Genetic evidence for social organization

The observational studies of elephant social relationships have implicitly assumed that association among female groups is directly proportional to relat-edness. Thus, in the larger families, the adult cows are related as sisters (or as mother-daughters), those in the kin groups are related as either sisters or cousins, and within a clan as distant cousins, aunts, and so on. Further, it has been generally believed that males establish their own home ranges at some distance away from their natal family or clan after becoming independent. Two recent studies, one in Asia and the other in Africa, using molecular genetic information have come to somewhat different conclusions.

Prithiviraj Fernando and Russell Lande analyzed mitochondrial DNA (mtDNA) sequences in seven female-led groups and several bulls from the Ruhuna National Park and two nearby sites, Uda Walawe National Park (30 km west) and Mirrijjawila (30 km southwest), in southeastern Sri Lanka. After extracting DNA from the dung of these known elephants, they analyzed a 630-nucleotide base pair segment of the D-loop region gene of the mtDNA. Since mitochondrial DNA is maternally inherited, it provides a means to trace maternal lineages (see chapter 1). Thus, individuals with different mitochondrial DNA sequences or "haplotypes" are not related to each other, while those with the same haplotypes may either be related or be unrelated as kin.

All elephants sampled within each of the seven groups had the same mito-chondrial haplotype, suggesting that animals constituting a group could very well be related. The social groups, however, showed certain variations in their haplotypes (table 4.6). Two groups at Ruhuna shared the same haplotype (labeled A), while another herd there had a unique haplotype (B). The fourth group sampled at Ruhuna shared a haplotype (E) with another group at Uda Walawe. The second group at Uda Walawe had its unique haplotype (D), and so did the herd at Mirrijjawila (type F). The occurrence of so many different haplotypes in female groups over such short distances is itself rather surprising. The combined results from telemetry (home range and associations) and genetics indicated no higher level of organization than the family group even if these groups are relatively large.

Other surprising results emerged from the haplotype analysis of bull elephants, all of them ranging within the Ruhuna National Park. Although four different haplotypes (A, B, E, and a unique C) were recorded, only 1 of the 11 bulls had a haplotype that differed from those of the female groups that ranged over the same area of the park. Fernando and Lande thus proposed that male dispersal is more limited in terms of distance from the natal area, and that more periodic, long-distance movements of the males during musth could be the mechanism promoting outbreeding.

Table 4.6

The distribution of mitochondrial haplotypes in female-led elephant groups in southeastern Sri Lanka.

Table 4.6

The distribution of mitochondrial haplotypes in female-led elephant groups in southeastern Sri Lanka.

Number of

Individuals

Mitochondrial

Location

Social Group

Samples

Haplotype

Ruhuna NP

Yala I

9

A

Ruhuna NP

Yale II

7

A

Ruhuna NP

Thambarawa

12

B

Ruhuna NP

Katagamuwa

4

E

Uda Walawe NP

Uda Walawe NP I

3

D

Uda Walawe NP

Uda Walawe NP II

4

E

Mirijjawila

Mirijjawila

3

F

Source: From Fernando & Lande (2000). Reproduced with permission of Springer-Verlag

Source: From Fernando & Lande (2000). Reproduced with permission of Springer-Verlag

Another study of three female groups at Sengwa in Zimbabwe confirmed that these corresponded to clans in the conventional sense. The mtDNA profiles, however, brought another surprise. The members of a clan were not necessarily matrilineally related. Of the two haplotypes found in these clans, two adult females from different families but within the same clan, seemingly associating as a bond group, were of different matrilines. This perhaps was not quite unexpected when Cynthia Moss preferred the term bond group to kin group at Amboseli. The corresponding telemetry data at Sengwa also showed that only some families within a clan coordinated their movements, while others used the space quite independently. A possible explanation is that Sengwa does not represent a natural condition in that large numbers of elephants have been culled in recent times; this may have resulted in significant changes in social organization.

Molecular genetics provides new tools to investigate the social organization of a species. Using both mitochondrial and nuclear DNA profiles, new facets of the mating system, dispersal, relatedness, and social relationships in elephant societies would undoubtedly be unraveled in the coming years.

Was this article helpful?

0 0

Post a comment