Metcalf Jessica L, Siegle Matthew R, Martin Andrew P
Department of Ecology and Evolutionary Biology, N122 Ramaley Biology, University of Colorado, Boulder, CO 80309, USA.
J Hered. 2008 Mar-Apr;99(2):149-56. doi: 10.1093/jhered/esm118. Epub 2008 Jan 30.
Newly formed hybrid populations provide an opportunity to examine the initial consequences of secondary contact between species and identify genetic patterns that may be important early in the evolution of hybrid inviability. Widespread introductions of rainbow trout (Oncorhynchus mykiss) into watersheds with native cutthroat trout (Oncorhynchus clarkii) have resulted in hybridization. These introductions have contributed to the decline of native cutthroat trout populations. Here, we examine the pattern of hybridization between introduced rainbow trout and 2 populations of cutthroat trout native to Colorado. For this study, we utilized 7 diagnostic, codominant nuclear markers and a diagnostic mitochondrial marker to investigate hybridization in a population of greenback cutthroat trout (Oncorhynchus clarkii stomias) and a population of Colorado River cutthroat trout (Oncorhynchus clarkii pleuriticus). We infer that cutthroat-rainbow trout hybrid swarms have formed in both populations. Although a mixture of hybrid genotypes was present, not all genotype combinations were detected at expected frequencies. We found evidence that mitochondrial DNA introgression in hybrids is asymmetric and more likely from rainbow trout than from cutthroat trout. A difference in spawning time of the 2 species or differences in the fitness between the reciprocal crosses may explain the asymmetry. Additionally, the presence of intraspecific cytonuclear associations found in both populations is concordant with current hypotheses regarding coevolution of mitochondrial and nuclear genomes.
新形成的杂交种群为研究物种间二次接触的初始后果提供了契机，并有助于识别在杂种不育进化早期可能重要的遗传模式。虹鳟（Oncorhynchus mykiss）被广泛引入到本土有溪鳟（Oncorhynchus clarkii）的流域中，导致了杂交现象的发生。这些引入行为致使本土溪鳟种群数量下降。在此，我们研究了引入的虹鳟与科罗拉多州的2个本土溪鳟种群之间的杂交模式。在本研究中，我们利用7个诊断性的共显性核标记和1个诊断性线粒体标记，对绿背溪鳟（Oncorhynchus clarkii stomias）种群和科罗拉多河溪鳟（Oncorhynchus clarkii pleuriticus）种群中的杂交情况进行调查。我们推断这两个种群中均已形成了溪鳟 - 虹鳟杂交群体。尽管存在杂种基因型的混合，但并非所有基因型组合都以预期频率被检测到。我们发现有证据表明杂种中线粒体DNA渐渗是不对称的，且更有可能来自虹鳟而非溪鳟。这两个物种产卵时间的差异或正反交之间适合度的差异可能解释了这种不对称性。此外，在两个种群中发现的种内细胞 - 核关联现象与当前关于线粒体和核基因组共同进化的假说相一致。
