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

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 Aphidomorpha (Hemiptera) that share a host‐plant pair: pecan [Carya illinoinensis (Wangenh.) K.Koch] and water hickory [Carya aquatica (F.Michx) Nutt., both Juglandaceae] 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 Phylloxera notabilis Pergande (Phylloxeridae), Phylloxera devastatrix Pergande, and Monelliopsis pecanis Bissel (Aphididae). Monellia caryella Fitch (Aphididae) displayed a pattern of partial HAD (i.e., the occurrence of only a genetically distinct pecan‐associated genotype). No HAD was found in Melanocallis caryaefoliae Davis (Aphididae) or Phylloxera texana Stoetzel. 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.

Temporal isolation between sympatric host plants cascades across multiple trophic levels of host-associated insects

“…Emerging from this perspective, cascading reproductive isolation describes the process whereby trait divergence that generates reproductive isolation (RI) between populations in one species transcends trophic levels to generate population divergence within interacting species [5]. The diversity of host-specific insect herbivores with their close ties to host plants offers opportunities to test whether cascading RI is a common mechanism promoting divergence [5][6][7][8].…”

Predicting the occurrence of host‐associated differentiation in parasitic arthropods: a quantitative literature review

“…In addition, three of the species were gallmakers, a factor believed to promote HAD. However, only three of these parasite species exhibited the genetic signature of HAD and one of the species that did not develop HAD was a gallmaker (Phylloxera texana Stoetzel) (Medina et al, 2017). These apparent inconsistencies in the theory of HAD development necessitate a quantitative comparison of potentially predictive factors and their relationship with HAD.…”

Host‐associated differentiation of target pests should be assessed before using gene drive as a pest control tool − an opinion

“…That is, one cannot assume that related species, even if sharing the same habitat and/or hosts, will show similar degrees of HAD. For example, the degree of HAD within closely related Aphidomorpha species co-existing within the same insect community varied markedly even though they fed on not only sympatric but syntopic tree species (Medina et al, 2017). Thus, the existence of HAD on any target species selected for gene drive pest control cannot just be predicted but it will need to be assessed.…”