Abstract

Hybridisation between invasive and native species represents a significant threat to biodiversity. The Mallard Duck (Anas platyrhynchos) is known to hybridise with numerous closely related Anas species in regions where they have been introduced, threatening the genetic integrity of native ducks and in some instances contributing to their extinction risk. Mallard Ducks were introduced into South Africa in the 1940s and are now naturalised and widespread in the country. It has been speculated that Mallard Ducks are hybridising with native Yellow-billed Ducks (A. undulata) in South Africa, but evidence for this remains observational or purely anecdotal. Here we use data from nuclear microsatellite markers and mitochondrial DNA sequencing to show that hybridisation is indeed occuring between these two species. We found evidence for the occurance of hybridisation, mostly as crosses between Mallard Duck hens and Yellow-billed Duck drakes. Surprisingly, our results suggest that introgressive hybridisation is primarily occuring into the invasive Mallard Duck population (mostly Mallard Duck backcrosses were detected), evidenced by directionally-skewed gene flow and sex-biased mating. Whether these findings reflect true assortative mating or a case of Haldane’s rule remains unknown. We also found evidence of high connectivity between Yellow-billed Duck populations, as far as 1000 km apart, in South Africa. Taken together these results suggest that hybrid genotypes can disperse over vast distances between populations and lead to genetic pollution, even in the absence of invasive Mallard Ducks. Active management of Mallard Duck populations has been met by public resistance in some areas in South Africa, partly because of a lack of evidence showing clear impacts by these birds. This study provides some of the first scientifically-documented evidence for such impacts.

中文翻译：

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南非入侵野鸭与本地黄嘴鸭杂交的发生率和杂交程度

摘要

入侵物种与本地物种之间的杂交对生物多样性构成了重大威胁。绿头野鸭（Anas platyrhynchos）在引入它们的地区与许多密切相关的Anas物种杂交，这威胁到野鸭的遗传完整性，并在某些情况下加剧了它们的灭绝风险。绿头野鸭在1940年代被引入南非，现已在该国归化并广泛传播。据推测，野鸭鸭正与本地的黄嘴鸭（A. undulata）杂交。），但有关证据仍为观察性或纯属轶事。在这里，我们使用来自核微卫星标记和线粒体DNA测序的数据来显示这两个物种之间确实发生了杂交。我们发现发生杂交的证据，主要是绿头野鸭母鸡和黄嘴野鸭杂交后代。出乎意料的是，我们的研究结果表明，渗入性杂交主要发生在侵入性野鸭种群中（主要检测到了野鸭回交），这通过方向偏向的基因流和性别偏向的交配得以证明。这些发现是否反映了真正的配偶交配或哈丹规则的情况仍然未知。我们还发现，在南非，相距1000公里的黄嘴鸭种群之间存在高度的联系。综上所述，这些结果表明，即使在没有侵入性绿头鸭的情况下，杂种基因型也可以分散在种群之间的远距离，并导致遗传污染。南非一些地区的公众抵制使积极管理野鸭的种群得到满足，部分原因是缺乏证据表明这些鸟类有明显的影响。这项研究提供了一些有关此类影响的科学证据。