Cooperation - An Introduction to Behavioural Ecology - page 356

Female helper Male helper

Table 12.4 The
direct and indirect
benefits of being
a helper in the
Seychelles warbler,
as measured in
offspring
equivalents
(Richardson et al .,
2002)

Direct fitness
(own offspring)

0.46 0.14

Indirect fitness
(through raising
primary breeder's
offspring)

0.07 0.04

the nest. Thirdly, male helpers can sometimes gain paternity, fathering an average of
0.14 offspring per year, so also gain direct benefits from helping. Overall, when these
different effects are added up, the direct benefits of being a helper far outweigh the
indirect benefits (Table 12.4).
These results could give the impression that direct fitness alone drives the evolution
of helping in the Seychelles warbler. However, more recent work has shown that this is
not the whole story, because even though the indirect component is small, selection has
still favoured individuals to maximize their indirect fitness, with kin discrimination.
Richardson et al . (2003) examined whether subordinate Seychelles warblers
preferentially directed their help at closer relatives by following the provisioning
behaviour of 32 subordinate helpers on 23 different territories. Overall, they found that
females subordinates fed closer relatives at a greater rate, but that male subordinates did
not (Fig. 12.11a). It is not known why kin discrimination does not occur with male
helpers, although helping by males is rare in this species. The mechanism of kin
discrimination in females appears to be that helpers only help feed young when they are
being raised by the same female that raised them (Fig. 12.11b), which should be a
relatively reliable cue for kin discrimination, indicating that they are helping raise a
sibling. In contrast, female subordinates do not adjust their level of helping in response
to the presence of the male that raised them (Fig. 12.11b). The presence of the same
male is likely to be a much less reliable cue of relatedness, because females often mate
with males from other territories, making individuals less likely to share the same father.
However, these results are observational and so it is hard to disentangle different cues of
relatedness. Ideally, cross-fostering experiments should be carried out, that would allow
the extent and mechanism of kin discrimination to be examined in greater detail, as
described above with long-tailed tits.

Both male and
female helpers
breed on the
territory where
they are helping

Female
subordinates
preferentially help
closer relatives …

… by directing
help towards
young produced
by their mother

Manipulation

Before concluding, a final complication is that some behaviours appear to be cooperation
but, in fact, turn out to be manipulation by the recipient (Dawkins, 1982). This is most
obvious, for example, when a parent bird feeds the offspring of a brood parasite, such as
a cuckoo. The host gains nothing from this; it has simply been tricked by the cuckoo into
feeding the wrong species (Chapter 4). Less well known, but equally striking are lycaenid