Subjective and objective components of resource value additively increase aggression in parasitoid contests

Abstract

Two major categories of factors are predicted to influence behaviour in dyadic contests; differences in the abilities of the contestants to acquire and retain resources (resource holding potential), and the value of the contested resource (resource value, RV; which comprises objective and subjective components). Recent studies indicate that subjective components affect contest behaviour in several animal taxa but few have simultaneously investigated objective RV components. We find that both an objective (host size) and a subjective (contestant age) component of RV affect contest intensity in the parasitoid wasp Goniozus legneri. These additively influence aggressiveness, with a larger effect from the subjective component than the objective component. The greater influence of subjective RV adds weight to the recent surge of recognition of this RV component's importance in contest behaviour.

Sustenance and Performance: Nutritional Reserves, Longevity, and Contest Outcomes of Fed and Starved Adult Parasitoid Wasps

“…due to their lower life-expectancy (Humphries et al, 2006;Stockermans and Hardy, 2013) and/or the opportunity to hostfeed, whereas fed wasps may perceive a host as having lower value due to their more abundant reserves. Thus, it remains possible that diet influences G. legneri contests between starved and fed wasps, but via opposing and coincidentally equal effects.…”

“…Older G. legneri females behave more aggressively during contests (Stockermans and Hardy, 2013), due to RV increasing as females age; thus Total 137 Results are from backwards stepwise logistic ANCOVAs on the probability of a contest being clearly resolved. Note that contestant weight differences (heaviest wasp-lightest wasp) were experimentally minimised.…”

“…Culturing and contest experiments were carried out in a climate room at 27 • C with a relative humidity of 60-70% maintained by water bath evaporation. The parasitoid strain was obtained from a commercial insectary in the USA, both host and parasitoid strains were the same as those utilised in several previous contest studies (Goubault et al, 2006;Bentley et al, 2009;Stockermans and Hardy, 2013).…”

“…Aggressive contest behaviour was additionally confirmed to have occurred by reviewing the video footage (Petersen and Hardy, 1996). For the purposes of this study, aggressive behaviour was considered to include any of the following categories: chasing, biting, stinging and fighting (mutual grappling), as outlined by Stockermans and Hardy (2013). Contest trials that did not result in aggressive behaviour were considered not to be clearly resolved.…”

“…indicate that G. legneri fed with honey live longer than starved adults, suggesting that G. legneri can use dietary carbohydrates as a maintenance energy supply. Feeding on honey has the potential to counter the effect of the increased value, V, that older contestants place on host possession (Stockermans and Hardy, 2013, see also Humphries et al, 2006); if so, we might expect starved wasps to win contests against similarly aged but fed wasps. Conversely, honey-fed contestants may have enhanced contest abilities, RHP, due to higher energy reserves (Tsai et al, 2014); if so we might expect starved wasps to lose such contests.…”