Data from: Adaptive shaping of the behavioural and neuroendocrine phenotype during adolescence

Environmental conditions during early life can adaptively shape the phenotype for the prevailing environment. Recently, it has been suggested that adolescence represents an additional temporal window for adaptive developmental plasticity, though supporting evidence is scarce. Previous work has shown that male guinea pigs living in large mixed-sex colonies develop a low-aggressive phenotype as part of a queuing strategy that is adaptive for integrating into large unfamiliar colonies. By contrast, males living in pairs during adolescence become highly aggressive towards strangers. Here, we tested whether the high-aggressive phenotype is adaptive under conditions of low population density, namely when directly competing with a single opponent for access to females. For that purpose, we established groups of one pair-housed male (PM), one colony-housed male (CM) and two females. PMs directed more aggression towards the male competitor and more courtship and mating towards females than did CMs. In consequence, PMs attained the dominant position in most cases and sired significantly more offspring. Moreover, they showed distinctly higher testosterone concentrations and elevated cortisol levels, which probably promoted enhanced aggressiveness while mobilizing necessary energy. Taken together, our results provide the clearest evidence to date for adaptive shaping of the phenotype by environmental influences during adolescence.

生命早期的环境条件可根据所处环境适应性塑造个体表型（phenotype）。近年来有研究提出，青春期是适应性发育可塑性的又一关键时间窗口，但相关佐证证据仍较为匮乏。过往研究表明，饲养于大型混合性别群体中的雄性豚鼠会形成低攻击性表型，这是一种排队策略的组成部分，该策略有助于它们融入陌生的大型群体。与之形成鲜明对比的是，青春期阶段成对饲养的雄性豚鼠会对陌生个体表现出极强攻击性。本研究旨在检验，在低种群密度条件下，即当雄性需与单一竞争对手直接争夺交配权时，高攻击性表型是否具有适应性优势。为此，我们构建了如下实验组：1只成对饲养雄性（PM）、1只群体饲养雄性（CM）以及2只雌性豚鼠。相较于群体饲养雄性（CM），成对饲养雄性（PM）会对雄性竞争对手发起更多攻击行为，同时对雌性豚鼠展现出更多求偶与交配行为。因此，在绝大多数实验组中，成对饲养雄性（PM）均占据主导地位，且其后代数量显著更多。此外，成对饲养雄性（PM）的睾酮浓度与皮质醇水平均显著升高，这或有助于提升攻击性，并调动机体所需的能量储备。综合来看，本研究结果为青春期阶段环境因素对个体表型的适应性塑造提供了迄今为止最为明确的证据。