Environmental unpredictability and offspring size: conservative versus diversified bet-hedging
Environmental unpredictability and offspring size: conservative versus diversified bet-hedging
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环境的不可预测性和后代的规模：保守与多元化的赌注对冲
DOI：
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发表时间：
2004
期刊：
影响因子：
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通讯作者：
Ian A. Fleming
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文献类型：
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作者：
S. Einum;Ian A. Fleming
经典的生活史理论及其扩展可以很容易地解释种群和个体之间蛋大小的变化。然而，大多数这样的模型都假设在后代环境中存在一定程度的可预测性。当环境发生不可预测的变化时，提供后代的问题更大，可能会导致更好的对冲(即减少适应度的差异)。套期保值可能涉及生产更少和更大的后代(保守的)或不同大小的后代(多样化的)。使用多样化的押注对冲理论来解释窝内变异是常见的，但也存在争议，模拟模型已经表明，这种变异的适应度收益关键取决于蛋大小-后代适应度曲线的形状。在这里，我们使用为数不多的经验性推导的蛋大小-后代适应度函数之一(来自大西洋鲑鱼)，并结合模拟来检验这种押注对冲策略演变的合理性。我们表明，保守的押注套期保值可以是应对不可预测环境的一种可行策略，而多样化的押注套期保值很少具有选择性优势(即仅在极端多变的环境下)，而且仅适用于纯年度生物体。这得到了来自大西洋(n=37个种群)和太平洋(n=26个种群)的经验证据的支持，在野生鱼类中，卵大小的变化不到3%是由于卵内的变异性。只有在新的(罕见的)饲养条件下，例如在淡水中圈养到成熟，才能观察到窝内变异的显著增加。这些模式结合建模结果表明，至少在鲑鱼中，卵内变异更可能反映了饲养环境对雌性平均分配资源能力的直接影响，而不是进化适应。未来在不可预测环境中的鸡蛋大小进化领域的工作可能会受益于更多地关注保守性而不是多样化的押注对冲。
Classic life-history theory and extensions thereof can readily explain variation in egg size among populations and individuals. However, most such models assume that there is some degree of predictability in offspring environment. Offspring provisioning when environments vary unpredictably is more problematic and may lead to bet-hedging (i.e. reducing variance in fitness). Bet-hedging may involve the production of fewer and larger offspring (conservative) or of variable-sized offspring (diversified). The use of diversified bet-hedging theory to explain within-clutch variation is common but controversial, and simulation models have shown that the fitness benefits of such variability depend critically on the shape of the egg size–offspring fitness curve. Here, we use one of the few empirically derived egg size– offspring fitness functions (from Atlantic salmon) in conjunction with simulations to examine the plausibility for the evolution of such bet-hedging strategies. We show that conservative bet-hedging can be a viable strategy for dealing with unpredictable environments, while diversified bet-hedging is rarely selectively advantageous (i.e. only under extremely variable environments), and then only for purely annual organisms. This is supported by empirical evidence from iteroparous Atlantic (n = 37 populations) and semelparous Pacific (n = 26 populations) salmon where less than 3% of the variation in egg size among wild fish is due to within-clutch variability. Only under novel (rare) rearing conditions, such as captive rearing to maturity in freshwater, was a significant increase in within-clutch variation observed. These patterns in conjunction with the modelling results indicate that within-clutch variation, at least in salmon, is more likely a reflection of the direct influences of the rearing environment on a female’s ability to allocate resources evenly than of evolutionary adaptation. Future work in the area of egg size evolution in unpredictable environments may benefit from a stronger focus on conservative rather than diversified bet-hedging.