Geographic variation in the level of melanism in common frogs (Rana temporaria) has been repeatedly observed. Vences et al. (2002) described a strong altitudinal cline (increasing melanism with altitude) and we observed a similar cline along a latitudinal gradient. A widely accepted intiutive explanation for these clines is thermal adaptation, as it has been shown for different ectotherm species that more melanistic individuals can heat up faster, which supposed to be beneficial in cold environments (e.g. Forsman 1995; Vences et al. 2002).
As a bold attempt to reveal the genetic background of melanism in common frogs, we (= Cim) went to the lab, and sequenced the coding region of the melanocortin-1 receptor gene (MC1R, it has been shown to regulate melanism in numerous mammals and birds, and even in few reptiles) of a bunch of frogs from two altitudinally divergent populations differing in dorsal melanism (see the pics).
Unfortunately, we only found five synonymous substitutions and our analyses did not show any sign of recombination effects with genetic regions linked to MC1R either. Interestingly, a pilot phylogenetic analysis revealed that amphibian MC1R forms a separate clade against all remaining vertebrates (fishes, reptiles, birds and mammals).
So the question remained open: what causes the striking differences in dorsal melanism in common frogs?
This journey into the field of serious genetics also gave a new experience to me; I had to learn how quickly can the coolness of certain methods disappear in this field – we were ca. half year late with this study to be able to publish it in some leading genetic or evolutionary journal. Luckily, AnZF has a tradition of publishing papers on ectotherm melanism, and accepted this paper too.
Herczeg G, Matsuba C, Merilä J. 2010. Sequence variation in the melanocortin-1 receptor gene (MC1R) does not explain variation in the degree of melanism in a widespread amphibian. Annales Zoologici Fennici in press.
Vences M, Galan P, Vieites DR, Puente M, Oetter K, Wanke S. 2002. Field body temperatures and heating rates in a montane frog population: the importance of black dorsal pattern for thermoregulation. Annales Zoologici Fennici 39:209-220.
Forsman A. 1995. Heating rates and body temperature variation in melanistic and zigzag Vipera berus: does colour make a difference? Annales Zoologici Fennici 32:365-374.