Biology Reference
In-Depth Information
Fig. 7.7
Male
bullfrogs compete
for good egg-
laying territories
by wrestling (left).
The winners then
advertise for
females by calling
(middle) and
females lay their
eggs in the male's
territory. From
Howard (1978a,b).
theoretical and empirical studies have tackled the problem of what benefits females may
gain from choice. It is useful to distinguish two broad types of benefit.
Good resources
In both the long-tailed widowbird and the sedge warbler, females nest in the
territories of their chosen male, so choice may enhance their access to good resources,
such as nest sites or food. Male long-tailed widowbirds do not help to feed their
young, but male sedge warblers do help and males with larger song repertoires are
better parents (Buchanan & Catchpole, 2000). Therefore, in both these cases choice
of a male trait (tail or song) could be a cue to resources that improve a female's
reproductive success.
In many animals, males compete to control resources which females need for
breeding. For example, male North American bullfrogs (
Rana catesbeiana
) defend
territories in ponds and small lakes where females come to lay their eggs (Fig. 7.7).
Some territories are much better for survival of eggs than others (warmer, hence faster
development, and less predation by leeches
Macrobdella decora
). Females prefer these
good laying sites and the preferred territories are hotly contested by males, with the
largest, strongest males gaining the best sites (Howard 1978a, 1978b). Thus, female
choice and male-male competition often go hand in hand.
In other cases, females may choose males on the basis of their ability to provide food.
Female hanging flies (
Hylobittacus apicalis
) will mate with a male only if he provides a
large insect for her to eat during copulation. The larger the insect, the longer the male is
allowed to copulate and the more eggs he fertilizes (Fig. 7.8). The female gains from a
large insect by having more food to put into her eggs. Gifts provided by insects during
courtship may help to protect, rather than nourish, the eggs. In the moth
Utethesia
ornatrix
, the male transfers alkaloids to the female during mating, which the female
uses in anti-predator defence. Further, the same alkaloids are used by the male as a
pheromonal attractant. The female is able to assess the quantity of poison she will
receive by the concentration in the pheromone (Dussourd
et al
., 1991).
Sometimes female
choice of males
increases a
female's access to
resources
