Data from: Faster isn't always better: selection on growth rate fluctuates across the life history and environments

Growth rate is increasingly recognised as a key life-history trait that may affect fitness directly, rather than evolving as a by-product of selection on size or age. An ongoing challenge is to explain the abundant levels of phenotypic and genetic variation in growth rates often seen in natural populations, despite what is expected to be consistently strong selection on this trait. Such a paradox suggests limits to how contemporary growth rates evolve. We explored limits arising from variation in selection, based on selection differentials for age-specific growth rates expressed under different ecological conditions. We present results from a field experiment that measured growth rates and reproductive output in wild individuals of a colonial marine invertebrate (Hippopodina iririkiensis), replicated within and across the natural range of succession in its local community. Colony growth rates varied phenotypically throughout this range, but not all such variation was available for selection, nor was it always targeted by selection as expected. While the maintenance of both phenotypic and genetic variation in growth rate is often attributed to costs of growing rapidly, our study highlights the potential for fluctuating selection pressures throughout the life history and across environments to play an important role in this process.生长速率（growth rate）日益被视为一项关键生活史性状（life-history trait），可直接影响适合度（fitness），而非作为体型或年龄选择的副产物演化而来。当前一项持续面临的核心挑战在于：尽管生长速率这一性状理应受到持续强劲的选择作用，自然种群中却常观测到大量该性状的表型与遗传变异。这一悖论暗示当代生长速率的演化存在局限。我们基于不同生态条件下测得的年龄特异性生长速率（age-specific growth rates）的选择差（selection differentials），探究了由选择变异带来的演化局限。本研究呈现一项野外实验（field experiment）结果：该实验针对群居海洋无脊椎动物（colonial marine invertebrate）Hippopodina iririkiensis的野生个体，测量了其生长速率与繁殖产出（reproductive output），并在其本地群落的自然演替（succession）范围内设置了重复样地。在该演替范围内，群体生长速率存在表型变异，但并非所有这类变异都可供选择作用靶向，也并非总能如预期般成为选择的目标。尽管生长速率的表型与遗传变异的维持常被归因于快速生长的演化代价，但本研究强调，贯穿生活史全程且跨环境的波动选择压力（fluctuating selection pressures），可能在该变异维持过程中发挥重要作用。