Correlated evolution of the association between aphids and ants and the association between aphids and plants with extrafloral nectaries

Abstract

The evolution of extrafloral nectaries (EFN) and the evolution of ant‐aphid associations may have influenced each other. Published records allowed me to determine whether aphid species are associated with ants and whether they are associated with host plant species with EFNs. On the basis of these results a comparative phylogenetic study was conducted on a subgroup of monoeocious aphid species living above the soil surface. As aphid phylogeny was unresolved below the family level, I analysed two families – Aphididae and Drepanosiphidae – separately. Within each family, a large number of random phylogenies were generated and each random tree was analysed with a standard phylogenetic approach. The results suggest, on the one hand, that being tended by ants increases the likelihood that an aphid species will evolve an association with host plants that produce EFNs, or on the other hand, that aphid species associated with host plants carrying EFNs were more likely than other species to evolve an association with ants. I present two new hypotheses – the host‐selection hypothesis and the host‐sharing hypothesis – to explain these evolutionary patterns. The hypothesis that ant‐attended homopterans may function as EFNs is rejected by the evolutionary patterns found in this study.