A tangled tale of two teal: population history of the grey Anas gracilis and chestnut teal A. castanea of Australia


  • Leo Joseph,

  • Gregory J. Adcock,

  • Celeste Linde,

  • Kevin E. Omland,

  • Robert Heinsohn,

  • R. Terry Chesser,

  • David Roshier

L. Joseph (correspondence), Austr. Natl. Wildlife Coll., CSIRO Sust. Ecosyst., GPO Box 284, Canberra, ACT, 2601, Australia. Email: Leo.Joseph@csiro.au. – G. J. Adcock and C. Linde, Dept. of Bot. and Zool., Austr. Natl. Univ., Canberra, ACT 0200, Australia. – K. E. Omland, Dept. of Biol. Sci., Univ. of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland 21250, USA. – R. Heinsohn, Fenner School of Environm. and Society, Austr. Natl. Univ., 0200, Canberra, ACT Australia. – R. T. Chesser, USGS Patuxent Wildl. Res. Center, Natl. Mus. of Natl. History, PO Box 37012, Washington D.C. 20013, USA. – D. Roshier, Ecol. and Biodiv. Group, Inst. for Land, Water & Society, Charles Sturt Univ., PO Box 789, Albury, NSW 2640, Australia.


Two Australian species of teal (Anseriformes: Anatidae: Anas), the grey teal Anas gracilis and the chestnut teal A. castanea, are remarkable for the zero or near-zero divergence recorded between them in earlier surveys of mitochondrial DNA (mtDNA) diversity. We confirmed this result through wider geographical and population sampling as well as nucleotide sampling in the more rapidly evolving mtDNA control region. Any data set where two species share polymorphism as is the case here can be explained by a model of gene flow through hybridization on one hand or by incomplete lineage sorting on the other hand. Ideally, analysis of such shared polymorphism would simultaneously estimate the likelihood of both phenomena. To do this, we used the underlying principle of the IMa package to explore ramifications to understanding population histories of A. gracilis and A. castanea. We cannot reject that hybridization occurs between the two species but an equally or more plausible finding for their nearly zero divergence is incomplete sorting following very recent divergence between the two, probably in the mid-late Pleistocene. Our data add to studies that explore intermediate stages in the evolution of reciprocal monophyly and paraphyletic or polyphyletic relationships in mtDNA diversity among widespread Australian birds.