Tricas T C, Maruska K P, Rasmussen L E
Department of Biological Sciences, Florida Institute of Technology, Melbourne 32901-6988, USA.
Gen Comp Endocrinol. 2000 May;118(2):209-25. doi: 10.1006/gcen.2000.7466.
The mating season of the Atlantic stingray (Dasyatis sabina), which begins in August and continues through April, is the longest documented for any elasmobranch fish. Despite this protracted mating period, female stingrays ovulate synchronously at the end of the mating season and there is no evidence for sperm storage by females. Thus, the proximate causal factors and ultimate function of this extended preovulatory mating are unknown. Annual cycles of the gonadal steroids testosterone (T), dihydrotestosterone (DHT), 17beta-estradiol (E2), and progesterone (P4) were measured for 26 months in a wild estuarine population of Atlantic stingrays to test for associations with their reproductive biology, gametogenesis, and sexual behavior. Serum androgen levels in males showed four phases within an annual cycle: (1) androgen suppression between reproductive seasons (April-July), (2) primary androgen increase during the onset of spermatocyte development (August-October), (3) androgen decrease following maximum testis growth and spermatocyte development (November-December), and (4) secondary androgen increase during the peak of sperm maturation (January-March). Increases in male E2 and P4 were correlated with spermatocyte/spermatocyst formation, maximum testis weight, and the primary (but not secondary) androgen surge. We propose that the production of male androgens across the full seven-month preovulatory mating period promotes their aggressive reproductive behavior and drives the protracted mating season of this species. In females, serum T and DHT showed relatively brief increases near ovulation, whereas E2 and P4 showed brief increases near both ovulation and parturition. The increase in female androgens near ovulation may increase female aggression when they are impregnable by courting males and enhance their choice of mates. This estuary sample population shows higher absolute steroid levels and distinct differences in temporal cycles compared to another Florida fresh water lake population, but the cause and significance of these differences are unknown. Experiments are needed to confirm that the aggressive and protracted mating behavior is the result of prolonged male androgen production and to determine whether the sustained preovulatory mating serves some function related to female reproduction.
大西洋黄貂鱼（Dasyatis sabina）的交配季节从8月开始，一直持续到4月，是有记录以来所有软骨鱼类中最长的。尽管交配期很长，但雌性黄貂鱼在交配季节结束时同步排卵，且没有证据表明雌性能储存精子。因此，这种延长的排卵前交配的近因和最终功能尚不清楚。对野生河口大西洋黄貂鱼种群进行了26个月的性腺类固醇睾酮（T）、双氢睾酮（DHT）、17β-雌二醇（E2）和孕酮（P4）年度周期测量，以测试它们与生殖生物学、配子发生和性行为之间的关联。雄性血清雄激素水平在年度周期内呈现四个阶段：（1）生殖季节之间（4月至7月）雄激素抑制；（2）精母细胞发育开始时（8月至10月）雄激素初次增加；（3）睾丸生长和精母细胞发育达到最大值后雄激素减少（11月至12月）；（4）精子成熟高峰期（1月至3月）雄激素再次增加。雄性E2和P4的增加与精母细胞/精囊形成、最大睾丸重量以及初次（而非再次）雄激素激增相关。我们认为，在长达七个月的排卵前交配期内雄性雄激素的产生促进了它们积极的生殖行为，并推动了该物种漫长的交配季节。在雌性中，血清T和DHT在排卵附近显示出相对短暂的增加，而E2和P4在排卵和分娩附近均显示出短暂增加。排卵附近雌性雄激素的增加可能会在它们对求偶雄性无受孕能力时增加雌性攻击性，并增强它们对配偶的选择。与佛罗里达州另一个淡水湖种群相比，并与另一个佛罗里达州淡水湖种群相比，这个河口样本种群显示出更高的绝对类固醇水平和时间周期上的明显差异，但这些差异的原因和意义尚不清楚。需要进行实验来证实积极且漫长的交配行为是雄性雄激素长期产生的结果，并确定持续排卵前交配是否具有与雌性繁殖相关的某种功能。
