Lifjeld Jan T, Kleven Oddmund, Fossøy Frode, Jacobsen Frode, Laskemoen Terje, Rudolfsen Geir, Robertson Raleigh J
Natural History Museum, University of Oslo, Norway.
Norwegian Institute for Nature Research, Trondheim, Norway.
Behav Ecol Sociobiol. 2022;76(5):61. doi: 10.1007/s00265-022-03170-0. Epub 2022 Apr 23.
In birds with extrapair mating, older males usually have higher fertilization success than younger males. Two hypotheses can potentially explain this pattern: 1) females prefer older, and often more ornamented males, or 2) older males invest more in reproduction and fertility than younger males. Here we studied factors associated with age-related male fertilization success in a population of barn swallows in Canada. We document that male fertilization success increased gradually up to a minimum age of four-year old. The age effect was especially strong for the number of extrapair offspring obtained and the occurrence of a second brood. The higher fertilization success of older males was also associated with an early start of breeding in spring. The length of the elongated outermost tail feathers, a postulated male ornament preferred by females, also increased with age (in both sexes), but it was not a significant predictor of male fertilization success within age classes. Male fertility traits, especially testis size, but also sperm motility and sperm velocity, increased significantly across age groups. Our results suggest that the higher fertilization success by older males is due to their higher reproductive investments and that their longer tails are an adaptation to early arrival on the breeding grounds.
The barn swallow is a socially monogamous passerine with extensive extrapair mating. We found that males become more successful in siring both withinpair and extrapair offspring as they become older. Their increased fertilization success was associated with a higher reproductive effort as indicated by larger testes, more motile sperm, and an earlier start of breeding in spring. The length of the outer tail feathers increased with age in both sexes, but long tails did not enhance male fertilization success among males of the same age. Long tails are probably an adaptation to rapid migration and earlier arrival on the breeding grounds. Our findings suggest that the commonly observed age-related increase in male fertilization success in passerine birds is better explained by life history theory than by sexual selection theory.
The online version contains supplementary material available at 10.1007/s00265-022-03170-0.
在存在配偶外交配的鸟类中，年长雄性通常比年轻雄性具有更高的受精成功率。有两种假说可能解释这种模式：1）雌性更喜欢年长且通常更具装饰性的雄性；2）年长雄性在繁殖和生育方面的投入比年轻雄性更多。在此，我们研究了加拿大一个家燕种群中与雄性年龄相关的受精成功率相关的因素。我们记录到，雄性受精成功率在达到四岁的最低年龄之前逐渐增加。年龄效应在获得的配偶外交配后代数量和第二窝繁殖的发生方面尤为明显。年长雄性较高的受精成功率还与春季较早开始繁殖有关。最外侧延长尾羽的长度，这是一种假定的雌性偏好的雄性装饰，也随年龄增加（两性皆是），但它并非同一年龄组内雄性受精成功率的显著预测指标。雄性生育特征，尤其是睾丸大小，还有精子活力和精子速度，在不同年龄组间显著增加。我们的结果表明，年长雄性较高的受精成功率归因于它们更高的繁殖投入，并且它们更长的尾巴是对较早到达繁殖地的一种适应。
家燕是一种社会性一夫一妻制的雀形目鸟类，有广泛的配偶外交配行为。我们发现，雄性随着年龄增长，在使配偶内和配偶外后代受孕方面变得更加成功。它们受精成功率的提高与更高的繁殖努力相关，表现为睾丸更大、精子活力更强以及春季更早开始繁殖。两性的外侧尾羽长度都随年龄增加，但长尾巴并没有提高同一年龄雄性的受精成功率。长尾巴可能是对快速迁徙和较早到达繁殖地的一种适应。我们的研究结果表明，在雀形目鸟类中普遍观察到的与年龄相关的雄性受精成功率增加，用生活史理论比用性选择理论能更好地解释。
在线版本包含可在10.1007/s002,65 - 022 - 03170 - 0获取的补充材料。
