Lohay George G, Lee Derek E, Wu-Cavener Lan, Pearce David L, Hou Xiaoyi, Bond Monica L, Cavener Douglas R
Biology Department Penn State University University Park Pennsylvania USA.
Research Innovation for the Serengeti Ecosystem, Grumeti Fund Mara Tanzania.
Ecol Evol. 2023 Jun 12;13(6):e10160. doi: 10.1002/ece3.10160. eCollection 2023 Jun.
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.
在过去三十年里，马赛长颈鹿的数量从7万头减少到了3.5万头，并于2019年被国际自然保护联盟宣布为濒危亚种。现存的马赛长颈鹿在地理上被坦桑尼亚和肯尼亚境内格雷戈里裂谷悬崖（GRE）的陡峭悬崖分隔开来，分成了两个种群，一个在GRE以西，一个在GRE以东。GRE的悬崖对东西方向的扩散和基因流动构成了巨大障碍，而穿越GRE的为数不多的自然走廊也被人类定居点占据。为了评估GRE对马赛长颈鹿基因流动的影响，我们检测了坦桑尼亚北部GRE以东（塔兰吉雷生态系统）和以西（塞伦盖蒂生态系统）种群的核DNA和线粒体DNA（mtDNA）变异的全基因组序列。来自mtDNA变异（衡量雌性介导的基因流动）的证据表明，在过去约28.9万年里，雌性没有在塞伦盖蒂和塔兰吉雷生态系统的种群之间穿越GRE迁移。与mtDNA变异相比，对核DNA变异的分析表明，雄性介导的穿越GRE的基因流动发生得更近，但在几千年前就停止了。我们的研究结果表明，马赛长颈鹿被分成了两个种群，符合被指定为不同进化显著单元（ESU）的标准，我们将其分别称为西部马赛长颈鹿和东部马赛长颈鹿。虽然在GRE上建立长颈鹿扩散走廊不切实际，但保护工作应集中在维持这两个种群各自内部种群之间的连通性上。我们发现这些马赛长颈鹿种群中的一些近亲繁殖系数很高，这可能会导致小而分散的种群出现近亲繁殖衰退，这凸显了这些保护工作的重要性。
