Biology Reference
In-Depth Information
(a)
Monogamy
♀
5.0
♂
5.0
♂
a
♂
♀
♀
♀
3.8
♀
3.8
♂
7.6
♀
6.7
♂
a
3.7
♂
b
3.0
Polygyny
Polyandry
(b)
Fig. 9.12
Male dunnock feeding a brood of chicks. Photo © W. B. Carr. (a) Sexual
conflict in dunnocks. Female territories (solid lines) are exclusive and may be defended by
one or two unrelated males (dashed lines). The numbers refer to the number of young
raised per season by males and females in the different mating combinations (maternity
and paternity measured by DNA fingerprinting; Burke
et al
. (1989)). Arrows indicate the
directions in which dominant (alpha) male and female behaviour encourage changes in
the mating system. A male does best with polygyny; the cost of polygyny to females is
shared male care. A female does best with polyandry; the cost of polyandry to males is
shared paternity. (b) Polygynandry as a stalemate to the conflict: the alpha male is unable
to drive the beta male off to claim polygyny, and neither female can evict the other to
claim polyandry. From Davies (1989, 1992).
Various factors influence the conflict outcome. Firstly, differences in individual
competitive ability are important. For example, young males are more likely to be
subordinate males and older, experienced, males are more likely to defend larger
territories which can encompass two female territories (polygyny or polygynandry).
Secondly, the adult sex ratio influences mating systems; after harsher winters the
breeding sex ratio is more male-biased (females are subordinate at feeding sites and
more likely to die), so there is more polyandry. Thirdly, territory characteristics can
influence the conflict outcome; on territories with denser vegetation, a female can
more easily escape dominant male guarding and so promote mixed paternity
(Davies, 1992).
