Genetic evidence of population subdivision among Masai giraffes separated by the Gregory Rift Valley in Tanzania,Ecology and Evolution

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Genetic evidence of population subdivision among Masai giraffes separated by the Gregory Rift Valley in Tanzania
Ecology and Evolution ( IF 2.3 ) Pub Date : 2023-06-12 , DOI: 10.1002/ece3.10160
George G Lohay _{1,

2} , Derek E Lee _{1,

3} , Lan Wu-Cavener ₁ , David L Pearce ₄ , Xiaoyi Hou ₁ , Monica L Bond _{1,

3,

5} , Douglas R Cavener ₁

Affiliation

The Masai giraffe has experienced a population decline from 70,000 to 35,000 in the past three decades and was declared an endangered subspecies by the IUCN in 2019. The remaining number of Masai giraffe are geographically separated by the steep cliffs of the Gregory Rift escarpments (GRE) in Tanzania and Kenya dividing them into two populations, one west and one east of the GRE. The cliffs of the GRE are formidable barriers to east–west dispersal and gene flow and the few remaining natural corridors through the GRE are occupied by human settlements. To assess the impact of the GRE on Masai giraffe gene flow, we examined whole genome sequences of nuclear and mitochondrial DNA (mtDNA) variation in populations located east (Tarangire ecosystem) and west (Serengeti ecosystem) of the GRE in northern Tanzania. Evidence from mtDNA variation, which measures female-mediated gene flow, suggests that females have not migrated across the GRE between populations in the Serengeti and Tarangire ecosystems in the past ~289,000 years. The analysis of nuclear DNA variation compared to mtDNA DNA variation suggests that male-mediated gene flow across the GRE has occurred more recently but stopped a few thousand years ago. Our findings show that Masai giraffes are split into two populations and fulfill the criteria for designation as distinct evolutionary significant units (ESUs), which we denote as western Masai giraffe and eastern Masai giraffe. While establishing giraffe dispersal corridors across the GRE is impractical, conservation efforts should be focused on maintaining connectivity among populations within each of these two populations. The importance of these efforts is heightened by our finding that the inbreeding coefficients are high in some of these Masai giraffe populations, which could result in inbreeding depression in the small and fragmented populations.

中文翻译：

坦桑尼亚格雷戈里裂谷分离的马赛长颈鹿种群细分的遗传证据

在过去的三十年里，马赛长颈鹿的数量从 70,000 只减少到 35,000 只，并于 2019 年被 IUCN 宣布为濒危亚种。马赛长颈鹿的剩余数量在地理上被格雷戈里裂谷 (GRE) 的陡峭悬崖所分隔。在坦桑尼亚和肯尼亚，将他们分为两个群体，一组位于 GRE 西部，一组位于 GRE 东部。 GRE 的悬崖是东西向传播和基因流动的巨大障碍，穿过 GRE 的仅存的几条自然走廊被人类住区占据。为了评估 GRE 对马赛长颈鹿基因流的影响，我们检查了坦桑尼亚北部 GRE 东部（塔兰吉雷生态系统）和西部（塞伦盖蒂生态系统）种群的核和线粒体 DNA (mtDNA) 变异的全基因组序列。线粒体 DNA 变异（测量雌性介导的基因流）的证据表明，在过去约 289,000 年中，雌性并未在塞伦盖蒂和塔兰吉雷生态系统的种群之间跨越 GRE 进行迁移。对核 DNA 变异与 mtDNA DNA 变异进行比较的分析表明，男性介导的穿过 GRE 的基因流最近才发生，但在几千年前就停止了。我们的研究结果表明，马赛长颈鹿分为两个种群，并且满足指定为不同进化重要单位（ESU）的标准，我们将其称为西部马赛长颈鹿和东部马赛长颈鹿。虽然在整个 GRE 地区建立长颈鹿扩散走廊是不切实际的，但保护工作应集中于维持这两个种群内种群之间的连通性。我们发现一些马赛长颈鹿种群的近交系数很高，这可能导致小而分散的种群的近交衰退，这凸显了这些努力的重要性。

更新日期：2023-06-13

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