Complex genetic patterns and distribution limits mediated by native congeners of the worldwide invasive red‐eared slider turtle

Non-native (invasive) species offer a unique opportunity to study the geographic distribution and range limits of species, wherein the evolutionary change driven by interspecific interactions between native and non-native closely related species is a key component. The red-eared slider turtle, Trachemys scripta elegans (TSE), has been introduced and successfully established worldwide. It can coexist with its native congeners T. cataspila, T. venusta and T. taylori in Mexico. We performed comprehensive fieldwork, executed a battery of genetic analyses and applied a novel species distribution modeling approach to evaluate their historical lineage relationships and contemporary population genetic patterns. Our findings support the historical common ancestry between native TSE and non-native (TSEalien), while also highlighting the genetic differentiation of the exotic lineage. Genetic patterns are associated with their range size/endemism gradient, the microendemic T. taylori showed significant reduced genetic diversity and high differentiation, whereas TSEalien showed the highest diversity and signals of population size expansion. Counter to our expectations, lower naturally occurring distribution overlap and little admixture patterns were found between TSE and its congeners, exhibiting reduced gene flow and clear genetic separation across neighboring species despite having zones of contact. We demonstrate that these native Trachemys species have distinct climatic niche suitability, likely preventing establishment of and displacement by the TSEalien. Moreover, we found major niche overlap between TSEalien and native species worldwide, supporting our prediction that sites with closer ecological optima to the invasive species have higher establishment risk than those that are closer to the niche-center of the native species.

非本土（入侵）物种为研究物种的地理分布与分布边界提供了独特契机，其中本土与外来近缘物种间的种间相互作用所驱动的演化改变，是该研究领域的核心组成部分。红耳彩龟（Trachemys scripta elegans，简称TSE）已被引入全球多地并成功建立野生种群。在墨西哥，该物种可与本土近缘种T. cataspila、T. venusta及T. taylori共存。本研究开展了全面的野外调查，实施了一系列遗传分析，并应用了全新的物种分布建模方法，以解析它们的历史谱系关系与当代种群遗传格局。研究结果证实，本土红耳彩龟与外来红耳彩龟（TSEalien）拥有共同的历史祖先，同时也凸显了该入侵谱系的遗传分化特征。种群遗传格局与其分布范围大小/特有性梯度密切相关：微特有种T. taylori表现出显著降低的遗传多样性与较高的遗传分化，而TSEalien则呈现出最高的遗传多样性及种群规模扩张的信号。与我们的预期相悖，红耳彩龟与其近缘种之间的自然分布重叠度较低，且几乎未检测到遗传渐渗现象；尽管存在物种接触区域，但相邻物种间的基因流受限，遗传分化清晰。本研究证实，这些本土彩龟属（Trachemys）物种具有独特的气候生态位适宜性，这可能阻碍了TSEalien的种群建立与物种取代。此外，我们发现全球范围内TSEalien与本土物种间存在广泛的生态位重叠，这验证了我们的预测：相较于生态位更贴近本土物种核心生态位的区域，生态位更接近入侵物种最适生态条件的区域，其入侵建立风险更高。