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

Recent studies have documented among-individual variation that is unexplained by genetic or apparent environmental differences, but it remains an open question whether such seemingly stochastic variation has fitness consequences. We perform a life-history experiment with naturally clonal fish (Poecilia formosa), separated directly after birth into near-identical (i.e., highly standardized) environments, quantifying 2522 offspring from 152 broods over 280 days. We find that (i) individuals differ consistently in the size of offspring and broods produced over consecutive broods, (ii) these differences are observed even when controlling for trade-offs between brood size, offspring size and reproductive onset, indicating individual differences in life-history productivity and (iii) early-life behavioral individuality in activity and feeding patterns, with among-individual differences in feeding being predictive of growth, and consequently offspring size. In this work, we provide experimental evidence that processes unexplained by genetic and apparent environmental differences translate into predictable differences in life-history measures and ultimately fitness.