Diversification rates in the Australasian endemic grass Austrostipa: 15 million years of constant evolution
- 196 Downloads
Patterns seen in other Australian flora have led to hypotheses that early Miocene shifts in climate drove rapid radiation of major taxonomic groups such as Eucalyptus. Little is known about absolute dates and rates for Australian monocots, particularly grasses. I tested this early Miocene radiation hypothesis for Australian grasses using a calibrated phylogeny of the endemic stipoid genus Austrostipa and an analysis of diversification rates. The phylogeny was developed from a Bayesian likelihood analysis of the nuclear internal transcribed spacers region, and three calibration points were set based on fossil evidence. The results indicate that the genus arose in the early Miocene and underwent a species radiation, but the rate of diversification was not rapid compared to the current rate or to those of other taxa. Following an 8 million year period of fast molecular evolution but no taxonomic radiation, diversification rates have been constant for the past 15 million years. Comparable measures such as the gamma statistic can be used across taxa to make general conclusions about evolutionary rate constancy.
KeywordsPoaceae Stipeae Phylogeny Radiation Molecular evolution
I thank the staff at the National Herbarium of Victoria, Australia, for providing the sequence data for Austrostipa specimens and Frank Udovicic for comments on the draft of this paper.
- Bendiksby M, Schumacher T, Gussarova G, Nais J, Mat-Salleh K, Sofiyanti N, Madulid D, Smith SA, Barkman T (2010) Elucidating the evolutionary history of the Southeast Asian, holoparasitic, giant-flowered Rafflesiaceae: Pliocene vicariance, morphological convergence and character displacement. Mol Phylogenet Evol 57(2):620–633. doi: 10.1016/j.ympev.2010.08.005 PubMedCrossRefGoogle Scholar
- Bouchenak-Khelladi Y, Salamin N, Savolainen V, Forest F, Mvd Bank, Chase MW, Hodkinson TR (2008) Large multi-gene phylogenetic trees of the grasses (Poaceae): progress towards complete tribal and generic level sampling. Mol Phylogenet Evol 47(2):488–505. doi: 10.1016/j.ympev.2008.01.035 PubMedCrossRefGoogle Scholar
- Drummond A, Ho S, Rawlence N, Rambaut A (2007) A Rough Guide to BEAST 1.4. www.beast.bio.ed.ac.uk
- Jones R (1997) The biogeography of the grasses and lowland grasses of south-eastern Australia. Adv Nat Conserv 2:11–18Google Scholar
- Macphail MK, Hill RS (2002) Paleobotany of the Poaceae. In: Mallett K (ed) Flora of Australia, vol 43. Australian Biological Resources Study/CSIRO Publishing, pp 37–70Google Scholar
- McCusker A (2002) Poaceae: family description. In: Mallett K (ed) Flora of Australia, vol 43. Australian Biological Resources Study/CSIRO Publishing, pp 1–3Google Scholar
- Rambaut A (2009) FigTree version 1.3.1. http://tree.bio.ed.ac.uk/software/figtree
- Rambaut A, Drummond A (2007) TRACER v1.4, Available from http://beast.bio.ed.ac.uk/Tracer
- Romaschenko K, Peterson PM, Soreng RJ, Garcia-Jacas N, Susanna A (2010) Phylogenetics of Stipeae (Poaceae: Pooidae) based on plastid and nuclear DNA sequences. In: Seberg O, Petersen G, Barfod A, Davis J (eds) Diversity, phylogeny and evolution in the monocotyledons. Aarhus University Press, AarhusGoogle Scholar
- Schneider J, Winterfeld G, Hoffmann MH, Roser M (2011) Duthieeae, a new tribe of grasses (Poaceae) identified among the early diverging lineages of subfamily Pooideae: molecular phylogenetics, morphological delineation, cytogenetics and biogeography. Syst Biodivers 9(1):27–44. doi: 10.1080/14772000.2010.544339 CrossRefGoogle Scholar