Lethal combats in the forest among wild western gorillas

Area of Science:

• Primate behavior
• Zoology
• Evolutionary biology

Background:

• Lethal intergroup encounters are common in species driven by sexual selection.
• Western gorillas were thought to lack these encounters due to social structure and diet.
• Mountain gorillas exhibit lethal intraspecific aggression linked to sexual selection.

Purpose of the Study:

• To determine the cause of injuries on deceased western gorillas.
• To investigate the occurrence of lethal intraspecific aggression in western gorillas.
• To compare injury patterns with known causes of death in gorillas and other species.

Main Methods:

• Analysis of injuries on four deceased western gorillas (three silverbacks, one adult female).
• Comparison of observed injury patterns with documented injuries from intraspecific gorilla aggression (mountain gorillas) and interspecific predation (leopards).
• Identification of distinct injury signatures for gorilla-inflicted wounds versus leopard predation.

Main Results:

• Two distinct injury patterns were identified: gorilla-inflicted (isolated lacerations, round wounds) and leopard-inflicted (clustered punctures on head/neck).
• The injury patterns on the deceased western gorillas were consistent with gorilla-inflicted wounds, not leopard predation.
• This suggests lethal intraspecific encounters occur in western gorillas, similar to mountain gorillas.

Conclusions:

• Lethal intraspecific encounters, driven by sexual selection, do occur in western gorillas, particularly in one-male societies.
• While sexual dimorphism and polygyny may favor aggression, the presence of multiple males in a group might reduce encounter frequency.
• These findings challenge previous assumptions about western gorilla social dynamics and aggression patterns.