Physiology M311: Biomedical, Biomolecular and Chemical Science, The University of Western Australia, 35 Stirling Highway, Crawley 6009, Western Australia, Australia.
Biol Lett. 2009 Dec 23;5(6):826-9. doi: 10.1098/rsbl.2009.0424. Epub 2009 Jul 22.
It was recently reported that the proportion of dark-coloured Soay sheep (Ovis aries) in the Hebrides has decreased, despite the fact that dark sheep tend to be larger than lighter sheep, and there exists a selective advantage to large body size. It was concluded that an apparent genetic linkage between loci for the coat colour polymorphism and loci with antagonistic effects on body size explained the decrease. Those results explain why the proportion of dark animals is not increasing, but not why it is decreasing. Between 1985 and 2005 there was a significant increase in mean ambient temperature near the islands. We suggest that, while in the past a dark coat has offset the metabolic costs of thermoregulation by absorbing solar radiation, the selective advantage of a dark coat may be waning as the climate warms in the North Atlantic. In parallel, Bergman's rule may be operating, reducing the selective advantage of large body size in the cold. Either or both of these mechanisms can explain the decrease in the proportion of dark-coloured larger sheep in this population in which smaller (and light-coloured) sheep should be favoured by their lower gross energy demand. If environmental effects are the cause of the decline, then we can expect the proportion of dark-coloured Soay sheep to decrease further.
最近有报道称，赫布里底群岛的深色斯莱羊（Ovis aries）的比例有所下降，尽管深色羊往往比浅色羊更大，而且大体型具有选择优势。结论是，毛色多态性的基因座与对体型有拮抗作用的基因座之间存在明显的遗传连锁，解释了这种下降。这些结果解释了为什么深色动物的比例没有增加，而不是为什么它在减少。在 1985 年至 2005 年期间，岛屿附近的环境温度显著升高。我们认为，虽然过去深色的皮毛通过吸收太阳辐射来抵消体温调节的代谢成本，但随着北大西洋气候变暖，深色皮毛的选择优势可能正在减弱。与此同时，伯格曼法则可能在起作用，降低了寒冷环境中大型体型的选择优势。这两种机制都可以解释在这个种群中深色、较大的羊的比例下降，在这个种群中，体型较小（和浅色）的羊由于其较低的总能量需求而应该更受青睐。如果环境影响是下降的原因，那么我们可以预期深色斯莱羊的比例将进一步下降。
