This is a Preprint and has not been peer reviewed. This is version 1 of this Preprint.

Born this way: individuality is seeded before birth and robust to environmental stress
Downloads
Authors
Abstract
Consistent individual differences in behavior, known as behavioral individuality, are pervasive across the animal world and have major ecological and evolutionary consequences. Nevertheless, we still have a limited understanding of what drives individuality and how it emerges during ontogeny. Here, we subjected clonal individuals to a ubiquitous yet critical environmental challenge—the threat of predation—to disentangle the developmental mechanisms of individuality. Under such a salient environmental stressor, among-individual differences may collapse or expand depending on whether there is a single or multiple optimal strategies, demonstrating that individuality itself is a developmentally plastic trait. If, however, the environment does not impact among-individual variation, this suggests that individuality is determined before birth. We continuously tracked the behavior of genetically identical fish (Amazon mollies, Poecilia formosa), reared with or without predation stress, from birth through their first month of life. Predation shifted mean-level behaviors, with predator-exposed individuals swimming more slowly and spending more time near their refuges. However, the magnitude of individuality (as evidenced by repeatability) increased similarly over development in both treatments, indicating that individuality crystallizes robustly over time, even under stress and in a vacuum of genetic variation. Predator-reared fish also exhibited greater within-individual variability in refuge use, suggesting increased behavioral flexibility or disrupted developmental canalization in response to stress. Surprisingly, maternal identity, but not maternal behavior, was the strongest predictor of swimming speed, pointing to non-behavioral maternal effects as a key pre-birth source of behavioral variation. Refuge use however was not at all predicted by maternal identity, indicating that major fitness-related behaviors can have entirely different developmental mechanisms. Collectively, we show that individuality persists despite environmental stress and is seeded before birth through non-genetic factors. Even in the face of a shared environmental challenge, the behavioral trajectories of individuals are unique.
DOI
https://doi.org/10.32942/X2ZH27
Subjects
Behavior and Ethology, Ecology and Evolutionary Biology
Keywords
development, animal personality, variance partitioning, developmental plasticity, individual variation, Animal personality, variance partitioning, Developmental plasticity, individual variation
Dates
Published: 2025-09-29 02:34
Last Updated: 2025-09-29 02:34
License
CC BY Attribution 4.0 International
Additional Metadata
Conflict of interest statement:
None
Data and Code Availability Statement:
Data are available upon request
Language:
English
There are no comments or no comments have been made public for this article.