Subcutaneous and cutaneous melanins in Rhabdomys: complementary ultraviolet radiation shields

Abstract

We describe the pigmented tissue layer covering the skull of Rhabdomys pumilio and test the hypotheses that it is melanin and that it functions in absorption of ultraviolet solar radiation. The parietals were covered by a dark tissue layer with smaller amounts of pigment extending over the frontals and nasals. Pigment granules also were observed in many skeletal muscles. Histologically, these tissues contained granules that stained black with hematoxylin and eosin, and silver impregnation. Spectrographic absorbency scans of pigment on the skull and in the skin showed two pigment layers absorbing maximally at different ultraviolet wavelengths. We suggest that both pigments are melanin acting in a complementary manner to provide an effective central nervous system radiation shield in Rhabdomys.