EFFECTS OF ANDROGENS ON MALE SEXUAL-BEHAVIOR AND SECONDARY SEX CHARACTERS IN THE EXPLOSIVELY BREEDING SPADEFOOT TOAD, SCAPHIOPUS0-COUCHII

In male Scaphiopus couchii, plasma elevations in androgens are associa ted with the seasonal expression of sexual behavior. To test the hypot hesis that androgens are necessary for the expression of one aspect of sexual behavior, amplexus, and for the development of secondary sex c haracteristics in male S. couchii, the effects of testosterone (T) and dihydrotestosterone (DHT) on clasping behavior and thumb pad growth w ere investigated. Forty toads were divided into five treatment groups as follows: (1) intact, with no hormonal or surgical treatment; (2) sh am-castrated, with silastic implants of cholesterol; (3) sham-castrate d, with implants of T and DHT; (4) castrated, with implants of cholest erol; and (5) castrated, with implants of T and DHT. Displays of sexua l behavior (amplexus) for each individual were counted during a 3-hr o bservation period at 2, 4, and 7 weeks after the surgical procedure. F or each observation trial, there was no significant difference in the amount of clasping among treatment groups: virtually all individuals f rom each group displayed vigorous clasping. No calling was noted at an y time. Thumb pad darkness of each individual was assessed at the 4- a nd 7-week time intervals. At both time periods, the thumb pads of andr ogen-treated males were significantly darker than those of cholesterol -treated males, while intact males remained intermediate. Measurement of plasma steroid levels from the treatment groups indicated that andr ogens were basal in the castrate group and higher in the implant treat ment. These results suggest that in S. couchii, although androgens are associated temporally with the onset of reproductive behavior, they a re not necessary for its expression. The elevation in androgens during the reproductive period may be instead important in the development a nd maintanence of secondary sex characteristics and possibly other rep roductive functions. (C) 1997 Academic Press.