Mitochondrial phylogeography of the Holarctic Parnassius phoebus complex supports a recent refugial model for alpine butterflies

Authors

  • Valentina Todisco,

    Corresponding author
    1. Department of Biology, University of Rome ‘Tor Vergata’, Via della Ricerca Scientifica 1, 00133 Rome, Italy
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    • These authors contributed equally.

  • Paolo Gratton,

    1. Department of Biology, University of Rome ‘Tor Vergata’, Via della Ricerca Scientifica 1, 00133 Rome, Italy
    2. Department of Biodiversity and Molecular Ecology, Fondazione E. Mach, 38010 San Michele all’Adige, TN, Italy
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    • These authors contributed equally.

  • Evgeny V. Zakharov,

    1. Department of Biological Sciences, University of Alberta, CW405 Biological Sciences Centre, Edmonton, AB, Canada
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    • Present address: Biodiversity Institute of Ontario, Canadian Centre for DNA Barcoding, University of Guelph, Guelph, ON, N1G 2W1, Canada.

  • Christopher W. Wheat,

    1. Department of Biological and Environmental Sciences, PL 65, Viikinkaari 1, 00014 University of Helsinki, Helsinki, Finland
    2. Centre for Ecology and Conservation, School of Biosciences, University of Exeter, Cornwall Campus, Penryn, Cornwall TR10 9EZ, UK
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  • Valerio Sbordoni,

    1. Department of Biology, University of Rome ‘Tor Vergata’, Via della Ricerca Scientifica 1, 00133 Rome, Italy
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  • Felix A.H. Sperling

    1. Department of Biological Sciences, University of Alberta, CW405 Biological Sciences Centre, Edmonton, AB, Canada
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Correspondence: Valentina Todisco, Department of Biology, University of Rome ‘Tor Vergata’, Via della Ricerca Scientifica 1, 00133 Rome, Italy.
E-mail: valentina.todisco@libero.it

Abstract

Aim  Our study provides a description of the mitogenetic structure of alpine butterflies of the Parnassius phoebus complex throughout their Holarctic distribution. Our analyses extend and reassess population history models for alpine butterflies under an explicit calibration of their mitochondrial DNA (mtDNA) substitution rate.

Location  Mountain ranges of the Holarctic region.

Methods  A fragment (824 bp) of the mitochondrial cytochrome c oxidase subunit I (COI) gene was sequenced in 203 samples (72 locations), and combined with previously available COI sequences (499 samples), to obtain full coverage of the Holarctic distribution of the P. phoebus complex. A global species distribution model (SDM) was calculated by the maximum entropy (Maxent) approach, allowing assignment of samples into geographically consistent ‘operational’ units. Phylogenetic and coalescent methods were applied to describe the global mitogenetic structure and estimate population genetics parameters. Geological and palaeoecological evidence was used for internal calibration and validation of a COI substitution rate.

Results  Eurasian (including Alaskan) and North American populations form two distinct mitochondrial clades. The mitochondrial time to most recent common ancestor (TMRCA) of the North American clade was estimated at less than 125 ka, and the TMRCA of the Eurasian–Alaskan clade at less than 80 ka, except for a single divergent sequence from Mongolia. Pairwise divergence times between all geographical units within each continent date well within the last 100 ka, and most likely, the last 50–10 ka.

Main conclusions  In contrast with its currently scattered distribution within each of Eurasia and North America, the mitogenetic structure of the P. phoebus complex in both continents is shallow and weak, and shows no evidence of geographical structure dating back earlier than the last glacial cycle. We argue that mtDNA data are consistent with recent (Würm/Wisconsin) range expansion across each of the two continents and with persistent glacial long-range gene flow which ceased during the Holocene. We propose that P. phoebus may represent a model for Holarctic alpine invertebrates with moderate dispersal abilities in that its genetic structure at a continental scale reflects extensive connectivity during the most recent glacial phases.

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