Female Color Change in the Keeled Earless Lizard, Holbrookia propinqua: Relationship to the Reproductive Cycle

Abstract

The orange and yellow coloration of female Holbrookia propinqua appears to be closely associated with ovarian events, intensifying rapidly during the final stages of vitellogenesis and reaching maximum brightness prior to ovulation. All females having recent corpora lutea or bearing oviducal eggs retained bright colors. Females with the dullest colors lacked orange and yellow pigmen- tation, had relatively small follicles, and were at early stages of the reproductive cycle. Further studies are needed to determine the course of chromatic variation between successive reproductive cycles and to evaluate the turn-on and turn-off hypotheses of the adaptive value of the female reproductive colora- tion. Distinctive changes in color pattern associated with reproduction occur in female iguanid lizards of several genera, including Crotaphytus (Cooper and Ferguson, 1972a, 1972b, 1973),Holbrookia (Clarke, 1965; Judd, 1973), Gambelia (Medica et al., 1975) and Sceloporus (Dixon, 1957). Female reproductive colora- tion may be induced by progesterone or testosterone injections and its onset may be hastened by estrogen injection in Crotaphytus collaris (Cooper and Ferguson, 1972a, 1972b, 1973) and Gambelia wislizeni (Medica et al., 1973). Although a hormonal basis for pigment depositions is well established, possible roles of the colors in reproductive behavior remain speculative and little is known regarding the relationships of the colors to reproductive cycling. Gravid females often show the most intense pigmentation (Judd, 1976; Fitch, 1956; Medica et al., 1973), usually orange to red, but the timing of pigment deposition with respect to courtship, copulation, follicular development, oviposition, and luteal activity remain largely unknown in most species. Only in Crotaphytus and Gambelia have some of these relationships been studied. Female C. collaris develop orange lateral spots, changing from a dull, non-breeding pattern to maximum birght- ness in a single day. This rapid color change occurs in preovulatory females approximately 10-13 days before oviposition (Ferguson, 1976; Fitch, 1956). Max- imal color intensity in G. wislizeni is also established during vitellogenesis, prior to ovulation (Medica et al., 1973). In this paper, intensity of orange and yellow pigmentation is correlated with reproductive state in the keeled earless lizard, Holbrookia propinqua, and impli- cations of this relationship for hypotheses about the adaptive significance of the coloration are discussed.