Constraints Imposed by a Natural Landscape Override Offspring Fitness Effects to Shape Oviposition Decisions in Wild Forked Fungus Beetles

Group and individual social network metrics are robust to changes in resource distribution in experimental populations of forked fungus beetles

Social interactions drive many important ecological and evolutionary processes. It is therefore essential to understand the intrinsic and extrinsic factors that underlie social patterns. A central tenet of the field of behavioural ecology is the expectation that the distribution of resources shapes patterns of social interactions.

We combined experimental manipulations with social network analyses to ask how patterns of resource distribution influence complex social interactions.

We experimentally manipulated the distribution of an essential food and reproductive resource in semi‐natural populations of forked fungus beetles Bolitotherus cornutus. We aggregated resources into discrete clumps in half of the populations and evenly dispersed resources in the other half. We then observed social interactions between individually marked beetles. Half‐way through the experiment, we reversed the resource distribution in each population, allowing us to control any demographic or behavioural differences between our experimental populations. At the end of the experiment, we compared individual and group social network characteristics between the two resource distribution treatments.

We found a statistically significant but quantitatively small effect of resource distribution on individual social network position and detected no effect on group social network structure. Individual connectivity (individual strength) and individual cliquishness (local clustering coefficient) increased in environments with clumped resources, but this difference explained very little of the variance in individual social network position. Individual centrality (individual betweenness) and measures of overall social structure (network density, average shortest path length and global clustering coefficient) did not differ between environments with dramatically different distributions of resources.

Our results illustrate that the resource environment, despite being fundamental to our understanding of social systems, does not always play a central role in shaping social interactions. Instead, our results suggest that sex differences and temporally fluctuating environmental conditions may be more important in determining patterns of social interactions.

Phenotypic Assortment Changes the Landscape of Selection

Social interactions with conspecifics can dramatically affect an individual's fitness. The positive or negative consequences of interacting with social partners typically depend on the value of traits that they express. These pathways of social selection connect the traits and genes expressed in some individuals to the fitness realized by others, thereby altering the total phenotypic selection on and evolutionary response of traits across the multivariate phenotype. The downstream effects of social selection are mediated by the patterns of phenotypic assortment between focal individuals and their social partners (the interactant covariance, Cij', or the multivariate form, CI). Depending on the sign and magnitude of the interactant covariance, the direction of social selection can be reinforced, reversed, or erased. We report estimates of Cij' from a variety of studies of forked fungus beetles to address the largely unexplored questions of consistency and plasticity of phenotypic assortment in natural populations. We found that phenotypic assortment of male beetles based on body size or horn length was highly variable among subpopulations, but that those differences also were broadly consistent from year to year. At the same time, the strength and direction of Cij' changed quickly in response to experimental changes in resource distribution and social properties of populations. Generally, interactant covariances were more negative in contexts in which the number of social interactions was greater in both field and experimental situations. These results suggest that patterns of phenotypic assortment could be important contributors to variability in multilevel selection through their mediation of social selection gradients.

The role of maternal effects on offspring performance in familiar and novel environments

Maternal effects are an important evolutionary force that may either facilitate adaptation to a new environment or buffer against unfavourable conditions. The degree of variation in traits expressed by siblings from different mothers is often sensitive to environmental conditions. This could generate a Maternal-by-Environment interaction (M × E) that inflates estimates of Genotype-by-Environment effects (G × E). We aimed to test for environment-specific maternal effects (M × E) using a paternal full-sib/half-sib breeding design in the seed beetle Callosobruchus maculatus, where we split and reared offspring from the same mother on two different bean host types-original and novel. Our quantitative genetic analysis indicated that maternal effects were very small on both host types for all the measured life-history traits. There was also little evidence that maternal oviposition preference for a particular host type predicted her offspring's performance on that host. Further, additive genetic variance for most traits was relatively high on both hosts. While there was higher heritability for offspring reared in the novel host, there was no evidence for G × Es, and most cross-host genetic correlations were positive. This suggests that offspring from the same family ranked similarly for performance on both host types. Our results point to a genetic basis of host adaptation in the seed beetle, rather than maternal effects. Even so, we encourage researchers to test for potential M × Es because, due to a lack of testing, it remains unclear how often they arise.

