Department of Ecology and Evolutionary Biology, University of Toronto, Canada.
Biol Rev Camb Philos Soc. 2011 Feb;86(1):97-116. doi: 10.1111/j.1469-185X.2010.00136.x.
According to life-history theory, growth rates are subject to strong directional selection due to reproductive and survival advantages associated with large adult body size. Yet, growth is commonly observed to occur at rates lower than the maximum that is physiologically possible and intrinsic growth rates often vary among populations. This implies that slower growth is favoured under certain conditions. Realized growth rate is thus the result of a compromise between the costs and advantages of growing rapidly, and the optimal rate of growth is not equivalent to the fundamental maximum rate. The ecological and evolutionary factors influencing growth rate are reviewed, with particular emphasis on how growth might be constrained by direct fitness costs. Costs of accelerating growth might contribute to the variance in fitness that is not attributable to age or size at maturity, as well as to the variation in life-history strategies observed within and among species. Two main approaches have been taken to study the fitness trade-offs relating to growth rate. First, environmental manipulations can be used to produce treatment groups with different rates of growth. Second, common garden experiments can be used to compare fitness correlates among populations with different intrinsic growth rates. Data from these studies reveal a number of potential costs for growth over both the short and long term. In order to acquire the energy needed for faster growth, animals must increase food intake. Accordingly, in many taxa, the major constraint on growth rate appears to arise from the trade-off between predation risk and foraging effort. However, growth rates are also frequently observed to be submaximal in the absence of predation, suggesting that growth trajectories also impact fitness via other channels, such as the reallocation of finite resources between growth and other traits and functions. Despite the prevalence of submaximal growth, even when predators are absent, there is surprisingly little evidence to date demonstrating predator-independent costs of growth acceleration. Evidence that does exist indicates that such costs may be most apparent under stressful conditions. Future studies should examine more closely the link between patterns of resource allocation to traits in the adult organism and lifetime fitness. Changes in body composition at maturation, for example, may determine the outcome of trade-offs between reproduction and survival or between early and late reproduction. A number of design issues for studies investigating costs of growth that are imposed over the long term are discussed, along with suggestions for alternative approaches. Despite these issues, identifying costs of growth acceleration may fill a gap in our understanding of life-history evolution: the relationships between growth rate, the environment, and fitness may contribute substantially to the diversification of life histories in nature.
根据生活史理论，由于与大型成体体型相关的生殖和生存优势，生长速度受到强烈的定向选择。然而，生长通常以低于生理上可能的最大速度发生，并且内在生长率经常在种群之间变化。这意味着在某些条件下，较慢的生长是有利的。因此，实际生长率是快速生长的成本和优势之间的妥协的结果，而最佳生长率与基本最大率并不等同。本文综述了影响生长速度的生态和进化因素，特别强调了直接适应成本如何限制生长。加速生长的成本可能会导致除成熟年龄或大小以外的适应性差异，以及在物种内和物种间观察到的生活史策略的变化。已经采取了两种主要方法来研究与生长速度有关的适应权衡。首先，可以进行环境处理以产生具有不同生长速度的处理组。其次，可以使用共同花园实验来比较具有不同内在生长率的种群之间的适应性相关因素。这些研究的数据揭示了短期和长期内生长的许多潜在成本。为了获得更快生长所需的能量，动物必须增加食物摄取量。因此，在许多分类群中，生长速度的主要限制似乎来自捕食风险和觅食努力之间的权衡。但是，即使在没有捕食的情况下，生长速度也经常观察到低于最大速度，这表明生长轨迹还通过其他途径（例如，将有限资源在生长和其他性状和功能之间重新分配）对适应性产生影响。尽管存在亚最大生长，即使没有捕食者，到目前为止，令人惊讶的是，几乎没有证据表明生长加速的独立于捕食者的成本。现有的证据表明，在压力条件下，这些成本可能最为明显。未来的研究应该更仔细地研究成年生物体内性状的资源分配模式与终生适应性之间的联系。例如，成熟时的身体成分变化可能决定繁殖和生存之间或早期和晚期繁殖之间的权衡的结果。本文讨论了研究长期生长成本的一些设计问题，并提出了替代方法的建议。尽管存在这些问题，但确定生长加速的成本可能会填补我们对生活史进化的理解中的空白：生长速度，环境和适应性之间的关系可能会极大地促进自然界中生活史的多样化。
