Chromosome Research

, Volume 16, Issue 6, pp 815–825

An XX/XY heteromorphic sex chromosome system in the Australian chelid turtle Emydura macquarii: A new piece in the puzzle of sex chromosome evolution in turtles

  • Pedro Alonzo Martinez
  • Tariq Ezaz
  • Nicole Valenzuela
  • Arthur Georges
  • Jennifer A. Marshall Graves
Article

Abstract

Chromosomal sex determination is the prevalent system found in animals but is rare among turtles. In fact, heteromorphic sex chromosomes are known in only seven of the turtles possessing genotypic sex determination (GSD), two of which correspond to cryptic sex microchromosomes detectable only with high-resolution cytogenetic techniques. Sex chromosomes were undetected in previous studies of Emydura macquarii, a GSD side-necked turtle. Using comparative genomic hybridization (CGH) and GTG-banding, a heteromorphic XX/XY sex chromosome system was detected in E. macquarii. The Y chromosome appears submetacentric and somewhat larger than the metacentric X, the first such report for turtles. CGH revealed a male-specific chromosomal region, which appeared heteromorphic using GTG-banding, and was restricted to the telomeric region of the p arm. Based on our observations and the current phylogeny of chelid turtles, we hypothesize that the sex chromosomes of E. macquarii might be the result of a translocation of an ancestral Y microchromosome as found in a turtle belonging to a sister clade, Chelodina longicollis, onto the tip of an autosome. However, in the absence of data from an outgroup, the opposite (fission of a large XY into an autosome and a micro-XY) is theoretically equally likely. Alternatively, the sex chromosome systems of E. macquarii and C. longicollis may have evolved independently. We discuss the potential causes and consequences of such putative chromosome rearrangements in the evolution of sex chromosomes and sex-determining systems of turtles in general.

Key words

CGH Emydura evolution G-banding sex chromosomes sex determination speciation turtles 

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Copyright information

© Springer Science+Business Media B.V. 2008

Authors and Affiliations

  • Pedro Alonzo Martinez
    • 1
  • Tariq Ezaz
    • 2
  • Nicole Valenzuela
    • 1
  • Arthur Georges
    • 3
  • Jennifer A. Marshall Graves
    • 2
  1. 1.Department of Ecology, Evolution, and Organismal BiologyIowa State UniversityAmesUSA
  2. 2.Comparative Genomics Group, Research School of Biological SciencesThe Australian National UniversityCanberraAustralia
  3. 3.Institute for Applied EcologyUniversity of CanberraCanberraAustralia

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