Host-associated differentiation (HAD) is widely recognized as a step towards speciation in phytophagous insects because adaptations to different host plants often lead to reproductive isolation. Various pre-mating and post-mating barriers can reduce gene flow between host-associated populations (HAPs), but establishing their relative contribution and the order in which they took effect during speciation is difficult, because thorough information is needed on past and present distribution ranges, behaviour and life history of the taxa involved. We investigated evidence for HAD in the gall-midge Dasyneuriola sp., which induces bud galls on the parapatric desert shrubs Suaeda fruticosa and Suaeda asphaltica in Israel. Based on mitochondrial sequence and amplified fragment length polymorphism analyses, we show that the populations from the two host plants are at an early stage of separation resulting from geographic and behavioural barriers between them. There was no assortative mating between the HAPs, but asymmetry between them was found in host fidelity by ovipositing females and in larval performance on the host plants. Together with findings on attack levels by natural enemies, these findings suggest that the original host plant in this system was S. asphaltica. We conclude that genetic differentiation in Dasyneuriola sp. was probably triggered by geographic separation, manifested by altitudinal rather than simple geographic distances, and that ecological barriers currently promote further divergence between the HAPs.
Bibliographical noteFunding Information:
We thank Maya Saar, Levona Bodner, Michaela Kolker, Inbal Tiano, and Alexandra Brodezki for their valuable help in field and laboratory work, Ofer Cohen for help in locating remote Suaeda asphaltica populations, and the staff at the Tel Aviv University Botanical Garden for help in propagating plants for the experiments. We are greatly indebted to Uri Eick, Michael J. Wise, and Jonathan Belmaker for statistical assistance, Roi Dor for advice on the genetic analyses, and Zoya Yefremova, Matthew Buffington, Elijah Talamas, and Richard Askew for the identification of parasitic Hymenoptera. Our sincere thanks go also to Michael J. Wise and six anonymous reviewers for their valuable and insightful comments on earlier versions of this manuscript. This research was supported by the Israel Science Foundation (grant no. 181/13).
© 2017 The Linnean Society of London.
- Assortative mating
- Enemy-free space
- Host fidelity
- Reproductive isolation
ASJC Scopus subject areas
- Ecology, Evolution, Behavior and Systematics