Authors:	Kramer, Jos
Title:	Influence of ecology and social interactions on the early evolution of family life
Online publication date:	19-Jan-2017
Year of first publication:	2017
Language:	english
Abstract:	A core research area in evolutionary biology is devoted to the investigation of mechanisms that drive transitions to social life. The formation of animal societies out of independent, solitary organisms has long taken center stage in the quest for these mechanisms. However, while transitions from simple family systems to the highly integrated societies of cooperatively breeding vertebrates and eusocial insects have been thoroughly explored, little attention has thus far been paid to the origin of the simple family systems themselves. Hence, the mechanisms promoting the early evolutionary stages of family life remain poorly understood, despite the pivotal role they might play in explaining transitions from solitary to social life. Here, we investigated mechanisms shaping the family life of the European earwig Forficula auricularia, a precocial insect with facultative post-hatching maternal care that recently emerged as a model system for the early evolution of family life. Specifically, we assessed the impact of social interactions, basic life-history characteristics, and environmental conditions on the costs and benefits of earwig family life, and thus sought to determine how their interplay might affect the origin and subsequent consolidation of family life. The first part of this thesis investigates the relationship between different types of social interaction among European earwigs to elucidate the mechanisms underlying the fitness effects of facultative social life. Chapter 1 shows that the food transfer among earwig nymphs increases if mothers do not provision their offspring at a sufficiently high level, indicating that sibling cooperation could complement the benefits of facultative parental care in driving the early evolution of family life. Chapter 2 demonstrates that the propensity of nymphs to share food depends on the condition of their mother. Offspring thus flexibly adjust their behavior toward siblings in response to changes in parental care. However, such complex behavioral patterns do not seem to promote gregariousness in adults; chapter 3 reveals that the intimate social interactions typical for family life hardly extend into the semisocial adult stage. Overall, these results affirm the pre-eminent role of the family group in the evolution of advanced societies, and demonstrate that early family systems reflect sophisticated social environments in their own right. The second part of this thesis explores how the complex interdependencies among social interactions, basic life-history characteristics, and environmental conditions affect the costs and benefits of family life. Chapter 4 shows that parent-offspring competition reduces offspring survival under food limitation, suggesting that this mechanism might hamper the evolution of family life under harsh environmental conditions. By contrast, chapter 5 demonstrates that maternal loss unexpectedly increases the body size of offspring, but impairs their expression of parental care in the adult stage – pointing at a crucial role of such long-term costs in the maintenance of early forms of family life. Finally, chapter 6 shows that life-history traits of family members vary between reproductive events in a partly population-specific manner, indicating that this variation reflects age-dependent changes in parental investment and population idiosyncrasies that likely arose as the result of different environmental conditions. Together, these findings point at a crucial role of the joint effects of environmental and life-history characteristics in the evolution of family life. The third part of this thesis takes a broader theoretical perspective and explores how the study of family life might integrate into the current theory of social evolution. In particular, chapter 7 reviews an enduring controversy surrounding two major theories of sociobiology – kin selection and multilevel selection theory – and suggests that both approaches provide different, but complementary perspectives on social evolution that could jointly advance our understanding of transitions from solitary to social life. In conclusion, this dissertation demonstrates that facultative family systems can give rise to sophisticated social environments that are shaped by a unique set of behavioral mechanisms, and thus often differ from the social environments in obligatory family systems: sophisticated forms of parental care are here paralleled by sophisticated forms of sibling cooperation, and parents not only provide long-term benefits to their own offspring, but also directly compete with them for resources. Importantly, the social behaviors expressed during family life resonate in the behaviors expressed in the adult stage, as well as affect life-history characteristics across populations. The interplay between all these parameters is ultimately likely to shape the evolution of family life and thus more generally the transition from simple to complex family systems.
DDC:	500 Naturwissenschaften 500 Natural sciences and mathematics
Institution:	Johannes Gutenberg-Universität Mainz
Department:	FB 10 Biologie
Place:	Mainz
ROR:	https://ror.org/023b0x485
DOI:	http://doi.org/10.25358/openscience-2787
URN:	urn:nbn:de:hebis:77-diss-1000009479
Version:	Original work
Publication type:	Dissertation
License:	In Copyright
Information on rights of use:	https://rightsstatements.org/vocab/InC/1.0/
Extent:	173 Seiten
Appears in collections:	JGU-Publikationen