Why are not all chilies hot? A trade-off limits pungency
Why are not all chilies hot? A trade-off limits pungency
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DOI：
10.1098/rspb.2011.2091
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发表时间：
2012-05
期刊：
影响因子：
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通讯作者：
D. Haak;L. A. McGinnis;D. Levey;J. Tewksbury
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文献类型：
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作者：
D. Haak;L. A. McGinnis;D. Levey;J. Tewksbury
进化生物学家越来越多地认识到，进化可能受到权衡的限制，但我们对这些限制如何以及何时表现出来以及它们是否限制了种群的适应性差异的理解仍然有限。在这里，我们表明，水分的空间异质性保持了野生辣椒（辣椒chacoense）的自然种群之间的辛辣（热）的多态性，因为影响水分利用效率的性状在功能上与控制辛辣（辣椒素类物质的生产）的性状相结合。在玻利维亚，辛辣和非辛辣的辣椒出现在沿着一个跨越其原产地的水分梯度中，辛辣植物在种群中的比例随着水分供应的增加而增加。在高湿度的环境中，辛辣是有益的，因为辣椒素保护水果免受病原真菌的侵害，并且不昂贵，因为辛辣和非辛辣的辣椒在良好的浇水条件下生长，产生相同数量的种子。在低湿度环境中，辛辣的好处较少，因为真菌感染的风险较低，而且成本很高，因为在干旱胁迫下，辛辣辣椒的种子产量比在相同条件下生长的非辛辣植物减少50%。在水分胁迫（WS）条件下，种子产量的这种巨大差异解释了以非辛辣植物为主的种群的存在，并且似乎是由辛辣和气孔密度之间的遗传相关性引起的：非辛辣植物，从种群内杂交分离，表现出显着较低的气孔密度（p = 0.003），从而减少了WS条件下的气体交换。这些结果表明，性状整合的重要性，在限制适应性群体之间的分歧。
Evolutionary biologists increasingly recognize that evolution can be constrained by trade-offs, yet our understanding of how and when such constraints are manifested and whether they restrict adaptive divergence in populations remains limited. Here, we show that spatial heterogeneity in moisture maintains a polymorphism for pungency (heat) among natural populations of wild chilies (Capsicum chacoense) because traits influencing water-use efficiency are functionally integrated with traits controlling pungency (the production of capsaicinoids). Pungent and non-pungent chilies occur along a cline in moisture that spans their native range in Bolivia, and the proportion of pungent plants in populations increases with greater moisture availability. In high moisture environments, pungency is beneficial because capsaicinoids protect the fruit from pathogenic fungi, and is not costly because pungent and non-pungent chilies grown in well-watered conditions produce equal numbers of seeds. In low moisture environments, pungency is less beneficial as the risk of fungal infection is lower, and carries a significant cost because, under drought stress, seed production in pungent chilies is reduced by 50 per cent relative to non-pungent plants grown in identical conditions. This large difference in seed production under water-stressed (WS) conditions explains the existence of populations dominated by non-pungent plants, and appears to result from a genetic correlation between pungency and stomatal density: non-pungent plants, segregating from intra-population crosses, exhibit significantly lower stomatal density (p = 0.003), thereby reducing gas exchange under WS conditions. These results demonstrate the importance of trait integration in constraining adaptive divergence among populations.