西亚试剂：南极软毛海豹的环境适应能力

南乔治亚鸟岛一个冰山上的南极软毛海豹(Arctocephalus gazella)到二十世纪初已几乎被捕猎殆尽，但当捕猎海豹的活动停止时其数量又开始恢复了，同时由于食物供应充足，大量这种海豹生存了下来。但软毛海豹面对气候变化尤其脆弱，因为它们生活的地区温度在快速变化，它们相对较长的世代时间也限制了其演化适应能力。

现在，对来自南乔治亚的三十年时间的数据所做的一项分析显示，这种海豹数量又在下降，其中雌性数量在2003年和2012年间下降了大约30%。然而，严酷的自然条件也使雌性海豹有了更高的遗传杂合度。

虽然这种现象本身并不是一种演化反应，但随着环境条件继续恶化，杂合子优势却有可能帮助维持遗传变异，从而有可能争取时间来让它们通过适应对环境变化做出反应。

原文摘要：

Climate change selects for heterozygosity in a declining fur seal population

Jaume Forcada & Joseph Ivan Hoffman

Global environmental change is expected to alter selection pressures in many biological systems, but the long-term molecular and life history data required to quantify changes in selection are rare. An unusual opportunity is afforded by three decades of individual-based data collected from a declining population of Antarctic fur seals in the South Atlantic. Here, climate change has reduced prey availability and caused a significant decline in seal birth weight. However, the mean age and size of females recruiting into the breeding population are increasing. We show that such females have significantly higher heterozygosity (a measure of within-individual genetic variation) than their non-recruiting siblings and their own mothers. Thus, breeding female heterozygosity has increased by 8.5% per generation over the last two decades. Nonetheless, as heterozygosity is not inherited from mothers to daughters, substantial heterozygote advantage is not transmitted from one generation to the next and the decreasing viability of homozygous individuals causes the population to decline. Our results provide compelling evidence that selection due to climate change is intensifying, with far-reaching consequences for demography as well as phenotypic and genetic variation.

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