Elsevier

Animal Behaviour

Volume 85, Issue 2, February 2013, Pages 463-470
Animal Behaviour

Genetic relatedness does not predict racoon social network structure

https://doi.org/10.1016/j.anbehav.2012.12.011Get rights and content

Social assortativity, preferentially associating with certain individuals, is a widespread behaviour among a diverse range of taxa. Animals often choose to associate with other individuals based on characteristics such as sex, age, body size, rank and genetic relatedness. These preferences can scale up to shape the overall social structure of an animal group or population. We investigated possible factors that might shape the social network structure of common racoons, Procyon lotor, in a high-density urban population in Cook County, Illinois, U.S.A. Racoon associations were recorded using proximity detecting radiocollars that recorded when individuals came within 1–1.5 m of each other. In addition, dyadic measures of home range overlap and genetic relatedness were calculated for all individuals included in our study. We used multiple regression quadratic assignment procedures to determine what factors influenced the structure of racoon association networks. The only variable that positively influenced racoon social structure was male–male homophily, which is consistent with previous studies that documented frequent social interactions between adult male racoons. Genetic relatedness had no effect on racoon social networks and there was no evidence that males or females preferentially associated with close relatives, despite the presence of kin in the population. This pattern, that kinship does not play a significant role in shaping social structure, is strikingly unusual among mammals and is not consistent with many socioecological models. Although racoon individuals showed strong social partner preferences, it is unclear what factors drove these choices. This unpredictability in partner choice shaped the structure of the racoon social networks and has important implications for disease transfer in this widespread animal vector.

Highlights

► We tested what factors influence racoon social proximity networks: age, sex, genetic relatedness and home range overlap. ► Age and kinship had no effect on social networks. ► Male–male associations influenced social networks during some months. ► Racoon association patterns appear unpredictable based on age, sex and relatedness.

Section snippets

Study Area

Fieldwork was conducted in a 20 ha area within the 1499 ha Ned Brown Forest Preserve in suburban Cook County, IL, U.S.A. (for further details, see: Prange et al. 2003). The size of the study area was determined by the local density of racoons, as it was important to monitor all, or nearly all, resident racoons (Prange et al. 2011). The high densities of racoons found at this site (40–70 racoons/km2) were likely due to an abundance of artificial food sources available from garbage cans (Prange

Results

Racoons spent an average ± SD of 96.58 ± 159.77 min per day in close proximity to other racoons (range 0–936 min). The average ± SD pairwise home range overlap between racoons in our social networks was 23 ± 21.01% (range 0–80%), and racoon home ranges in our study area ranged from 25.2 to 52.8 ha (Prange et al. 2004). The average ± SD pairwise genetic relatedness between racoons was 0.011 ± 0.134, and 16% of dyads were closely related (r > 0.125). Average pairwise relatedness did not differ significantly with

Discussion

In general, very few of the factors that we measured affected the structure of racoon social networks. We found that racoon social network structure was not influenced by genetic relatedness or age. During some months outside the mating season, male–male homophily was a significant predictor of racoon network structure. Neither age nor genetic relatedness was a significant predictor variable shaping these male–male interactions. This result is consistent with Gehrt et al. (2008), who found that

Acknowledgments

This project was funded in part by the National Science Foundation (ID-0425203), Cook County Animal and Rabies Control and the Max McGraw Wildlife Foundation. We thank the Cook County Forest Preserve District and C. Anchor for access to our study site, and are especially grateful for the support of D. Parmer (deceased). We also thank The Ohio State University's Terrestrial Wildlife Ecology Lab for support. Genetic analysis was conducted at the Brookfield Zoo in Chicago, IL under the supervision

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