The role of genetic relatedness in urban raccoon sociality
Stephanie A. Hauver, MS
Advisor: Stan Gehrt
Raccoons (Procyon lotor) are one of the most ubiquitous mammals in North America, yet the details of their social behavior remain enigmatic. Recent research, however, suggests that raccoons possess a more complex social system than previously believed (Prange and Gehrt unpublished data). Raccoons carry a wide variety of zoonotic diseases, including rabies, that are transmitted through close contact. Therefore, a more complete understanding of raccoon social behavior, or interaction rate, is helpful in modeling disease transmission rates. Additionally, the emerging social associations among raccoons afford us a unique opportunity to examine which mechanism(s) is (are) responsible for their complex and selective sociality.
I examined the extent to which social associations among adult raccoons can be attributed to their degree of relatedness. I examine five predictions that pertain to this objective: 1) related individuals share greater proportions of their home ranges than unrelated individuals, 2) related individuals exhibit a negative correlation between relatedness and geographic distance between activity centroids, 3) related dyads contact each other more frequently than unrelated dyads, 4) related individuals have consistently higher rates of contact than unrelated dyads, and 5) related individuals den share more often than unrelated individuals. Captured adult raccoons (n=42; 20M, 22F) were sampled for genetic analysis and fitted with proximity detecting radio collars. Proximity detectors allow for the collection of spatial data via traditional VHF radio telemetry. Additionally, proximity detectors record when two or more individuals come within approximately 1m of each other. A series of randomization tests were used to analyze social data in conjunction with relatedness values. Highly related dyads did not share greater home range overlap, live in closer proximity, or have higher contact rates than unrelated individuals (all P >0.156). Male-male pairs had more stable associations than female-female or male-female dyads (Prange and Gehrt, unpublished data) throughout the year, but relatedness was not greater among consistently social pairs than seasonally social pairs. I found that relatedness is not the main factor driving social associations among raccoons. I suggest that a high-density population and abundant, highly concentrated resources, such as occurred at my study site, are more likely the factors responsible for raccoon social tolerance.
Another aspect of raccoon biology that is poorly understood is their mating behavior. Raccoons reportedly engage in a polygynous or promiscuous system depending on the synchronicity of estrus periods, and such systems are facilitated by the formation of male coalitions. However, these assertions are based solely on denning associations and coarse-grained radio-telemetry studies. Although denning associations are often used as a surrogate for matings, no studies have determined if instances of co-denning result in progeny. Moreover, no studies have examined the relatedness among male coalition members, or the mating success of coalition members versus solitary males. To answer these questions, I addressed three specific objectives: 1) determine the mating system for a high-density population of raccoons, 2) describe the social associations (spatial relationships, contact rates, and denning associations) for identified parents, and 3) determine if instances of multiple paternity are reserved for coalition members.
I captured 44 juveniles within an area where adult raccoons had been monitored extensively using proximity detecting radio collars. All adults and juveniles were genotyped using 16 highly variable microsatellite loci. Based on analysis of littermates, I found a high rate of multiple paternity (83.3%) and evidence for a promiscuous breeding system as both males and females bred with multiple mates. Females often exhibited the greatest spatial overlap and highest contact rates with males that sired their litters. Males, however, associated with many females other than those whose litters they sired. Male coalition members did not sire the majority of assigned young. Overall, I found a low percentage of parental assignment, but twice as many resident females were assigned parentage than resident males. Similar results were observed in another study on raccoon multiple paternity, and this may be an indication of male roaming behavior in raccoons. Of the four parental dyads, none were recorded to share dens during winter. Although den sharing occurred throughout the winter, the incidence of den sharing increased markedly during the peak of the mating season. These results suggest that although denning associations increase during the mating period, den sharing may not be a common mating strategy, or reserved solely for mating associations.