The Effects of Environmental Temperature on Coat Color in Diverse Genotypes of the Guinea Pig.

Although the physiological genetics of guinea pig coat color has been studied from the point of view of gene interaction in the amount of pigment produced (HEIDENTHAL 1940, RUSSELL 1939, WRIGHT 1941, 1942, 1949, WRIGHT and BRADDOCK 1949) and from a biochemical basis (FOSTER 1952, GINSBURG 1944, RUSSELL 1939), no attack on the problem by means of an investigation of the interaction of the genotype with the environment seems to have been made previously except for some studies of albino guinea pigs by ILJIN (1927) and SCHULTZ (1922) and preliminary experiments by WRIGHT (1927) on a number of colored genotypes. In various papers WRIGHT (1949 and previous) has reported the observation that the intensity of the guinea pig hair color changes over a period of time but whether this was due to an age effect, the environmental temperature or to a combination of these or possibly still other factors was not known. The investigations of the effects of cold on the pigmentation of the Himalayan rabbit by DANNEEL (1941), DANNEEL and PAUL (1940), DANNEEL and SCHAUMANN (1938), ENGELSMEIER (1937), ILJIN (1926, 1927, 1931), KAUFMANN (1925), and SCHULTZ (1922, 1928) and the pronounced darkening of the ears, nose, and feet of certain albino guinea pigs in addition to the appearance of dark hairs in these animals after losing part of their coat pointed to a possible parallelism in the effects of cold on pigment production in these two species. The purpose of the present study was to discriminate between changes in pigmentation that do and do not depend on a reduction of the skin temperature. Previous measurements of the intensity and quality of guinea pig hair pigment were made by means of visual grades (WRIGHT 1949) or by colorimetrically measuring the pigment extracted from weighed samples of hair by solution in dilute alkali (HEIDENTHAL 1940, RUSSELL 1939, WRIGHT and BRADDOCK 1949). Although measurements obtained by these methods agree Guite well (WRIGHT 1949), the visual grades are not objective for sufficiently small dserences for the present purpose. The Photovolt photoelectric reflection meter, used in obtaining the data to be reported here, makes objectivity possible in the measurement of small qualitative and quantitative differences (in the sense of order) in the pigment present in the