From facultative to obligate family life and back: ultimate and proximate aspects of variation in offspring dependence on parental care

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Family life, i.e. the association of at least one parent with their offspring, is a taxonomically widespread phenomenon in the animal kingdom, occurring not only in birds and mammals but also in a wide range of invertebrates. Family aggregations vary greatly in terms of duration, composition and the strength of social interactions among family members. Family life is usually associated with the expression of care behaviour from parents to juveniles, which ultimately enhances offspring growth and survival. However, how much offspring depend on their parents’ care differs tremendously between taxa. In some family systems, care is obligate and offspring cannot survive anymore in the absence of parents. The evolution of such high dependency is puzzling, as it can come with high costs to parents and offspring. Offspring dependence on parental care has been hypothesized to be the outcome of a co-evolutionary process between parental and offspring traits, however, the mechanisms underlying this process and the conditions leading to variation in offspring dependency between and within species are surprisingly understudied and not well understood. In the first funding phase, we studied burying beetles (genus Nicrophorus) and revealed that even within a genus, offspring dependence on care can vary remarkably. We found no evidence that offspring dependence is linked to the body size, development time, clutch or brood size of a species, but we found a phylogenetic signal in dependency. To further promote our understanding of the evolution of offspring dependence (and independence), we will (1) analyze how prenatal parental and environmental effects influence offspring dependence, (2) exploit variation between populations to explore the proximate mechanisms underlying the difference in dependency and test whether the divergence in dependency is linked to the reliability of care the parents provide, and (3) use experimental evolution to better understand whether and how offspring adaptations to the parental environment can cause increased offspring dependence. By doing this, our project will contribute fundamental insights into the intricacy of family living and its impact on offspring development.