Does Host Value Influence Female Aggressiveness, Contest Outcome and Fitness Gain in Parasitoids? (original) (raw)
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Can subjective resource value affect aggressiveness and contest outcome in parasitoid wasps?
Animal Behaviour, 2010
agonistic interaction Eupelmus vuilleti female egg load femaleefemale contest past experience physiological status previous habitat quality Although animal contests for resources are often settled in favour of individuals with the greatest fighting abilities, other factors, such as those affecting the value that contestants place on the resource, can also influence contest resolution and aggressiveness. For example, competitors should fight more fiercely for access to larger than smaller food items. However, this also depends on contestants' subjective value of the resource: individuals deprived of a given resource should value it more highly than individuals that recently had access to it. They should therefore be more aggressive and win contests more frequently. In some parasitoid species, adult females fight for hosts on which to lay eggs and feed. Using the parasitoid Eupelmus vuilleti, we investigated the effect on contest outcome of two factors affecting females' subjective host value: the quality of the habitat previously encountered by females (either rich or poor in hosts) and females' physiological state (i.e. the number of ready-to-lay eggs in their ovaries). Subjective host value should increase with both host scarcity and egg load. We first described the agonistic behaviours displayed by E. vuilleti females during contests and then verified that difference in habitat quality was perceived by females (they modified their host exploitation behaviours accordingly) but did not affect their egg load, so that the effects of both factors could be separated. Both habitat quality experience and egg load affected contest outcomes, with egg load asymmetry being the main factor in this species. Our results support game theoretical predictions. Ó
The elusive paradox: owner-intruder roles, strategies, and outcomes in parasitoid contests
Behavioral Ecology, 2009
Models of dyadic contests for indivisible resources have predicted that the owner-intruder role distinction can suffice as a cue for evolutionarily stable resolution. This outcome may be ''common sense'' (prior owners retain the resource) or counterintuitively ''paradoxical'' (the intruder takes over), but the most recent models predict paradoxes to be an infrequent result, and there are also very few candidate examples provided by empirical study. Possible paradoxical outcomes were recently reported from the parasitoid wasp Goniozus legneri in which adult females compete directly for hosts. Here we provide further investigation, taking into account influences of contest ability (body size) and the value of the host to each contestant (correlated with the developmental stage of the owner's brood). We additionally evaluate contest strategies in terms of respect for ownership as evidenced by attack behavior during contests. Goniozus legneri shows weak, and thus only partial, respect for role asymmetries: such mixed strategies are predicted by recent models that assume population-level feedback on resource value parameters. Contest outcomes are influenced by asymmetries in resource value and body size and are generally common sense. Instances of paradoxical contests remain predictably elusive.
Animal Behaviour, 2006
When two animals compete directly for an indivisible resource, the outcome may be influenced by differences in the contestants' intrinsic contest abilities and prior owner status, collectively termed 'resourceholding potential', and also by any difference in the values that contestants place on the resource. Using ownereintruder contests and ownereowner contests between females of the parasitoid wasp Goniozus nephantidis, we investigated the influence of resource value asymmetries generated by differences in contestant age and by the size of the host resource, while taking resource-holding potentials into account. When owners and intruders competed, intruder success increased with both intruder age and relative body size, suggesting that larger females had greater contest ability and that older intruders valued more greatly the opportunity to obtain a host. The size of the host did not influence the outcome of ownereintruder contests but in ownereowner contests, in which asymmetries in ownership status were absent, both larger females and owners of the larger, more valued, hosts were advantaged. Overall, studies of G. nephantidis show that asymmetries in both resource-holding potentials and resource values interact to influence contest outcomes. Despite a large literature on animal contests, there have been few studies that have evaluated these influences both simultaneously and separately.
Environmental Entomology, 2004
In solitary parasitoid species, superparasitism incurs a high cost because only one individual can emerge per host. While avoiding already-parasitized hosts seems advantageous, it requires an ability to discriminate between parasitized and unparasitized hosts. The ability to discriminate can be based on physical or chemical cues or signal associated either internally or externally with a given host. The type of stimuli used to recognize parasitized hosts generally depends on the features of these hosts but also on costs and beneÞts associated with reusing them. Some local factors such as mortality rate of females, host availability, and competition level can inßuence this trade-off. In species that occupy a large geographic range, local conditions may favor either external or internal mechanisms of host discrimination. We describe the behaviors associated with host discrimination in Pachycrepoideus vindemmiae Rondani (Hymenoptera: Pteromalidae), a solitary pupal parasitoid of cyclorraphous dipteran species. To detect potential intraspeciÞc variability in their host discrimination behavior, we compared two P. vindemmiae populations originating from different geographical areas in France. Our results revealed different host discrimination strategies in both populations and indicated a potential trade-off between the speed and the accuracy of host discrimination. One population discriminated hosts externally (faster but less accurately), whereas the other discriminated internally (more slowly but more accurately). In our experimental conditions, these two strategies resulted in differences in the Þtness gains of both populations. The ecological conditions that could have selected for such differences in the host discrimination and oviposition strategies of the two populations remain to be investigated.
