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.