Abstract
Rapid phenotypic adaptation is critical for populations facing environmental changes and can be facilitated by phenotypic plasticity in the selected traits. Whereas recurrent environmental fluctuations can favour the maintenance or de novo evolution of plasticity, strong selection is hypothesized to decrease plasticity or even fix the trait (genetic assimilation). Despite advances in the theoretical understanding of the impact of plasticity on diversification processes, comparatively little empirical data of populations undergoing diversification mediated by plasticity are available. Here we use the planktonic freshwater copepod Acanthodiaptomus denticornis from two lakes as model system to study UV stress responses of two phenotypically different populations under laboratory conditions. Our study reveals heritable lake- and sex-specific differences of behaviour, physiological plasticity, and mortality. We discuss specific selective scenarios causing these differences and argue that phenotypic plasticity will be higher when selection pressure is moderate, but will decrease or even be lost under stronger pressure.
Highlights
Population divergence can be driven by disruptive selection or– if migration is absent–by genetic drift
We argue that LP females, in contrast, maximize fitness by moving into deeper water during daytime, simultaneously escaping excessive mating trials and ultraviolet radiation (UV) radiation, both of which substantially increased their mortality compared to LP males and to the negative control (Fig. 4A, Table 2)
As all other described European populations of A. denticornis are pigmented, it appears reasonable to assume that the plastic red LP morph is ancestral and the translucent LM morph derived
Summary
Population divergence can be driven by disruptive selection or– if migration is absent–by genetic drift The former process constitutes a case of adaptation to different fitness optima and can be facilitated by phenotypic plasticity (PP) in the selected trait [1]. The phenotypes may become fixed and gene flow between populations will cease due to selection against (maladapted) migrants [2] This process can lead to the adaptive evolution of species with fixed traits, derived from a common plastic ancestral population. The genetic assimilation of a less melanised phenotype in a free-living Daphnia population required only a dozen generations under increased predation pressure [9] Such rapid phenotypic adaptation is critical for populations facing rapid environmental changes in their native range or while invading new habitats. This is partly due to the lack of suitable model systems
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