Combined use of mitochondrial and nuclear genetic markers further reveal immature marine turtle hybrids along the South Western Atlantic

Abstract Marine turtle hybridization is usually sporadic and involves reports of only a few individuals; however, Brazilian populations have high hybridization rates. Here we investigated the presence of hybrids in morphologically identified immature hawksbills (Eretmochelys imbricata) along the South Western Atlantic (SWA). We sequenced one mitochondrial (D-Loop) and three nuclear DNA (RAG1, RAG2, and CMOS) markers to better understand the patterns and characteristics of hybrids. We identified 22 hybrids (n = 270), 11 of them at the extreme South of the SWA. Uruguay had the highest hybrid frequency in the SWA (~37.5%) followed by southern Brazil with 30%. These are common areas for loggerheads (Caretta caretta) but uncommon for hawksbills, and these hybrids may be adopting the behavior of loggerheads. By analyzing nuclear markers, we can infer that 50% of the sampled hybrids are first generation (F1) and 36% are the result of backcrosses between hybrids and pure E. imbricata (> F1). We also report for the first time immature E. imbricata x Lepidochelys olivacea hybrids at the Brazilian coast. Considering the high frequency of hybrids in the SWA, continuous monitoring should be performed to assess the fitness, genetic integrity, and extent of changes in the gene pools of involved populations.

摘要：海龟杂交事件通常呈散发性，既往相关报道仅涉及少量个体，但巴西海域的海龟种群却表现出较高的杂交率。本研究针对西南大西洋（South Western Atlantic, SWA）海域内经形态学鉴定的未成熟玳瑁（Eretmochelys imbricata）个体，开展杂交个体检测分析。我们通过测序1个线粒体（D-Loop）标记与3个核DNA（RAG1、RAG2及CMOS）标记，以深入解析杂交个体的遗传模式与特征。本次研究共检出22例杂交个体（总样本量n=270），其中11例分布于西南大西洋最南端海域。乌拉圭的杂交个体检出率在西南大西洋海域中居首（约37.5%），其次为巴西南部海域（30%）。该海域为蠵龟（Caretta caretta）的典型栖息分布区，但玳瑁在此区域较为少见，推测这些杂交个体或许具备了蠵龟的行为习性。通过核标记分析，我们推断本次采样的杂交个体中，50%为第一代杂交个体（F1），36%为杂交个体与纯合玳瑁（Eretmochelys imbricata）回交所产生的后代（>F1）。本研究还首次在巴西沿岸报道了未成熟的玳瑁（Eretmochelys imbricata）与丽龟（Lepidochelys olivacea）的杂交个体。鉴于西南大西洋海域较高的杂交个体检出率，需开展持续监测以评估相关种群的适合度、遗传完整性及其基因库的变化程度。