Abstract:
Polygyny is a widespread and evolutionarily significant mating system in
vertebrates. The southern elephant seal, Mirounga leonina, has often been cited
as an example of an animal with an extremely polygynous mating system, thus
providing an important reference point for studies on mating systems. During
the breeding season, these animals form terrestrial harems in which one
dominant male controls tens to hundreds of females. Our current understanding
of polygynous mating systems seems to imply that, unlike males, females are not
under selective pressure to adopt alternative mating strategies, and in the case of
the southern elephant seal, the possibility of mating at sea, off these harems, has
not been considered. Furthermore, elephant seal females are thought to breed
annually from primiparity to death. We use a 25-year mark-recapture dataset to
show that elephant seal females skip breeding seasons, often returning to pup in
the following breeding season. We show that elephant seal females do not need to
haul out on land in order to breed in the following season thus providing
evidence for mating at sea by virgin and multiparous females. Non-polygynous,
opportunistic mating at sea could be an important alternative mating strategy in
a supposedly strictly polygynous species. This has implications for our
understanding of elephant seal ecology, demography, behaviour, and of the
evolution of vertebrate polygyny in general. If polygyny does not preclude
females from adopting alternative mating strategies, the term ‘polygyny’ may be
misleading. Traditional concentration on male strategies has hampered our
understanding of mating systems, in assuming that females capitulate to these
strategies. We suggest similar misinterpretations could occur in other
polygynous species.
