Data from: Subtle individual variation in indeterminate growth leads to major variation in survival and lifetime reproductive output in a long-lived reptile

1. The consequences of individual variation in life-history traits have been well studied due to their importance in evolutionary ecology. However, a trait that has received little empirical attention is the rate of indeterminate growth. In long-lived ectotherms, subtle variation in growth after maturity could have major effects over the animals’ lifetimes. 2. These effects are difficult to measure due to the challenges involved in reliably estimating individual variation in the face of environmental stochasticity, and the need to account for trade-offs among growth, reproduction and survival. However, modelling advances have made such analysis possible if long-term high-quality data sets are available. 3. We used an integrated state-space modelling framework to reveal relationships between indeterminate growth, reproduction and survival in a population of North American snapping turtles (Chelydra serpentina) using a 41-year data set for 298 adult females. 4. A hierarchical version of the von Bertalanffy model fitted to data on carapace lengths showed substantial individual variation in growth trajectories, and hierarchical models fitted to clutch-mass data and recapture histories showed that reproductive output and survival probability increased with size. Integration of these models revealed no detectable trade-offs – i.e., individual growth parameters were not correlated with size-specific survival or reproduction rates, and individual variation in reproductive output did not affect the size-specific survival rate. Consequently, individual variation in growth parameters was estimated to result in > 2-fold variation in post-maturity life expectancy and > 4-fold variation in expected lifetime reproductive output. 5. These results illustrate that indeterminate growth can have major fitness consequences in long-lived species. We suggest that the individual variation in growth rates reflects variation in environments experienced during development or later life. An understanding of this variation may be essential for predicting the population dynamics of long-lived species under threat and identifying the most important environments to protect.

1. 生活史性状的个体变异所带来的演化生态学后果已得到充分研究，因其在进化生态学中具有重要意义。然而，极少受到实证关注的一类性状是不定生长速率（indeterminate growth）。在长寿变温动物（ectotherms）中，成熟后生长的细微变异可能会对动物的整个生命周期产生重大影响。2. 这类效应的测量颇具难度，一方面难以在环境随机性的干扰下可靠估算个体变异，另一方面需要考量生长、繁殖与存活之间的权衡关系。不过，若拥有长期高质量的数据集，建模技术的进步已使得此类分析成为可能。3. 本研究依托覆盖41年、包含298只成年雌性个体的数据集，采用整合式状态空间建模（state-space modelling）框架，揭示了北美鳄龟（Chelydra serpentina）种群中不定生长、繁殖与存活之间的关联。4. 针对背甲长度（carapace lengths）数据拟合的冯·贝塔朗菲模型（von Bertalanffy model）分层版本显示，生长轨迹存在显著的个体变异；针对窝卵质量（clutch-mass）数据和重捕历史拟合的分层模型则表明，繁殖输出与存活概率随体型增大而提升。对这些模型进行整合后发现，不存在可检测到的权衡关系——即个体生长参数与体型特异性存活或繁殖速率并无关联，且繁殖输出的个体变异不会影响体型特异性存活概率。据此估算，生长参数的个体变异会导致成熟后预期寿命产生2倍以上的差异，且预期终身繁殖输出存在4倍以上的差异。5. 这些结果表明，不定生长在长寿物种中可产生重大的适合度后果。我们推测，生长速率的个体变异反映了个体在发育阶段或后续生命中所经历的环境差异。厘清这类变异，对于预测受威胁长寿物种的种群动态、识别最需保护的关键环境而言，或许至关重要。