Spiny Mice Modulate Eumelanin to Pheomelanin Ratio to Achieve Cryptic Coloration in “Evolution Canyon,” Israel

Abstract

BackgroundCoat coloration in mammals is an explicit adaptation through natural selection. Camouflaging with the environment is the foremost evolutionary drive in explaining overall coloration. Decades of enquiries on this topic have been limited to repetitive coat color measurements to correlate the morphs with background/habitat blending. This led to an overwhelming endorsement of concealing coloration as a local phenotypic adaptation in animals, primarily rodents to evade predators. However, most such studies overlooked how rodents actually achieve such cryptic coloration. Cryptic coloration could be attained only through optimization between the yellow- to brown-colored “pheomelanin” and gray to black-colored “eumelanin” in the hairs. However, no study has explored this conjecture yet. “Evolution Canyon” (EC) in Israel is a natural microscale laboratory where the relationship between organism and environment can be explored. EC is comprised of an “African” slope (AS), which exhibits a yellow-brownish background habitat, and a “European” slope (ES), exhibiting a dark grayish habitat; both slopes harbor spiny mice (Acomys cahirinus). Here, we examine how hair melanin content of spiny mice living in the opposing slopes of EC evolves toward blending with their respective background habitat.Methodology/Principal FindingsWe measured hair-melanin (both eumelanin and pheomelanin) contents of 30 spiny mice from the EC using high-performance liquid chromatography (HPLC) that detects specific degradation products of eumelanin and pheomelanin. The melanin pattern of A. cahirinus approximates the background color of the slope on which they dwell. Pheomelanin is slightly (insignificantly) higher in individuals found on the AS to match the brownish background, whereas individuals of the ES had significantly greater eumelanin content to mimic the dark grayish background. This is further substantiated by a significantly higher eumelanin and pheomelanin ratio on the ES than on the AS.Conclusion/SignificanceIt appears that rodents adaptively modulate eumelanin and pheomelanin contents to achieve cryptic coloration in contrasting habitats even at a microscale.

Large Spatial Scale of the Phenotype-Environment Color Matching in Two Cryptic Species of African Desert Jerboas (Dipodidae: Jaculus)

“…It has been shown in previous studies on rodents that adaptive dorsal fur coloration can evolve rapidly [40] in response to selection pressures caused by predation [19] and that the molecular and structural mechanisms for coloration seem to be relatively labile [20] [41] [42] [43]. Though there are studies on geography of fur color polymorphisms, they have focused mainly on few local populations.…”

Sexual Dimorphism in Melanin Pigmentation, Feather Coloration and Its Heritability in the Barn Swallow (Hirundo rustica)

“…Due to the diverse and potentially contrasting natural and sexual selection pressures that act on coloration, the functional analysis of such variation occurring both at the intra- and inter-specific level is complex [1]–[5]. Coloration can affect body thermal balance via differential reflection of solar radiation and is crucial to crypsis and mimicry of both prey and predators [6]–[9]. In addition, socio-sexual communication and species recognition are often mediated by colorful signals [2], [4], [10], [11].…”

Sympatric speciation of spiny mice, Acomys , unfolded transcriptomically at Evolution Canyon, Israel

“…At EC I, Acomys first inhabited the tropical hot and dry AS and then, dispersed to the temperate cooler and humid ES (16). Although the interslope distance of Acomys populations at EC I is, on average, only 250 m apart, the animals from the two slopes display different body size and pelage color (19) as well as allozymic, DNA (20), mtDNA, and amplified fragment-length polymorphism (AFLP) differences (16).…”