An experimental investigation of the evolutionary dynamics of phenotypic plasticity under relaxed selection in threespine sticklebacks (Gasterosteus aculeatus)

Abstract

Here I provide an overview of the ways in which phenotypic plasticity is suggested to be relevant to evolutionary dynamics, and examine the various predicted dynamics of plastic traits in novel environments. Following on from this, I use adaptive radiation of threespine stickleback (Gasterosteus aculeatus) into freshwater environments as a model system to examine the dynamics of multiple plastic traits under relaxed selection. I find that - as expected - overall survival plasticity appears to initially increase upon exposure to a novel environment before generally (but not always) decreasing under relaxed selection over time. My results suggest that morphological variation increases in the environments no longer experienced by daughter populations, implying that plasticity declines chiefly through accumulation of drifted cryptic genetic variation. From this I conclude that the plasticity of a trait may be relevant to its evolutionary dynamics (and those of the lineage) in novel environments - and that environment-dependent expression of alleles in rare environmental conditions may represent a limiting factor of adaptive phenotypic plasticity.