Parasitoids flip a coin before deciding to superparasitize

Decision-making in a bisexual line and a thelytokous Wolbachia-infected line of Trichogramma dendrolimi Matsumura (Hymenoptera: Trichogrammatidae) regarding behavior toward their hosts

BACKGROUND

The use of thelytokous Wolbachia-infected Trichogramma (parasitic wasps) has long been considered as a way to enhance the efficacy of biocontrol. However, Wolbachia can affect the host physiology. We compared decision-making between bisexual and thelytokous Wolbachia-infected lines of Trichogramma dendrolimi Matsumura regarding behavior toward fresh and old eggs of Corcyra cephalonica at 25 ± 1 °C and 70 ± 5% relative humidity.

RESULTS

The behavioral patterns and sequences of the two lines were basically the same. The durations of various behavioral patterns and values of fitness indicators of the bisexual line on fresh eggs were generally significantly shorter and better, respectively, than on old eggs, whereas the thelytokous line behaved similarly toward the two types of eggs, and differences in most fitness indicators between fresh and old eggs were not significant. On fresh eggs, the durations of various behaviors in the bisexual line were generally significantly shorter than in the thelytokous line and the fitness indicators were generally significantly better.

CONCLUSION

Wolbachia affected the fitness of T. dendrolimi negatively. The potential of the thelytokous line as a biocontrol agent would not be as good as that of the bisexual line when decision-making only is considered. Therefore, further evaluations need to be carried out before the thelytokous line can be used in practical biocontrol. © 2018 Society of Chemical Industry.

Evolution of Site-Selection Stabilizes Population Dynamics, Promotes Even Distribution of Individuals, and Occasionally Causes Evolutionary Suicide

Species that compete for access to or use of sites, such as parasitic mites attaching to honey bees or apple maggots laying eggs in fruits, can potentially increase their fitness by carefully selecting sites at which they face little or no competition. Here, we systematically investigate the evolution of site-selection strategies among animals competing for discrete sites. By developing and analyzing a mechanistic and population-dynamical model of site selection in which searching individuals encounter sites sequentially and can choose to accept or continue to search based on how many conspecifics are already there, we give a complete characterization of the different site-selection strategies that can evolve. We find that evolution of site-selection stabilizes population dynamics, promotes even distribution of individuals among sites, and occasionally causes evolutionary suicide. We also discuss the broader implications of our findings and propose how they can be reconciled with an earlier study (Nonaka et al. in J Theor Biol 317:96–104, 2013) that reported selection toward ever higher levels of aggregation among sites as a consequence of site-selection.

Insects Can Count: Sensory Basis of Host Discrimination in Parasitoid Wasps Revealed

The solitary parasitoid Leptopilina heterotoma is one of the best studied organisms concerning the ecology, behaviour and physiology of host discrimination. Behavioural evidence shows that L. heterotoma uses its ovipositor to discriminate not only between parasitized and unparasitized Drosophila melanogaster larvae, but also to discriminate between hosts with different numbers of parasitoid eggs. The existing knowledge about how and when the parasitoid marks the host motivated us to unravel the chemosensory basis of host discrimination by L. heterotoma that allows it to choose the “best” host available. In this paper we report on electrophysiological recordings of multi-neural responses from the single taste sensillum on the tip of the unpaired ovipositor valve. We stimulated this sensillum with haemolymph of unparasitized, one-time-parasitized and two-times-parasitized Drosophila larvae. We demonstrate for the first time that quantitative characteristics of the neural responses to these haemolymph samples differed significantly, implying that host discrimination is encoded by taste receptor neurons in the multi-neuron coeloconic ovipositor sensillum. The activity of three of the six neurons present in the sensillum suffices for host discrimination and support the hypothesis that L. heterotoma females employ an ensemble code of parasitization status of the host.

