Roles of, and Interplay between, Plasticity, Symbiosis, and Niche Construction in Development and Evolution: Insights from the Study of Onthophagus Beetles

摘要

Traditional perspectives on the ecology and evolution of developmental plasticity treat environments as being passive, external to, and separable from the organisms that experience them. Yet, environmental conditions internal to the organism (e.g. nutrition, hormones) can substantially bias the nature and outcomes of plastic responses, whereas external environments may themselves consist of other responsive and evolving organisms (e.g. developmental symbionts), and both internal and external environments can be shaped by the developing organisms themselves (e.g. via niche construction). Here, I use horn-polyphenic dung beetles in the genus Onthophagus to illustrate how integrating developmental symbiosis and niche construction alongside traditional evo-devo approaches enhances our understanding of the mechanisms and evolutionary consequences of development and plasticity. First, resource allocation decisions bias developmental outcomes and may have contributed to the diversification of horn polyphenism. Next, I show that the normative development of larvae is contingent on benefits (e.g. increased growth, developmental rate) derived from maternally-inherited microbial symbionts. Intriguingly, these benefits appear to be highly context-dependent, shaping norms of reaction under ecologically-relevant stressors. Finally, I present emerging evidence that larvae behaviorally modify their developmental environment (i.e. niche construct), and show that these modifications generate environmental feedbacks that (i) shape plasticity in fitness-related traits and (ii) are necessary for the maintenance of sexual dimorphism. I end by discussing how the integration of internalistic and externalistic approaches offers a more holistic and complete account of plasticity and its evolution.