Ecogeographical variation of body size in the newt Triturus carnifex: comparing the hypotheses using an information‐theoretic approach

Abstract

Aim Ecogeographical variation of body size in vertebrates (e.g. Bergmann's rule) has long been recognized. However, the patterns and causes of intra-specific ecogeographical variation of body size in ectotherms, and in amphibians in particular, are strongly debated. We identified the relationship between bioclimatic variables and body size predicted a priori by alternative hypotheses (heat balance, endurance, seasonality, starvation resistance, water availability, primary productivity, parental investment) proposed to explain ecogeographical patterns of body size in ectotherms, and we evaluated the relative support of these hypotheses in explaining variation in body size of the Italian crested newt, Triturus carnifex.Location Twenty-three populations covering the whole range of T. carnifex (Austria, Croatia, Italy and Slovenia). MethodsWe obtained data on body size (snout-vent length, SVL) of 2639 adult newts from direct measurements and the literature; we obtained high-resolution environmental data for the sampled localities. We used an information-theoretic approach to evaluate the support of the data for the different hypotheses. We also integrated information on population genetics in our models. ResultsWe observed strong geographical variation of body size. The best Akaike information criterion (AIC) models showed that populations with larger body size are associated with cold climates and secondarily with high primary productivity. Furthermore, sexual dimorphism increases in cold climates, as the increase in body size was stronger for females. When taking into account population genetics, we did not find support for relationships with the other variables. Main conclusionOur results are consistent with three hypotheses proposed to explain ecogeographical variation in amphibians: heat balance, increased parental investment of females and productivity. Information theory provides the framework for comparing hypotheses rather than looking for patterns. We suggest that evaluating the support for mechanisms can provide better insights than simply assessing whether ecogeographical variation is in agreement with some 'rule' .

Life history traits in Bufotes variabilis (Pallas, 1769) from 2 different altitudes in Turkey

“…The most well-known ecogeographic trend, known as Bergmann's (1847) rule, states that, in wide-ranging endothermic animal species, individuals living in a cold climate tend to be larger than individuals living in a warm climate. Amphibians usually do not conform to this rule (Laugen et al, 2005;Adams and Church, 2008;Ficetola et al, 2010). Some amphibians even follow the reverse of Bergmann's rule (decreasing body size with cooler climate) (Ashton, 2002;Ma et al, 2009).…”

Ecogeographic variation of body size in the spectacled salamanders (Salamandrina): influence of genetic structure and local factors

“…We used WorldClim (Hijmans et al. , 2005) at a resolution of 30 arcseconds to obtain a series of climatic features describing the thermal environment of populations, as well as water availability, corresponding to the multiple hypotheses proposed to explain the relationship between body size and climate (see ; reviewed in Ficetola et al. , 2010).…”

“…, 2006). Several mechanisms involving multiple climatic variables have been proposed to explain ecogeographical variation in the body size of amphibians (Ficetola et al. , 2010; see section ‘’).…”

Rethinking biogeographic patterns: high local variation in relation to latitudinal clines for a widely distributed species

“…Rensch's rule (that sexual dimorphism is larger for larger-bodied species) is another macro-evolutionary pattern that relies on obtaining accurate species trait data (Halámková et al 2013). For wide-ranging species with large local or clinal trait variation, or both as we found for painted turtles [see also newts, Triturus carnifex (Ficetola et al 2010)], it is extremely challenging to determine what values to use for a given species. For example, Ceballos et al (2013) assess Rensch's rule in chelonians, but find inconsistent patterns.…”