Hews D K, Knapp R, Moore M C
Department of Zoology, Arizona State University, Tempe 85287-1501.
Horm Behav. 1994 Mar;28(1):96-115. doi: 10.1006/hbeh.1994.1008.
Males of many species exhibit strongly dimorphic reproductive behavior and morphology associated with alternative reproductive tactics. Little is known about the physiological control of these individual differences. The relative plasticity hypothesis proposes that such within-sex differences arise from either organizational or activational actions of sex steroid hormones depending on whether adults can switch tactics or not. This hypothesis predicts that differences between individuals in a species where adults cannot switch between tactics (are "fixed") should be organized by early actions of hormones. Three experiments explored the possible organizational role of testosterone (T) on the development of male alternatives in the tree lizard (Urosaurus ornatus), which has two fixed male morphs. Orange (O) males have a mostly orange throat fan (dewlap), are nonterritorial nomads, and are larger than orange-blue (OB) males which have an orange dewlap with a central blue patch and are territorial. In the first experiment intact males on the day of hatching were (1) sham-operated and implanted with empty capsules, (2) castrated, or (3) testosterone-implanted. As adults, the castration group had more O males than the control and the T-implanted group had more OB males than the control. Adult body size in castrated and T-implanted groups parallelled naturally occurring morph differences, but both were smaller than controls. A second experiment with a lower dose yielded similar results for dewlap type and growth. In a third experiment, intact males were given an empty capsule or a T-implant at 30 days posthatching. Again, the frequency of OB males in the T-implanted group was significantly greater than that in the empty implant group, indicating that either the critical period extends past Day 30 or there is no well-defined critical period. Together, these results support the hypothesis that the organizational action of T or one of its metabolites contributes to the differentiation of these within-sex differences.
许多物种的雄性表现出与替代生殖策略相关的强烈二态性生殖行为和形态。关于这些个体差异的生理控制知之甚少。相对可塑性假说提出，这种性别内差异源于性类固醇激素的组织作用或激活作用，这取决于成年个体是否能够切换策略。该假说预测，在成年个体无法在策略之间切换（即“固定”）的物种中，个体之间的差异应该由激素的早期作用来组织。三项实验探讨了睾酮（T）对树蜥（饰纹强棱蜥）雄性替代形态发育可能的组织作用，该树蜥有两种固定的雄性形态。橙色（O）雄性有一个主要为橙色的喉部扇状物（喉囊），是非领地性的流浪者，且比橙色 - 蓝色（OB）雄性体型更大，OB雄性有一个带有中央蓝色斑块的橙色喉囊，且具有领地性。在第一个实验中，刚孵化当天的完整雄性被（1）假手术并植入空胶囊，（2）阉割，或（3）植入睾酮。成年后，阉割组的O雄性比对照组更多，而植入睾酮组的OB雄性比对照组更多。阉割组和植入睾酮组的成年体型与自然出现的形态差异相似，但两者都比对照组小。第二个使用较低剂量的实验在喉囊类型和生长方面产生了类似的结果。在第三个实验中，完整雄性在孵化后30天被给予空胶囊或睾酮植入物。同样，植入睾酮组中OB雄性的频率显著高于植入空胶囊组，这表明关键期要么延长到30天之后，要么不存在明确界定的关键期。总之，这些结果支持了这样的假说，即T或其一种代谢产物的组织作用有助于这些性别内差异的分化。
