We (myself, Erin Siracusa and Julia Kilgour) are really excited to be hosting a symposium at the up coming Canadian Society for Ecology and Evolution meeting in Victoria, British Columbia (7-11th May). Details of the meeting itself here.
The title of our symposium is “Ecology and Evolution in a Social Context” and we’ve got some great speakers lined up:
The outline of the symposium as follows:
Well established ecological and evolutionary processes such as density-dependence, communication, and sexual selection are inherently social processes, but are not traditionally explored through a social lens. In spite of the prevalence of social forces in these diverse areas of research, the social environment has typically been studied at a coarse scale; measured as a general variable of “density” or “sex ratio”, without consideration of finer scale features, such as the mix of ages or behavioural types present in each individual’s social environment. It is now well acknowledged that the social environment can vary importantly in terms of composition, including demographically, morphologically, and behaviourally, and that this variation can have profound impacts on individual fitness as well as having intriguing ecological and evolutionary implications. Advancements in technology, such as GPS tracking, genetic markers of relatedness, video and acoustic techniques have enabled scientists to take new approaches to questions about the social environment, both in the field and in the lab. The goals of this symposium are twofold. We will highlight how ecologists and evolutionary biologists are 1) incorporating features of the social environment into their study of longstanding questions in our field; and 2) showcase new insights into how the composition of the social environment is impacting individual fitness and the evolutionary and ecological dynamics of populations.
Our speakers, affiliations and talk titles are:
Individuals possessing extreme phenotypes often exhibit a large influence over the collective behavior of their groups. In the spider Stegodyphus dumicola, bold individuals catalyze greater foraging aggressiveness in their shy colony mates at desert sites, but not in at savannah sites. To evaluate whether the apparent site-specific social influence of bold individuals is a consequence of their traits or the social susceptibility of shy individuals, we mixed shy individuals from arid sites with bold individuals from wet sites and vice versa. Our results suggest that it is the social susceptibility of shy individuals that fuels the social influence of bold individuals. Shy individuals from arid sites increase their foraging aggressiveness in the presence of bold individuals regardless of where the bold individuals come from (wet or dry sites), and even respond to bold, non-social congeners. Shy individuals from wet sites exhibited no such susceptibility. Using 240 non-chimeric experimental colonies deployed across southern Africa, we found that colony foraging aggressiveness is under positive selection at arid sites but not savannah habitats. Thus, the socially susceptibility of shy spiders from arid sites helps to create colony phenotypes that are advantageous at arid sites, but not elsewhere. These results suggest that social susceptibility is possibly locally adapted in this system.
The dawn chorus is an impressive display in which male songbirds sing at a high rate just before sunrise. The simultaneous singing by many individuals suggests that vocal interactions may be prevalent and shaped by the social relationships among singers (Social Dynamics Hypothesis). Black-capped Chickadees are an excellent model species to test the Social Dynamics Hypothesis because they are resident and we can determine the social relationships of males during the winter. To determine within-flock dominance hierarchies, we observed dominance interactions among colour banded birds at feeding stations at Queen’s University Biological Station. We also followed flocks away from feeding stations to determine flock composition. In spring, we used a 16-microphone acoustic array to record the dawn chorus in 15 neighbourhoods over three field seasons. We found that male chickadees match the frequency of their neighbours’ songs at dawn and that matching interactions regularly extend beyond the dyadic level. Vocal matching occurred most often between males from different flocks and between males of disparate ranks. We show that a pair’s breeding stage influences how far males move at dawn and the intensity at which they sing. Finally, we show that males attend to the start time of conspecifics and begin to sing earlier in response to simulated insertions. We show that the dawn chorus is an interactive communication network where information exchange is influenced by the social environment. The dawn chorus provides a good opportunity for receivers to assess the social relationships of vocalizing males.
