Individuals differ. This is a fundamental observation that forms the cornerstone organismal biology. Historically, variation in behavior was viewed as noise around the mean, but recently further investigation of this variation has shown its significant and consequential. We now know repeatable among individual variation in single traits (or personality), correlated suites of traits (or behavioral syndromes) or the plasticity of behavioral traits can affect both individual (e.g., mate choice, dominance rank, dispersal, etc.) and population (e.g., between species interactions, adaptive evolution of species and invasive species potential) level processes. I focus on the holisitc integration and application of ecological and evolutionary concepts with strong theoretical backgrounds that predict how and why trait variation exists and is maintained within and between populations. More specifically, my interests lie in integrating our understanding of behavioral variation, life history theory, and ecological community dynamics into cohesive frameworks. Specifically, I ask: Why do individuals vary in their behavior? What are the consequences of behavioral variation for individuals, populations or species?
The evolutionary bifurcation of socially parasitic strategy
Social parasitism in ants is diverse in form and has multiple evolutionary origins. It is often proposed that most socially parasitic species are very closely related (or sister species) to their hosts. I am the first to discover social parasitism in any western Temnothorax ant species. T. rugatulus shows facultative interspecific slave-making (using workers of different species as part of the workforce) in northern, highly risk-tolerant populations. Alternatively, southern populations of the same species show reproductive skew between queen types. Smaller, microgyne queens, exhibiting many of the morphological traits considered part of an intraspecific “parasite syndrome”, produce proportionally more reproductives than workers compared to the cooperative macrogynes. Additionally, there is preliminary evidence of reproductive isolation between macrogynes and microgynes. These southern populations appear to be in the early stages of ecological sympatric speciation into host and parasite (Bengston & Rabeling, in prep).
With such a startling difference in parasitic strategy between the northern and southern populations, this system may represent an exciting evolutionary bifurcation of socially parasitic strategy. I am working to formally describe this bifurcation, the geographic extent of each form and if either form may be a precursor for sympatric speciation as seen in other ants (Rabeling et al. 2014).
Behavioral type and life history strategy
Life history theory predicts that risk-tolerance is necessarily tied to trade-offs in energy allocation between somatic and reproductive effort. If this theory is relevant at the level of the colony, then I predicted that risk-tolerant colonies grow faster and invest more energy in reproduction than somatic maintenance, while risk-averse colonies are most invested in somatic mainntenance. Indeed, I found that risk-tolerant colonies produce more ants per day and a higher proportion of those ants are reproductive, i.e., queens and males, compared to non-risk-tolerant colonies. This supports my predictions that risk-tolerance should be associated with faster growth and disproportionate investment in reproduction relative to somatic growth rate. This is congruent with the predictions generated by life history theory, but has never before been demonstrated at a collective level of organization (Bengston et al., 2016, Oikos).
Colony- level behavioral syndromes
We know that individuals can have a behavioral syndrome. Can a group? In this study I focused on the emergent properties of a social insect colony, meaning the way a colony behaves as an entity rather than simply an additive result of the individual workers within the colony. I emphasize focusing on the natural history of my study species, Temnothorax rugatulus, because this will lead to an understanding of ecologically relevant behaviors. These behaviors are thus the most likely to have an impact the evolution of the species, though they can also be used to infer generalized patterns in the behavioral species of animals. Thus far I have shown a a colony level behavioral syndrome that requires a trade-off between foraging effort and defense capabilities, which varies across a latitudinal gradient and may reflect risk-tolerance variation. [Bengston & Dornhaus, Proc. B, 2014; Bengston & Jandt, Frontiers in Eco. Evo., 2015 ]
Ecology and behavioral syndromes: linking natural environment to behavioral type
Expanding upon the risk-tolerance variation across a latitudinal gradient, I collect colonies across the entire U.S. range, while also measuring a wide range of environmental conditions. I found found that nest site availability is a strong predictor in behavioral type, with colonies in areas of high levels of competition are significantly more risk tolerant than those in areas of low competition. A similar pattern can be seen with spatial clustering, where high clustering is associated with increased risk-taking. Additionally, the structure of the behavioral syndrome, meaning the way in which the behaviors are correlated is affected by spatial clustering. In areas of high spatial clustering, aggressive behavior is the strongest driver of phenotype.
[Bengston & Dornhaus, 2015, Behavioral Ecology & Sociobiology]