Cascading indirect genetic effects in a clonal vertebrate

Understanding how individual differences arise and how their effects propagate through groups are fundamental issues in biology. Individual differences can arise from indirect genetic effects (IGE): genetically-based variation in the conspecifics with which an individual interacts. Using a clonal species, the Amazon molly (<em>Poecilia formosa</em>), we test the hypothesis that IGE not only occur, but propagate to influence phenotypes of the individuals that do not experience them firsthand. We tested this hypothesis by exposing genetically identical Amazon mollies, reared under identical conditions, to conspecific social partners of different clonal lineages, and then moving these focal individuals to new social groups in which they were the only member to have experienced the IGE. We found that genetically different social environments resulted in the focal animals experiencing different levels of aggression, and that these IGE carried over into new social groups to influence the behavior of naïve individuals. These data reveal that IGE can cascade beyond the individuals that experience them. Opportunity for cascading IGE is ubiquitous, especially in species with long-distance dispersal or fission-fusion group dynamics. Expansion of the quantitative-genetic IGE framework to include cascading and other types of carry-over effects will improve current understanding of social behavior and its evolution.

探究个体差异的产生机制及其在种群中的传播效应，是生物学领域的核心基础问题。个体差异可源于间接遗传效应（indirect genetic effects, IGE）：即与个体互动的同种个体间存在基于遗传的变异。本研究以克隆繁殖物种亚马逊花鳉（<em>Poecilia formosa</em>）为实验对象，验证了如下假说：间接遗传效应不仅存在，还可传播并影响未直接接触该效应的个体的表型。我们通过如下实验验证该假说：将饲养条件完全一致的遗传同质亚马逊花鳉，暴露于不同克隆谱系的同种社交伙伴中；随后将这些目标个体转移至全新的社交群体中，此时群体内仅该目标个体曾接触过间接遗传效应。实验结果表明，遗传背景各异的社交环境会使目标个体遭受不同程度的攻击行为，且此类间接遗传效应可延续至新的社交群体中，进而影响未接触过该效应的个体的行为表现。本研究数据证实，间接遗传效应可突破直接接触个体的范围，产生级联传播效应。级联型间接遗传效应的发生场景无处不在，尤其在具备长距离扩散能力或分裂-融合型群体动态的物种中更为普遍。将量化遗传框架拓展至涵盖级联效应及其他类型的延续效应，将有助于深化我们对社交行为及其演化的现有认知。