Literaturdatenbank
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Fielder, D. P. (2010). Population ecology, ecophysiology, phylogenetics and taxonomy of the threatened western sawshelled turtle, myuchelys bellii, from the murray-darling basin of australia. Unpublished thesis , University of New England.
Added by: Sarina Wunderlich (30 Oct 2011 14:52:34 UTC) |
| Resource type: Thesis/Dissertation BibTeX citation key: Fielder2010 View all bibliographic details  |
Categories: General Keywords: Australien = Australia, Chelidae, Chelodina, Chelodina bellii, Chelodina georgesi, Chelodina purvisi, Habitat = habitat, Rheodytes, Rheodytes leukops, Schildkröten = turtles + tortoises Creators: Fielder Publisher: University of New England |
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| Abstract |
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Myuchelys belli Elseya Resolving the evolutionary relationships among species remains an important focus of biodiversity conservation, and is key for assessing and reversing global trends in biodiversity decline. International and national systems of biodiversity protection rely on good taxonomic knowledge at the species level and good information about their biology and life history traits, knowledge that is often incomplete and therefore an impediment to effective conservation action. Over half of the world‟s turtle species are considered threatened, yet the taxonomy of many turtles species is not adequately resolved, and much work needs to be done to understand relationships between closely related taxa, and for uncovering cryptic species and genera. The Myuchelys genus is a little known group of Australian freshwater turtles. The focal species, the vulnerable western sawshelled turtle Myuchelys bellii located in the Murray-Darling Basin in eastern Australia, is both taxonomically confused and poorly studied. I surveyed populations of Myuchelys species from within their natural ranges using a combination of baited traps or by hand using a snorkel. Most specimens were live captured and released. For genetic analysis, small skin tissue samples were taken from M. bellii individuals while previously collected blood and liver samples (snap frozen at -80˚C) were used for other study species. One-off surveys of populations of M. latisternum in the Albert River and Lockyer Creek (Brisbane River catchment) were conducted in 2007-2008, while M. georgesi and M. purvisi were sampled in 2007 from the Bellinger and Manning Rivers located in northern coastal New South Wales (NSW). The study sites of M. bellii were located in the New England Tablelands Bioregion (NET) in the Murray-Darling Basin which experiences a temperate climate with cold winters and warm summers. It is not unusual for upland streams in the NET to freeze over and periodic winter snow falls across years to occur. Capture-mark-recapture surveys of M. bellii populations were conducted from 2002-2010 in Bald Rock Creek (Border Rivers) from southern Queensland and from 2005-2007 in the Namoi and Gwydir Rivers in NSW. The phylogeny for the Myuchelys genus using 960 bp of the mitochondrial control and ND4 regions revealed a shallow genetic structure of 0.1-0.3% divergence across M. bellii’s range in the Namoi, Gwydir and Border Rivers. The phylogeographic patterns vi observed for M. bellii indicates a recent range contraction to the headwater streams of the Darling River resulting in the three relict populations of today. Similarly, no diagnostic morphological differences between M. bellii populations were found but the holotype specimen was confirmed to be an M. bellii. Consequently, the genetic and morphological data were concordant in finding no support for the taxonomic distinction of the Queensland population of M. bellii to its southern congeners, thus rejecting earlier assertions of a cryptic species in M. bellii. Many turtle species, including those native to Australia, are poorly understood in terms of the life history, ecology, and physiological tolerances. In particular, an understanding of the aquatic respiration abilities in freshwater turtles is essential as a result of habitat modification and loss through worldwide increases in water resource development. My results showed M. bellii to have delayed age at first breeding, low reproductive effort (14.3 eggs per adult female) and high survivorship with a predicted lifespan of over 40 years (Type III survivorship). Growth increment data from mark-recapture data provided an estimate of age at maturity with males taking nearly 10 years to mature and females approaching 20 years. Annual breeding rates were found to vary greatly between years with on average 78% of females breeding in any one year. These life history traits mean that M. bellii is intrinsically vulnerable to population declines through high levels of nest and hatchling predation (e.g., foxes, exotic fish) and altered habitat. Not unlike Ryeodytes leukops, which is considered to be a habitat specialist associated with well oxygenated riffle zones in the Fitzroy River, M. bellii is only found above about 700 masl in presumably well oxygenated cold flowing streams. It is restricted to riverine habitats and requires permanent aquatic refugia to persist at the local scale. My study was the first to describe the extraordinary aquatic respiration abilities of M. bellii which allow for extended aerobic dives of up to weeks during winter hibernation which I attribute to its cloacal bursae and temperate climate across its range. Despite its moderately specialised bursae morphology in comparison to other Australian chelids, M. bellii is second only to Rheodytes luekops in having the longest recorded dive for any freely diving freshwater or marine turtle at 15.5 days (maximum). The seasonal diving behaviour of M. bellii corresponds closely to those observed for R. leukops. In view of that, the intermediate complexity of the bursae structure for M. bellii may allow for an unexpected level of aquatic oxygen uptake, particularly at low temperatures and at depth. Furthermore, the evolutionary forces of a temperate climate have meant that highly specialised bursae like those in R. leukops are not required to undertake aquatic hibernation during winter. These findings are important to better understanding the role of the cloacal bursae in pleurodires from temperate zones, and more generally, the lessor studied species within Australia. In summary, the molecular and morphological evidence of this research do not support the presence of a cryptic species within M. bellii. Consequently, the three major populations of M. bellii from the Gwydir, Namoi and Border Rivers need to be managed as a single species entity. The relatively small size and extent of each population also means that M. bellii is certainly worthy of its national vulnerable status and international endangered status. Of particular concern for M. bellii, is the long term conservation of the isolated Queensland population . This thesis provides a clear foundation and insight into the conservation priorities for Myuchelys species, and in particular, for the threatened western sawshelled turtle M. bellii.
Added by: Sarina Wunderlich |