title: Extensive variation in chromosome number and genome size in sexual and parthenogenetic species of the jumping-bristletail genus Machilis (Archaeognatha).
abstract: Parthenogenesis in animals is often associated with polyploidy and restriction to extreme habitats or recently deglaciated areas. It has been hypothesized that benefits conferred by asexual reproduction and polyploidy are essential for colonizing these habitats. However, while evolutionary routes to parthenogenesis are manifold, study systems including polyploids are scarce in arthropods. The jumping-bristletail genus Machilis (Insecta: Archaeognatha) includes both sexual and parthenogenetic species, and recently, the occurrence of polyploidy has been postulated. Here, we applied flow cytometry, karyotyping, and mitochondrial DNA sequencing to three sexual and five putatively parthenogenetic Eastern-Alpine Machilis species to investigate whether (1) parthenogenesis originated once or multiply and (2) whether parthenogenesis is strictly associated with polyploidy. The mitochondrial phylogeny revealed that parthenogenesis evolved at least five times independently among Eastern-Alpine representatives of this genus. One parthenogenetic species was exclusively triploid, while a second consisted of both diploid and triploid populations. The three other parthenogenetic species and all sexual species were diploid. Our results thus indicate that polyploidy can co-occur with parthenogenesis, but that it was not mandatory for the emergence of parthenogenesis in Machilis. Overall, we found a weak negative correlation of monoploid genome size (Cx) and chromosome base number (x), and this connection is stronger among parthenogenetic species alone. Likewise, monoploid genome size decreased with elevation, and we therefore hypothesize that genome downsizing could have been crucial for the persistence of alpine Machilis species. Finally, we discuss the evolutionary consequences of intraspecific chromosomal rearrangements and the presence of B chromosomes. In doing so, we highlight the potential of Alpine Machilis species for research on chromosomal and genome-size alterations during speciation.
authors.affiliation: Institute of Ecology, University of Innsbruck Technikerstraße 25, Innsbruck, 6020, Austria.
authors.forename: Melitta
authors.initials: M
authors.lastname: Gassner
authors.affiliation: Institute of Ecology, University of Innsbruck Technikerstraße 25, Innsbruck, 6020, Austria.
authors.forename: Thomas
authors.initials: T
authors.lastname: Dejaco
authors.affiliation: Institute of Botany, University of Innsbruck Sternwartestraße 15, Innsbruck, 6020, Austria.
authors.forename: Peter
authors.initials: P
authors.lastname: Schönswetter
authors.affiliation: Institute of Entomology, Biology Centre ASCR Branisovska 31, Ceské Budejovice, 37005, Czech Republic.
authors.forename: František
authors.initials: F
authors.lastname: Marec
authors.affiliation: Institute of Ecology, University of Innsbruck Technikerstraße 25, Innsbruck, 6020, Austria.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Arthofer
authors.affiliation: Institute of Ecology, University of Innsbruck Technikerstraße 25, Innsbruck, 6020, Austria.
authors.forename: Birgit C
authors.initials: BC
authors.lastname: Schlick-Steiner
authors.affiliation: Institute of Ecology, University of Innsbruck Technikerstraße 25, Innsbruck, 6020, Austria.
authors.forename: Florian M
authors.initials: FM
authors.lastname: Steiner
keywords: Asexuality; chromosomal speciation; genome downsizing; parthenogenesis; polyploidy