Responses to simulated winter conditions differ between threespine stickleback ecotypes

Abstract

Abiotic factors can act as barriers to colonization and drive local adaptation. During colonization, organisms may cope with changes in abiotic factors using existing phenotypic plasticity, but the role of phenotypic plasticity in assisting or hindering the process of local adaptation remains unclear. To address these questions, we explore the role of winter conditions in driving divergence during freshwater colonization and the effects of plasticity on local adaptation in ancestral marine and derived freshwater ecotypes of threespine stickleback (Gasterosteus aculeatus). We found that freshwater-resident stickleback had greater tolerance of acute exposure to low temperatures than marine stickleback, but these differences were abolished after acclimation to simulated winter conditions (9L:15D photoperiod at 4 °C). Plasma chloride levels differed between the ecotypes, but showed a similar degree of plasticity between ecotypes. Gene expression of the epithelial calcium channel (ECaC) differed between ecotypes, with the freshwater ecotype demonstrating substantially greater expression than the marine ecotype, but there was no plasticity in this trait under these conditions in either ecotype. In contrast, growth (assessed as final mass) and the expression of an isoform of the electroneutral Na(+)/H(+) exchanger (NHE3) exhibited substantial change with temperature in the marine ecotype that was not observed in the freshwater ecotype under the conditions tested here, which is consistent with evolution of these traits by a process such as genetic assimilation. These data demonstrate substantial divergence in many of these traits between freshwater and marine stickleback, but also illustrate the complexity of possible relationships between plasticity and local adaptation.

Gene expression plasticity in response to salinity acclimation in threespine stickleback ecotypes from different salinity habitats

“…This pattern is consistent with our previous study that showed that the freshwater ecotype maintains higher ECaC expression at low salinity than the marine ecotype (Gibbons et al . ), and suggests the evolution of enhanced plasticity in the freshwater ecotype, potentially resulting in improved uptake of this ion, resulting in a pattern of cogradient variation in the expression of this gene. Similarly for NKA, qRT–PCR detected a significant difference in gill gene expression between the two ecotypes, which was not detected in the RNA‐seq data, with the freshwater ecotype having slightly higher expression at each acclimation salinity.…”

“…Primer sequences were as in Gibbons et al . () and are reported here in Table (Supporting information). qRT–PCR was performed essentially as in Gibbons et al .…”

Ionome and elemental transport kinetics shaped by parallel evolution in threespine stickleback

“…Marine and freshwater stickleback crosses have high viability in either salinity (Marchinko & Schluter ; Gibbons et al . ). Tanks were kept at 18 °C on a seasonally variable photoperiod, were held at similar densities, and allowed to grow for c .…”

The adaptive potential of plant populations in response to extreme climate events

“…; Gibbons et al . ). In situ evolution may be particularly important for organisms that cannot track their optimal climate conditions through space due to limited inherent dispersal abilities or extensive distances between habitat patches (Aitken et al .…”

“…Substantial evidence indicates that these responses are often mediated by genetic and physiological constraints that exist within populations (Etterson & Shaw 2001;Norberg et al 2012;Anderson 2016), underscoring the importance of evolutionary history in shaping species' responses to ongoing and future environmental change. Most recently, scientists have been evaluating the extent to which ongoing and future evolutionary change, such as rapid adaptation, can facilitate persistence in the face of global warming (Franks et al 2007;Anderson et al 2012;Gibbons et al 2016). In situ evolution may be particularly important for organisms that cannot track their optimal climate conditions through space due to limited inherent dispersal abilities or extensive distances between habitat patches (Aitken et al 2008;Angert et al 2011;Schloss et al 2012).…”