NEGATIVELY ASSORTED GAMETE FERTILIZATION FOR SUPERNUMERARY HETEROCHROMATIN IN 2 GRASSHOPPER SPECIES

The analysis of controlled crosses and gravid females in two grasshopp er species has shown nonrandom gamete fertilization, caused in both ca ses by a preference for ova and sperm to fuse with gametes carrying an allele different from their own. Such a fertilization bias was observ ed for a B chromosome in Eyprepocnemis plorans and a supernumerary chr omosome segment on the M(7) autosome in Chorthippus jacobsi. In additi on, a male-biased sex ratio was observed in E. plorans among the embry o offspring produced by 1B gravid females which had mated with a 1B ma le in the field, but no sex ratio distortion was apparent in the same type of crosses performed in the laboratory. The possible causes of th ese distortions, and the role which negatively assorted fertilization may play upon the maintenance of these polymorphisms in natural popula tions, are discussed.