November 23, 2017
Cooperatively breeding birds and
fish may have evolved the adaptive ability to reduce the size of their eggs
when helpers are available to lighten the parental load, a new study suggests.
The findings indicate that in some species, the social environment may
influence female reproductive decisions even prior to the birth of offspring.
According to the research from
the University of Cambridge, females in species such as the
sociable weaver, superb fairy-wren and daffodil cichlid fish, tend to produce
smaller eggs when
help with rearing offspring is at hand compared to when parents are on their
own.
The authors of the paper, which
was published today in the journal PeerJ, looked at data from 12 studies
on 10 species of cooperatively breeding vertebrates in order to analyse the
relationship between the number of helpers present and egg size. The reduction
in egg size in relation to helper availability was stronger in species where
mothers also reduce the energy they put into post-natal care when other members
of the social group are available to help protect, incubate and feed offspring
after laying.
The findings suggest that
breeding females, by laying smaller, less energy-consuming eggs and providing
less food to offspring at the nest, may conserve energy to increase their own
chances of survival to the next year or to have the next set of offspring
sooner. If helpers compensate for the reduced investment into the current
offspring, this could lead to females producing more offspring in total over
the course of their lifetimes.
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