Why do predators attack parasitized prey? Insights from a probabilistic model and a literature survey

Predators and parasitoids often encounter parasitized prey or hosts during foraging. While the outcomes of such encounters have been extensively studied for insect parasitoids, the consequences of a predator encountering parasitized prey have received less attention. One extreme example involves the potter wasp Delta dimidiatipenne that frequently provision their nest with parasitized caterpillars, despite the low suitability of this prey for consumption by their offspring. This raises two main questions: (1) why do female potter wasps continue collecting parasitized caterpillars? and (2) is this an exceptional example, or do predatory insects often suffer from fitness costs due to encounters with parasitized prey? We addressed the first question using a probabilistic mathematical model predicting the value of discrimination between parasitized and unparasitized prey for the potter wasp, and the second question by surveying the literature for examples in which the parasitism status of prey affected prey susceptibility, suitability, or prey choice by a predator. The model demonstrates that only under certain conditions is discrimination against parasitized prey beneficial in terms of the potter wasp's lifetime reproductive success. The literature survey suggests that the occurrence of encounters and consumption of parasitized prey is common, but the overall consequences of such interactions have rarely been quantified. We conclude that the profitability and ability of a predator to discriminate against parasitized prey under natural conditions may be limited and call for additional studies quantifying the outcome of such interactions.

Lessons from the multitudes: insights from polyembryonic wasps for behavioral ecology

Even for parasitic Hymenoptera, polyembryonic wasps are unusual creatures. Two features in particular, allow for novel exploration of major questions in behavioral ecology: the production of multiple offspring per egg and, in some species, the production of a soldier caste. Because final brood sizes of polyembryonic species are not constrained by trade-offs between current and future parental reproductive effort, we can clearly examine the selective forces at play that drive the balance between the number of offspring and their body size. Polyembryony also provides excellent opportunities to compare the performance of identical genotypes under different environmental conditions. Finally, polyembryonic species can provide unique tests of how genetic conflicts at multiple levels are resolved.

Clonal fish are more aggressive to distant relatives in a low resource environment

Kin selection explains conditions under which closely related individuals should be less antagonistic towards one another. One benefit of kin selection is a reduction in aggression towards kin in various social contexts, such as foraging. In the gynogenetic Amazon molly, females have been shown to differentiate between clone types, preferring to associate with clonal sisters to non-sisters, regulating their aggressive behaviours accordingly. We ask if Amazon mollies in resource-limited environments retain the ability to regulate aggressive behaviours according to relatedness. We found that focal females regulated their aggressive behaviours depending on partner type. Females spent more time behaving aggressively towards the heterospecific females than either of the clonal lineages, and towards non-sister clones compared to clonal sisters. We are able to confirm that kin discrimination is maintained, resulting in females showing more aggression towards heterospecific females and non-sister clones in a food-limited environment, and that this aggression scales with relatedness.

Kin Recognition in a Clonal Fish, Poecilia formosa

Relatedness strongly influences social behaviors in a wide variety of species. For most species, the highest typical degree of relatedness is between full siblings with 50% shared genes. However, this is poorly understood in species with unusually high relatedness between individuals: clonal organisms. Although there has been some investigation into clonal invertebrates and yeast, nothing is known about kin selection in clonal vertebrates. We show that a clonal fish, the Amazon molly (Poecilia formosa), can distinguish between different clonal lineages, associating with genetically identical, sister clones, and use multiple sensory modalities. Also, they scale their aggressive behaviors according to the relatedness to other females: they are more aggressive to non-related clones. Our results demonstrate that even in species with very small genetic differences between individuals, kin recognition can be adaptive. Their discriminatory abilities and regulation of costly behaviors provides a powerful example of natural selection in species with limited genetic diversity.

Self-/conspecific discrimination and superparasitism strategy in the ovicidal parasitoid Echthrodelphax fairchildii (Hymenoptera: Dryinidae)

Superparasitism in solitary parasitoids results in fatal competition between the immature parasitoids, and consequently only one individual can emerge. In the semisolitary ovicidal parasitoid Echthrodelphax fairchildii (Hymenoptera: Dryinidae), 2 adults can emerge under superparasitism with a short interval (<24 h) between the first and second ovipositions. We determined the female parasitoid's behavioral responses under self- and conspecific superparasitism bouts with first-to-second oviposition intervals of ≤2 h. The self- and conspecific superparasitizing frequencies increased up to an oviposition interval of 0.75 h, with the former remaining lower than the latter, particularly for oviposition intervals of ≤0.25 h, suggesting the existence of self-/conspecific discrimination. The superparasitizing frequency plateaued for oviposition intervals of ≥0.75 h, with no difference between self- and conspecific superparasitism. The ovicidal-probing frequency did not differ under self- and conspecific superparasitism, and was usually <20%. The females exhibited no preference for the oviposition side (i.e., ovipositing on the side with or without the first progeny) and almost always laid female eggs for any oviposition interval under self- and conspecific superparasitism. The sex ratio was not affected by the type of superparasitism, oviposition sides, or the occurrence of ovicidal probing. These observed results about the oviposition side, ovicidal probing, and sex ratios differed from the predictions obtained assuming that the females behave optimally. Possible reasons for the discrepancies are discussed: likely candidates include the high cost of selecting oviposition sides and ovicidal probing, and, for the sex ratio, the low frequency of encountering suitable hosts before superparasitism bouts.

Kin selection and local competition in a heterogeneous community

When should an individual be willing to pay a cost in order to help or harm another individual in its community? Kin selection suggests that relatives should help each other, while competition for limited resources may select for harming behaviour against neighbours. This study considers social interactions between two individuals. For actions influencing non-dispersing reproduction, a condition is derived for selection to favour helping or harming, as a function of the actor's relationship to the rest of its community and to the recipient. Where two individuals differ in their relatedness to the community, the individual which is less related to the community will be the more helpful. Two individuals with a given relatedness to each other will be more helpful to each other as they jointly become less related to their community. The implications of these results are explored through an example involving a community derived from two ancestral groups. The directional selective effects will depend on the extent to which social interactions are assortative rather than random, and the distribution of opportunities for helping and harming.

Phenotypically plastic traits regulate caste formation and soldier function in polyembryonic wasps

Polyembryonic encyrtid wasps are parasitoids that have evolved a clonal form of embryogenesis and a caste system where some progeny become reproducing wasps whereas others develop into a sterile soldier caste. Theory based on the biology of Copidosoma floridanum predicts that the primary role of soldier larvae is to mediate conflict over sex ratio, which also favours female-biased soldier production. Other data, however, suggest that female-biased soldier production reflects a developmental constraint. Here, we assessed whether female-biased soldier function by polyembryonic wasps reflects sex-specific adaptation or constraint by conducting comparative studies with Copidosoma bakeri, a species that produces clutch sizes similar to C. floridanum yet rarely produces broods associated with sex ratio conflict. Our results indicate that the oviposition behaviour of adults, development of progeny and function of soldier larvae differ greatly between C. bakeri and C. floridanum. These findings indicate that caste formation and soldier function in polyembryonic encyrtid wasps are regulated by phenotypically plastic traits. Our results further suggest that the primary function of the soldier caste in some species is defence of host resources from competitors whereas in others it is the resolution of sex ratio conflict.