Organisms often express plastic phenotypic changes during social interactions. Such social plasticity can influence phenotypic evolution by altering the variation available for selection and the evolutionary response. The implications of social plasticity for social evolution have been explored in depth, but so far, this work has relied on relatively simple models of social structure. It is unclear how the predictions of social evolution theory apply to more complex social networks. Here, we extend this work to include general models of social structure. First, we develop an approximation of previous interacting phenotypes models that apply to general social networks. Second, we use simulations to test these analytical models to explore how the number of social connections between individuals and preferential associations with phenotypically similar conspecifics affects phenotypic variation and response to selection. Phenotypic variation within groups was maximal when individuals interacted on average with half of their group members. In such cases, populations exhibited a greater proportion of phenotypic variation within groups than among groups. By contrast, in cases where individuals interacted with all the other group members, populations exhibited a greater portion of phenotypic variation among groups and reduced phenotypic variation within groups. Preferential associations among phenotypically similar individuals increased the phenotypic variance observed among group members. Our results establish a first set of predictions regarding the evolutionary implications of social structure in modulating the contribution of phenotypic plasticity to phenotypic variation and heritability. Our predictions can apply to study the evolution of social behavior and specialization within populations.
Ecological variation in resources can influence the distributions and encounter rates of potential mates and competitors, and consequently the opportunity for sexual selection. In systems with sperm competition, ecological factors that influence the likelihood that females mate multiply could also affect the potential number of sperm competitors. In Wellington tree weta (Hemideina crassidens), the size of tree cavities (called galleries) used as refuges and mating sites is an important determinant of female distribution and, as a result, opportunity for sexual selection and directional selection on male weaponry. Female tree weta mate multiply and store sperm, but patterns of potential sperm competition have not been systematically investigated. In this study, we asked if gallery size or male weaponry size affected the structure of connections among potential sperm competitors. We found that female weta were more likely to mate multiply in small galleries and that potential sperm competition intensity was higher in small galleries. However, male weaponry was not associated with differences in number of potential sperm competitors, and the number of potential sperm competitors was negatively correlated with estimated mating success regardless of gallery size. Overall our results indicate that ecological variation in a resource is likely to influence numbers of sperm competitors and that post-copulatory sexual selection in this system could increase expected variation in overall reproductive success.
Competition has been traditionally viewed in a deterministic fashion, leading to familiar terms such as competition coefficients and competitive hierarchies. Competitive determinism has had outsized influence in ecology, and assumes that either individuals are unable to make behavioural adjustments in response to the specific set of encounters they face, or that these adjustments ‘average out’ within a population. A wealth of recent evidence is demonstrating that minute details of the social environment have substantial impacts on individual behavior, competitive dynamics, and species co-existence. Here I present results from several experiments testing how the genetic composition of a plant’s neighborhood impacts competitive outcomes and interpretations. Using Arabidopsis thaliana, we found reduced ‘competitive struggle’ among kin than among unrelated individuals. This kin effect was contingent upon resource levels, consistent with socio-behavioural theory. Further, there was no evidence of a robust competitive hierarchy, and instead intransitivity was common and provides a potential coexistence mechanism based upon social complexity. This finding is also supported from additional experiments in which we are finding plant trait expression and competitive outcomes are a result of complex interactions among neighbour identity and resource levels. Combined, we are finding substantial evidence that seemingly subtle differences in plant neighborhoods have meaningful impacts on the expression of traits and the nature of plant interactions. Viewing competing plants as individuals, rather than average representatives of a species, requires seeing them in a social context. Such an approach allows for the development and testing of new questions in this well-worn area of research.
Evolutionary quantitative genetics almost always assumes that genotypes and environments have independent effects on phenotypic variation. At the same time, animals have near-unlimited opportunities to determine the environments they experience, especially their social environments. When genotypes differ in behaviors that influence their social environments, then genetic and environmental variation become correlated. Here, I describe theory and data suggesting that this phenomenon is likely to be common and exploring its implications for fundamental evolutionary genetics parameters. I suggest that studying linkages between genotype and environment will reveal novel pathways by which behavior develops and evolves.