Encountering competitors reduces clutch size and increases offspring size in a parasitoid with female–female fighting

Understanding the size of clutches produced by only one parent may require a game-theoretic approach: clutch size may affect offspring fitness in terms of future competitive ability. If larger clutches generate smaller offspring and larger adults are more successful in acquiring and retaining resources, clutch size optima should be reduced when the probability of future competitive encounters is higher. We test this using Goniozus nephantidis, a gregarious parasitoid wasp in which the assumption of size-dependent resource acquisition is met via female–female contests for hosts. As predicted, smaller clutches are produced by mothers experiencing competition, due to fewer eggs being matured and to a reduced proportion of matured eggs being laid. As assumed, smaller clutches generate fewer but larger offspring. We believe this is the first direct evidence for pre-ovipositional and game-theoretic clutch size adjustment in response to an intergenerational fitness effect when clutches are produced by a single individual

Patch exploitation strategies of parasitic wasps under intraspecific competition. Behav Ecol.

The optimal residence time of a forager exploiting a resource patch in the absence of competitors has been much studied since the development of the marginal value theorem. However, several foragers are frequently observed exploiting the same patch simultaneously, and patch residence time has been surprisingly little studied in such competitive situations. The few theoretical models developed on this topic predict that foragers should engage in a war of attrition and stay in the patch longer than when foraging alone. We tested this prediction in Pachycrepoideus vindemmiae (Hymenoptera: Pteromalidae), a solitary parasitoid species in which females are known to defend the hosts they are exploiting via intraspecific fighting. By measuring the effect of direct (i.e., presence of conspecifics) and indirect (i.e., presence of already-parasitized hosts) competition on patch exploitation strategies, we revealed an apparent polymorphism of strategies. Indeed, in competitive situations, some members of the population tended to retreat almost immediately from the patch whereas other members tended to remain, further exploit the patch, and be more involved in interactions with conspecifics. The proportion of ''retreaters'' strongly depended on competition intensity and prior experience of competition. The forager's physiological state (age) also affects patch exploitation strategy and the intensity of interactions between competing females. Our results highlight the necessity for further theoretical studies that consider cases where contests between foragers are costly and take into account prior experience of competition and the forager's physiological state

Volatile chemical emission as a weapon of rearguard action: a game-theoretic model of contest behavior

We use a game-theoretic model to explore whether volatile chemical (spiroacetal) emissions can serve as a weapon of rearguard action. Our basic model explores whether such emissions serve as a means of temporary withdrawal, preventing the winner of the current round of a contest from translating its victory into permanent possession of a contested resource. A variant of this model explores an alternative possibility, namely, that such emissions serve as a means of permanent retreat, attempting to prevent a winner from inflicting costs on a fleeing loser. Our results confirm that the underlying logic of either interpretation of weapons of rearguard action is sound; however, empirical observations on parasitoid wasp contests suggest that the more likely function of chemical weapons is to serve as a means of temporary withdrawal. While our work is centered around the particular biology of contest behavior in parasitoid wasps, it also provides the first contest model to explicitly consider self-inflicted damage costs, and thus responds to a recent call by empiricists for theory in this area

Previous Experience and Contest Outcome: Winner Effects Persist in Absence of Evident Loser Effects in a Parasitoid Wasp

International audienceThe experience of a previous conflict can affect animals' performance during a later contest: a victory usually increases and a defeat usually decreases the probability of winning a subsequent conflict. These winner and loser effects could result from a reassessment by contestants of their perceived fighting abilities. Gametheoretic models based on this assumption predict that a loser effect can exist alone or in the presence of a winner effect, but a winner effect cannot persist alone, at least when contestants are young and without experience of contest. Moreover, when both effects coexist, the loser effect is expected to be of a greater magnitude and last longer than the winner effect. To date, these predictions have been supported by empirical evidence. Here we show for the first time that a winner effect can exist in the absence of any evident loser effect in a parasitoid wasp, Eupelmus vuilleti, when fighting for hosts. This finding consequently raises questions about the possible mechanisms involved and challenges the main assumption of previous theoretical models. We suggest an alternative explanation for the evolution of only winner effects that is based on the modification of contestants' subjective value of the resource rather than on a reestimation of their fighting abilities

Data from: Prior experience and contest outcome: winner effects persist in absence of evident loser effects in a parasitoid wasp

The experience of a prior conflict can affect animals' performance during a later contest: a victory usually increases while a defeat decreases the probability of winning a subsequent conflict. These winner and loser effects could result from a reassessment by contestants of their perceived fighting abilities. Game-theoretic models based on this assumption predict that a loser effect can exist alone or in the presence of a winner effect, but a winner effect cannot persist alone, at least when contestants are young and without experience of contest. Moreover, when both effects coexist, the loser effect is expected to be of a greater magnitude and last longer than the winner effect. To date, these predictions have been supported by empirical evidence. Here, we show for the first time that a winner effect can exist in the absence of any evident loser effect, in a parasitoid wasp, Eupelmus vuilleti, when fighting for hosts. It consequently raises questions about the possible mechanisms involved and challenges the main assumption of previous theoretical models. We suggest an alternative explanation for the evolution of only winner effects, based on the modification of contestants' subjective value of the resource rather than on a re-estimation of their fighting abilities

Do males choose their mates in the lekking moth Achroia grisella ? Influence of female body mass and male reproductive status on male mate choice

International audienc

Self‐superparasitism, oviposition order, and delay: does offspring survival explain host exploitation strategies of females under interspecific competition in a solitary parasitoid wasp?

