Sex‐biased dispersal in western lowland gorillas (Gorilla gorilla gorilla)

Abstract

We explored two hypotheses related to potential differences between sexes in dispersal behaviour in western lowland gorillas (Gorilla gorilla gorilla). Direct observations suggest that immature females have more opportunities to move between breeding groups than immature males. The distribution of kin dyadic relationships within and between groups does not, however, support this hypothesis. At larger geographical scales, dispersal is likely to be easier for males than females because of the solitary phase most blackbacks experience before founding their own breeding group. However, previous work indicates that males settle preferentially close to male kin. By specifically tracing female and male lineages with mitochondrial and Y-chromosomal genetic markers, we found that male gorillas in the 6000 km2 area we surveyed form a single population whereas females are restricted to the individual sites we sampled and do not freely move around this area. These differences are more correctly described as differences in dispersal distances, rather than differences in dispersal rates between sexes (both sexes emigrate from their natal group in this species). Differences in resource competition and dispersal costs between female and male gorillas are compatible with the observed pattern, but more work is needed to understand if these ultimate causes are responsible for sex-biased dispersal distances in western lowland gorillas.

Noninvasive Follow-Up of Simian Immunodeficiency Virus Infection in Wild-Living Nonhabituated Western Lowland Gorillas in Cameroon

“…Mother-to-infant viral transmission (MTIT) could occur in utero or by breastfeeding, since gorillas are weaned at approximately 4 years of age and therefore can be infected after birth (21,64). Sexual transmission between related individuals (at first degree) is unlikely, as females and males leave the natal group at sexual maturity to avoid inbreeding (12,24,47). By deducting microsatellite matches and highly related viruses, we identified five putative vertical transmissions, but because we had no data on the ages of the apes, it was impossible to ascertain whether we were looking at father-daughter pairs or mother-son pairs or to discriminate mothers or daughters among linked female pairs.…”

A time- and cost-effective strategy to sequence mammalian Y Chromosomes: an application to the de novo assembly of gorilla Y

“…To enable future studies of gorilla male-specific dispersal and migration (Douadi et al 2007), we designed a panel of Y-specific microsatellite markers based on the assembly generated in this study (see Methods). This panel includes seven novel fluorescently labeled tri-and tetranucleotide microsatellite markers that can be assayed in a single run on ABI3700 and are polymorphic when tested in 14 wild-born gorillas (Supplemental Table S16).…”

“…The novel fluorescent Y-Chromosome microsatellite multiplex assay presented here can be used to investigate gorilla male dispersal patterns determining the genetic diversity of gorilla populations in the wild (Douadi et al 2007). Such patterns influence population structure; thus, their analyses will ultimately aid conservation efforts on behalf of this endangered species that faces numerous threats, including habitat loss and disease impacts (Genton et al 2014).…”

Molecular Epidemiology of Simian Immunodeficiency Virus Infection in Wild-Living Gorillas

“…Interestingly, we observed a predominance of SIVgor infection in females, and whether this is related to a sample bias and/or the social organization of gorilla groups needs to be studied further. Western lowland gorillas live in social breeding groups usually formed by one silverback male, three adult females (on average), and their offspring (7,9,20,24). Before reaching sexual maturity, male gorillas leave their natal group and go through a bachelor stage that can last several years (9,19).…”