Life-history strategy and behavioral type: risk-tolerance reflects growth rate and energy allocation in ant colonies

Despite the recent interest in animal personality and behavioral syndromes, there is a paucity of explanations for why distinct behavioral traits should evolve to correlate. We investigate whether such correlations across apparently distinct behavioral traits may be explained by variation in life history strategy among individual ant colonies. Life history theory predicts that the way in which individuals allocate energy towards somatic maintenance or reproduction drives several distinct traits in physiology, morphology, and energy use; it also predicts that an individual's willingness to engage in risky behaviors should depend on reproductive strategy. We use Temnothorax ants, which have been shown to exhibit ‘personalities’ and a syndrome that may reflect risk tolerance at the colony level. We measure colonies' relative investment in growth rate (new workers produced) compared to reproductive effort (males and queens produced). Comparing sterile worker production to reproductive alate production provides a direct measure of how colonies are investing their energy, analogous to investment in growth versus reproduction in a unitary organism. Consistently with this idea, we found that behavioral type of ant colonies was associated with their life history strategy: risk-tolerant colonies grew faster and invested more in reproduction, whereas risk-averse colonies had lower growth rate but invested relatively more in workers. This provides evidence that behavioral syndromes can be a consequence of life-history strategy variation, linking the two fields and supporting the use of an integrative approach.

尽管近年来学界对动物个性与行为综合征的研究兴趣日益浓厚，但针对为何不同的行为性状会演化出相关性，目前仍缺乏充分的解释。本研究旨在探究这些看似迥异的行为性状间的相关性，是否可通过单个蚁群的生活史策略差异得到解释。生活史理论预测，个体将能量分配至躯体维持或繁殖的方式，会塑造其生理、形态与能量利用模式下的多种性状；同时该理论还指出，个体参与风险性行为的意愿，应与其繁殖策略相关联。本研究以Temnothorax蚁（凹头蚁属）为研究对象，已有研究表明该类蚂蚁的蚁群具备‘个性’特征，且存在可反映蚁群层面风险耐受度的行为综合征。我们对比测量了蚁群在生长速率（即新增工蚁产出）与繁殖投入（即产生雄蚁与处女蚁后）两方面的相对资源分配。将不育工蚁产出与有翅生殖蚁产出进行对比，可直接量化蚁群的能量分配模式，这与单体生物在生长与繁殖间的资源投资逻辑相似。与上述理论预期一致，本研究发现蚁群的行为类型与其生活史策略显著相关：风险耐受型蚁群生长速率更快，且对繁殖的投入更高；而风险规避型蚁群生长速率较低，但对工蚁培育的相对投入更多。该研究结果表明，行为综合征可由生活史策略的差异所导致，这为连接动物个性与生活史理论两个研究领域提供了实证支持，并佐证了整合研究方法的应用价值。