Old wine in new bottles: reaction norms in salmonid fishes

Abstract

Genetic variability in reaction norms reflects differences in the ability of individuals, populations and ultimately species to respond to environmental change. By increasing our understanding of how genotype  environment interactions influence evolution, studies of genetic variation in phenotypic plasticity serve to refine our capacity to predict how populations will respond to natural and anthropogenic environmental variability, including climate change. Given the extraordinary variability in morphology, behaviour and life history in salmonids, one might anticipate the research milieu on reaction norms in these fishes to be empirically rich and intellectually engaging. Here, I undertake a review of genetic variability in continuous and discontinuous (threshold) norms of reaction in salmonid fishes, as determined primarily (but not exclusively) by common-garden experiments. Although in its infancy from a numerical publication perspective, there is taxonomically broad evidence of genetic differentiation in continuous, threshold and bivariate reaction norms among individuals, families and populations (including inter-population hybrids and backcrosses) for traits as divergent as embryonic development, age and size at maturity, and gene expression. There is compelling inferential evidence that plasticity is heritable and that population differences in reaction norms can reflect adaptive responses, by natural selection, to local environments. As a stimulus for future work, a series of 20 research questions are identified that focus on reaction-norm variability, selection, costs and constraints, demographic and conservation consequences, and genetic markers and correlates of phenotypic plasticity.

Migration costs drive convergence of threshold traits for migratory tactics

“…The threshold size at maturity of fishes is thought to be influenced by both genetic [33] and environmental (i.e. plastic) [34] factors, but their relative contributions to the PMRN remain unclear [17]. With respect to plasticity, Jonsson et al [35,36] noted that the threshold size at maturity in Atlantic salmon was affected by both water temperature and food quality.…”

“…Anadromous males have high fertilization success by competing for females using their large body size, whereas smaller precocious mature parr achieve fertilizations by adopting a sneaking behaviour [16]. In salmonid males, life-history divergence is thought to depend on whether the current size or growth rate at the time of the life-history decision will result in the male exceeding a threshold size [17,18], such as the size at maturity for parr. Males that exceed this size become precocious mature parr, whereas those below this size become anadromous (see electronic supplementary material, figure S1a).…”

Environmental and genetic determinants of innovativeness in a natural population of birds

“…Plasticity and microevolution are not necessarily independent processes, however, because the extent to which traits change over a gradient might also be heritable [3,4]. In general, the majority of evolutionary ecology studies in wild populations have primarily focused on morphological and life-history traits.…”

Salt sensitivity of the morphometry of Artemia franciscana during development: A demonstration of 3-D critical windows

“…Developmental phenotypic plasticity involves the ability of a developing animal to alter its phenotype in response to intrinsic (genetic) or extrinsic (environmental) variables (Pigliucci et al, 2006;Burggren and Reyna, 2011;Hutchings, 2011). For example, during development, periods may exist when the emerging phenotype of an animal is particularly plastic or susceptible to an environmental stressor -these periods are often termed 'critical windows' or 'sensitive periods' (Pinkerton and Joad, 2000;Rice and Barone, 2000;van Aerle et al, 2002;Chan and Burggren, 2005;Hogan et al, 2008;Burggren and Reyna, 2011;Burggren et al, 2014;Burggren and Mueller, 2015).…”