Influence of climate on the presence of colour polymorphism in two montane reptile species

Abstract

The coloration of ectotherms plays an important role in thermoregulation processes. Dark individuals should heat up faster and be able to reach a higher body temperature than light individuals and should therefore have benefits in cool areas. In central Europe, montane local populations of adder (Vipera berus) and asp viper (Vipera aspis) exhibit a varying proportion of melanistic individuals. We tested whether the presence of melanistic V. aspis and V. berus could be explained by climatic conditions. We measured the climatic niche position and breadth of monomorphic (including strictly patterned individuals) and polymorphic local populations, calculated their niche overlap and tested for niche equivalency and similarity. In accordance with expectations, niche overlap between polymorphic local populations of both species is high, and even higher than that of polymorphic versus monomorphic montane local populations of V. aspis, suggesting a predominant role of melanism in determining the niche of ectothermic vertebrates. However, unexpectedly, the niche of polymorphic local populations of both species is narrower than that of monomorphic ones, indicating that colour polymorphism does not always enable the exploitation of a greater variability of resources, at least at the intraspecific level. Overall, our results suggest that melanism might be present only when the thermoregulatory benefit is higher than the cost of predation.

ecospat: an R package to support spatial analyses and modeling of species niches and distributions

“…It is important to notice here that all functions in Broennimann et al (2007Broennimann et al ( , 2012Broennimann et al ( , 2014a, and Petitpierre et al (2012) are uniquely found in ecospat (see also Guisan et al 2014). These functions were designed to investigate changes in the niche of invasive species, but they can also be used to compare niches between sister species (Broennimann et al 2014b). This approach consists of the following steps.…”

The effect of skin reflectance on thermal traits in a small heliothermic ectotherm

“…For instance, the presence of a strong latitudinal cline in morph frequency, where the relative frequency of striped versus unstriped individuals decreases from north (e.g., tropical climate) to south (e.g., temperate climate), suggests that climate may play a role in the evolution of colour variation (Forsman and Shine, 1995). Similar latitudinal and altitudinal patterns have been exhibited in other ectothermic vertebrates such as the White's skink (Liopholis whittii) as well as montane populations of adders (V. berus) and asp viper (V. aspis) (Broennimann et al, 2014;Chapple et al, 2008). Likewise, further research is warranted given that we did not assess thermal traits under varying solar conditions.…”

“…One reason could be inconsistency in the methodology employed, particularly with respect to quantifying colour (Geen and Johnston, 2014). The use of standard techniques, such as spectrometry, or natural colour variants were not always utilized by previous authors, but instead, colour was described qualitatively or animals were painted as a means of comparing different phenotypes (Ahnesjö and Forsman, 2006;Alho et al, 2010;Bittner et al, 2002;Broennimann et al, 2014;Forsman, 1995;Forsman et al, 2002). Thus, in order to acquire greater insight into the generality of the colour-mediated thermoregulatory hypothesis we evaluated the relationship between reflectance (a proxy of colour) and four thermal traits, optimal performance temperature (T opt ), thermal preferences (Ernst et al), and heating and cooling rates of untreated (e.g., not painted) delicate skinks (Lampropholis delicata) using standard methods.…”

Thermoregulation and microhabitat choice in the polymorphic asp viper (Vipera aspis)

“…It exhibits intrapopulational colour polymorphism with the presence of melanistic and non-melanistic individuals in mountainous areas of central Europe, likely for thermoregulatory reasons (Supplementary online materials 1; Castella et al, 2013;Broennimann et al, 2014). In addition, it can be found in very heterogeneous habitat types (see e.g.…”