Changes in Plasma Sex Steroids in Relation to Reproductive Behavior of the Toad, Bufo melanostictus (Schn.)
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.
(A) Changes in the plasma testosterone (T) levels of Bufo melanostictus males engaged in different sexual activities. Note the increase in T levels from calling group to reach a maximum in the amplexus group before falling in the spawning and post-spawning groups. Data are represented as mean±SE. (B) Changes in the plasma Estradiol (E2) concentrations of female Bufo melanostictus engaged in different reproductive behaviors. Note the increase in plasma E2 levels from vitellogenic group to reach a peak in spawning group followed by a decline in the post-spawning group. Data are represented as mean±SE. (C) Changes in the plasma Progesterone (P) concentrations of female Bufo melanostictus engaged in different breeding activities. Note the increase in plasma P levels from the vitellogenic group to the amplecting group, reaching a peak in spawning group followed by a decline in post-spawning group. Data are represented as mean±SE.
Contributor Notes
Associate Editor: K. Martin.