Adaptive divergence of the moor frog (Rana arvalis) along an acidification gradient

Abstract

BackgroundEnvironmental stress can result in strong ecological and evolutionary effects on natural populations, but to what extent it drives adaptive divergence of natural populations is little explored. We used common garden experiments to study adaptive divergence in embryonic and larval fitness traits (embryonic survival, larval growth, and age and size at metamorphosis) in eight moor frog, Rana arvalis, populations inhabiting an acidification gradient (breeding pond pH 4.0 to 7.5) in southwestern Sweden. Embryos were raised until hatching at three (pH 4.0, 4.3 and 7.5) and larvae until metamorphosis at two (pH 4.3 and 7.5) pH treatments. To get insight into the putative selective agents along this environmental gradient, we measured relevant abiotic and biotic environmental variables from each breeding pond, and used linear models to test for phenotype-environment correlations.ResultsWe found that acid origin populations had higher embryonic and larval acid tolerance (survival and larval period were less negatively affected by low pH), higher larval growth but slower larval development rates, and metamorphosed at a larger size. The phenotype-environment correlations revealed that divergence in embryonic acid tolerance and metamorphic size correlated most strongly with breeding pond pH, whereas divergence in larval period and larval growth correlated most strongly with latitude and predator density, respectively.ConclusionOur results suggest that R. arvalis has diverged in response to pH mediated selection along this acidification gradient. However, as latitude and pH were closely spatially correlated in this study, further studies are needed to disentangle the specific agents of natural selection along acidification gradients. Our study highlights the need to consider the multiple interacting selective forces that drive adaptive divergence of natural populations along environmental stress gradients.

The roles of genetic drift and natural selection in quantitative trait divergence along an altitudinal gradient in Arabidopsis thaliana

“…Q ST = F ST is often interpreted as divergence driven by selectively neutral processes (Merilä and Crnokrak, 2001;Whitlock, 2008;Leinonen et al, 2013). However, neutral divergence would also be expected to lead to pairwise Q ST -F ST associations (Hangartner et al, 2011;Kawakami et al, 2011), but these were not significant indicating that we have no evidence for neutral divergence in these traits. Our findings differ from other studies on Iberian populations reporting flowering time increase as one of the most prominent patterns of adaptive divergence with altitude (Mendez-Vigo et al, 2011, 2013Montesinos-Navarro et al, 2011).…”

Phenotypic divergence of the common toad (Bufo bufo) along an altitudinal gradient: evidence for local adaptation

“…In the face of gene flow (small spatial scale), the phenotypic divergence observed along the gradient can result from both selection (when strong enough to counter the homogenizing effect of gene flow) and/or nonrandom gene flow because of IBA (Richter-Boix et al, 2010. Many studies show phenotypic divergence among populations along environmental gradients (for example, latitudinal gradient: Palo et al, 2003, Antoniazza et al, 2010; environmental stress gradient: Räsänen et al, 2003;Gomez-Mestre and Tejedo, 2004;Hangartner et al, 2011). When conducted as common garden or transplant experiments, these studies provide evidence for a genetic basis for quantitative trait differentiation among populations (Connover and Schultz, 1995).…”

“…When conducted as common garden or transplant experiments, these studies provide evidence for a genetic basis for quantitative trait differentiation among populations (Connover and Schultz, 1995). However, few studies have attempted to determine the relative contributions of different processes that contribute to genetic and phenotypic divergence along environmental gradients (but see Antoniazza et al, 2010;Hangartner et al, 2012;Muir et al, 2014).…”

Amphibian recovery after a decrease in acidic precipitation

“…Lower tolerance limits have been reported, but many of the studies have been achieved in the laboratory, not in the wild, and therefore should not be directly compared to natural conditions (Persson et al 2007). However, populations from acidified areas tend to tolerate lower pH than populations from non-acidified areas (Glos et al 2003;Hangartner et al 2011).…”

“…Only R. arvalis ( n = 61) had a lower minimum (pH 4.4) in Strand's studies (cf. Andrén et al 1988;Hangartner et al 2011). The lower pH limit seen in our study coincides well with the overviews by Barr (2011) and EPA (2012) who mention that most amphibians require a pH higher than 4.5-5.0 for embryo survival and metamorphosis.…”