Social Behavior in Voles

In one of our current student research projects, we are interested in understanding the population cycles of microtine rodents and how social behaviors and genetic relatedness may affect the natural regulation of animal populations. Recently, a new hypothesis has been proposed to explain microtine rodent population cycles. This hypothesis, known as the "kin selection hypothesis of population regulation," or the Charnov-Finerty hypothesis, proposes that population cycles in voles are the result of changes in the genetic relatedness of the animals in the population. In an experiment being conducted in my laboratory, I and three undergraduate students, Kathy Hayes, Carolyn Tai, and John McGrath, are testing some of the assumptions and predictions of the Charnov-Finerty hypothesis. This work will help in understanding the population dynamics of voles and may be instrumental in allowing for the biological control of pest rodents.

We are examining small, artificially created prairie vole (Microtus ochrogaster) populations that vary in degree of genetic relatedness and degree of social familiarity. We are creating four types of groups: genetically related/familiar (raised together), unrelated/unfamiliar (raised apart), related/unfamiliar, and unrelated/familiar. One group at a time (six animals, three females, and three males) is released into a behavioral observation room. Using a series of different approaches, we monitor the frequency of aggressive and amicable behaviors, communal nesting, spacing patterns, and attempted dispersal. To stimulate dispersal, we have set up an "obstacle course" (i.e., vertical cliff, water barriers, tangle of wires) that the voles must get through in order to escape the room. After three weeks-a sufficiently long period for voles to form pair bonds and become pregnant-we remove all animals from the room and monitor the females to determine if they are pregnant.

Results so far indicate that in the minipopulations made up of related/familiar animals, voles have shown little aggression and high levels of amicable behaviors. Animals in these groups tend to nest together, often cramming themselves into one nest box (six nest boxes, one per animal, are provided). Dispersal among them is nonexistent. On the other hand, in minpopulations of unrelated/unfamiliar animals, we have recorded high levels of aggression, low levels of amicable behaviors, and high frequencies of dispersal attempts. Additionally, these animals tend to occupy separate nest boxes. Lastly, reproductive success among the related/familiar animals has been higher than that in the unrelated/unfamiliar animals. These preliminary results support many of the assumptions of the Charnov-Finerty hypothesis. Next, we will attempt to test the two other types of groups. In the future, I would like to test the assumptions and predictions of the hypothesis under field conditions.