Among and within individual variation in behaviour in wild field crickets Gryllus campestris Linneaus

Abstract

Behavioural traits have the potential to vary enormously both within- and among individuals, and over much shorter timescales than most other traits. In a population, animals of the same species can show consistent among individual behavioural variation across time and situations. We tested the behaviour of European field cricket, G. campestris in a natural population living in and around their burrows. We examined potential differences between the sexes in age-related changes in trait expression across the adult lifespan and investigated among individual variation in daily activity patterns. Our prediction is that crickets will change their patterns of activity with age, and that the pattern of this change will differ between the sexes. Following individuals of both sexes through their adult lives, we recorded a range of behaviours, including how often they moved in and out of their burrows, how long they spent in or out, how quickly they left a burrow after fleeing inside to escape predation, and whether they fed. By analysing the behaviour of crickets living in the wild as they aged, we found that this early effort may take a toll on males: Males declined in their physical performance as they aged, whereas females did not. We found evidence for senescent declines in two of the traits in males, but not in females. Males moved less often and spent less time outside their burrow as they aged, whereas females showed no age-related changes in either trait. Both sexes spent more time at the entrance of their burrows with age, and neither sex showed age-related changes in the time to leave the burrow after fleeing. We found evidence of among-individual differences in 3 traits (how many times the cricket moved in and out of its burrow (moves), how long it spent outside the burrow (outside) and how likely it was to be observed feeding (feeding) according to the time of day. We found evidence for sex differences in 2 traits (feeding, outside) whereas there is no evidence of sex differences for moves. Our findings support the prediction that males senesce faster than females; experiments in nature will be needed to determine whether this pattern arises from the trade-offs that have been hypothesised. Keywords: Aging, wild behaviour, Gryllus, diel activity, chronotype, senescence, personality.