Standing geographic variation in eclosion time and the genomics of host race formation in Rhagoletis pomonella fruit flies
Standing geographic variation in eclosion time and the genomics of host race formation in Rhagoletis pomonella fruit flies
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DOI：
10.1002/ece3.4758
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发表时间：
2019-01-01
影响因子：
2.6
通讯作者：
Feder, Jeffrey L.
中科院分区：
文献类型：
--
作者：
Doellman, Meredith M.;Egan, Scott P.;Feder, Jeffrey L.
具有高度现存量变异的分类群可能更有可能适应快速的环境变化和经历生态物种形成。在这里，我们描述了10,241个单核苷酸多态在果蝇Rhagoltis pomonella中的地理分化和与寄主相关的分化，以推测侵染山楂(Crataegus spp.)的寄主种群在成虫羽化时间上的站立遗传变异，而不是新的突变，是否在很大程度上促进了它最近转向早实苹果(Malus Home Tica)。在美国中西部从北向南排列的430公里样带上，每个寄主小种内与早熟和晚羽化时间相关的等位基因频率差异与地理遗传变异和寄主小种分化显著相关，在那里寄主小种共同出现。寄主的结果物候是斜生的，苹果树和山楂树在北方结果较早，在南方结果较晚。因此，我们预计与早期羽化相关的等位基因在北方种群中出现的频率更高。在所有四个群体的山楂小种中都观察到了这种模式；然而，苹果小种的等位基因频率模式更为复杂。尽管苹果果蝇一般具有较早的羽化时间和相应的结果物候期，但与较早羽化相关的第2和3号染色体上的等位基因在苹果中的出现频率低于山楂寄主，在所有四个共生地点上都是矛盾的。然而，1号染色体上的基因座在苹果和山楂寄主中的早羽化相关等位基因频率确实高于山楂寄主，这可能是它们较早羽化表型的原因。因此，尽管祖先山楂小种中存在广泛的克隆遗传变异，并促进了寄主向苹果的转移，但关于这种长期变异是如何被选择来产生更早在北方繁殖的苹果蝇种群的细节，还需要进一步研究。
Taxa harboring high levels of standing variation may be more likely to adapt to rapid environmental shifts and experience ecological speciation. Here, we characterize geographic and host-related differentiation for 10,241 single nucleotide polymorphisms in Rhagoletis pomonella fruit flies to infer whether standing genetic variation in adult eclosion time in the ancestral hawthorn (Crataegus spp.)-infesting host race, as opposed to new mutations, contributed substantially to its recent shift to earlier fruiting apple (Malus domestica). Allele frequency differences associated with early vs. late eclosion time within each host race were significantly related to geographic genetic variation and host race differentiation across four sites, arrayed from north to south along a 430-km transect, where the host races co-occur in sympatry in the Midwest United States. Host fruiting phenology is clinal, with both apple and hawthorn trees fruiting earlier in the North and later in the South. Thus, we expected alleles associated with earlier eclosion to be at higher frequencies in northern populations. This pattern was observed in the hawthorn race across all four populations; however, allele frequency patterns in the apple race were more complex. Despite the generally earlier eclosion timing of apple flies and corresponding apple fruiting phenology, alleles on chromosomes 2 and 3 associated with earlier emergence were paradoxically at lower frequency in the apple than hawthorn host race across all four sympatric sites. However, loci on chromosome 1 did show higher frequencies of early eclosion-associated alleles in the apple than hawthorn host race at the two southern sites, potentially accounting for their earlier eclosion phenotype. Thus, although extensive clinal genetic variation in the ancestral hawthorn race exists and contributed to the host shift to apple, further study is needed to resolve details of how this standing variation was selected to generate earlier eclosing apple fly populations in the North.