Neonatal personality is associated with sex-specific developmental trajectories in a wild mammal

In wild fallow deer (Dama dama), neonatal behavioural reaction and heart rate show repeatable among-individual differences, and male reactivity predicts shorter yearling antlers via reduced early-life growth.

• Why it matters: Animal personality’s developmental origins and links to later traits are unclear, especially whether early behavioural differences persist and shape growth and morphology differently by sex.
• What they did: Over eight years, neonatal heart rate and behavioural reaction plus early-life growth were measured in wild Dama dama, repeatability and among-individual correlations were estimated, and structural equation modelling tested links to yearling male antler length.
• The result: Heart rate and behavioural reaction were repeatable shortly after birth; behavioural reaction correlated negatively with growth in males only, and in males its effects on antlers persisted indirectly through reduced early-life growth.

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