Biology Reference
In-Depth Information
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Nestling begging call intensity
Level of maternal provisioning
when caring for foster offspring
Fig. 8.11
Cross-fostering experiments reveal that within families parental supply is
coadapted to offspring demand. (a) Great tits: each point refers to a different brood.
Offspring begging intensity (measured in a foster-parent's nest) is correlated with its
genetic mother's generosity (measured as increased provisioning response to begging
playbacks). From Kölliker
et al
. (2000). (b) Burying beetles: each point again refers to a
different brood. More generous mothers (response to foster offspring) have offspring
which beg more strongly (response measured when raised by a foster mother). From
Lock
et al
. (2004).
(a review is given in Kilner & Hinde, 2008). These maternal effects arise because
mothers influence how genes are expressed in their offspring.
Maternal effects can also influence offspring begging behaviour. In canaries, an
experimental increase in yolk testosterone leads to more vigorous nestling begging at
hatching, suggesting that mothers could vary their nestlings' demand through varying
maternal hormones in the egg (Schwabl, 1996). Camilla Hinde and Rebecca Kilner
tested this by varying the food available to female canaries before and during egg laying,
and then cross-fostering broods so offspring begging and parental provisioning could be
measured independently. They found that an increase in food quality led to increased
maternal androgens and increased provisioning effort by the mother, and also to an
increase in nestling androgens and nestling begging intensity (Hinde
et al
., 2009).
Thus, nestling demand was matched to maternal provisioning capacity, most likely by
means of maternal hormones in the egg.
The discovery of maternal control of offspring begging behaviour then enabled an
elegant test of the consequences of parent-offspring conflict. By cross-fostering
nestlings, parent canaries were exposed to foster broods that begged more, less or
appropriately for the parents' capacity for parental care (Hinde
et al
., 2010). The results
showed that foster young did best when their begging levels matched those that the
parents expected from their own brood (Fig. 8.12). Foster broods that begged less than
the parents expected under-demanded and grew less well, but broods that over-demanded
Maternal effects
can match
offspring demand
to maternal
capacity
An experiment
with canaries
