Genetic structure of a galling aphid Slavum wertheimae and its host tree Pistacia atlantica across an Irano-Turanian distribution: From fragmentation to speciation?

The Irano-Turanian distribution zone in the Levant crossroad is fragmented along different phyto- and zoogeographic and climatic regions, a relict of wider distribution in moister conditions during the Pleistocene and the Holocene. We examined the effect of the disjunct Irano-Turanian distribution among distinct mesic and xeric habitats on the genetic structure of the gall-forming aphid Slavum wertheimae and its obligate host tree Pistacia atlantica in Israel and Jordan. The genetic study included amplified fragment length polymorphism analysis of the trees and aphids and sequence analysis of fragments of the mitochondrial genes cytochrome oxidase I and II (COI and COII) of the aphids. P. atlantica trees did not show any differentiation or genetic structure among climatic regions. S. wertheimae aphids in Israel exhibited two distinct phylogenetic groups, one occupying the mesic region in the north and the other inhabiting the xeric south. The Jordanian aphids clustered within the Israeli northern populations. The results suggest that while the fragmented Irano-Turanian distribution in the Levant does not affect the genetic structure of P. atlantica trees, it promotes genetic differentiation among the aphids' populations and may initiate an allopatric speciation.