Sociality shapes the adaptive response of breeders to harsh thermal environments? An experiment in a burying beetle

1. The rapid pace of environmental change seems to outstrip the evolutionary response rates of many species. Physiological, morphological, and behavioral plasticity alone may not suffice to cope with environments’ drastic changes, potentially hindering individuals’ ability to adapt. Therefore, it has been proposed that social flexibility may be a powerful mechanism for fast adaptation, but empirical evidence is lacking.

2. We investigated the combined effects of social conditions and ambient temperature during the reproductive and developmental phases on parental care, reproduction and offspring fitness, in the burying beetles Nicrophorus vespilloides, which utilize carcasses for breeding and facultatively exhibit varied social forms of breeding and parental care.

3. We conducted a mixed factorial design experiment, establishing four categories of social conditions during breeding (i.e., no-care, unifemale-care, biparenta-care, and multiple-care) alongside two thermal conditions (benign: 20°C and harsh: 23°C). Additionally, dispersed larvae produced from each of these breeding conditions were allocated to either 20°C or 23°C for pupation. Measures for reproductive success (e.g., brood size and mass), offspring performance (e.g., larval weight, body size and lifespan of newly-eclosed beetles), and larval developmental duration were collected, and the levels of individual and total parental care were investigated.

4. Our results showed that (1) harsh temperature led to a significant reduction in reproduction and offspring fitness traits (brood size and mass, larval weight and size of newly-eclosed beetles), and the diminished fitness traits were found in no-care; (2) when comparing the harsh to benign thermal conditions, larval development was shortened in no-care, and lighter larvae and a shorter lifespan were observed in biparental care; (3) while harsh temperature led to a decrease in both individual and total parental care, whereas social conditions did not adjust the levels of care impacted by thermal temperature.

5. Our findings shed light on the critical role of sociality in modulating the adaptive response of individuals to harsh thermal environments, one of the ecological problems exacerbated by ongoing global warming.