Females are expected to have different mating preferences because of the variation in costs and benefits of mate choice both between females and within individual females over a lifetime. Workers have begun to look for, and find, the expected variation among females in expressed mating preferences. However, variation within females caused by changes in intrinsic influences has not been examined in detail. Here we show that reproductive aging caused by delayed mating resulted in reduced choosiness by female Nauphoeta cinerea, a cockroach that has reproductive cycles and gives live birth. Male willingness to mate was unaffected by variation in female age. Females who were beyond the optimal mating age, 6 days postadult molt, required considerably less courtship than their younger counterparts. Females who were older when they mated had fewer offspring per clutch and fewer clutches than females who mated young. Thus, reduced choosiness was correlated with a permanent reduction in fertility. There was no difference in overall senescence among females, and thus the reduction in clutch size did not result in the expected increased lifespan. We suggest that reproductive aging in N. cinerea, similar to aging in general, occurs because the maintenance of oocytes is costly, and selection is relaxed after the optimal mating period. Our results further suggest that selection for continued choosiness is also relaxed and supports direct selection on female choosiness and a cost to choosiness.aging ͉ female mate choice ͉ fitness ͉ mate quality ͉ sexual selection S exual selection theory predicts that mate choice, usually by females, evolves because of variation in benefits provided by mating with particular mates. Much of the recent research on sexual selection therefore has been directed at detecting the benefit provided by males to females (reviewed in refs. 1 and 2). Considerably less research effort has addressed variation in female preferences (3-7). During female mate choice, however, females must tradeoff the benefits gained by being choosy against the costs of stronger preferences (2). This cost͞benefit tradeoff should result in variation in the expression of female mate preferences both between females and by an individual female over her lifetime.Variation in female mate preferences can result from extrinsic or intrinsic factors. Examples of external conditions that may cause females to be less choosy when making mating decisions include environmental conditions that increase the energy output required to search for and compare different males (8) or high predation risk (9-11). Seasonal constraints on reproduction can also influence female choosiness (12).Intrinsic factors should also inf luence the expression of female mate choice (13, 14). Parker's ESS model of mate choice (13) suggests that the level of choosiness is a function of female reproductive quality. Females with a reproductive quality above a certain threshold should only accept mates of similarly high quality. However, females with a reproductive qualit...