Discussion: Stimulus ↔ Response ↔ Stimulus

Abstract

The Discussion section highlights themes inherent to theoretical and empirical research on “phenotypic plasticity,” summarizing their import to mammalian thermal tolerances, within and between environmental regimes. In particular, the idea that genes are followers not leaders evolutionarily is inherent to many treatments of “phenotypic plasticity,” is evaluated critically. Related to the differential roles of genotypes and phenotypes in evolution, evolvability is considered within the context of thermal tolerances, reflecting endogenous regulatory feedback mechanisms expressed on surfaces of whole organisms, potentially exposed to Darwinian processes. Assessments of “phenotypic plasticity” relative to inclusive fitness of females are commonly omitted from theoretical and empirical treatments of the topic, considered in this section within an ecological (economic) context. Following Nijhout (2003), “phenotypic plasticity” may be viewed as mean reaction norms or polyphenisms, including alternative responses to exogenous variability. Employing a simple quantitative model, social parasitism is evaluated as an alternative response reflecting coevolved parasite–host associations, differential access to limiting resources (energy exploitation strategies), and differential costs and benefits to parasite and host. Topics highlighted in this and previous sections might be subsumed within a comprehensive program of research targeting causes, mechanisms, and consequences of thermal evolvability in mammals.