Olivieri Isabelle, Singer Michael C, Magalhães Sara, Courtiol Alexandre, Dubois Yvain, Carbonell David, Justy Fabienne, Beldade Patrícia, Parmesan Camille, Michalakis Yannis
Institut des Sciences de l'Evolution, Université Montpellier Montpellier, France.
Integrative Biology, University of Texas Austin, TX, USA.
Evol Appl. 2008 Feb;1(1):112-28. doi: 10.1111/j.1752-4571.2007.00010.x.
Because weevils are used as biocontrol agents against thistles, it is important to document and understand host shifts and the evolution of host-specificity in these insects. Furthermore, such host shifts are of fundamental interest to mechanisms of speciation. The mediterranean weevil Larinus cynarae normally parasitizes either one of two thistle genera, Onopordum and Cynara, being locally monophagous. In Sardinia, however, both host genera are used. We used three types of data to help understand this complex host use: (i) weevil attack rates on the two host genera among 53 different populations in Sardinia and nearby Corsica, (ii) host preference in a lab setting, and (iii) genetic (allozyme) differentiation among weevil populations exploiting the same or different hosts. Using a subset of populations from northern Sardinia, we attempted to relate interpopulation differences in host preference to gene flow among populations by comparing pairwise differences in oviposition preference (Qst) and in allozyme frequencies (Fst). Overall, Qst and Fst were positively correlated. Fst was positively correlated with geographic distance among pairs of populations using the same host, but not among different-host population pairs. As mating occurs on the hosts, this result suggests reinforcement. Genetic evidence indicates Cynara as the ancestral host of the weevils from both islands and our current studies suggest repeated attempts to colonize Onopordum, with a successful shift in Corsica and a partial shift in Sardinia. This scenario would explain why in Sardinia the level of attack was higher on Cynara than on Onopordum and why, when given a choice in the laboratory, Sardinian weevils preferred Cynara even when sampled from Onopordum. The lability of host shifts in L. cynarae supports caution in using these or related weevils as biocontrol agents of exotic thistles.
由于象鼻虫被用作防治蓟类植物的生物防治剂，记录和了解这些昆虫的寄主转移以及寄主特异性的进化非常重要。此外，这种寄主转移对于物种形成机制具有根本意义。地中海象鼻虫Larinus cynarae通常寄生于两个蓟属植物之一，即Onopordum属和Cynara属，在当地是单食性的。然而，在撒丁岛，这两个寄主属都被利用。我们使用了三种类型的数据来帮助理解这种复杂的寄主利用情况：（i）撒丁岛和附近科西嘉岛53个不同种群中象鼻虫对这两个寄主属的攻击率，（ii）实验室环境中的寄主偏好，以及（iii）利用相同或不同寄主的象鼻虫种群之间的遗传（等位酶）分化。我们利用撒丁岛北部的一部分种群，通过比较产卵偏好（Qst）和等位酶频率（Fst）的成对差异，试图将寄主偏好的种群间差异与种群间的基因流联系起来。总体而言，Qst和Fst呈正相关。对于使用相同寄主的种群对，Fst与地理距离呈正相关，但对于不同寄主的种群对则不然。由于交配发生在寄主上，这一结果表明存在强化现象。遗传证据表明Cynara属是来自两个岛屿的象鼻虫的祖先寄主，我们目前的研究表明，象鼻虫多次尝试在Onopordum属植物上定殖，在科西嘉岛成功转移，在撒丁岛部分转移。这种情况可以解释为什么在撒丁岛，Cynara属植物上的攻击水平高于Onopordum属植物，以及为什么在实验室选择时，即使是从Onopordum属植物上采集的撒丁岛象鼻虫也更喜欢Cynara属植物。L. cynarae寄主转移的不稳定性支持在将这些或相关象鼻虫用作外来蓟类植物的生物防治剂时要谨慎。
