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, 273 (1586), 513-22

The Ties That Bind: Genetic Relatedness Predicts the Fission and Fusion of Social Groups in Wild African Elephants

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The Ties That Bind: Genetic Relatedness Predicts the Fission and Fusion of Social Groups in Wild African Elephants

Elizabeth A Archie et al. Proc Biol Sci.

Abstract

Many social animals live in stable groups. In contrast, African savannah elephants (Loxodonta africana) live in unusually fluid, fission-fusion societies. That is, 'core' social groups are composed of predictable sets of individuals; however, over the course of hours or days, these groups may temporarily divide and reunite, or they may fuse with other social groups to form much larger social units. Here, we test the hypothesis that genetic relatedness predicts patterns of group fission and fusion among wild, female African elephants. Our study of a single Kenyan population spans 236 individuals in 45 core social groups, genotyped at 11 microsatellite and one mitochondrial DNA (mtDNA) locus. We found that genetic relatedness predicted group fission; adult females remained with their first order maternal relatives when core groups fissioned temporarily. Relatedness also predicted temporary fusion between social groups; core groups were more likely to fuse with each other when the oldest females in each group were genetic relatives. Groups that shared mtDNA haplotypes were also significantly more likely to fuse than groups that did not share mtDNA. Our results suggest that associations between core social groups persist for decades after the original maternal kin have died. We discuss these results in the context of kin selection and its possible role in the evolution of elephant sociality.

Figures

Figure 1
Figure 1
Histogram of the frequency of pairwise genetic relatedness values calculated for all pairs of adult females who were members of the same core social group (grey bars, n=865 pairs) and all pairs who were members of different core social groups (black bars, n=26 864 pairs). Genetic relatedness was calculated from the complete genotypes of 236 adult females at 11 microsatellite loci. Average pairwise genetic relatedness within the entire population is, by definition, zero.
Figure 2
Figure 2
(a) UPGMA trees of AI for the AA and the GB core social groups. The grey box encompasses the clusters that have average AI >0.9; average pairwise genetic relatedness within these clusters, across all ten focal core groups, was 0.42 (see b). (b) A plot created by ‘cutting’ the association distance trees at set association intervals, and then calculating average pairwise genetic relatedness within the resulting clusters. Values are calculated for 80 adult female elephants from 10 different focal core groups. Standard errors for genetic relatedness were calculated by jack-knifing across loci.
Figure 3
Figure 3
(a) UPGMA tree of AI between 51 (out of 55) of the most frequently seen core social groups in Amboseli. Black and grey boxes on the left contain core group names and each greyscale combination represents a different mitochondrial DNA d-loop haplotype (black with white letters=AMB1, light grey with black letters=AMB2, dark grey with black letters=AMB3, dark grey with white letters=AMB4, and no box with grey letters=un-genotyped core group). Bond group clusters (defined in figure 2b) are encompassed by light grey boxes. (b) Plot of the accumulation of clusters (or nodes) on the tree in figure 2a as a function of association index. The vertical line at association index 0.17 indicates where the slope changes. The 13 points to the left of this are derived from all the clusters that comprise the nine bond groups in Amboseli.

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