Fixed or flexible? Winner/loser effects vary with habitat quality in a parasitoid wasp
Behavioral Ecology and Sociobiology, 2019
Prior experience of fighting affects the outcome of subsequent contests, with prior winners being more likely to win and prior losers being more likely to lose a future encounter. These winner and loser effects have been shown in numerous species but have usually been tested in only one set of conditions. However, if such effects are not fixed but context dependent, we can expect their strength to change according to the situation. In particular, their magnitude could covary with other factors, such as those influencing contestants' fighting abilities or the value they place on the contested resource, which in turn are known to influence contest behaviors and outcomes. Here, we tested the effect that prior experience of resource availability had on the expression of winner and loser effects in Eupelmus vuilleti, a parasitoid wasp fighting for hosts on which to lay their eggs. We showed that a loser effect was observable only when females experienced a habitat rich in hosts (hence placed low value on the contested individual host) but not when they were deprived of hosts (leading to individual hosts having high value). Contrary with a prior study, no clear winner effect was observed. These results suggest that the strength of winner and loser effects are context dependent in E. vuilleti, and interactions with other factors can either accentuate or attenuate the effects. Our data further raise the question of whether the intensity of the first encounter, not only its outcome, influences the behavioral decisions of individuals during a subsequent contest. Significance statement A previous victory can increase the chance of winning a subsequent fight, while a prior defeat can increase the chance of losing. Such winner and loser effects have been shown in numerous species but have usually been studied in only one set of conditions. We show that the strength of these effects can be context dependent, such that they are accentuated or attenuated when experience interacts with factors such as habitat quality. Our data further raise the question of whether the intensity of the first encounter (how Bhard^it was to win or lose), not just the outcome, influences behavioral decisions during subsequent contests.
Journal of Insect Behavior, 2000
Host rejection, superparasitism, and ovicide are three possible host selection strategies that parasitoid females can adopt when they encounter parasitized hosts. These differ in costs (in terms of time and energy required) and benefits (in terms of number and quality of offspring produced). Their relative payoff should vary with patch quality, (i.e., proportion of parasitized hosts present), and female choice between them should be adapted accordingly. We conducted behavioral observations to test the effect of the ratio of parasitized/unparasitized hosts present in a patch on the host selection strategies of Pachycrepoideus vindemmiae Rondani (Hymenoptera: Pteromalidae). This species being a generalist known to attack hosts of a great range of size, we also tested the impact of host size on female decisions with two host species differing greatly in size (Drosophila melanogaster and Delia radicum). We evaluated the adaptive value of each strategy in relation to host parasitization status and host size by measuring their duration and the potential number of offspring produced.
The importance of offspring value: maternal defence in parasitoid contests
Animal Behaviour, 2007
Parent investment theory predicts that parents should adjust their investment in offspring defence according to offspring value. For instance, parents should protect older, more valuable, offspring more intensively than younger offspring against a given risk of mortality. The benefits of protection may, however, vary with offspring age and parents should thus behave according to the harm that offspring would suffer in the absence of parental defence. Prior studies on this topic have focused mainly on birds and mammals with data on other taxa largely lacking. We used the parasitoid wasp Goniozus nephantidis to investigate the effect of offspring developmental stage on maternal defence against infanticidal conspecific females. On finding a host caterpillar, a G. nephantidis female paralyses it and lays eggs onto it approximately 1 day later, then remains with the offspring during development until the offspring pupate. If the host is encountered by a second female, classic ownereintruder contests ensue, with the loser being aggressively excluded from the vicinity of the host. We tested the effect of brood developmental stage on contest outcomes and also assessed the consequences of offspring age for their survival in the event that an intruder female wins the contest. We found that females defend younger offspring more than older offspring. Explanations for this behaviour are discussed in terms of ownereintruder asymmetries in resource value and the 'harm to offspring hypothesis'.
Animal Behaviour, 1996
One of the most important relationships in parasitoid behavioural ecology is that between adult female size and fitness. However, surprisingly few studies have attempted to assess size-related components of fitness beyond fecundity and longevity. This paper provides a more complete appraisal of the size-fitness relationship in the bethylid wasp Goniozus nephantidis by investigating the influences of female size and ownership-status on the outcome of owner-intruder contests for paralysed hosts. Both influenced contest outcomes: larger females tended to win, but outcome was modified in favour of owners when intruders were only moderately larger. Aggressive behaviour during contests is described. The size-fitness relationship, based on fecundity and longevity as correlates of fitness, has previously been used to estimate optimal clutch size in G. nephantidis and a large discrepancy was found between observed and predicted clutch sizes. Here it is argued that because female fitness is determined, at least in part, by body size relative to competitors, an evolutionarily stable strategy approach is required to calculate optimal clutch size when host ownership contests occur. Clutch sizes could be influenced greatly and this provides a candidate explanation for the previously reported discrepancy.
The importance of being gravid: egg load and contest outcome in a parasitoid wasp
Animal Behaviour, 2000
Owners have often been found to have an advantage in animal contests. One explanation of this is that the resource under dispute is of greater value to the owner than to the intruder (nonowner). Such 'resource value asymmetries' may be caused by intrinsic factors, such as the physiological state of the contestants. Females of the bethylid wasp Goniozus nephantidis fight for possession of paralysed hosts. A recent study found that larger females tend to win but owner status also confers an advantage. We tested the hypothesis that ownership advantage is linked to differences in egg load (the number of unlaid ripe eggs) between contestant females. Egg loads were highly variable and positively influenced by age, nutrition, body size and host ownership. Owners almost always won owner-intruder contests. The outcomes of owner-owner contests (in which size and status asymmetries were absent) were strongly influenced by differences in egg load.