Biology Reference
In-Depth Information
Filial cannibalism
The act of eating one's own offspring (filial cannibalism) seems bizarre at first. It is
particularly common in fish and was long regarded as abnormal behaviour. However,
Sievert Rohwer (1978) suggested that it might sometimes be adaptive for a parent to use
its offspring as an extra source of food, eating part of a brood to improve parental care
of the current brood, or eating the whole brood to cut parental losses and improve
future reproductive success.
Andrea Manica (2002, 2004) has shown that male scissor-tailed sergeant fish
Abudefduf sexfasciatus
vary filial cannibalism in response to experimental changes in the
costs and benefits of care. Males defend territories on coral reefs. They alternate between
a two to three day mating phase, when they become golden in colour and display to
attract egg laying females to their territories, and a four to five day parental phase, when
they lose their gold colour, cease displays and guard their eggs until they hatch. When
males had their clutches reduced by 75% on the first day of the parental phase they
were more likely to cannibalize the remaining eggs and revert to the mating phase than
control males, who had the same disturbance but without egg reduction. Egg reduction
on the third day of the parental phase led to no increase in cannibalism, most likely
because parental care was then less costly (fewer days to hatching). In another
experiment, the provision of supplemental food (conspecific eggs or crabmeat) led to a
reduction in partial filial cannibalism compared to control males, suggesting that males
sometimes ate part of their brood to fuel their energy requirements for parental care.
In other fish, increased cuckoldry during spawning (which reduces the benefit of
care) also led guarding males to increased cannibalism (Gray
et al
., 2007) or reduced
care (Neff, 2003).
It sometimes pays
a parent to eat all
or part of its
brood
Varying investment in response to mate attractiveness
In theory, a parent should invest more when paired with a mate of better phenotypic or
genetic quality, to take advantage of the enhanced potential benefits of the current
breeding attempt (Burley, 1986; Sheldon, 2000).
Nancy Burley (1988) was the first to show this with classic experiments involving
zebra finches,
Taeniopygia guttata
. Males have bright red beaks and they can be made
more attractive to females experimentally, by giving them red leg bands. When paired to
these attractive males, females increased their effort in chick-feeding, and raised more
young, compared to when given less attractive males with blue or green leg bands.
Similarly, experiments have shown that female mallard ducks lay larger (better
provisioned) eggs when paired with more attractive males (Cunningham & Russell,
2000), and female peacocks lay more eggs after copulating with males with more
elaborate tails (Petrie & Williams, 1993).
Females may
invest more when
paired to an
attractive male
Sexual conflict
The examples we have discussed so far reveal the first of the conflicts we shall encounter
in this chapter, namely sexual conflict. It is useful to consider this in two stages: conflict
over who should care, and conflict over how much care to provide.
