),Libellula depressa L. (n=1213),Orthetrum coerulescens (Fabr.) (n=1213),Diplacodes bipunctata (Br.) (n=1315) andD. haematodes (Burm.) (n=1213) is discussed. Original material ofMecistogaster andHetaerina was not available.Fragmentations were found to be the only way in which the recombination index is obligatorily changed (increased) in dragonflies. In at least five out of the seven cases considered the chromosome number is not stabilised: cells in which fragmentation occurred and those in which it did not are found in the same individual (Enallagma, Libellula, Orthetrum, Diplacodes). Fragmentation results in an increase of chromosome number (a) up to the family type number level (Libellula, Orthetrum, D. haematodes), (b) above the latter (Hetaerina) and (c) above any chromosome number ever reported in dragonflies (Mecistogaster, D. bipunctata). In our material the element or elements formed by fragmentation have always the size and usually also the heterochromatic features of the m-chromosomes, irrespective of the presence or absence of the latter in the original complement.A review of species in which fusions of autosomes were recorded or can be assumed is given.Orthetrum brachiale (Beauv.) (n=11) is added to the list. The situation in this species and inSympetrum eroticum Sel. is discussed in detail.The most essential differences between the fusion of (an) autosome (s) with the sex element on one hand (cf.Kiauta, 1969), and the fusion of two or more autosomes on the other, lies in the observations: (a) that in the former case, fused and unfused complements occur in one individual, whereas the latter is specifically characteristic and occurs in all cells, all individuals and all populations of the species, and (b) that autosomal fusion results in an increase of chiasma frequency, due to which the recombination index in secondarily low-n complements remains the same as it was in the primary high-n sets, or becomes even higher (O. brachiale, S. eroticum).Autosomal fragmentation (found so far in some advanced forms only) is considered as a character of phylogenetic advancement. Autosomal fusion, on the other hand, does not have any relation with phylogeny.