Molecular techniques such as microsatellite genotyping and DNA sequencing together with behavioral and ecological data from a longitudinal field study provide a powerful tool to approach evolutionary questions. Alliance formation among males for the purpose of competition over oestrous females provides an evolutionary conundrum, as males cooperate to obtain paternities - a resource that cannot be shared. In Shark Bay, Western Australia, male bottlenose dolphins (Tursiops sp.) form multi-level alliances. The first level is highly associated with herding of receptive females by two or three males (first-order alliance), whereas on the second level, cooperating first-order alliances (second-order alliance) may take females from other alliances or defend against such attacks.
In order to assess evolutionary explanations for male cooperation two hypotheses have been tested:
- How are paternities distributed within and among alliances? Is reproduction restricted to allied males?
A paternity assessment shed light on direct reproductive success.
- Hamilton’s kin selection theory provides indirect fitness benefits through cooperation with relatives. Are males within alliances more closely related than expected by chance?