Pace-of-life in a social insect: Behavioral syndromes in ants shift along a climatic gradient

Behavioral syndromes are correlations between behavioral traits, but their selective advantage under different environmental conditions is not well understood. Here, we used the pace-of-life hypothesis to predict how behavioral syndromes could vary along climatic gradients. This hypothesis states that populations experiencing different ecological conditions should differ in suites of physiological characteristics associated with behavioral and life-history traits. We examined the persistence of behavioral syndromes at multiple levels in the ant Temnothorax longispinosus along a climatic gradient in north-eastern USA. "Across populations", we predicted that proactive phenotypes, which show higher activity, aggression and exploration, are more likely to persist in warmer climates. "Within populations", we expected positive associations among proactive behaviors to be more pronounced at warmer sites. Additionally, we measured colony productivity to test whether deviation from the population-level syndrome influences their success, and whether such deviations could vary among populations. Behavioral syndromes clearly occurred across populations, with colonies from warmer environments exhibiting more exploration and foraging but slightly less aggressiveness than colonies from colder sites. However, the presence of behavioral syndromes within sites was population-specific. Positive associations between foraging, exploration and aggression, albeit rarely found, were more pronounced at the warmest sites, whereas negative associations were more common at colder sites. Furthermore, colonies from colder environments showed higher syndrome deviations than colonies from warmer environments, which may be linked to resource limitation and may also negatively affect colony productivity. This study partially corroborates the pace-of-life hypothesis and yields insights into the adaptive value of behavioral syndromes along climatic gradients.