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.