Reproductive individuality of clonal fish raised in identical environments and its link to early-life behavioral individuality

Genetic and environmental differences are by far the most studied drivers underlying phenotypic variation. However, a growing number of studies finds among-individual variation that is unexplained by genetic or apparent environmental differences. Up to now, it remains an open question whether such seemingly stochastic variation has fitness consequences. To address this question, we performed a tightly controlled long-term life-history experiment with naturally clonal fish (Poecilia formosa) separated directly after birth into near-identical environments. Maintaining highly standardized conditions for 280 days, we first recorded individuals for 10 hours per day over the first 28 days of their lives, characterizing early-life behavioral profiles (activity and feeding behavior). We then measured the complete reproductive profiles of these individuals over an average of 4.5 successive broods per individual, quantifying in total 2522 offspring from 152 broods. Standard lengths of focal individuals were measured once a week. We estimated the growth coefficient (K), maximum predicted (i.e., asymptotic) size (Linf), and predicted size at parturition for each focal individual by fitting individual von Bertalanffy growth curves.

迄今为止，遗传与环境差异是学界研究最为深入的表型变异（phenotypic variation）驱动因子。然而，越来越多的研究观测到一类个体间变异无法通过遗传或可观测的环境差异得到解释。直至今日，这类看似随机的变异是否会带来适合度（fitness）后果，仍是一个尚未解决的开放性科学问题。为解答这一科学问题，我们以天然克隆鱼——亚马逊花鳉（Poecilia formosa）为实验材料，开展了严格可控的长期生活史（life-history）实验：在幼鱼出生后即刻将其分配至近乎一致的饲养环境中。在高度标准化的饲养条件下连续饲养280天，我们首先在幼鱼出生后的前28天内，每日对个体进行10小时的行为记录，以此表征其早期行为谱（behavioral profiles，涵盖活动与摄食行为）。随后，我们针对每尾个体平均4.5胎的连续繁殖周期，完整记录其繁殖谱（reproductive profiles），累计统计了152胎共计2522尾幼鱼。我们每周测量一次受试个体的标准体长（standard length）。通过拟合受试个体的冯·贝塔朗菲生长曲线（von Bertalanffy growth curves），我们估算出每尾受试个体的生长系数（K）、理论渐近最大体长（Linf）以及产仔（parturition）时的预测体长。