Emerson S B, Carroll L, Hess D L
Department of Biology, University of Utah, Salt Lake City 84112, USA.
J Exp Zool. 1997 Dec 15;279(6):587-96. doi: 10.1002/(sici)1097-010x(19971215)279:6<587::aid-jez7>3.0.co;2-j.
The fanged frogs of Southeast Asia do not express most of the hormone-dependent secondary sexual characteristics such as thumb pads that are common to other ranid frogs. At the same point in the evolutionary history of the group that these androgen-mediated characteristics are lost, male parental care first evolves. This behavior is often correlated with low androgen levels. Prior work indicates that in one of the fanged frogs, Rana blythii, adult males have low androgen levels compared to North Temperate species of Rana. This leads to the question of whether these low androgen levels are related to the unusual male parental care and the lack of expression of the thumb pad and other hormone-dependent secondary sexual characteristics in this species. We tested that hypothesis by examining the effects of exogenous dihydrotestosterone supplements on the expression of thumb pads in Rana blythii. Dihydrotestosterone injections appear to stimulate the expression of the thumb pad in R. blythii. These results support the hypothesis that low androgen levels are involved in the loss of the thumb pad in R. blythii. This work provides an example of how mapping characters on phylogenies can be a powerful approach for gaining insights into proximate physiological mechanisms of selection at the evolutionary level.
东南亚的有齿蛙并不表现出大多数依赖激素的第二性征，比如其他蛙科青蛙常见的拇指垫。在该类群进化史中这些由雄激素介导的特征消失的同时，雄性亲代抚育首次出现。这种行为通常与低雄激素水平相关。先前的研究表明，在一种有齿蛙——滇蛙中，成年雄性的雄激素水平低于北温带的林蛙物种。这就引出了一个问题，即这些低雄激素水平是否与该物种不同寻常的雄性亲代抚育以及拇指垫和其他依赖激素的第二性征的缺失有关。我们通过研究外源性双氢睾酮补充剂对滇蛙拇指垫表达的影响来验证这一假设。双氢睾酮注射似乎能刺激滇蛙拇指垫的表达。这些结果支持了低雄激素水平与滇蛙拇指垫缺失有关的假设。这项研究提供了一个例子，说明如何在系统发育树上绘制特征对于深入了解进化水平上选择的近因生理机制是一种强有力的方法。