Abstract If the risk of larval competition is high and its consequence on offspring mortality is important, we expect female behavioural strategies favouring the survival of their offspring to be selected for. In parasitoids, hosts can be parasitized several times, in some cases by females of different species (i.e., multiparasitism). In solitary parasitoids, only one offspring can develop per host: supernumerary individuals are eliminated through larval competition. Under these conditions, mothers can lay additional eggs in/on the same host (i.e., self‐superparasitism) to increase the chances of one of their offspring winning the competition. They can also aggressively protect their offspring against competing females to prevent them from multiparasitism and ovicide. Both strategies (self‐superparasitism and host defence) are observed in females of the solitary ectoparasitoid wasp, Dinarmus basalis Rondani (Hymenoptera: Pteromalidae), when facing females of another solitary ectoparasitoid species, Eupelmus vuilleti (Hymenoptera: Eupelmidae), during host exploitation. Here, we aimed to explore whether D. basalis females' behaviours relate to their offspring survival chances during larval competition: we expect mothers to defend their hosts only during the vulnerability period of their offspring and self‐superparasitize to increase the chances of their offspring winning the larval competition. We thus measured the effect of oviposition order ( D. basalis females oviposited first or second), delay between ovipositions (30–60 min or 3–4 h) and the occurrence of D. basalis females' self‐superparasitism on D. basalis offspring survival when competing with E. vuilleti juveniles. Our results showed D. basalis offspring constantly had a lower survival probability than E. vuilleti offspring. Only being laid first increased D. basalis offspring survival rate, whereas the time delay between ovipositions and self‐superparasitism did not significantly increase it further. The fact that offspring survival chances under interspecific competition may not be the main driver of maternal host protection and self‐superparasitism is discussed

Sperm limitation affects sex allocation in a parasitoid wasp Nasonia vitripennis

International audienceInsect reproduction is influenced by various external factors including temperature, a well‐studied constraint. We investigated to what extent different levels of sperm limitation of males exposed to different heat stresses (34 and 36 °C) affect females’ offspring production and sex allocation in Nasonia vitripennis. In this haplodiploid parasitoid wasp attacking different species of pest flies, we investigated the effect of the quantity of sperm females received and stored in their spermatheca on their sperm use decisions, hence sex allocation, over successive ovipositions. In particular, we compared the sex allocation of females presenting three levels of sperm limitation (i.e., mated with control, 34 °C heat‐stressed or 36 °C heat‐stressed males) on each host they parasitized. To disentangle the potential reduction of sperm quality after a heat stress exposure from that of sperm quantity, we also explored the clutch size and sex ratio produced by females that were partially sperm limited after copulating with multiply mated males. Independently of their sperm numbers, all types of females produced a similar total number of offspring, but the more limited ones had fewer daughters. Sperm limitation further affected the distribution of daughters’ production across time. In addition to constraints acting on female physiology, male fertility should therefore be considered in studies measuring reproductive outputs of insects submitted to heat stresses

Exploitation des hôtes chez un hyménoptère parasitoïde solitaire (conséquences adaptatives de la compétition intraspécifique sur les stratégies comportementales des femelles)

Les individus d'une même espèce exploitent les mêmes ressources et peuvent entrer en compétition pour l'acquisition de certaines d'entre elles. Chez les parasitoïdes, les décisions prises par les femelles concernant l'exploitation des hôtes influencent directement leur gain de fitness. Les hôtes sont donc la ressource la plus importante pour laquelle les femelles sont en concurrence. Les femelles parasitoïdes peuvent entrer en compétition pour les hôtes soit de manière indirecte, lorsqu'elles rencontrent des hôtes déjà parasités (compétition "par exploitation"), soit de manière directe, lorsque les différentes femelles présentes sur un même site interagissent (compétition "par interférence"). Pour maximiser leur fitness, les femelles doivent adapter leurs stratégies comportementales en fonction du type de compétition rencontré. Nous avons étudié l'influence de ces deux niveaux de compétition intraspécifique sur les stratégies d'exploitation des hôtes chez un parasitoïde solitaire.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Fixed or flexible? Winner/loser effects vary with habitat quality in a parasitoid wasp

Prior experience of fighting affects the outcome of subsequent contests, with prior winners being more likely to win and priorlosers being more likely to lose a future encounter. These winner and loser effects have been shown in numerous species but haveusually been tested in only one set of conditions. However, if such effects are not fixed but context dependent, we can expect theirstrength to change according to the situation. In particular, their magnitude could covary with other factors, such as thoseinfluencing contestants’ fighting abilities or the value they place on the contested resource, which in turn are known to influencecontest behaviors and outcomes. Here, we tested the effect that prior experience of resource availability had on the expression ofwinner and loser effects in Eupelmus vuilleti, a parasitoid wasp fighting for hosts on which to lay their eggs. We showed that aloser effect was observable only when females experienced a habitat rich in hosts (hence placed low value on the contestedindividual host) but not when they were deprived of hosts (leading to individual hosts having high value). Contrary with a priorstudy, no clear winner effect was observed. These results suggest that the strength of winner and loser effects are contextdependent in E. vuilleti, and interactions with other factors can either accentuate or attenuate the effects. Our data further raisethe question of whether the intensity of the first encounter, not only its outcome, influences the behavioral decisions of individualsduring a subsequent contest