Infanticide and social flexibility in the genus <Emphasis Type="Italic">Gorilla</Emphasis> |
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Authors: | Juichi Yamagiwa John Kahekwa Augustin Kanyunyi Basabose |
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Institution: | (1) Laboratory of Human Evolution Studies, Graduate School of Science, Kyoto University, Sakyo Kyoto, 606-8502, Japan;(2) Parc National de Kahuzi-Biega, Institut Congolais pour Conservation de la Nature, B.P. 895, Bukavu, Democratic Republic of Congo;(3) Centre de Recherche en Sciences Naturelles, Lwiro, D.S. Bukavu, Democratic Republic of Congo |
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Abstract: | Based on the cases of infanticide by male mountain gorillas reported from the Virunga volcanic region, the socioecological
and life history features of gorillas satisfy the conditions for which infanticide may be expected. However, there are considerable
variations in the occurrence of infanticide between habitats. We analyze the recent reports of infanticides that were directly
observed or are suspected based on field evidence in two populations of eastern and western lowland gorillas (Kahuzi and Mbeli
Bai, respectively) along with previous reports on mountain gorillas, and consider which social features are linked with and
which factors influence the occurrence of infanticide in the gorilla populations. All victims were suckling infants and most
of them were killed by males who seemed unrelated to them. Dependent infants are most vulnerable to infanticide when the protector
male (its putative father in most cases) is absent, and so male protection ability seems to be important in determining female
transfer decisions. Two cases observed in Kahuzi suggest that the infanticidal male may discriminate between infants to accept
and those to kill according to his previous interactions with their mothers. Mating for a prolonged period prior to parturition
is necessary for immigrant females to avoid infanticide by the new male of the group that they join. Infanticide was usually
associated with female transfer, and the patterns of female association at transfer may shape variations in social structure
between populations. Female mountain gorillas prefer large groups with multiple males and tend to transfer alone in order
to seek more protection against infanticide in Virunga. By contrast, female eastern and western lowland gorillas tend to transfer
with other females to small groups or solitary males, and maturing silverbacks take females to establish new groups through
group fission in Kahuzi and Mbeli Bai. These differences may result in more multi-male and larger groups in the Virungas than
in Kahuzi and Mbeli Bai. Rapid changes in density of gorilla social units and their relations following drastic environmental
changes caused by recent human disturbances may also increase the probability of infanticide. |
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