Do ants drive speciation in aphids? A possible case of ant-driven speciation in the aphid genus Stomaphis Walker (Aphidoidea, Lachninae)

Abstract

Ecological divergence is an accepted mode of speciation in phytophagous insects such as aphids. Adaptations of ancestral populations to various feeding locations on a plant seem to be a promoted mode of such speciation. In this study we present a thesis that for obligatorily myrmecophilous aphids it is a mutualistic relationship with distinct ants that constitutes a significant selective factor. It leads to the separation of ecological niches of ancestral aphid populations and development of sibling species. The thesis is supported by the example of two sibling aphid species of the genus Stomaphis, S. quercus (L.) and S. wojciechowskii Depa, which show very peculiar adaptations to feeding on trees and are both undoubtedly obligatorily myrmecophilous species. Their separateness is proven by mitochondrial markers, as well as their life modes and ecological adaptations: they all follow the biology of their respective ant hosts: Lasius (Dendrolasius) fuliginosus and L. (L.) brunneus. Proven and modelled geographical distributions indicate a high level of sympatry and the fact that environmental requirements of both aphid species overlap. It is suggested that their divergence has resulted from having adapted to living with ants of distinct life modes, foraging strategies and positions in the hierarchy of ant assemblages. This, in turn, indirectly affected their adaptations to exploit different host plant genera.