Harrison J S, Edmands S
Marine Biology Research Division, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0202, USA.
J Evol Biol. 2006 Nov;19(6):2040-51. doi: 10.1111/j.1420-9101.2006.01145.x.
Crosses between populations of Tigriopus californicus result in backcross and F2 hybrid breakdown for a variety of fitness related measures. The magnitude of this hybrid breakdown is correlated with evolutionary divergence. We assessed the chromosomal basis of viability differences in nonrecombinant backcross hybrids using markers mapped to individual chromosomes. To assess effects of evolutionary divergence we crossed one population to three different populations: two distantly related (approximately 18% mitochondrial COI sequence divergence) and one closely related (approximately 1% mitochondrial COI sequence divergence). We found that all three interpopulation crosses resulted in significant deviations from expected Mendelian ratios at a majority of the loci studied. In all but one case, deviations were due to a deficit of parental homozygotes. This pattern implies that populations of T. californicus carry a significant genetic load, and that a combination of beneficial dominance and deleterious homozygote-heterozygote interactions significantly affects hybrid viability. Pairwise tests of linkage disequilibrium detected relatively few significant interactions. For the two divergent crosses, effects of individual chromosomes were highly concordant. These two crosses also showed higher heterozygote excess in females than males across the vast majority of chromosomes.
加州虎猛水蚤种群之间的杂交会导致回交和F2杂种在多种与适应性相关的指标上出现衰退。这种杂种衰退的程度与进化分歧相关。我们使用定位到单个染色体的标记，评估了非重组回交杂种中生存力差异的染色体基础。为了评估进化分歧的影响，我们将一个种群与三个不同的种群进行杂交：两个远缘相关种群（线粒体COI序列分歧约为18%）和一个近缘相关种群（线粒体COI序列分歧约为1%）。我们发现，在大多数研究的位点上，所有三个种群间杂交的结果都显著偏离了预期的孟德尔比率。除了一个案例外，所有偏差都是由于亲本纯合子的不足。这种模式意味着加州虎猛水蚤种群携带显著的遗传负荷，有益的显性作用和有害的纯合子 - 杂合子相互作用的组合显著影响杂种生存力。连锁不平衡的成对检验检测到相对较少的显著相互作用。对于两个分歧较大的杂交组合，单个染色体的影响高度一致。在绝大多数染色体上，这两个杂交组合在雌性中也比雄性表现出更高的杂合子过剩。
