I study the evolution of social behavior, using the forked fungus beetle Bolitotherus cornutus as a model system. Prior work in this species has shown that the position an individual holds in the social network of its population has fitness consequences. My research attempts to better understand the causes and consequences of variation in social behavior, from the individual to the structure of the group as a whole.
Individual social personality
My first work in the lab helped establish that forked fungus beetles consistently hold the same social network position when they remain with the same partners, even after they are separated and allowed to re-associate (Formica et al 2017). I worked with an REU student to show that some of this consistency may be due to the fact that these sub-social insects maintain differentiated relationships with other individuals over time. I have now shown that social network position is repeatable across social contexts (Cook et al 2022).
Personality composition and network structure
I experimentally manipulated the composition of personalities within groups to see if this alters the network structure. The result is clearly yes, individual behavioral variation is maintained in new contexts and scales up to create variation in the overall structure of social interactions. One of the most exciting implications of this work is that it suggests a possible mechanism for the evolution of social networks (Cook et al 2022).
In an offshoot of this work, I found that altering the personality composition of grounds led to significant change in the interactant covariance. This indicates that the individual personalities in a group can dramatically shift the patterns of phenotypic assortment and thereby the total strength of phenotypic selection. See Brodie et al 2022 for a thorough exploration of the importance of phenotypic assortment and some speculation about this result.
Groups of beetles with more social personalities (top row) differ from groups of less social beetles (bottom row)
in every metric of network structure we measured.
Age as social environment
The newest direction of my work considers age as a potential source of variation in individuals and social groups. Preliminary results suggest that age composition affects network structure, although less dramatically than personality composition. Beetles also assort by age within populations, creating social "neighborhoods" of old or young individuals, and the age of an individuals' social partners seems to have significant impacts on fitness!
You can watch the talk I gave at Evolution 2021 on these results here.
I use enclosures similar to aviaries, affectionately known as "beetlearies," to create populations I can experimentally manipulate. This approach allows me to rigorously test questions under controlled conditions with hundreds of individuals in as many as twelve replicate populations. This is a powerful tool for answering fundamental social network questions. It's also a lot of work, and a massive number of people have helped every step of the way! In particular, the creation of the beetlearies was a team effort with Robin Costello. Robin's work has used this system to ask whether the spatial distribution of resources affects social structures (Costello et al 2022a) and whether these structures experience multi-level selection (Costello et al 2022b).
An REU student working in one of our twelve "beetlearies," each of which can hold a population of up to 36 beetles.
Each has a shelf as an "artificial log" studded with fungus brackets.
A labeled beetle sits on a fungus bracket His location is described by a grid system.