Pleistocene Refugia Inferred from Molecular Evidence in a Forest-Dwelling Harvestman (Arachnida, Opiliones, Gonyleptidae) Support a Biogeographic Split in Subtropical Argentina

Abstract

This paper addresses the population genetic structure of the forest-dwelling gonyleptid Geraeocormobius sylvarum (Arachnida, Opiliones). Phylogeographic analyses using cytochrome oxidase subunit I (COI) were conducted on 186 individuals from 43 localities in Argentina and Paraguay, arranged into nine operational sectors and defined upon geographic and vegetation features. Given the current environmental uniformity, it was aimed to assess whether molecular fingerprints of G. sylvarum correlate with Pleistocene fragmentation events, inferred through forest contraction/expansion cycles. The network of 87 haplotypes displayed an unstructured pattern; 75 were found in unique localities (54 on single individuals), with most haplotypes restricted to a single operational sector. The calibrated phylogenetic tree revealed significant admixture, with each clade mainly related to one operational sector. Results suggest multiple fragmentation events; most COI diversity arose in the Late Pleistocene/Early Holocene; recent and relict lineages coexist at a few sites. Banks of major rivers (Paraná and Uruguay) in Misiones Province may have served as main refuge areas, with dispersal within each basin being frequent but sporadic across the watershed divide, keeping basins separated for long periods. The split of the Misiones opiliogeographical area into two sectors corresponding to the major basins is proposed.

Keywords

biogeography / Paranaense forests / phylogeny / phylogeography / Pleistocene refugia

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2025 International Society of Zoological Sciences, Institute of Zoology/Chinese Academy of Sciences and John Wiley & Sons Australia, Ltd.