Do mountain gorillas avoid inbreeding?

May 21, 2015

Do mountain gorillas avoid inbreeding?

The long-term studies of mountain gorillas conducted at the Dian Fossey Gorilla Fund’s Karisoke Research Center continue to yield important information about many aspects of gorilla life. A study just published in the journal Behavioral Ecology and Sociobiology, focusing on gorillas monitored by the Fossey Fund, used genetic analysis based on fecal samples that have been collected since 1999. They were analyzed to determine paternity patterns and to look at whether gorillas avoid breeding with close relatives.

The study was co-authored by Fossey Fund CEO and Chief Scientific Officer Tara Stoinski, Ph.D., in collaboration with our long-term scientific collaborators at the Max Planck Institute for Anthropology.

Silverback Cantsbee has sired more than 20 offspring.The new study built on an earlier one, which examined paternity patterns through the late 1990s and found that in groups containing two or three fully adult males, the dominant silverback still sired the majority (85 percent) of offspring.

The current study included another decade of paternity data, which represented a time when the Karisoke gorilla groups grew very large and contained many more males ─ sometimes up to eight silverbacks. Under these conditions, the dominant males sired fewer offspring, although they still maintained the lion’s share of reproduction. Perhaps the costs of losing reproductive opportunities might be offset by the benefits of having male successors, who can keep the group together upon the dominant male’s death.

Another focus of the current study was to look at inbreeding avoidance. Roughly half of females reproduce in the group where they were born, resulting in the potential for them to reproduce with their fathers. However, the genetic analyses in this study found no evidence of father-daughter reproduction, although half siblings were observed to occasionally reproduce.

How fathers and daughters avoid breeding with each other is unknown — the authors suggest that females may use male age as a cue, since the daughters of dominant males all bred with males who were much younger than their fathers.

As the authors state, these results emphasize “the complexity of social dynamics in one of our closest living relatives.”