1.2 Alliance formation in bottlenose dolphins (tursiops sp.)

Author: Natasha Sotolongo

Introduction

The formation of alliances between organisms has been an area of active study for many years (Connor and Norris 1982). The motives behind alliance formation within groups are not fully understood because when animals cooperate in groups, not all of the group members reap the same benefit. In Shark Bay, Australia, scientists have been studying a society of more than 600 Indian Ocean bottlenose dolphins (Tursiops aduncus) in a territory that extends over 200 km2, peppered with overlapping ranges of populations without apparent boundaries (Connor 2007). These bottlenose dolphins demonstrate a fission-fusion grouping pattern in which alliances are frequently formed and disbanded (Connor 2007). The stability of fission-fusion relationships is usually based upon benefits attained while allied, such as defense against predators, increased food acquisition, and social support (Gero et al. 2005).

Male bottlenose dolphins form primary alliances that usually consist of two or three males and vary in stability and relatedness. Alliances compete against each other over females. Two primary alliances may combine to form a secondary alliance that works together to steal females from other primary alliances. A very large secondary alliance is called a “super-alliance,” consisting of up to fourteen members that frequently change their primary alignment. Alliances among males occur to create a stronger group that will acquire more females (Connor 2000). In response to male aggression, female bottlenose dolphins form groups of their own, consisting of only females and their calves.

Several theories have been proposed to explain alliances in bottlenose dolphins. The first of the theories is kin selection , where members form alliances of related members, creating an inclusive fitness advantage by aiding relatives. Individuals act according to Hamilton’s rule , where relatedness between actor and recipient, benefit to the recipient, and cost to the actor are taken into account. A second theory is reciprocal altruism , where a dolphin will perform a seemingly altruistic act toward an ally, but expect future remuneration and cease to act altruistically if the favors are not reciprocated (Connor&Norris 1982).