Reproductive Ecology and Biology Group, Museo Nacional de Ciencias Naturales (CSIC), c/José Gutiérrez Abascal 2, 28006, Madrid, Spain.
Conserv Biol. 2012 Dec;26(6):1121-9. doi: 10.1111/j.1523-1739.2012.01916.x. Epub 2012 Aug 16.
The relation among inbreeding, heterozygosity, and fitness has been studied primarily among outbred populations, and little is known about these phenomena in endangered populations. Most researchers conclude that the relation between coefficient of inbreeding estimated from pedigrees and fitness traits (inbreeding-fitness correlations) better reflects inbreeding depression than the relation between marker heterozygosity and fitness traits (heterozygosity-fitness correlations). However, it has been suggested recently that heterozygosity-fitness correlations should only be expected when inbreeding generates extensive identity disequilibrium (correlations in heterozygosity and homozygosity across loci throughout the genome). We tested this hypothesis in Mohor gazelle (Gazella dama mhorr) and Iberian lynx (Lynx pardinus). For Mohor gazelle, we calculated the inbreeding coefficient and measured heterozygosity at 17 microsatellite loci. For Iberian lynx, we measured heterozygosity at 36 microsatellite loci. In both species we estimated semen quality, a phenotypic trait directly related to fitness that is controlled by many loci and is affected by inbreeding depression. Both species showed evidence of extensive identity disequilibrium, and in both species heterozygosity was associated with semen quality. In the Iberian lynx the low proportion of normal sperm associated with low levels of heterozygosity was so extreme that it is likely to limit the fertility of males. In Mohor gazelle, although heterozygosity was associated with semen quality, inbreeding coefficient was not. This result suggests that when coefficient of inbreeding is calculated on the basis of a genealogy that begins after a long history of inbreeding, the coefficient of inbreeding fails to capture previous demographic information because it is a poor estimator of accumulated individual inbreeding. We conclude that among highly endangered species with extensive identity disequilibrium, examination of heterozygosity-fitness correlations may be an effective way to detect inbreeding depression, whereas inbreeding-fitness correlations may be poor indicators of inbreeding depression if the pedigree does not accurately reflect the history of inbreeding.
近亲繁殖、杂合性和适合度之间的关系主要在杂交种群中进行了研究，而在濒危种群中对这些现象知之甚少。大多数研究人员得出的结论是，从系谱中估计的近亲繁殖系数与适合度特征（近亲繁殖与适合度的相关性）之间的关系比标记杂合性与适合度特征（杂合性与适合度的相关性）之间的关系更好地反映了近亲繁殖的衰退。然而，最近有人提出，只有当近亲繁殖产生广泛的同质性不平衡（整个基因组中各个基因座的杂合性和纯合性之间的相关性）时，才应该期望存在杂合性与适合度的相关性。我们在Mohor 瞪羚（Gazella dama mhorr）和伊比利亚猞猁（Lynx pardinus）中检验了这一假设。对于 Mohor 瞪羚，我们计算了近亲繁殖系数，并测量了 17 个微卫星基因座的杂合性。对于伊比利亚猞猁，我们测量了 36 个微卫星基因座的杂合性。在这两个物种中，我们估计了精液质量，这是一个与适合度直接相关的表型特征，受许多基因座控制，并受到近亲繁殖衰退的影响。这两个物种都表现出广泛的同质性不平衡的证据，而且在这两个物种中，杂合性都与精液质量有关。在伊比利亚猞猁中，与低水平杂合性相关的正常精子比例如此之低，以至于很可能限制雄性的生育能力。在 Mohor 瞪羚中，尽管杂合性与精液质量有关，但近亲繁殖系数却没有。这一结果表明，当基于一个在长期近亲繁殖历史之后开始的家谱来计算近亲繁殖系数时，该系数不能捕捉到以前的人口信息，因为它是个体近亲繁殖积累的一个很差的估计值。我们得出的结论是，在具有广泛同质性不平衡的高度濒危物种中，检查杂合性与适合度的相关性可能是检测近亲繁殖衰退的有效方法，而如果系谱不能准确反映近亲繁殖的历史，则近亲繁殖与适合度的相关性可能是近亲繁殖衰退的不良指标。
