Where sociality and relatedness diverge: the genetic basis for hierarchical social organization in African elephants

Abstract

Hierarchical properties characterize elephant fission -fusion social organization whereby stable groups of individuals coalesce into higher order groups or split in a predictable manner. This hierarchical complexity is rare among animals and, as such, an examination of the factors driving its emergence offers unique insight into the evolution of social behaviour. Investigation of the genetic basis for such social affiliation demonstrates that while the majority of core social groups (second-tier affiliates) are significantly related, this is not exclusively the case. As such, direct benefits received through membership of these groups appear to be salient to their formation and maintenance. Further analysis revealed that the majority of groups in the two higher social echelons (third and fourth tiers) are typically not significantly related. The majority of third-tier members are matrilocal, carrying the same mtDNA control region haplotype, while matrilocality among fourth-tier groups was slightly less than expected at random. Comparison of results to those from a less disturbed population suggests that human depredation, leading to social disruption, altered the genetic underpinning of social relations in the study population. These results suggest that inclusive fitness benefits may crystallize elephant hierarchical social structuring along genetic lines when populations are undisturbed. However, indirect benefits are not critical to the formation and maintenance of second-, third-or fourth-tier level bonds, indicating the importance of direct benefits in the emergence of complex, hierarchical social relations among elephants. Future directions and conservation implications are discussed.

Comparative Demography of an At-Risk African Elephant Population

“…These orphans take different strategies in relation to their social context, remaining solitary, clustering with other orphans or joining other groups. Such processes were first noted by genetic studies of the population [52], but the number of orphaned individuals has risen sharply. In addition, the relative density of individuals in older age classes has declined compared with densities during the study onset.…”

Inferring ecological and behavioral drivers of African elephant movement using a linear filtering approach

“…Thus the movement paths analyzed here are not restricted by fences or impassible geographic barriers. The 13 elephants tracked represent 13 distinct social groups ranging in size from 6 to 19 individuals, and represent .25% of the resident elephants using the study area (Wittemyer et al 2009b). Separate analysis demonstrated that group members are consistently in direct proximity (Wittemyer et al 2009b); therefore the movements of the tracked individuals are assumed to represent the group's movements.…”

Bats are able to maintain long-term social relationships despite the high fission–fusion dynamics of their groups

“…If bats are limited in their sociocognitive abilities, species living in colonies with high fission -fusion dynamics should either form no longterm social relationships, or apply simple behavioural rules that do not require high cognitive abilities, such as aggregating according to size, age, reproductive status or relatedness [7]. Conversely, long-term social relationships between bats that differ in their morphological, demographical and genetic characteristics would be evidence that bats are capable of maintaining individualized relationships in highly dynamic societies, comparable to that of elephants, dolphins and some primates [4,6,7].…”