Effects of social and non-social environmental conditions on offspring immune responses and their implications on family life evolution in insects

KO 6510/1-1

During family life, parents create a nurturing and protective social environment for their offspring by providing food and shielding them from threats like pathogens. This social environment relaxes selection on offspring survival traits like immunity and facilitates the evolution of vulnerable, obligately dependent offspring. For parents, adjusting to this social environment primarily involves optimization of care behaviors, but also responses to non-social environmental factors like resource availability or pathogen pressure. On the offspring side, however, flexible responses to the social environment of parental care remain poorly understood, especially when considering non-social environmental factors which can confound the results of parent-offspring interactions. For instance, larvae of Nicrophorus burying beetles reduce immune investment when parents provide care, but it is unclear whether this voluntary vulnerability also occurs when conditions are poor (i.e., microbial pressure is high), or when parents are struggling to maintain the protection. Furthermore, it is unknown whether offspring in obligately dependent or completely independent closely related species also show these flexible responses to social- and non-social environmental conditions. Finally, we lack the knowledge on the molecular underpinnings of offspring responses to care that we need to better understand their evolutionary origin (novel or co-opted) as well as their role in offspring development and dependency on care. This project is designed to address these important questions by recording offspring responses to manipulations of both social- and non-social environmental factors, namely presence and quality of care as well as microbial prevalence in the nursery, in the uniquely suited system of Nicrophorus burying beetles. Nicrophorus beetles breed on vertebrate carcasses while managing strong microbial pressure prior to and during family life which often involves biparental care, offering key social- and non-social environmental variables. Furthermore, there is high variation in offspring dependency on care in this genus. In this project, I propose to conduct several experiments using life-history, immunity, and gene expression analyses on multiple Nicrophorus species to investigate 1) how offspring of different care dependency (facultative, intermediate, and obligate) respond to the presence of care and the quality of their non-social environment, 2) the genetic underpinnings of offspring responses, 3) differential effects of uni- and biparental care, and 4) whether parental presence itself or its effects on environmental quality drives offspring responses. Ultimately, by demonstrating offspring responses and their underlying gene expression in both dependent and independent offspring, this project will shed light on key aspects of parent-offspring coadaptation in a simple social system ideally suited to investigate the evolution and consolidation of family life.