716 Comparative Animal Physiology 



coloration (Fig. 276). Fishes with more rapid and striking color changes 

 seem to have their choice more strongly modified along with background 

 adaptation than do ones with less effective changes. The crayfish, Camharns, 

 also appears to possess an adaptive background selection.-^ 



Chromatophores appear also to serve in the protection of animals from 

 bright illumination which may be deleterious. In some animals, e.g., certain 

 leeches and sea-urchins, the chromatophore pigment disperses only in re 

 sponse to bright illumination and with no regard to a possible protective col- 

 oration in relation to the background. The black and white pigments in the 

 crab, Uca, are normally dispersed in light during the daytime and concen- 

 trated in darkness at night. This is due partly to an inherent rhythm and 

 partly to a response to total illumination. It is also noteworthy in this re- 

 gard that the white chromatophores of such brilliant-light-inhabiting Sar- 

 gasso-weed crustaceans as Latreutes fucorum, Leander tenuicornis, and Hip- 

 polyte acuminata are very abundant and richly charged with white pig- 

 ment. In bright illumination this pigment disperses bi-oadly, providing a con- 

 tinuous layer of a very effective diffusing reflector. In view of the character 

 of the primary color responses of animals being that of pigment dispersal 

 in light and pigment concentration in darkness, it appears reasonable to 

 suspect that this light-protective function of chromatophores is a most primi- 

 tive one, with the role of production of obliteratixe coloration evolving later. 



Another function which has been attributed to chromatophores is that of 

 thermoregulation.^^' ^^^ The desert lizard Phryn.osoma is light at night and 

 during midday, and dark during the early morning and late afternoon^*^^ (Ch. 

 10). These and similar observations have led to the hypothesis that the 

 chromatophores function in thermoregulation in this species. The animal 

 apparently is adaptively controlling heat absorption and radiation at the 

 various times of day by chromatophore activities. Strongly supporting this 

 view are the observations of numerous investigators of reptilian color 

 change that elevation of the body temperature to approximately 40° C. leads 

 to melanin concentration and that lowering of the temperature to about 5° C. 

 leads to dispersion. ^^'^ The black pigment of the crab, Uca, also tends to con- 

 centrate as the body temperature is elevated above 25 to 30° C.'^'* These condi- 

 tions obviously result in control of the amount of light absorbed by the black 

 pigment in a manner beneficial to the animal. 



One additional role of color changes in animals is suggested by the color 

 displays that sometimes accompany mating behavior in such species as Ano- 

 lisf'- During pairing the males show a striking change from green to brown. 

 Color displays are also associated with the breeding season in certain tele- 

 osts and cephalopods. The importance of these mating color displays is un- 

 known. Special nuptial morphological color changes are not infrequently as- 

 sociated with the breeding season. '^^ 



SUMMARY 



Color changes involving movements of pigments, and formation or accum- 

 ulation and destruction or loss of pigments, within special bodies in the in- 

 tegument, the chromatophores, have been observed among reptiles, amphib- 

 ians, teleosts, elasmobranchs, cyclostomes, crustaceans, insects, cephalopods, 

 annelids, and echinoderms. These color changes are most characteristically 



