Data from: Large-scale introduction of the Indo-Pacific damselfish Abudefduf viagiensis into Hawai‘i promotes genetic swamping of the endemic congener A. abdominalis

Hybridization in the ocean was once considered rare, a process prohibited by the rapid evolution of intrinsic reproductive barriers in a high-dispersal medium. However, recent genetic surveys have prompted a reappraisal of marine hybridization as an important demographic and evolutionary process. The Hawaiian Archipelago offers an unusual case history in this arena, due to the recent arrival of the widely distributed Indo-Pacific Sergeant (Abudefduf vaigiensis), which is hybridizing with the endemic congener, A. abdominals. Surveys of mtDNA and three nuclear loci across Hawai'i (N = 396, A. abdominalis and N = 314, A. vaigiensis) reveal that hybridization is significantly higher in the human-perturbed southeast archipelago (19.8%), tapering off to 5.9% in the pristine northwest archipelago. While densities of the two species varied throughout Hawai'i, hybridization was highest in regions with similar species densities, contradicting the generalization that the rarity of one species promotes interspecific mating. Our finding of later generation hybrids throughout the archipelago invokes the possibility of genetic swamping of the endemic species. An exaptation, an adaptation with unintended consequences, may explain these findings: the endemic species has transient yellow coloration during reproduction, whereas the introduced species has yellow coloration continuously as adults, in effect a permanent signal of reproductive receptivity. Haplotype diversity is higher in Hawaiian A. vaigiensis than in our samples from the native range, indicating large-scale colonization almost certainly facilitated by the historically recent surge of marine debris. In this chain of events, marine debris promotes colonization, exaptation promotes hybridization, and introgression invokes the possible collapse of an endemic species.

海洋杂交现象曾被视作罕见事件，是高扩散介质中内在生殖屏障快速演化所抑制的过程。然而，近期的遗传学调查促使学界重新评估海洋杂交的重要性，将其视为关键的种群动态与演化过程。夏威夷群岛为该研究领域提供了一个非同寻常的案例：近期广泛分布的印度-太平洋豆娘鱼（Indo-Pacific Sergeant，*Abudefduf vaigiensis*）抵达该海域，并与特有近缘种夏威夷豆娘鱼（*Abudefduf abdominalis*，原文笔误为A. abdominals）发生杂交。对夏威夷群岛全境的线粒体DNA（mtDNA）与3个核基因位点的调查（样本量：夏威夷豆娘鱼N=396，印度-太平洋豆娘鱼N=314）显示，受人类活动干扰的东南部群岛杂交率显著更高（19.8%），并向未受干扰的西北部群岛逐渐降至5.9%。尽管两种豆娘鱼的种群密度在夏威夷各处存在差异，但杂交率在两种群密度相近的区域达到峰值，这与"单一物种的稀有性会促进种间交配"的通用结论相悖。我们在整个群岛中均发现了多世代杂交个体，这提示特有种存在遭遇遗传淹没（genetic swamping）的可能性。副适应（exaptation，即附带非预期后果的适应性特征）或可解释上述发现：特有种夏威夷豆娘鱼仅在繁殖期呈现暂时性黄色体色，而引入种印度-太平洋豆娘鱼的成体则始终保持黄色体色，本质上是永久性的繁殖接受性信号。夏威夷种群的印度-太平洋豆娘鱼单倍型多样性高于我们在其原生分布区采集的样本，表明其大规模定殖几乎肯定得益于近期海洋垃圾数量激增的助力。在这一事件链中，海洋垃圾促进物种定殖，副适应推动杂交发生，而基因渐渗（introgression）则可能引发特有物种的种群崩溃。