Reproduction of Pisidium casertanum (Poli, 1791) in Arctic lake

Freshwater invertebrates are able to develop specific ecological adaptations that enable them to successfully inhabit an extreme environment. We investigated the brooding bivalve of Pisidium casertanum in Talatinskoe Lake, Vaigach Island, Arctic Russia. Here, quantitative surveys were conducted, with the collection and dissections of 765 molluscs, on the basis of which analyses on the brood sacs length (marsupia) and the number and size of embryos, were performed. In this study, the number of brooded embryos was positively correlated with the parent's shell length. The number of extramarsupial embryos was much lower than the number of intramarsupial embryos. Our research also showed that the brood sac length and embryos within one individual can vary significantly. Thus, we detected that P. casertanum has a specific brooding mechanism, accompanied by asynchronous development and embryos release by the parent. We suggest that such a mode could result in the coin-flipping effect that, presumably, increases the population breeding success in the harsh environment of the Arctic lake.

Superparasitism as a differential game

Superparasitism refers to a female parasitoid laying an egg in a host already parasitized by a conspecific. In solitary species, only one offspring per host is expected to complete development, hence the game. Hosts are often clumped in patches and several females exploiting such an aggregate of resource make its state change over time, hence the dynamical character of the game. Two coupled questions arise: (i) Is it worth accepting a parasitized host? (ii) When to leave the host patch? Through these decisions (i) the competition for healthy hosts and (ii) the trade-off between leaving in quest of a better patch and staying to make the patch less profitable for other parasitoids (this is a way to lower superparasitism likely to occur after having left the patch) are addressed. The aim of this work is to characterize a strategy that would be evolutionarily relevant in such a situation, as it directly concerns females' reproductive success. Investigating a (synchronous) nonzero-sum two-player differential game allows us to characterize candidate dynamic evolutionarily stable policies in terms of both oviposition and patch-leaving decisions. For that matter, the game is (in the most part of the parameter space) completely solved if the probability that superparasitism succeeds is assumed to be close to one-half, a fair value under direct competition. The strategic equilibrium consists, for each females, in (i) superparasitizing consistently upon arrival on the patch, and (ii) leaving when the loss of fitness due to superparasitism likely to occur after its departure is reduced to zero. The competing females are thus expected to leave the patch as they arrived: synchronously. Superparasitism does not necessarily lead to a war of attrition.

Interpopulation variation in predator foraging behaviour promotes the evolutionary divergence of prey

Despite intensive investigation of the role of predation on evolutionary processes, few studies have questioned the possibility of the evolutionary divergence of prey populations in response to interpopulation variation in predator foraging behaviour. In an interaction between a seed-predatory insect, the camellia weevil (Curculio camelliae), and its host plant, the Japanese camellia (Camellia japonica), I tested whether the evolutionary differentiation of the plant's defensive trait, pericarp thickness, was related to the interpopulation variation in the foraging behaviour of female weevils. I found that the preference of weevils for the plant fruit based on pericarp thickness varied across 13 populations in Japan. Importantly, variation in weevil behaviour explained interpopulation variation in pericarp thickness and the direction/strength of natural selection on the trait. Overall, I show that adaptive foraging of predators can result in the evolutionary divergence of predator-prey interactions.

Superparasitism Evolution: Adaptation or Manipulation?

Superparasitism refers to the oviposition behavior of parasitoid females who lay their eggs in an already parasitized host. This often yields intense competition among larvae that are sharing the same host. Why would a female oviposit in such hostile habitat instead of looking for a better quality, unparasitized host? Here we present a continuous-time model of host-parasitoid interaction and discuss alternative scenarios. This model is first used to analyze the evolution of the superparasitism behavior of a solitary proovigenic parasitoid under both time and egg limitation. Then, following the recent discovery by Varaldi et al., we allow the parasitoid to be infected by a virus that alters the superparasitism behavior of its host to enhance its own horizontal transmission. The analysis of the coevolution of this manipulative behavior with the oviposition behavior of uninfected females clarifies and quantifies the conflict that emerges between the parasitoid and its virus. The model also yields new testable predictions. For example, we expect that uninfected parasitoids should superparasite less after coevolving with the manipulative virus. More generally, this model provides a theoretical framework for analyzing the evolution of the manipulation of parasitoid life-history traits by microparasites.