Senescence in field crickets (Orthoptera; Gryllidae): examining the effects of sex and a sex-biased parasitoid

The evolutionary theory of aging proposes that senescence is related to dec reased selection against deleterious mutations acting late in life. Senesce nce, i.e., an increase in intrinsic mortality with age, should reflect leve ls of extrinsic mortality early in life. We tested these predictions using two species of field cricket, Gryllus integer and Gryllus pennsylvanicus. G ryllus integer males are host to a sex-biased parasitoid fly, which orients to the male calling song. As a result, males have reduced life expectancy compared with females in the field. In contrast, G. pennsylvanicus males an d females appear to have similar life expectancies in the wild. Thus, we pr edicted that there would be a significant species + sex interaction, with G . integer males having the shortest life-span. In two replicates, we found that males of both species died at a significantly younger age than females . However, no evidence of a species + sex interaction was found: in the fir st replicate, G. integer males died earliest, in the second replicate, G. p ennsylvanicus males died earliest.