Genetic consequences of many generations of hybridization between divergent copepod populations
Genetic consequences of many generations of hybridization between divergent copepod populations
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DOI：
10.1093/jhered/esi014
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发表时间：
2005-03-01
影响因子：
3.1
通讯作者：
Timmerman, CC
中科院分区：
文献类型：
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作者：
Edmands, S;Feaman, HV;Timmerman, CC
桡足类 Tigriopus californicus 种群之间的杂交通常会导致远交衰退。在这项研究中，复制杂交种群是从来自加利福尼亚州的两个遗传上不同的种群：皇家棕榈树 (RP) 和圣地亚哥 (SD) 之间的第一代回交杂交开始的。相互的 F-1 与 SD 回交，在纯 RP 细胞质或纯 SD 细胞质背景上产生 25% RP/75% SD 核基因的预期起始频率。杂交 1 年（最多 15 代）后，在每个细胞质背景上重复两次，对 7 个微卫星位点进行评分。无论细胞质来源如何，较稀有 RP 等位基因的频率在所有四个重复中均显着增加，产生 0.97（最大值 = 1）的平均杂交度，而不是预期的 0.50。对跨基因座和重复的杂合子过量的明确测试显示出显着的偏差。在所有重复中，只有两个物理连锁标记显示连锁不平衡。随后对亲本群体和早期杂交后代的适应性测定显示，RP 的适应性低于 SD，并且 F-2 分解显着。计算机模拟表明，必须调用选择来解释等位基因频率的变化。总之，这些结果表明，早期世代的杂交劣势被后代的杂交优势所取代。
Crosses between populations of the copepod Tigriopus californicus typically result in outbreeding depression. In this study, replicate hybrid populations were initiated with first generation backcross hybrids between two genetically distinct populations from California: Royal Palms (RP) and San Diego (SD). Reciprocal F-1 were backcrossed to SD, resulting in expected starting frequencies of 25% RP/75% SD nuclear genes on either a pure RP cytoplasmic or a pure SD cytoplasmic background. After 1 year of hybridization (up to 15 generations), seven microsatellite loci were scored in two replicates on each cytoplasmic background. Frequencies of the rarer RP alleles increased significantly in all four replicates, regardless of cytoplasmic source, producing a mean hybridity of 0.97 (maximum = 1), instead of the expected 0.50. Explicit tests for heterozygote excess across loci and replicates showed significant deviations. Only the two physically linked markers showed linkage disequilibrium in all replicates. Subsequent fitness assays in parental populations and early generation hybrids revealed lower fitness in RP than SD, and significant F-2 breakdown. Computer simulations showed that selection must be invoked to explain the shift in allele frequencies. Together, these results suggest that hybrid inferiority in early generations gave way to hybrid superiority in later generations.