Population genetic structure and phenotypic diversity of Aspidodera raillieti (Nematoda: Heterakoidea), a parasite of Didelphini marsupials in Brazil’s South and Southeast Atlantic Forest

Abstract

Background: Population genetics of parasites may be influenced by host specificity, life-cycle, geographical distance, evolutionary history, and host-populations structure. The nematode Aspidodera raillieti infects different marsupial and rodent hosts in the Nearctic and Neotropical regions, implying a presumably significant gene flow among populations. However, niche diversification of A. raillieti main hosts in superimposed areas may provide conditions for population genetic structuring within this parasite species. We examined the genetic structuring of A. raillieti infecting three marsupial species co-occurring along South and Southeast Brazilian Atlantic Forest, a hotspot of biodiversity.Methods: We employed morphometric analyses and partial mitochondrial cytochrome c oxidase I gene sequences (MT-CO1) to characterize populations via phylogenetic and phylogeographic analyses.Results: Among 175 A. raillieti specimens recovered from marsupial hosts Didelphis aurita, D. albiventris, and Philander quica, we identified 99 MT-CO1 haplotypes forming four groups in phylogenetic trees and networks. Clades I and II encompassed parasites of D. albiventris from the South region, Clade III comprised parasites of D. aurita from the South and Southeast regions, and Clade IV encompassed parasites of D. aurita and D. albiventris from the South and Southeast regions and parasites of Philander quica from the South region. High genetic differentiation between clades, with a high fixation index and greater genetic variation in the analysis of molecular variance (AMOVA), indicated low gene flow between clades. Haplotypes shared among host species revealed a lack of host specificity. Significant correlation in the Mantel test, suggested parasite isolation by distance, although there was no evidence of geographic structure between populations. Negative values in neutrality tests for Clades III and IV suggested recent population expansion. Morphometric differentiation between A. raillieti specimens recovered from different host species, as well as from different localities, was more evident in males.Conclusion: The genetic structure of A. raillieti populations in the South and Southeast Atlantic Forest resulted from historical events rather than from current geographical distribution or host specificity. We also demonstrate morphometric variation associated with host species and localities, suggesting phenotypic plasticity to host attributes and to spatial variables.