Data from: Chromosome-wide impacts on the expression of incompatibilities in hybrids of Tigriopus californicus

Chromosome rearrangements such as inversions have been recognized previously as contributing to reproductive isolation by maintaining alleles together that jointly contribute to deleterious genetic interactions and postzygotic reproductive isolation. In this study an impact of potential incompatibilities merely residing on the same chromosome is found in crosses of populations of the copepod Tigriopus californicus. When genetically divergent populations of this copepod are crossed, hybrids show reduced fitness and deviations from expected genotypic ratios can be used to determine regions of the genome involved in deleterious interactions. In this study a set of markers is genotyped for a cross of two populations of T. californicus and these markers show widespread deviations from Mendelian expectations with entire chromosomes showing marked skew. Despite the importance of mtDNA/nuclear interactions in incompatibilities in this system in previous studies, in these crosses the expected patterns stemming from these interactions are not widely apparent. Females lack recombination in this species and a striking difference is observed between male and female backcrosses. This suggests that the maintenance of multiple loci on individual chromosomes can enable some incompatibilities, perhaps playing a similar role in the initial rounds of hybridization to chromosomal rearrangements in preserving sets of alleles together that contribute to incompatibilities. Finally, it is observed that candidate pairs of incompatibility regions are not consistently interacting across replicates or subsets of these crosses despite the repeatability of the deviations at many of the single loci themselves, suggesting that more complicated models of Dobzhansky-Muller incompatibilities may need to be considered.

此前学界已证实，染色体倒位等染色体重排可通过维系等位基因的连锁状态，使共同参与有害遗传互作的等位基因得以保留，从而推动合子后生殖隔离的产生。本研究以加州胸刺水蚤（Tigriopus californicus）的种群杂交为研究对象，发现仅位于同一染色体上的潜在不相容位点即可产生显著影响。当该桡足类的遗传分化种群进行杂交时，杂交后代的适合度会降低，而实际基因型比例与孟德尔遗传预期的偏离情况，可用于定位基因组中参与有害遗传互作的区域。本研究对加州胸刺水蚤两个种群的杂交后代开展了一组分子标记的基因分型，结果显示诸多标记均广泛偏离孟德尔遗传预期，整条染色体均呈现显著的等位基因频率偏斜。尽管此前研究表明，该体系中线粒体DNA（mtDNA）与核基因组的互作在不相容机制中发挥关键作用，但本研究的杂交实验中，由这类互作所预期产生的遗传模式并未广泛显现。该物种的雌性个体不存在重组现象，且雄性与雌性回交后代间呈现出极为显著的差异。这表明，单个染色体上多个位点的连锁维系可促成部分遗传不相容，其在杂交初期的作用或与染色体重排类似——通过保留参与不相容互作的等位基因连锁群来发挥功能。最后，尽管诸多单基因座的偏离现象具有可重复性，但本研究的多个杂交重复组与亚组中，候选不相容区域的配对互作模式并不一致，这提示我们需要引入更为复杂的多布赞斯基-穆勒不相容性（Dobzhansky-Muller incompatibilities）模型来阐释相关机制。