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Spiny mice modulate eumelanin to pheomelanin ratio to achieve cryptic coloration in "evolution canyon," Israel.

Singaravelan N, Pavlicek T, Beharav A, Wakamatsu K, Ito S, Nevo E - PLoS ONE (2010)

Bottom Line: 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.It appears that rodents adaptively modulate eumelanin and pheomelanin contents to achieve cryptic coloration in contrasting habitats even at a microscale.

View Article: PubMed Central - PubMed

Affiliation: Institute of Evolution, University of Haifa, Mount Carmel, Haifa, Israel. yoursings@gmail.com

ABSTRACT

Background: Coat 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 findings: We 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/significance: It appears that rodents adaptively modulate eumelanin and pheomelanin contents to achieve cryptic coloration in contrasting habitats even at a microscale.

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Habitat divergence in “Evolution Canyon”.(A) photo showing part of the “African” slope (AS)/south-facing slope (SFS) of EC, characterized by light terra rossa soil with a stretch of grass cover that generates a yellow-brownish background. (B) Photo of part of the “European” slope (ES)/north-facing slope (NFS), characterized by dark terra rossa soil and shady, humus-laden dark background.
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pone-0008708-g002: Habitat divergence in “Evolution Canyon”.(A) photo showing part of the “African” slope (AS)/south-facing slope (SFS) of EC, characterized by light terra rossa soil with a stretch of grass cover that generates a yellow-brownish background. (B) Photo of part of the “European” slope (ES)/north-facing slope (NFS), characterized by dark terra rossa soil and shady, humus-laden dark background.

Mentions: The “African” slope is characterized by light terra rossa soil with a stretch of yellow grass cover displaying a yellow-brown colored milieu (Figure 2A); by contrast, the “European” slope is characterized by dark gray terra rossa soil with shade from the dense foliage covering trees and shrubs spread across the slope displaying a dark grayish milieu (Figure 2B) [36]. Thus, EC displays a fairly uniform color pattern of the habitats within each slope but places conflicting selection pressures on spiny mouse (A. cahirinus) to mimic differently colored habitats between the slopes (e.g., AS vs. ES). Individuals of A. cahirinus on the opposing slopes exhibit visible differences in their overall coat color: AS individuals tend to be lighter and ES individuals tend to be darker (Figure 3A–3D). Here we investigate how hair melanin contents of A. cahirinus evolved in response to alternative selection pressures inflicted by contrasting colored habitats of EC. Our working hypothesis is that spiny mice would exert a relatively higher pheomelanin content on the AS (than on the ES) where the demand is to mimic yellow-brown backgrounds and higher eumelanin content on the ES (than on the AS) where the demand is to mimic dark gray backgrounds to increase survival fitness by reducing the potential to be detected by predators.


Spiny mice modulate eumelanin to pheomelanin ratio to achieve cryptic coloration in "evolution canyon," Israel.

Singaravelan N, Pavlicek T, Beharav A, Wakamatsu K, Ito S, Nevo E - PLoS ONE (2010)

Habitat divergence in “Evolution Canyon”.(A) photo showing part of the “African” slope (AS)/south-facing slope (SFS) of EC, characterized by light terra rossa soil with a stretch of grass cover that generates a yellow-brownish background. (B) Photo of part of the “European” slope (ES)/north-facing slope (NFS), characterized by dark terra rossa soil and shady, humus-laden dark background.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2806840&req=5

pone-0008708-g002: Habitat divergence in “Evolution Canyon”.(A) photo showing part of the “African” slope (AS)/south-facing slope (SFS) of EC, characterized by light terra rossa soil with a stretch of grass cover that generates a yellow-brownish background. (B) Photo of part of the “European” slope (ES)/north-facing slope (NFS), characterized by dark terra rossa soil and shady, humus-laden dark background.
Mentions: The “African” slope is characterized by light terra rossa soil with a stretch of yellow grass cover displaying a yellow-brown colored milieu (Figure 2A); by contrast, the “European” slope is characterized by dark gray terra rossa soil with shade from the dense foliage covering trees and shrubs spread across the slope displaying a dark grayish milieu (Figure 2B) [36]. Thus, EC displays a fairly uniform color pattern of the habitats within each slope but places conflicting selection pressures on spiny mouse (A. cahirinus) to mimic differently colored habitats between the slopes (e.g., AS vs. ES). Individuals of A. cahirinus on the opposing slopes exhibit visible differences in their overall coat color: AS individuals tend to be lighter and ES individuals tend to be darker (Figure 3A–3D). Here we investigate how hair melanin contents of A. cahirinus evolved in response to alternative selection pressures inflicted by contrasting colored habitats of EC. Our working hypothesis is that spiny mice would exert a relatively higher pheomelanin content on the AS (than on the ES) where the demand is to mimic yellow-brown backgrounds and higher eumelanin content on the ES (than on the AS) where the demand is to mimic dark gray backgrounds to increase survival fitness by reducing the potential to be detected by predators.

Bottom Line: 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.It appears that rodents adaptively modulate eumelanin and pheomelanin contents to achieve cryptic coloration in contrasting habitats even at a microscale.

View Article: PubMed Central - PubMed

Affiliation: Institute of Evolution, University of Haifa, Mount Carmel, Haifa, Israel. yoursings@gmail.com

ABSTRACT

Background: Coat 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 findings: We 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/significance: It appears that rodents adaptively modulate eumelanin and pheomelanin contents to achieve cryptic coloration in contrasting habitats even at a microscale.

Show MeSH
Related in: MedlinePlus