The other facets of family life and their role in the evolution of animal sociality

Abstract

Family life forms an integral part of the life history of species across the animal kingdom and plays a crucial role in the evolution of animal sociality. Our current understanding of family life, however, is almost exclusively based on studies that (i) focus on parental care and associated family interactions (such as those arising from sibling rivalry and parent-offspring conflict), and (ii) investigate these phenomena in the advanced family systems of mammals, birds, and eusocial insects. Here, we argue that these historical biases have fostered the neglect of key processes shaping social life in ancestral family systems, and thus profoundly hamper our understanding of the (early) evolution of family life. Based on a comprehensive survey of the literature, we first illustrate that the strong focus on parental care in advanced social systems has deflected scrutiny of other important social processes such as sibling cooperation, parent-offspring competition and offspring assistance. We then show that accounting for these neglected processes - and their changing role over time - could profoundly alter our understanding of the origin and subsequent evolution of family life. Finally, we outline how this 'diachronic' perspective on the evolution of family living provides novel insights into general processes driving the evolution of animal sociality. Overall, we infer that the explicit consideration of thus-far neglected facets of family life, together with their study across the whole diversity of family systems, are crucial to advance our understanding of the processes that shape the evolution of social life.

Catalyzing Transitions to Sociality: Ecology Builds on Parental Care

“…This important distinction allows the targeting of efforts at understanding the origins of animal groups independently from the origins of family living. Although recent studies have attempted to integrate studies on the origins of sociality with those of family living (Costa, 2018;Kramer and Meunier, 2018), we prefer to keep sociality and family living conceptually separated in this review for several reasons. First, most current frameworks on social evolution consider variation in adult group size and sex composition (i.e., social organization) as the core for defining different social categories (Rubenstein and Abbot, 2017b).…”

“…Thus, the caring system of eusocial lineages, and not only their average relatedness coefficients, may have to be considered in explanations of the origins of sociality. Kramer and Meunier (2018) recently discussed the origins of invertebrate families with post-natal parental care and its relation to the evolution of sociality. They widened the taxonomic diversity considered by giving weight to examples of family interactions in precocial species.…”

“…It is suggested that parental care is favored because of positive feedback loops that maximize the benefits of such behaviors for offspring. These loops are based on the evolving adaptation of the offspring phenotype that becomes increasingly dependent on the parents for correct development and survival (Royle et al, 2016;Kramer and Meunier, 2018).…”

“…Once parental care behaviors have evolved, two processes foster a further increase in parental expenditure. On the one hand, a self-reinforcing process on parental care arises from the fact that offspring adapt their mode of development to the care behaviors and become more dependent in a unidirectional trend (2, Figure 1) (Gardner and Smiseth, 2011;Royle et al, 2016;Kramer and Meunier, 2018). Simultaneously, coevolution with predators and parasites that challenge developing offspring sets up an arms race (3, Figure 1), generating more significant investment in parental care behaviors in turn (4, Figure 1) (Field and Brace, 2004;Royle et al, 2012;Yip and Rayor, 2014;Pike et al, 2016).…”

Unbalanced biparental care during colony foundation in two subterranean termites

“…Although most studies on sexual conflict explore its resolution in species where parents can do extra pair copulations and/or have novel mating partners at each reproductive season (Jennions, Kahn, Kelly, & Kokko, 2012), the expression and organization of biparental care remain unclear when the lifetime fitness of each parent tightly relies on its partner's. This is the case, for instance, in the biparental family units often present in termites (Kramer & Meunier, 2018;Wilson, 1971). In this eusocial insect, mothers (queens) and fathers (kings) form pairs quickly after they reach adulthood and remain together during their entire lives, which can last decades (Boomsma, 2009).…”