Group-level phenotypes are idiosyncratic yet unpredictable over development in a clonal fish.

Group-level phenotypes in clonal Amazon mollies are initially stable but become highly unpredictable and shuffled during development after 4-5 weeks.

• Why it matters: Understanding how group behaviors develop and change is crucial because they significantly influence individual fitness, yet the origins and stability of these behaviors over time remain unclear.
• What they did: Researchers established replicate groups of genetically identical Amazon mollies and tracked their behavior from birth to 55 days, controlling for genetic and environmental factors to observe developmental trajectories.
• The result: Early in life, group behaviors follow predictable patterns driven by individual differences, but later, social feedback causes group phenotypes to diverge unpredictably, enabling insights into social development dynamics.