Males and females differ in how their behaviour changes with age in wild crickets (article)

Abstract

Because females produce and lay eggs or nurture embryos, they are constrained in the timing of their investment in reproduction. Males may have more opportunity to concentrate reproductive investment earlier in life, mating with as many females as possible soon after becoming adult. This fundamental difference leads to the prediction that because males can bias allocation towards increased reproductive investment early in life, they will use up resources earlier in their lives and hence senesce faster than females. A first step towards testing this prediction is to determine whether there are between-sex differences in age-related changes in behaviour. To do this we recorded the behaviour of crickets, Gryllus campestris, in a natural population living in and around their burrows in a meadow in northern Spain. Following individuals of both sexes through their adult lives, we recorded a range of nonreproductive behaviours, including how often they moved in and out of their burrows, how long they spent at the entrance, how long they spent outside, how quickly they left a burrow after fleeing inside to escape predation and whether they fed. We found evidence for substantial age-related changes in two of the movement traits in males, but not in females. Males moved less often and spent less time outside their burrows as they aged, whereas females showed no age-related changes in either trait. Feeding was not affected by age in males, but females fed more often as they got older. Our findings are consistent with the prediction that males senesce faster than females; experiments in nature will be needed to determine whether this pattern arises from life history trade-offs between reproduction and other traits.