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

家庭生活，即至少有一位父母与其后代的联系，在动物界是一种广泛存在的分类现象，不仅在鸟类和哺乳动物中存在，而且在广泛的无脊椎动物中也存在。家庭聚集在家庭成员之间的社会互动的持续时间、组成和强度方面差异很大。家庭生活通常与父母对青少年的关怀行为有关，这最终会促进后代的成长和存活。然而，后代在多大程度上依赖于父母的照顾在不同的分类群之间存在着巨大的差异。在一些家庭系统中，照顾是义务的，子女在父母不在的情况下无法存活。这种高度依赖的演变令人费解，因为它可能会给父母和后代带来高昂的成本。后代对父母照料的依赖一直被认为是亲代和后代性状共同进化过程的结果，然而，这一过程背后的机制以及导致物种间和物种内后代依赖差异的条件，令人惊讶的是研究不足，也没有被很好地理解。在第一个资助阶段，我们研究了埋葬甲虫(夜光甲属)，发现即使在一个属内，后代对照顾的依赖也可能有显著的差异。我们没有发现任何证据表明对后代的依赖与物种的身体大小、发育时间、孵化或孵化的大小有关，但我们发现了依赖的系统发育信号。为了进一步促进我们对子女依赖(和独立性)进化的理解，我们将(1)分析产前父母和环境效应如何影响子女依赖，(2)利用种群之间的差异来探索依赖差异的基本机制，并测试依赖差异是否与父母提供的护理的可靠性有关，以及(3)利用实验进化来更好地了解后代对父母环境的适应是否以及如何导致对子女更多的依赖。通过这样做，我们的项目将有助于对家庭生活的错综复杂及其对后代发展的影响的基本见解。

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.