Abstract
Phenotypic plasticity and local adaptation via genetic change are two major mechanisms of response to dynamic environmental conditions. These mechanisms are not mutually exclusive, since genetic change can establish similar phenotypes to plasticity. This connection between both mechanisms raises the question of how much of the variation observed between species or populations is plastic and how much of it is genetic. In this study, we used a structured population of fire salamanders (Salamandra salamandra), in which two subpopulations differ in terms of physiology, genetics, mate-, and habitat preferences. Our goal was to identify candidate genes for differential habitat adaptation in this system, and to explore the degree of plasticity compared to local adaptation. We therefore performed a reciprocal transfer experiment of stream- and pond-originated salamander larvae and analyzed changes in morphology and transcriptomic profile (using species-specific microarrays). We observed that stream- and pond-originated individuals diverge in morphology and gene expression. For instance, pond-originated larvae have larger gills, likely to cope with oxygen-poor ponds. When transferred to streams, pond-originated larvae showed a high degree of plasticity, resembling the morphology and gene expression of stream-originated larvae (reversion); however the same was not found for stream-originated larvae when transferred to ponds, where the expression of genes related to reduction-oxidation processes was increased, possibly to cope with environmental stress. The lack of symmetrical responses between transplanted animals highlights the fact that the adaptations are not fully plastic and that some level of local adaptation has already occurred in this population. This study illuminates the process by which phenotypic plasticity allows local adaptation to new environments and its potential role in the pathway of incipient speciation.
Highlights
Phenotypic plasticity and local adaptation are two major mechanisms of response to dynamic environmental conditions
P-P and S-S individuals differed from each other (Figure 3, Supplementary Figure S3A–C) in body condition, gill size, and gene expression
Our results demonstrate that stream and pond salamanders differ in their regulatory networks, due to phenotypic plasticity, and due to local adaption to their home habitats
Summary
Phenotypic plasticity and local adaptation are two major mechanisms of response to dynamic environmental conditions. Modern research demonstrates that—by reinforcing the survival of organisms under varying environmental conditions—phenotypic plasticity exposes other traits to natural selection that are related but not directly involved in a given plastic response (plastic acclimatization) [15,16,17,18]. This way, plastic acclimatization serves as a key initial step towards the evolutionary divergence of other traits and characters [19,20]. Some plastic responses are heritable, and if subject to selection can evolve via genetic adaptation (i.e., genetic accommodation) [21,22,23]
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