Biology Reference
In-Depth Information
These false gapes spur the hosts into collecting more food; hosts sometimes try to place
food into a patch instead of the gape, and experimental darkening of the patches with
dyes reduces provisioning (Tanaka & Ueda, 2005).
These tricks of brood parasites suggest that begging displays are likely to involve two
components; a cooperative component in which increased signalling by the brood
leads to more food brought by the parents, and a competitive component, where
nestlings compete for the food once it has been brought (Johnstone, 2004).
Future experiments should investigate how the displays of individual chicks
(e.g. larger, smaller) contribute to these two components.
Two components
of begging
signals:
stimulating
provisioning to
the brood and
competing for the
food brought
Summary
In some species there is no parental care (most invertebrates), in some only the female
cares (most mammals), in others only the male (many fish), and in some both sexes care
(most birds). These differences reflect differences in life history constraints, in the
benefits of care and the costs in terms of missed further mating opportunities. There is
often sexual conflict over which parent should provide care and over how much care to
provide. Game theory models predict the evolutionarily stable strategies of the two
sexes, but current models often do not incorporate all the complexities of nature, such
as sequential desertion by the sexes and how parents can learn from each other about
brood needs. Robert Trivers (1974) showed that individual offspring are selected to
demand more care than is optimal from a parent's point of view. There is good evidence
for both interbrood conflict (e.g. Galapagos fur seals) and intrabrood conflict (begging
nestlings in a brood). As predicted, conflict increases as sibling relatedness declines. The
resultant conflict between parents and offspring is evident as a 'battleground', for
example tugs of war over optimal sex ratios in hymenopteran societies and over
maternal investment during pregnancy in mice. The conflict can also lead to an
evolutionary resolution, for example costly begging displays in nestling birds, where
parent supply and offspring demand become coadapted (e.g. canaries). Brood parasites
reveal extreme examples of offspring selfishness; nevertheless, the parasitic offspring
have to 'tune in' to their host's provisioning systems.
Further reading
Clutton-Brock (1991) reviews the evolution of parental care. Klug and Bonsall (2007)
consider the life history characteristics likely to lead to the evolution of parental care,
offspring desertion or offspring consumption. David Queller (1997) provides an elegant
model to show how lower probability of parentage for males tends to make males less
likely to provide care than females. Mock and Parker (1997) provide a superb review of
sibling rivalry, both theory and evidence. Royle
et al
. (2002) discuss begging and
honest signalling. Kilner and Hinde (2008) review parent-offspring conflict and
suggest that the outcome is influenced by the information each party has concerning
supply and demand for resources. Grodzinski and Lotem (2007) show, by means of hand-
feeding broods of nestlings, that allocating food in response to begging intensity leads to
better nestling growth than allocating the same amount of food at random among the
