Fine-scale genetic structure analyses suggest further male than female dispersal in mountain gorillas

Abstract

BackgroundMolecular studies in social mammals rarely compare the inferences gained from genetic analyses with field information, especially in the context of dispersal. In this study, we used genetic data to elucidate sex-specific dispersal dynamics in the Virunga Massif mountain gorilla population (Gorilla beringei beringei), a primate species characterized by routine male and female dispersal from stable mixed-sex social groups. Specifically, we conducted spatial genetic structure analyses for each sex and linked our genetically-based observations with some key demographic and behavioural data from this population.ResultsTo investigate the spatial genetic structure of mountain gorillas, we analysed the genotypes of 193 mature individuals at 11 microsatellite loci by means of isolation-by-distance and spatial autocorrelation analyses. Although not all males and females disperse, female gorillas displayed an isolation-by-distance pattern among groups and a signal of dispersal at short distances from their natal group based on spatial autocorrelation analyses. In contrast, male genotypes were not correlated with spatial distance, thus suggesting a larger mean dispersal distance for males as compared to females. Both within sex and mixed-sex pairs were on average genetically more related within groups than among groups.ConclusionsOur study provides evidence for an intersexual difference in dispersal distance in the mountain gorilla. Overall, it stresses the importance of investigating spatial genetic structure patterns on a sex-specific basis to better understand the dispersal dynamics of the species under investigation. It is currently poorly understood why some male and female gorillas disperse while others remain in the natal group. Our results on average relatedness within and across groups confirm that groups often contain close relatives. While inbreeding avoidance may play a role in driving female dispersal, we note that more detailed dyadic genetic analyses are needed to shed light on the role of inbreeding avoidance as an ultimate cause of female dispersal in mountain gorillas.

Variation in the social organization of gorillas: Life history and socioecological perspectives

“…Father‐daughter inbreeding avoidance was observed within multimale groups, but approximately 10% of infants had parents who were either mother‐son pairs or half‐siblings . The risk of inbreeding can be reduced through sex‐biased differences in dispersal distances, and male mountain gorillas disperse farther than females . Nonetheless, the influences of inbreeding and familiarity among adults on the dispersal patterns of both sexes warrant additional research …”

“…In addition to the potential influences of poaching and habituation, humans may have altered the dispersal patterns and social organization of mountain gorillas by reducing the suitable habitat in which to move. Although some emigrating western gorillas and mountain gorillas remain near their natal area, genetic studies have shown long dispersal distances for others . Options to disperse long distances have declined for mountain gorillas in recent decades, as many mountain gorillas now live along a park boundary .…”

Genetic Analysis of the Indri Reveals No Evidence of Distinct Subspecies

“…Survey work around Betampona has shown populations of Indri to be susceptible to habitat fragmentation, with populations possibly becoming locally extinct or being driven out of their historical habitats in as little as 2 yr (Glessner and Britt 2005). Data are lacking on dispersal capabilities of Indri across fragmented landscapes and about dispersal differences between sexes [such as those observed in gorillas by Roy et al (2014)], which may also contribute to these genetic patterns.…”

The Status of Captive Apes

“…However, the ability to retain connectivity between patches, as well as the level of genetic diversity within and between patches, depends on more than absolute distance, as dispersal patterns differ for males and females. Female gorillas always disperse directly between social units and do not travel on their own, but males disperse alone and travel greater distances (Yamagiwa, Kahekwa and Basabose, 2003;Harcourt and Stewart, 2007;Guschanski et al, 2009;Arandjelovic et al, 2014;Roy et al, 2014a). As a result, males may have more of an impact on gene flow within populations and among isolated subpopulations (Bergl et al, 2008;Guschanski et al, 2009;Roy et al, 2014a).…”

“…Female gorillas always disperse directly between social units and do not travel on their own, but males disperse alone and travel greater distances (Yamagiwa, Kahekwa and Basabose, 2003;Harcourt and Stewart, 2007;Guschanski et al, 2009;Arandjelovic et al, 2014;Roy et al, 2014a). As a result, males may have more of an impact on gene flow within populations and among isolated subpopulations (Bergl et al, 2008;Guschanski et al, 2009;Roy et al, 2014a). Human disturbance is believed to have resulted in an abrupt reduction not only in population size, but also in genetic diversity in Cross River gorillas, emphasizing that the impacts of altered landscapes are far more complex than only having fewer apes (Bergl and Vigilant, 2007;Bergl et al, 2008).…”