Environmental Sciences Graduate Program, Oregon State University, Corvallis, OR, 97331, USA.
Department of Fisheries and Wildlife, Oregon State University, Corvallis, OR, 97331, USA.
Sci Rep. 2020 Oct 1;10(1):16271. doi: 10.1038/s41598-020-73206-w.
Invasive species pose a major threat to global biodiversity. The effects of invasive species can be strongly influenced and potentially mediated by their reproductive characteristics, such as fecundity, egg production, and duration and number of reproductive events. Selection for smaller body size at first reproduction can also play a role in their establishment, facilitating colonization and spread. The American bullfrog, native to the eastern U.S. (Lithobates catesbeianus), is a species that has invaded more than 40 countries across 4 continents. This species has become especially prevalent in the western United States since its introduction in the early 1900s. This study characterized reproductive characteristics of bullfrogs with emphasis on the minimum size at which males and females reach sexual maturity in the Willamette Valley, Oregon, USA invasion range. We collected and dissected 121 individuals in 2013 and 2017, quantifying characteristics of sexual maturity including snout-vent length, total length, sex, tympanum diameter, presence of distended oviducts or eggs for females, and testes length and sperm activity in males. Our results showed that the minimum reproductive size of both males and females was smaller relative to bullfrogs in their native range as well as in populations across their invasive range. Reduction in size at reproductive maturity is likely impacting the invasive success of American bullfrogs and this study gives us insight on management actions to control the invasion. Applying this insight, managers can adjust their definition of reproductively active adults, increasing the target population of culling and other control methods.
入侵物种对全球生物多样性构成重大威胁。入侵物种的影响可以通过其繁殖特征（如繁殖力、产卵量以及繁殖事件的持续时间和次数）得到强烈影响和潜在调节。在初次繁殖时选择较小的体型也可以在其建立过程中发挥作用，促进殖民化和传播。美洲牛蛙原产于美国东部（Lithobates catesbeianus），是一种已入侵全球 4 大洲 40 多个国家的物种。自 20 世纪初引入以来，该物种在美国西部尤其普遍。本研究描述了牛蛙的繁殖特征，重点是雄性和雌性在俄勒冈州威拉米特谷（美国）入侵范围内达到性成熟的最小体型。我们在 2013 年和 2017 年收集并解剖了 121 个个体，量化了性成熟的特征，包括吻肛长、全长、性别、鼓膜直径、雌性扩张的输卵管或卵子的存在，以及雄性的睾丸长度和精子活力。我们的结果表明，相对于原产范围内以及整个入侵范围内的牛蛙，雄性和雌性的最小繁殖体型更小。生殖成熟体型的减小可能会影响美洲牛蛙的入侵成功，本研究为我们提供了控制入侵的管理措施的见解。应用这种洞察力，管理者可以调整他们对有生殖能力的成年个体的定义，增加捕杀和其他控制方法的目标种群。
