Behavioral Ecology and Sociobiology ( IF 1.9 ) Pub Date : 2022-04-23 , DOI: 10.1007/s00265-022-03170-0 Jan T Lifjeld 1 , Oddmund Kleven 1, 2 , Frode Fossøy 1, 2 , Frode Jacobsen 1 , Terje Laskemoen 1, 3 , Geir Rudolfsen 4, 5 , Raleigh J Robertson 6
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Abstract
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 Hirundo rustica 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.
Significance statement
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.
中文翻译：
当年长的男性生育更多的后代时——增加吸引力或更高的生育能力？
摘要
在具有外对交配的鸟类中，年长的雄性通常比年轻的雄性具有更高的受精成功率。有两个假设可以解释这种模式：1) 女性更喜欢年长的，通常更喜欢装饰的男性，或者 2) 年长的男性比年轻的男性在繁殖和生育方面的投资更多。在这里，我们研究了与谷仓燕子Hirundo rustica种群中与年龄相关的雄性受精成功相关的因素在加拿大。我们记录了男性受精成功率逐渐增加，直到最小年龄为 4 岁。对于获得的外对后代的数量和第二个育雏的出现，年龄效应尤其强烈。年长雄性的较高受精成功率也与春季较早开始繁殖有关。拉长的最外层尾羽是女性喜欢的一种假定的雄性装饰物，其长度也随着年龄的增长而增加（在两性中），但这并不是年龄组内雄性受精成功的重要预测因素。男性生育特征，尤其是睾丸大小，以及精子活力和精子速度，在不同年龄组中显着增加。
意义陈述
谷仓燕子是一种社会一夫一妻制的雀形目，具有广泛的外对交配。我们发现，随着年龄的增长，雄性在繁殖配对内和配对外的后代方面变得更加成功。它们增加的受精成功与更高的生殖努力有关，这表现为更大的睾丸、更多的活动精子和更早的春季繁殖开始。外尾羽的长度在两性中都随着年龄的增长而增加，但长尾并没有提高同龄雄性雄性受精的成功率。长尾巴可能是为了适应快速迁徙和较早到达繁殖地。我们的研究结果表明，生活史理论比性选择理论更好地解释了雀形目鸟类雄性受精成功率与年龄相关的普遍增加。
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