For a long time, parental care was regarded as a key evolutionary factor driving the formation of family groups in the animal kingdom. However, a growing body of research now highlights the positive effects of sibling interactions on offspring development. “This has increasingly directed scientific attention towards cooperation among siblings as an early factor in the evolution of social and family life,” says Paul Huber, doctoral researcher at the Evolutionary Animal Ecology research group at the University of Bayreuth and first author of the study. Of particular interest today is how interactions between different family members may reduce the effects of so-called abiotic stressors such as temperature or water availability. “We wanted to find out whether sibling interactions mitigate abiotic stress in a similar way to parental care, whether they may act synergistically with parental care, or whether they lose their positive effect under certain conditions,” Huber explains.
The researchers studied burying beetles of the species Nicrophorus vespilloides. “This beetle is an excellent model organism for investigating social interactions because parental care can occur, although the larvae do not strictly require care for survival. At the same time, cooperation also occurs among the offspring,” says Prof. Dr. Sandra Steiger, Chair of Evolutionary Animal Ecology at the University of Bayreuth.
In the first experiment, the researchers varied temperature conditions in order to simulate cold stress and heatwaves. In a second experiment, they reduced and increased soil moisture levels. In both experimental set-ups, larvae were reared either in the presence of both siblings and parents, in the presence of siblings only, or individually and thus isolated from both siblings and parents. The researchers then monitored larval growth and survival until pupation.
The results showed that parental care consistently improved offspring growth and survival. Although interactions among siblings also provided benefits, these were considerably less consistent and depended strongly on specific environmental conditions and the social context. “In our experiment, the negative effects of low temperatures could be buffered through the combined influence of sibling interactions and parental care. At high temperatures, however, this effect is reversed. Under these conditions, the simultaneous presence of siblings and parents is actually disadvantageous,” says Steiger. One possible explanation is increased competition among larvae as a result of enhanced microbial growth on the carrion on which they feed.
“Overall, our study demonstrates that social interactions can help offspring cope with climate-related challenges. However, their specific benefits are highly context-dependent and can only be understood by considering both social and environmental conditions,” says Huber.
The study was conducted as part of the project “The effect of social isolation on offspring performance: an evolutionary, ecological and molecular perspective”, funded by the German Research Foundation (DFG) (STE 1874/12-1).
