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Chapter One: General Introduction
shape local dolphin populations. This finding was supported by behavioural data that
suggested natal philopatry for Shark Bay dolphins (Connor et al. 1992, Smolker et al.
1992, Richards 1996). However, on a larger scale, no such relation of isolation-bydistance
was found between the populations of bottlenose dolphins from Moray Firth,
north Scotland, and the neighbouring populations (Parsons et al. 2002).
Krützen et al. (2004b) suggested that population structure in male bottlenose
dolphins in Shark Bay may also be related to the evolution of mating systems. Males
are known to form alliances which permit these allied males to more successfully
compete for access to females (Connor et al. 1992). Evolutionary theory predicts that
if the males cooperating in this manner are related to each other, then they may gain
inclusive fitness benefits (Hamilton 1964a, b). Long-range dispersal of males to other
areas would thus minimise the chance of allying with a related partner (it was shown
that long-lasting alliances are biased toward related males, Krützen et al. 2003).
Therefore, social system would be simultaneously impacting with geographical
distances on the structure of the population.
At Sarasota Bay, central west Florida, USA, genetic analyses and extensive
behavioural data also support the hypothesis that the genetic distinction of a small
community of bottlenose dolphins (in regards to similar neighbouring communities) is
due to their social system (Wells 1986, Duffield & Wells 1991, Sellas et al. 2005).
There is, however, some gene flow with adjacent communities, thought to be largely
but not exclusively driven by male movements, as illustrated by the sharing of mtDNA
haplotypes between communities (Duffield & Wells 2002).
Finally, historical processes might also shape the structure of contemporary dolphin
populations. In particular, the glacial/interglacial events of the Pleistocene epoch
(1,808,000 to 11,550 years BP) could have played an important role, considering the
recent radiation of dolphin species. Hayano et al. (2004) suggested that the lowering
of the sea level during the late Pleistocene resulted in the isolation of some Pacific
white-sided dolphins in the Sea of Japan from the rest of the North Pacific population.
This may explain the genetic differentiation currently observed between the
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