Reproductive costs to heterospecific mating between two hybridizing katydids (Orthoptera : Tettigoniidae)

Animal taxa meeting in hybrid zones often exhibit partial reproductive isol ation. This isolation may result from a variety of causes both before matin g (e.g., incompatibilities in courtship behaviors) and subsequent to mating . Understanding the factors effecting reproductive isolation in hybrid zone s can offer important insights into the process of speciation and the maint enance of species boundaries. The katydids Orchelimum nigripes Scudder and O. pulchellum Davis (Orthoptera: Tettigoniidae) form 2 hybrid zones in the eastern United States. I carried out breeding studies in the laboratory usi ng animals from pure O. nigripes and O. pulchellum populations in the vicin ity of one of these hybrid zones to examine possible modes of postmating re productive isolation. The number of eggs produced by females mated to heter ospecific males was dramatically lower than that of females mated conspecif ically, but there was no evidence of any differences in hutch rate or offsp ring viability between egg clutches from heterospecific and conspecific cro sses. Hatch rate, offspring viability, development time, and adult weight o f hybrid progenies were all intermediate relative to corresponding values f or progenies resulting from the 2 types of conspecific matings, although mo st of the differences between hybrids and each of the 2 classes of nonhybri d progenies were not statistically significant. The reduced oviposition of heterospecifically mated females suggests that females mated to heterospeci fic males do not receive the necessary stimulation to trigger oocyte matura tion or oviposition behavior. The results reported here show that although some females will mate with heterospecific males, these matings tend to res ult in substantially reduced reproductive success relative to conspecific m atings.