Biology Reference
In-Depth Information
Females compete to takeover neighbouring male territories and sometimes kill other
female's chicks in order to make extra males available to receive their clutches (Emlen
et al
., 1989). Such female infanticide is the sex role reversed analogy of male infanticide
in lions (Chapter 1), where males attempt to make more fertile females available.
While polyandry benefits a female jacana, it brings potential costs to a male because
other males in the female's harem (co-mates) may fertilize the eggs laid in his territory.
Indeed, a female often copulates with several males while she lays a clutch for one of
them. In the bronze-winged jacana
Metopidius indicus
co-mates compete for their
female's attention by yelling for copulations (Butchart
et al
., 1999b). A study of the
wattled jacana
Jacana jacana
, in Panama revealed that monandrous males (one female
with one male) gained full paternity of their clutches while in polyandry 41% of broods
had chicks sired by other males in the harem (17% of all chicks were sired by co-mates;
Emlen
et al
., 1998). Co-mates are, therefore, competitors both for receipt of clutches
and for copulations.
Female jacanas
compete for male
care
A hierarchical approach to mating
system diversity
We have discussed three broad themes that might influence mating systems:
(i)
Life history constraints
. For example, male mammals (which do not lactate) might
often be less able to make a worthwhile contribution to the feeding of offspring
than male birds.
(ii)
Ecological factors
. For example, the dispersion of food and nest sites will influence
the dispersion of potential mates and, hence, their economic defendability.
(iii)
Social conflicts
. Individuals often behave to limit the choices of their mates through
coercion or deception.
How well do these three themes explain the diversity of mating systems in Table 9.1?
Ian Owens and Peter Bennett (1997) have suggested that we need all three themes
but that each will be most relevant at a different taxonomic level of analysis (Table 9.3).
Consider bird mating systems. If we want to explain differences between higher
taxonomic levels, for example different orders or families, then differences in life history
constraints are likely to be important (theme (i) above). For example, the offspring of
pheasants (family Phasianidae) are precocial and can run about and feed themselves
soon after hatching. Therefore, it is not too costly for a male to desert and seek further
mates because the female can care for a brood alone. By contrast, young hawks (family
Accipitridae) are born naked and helpless and need the care of both parents. Initially
the female guards the nest and keeps the young warm while the male does all the
hunting for the family.
If we want to explain differences in mating systems at lower taxonomic levels, for
example differences between species within a genus, then here differences in ecology
are likely to be most important (theme (ii) above). Thus, weaverbird species that exploit
seeds (large patches of easily-found food) are more likely to be polygynous than
Differences
between orders
or families reflect
life history
differences
