Natural selection favors local specialization in a widespread habitat generalist

Abstract

The ecological success of widespread species is attributed to an ability to generalize across diverse habitats, a so-called "jack of all trades" scenario. However, this assumption ignores the potential for local specialization, an alternative scenario whereby spatial variation in natural selection generates habitat-specific fitness surfaces. Despite a growing recognition of spatial variation in selection in nature, and the inevitable exploitation of distinct habitat types across an extensive geographic range, attention to this hypothesis has been lacking for widespread taxa. We test this hypothesis using data from four populations of a widespread species drawing from two distinct habitat types (tree- and boulder-dominated, respectively). Specifically, we compare major physiological traits of male and female lizards by habitat type and then estimate the shape of natural selection gradients on those traits for each sex in each habitat (i.e., their fitness surfaces). We detected significant differences in morphology and performance across habitats that mirror interspecific patterns. Importantly, patterns of linear and nonlinear selection on these traits were habitat-specific for both sexes, supporting a clear but underappreciated capacity for local specialization. Our findings challenge assumptions of habitat generalism in widespread taxa, and instead provide some evidence for adaptive diversification in driving their ecological success.

Selection favors adaptive plasticity in a long‐term reciprocal transplant experiment

“…Similarly, highly plastic lines could also experience reduced fitness if they are too phenotypically labile or developmentally unstable (e.g., Relyea 2002;Tonsor et al 2013). Thus, we might expect that fitness would be maximized at intermediate trait plasticity (Scheiner and Holt 2012;Scheiner 2013), just as stabilizing selection can favor intermediate trait expression in multivariate trait space (Dudley 1996;Brooks et al 2005; e.g., Wadgymar et al 2017;Taylor et al 2018). Logistical constraints often preclude the sample sizes necessary to gain sufficient statistical power for these analyses and the duration of the field studies from which to estimate plasticity and fitness.…”

Breadth of the thermal response captures individual and geographic variation in temperature‐dependent sex determination

“…How organisms respond to changing environments is a guiding question of macroecology. Species with broad geographic or elevational distributions often exhibit population‐specific responses to local environmental conditions (Taylor, Ternes, & Lattanzio, ). Thus, detecting within‐ and among‐population variation in important traits is key for understanding if, and how, species can respond to temporal or spatial environmental shifts.…”

The Evolution of Immigration Strategies Facilitates Niche Expansion by Divergent Adaptation in a Structured Metapopulation Model

“…In a similar vein, individual bees have been found to prefer one or the other of two columbine species, Aquilegia formosa and A. pubescens (Fulton and Hodges 1999). Generalist species may fill their wide niche due to within-species variability under contrasting selection in different habitats, as shown for tree lizards by Taylor et al (2018).…”