Population genetic structure of raccoons (Procyon lotor) inhabiting a highly fragmented landscape

Abstract

The raccoon (Procyon lotor (L., 1758)), a generalist mesocarnivore, has thrived in anthropogenically fragmented landscapes. In this study we utilized 13 microsatellites to analyze the population genetic structure in raccoons occupying an agriculturally fragmented habitat. Our analyses revealed low, but significant, levels of genetic structure (FST = 0.022, P < 0.001) among 645 raccoons inhabiting 29 spatially distinct habitat patches (neighborhoods). We found no evidence for the presence of either isolation by distance or barriers. However, spatial autocorrelation revealed evidence for social structure at the raccoon-neighborhood scale. About 30% of the variance in levels of social structure among raccoon neighborhoods was explained by effects of habitat-patch size and the percentage of land cover represented by forest around the individual habitat patch. We found strong evidence of sex-biased dispersal using direct (parentage analysis) and indirect (relatedness and assignment indices) genetic estimators. However, our analysis revealed that among dispersing raccoons there was no difference in dispersal distance between sexes and that dispersal events are randomly distributed with respect to distance. Our study provides evidence that demographic and behavioral processes affecting raccoon spatial organization may be most critical at very fine scales of biological organization, such as within individual habitat patches.Résumé : Le raton laveur (Procyon lotor (L., 1758)), un mésocarnivore généraliste, a prospéré dans les paysages fragmentés par l'activité humaine. Nous utilisons, dans notre étude, 13 microsatellites pour déterminer la structure génétique de la population chez des ratons laveurs qui vivent dans un habitat fragmenté par l'agriculture. Nos analyses révèlent des niveaux bas, mais significatifs, de structure génétique (F ST = 0,022, P < 0,001) parmi 645 ratons laveurs vivant dans 29 taches d'habitat distinctes (quartiers). Il n'y a aucune indication d'isolement par la distance, ni de barrières. Cependant, l'autocorrélation spatiale donne des indications d'une structure sociale à l'échelle des quartiers de ratons laveurs. Environ 30 % de la variance des niveaux de structure sociale entre les quartiers de ratons laveurs s'explique par les effets de la taille de la tache d'habitat et le pourcentage de la couverture du sol autour des taches individuelles d'habitat qui est repré-senté par de la forêt. Des estimateurs génétiques directs (analyse de filiation) et indirects (indices de consanguinité et d'attribution) indiquent clairement une dispersion variable en fonction du sexe. Cependant, notre analyse révèle que, parmi les ratons laveurs qui se dispersent, il n'y a pas de différence de distance de dispersion en fonction des sexes et que les événe-ments de dispersion sont répartis au hasard en fonction de la distance. Notre étude fournit des indications que les processus démographiques et comportementaux qui affectent l'organisation spatiale des ratons laveurs peuvent agir de la façon la plus critique aux éch...

Heterozygote deficiencies in parasite populations: an evaluation of interrelated hypotheses in the raccoon tick, Ixodes texanus

“…The patches were separated by distances ranging from 5.98 to 28.06 km, and raccoons inhabiting them were genetically differentiated (0.02pF ST p0.06; Po0.001 for all pairwise comparisons; Dharmarajan et al, 2009a). Raccoon trapping, immobilization and post-capture processing have been described earlier (Beasley et al, 2007;Beasley and Rhodes, 2008).…”

“…Sample collection and microsatellite data I. texanus ticks (n ¼ 736) were collected in the spring of 2006 from 91 raccoons trapped in five habitat patches (Pop_01, Pop_03, Pop_14, Pop_16 and Pop_17) located in the Upper Wabash River Basin, Indiana (Supplementary Figure S1; see Table 1 for sampling details; patch numbers follow Dharmarajan et al, 2009a). The patches were separated by distances ranging from 5.98 to 28.06 km, and raccoons inhabiting them were genetically differentiated (0.02pF ST p0.06; Po0.001 for all pairwise comparisons; Dharmarajan et al, 2009a).…”

Melding kin structure and demography to elucidate source and sink habitats in fragmented landscapes

“…Their study revealed that local populations sorted into two distinct groups, exhibiting either significantly greater or lesser (non-significant) levels of kin-structure than would be expected at random, a pattern primarily driven by the fact that contributions to population persistence stemming from immigration versus natality differed markedly among local populations. This finding, in combination with strong evidence for a high degree of site fidelity of female raccoons to their natal patch (Gehrt and Fritzell 1998, Ratnayeke et al 2002, Cullingham et al 2008, Dharmarajan et a. 2009, Beasley et al 2013, led (Dharmarajan et al 2014) to hypothesize that significant spatial variation in vital rates exists for raccoons inhabiting fragmented agricultural ecosystems, consistent with expectations of a sourcesink population structure.…”

“…However, we believe apparent survival of adult female raccoons closely resembles true survival in our study area. Dispersal in raccoons is male-biased (Ratnayeke et al 2002, Cullingham et al 2008, Dharmarajan et al 2009) and predominantly occurs between 0.5 and 1.5 years of age (Gehrt 2003). Moreover, adult females maintain small home ranges within our study area (58 ha) and no permanent emigration was observed among 37 females tracked using radiotelemetry during previous research conducted within our study landscape (maximum home range size was 160 ha; Beasley et al 2007.…”

“…The total number of traps per grid varied with forest patch size, with a maximum of 30 traps placed in any single forest patch. Captured raccoons were marked with uniquely numbered ear tags (National Band and Tag Company, Newport, Kentucky, USA) and we collected standard morphometric and demographic data, including an ear biopsy for genetic analyses (Dharmarajan et al 2009(Dharmarajan et al , 2014. Raccoons were classified as juveniles (1 yr), yearlings (2 yr), or adults (!3 yr) by examining tooth wear.…”