Evolution of growth by genetic accommodation in Icelandic freshwater stickleback

Abstract

Classical Darwinian adaptation to a change in environment can ensue when selection favours beneficial genetic variation. How plastic trait responses to new conditions affect this process depends on how plasticity reveals to selection the influence of genotype on phenotype. Genetic accommodation theory predicts that evolutionary rate may sharply increase when a new environment induces plastic responses and selects on sufficient genetic variation in those responses to produce an immediate evolutionary response, but natural examples are rare. In Iceland, marine threespine stickleback that have colonized freshwater habitats have evolved more rapid individual growth. Heritable variation in growth is greater for marine full-siblings reared at low versus high salinity, and genetic variation exists in plastic growth responses to low salinity. In fish from recently founded freshwater populations reared at low salinity, the plastic response was strongly correlated with growth. Plasticity and growth were not correlated in full-siblings reared at high salinity nor in marine fish at either salinity. In well-adapted lake populations, rapid growth evolved jointly with stronger plastic responses to low salinity and the persistence of strong plastic responses indicates that growth is not genetically assimilated. Thus, beneficial plastic growth responses to low salinity have both guided and evolved along with rapid growth as stickleback adapted to freshwater.

Mechanisms by Which Phenotypic Plasticity Affects Adaptive Divergence and Ecological Speciation

“…Crispo (2008) suggests that positive correlation between genetically based bias in phenotypes and plasticity may contribute to initial phenotypic divergence followed by genetic changes in the direction of the plastic response. This view is corroborated by empirical studies showing that populations colonizing new environments often possess or evolve high degrees of plasticity relatively quickly (Svanbäck and Schluter 2012;Robinson 2013) or that plastic responses to novel environmental conditions can produce evolutionary innovations (Moczek et al 2011). In total, this study substantiates the function and significance of the environmental and genetic bases of phenotypic diversity for divergent evolution and ecological speciation.…”

Resurrecting complexity: the interplay of plasticity and rapid evolution in the multiple trait response to strong changes in predation pressure in the water fleaDaphnia magna

“…Such evolutionary increases in phenotypic plasticity during rapid increases of a novel selection pressure are predicted by theory (Lande ; Crispo et al . ; Robinson ). For five other traits (the four size traits, and relative spine length at maturity), the direction of ancestral plasticity (slope of the ancestral sub‐population reaction norm) was, however, maladaptive at the sub‐population level and for each of these traits plasticity had to evolve to arrive at an adaptive slope of the sub‐population reaction norm (Ghalambor et al .…”

Responses to simulated winter conditions differ between threespine stickleback ecotypes

“…, ). In addition, differences in growth rate and growth rate plasticity exist between marine and freshwater stickleback raised in fresh water vs. salt water (Robinson ). However, no previous studies have explicitly assessed how conditions during winter in fresh water impact growth in stickleback ecotypes.…”

“…In stickleback, several studies have provided strong evidence showing that selection on growth probably played a role in the evolution of the prominent differences between marine and freshwater stickleback ecotypes (Marchinko & Schluter 2007;Barrett et al 2008Barrett et al , 2009). In addition, differences in growth rate and growth rate plasticity exist between marine and freshwater stickleback raised in fresh water vs. salt water (Robinson 2013). However, no previous studies have explicitly assessed how conditions during winter in fresh water impact growth in stickleback ecotypes.…”