Mate Preference of Female Blue Tits Varies with Experimental Photoperiod

Organisms use environmental cues to time their life-cycles and among these cues, photoperiod is the main trigger of reproductive behaviours such as territory defence or song activity. Whether photoperiod is also important for another behaviour closely associated with reproduction, mate choice, is unknown. In many bird species, mate choice occurs at two different times during the annual cycle that strongly differ in daylength: in late winter when photoperiod is short and social mates are chosen, and again around egg-laying when photoperiod is longer and extra-pair mates are chosen. This duality makes the role that photoperiod plays on mate choice behaviours intriguing. We investigated the effect of photoperiod on mate choice using three experimental photoperiodic treatments (9 L:15 D, 14 L:10 D, 18 L:6 D), using blue tits (Cyanistes caeruleus) as a biological model. We show that female choice was stronger under long photoperiods. In addition, female blue tits spent significantly more time near males with long tarsi and long wings. This latter preference was only expressed under long photoperiods, suggesting that some indices of male quality only become significant to females when they are strongly photostimulated, and therefore that females could select their social and extra-pair mates based on different phenotypic traits. These results shed light on the roles that photoperiod may play in stimulating pair-bonding and in refining female selectivity for male traits.

生物依赖环境信号调控生命周期时序，而在各类环境信号中，光周期（photoperiod）是触发领地防御、鸣唱活动等繁殖行为的核心诱因。目前尚不清楚光周期对另一种与繁殖紧密相关的行为——配偶选择（mate choice）——是否同样重要。诸多鸟类物种的配偶选择发生在年周期中两个昼长差异显著的时段：一是在光周期较短的晚冬，此时雌性选择社会配偶；二是在产卵前后，此时光周期更长，雌性选择婚外配偶。这种双重选择模式令光周期在配偶选择行为中所扮演的角色引人关注。本研究以青山雀（Cyanistes caeruleus）为实验模型，设置三种光周期处理组（9 L:15 D、14 L:10 D、18 L:6 D），探究光周期对配偶选择的影响。实验结果表明，雌性配偶选择偏好会在较长光周期下显著增强。此外，雌性青山雀会在跗跖修长、翅长较长的雄性个体附近花费更多时间。该偏好仅在长光周期条件下才会显现，这意味着部分雄性质量指标仅在雌性受到较强光周期刺激时才会被雌性纳入考量；由此推测，雌性可基于不同的表型特征分别选择社会配偶与婚外配偶。本研究结果阐明了光周期在促进配对结合以及强化雌性对雄性表型的选择偏好中可能发挥的作用。