Year of Award


Document Type


Degree Type

Doctor of Philosophy (PhD)

Degree Name

Experimental Psychology

Other Degree Name/Area of Focus

Animal Behavior

Department or School/College

Department of Psychology

Committee Chair

Nathan Insel

Commitee Members

Allen D. Szalda-Petree, Daniel Denis, Yoonhee Jang, Creagh Breuner


development, familiarization, octodon degus, relationship formation, social relationships, variability


University of Montana


Social relationships are a necessary part of group formation and cohesion across many animal species and can increase the health and fitness of the individuals involved. These benefits are seen across the lifespan, although the exact advantages and functions differ across developmental stages. Our current understanding of how relationships are formed and maintained is incomplete. Previous findings suggest that a measure of stability may be a useful method for understanding how relationships are formed and how this process may differ across development. The goal of this dissertation is to investigate the variability of social interactions over time and how it is affected by familiarity, sex, and age. We focused on same-sex peer relationships in degus, a highly gregarious rodent species native to Chile. Animals were repeatedly exposed to familiar and unfamiliar same-sex conspecifics in two sets of experiments. The first assessed the effects of sex and familiarity on social interaction variability in adults, while the second examined how this changed over stages of development. We found that total interaction levels depended on familiarity, sex, and age. Variability of interactions differed between strangers and cagemates in adult degus, with female strangers displaying more consistency in their social interactions than female cagemates and adult males. Juvenile and adolescent female degus did not show differences in the variability of social interactions due to familiarity, and variability of the interactions decreased over time. Together these results, while unexpected, suggest that the variability of social interactions cannot be used alone as a general method of describing relationship development. They do indicate that in females, familiar individuals have more variability of interactions while unfamiliar individuals act in a less variable, more predictable manner. These differences warrant further research using variability, in addition to other measures, to describe and understand social relationships and their development.


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