Data from: Cryptic introductions and the interpretation of island biodiversity

Species with cryptic origins (i.e. those that cannot be reliably classed as native or non-native) present a particular challenge to our understanding of the generation and maintenance of biodiversity. Such species may be especially common on islands given that some islands have had a relatively recent history of human settlement. It is likely that select island species considered native might have achieved their current distributions via direct or indirect human actions. As an example, we explore the origins of eastern bluebirds (Sialia sialis bermudensis) on the island of Bermuda. Considered native to the island and a distinct subspecies, this population has diverged in morphology relative to mainland North America. Using microsatellite markers and simulation of island colonization, we show that the Bermuda population of bluebirds is the likely result of a single colonization event that occurred during the 1600s, making this a cryptic invader. To our knowledge, this is one of the youngest examples of a terrestrial vertebrate cryptic invader. We suggest that the eastern bluebird is not an isolated case of cryptic invader on either Bermuda or elsewhere and that caution be exercised when studying present-day distributions of organisms.

起源隐秘的物种（即无法可靠归类为本土或外来物种的类群），对我们理解生物多样性的产生与维持构成了特殊挑战。鉴于部分岛屿的人类定居史相对较新，这类物种在岛屿上或许尤为常见。部分被认定为本土的岛屿物种，其当前分布格局很可能是通过人类直接或间接活动形成的。
以百慕大群岛的东蓝鸲（Sialia sialis bermudensis）为例，本研究探讨了该物种的起源。该种群曾被认定为百慕大本土的独特亚种，其形态与北美大陆的东蓝鸲已发生分化。
本研究通过微卫星标记与岛屿定殖模拟实验，证实百慕大蓝鸲种群大概率起源于17世纪的单次定殖事件，因此该物种实为隐秘入侵种。据我们所知，这是目前已知最年轻的陆生脊椎动物隐秘入侵种案例之一。
本研究认为，东蓝鸲并非百慕大或其他地区仅有的隐秘入侵物种案例，因此在研究生物当前分布格局时需保持谨慎。