The ontogeny and distribution of countershading in colonies of the naked mole‐rat (Heterocephalus glaber)

Abstract

Most naked mole-rats Heterocephalus glaber are countershaded, with purple-grey dorsal but pale pink ventral skin. The exceptions to this coloration pattern are uniformly pink, and include newborn pups, most queens and breeding males, and very old animals. Countershading begins to appear at 2±3 weeks of age and begins to disappear at c. 7 years of age. Countershading may provide camou¯age when young naked mole-rats are above ground attempting to disperse. Therefore, reproductives and older workers may lose this coloration once they are unlikely to leave the burrow. Alternative hypotheses for pigmentation that we considered include: thermoregulation, and protection from abrasion or from damaging ultraviolet radiation. These hypotheses are not necessarily mutually exclusive, but do lead to different predictions regarding the development of pigmentation and which colony members should be countershaded.

From Abbott Thayer to the present day: what have we learned about the function of countershading?

“…Naked mole rat body temperature has been shown to vary with ambient temperature (Buffernstein & Yahav 1991), with countershading proposed as a mechanism that might help the mole rats maintain a constant body temperature. However, Braude et al (2001) found no evidence to suggest a role of thermoregulation for countershading in this species.…”

Testing the role of background matching and self-shadow concealment in explaining countershading coloration in wild-caught rainbowfish

“…Burtt (1981) proposed that dark dorsal coloration might serve for abrasion resistance (e.g. in bur-rowing animals), although a study of countershading in naked mole rats (Heterocephalus glaber, Ruppell, 1842) found little support for this hypothesis (Braude et al, 2001). DPD could also arise if selection for BM operates on only one surface of the body; for example, flatfishes exhibit DPD but, because of their benthic habit, would typically only be viewed from above.…”

Orientation to the sun by animals and its interaction with crypsis

“…Dark coloration on the back may also result from selection through protection from UV radiation (Braude et al . ). Both thermoregulation and UV protection may be better achieved through a uniform (dark) pigmentation.…”

“…Pigmentation will also affect thermoregulation by influencing the absorption of radiation (Braude et al 2001). The sun's rays most commonly strike dorsal parts of an animal, so darkening upper parts of the body could maximize heat gain from the sun and result in countershading.…”

“…Note that a darker skin or pelt is not always associated with greater solar heat load (Lustick, Adam & Hinko 1980;Walsberg 1983;Dawson, Webster & Maloney 2013). Dark coloration on the back may also result from selection through protection from UV radiation (Braude et al 2001). Both thermoregulation and UV protection may be better achieved through a uniform (dark) pigmentation.…”