1. The ecology and biogeography of social evolution
The recent accumulation of comparative data on social behavior in animals makes the time particularly ripe for a synthesis of the genetic and ecological factors influencing social evolution. Whereas there is a cohesive body of theory on the genetic aspects of sociality, ecological factors have been more difficult to subsume within a single unifying framework. NSERC funded research in our lab is taking a two-pronged approach to understanding the ecology of social evolution: (a) Through empirical studies on social spiders, we are exploring the main environmental factors that may be responsible for the geographical distribution of their social systems. (b) By modelling within a common framework diverse drivers of sociality, we are investigating how group living and cooperation arise very generally when organisms with particular intrinsic characteristics face external opportunities or challenges that single individuals cannot meet.
2. Sociality and community assembly
The question of what determines the composition of plant and animal communities is central to ecology, but one not easily addressed given the large spatial scales and difficult manipulation of most systems. Social spiders, and the inquilines that colonize their webs, are tractable systems to address key questions in community and metacommunity ecology at multiple scales. We have shown that communities of the social spider genus Anelosimus across the Americas exhibit the distinct signatures of environmental filtering at the continental scale and limiting similarity at the local scale. We plan to further explore the roles of resource partitioning and environmental and temporal heterogeneity in niche differentiation in these communities through remote sensing and fieldwork in Ecuador, Costa Rica/Panama, and Brazil. We are also investigating the composition of inquiline communities in spider webs, which we have shown can serve as models for metacommunities. To address the factors that impact inquiline density and diversity, we are studying the interplay between dispersal and local interactions, as well as host hygiene behaviours, in determining local community composition. We plan to replicate these studies across elevation and precipitation gradients in Ecuador.
3. Evolution of life histories in metapopulations
Boom and bust patterns of population growth may be unsustainable over long periods because of increased vulnerability to extinction when population size fluctuates to low levels. Dynamically unstable but fast-growing local populations, however, may also be more likely to produce the dispersers that recolonize sites vacated when local populations go extinct. Rates of extinction, dispersal, and recolonization may thus attain a balance at the metapopulation level. To test these ideas, we are developing models that explore the evolution of traits that affect the dynamics of local populations in a metapopulation. Predictions from these models can be empirically tested using social spiders, as they form metapopulations of manageable dimensions both in space and time: their colonies constitute self-sustaining populations that grow, proliferate and become extinct with little or no mixing with one another; they undergo relatively frequent extinction and proliferation; and they can be sampled, manipulated, and artificially established.
4. The short and long term consequences of inbreeding
Most organisms, including group-living ones, go to great lengths to avoid inbreeding through the dispersal of one or both sexes. Social spiders, and a few other social organisms (e.g., some thrips, naked mole rats, ambrosia beetles), however, have evolved strongly inbred systems.By artificially inbreeding a naturally outbred subsocial spider we have found a potential explanation for this pattern: costs of inbreeding depression would not be as high as costs of dispersing in the habitats where social spiders occur. In the long term, however, we have found that inbred spider sociality may represent an evolutionary dead end.
Check out photos of our recent field season