ASYMMETRICAL HOMOGAMY AND UNEQUAL SEX-RATIO FROM RECIPROCAL MATING-ORDER CROSSES BETWEEN CHORTHIPPUS PARALLELUS SUBSPECIES

To study the evolution of this Pyrenean hybrid zone following postglac ial secondary contact, a crossing programme was performed involving se quential mating of single females by males of both subspecies in both orders. Progeny were scored as embryos using Acridine orange and C-ban ding to identify their male parent. This revealed a number of signific ant departures from straightforward inheritance. There was an excess o f pure over hybrid progeny. This homogamy is produced at fertilization but may have been determined before through sperm preference or compe tition. There was also sperm precedence with the second mating produci ng most of the progeny. This may be due to sperm ageing or differentia l storage and utilization by the female. The fundamental sex ratio in the progeny was biased towards males. Of particular interest is the fi nding that homogamy is markedly greater when C.p. parallelus is the mo ther, suggesting some form of differential biochemical recognition. Th is asymmetry should have important consequences for the dynamics of th e hybrid zone. All these results are discussed in the light of the div ergence of the two subspecies and the mixing of their genomes in the h ybrid zone.