Testing the predictability of morphological evolution in contrasting thermal environments

Abstract

In light of climate change, the ability to predict evolutionary responses to temperature changes is of central importance for conservation efforts. Studying parallel evolution in natural populations inhabiting contrasting thermal environments presents a powerful approach for understanding and predicting responses to increasing temperatures. In this study, we used a natural experiment in Iceland, where freshwater populations of threespine sticklebacks are found in waters warmed by geothermal activity, adjacent to populations in ambient-temperature water bodies. We used three sympatric and three allopatric warm-cold population pairs to test for morphological divergence in relation to thermal habitat. We found that thermal habitat explained over 50% of body shape variation: fish from warm habitats had a deeper mid-body, a shorter jaw, smaller eyes, and longer dorsal spines. Population age did not influence the magnitude or direction of morphological divergence between warm and cold habitats. However, the absence of gene flow seemed to facilitate parallel evolution across thermal habitats: all three allopatric population pairs were on a common evolutionary trajectory, but this was not the case for sympatric population pairs. Our findings therefore suggest that morphological evolution in response to rising temperatures can be predictable to some extent but only if there is restricted gene flow.

Diversification rates have no effect on the convergent evolution of foraging strategies in the most speciose genus of bats,Myotis*

“…A fundamental challenge is to understand whether evolution can be predictable and what evolutionary processes lead to repeated adaptations. Evidence from ecological, genetic, and morphological studies show that adaptive radiations can occur into niches that constrain morphological evolution and lead evolutionary convergence of phenotypes and ecological roles (Schluter and Nagel 1995;McGhee 2011;Conte et al 2012;Wagner et al 2012;Pilakouta et al 2019). We propose that when ecomorphological convergence occurs, first, lineages colonize new environments and initial stages of genetic divergence occur stochastically without any evident morphological or ecological modifications.…”

“…; Pilakouta et al. ). We propose that when ecomorphological convergence occurs, first, lineages colonize new environments and initial stages of genetic divergence occur stochastically without any evident morphological or ecological modifications.…”

Metabolic adaptation to warm water in fish

“…In addition to metabolic rate, the Icelandic stickleback populations are currently being used to investigate other aspects of thermal adaptation in fish, such as behavioural thermal preference (Pilakouta, Killen, et al, 2019), and morphology (Pilakouta, Humble, et al, 2019). Future studies using this system may additionally address questions regarding the mechanisms underlying the observed thermal adaptation.…”

Does phenotypic plasticity initiate developmental bias?

“…For example, in Wund et al (2008), it could be that populations of marine sticklebacks have responded to diet treatments similarly because they represent "tried and tested" phenotypes F I G U R E 1 The preorbital region of fishes appears to possess developmental bias affecting its size and length. However, in (c), divergence is occurring along a thermal habitat gradient between geothermally warmed and ambient populations (red = warmed, blue = ambient; Pilakouta et al, 2019), whereas in (d) divergence is occurring along a limnetic (long side) and benthic (short side) gradient (image credit, Elizabeth Carefoot). In some cases, patterns of evolution match patterns of plasticity.…”