Tymchuk Wendy E, Sundström L Fredrik, Devlin Robert H
Department of Zoology, University of British Columbia, 6270 University Boulevard, Vancouver, British Columbia V6T 1Z4, Canada.
Evolution. 2007 May;61(5):1225-37. doi: 10.1111/j.1558-5646.2007.00102.x.
The purpose of this study was to examine, using a rainbow trout (Oncorhynchus mykiss) model system, the fitness consequences of three generations of introgression of genotypes adapted to two different environments (culture and nature). The experiments also isolated the influence of competitive interactions and risk of predation on the relative growth and survival of the wild and backcrossed lines. Line crosses representing fast-growing pure domestic (D), slow-growing pure wild (W), domestic x wild hybrids (F1), F1 x wild backcrosses (B1), and B1 x wild backcrosses (B2) were generated and reared under (1) culture conditions, (2) seminatural conditions with competition among genotypes, and (3) seminatural conditions under risk of predation. Survival of the fry in a seminatural environment with competition fit an additive model of gene action with the domestic fish having the highest survival and the wild fish the lowest, but under risk of predation outbreeding depression was suggested by low survival of the B2 lines. Evidence of a trade-off in growth and survival under risk of predation along with observations of genetically determined behavioral differences among the strains may provide some explanation for the observed differences in survival among the strains. This information is relevant to improving our evolutionary understanding of the interaction among genomes, and the influence of environment, during hybridization events. Results from this experiment indicate that alteration of phenotype likely played a prominent role in the reduced fitness experienced by progeny produced after three generations of introgression, supporting the theory that disruption of genotypes selected for adaptation to local conditions may be a primary cause of outbreeding depression in species such as salmon.
本研究的目的是利用虹鳟（Oncorhynchus mykiss）模型系统，研究适应两种不同环境（养殖和自然环境）的基因型三代渐渗的适合度后果。实验还分离出竞争相互作用和捕食风险对野生和回交品系相对生长和存活的影响。构建了代表快速生长的纯养殖品系（D）、缓慢生长的纯野生品系（W）、养殖×野生杂交种（F1）、F1×野生回交种（B1）以及B1×野生回交种（B2）的品系杂交组合，并在以下条件下饲养：（1）养殖条件；（2）基因型间存在竞争的半自然条件；（3）存在捕食风险的半自然条件。在存在竞争的半自然环境中，鱼苗的存活符合基因作用的加性模型，养殖鱼的存活率最高，野生鱼的存活率最低，但在存在捕食风险的情况下，B2品系的低存活率表明出现了远交衰退。捕食风险下生长与存活之间权衡的证据，以及各品系间遗传决定的行为差异观察结果，可能为各品系间观察到的存活差异提供一些解释。这些信息对于增进我们对杂交事件中基因组间相互作用以及环境影响的进化理解具有重要意义。本实验结果表明，表型改变可能在三代渐渗后产生的后代适合度降低中起了重要作用，支持了这样一种理论，即适应本地条件的基因型受到破坏可能是鲑鱼等物种远交衰退的主要原因。
