Research
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Social Behavior and Evolution

Social interactions are among the most common and important events in the life of individuals (Frank 2009). Social behaviors are important to the evolutionary process because their outcomes often generate high variance in fitness among individuals in a population (McGlothlin et al. 2010). Recent advances in quantitative genetic and selection theory suggest that heterogeneity in the social environment (i.e. the environment created by the interaction with conspecifics) is important in phenotypic evolution (Moore et al. 1997, Wolf 1999). The social environment can generate “social selection,” which occurs when the phenotypes of social partners affect the fitness of focal individuals (West-Eberhard 1979, 1983, Wolf et al. 1999).  Social selection theory is vital to our understanding of selective processes because it allows researchers to quantify the effects social interactions have on total selection.

My research explores how the social environment affects the process of natural selection. Specifically, I am interested in how social interactions can lead to phenotypic evolution. I strive to elucidate how the social partners with whom an individual interacts shapes the selective régime they experience. Individuals can also modify their social environment by altering with whom they interact. These behavioral processes can cause variance in the intensity of selection within a population. To solve these problems, I utilize techniques from behavioral ecology, quantitative genetics, molecular ecology and Geographic Information Systems (GIS) to map social phenomena across space and time.

Recently I have also become interested in exploring the role animal social networks in phenotypic evolution. Social networks fascinate me because network structure can be viewed as an emergent property that is necessarily influenced by all members of a population or social group and an individual's position in that network is the result of their own behaviors as well as those of the entire population. I think that social networks could be an interesting place to examine processes involved in multilevel selection.

I study social behavior and selection in two animal systems:

  1. Forked fungus beetles (Bolitotherus cornutus)
  2. White-throated sparrows (Zonotrichia albicollis)


The physical or ecological landscape (left) and a social landscape (predicted cuckoldry risk for white-throated
sparrow males; right) from the same location on the two landscapes. I hypothesize that animals use information from both realms when making spatial decisions. My research examines the contribution of both landscapes to selective regime a population experiences.



 

Forked Fungus Beetles:

 

In collaboration with Butch Brodie, I have recently begun a long-term study of social selection in forked fungus beetles. 


A large horned forked fungus beetle male.

Building on Jeff Conner and Mike Whitlock’s work on this species, we are conducting a social selection analysis on several wild populations at Mountain Lake Biological Station.  Social selection analysis (as described by Wolf et al. 1999) takes a standard multiple regression selection analysis (many traits regressed on fitness, i.e. selection gradient) and adds the effects of the traits of social partners on a focal individual’s fitness.
 

Forked fungus beetles are ideal for this type of analysis, because they live most of their lives on a single fallen log in deciduous forests.  Adult beetles do not disperse very often and can live for up to eight years.  Additionally, forked fungus beetles have prolonged combat, courtship, and mate guarding behaviors, allowing us to record relevant and important components of fitness necessary for complete social selection analysis. 

We have marked several populations and are currently conducting intense scan sampling and continuous behavioral observations.  We treat each log as a landscape, just as one would for a larger animal, and employ similar spatial analyses using GIS technology.  Our ultimate goal is to determine if social selection analyses improve our understanding of phenotypic evolution.


     Macro photograph of a large horned male,demonstrating a few of
the phenotypes we are using in our analysis.

 

 

Visit our Video Page to watch Forked Fungus Beetle fight!

 

White-throated Sparrows


A female white-throated sparrow on her cryptic nest.

Social environments are inherently dynamic, changing depending on the frequency and outcomes of conspecific interactions – they can be simultaneously the targets and agents of selection.  Understanding how organisms settle in heterogeneous social environments and the effects this has on reproductive success is vital to our understanding of the selective forces at work in wild populations. 

For my dissertation I conducted an intensive behavioral, evolutionary, and ecological study of territoriality in the polymorphic white-throated sparrow (Zonotrichia albicollis)

White-throated sparrows are a fascinating study system because they exhibit a stable genetic polymorphism caused by a complex rearrangement of the second chromosome (Thorneycroft 1966, 1975, Thomas et al. 2008, Romanov et al. 2009).  The presence or absence of the rearrangement corresponds to two distinct plumage morphs, white and tan, that are found in both sexes.  White morphs are heterozygous, whereas tan morphs are homozygous and do not carry the rearrangement. In addition to plumage, morphology, behavior, and life-history characteristics all appear to have a genetic basis as they are also correlated with morph.  White and tan birds mate disassortatively (i.e. tan males typically mate with white females and white males with tan females). White and tan males attempt to maximize their reproductive success by pursuing alternative reproductive strategies (Tuttle 1993, 2003).  White males are more aggressive, sing more, intrude frequently, and are promiscuous (pursue extra-pair copulations or EPCs).  Tan males guard their mates more, do not pursue EPCs (Tuttle 1993, 2003), and invest more effort in parental care.  White males are no more likely to win antagonistic interactions than tan males . 

WTSP-COVERI demonstrated that males of the two morphs inhabit different social niches that correspond to their respective alternative reproductive strategies.  By integrating molecular ecology and Geographic Information Systems, we generated continuous, socio-spatial models of local conspecific density and cuckoldry risk (Figure 1). My results suggest that the morphs segregate their territories based on socio-spatial variables, creating a heterogeneous social landscape that matches each behavioral phenotype with a favorable social environment.  Specifically, the monogamous tan males, tended to settle in low density areas that were also low for cuckoldry risk, while the opposite was true for the promiscuous white males. This pattern of socio-spatial heterogeneity combined with the social niche partitioning I observed might act as a social niche polymorphism, and play an important role in maintenance of the alternative reproductive strategies of the white-throated sparrow.  Socio-spatial factors, similar to those seen in the white-throated sparrow, may play important roles in the evolution of mating systems in other species, even those with more continuous or cryptic variation. 

My PhD advisor was Elaina Tuttle (Indiana State University), and I continue to collaborate on the white-throated sparrow system with Elaina and her lab.  Our current studies include the incorporation of song and dawn chorus into our models of the social landscape as well as conducting more formal social selection analyses.

Dr. Joan Strassmann's blog entry on my dissertation work

 

Collaborators:

In addition to Butch Brodie and Elaina Tuttle, my other collaborators include:

Ani Hsieh (Mechanical Engineering & Mechanics Department at Drexel University) – Ani and I met at Swarthmore College during our teaching post-docs and in a truly liberal arts moment at a faculty luncheon, we realized that her research on biology inspired multi-team and my interest in emergent group phenomena would benefit from a cross-disciplinary collaboration.  We are developing an automated tracking system for forked fungus beetles, which will eventually record every individual social interaction within our populations.  It is our hope that the high resolution information from beetle social behavior and the resultant emergent group phenomena will lead to advances in theoretical robotics, as well as beetle biology.

Alison Holliday (Chemistry and Biochemistry Department at Swarthmore College) – Alison and her lab of industrious undergraduates are examining the volatile compounds generated by forked fungus beetles.  Currently we are examining if defensive compounds differ between sexes and the species of fungus forked fungus beetles inhabit.

Ron Sarno (Department of Biology at Hofstra University)-  Ron and I are beginning a project to quantify sexual selection in Darwin’s Rheas.  Little work has been done on these ancient and fascinating species.  We are currently developing and testing molecular markers that will allow us to examine reproductive success and population genetics.