title: Adaptation to different host plant ages facilitates insect divergence without a host shift.
abstract: Host shifts and subsequent adaption to novel host plants are important drivers of speciation among phytophagous insects. However, there is considerably less evidence for host plant-mediated speciation in the absence of a host shift. Here, we investigated divergence of two sympatric sister elm leaf beetles, Pyrrhalta maculicollis and P. aenescens, which feed on different age classes of the elm Ulmus pumila L. (seedling versus adult trees). Using a field survey coupled with preference and performance trials, we show that these beetle species are highly divergent in both feeding and oviposition preference and specialize on either seedling or adult stages of their host plant. An experiment using artificial leaf discs painted with leaf surface wax extracts showed that host plant chemistry is a critical element that shapes preference. Specialization appears to be driven by adaptive divergence as there was also evidence of divergent selection; beetles had significantly higher survival and fecundity when reared on their natal host plant age class. Together, the results identify the first probable example of divergence induced by host plant age, thus extending how phytophagous insects might diversify in the absence of host shifts.
authors.affiliation: Key Laboratory of Zoological Systematics and Evolution, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, People's Republic of China University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China.
authors.forename: Bin
authors.initials: B
authors.lastname: Zhang
authors.affiliation: Department of Biology, Syracuse University, 107 College Place, Syracuse, NY 13244, USA.
authors.forename: Kari A
authors.initials: KA
authors.lastname: Segraves
authors.affiliation: Key Laboratory of Zoological Systematics and Evolution, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, People's Republic of China xue@ioz.ac.cn.
authors.forename: Huai-Jun
authors.initials: HJ
authors.lastname: Xue
authors.affiliation: Key Laboratory of Zoological Systematics and Evolution, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, People's Republic of China.
authors.forename: Rui-E
authors.initials: RE
authors.lastname: Nie
authors.affiliation: Key Laboratory of Zoological Systematics and Evolution, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, People's Republic of China.
authors.forename: Wen-Zhu
authors.initials: WZ
authors.lastname: Li
authors.affiliation: Key Laboratory of Zoological Systematics and Evolution, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, People's Republic of China yangxk@ioz.ac.cn.
authors.forename: Xing-Ke
authors.initials: XK
authors.lastname: Yang
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D001517:Coleoptera / Q000254:growth & development / Q000502:physiology*; D005247:Feeding Behavior; D005260:Female; D008297:Male; D010058:Oviposition; D018515:Plant Leaves / Q000737:chemistry; D036226:Seedlings; D013045:Species Specificity; D061350:Sympatry; D014197:Trees; D034403:Ulmus
keywords: divergent selection; host-associated divergence; leaf surface wax; performance; preference; speciation