Ellison Christopher K, Burton Ronald S
Marine Biology Research Division 0202, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0202, USA.
Evolution. 2006 Jul;60(7):1382-91.
Electron transport system (ETS) function in mitochondria is essential for the aerobic production of energy. Because ETS function requires extensive interactions between mitochondrial and nuclear gene products, coadaptation between mitochondrial and nuclear genomes may evolve within populations. Hybridization between allopatric populations may then expose functional incompatibilities between genomes that have not coevolved. The intertidal copepod Tigriopus californicus has high levels of nucleotide divergence among populations at mitochondrial loci and suffers F2 hybrid breakdown in interpopulation hybrids. We hypothesize that hybridization results in incompatibilities among subunits in ETS enzyme complexes and that these incompatibilities result in diminished mitochondrial function and fitness. To test this hypothesis, we measured fitness, mitochondrial function, and ETS enzyme activity in inbred recombinant hybrid lines of Tigriopus californicus. We found that (1) both fitness and mitochondrial function are reduced in hybrid lines, (2) only those ETS enzymes with both nuclear and mitochondrial subunits show a loss of activity in hybrid lines, and (3) positive relationships exist between ETS enzyme activity and mitochondrial function and between mitochondrial function and fitness. We also present evidence that hybrid lines harboring mitochondrial DNA (mtDNA) and mitochondrial RNA polymerase (mtRPOL) from the same parental source population have higher fitness than those with mtDNA and mtRPOL from different populations, suggesting that mitochondrial gene regulation may play a role in disruption of mitochondrial performance and fitness of hybrids. These results suggest that disruption of coadaptation between nuclear and mitochondrial genes contributes to the phenomenon of hybrid breakdown.
线粒体中的电子传递系统（ETS）功能对于需氧能量产生至关重要。由于ETS功能需要线粒体和核基因产物之间广泛的相互作用，线粒体和核基因组之间的协同适应可能会在种群中进化。异域种群之间的杂交可能会暴露未共同进化的基因组之间的功能不相容性。潮间带桡足类动物加州虎斑猛水蚤在不同种群的线粒体基因座上具有高水平的核苷酸差异，并且在种群间杂交中会出现F2杂种衰败现象。我们假设杂交会导致ETS酶复合物中亚基之间的不相容性，并且这些不相容性会导致线粒体功能和适应性下降。为了验证这一假设，我们测量了加州虎斑猛水蚤近交重组杂交系的适应性、线粒体功能和ETS酶活性。我们发现：（1）杂交系中的适应性和线粒体功能均降低；（2）只有那些同时具有核亚基和线粒体亚基的ETS酶在杂交系中表现出活性丧失；（3）ETS酶活性与线粒体功能之间以及线粒体功能与适应性之间存在正相关关系。我们还提供证据表明，携带来自相同亲本源种群的线粒体DNA（mtDNA）和线粒体RNA聚合酶（mtRPOL）的杂交系比携带来自不同种群的mtDNA和mtRPOL的杂交系具有更高的适应性，这表明线粒体基因调控可能在杂种线粒体性能和适应性的破坏中起作用。这些结果表明，核基因与线粒体基因之间协同适应的破坏导致了杂种衰败现象。
