Magalhães Sara, Blanchet Elodie, Egas Martijn, Olivieri Isabelle
Laboratoire de Génétique et Environnement, Institut des Sciences de l'Evolution, Université de Montpellier II, Place Eugène Bataillon Bâtiment 22 cc65, 34095 Montpellier, France.
BMC Evol Biol. 2009 Aug 3;9:182. doi: 10.1186/1471-2148-9-182.
Ecological specialization is pervasive in phytophagous arthropods. In such specialization mode, limits to host range are imposed by trade-offs preventing adaptation to several hosts. The occurrence of such trade-offs is inferred by a pattern of local adaptation, i.e., a negative correlation between relative performance on different hosts.
To establish a causal link between local adaptation and trade-offs, we performed experimental evolution of spider mites on cucumber, tomato and pepper, starting from a population adapted to cucumber. Spider mites adapted to each novel host within 15 generations and no further evolution was observed at generation 25. A pattern of local adaptation was found, as lines evolving on a novel host performed better on that host than lines evolving on other hosts. However, costs of adaptation were absent. Indeed, lines adapted to tomato had similar or higher performance on pepper than lines evolving on the ancestral host (which represent the initial performance of all lines) and the converse was also true, e.g. negatively correlated responses were not observed on the alternative novel host. Moreover, adapting to novel hosts did not result in decreased performance on the ancestral host. Adaptation did not modify host ranking, as all lines performed best on the ancestral host. Furthermore, mites from all lines preferred the ancestral to novel hosts. Mate choice experiments indicated that crosses between individuals from the same or from a different selection regime were equally likely, hence development of reproductive isolation among lines adapted to different hosts is unlikely.
Therefore, performance and preference are not expected to impose limits to host range in our study species. Our results show that the evolution of a local adaptation pattern is not necessarily associated with the evolution of an adaptation cost.
生态特化在植食性节肢动物中普遍存在。在这种特化模式下，宿主范围的限制是由权衡取舍造成的，这种权衡阻碍了对多种宿主的适应。这种权衡的发生是通过局部适应模式推断出来的，即不同宿主上的相对表现之间呈负相关。
为了建立局部适应与权衡之间的因果联系，我们以适应黄瓜的种群为起点，在黄瓜、番茄和辣椒上对叶螨进行了实验进化。叶螨在15代内适应了每个新宿主，在第25代时未观察到进一步的进化。发现了局部适应模式，即在新宿主上进化的品系在该宿主上的表现优于在其他宿主上进化的品系。然而，不存在适应成本。实际上，适应番茄的品系在辣椒上的表现与在祖先宿主上进化的品系（代表所有品系的初始表现）相似或更高，反之亦然，例如在替代新宿主上未观察到负相关反应。此外，适应新宿主并未导致在祖先宿主上的表现下降。适应并未改变宿主排名，因为所有品系在祖先宿主上表现最佳。此外，所有品系的叶螨都更喜欢祖先宿主而非新宿主。配偶选择实验表明，来自相同或不同选择体系的个体之间杂交的可能性相同，因此适应不同宿主的品系之间不太可能出现生殖隔离。
因此，在我们的研究物种中，表现和偏好预计不会对宿主范围造成限制。我们的结果表明，局部适应模式的进化不一定与适应成本的进化相关。
