Surviving in the fast lane: no increased mortality, but faster growth for pathogen-exposed larvae of a family-living beetle

Animal taxa exhibiting post-hatching care can be found throughout the animal kingdom. During this period, parents aggregate with their offspring and allow them to invest their resources into growth and development as parents take over energy consuming tasks. Studies show that food provisioning and social immunity by parents can alleviate the costs of an offspring's immune response to pathogen exposure. However, this issue has rarely been explored in offspring of species showing plasticity in their dependency on parental care. Here, we raise the question of how offspring are affected by pathogen exposure if they have access to social immunity through a caring parent. Parents of Nicrophorus vespilloides, a species exhibiting facultative post-hatching care, control the carcass microbiome via their antimicrobial exudates, stopping further decay and protecting their offspring from potential pathogens. We exposed N. vespilloides offspring to a generalist entomopathogenic fungus, Beauveria bassiana, while manipulating the post-hatching parental care. We monitored offspring performance throughout their development and found, curiously, larvae showed an increase in mean weight and growth rate after being exposed to the pathogen, regardless of parental care, while their survival and adult immunity were unaffected. Simultaneously, our results indicate that females invest fewer resources into their offspring if they have been exposed to the pathogen. Overall, we show that offspring of facultative subsocial species may not respond differently to pathogen exposure depending on their parents' aid. Additionally, our results indicate that offspring of facultatively subsocial species may adjust their growth rate in response to pathogen exposure.