DISTRIBUTION OF CHIASMATA AND CHROMOSOME- PAIRING IN GRASSHOPPER SPECIES OF SUBFAMILY OEDIPODINAE

Distribution of chiasmata and the formation of the synaptonemal comple x (SC) was studied in 12 grasshopper species belonging to three tribes of the family Oedipodinae. Three types of distribution of exchanges i n long and middle bivalents were observed: (1) Chiasmata were formed a long the whole length of bivalents, being slightly more numerous in th eir distal segments (Oedaleus decorus and Celes variabilis); (2) chias mata were located predominantly in distal and proximal segments of biv alents (Pyrgodera armata); and (3) chiasmata were necessarily formed i n the proximal segments and, in certain cells, also in distal segments . Exchanges between medial parts of bivalents were absent (tribe Bryod emini and C. skalozubovi). The relationship between the type of chiasm a distribution and the taxonomic positions of the study species was an alyzed. It was concluded that the evolution of grasshoppers was accomp anied by the formation of long chromosome segments with restricted rec ombination capacity, or even with complete linkage. Genus Celes can be regarded as a transition taxon, because two species of this genus sho wed types of chiasma formation that differed in principle, and C. vari abilis demonstrated a considerable intraspecific variability in the di stribution of exchanges over the length of bivalents. A correspondence between distribution of-exchanges and the type of SC formation was ob served: in parts of bivalents with low chiasma frequencies or without chiasmata, SC were found irregularly or were absent.