Data from: Density drives polyandry and relatedness influences paternal success in the Pacific gooseneck barnacle, Pollicipes elegans

Background: Polyandry is a common mating strategy in animals, increasing female fitness through direct (material) and indirect (genetic) benefits. Most theories about the benefits of polyandry come from studies of terrestrial animals, which have relatively complex mating systems and behaviors; less is known about the potential benefits of polyandry in sessile marine animals, for which potential mates may be scarce and females have less control over pre-copulatory mate choice. Here, we used microsatellite markers to examine multiple paternity in natural aggregations of the Pacific gooseneck barnacle Pollicipes elegans, testing the effect of density on paternity and mate relatedness on male reproductive success.
Results: We found that multiple paternity was very common (79% of broods), with up to five fathers contributing to a brood, though power was relatively low to detect more than four fathers. Density had a significant and positive linear effect on the number of fathers siring a brood, though this relationship leveled off at high numbers of fathers, which may reflect a lack of power and/or an upper limit to polyandry in this species. Significant skew in male reproductive contribution in multiply-sired broods was observed and we found a positive and significant relationship between the proportion of offspring sired and the genetic similarity between mates, suggesting that genetic compatibility may influence reproductive success in this species.
Conclusions: To our knowledge, this is the first study to show high levels of multiple paternity in a barnacle, and overall, patterns of paternity in P. elegans appear to be driven primarily by mate availability. Evidence of paternity bias for males with higher relatedness suggests some form of post-copulatory sexual selection is taking place, but more work is needed to determine whether it operates during or post-fertilization. Overall, our results suggest that while polyandry in P. elegans is driven by mate availability, it may also provide a mechanism for females to ensure fertilization by compatible gametes and increase reproductive success in this sessile species.

研究背景：一妻多夫制（polyandry）是动物界常见的交配策略，可通过直接（物质）与间接（遗传）收益提升雌性的繁殖适合度。当前学界关于一妻多夫制收益的理论多源于陆生动物研究——这类动物拥有相对复杂的交配系统与行为；而对于固着海洋动物而言，其潜在配偶往往较为稀缺，且雌性对交配前配偶选择的控制权较弱，因此学界对一妻多夫制在该类群中可能带来的收益仍知之甚少。本研究借助微卫星标记（microsatellite markers），对太平洋鹅颈藤壶（Pollicipes elegans）自然聚集种群中的多重父权（multiple paternity）现象展开探究，检验种群密度对父权模式的影响，以及配偶亲缘关系对雄性繁殖成功率的作用。
研究结果：本研究发现多重父权现象极为普遍（占79%的抱卵集群），单个抱卵集群最多可由5只雄性父本贡献，但检测到4只以上父本的统计效力相对有限。种群密度对单个抱卵集群的父本数量存在显著正向线性影响，不过当父本数量较多时该关系趋于平缓，这或许反映了检测效力不足，或是该物种一妻多夫制存在上限。此外，本研究观察到多父本抱卵集群中雄性繁殖贡献存在显著偏斜，且子代父本占比与配偶间遗传相似度呈显著正相关，这表明遗传相容性或可影响该物种的繁殖成功率。
研究结论：据我们所知，本研究首次在藤壶类群中发现高水平的多重父权现象；总体而言，P. elegans的父权模式似乎主要由配偶可获得性驱动。针对亲缘关系较高雄性的父权偏好证据表明，该物种存在某种形式的交配后性选择，但尚需更多研究以明确其作用发生于受精过程中还是受精之后。综合来看，本研究结果提示：尽管P. elegans的一妻多夫制由配偶可获得性驱动，但这或许也为雌性提供了一种通过相容性配子完成受精的机制，进而提升该固着物种的繁殖成功率。