Multiple lines of evidence suggest mosaic polyploidy in the hybrid parthenogenetic stick insect lineage Acanthoxyla

Authors

  • Shelley S. Myers,

    1. Ecology Group, Institute of Natural Resources, Massey University, Palmerston North, New Zealand
    Current affiliation:
    1. School of Biological Sciences, University of Auckland, Auckland, New Zealand
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  • Steven A. Trewick,

    Corresponding author
    • Ecology Group, Institute of Natural Resources, Massey University, Palmerston North, New Zealand
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  • Mary Morgan-Richards

    1. Ecology Group, Institute of Natural Resources, Massey University, Palmerston North, New Zealand
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Correspondence: Steve Trewick, Ecology Group, Institute of Natural Resources, Massey University, Private Bag 11-222, Palmerston North 4442, New Zealand. E-mail: s.trewick@massey.ac.nz

Abstract

  1. Although hybridisation is common in animals, it rarely results in speciation. Yet, many examples of hybrid species have been documented in one animal group, the stick insects (Phasmida).
  2. The New Zealand stick insect Acanthoxyla is of particular interest as the entire genus is of hybrid origin and consists of eight morphological forms recognised as species, all of which are obligate parthenogens.
  3. Using five complementary techniques on the same individuals, our study confirms that both triploids and diploids are present in Acanthoxyla populations, and further, that some individuals contain both diploid and triploid cells.
  4. Chromosome spreads and estimates of relative DNA content from flow cytometry provided contrasting information about the ploidy of this unusual parthenogenetic genus.
  5. Analysis of morphometric variation showed no correlation with ploidy level in Acanthoxyla, and also mtDNA sequence networks failed to distinguish morphospecies or ploidy level.
  6. Unexpectedly, cloned sequences of a putatively single-copy nuclear marker were also unhelpful in distinguishing ploidy, instead indicating that phosphoglucose isomerase is likely to be a multiple copy gene.
  7. We propose a mechanism for the evolution of the Acanthoxyla lineage and suggest that interpretation may be complicated by the presence of individuals that are diploid and triploid mosaics.

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