New life in the Dead Sea - ecological speciation of gall inducing insects and their natural enemies

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, 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, behavior 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 along the Dead Sea in Israel. Based on mitochondrial sequence and AFLP analyses, we show that the populations from the two host plants are at an early stage of separation due to geographic and behavioral barriers between them. We did not find assortative mating between the host-associated populations (HAPs), but asymmetry between them was found in host fidelity by ovipositing females and in larval performance on the host-plant. Together with data on levels of attack by natural enemies, our findings suggest that the gall midges shifted from S. asphaltica to S. fruticosa. We conclude that genetic differentiation in Dasyneuriola sp. was possibly triggered by geographic separation and that post-mating ecological barriers currently promote further divergence between the HAPs.