Behavioral Plasticity of Dung Beetles During Reproduction Does Not Fully Rescue Offspring from Climate Warming

Empirical studies have documented a global shift in temperature that threatens the survival of many species. Often, an animal's first response to changing environmental conditions is to alter behavioral phenotypes, such as parental care. When adaptive, behavioral plasticity of parental care can buffer offspring from changing environmental conditions to maintain fitness. However, we have limited understanding of how adult behaviors during warming impact offspring phenotypes and survival. In addition, comparatively few studies of behavioral responses to experimental warming use a repeated measures design, making it difficult to identify when observed differences are due to behavioral plasticity or interindividual differences in behavior. In this study, we used the dung beetle Phanaeus vindex to understand how increases in mean temperature affect parental behavior during nesting and reproductive success. In the lab we exposed breeding female P. vindex to three experimental temperature environments in randomized order: a control environment (26.0°C constant soil temperature), and a low warming (temperature gradient of 30.7°C at the soil surface to 26.0°C at the bottom of the bucket) and high warming (temperature gradient of 34.3°C at the soil surface to 26.0°C at the bottom of the bucket) treatment. After breeding, we searched the enclosures and recorded metrics of parental care (brood ball burial depth and size) and reproductive success (number of brood balls and offspring survival and body size). We repeated this protocol for each female for all three experimental conditions, allowing us to create reaction norms for individuals. We reared offspring in incubators at the temperatures they would have experienced, which included 26 (n = 38), 28 (n = 5), 29 (n = 119), or 33°C (n = 3). We found that in the high warming treatment, females placed brood balls significantly deeper than in the control and low warming treatment, but females showed similar investment in brood ball size and number regardless of treatment. Additionally, we found a significant effect of treatment on offspring survival; more offspring from the low warming treatment survived compared to the high warming treatment even when reared at the same temperature. Taken together our results show that female behavioral plasticity buffers offspring from the warmest temperatures, but despite the same developmental temperatures, the warmest experimental temperatures during nesting negatively impacted offspring survival. Thus, the female behavior of placing brood balls deeper in the warmest temperatures only partially rescued the offspring from the effects of climate warming.