Host‐associated differentiation in a pecan and water hickory Aphidomorpha community

Abstract

Abstract Host‐associated differentiation ( HAD ) is the formation of genetically distinct, host‐associated populations created and maintained by ecologically mediated reproductive isolation. HAD potentially accounts for species origins in parasites, including herbivorous insects. Although case studies testing the occurrence of HAD are accumulating, it is still unclear how common HAD is and which specific ecological traits explain its occurrence. To address these issues, studies are needed that include negative results (i.e., instances in which parasite populations do not exhibit HAD ) and test for HAD across communities (i.e., several parasite species on the same set of host species). In this study, HAD was tested in a community of six species of A phidomorpha ( H emiptera) that share a host‐plant pair: pecan [ C arya illinoinensis ( W angenh.) K.Koch] and water hickory [ C arya aquatica (F.Michx) Nutt., both J uglandaceae] trees. All six species are parthenogenetic and three species are endophagous, traits that can exacerbate host‐specific selection. AFLP markers were employed to detect the presence of genetically distinct, host‐associated populations for each insect species. Strict HAD (i.e., the occurrence of genetically distinct pecan‐associated and water hickory‐associated genotypes) was found in P hylloxera notabilis P ergande ( P hylloxeridae), P hylloxera devastatrix P ergande, and M onelliopsis pecanis B issel ( A phididae). M onellia caryella F itch ( A phididae) displayed a pattern of partial HAD (i.e., the occurrence of only a genetically distinct pecan‐associated genotype). No HAD was found in M elanocallis caryaefoliae D avis ( A phididae) or P hylloxera texana S toetzel. The pattern of HAD occurrence in the pecan and water hickory Aphidomorpha community indicated that neither parthenogenesis nor endophagy sufficiently explain the occurrence of HAD in this system.