Mercader R J, Aardema M L, Scriber J M
Department of Entomology, Michigan State University, 243 Natural Sciences Building, East Lansing, MI, 48824, USA.
Oecologia. 2009 Jan;158(4):651-62. doi: 10.1007/s00442-008-1177-9. Epub 2008 Oct 24.
Climate warming has lead to increased genetic introgression across a narrow hybrid zone separating the eastern and Canadian tiger swallowtails (Papilio glaucus and Papilio canadensis). This situation has led to the formation of an allochronically separated hybrid population with a delayed emerging phenotype or "late flight". Here, we assess how the recombination of the parental genomes that lead to this phenotype may have facilitated another major ecological shift, host-use divergence. We first contrast the ovipositional profiles of the late flight population to that of the parental species P. glaucus and P. canadensis. Subsequently we contrast the larval survival and growth of the late flight, a P. canadensis and a P. glaucus population, and a population from the northern edge of the hybrid zone on five hosts. Our results indicate that the ovipositional preference of this hybrid swarm is identical to that of the introgressing parental species, P. glaucus. Due to the absence of the preferred hosts of P. glaucus (Liriodendron tulipifera L. and Ptelea trifoliata L.) where the late flight occurs, this ovipositional pattern implies a functional specialization onto a secondary host of both parental species, Fraxinus americana L. In contrast, the larval host-use abilities represent a mixture of P. glaucus and P. canadensis, indicating divergence in larval host-use abilities has not taken place. However, high genetic variability (genetic coefficient of variation) is present for growth on F. americana in the late flight hybrid swarm and tradeoffs for larval performance on the preferred hosts of the parental species are evident; indicating a strong potential for future specialization in larval host-use abilities. This current scenario represents an instance where a shift in a major ecological trait, host use, is likely occurring as a byproduct of a shift in an unrelated trait (delayed emergence) leading to partial reproductive isolation.
气候变暖导致在分隔东部虎凤蝶和加拿大虎凤蝶（北美黄风蝶和加拿大凤蝶）的狭窄杂交区域内，基因渐渗增加。这种情况导致形成了一个异时性隔离的杂交种群，具有延迟出现的表型或“晚飞”现象。在此，我们评估导致这种表型的亲本基因组重组如何可能促进了另一个主要的生态转变，即寄主利用分化。我们首先将晚飞种群的产卵概况与亲本物种北美黄风蝶和加拿大凤蝶的产卵概况进行对比。随后，我们对比晚飞种群、一个加拿大凤蝶种群、一个北美黄风蝶种群以及杂交区域北缘一个种群在五种寄主上的幼虫存活和生长情况。我们的结果表明，这个杂交群体的产卵偏好与渐渗亲本物种北美黄风蝶的产卵偏好相同。由于晚飞现象出现的地方没有北美黄风蝶的首选寄主（北美鹅掌楸和三叶漆），这种产卵模式意味着在双亲物种的次要寄主美国白蜡树上实现了功能特化。相比之下，幼虫对寄主的利用能力表现为北美黄风蝶和加拿大凤蝶的混合，表明幼虫对寄主的利用能力尚未发生分化。然而，晚飞杂交群体在美国白蜡树上生长时存在高遗传变异性（遗传变异系数），并且在亲本物种的首选寄主上幼虫表现存在权衡；这表明未来幼虫对寄主的利用能力有很强的特化潜力。当前这种情况代表了一个实例，即在一个主要生态特征（寄主利用）的转变可能作为一个不相关特征（延迟出现）转变导致部分生殖隔离所产生的副产品而发生。
