Kraaijeveld-Smit F J L, Ward S J, Temple-Smith P D
Department of Zoology, University of Melbourne, Victoria, Australia.
Mol Ecol. 2003 Feb;12(2):475-84. doi: 10.1046/j.1365-294x.2003.01745.x.
Antechinus agilis is a small sexually size dimorphic marsupial with a brief annual mating period of 2-3 weeks. All males die after this period, and females give birth to up to 10 young. Mating is thought to be promiscuous, however, there is no field data to confirm this. Using microsatellites, we investigated paternity patterns over two seasons in a wild population. Male weight was significantly positively related to the number of females fertilized and with the number of offspring sired, in both years. Furthermore, selection gradients indicated selection for larger males. Both results suggest that size dimorphism in A. agilis can be explained by sexual selection for larger males. The proportion of offspring sired within litters, did not relate to male size. Therefore, larger males are more successful through higher mating access, not through their sperm outcompeting that of smaller males. As expected from their known ranging behaviour, the number of offspring within litters left unassigned to a father did not depend on the grid location of the mother. Female size did not differ between successful reproducing and unsuccessful females. However, females that weaned offspring had larger heads than females that did not wean offspring. Males did not 'prefer' mating with larger females, nor did assortative mating occur. From our results, the mating system of A. agilis is clearly promiscuous. Selection for larger males occurred in both years, even though in one year the operational sex ratio was highly female biased, suggesting that the potential reproductive rate is a better predictor of the direction of sexual selection in A. agilis.
敏捷狭足袋鼩是一种体型具有性别二态性的小型有袋动物，每年有2至3周的短暂交配期。在此期间过后，所有雄性都会死亡，而雌性最多可产下10只幼崽。人们认为交配是杂乱的，然而，尚无实地数据证实这一点。我们利用微卫星技术，对一个野生种群两个季节的父系模式进行了调查。在这两年中，雄性体重与受精雌性的数量以及所产幼崽的数量均呈显著正相关。此外，选择梯度表明对体型较大的雄性存在选择。这两个结果都表明，敏捷狭足袋鼩的体型二态性可通过对体型较大雄性的性选择来解释。一窝幼崽中由某一雄性所生幼崽的比例与雄性体型无关。因此，体型较大的雄性通过获得更多的交配机会而更成功，而非通过其精子在竞争中胜过体型较小的雄性的精子。根据它们已知的活动范围行为，一窝中未确定父系的幼崽数量并不取决于母亲的网格位置。成功繁殖的雌性与未成功繁殖的雌性在体型上没有差异。然而，成功哺育幼崽的雌性比未哺育幼崽的雌性头部更大。雄性并不“偏好”与体型较大的雌性交配，也不存在选型交配现象。从我们的结果来看，敏捷狭足袋鼩显然是杂乱交配的。在这两年中都存在对体型较大雄性的选择，尽管其中一年的两性 operational sex ratio 严重偏向雌性，这表明潜在繁殖率是敏捷狭足袋鼩中性选择方向的更好预测指标。 （注：原文中“operational sex ratio”未翻译，因为没有合适的中文术语，可根据具体语境理解，这里保留英文更合适）