Social network position experiences more variable selection than weaponry in wild subpopulations of forked fungus beetles

The phenotypic expression and fitness consequences of behaviours that are exhibited during social interactions are especially sensitive to their local social context. This context-dependence is expected to generate more variation in the sign and magnitude of selection on social behaviour than that experienced by static characters like morphology. Relatively few studies, however, have examined selection on behavioural traits in multiple populations. We estimated sexual selection in the wild to determine if the strength and form of selection on social phenotypes is more variable than that on morphology. We compared selection gradients on social network position, body size, and weaponry of male forked fungus beetles Bolitotherus cornutus as they influenced mating success across nine natural subpopulations. Male horn length consistently experienced positive sexual selection. However, the sign and magnitude of selection on individual measures of network centrality (strength and betweenness) differed significantly among subpopulations. Moreover, selection on social behaviours occurred at a local scale ('soft selection'), whereas selection on horn length occurred at the metapopulation scale ('hard selection'). These results indicate that an individual with a given social phenotype could experience different fitness consequences depending on the network it occupies. While individuals seem to be unable to escape the fitness effects of their morphology, they may have the potential to mediate the pressures of selection on behavioural phenotypes by moving among subpopulations or altering social connections within a network.

Does Divergence in Habitat Breadth Associate with Species Differences in Decision Making in Drosophila Sechellia and Drosophila Simulans?

Decision making is involved in many behaviors contributing to fitness, such as habitat choice, mate selection, and foraging. Because of this, high decision-making accuracy (i.e., selecting the option most beneficial for fitness) should be under strong selection. However, decision making is energetically costly, often involving substantial time and energy to survey the environment to obtain high-quality information. Thus, for high decision making accuracy to evolve, its benefits should outweigh its costs. Inconsistency in the net benefits of decision making across environments is hypothesized to be an important means for maintaining variation in this trait. However, very little is known about how environmental factors influence the evolution of decision making to produce variation among individuals, genotypes, and species. Here, we compared two recently diverged species of Drosophila differing substantially in habitat breadth and degree of environmental predictability and variability: Drosophilasechellia and Drosophilasimulans. We found that the species evolving under higher environmental unpredictability and variability showed higher decision-making accuracy, but not higher environmental sampling.

Interference mechanism of Sophora alopecuroides L. alkaloids extract on host finding and selection of the Asian citrus psyllid Diaphorina citri Kuwayama (Hemiptera: Psyllidae)

Manipulating insect behavior through the deployment of semiochemicals offers a promising opportunity for protecting crops in a sustainable manner. Therefore, there is still a significant opportunity for the development of natural crop protectants as eco-friendly tools in pest management. In this context, the aim of the current investigation is to find a novel prophylactic against the Asian citrus psyllid (ACP) and to gain a better understanding of the host-finding and selection ability of the ACP towards Murraya paniculata seedlings treated with Sophora alopecuroides alkaloids extract (SAAE). Our results indicate that foliar application of SAAE influences the psyllid host-finding and selection process. The behavioral assay with M. paniculata seedlings treated with 15 and 30 mg/mL of SAAE, with masked visual cues, revealed that only 6.6 and 10.4% psyllids were able to locate the host in the vials. The results also indicate that citrus psyllids mainly rely on both visual and olfaction in host-finding and selection. In choice settling experiments, psyllids settled almost completely on control seedlings rather than on seedlings treated with SAAE at a concentration of 30 mg/mL. Chemical analyses of the alkaloids extract revealed the presence of sophocarpine (33.90%), sophoridine (6.23%), anagyrine (2.77%), matrine (2.38%), lupanine (1.68%) aphylline (0.89%), and sophoramine (0.75%). In further behavioral bioassays with the dominant alkaloids sophocarpine and sophoridine, the alkaloids repelled ACP at higher concentrations of 50 and 70 mg/mL as compared to SAAE. Furthermore, the 50 mg/mL (1:1, v/v) combination of sophocarpine and sophoridine displayed a synergistic effect and showed the maximum behavioral effect as compared to the individual alkaloid. Based on our results, SAAE makes M. paniculata seedlings unattractive to the psyllids, and therefore, alkaloids could be used in reducing the colonization of citrus plants, subsequently curtailing HLB infection.