Changes in Plasma Sex Steroids in Relation to Reproductive Behavior of the Toad, Bufo melanostictus (Schn.)

Abstract

Steroid hormones play a critical role in the regulation of reproductive behavior of many amphibians. Changes in the plasma concentration of steroid hormones (testosterone, estradiol, and progesterone) in relation to sexual behavior of males and females were studied in a natural population of the toad (Bufo melanostictus) during the breeding season. Changes in plasma sex steroids were positively correlated with the sexual behavior of male and female toads. Plasma testosterone was low in calling males but reached a peak during amplexus before declining in the spawning and post-spawning males. Plasma estradiol and progesterone increased with the onset of sexual behavior in solitary females ready to breed, reaching a peak during spawning before declining in post-spawning females. The study reveals that B. melanostictus belongs to the type of ‘associated reproductive pattern’ in which plasma steroid hormone concentration is highly correlated with the sexual behavior of male and female toads.