Nigenda-Morales Sergio, Flores-Ramírez Sergio, Urbán-R Jorge, Vázquez-Juárez Ricardo
Laboratorio de Ecología Molecular, Departamento de Biología Marina, Universidad Autónoma de Baja California Sur, Carretera al Sur Km. 5.5, La Paz, BCS, México 23080.
J Hered. 2008 Jan-Feb;99(1):14-21. doi: 10.1093/jhered/esm087. Epub 2007 Nov 6.
One of the most isolated populations of fin whales occurs in the Gulf of California (GOC) with 400-800 individuals. This population shows reduced neutral genetic variation in comparison to the North Pacific population and thus might also display limited adaptive polymorphism. We sampled 36 fin whales from the GOC and assessed genetic variation at exon 2 of the major histocompatibility complex class II DQB-1 genes responsible for eliciting immune responses. Three divergent alleles were found with higher nonsynonymous than synonymous substitution rates within the peptide-binding region positions as well as the likely retention of ancient alleles, indicating that positive selection has shaped diversity in this species. Limited levels of nonneutral polymorphism, in addition to previously described low levels of neutral polymorphism, are consistent with the results of previous studies on vertebrate populations that have remained small and demographically stable for a very long time. Such low genetic variation in the GOC fin whales could be explained by 2 demographic scenarios: an ancient isolated population with limited gene flow or a more recent founder event after the last glacial maximum with very restricted gene flow.
灰鲸最孤立的种群之一出现在加利福尼亚湾（GOC），数量为400 - 800头。与北太平洋种群相比，这个种群的中性遗传变异减少，因此可能也表现出有限的适应性多态性。我们从GOC采集了36头灰鲸样本，并评估了主要组织相容性复合体II类DQB - 1基因外显子2的遗传变异，该基因负责引发免疫反应。在肽结合区域位置发现了三个不同的等位基因，非同义替换率高于同义替换率，以及可能保留的古老等位基因，表明正选择塑造了该物种的多样性。除了先前描述的低水平中性多态性外，有限的非中性多态性水平与先前对长期保持小种群且人口统计学稳定的脊椎动物种群的研究结果一致。GOC灰鲸如此低的遗传变异可以用两种人口统计学情景来解释：一个古老的孤立种群，基因流动有限；或者是末次盛冰期之后最近的一次奠基者事件，基因流动非常受限。
