Environment Institute Leaders publications

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Browsing Environment Institute Leaders publications by Advisors "Breed, William Godfrey"

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    The effect of habitat fragmentation and population isolation on the genetic diversity, reproductive status and population viability of the southern hairy-nosed wombat (Lasiorhinus latifrons) in South Australia.
    (2010) Sparrow, Elisa; Taggart, David Augustine; Breed, William Godfrey; Cooper, Steven John Baynard; School of Earth and Environmental Sciences : Ecology and Evolutionary Biology
    A range of negative consequences associated with habitat fragmentation and population isolation have been demonstrated in a variety of animal species. Such consequences include inbreeding, reduced genetic diversity, increased mortality of young, reduced fecundity and compromised male fertility. Since the time of European settlement, many populations of the southern hairy-nosed wombat (Lasiorhinus latifrons) have become fragmented and isolated throughout South Australia, particularly on the Yorke Peninsula. This study aimed to examine the impact of habitat fragmentation and population isolation on the genetic diversity, seminal quality and reproductive success of the southern hairy-nosed wombat. The results showed there were very few wombats remaining on the Yorke Peninsula, with a total of 643 individuals estimated within 24 colonies all of which were geographically isolated by cleared agricultural land. Of these 24 colonies, 21 were estimated to have < 20 animals. Southern hairy-nosed wombats from two of these small isolated Yorke Peninsula colonies, namely Urania and Kulpara, were found to be genetically differentiated from one another, suggesting minimal current migration between these two colonies. These wombats were also genetically differentiated from wombats within the large population at Swan Reach, which is part of a continuous population in the Murraylands. High mean observed heterozygosity values were found in wombats from Urania and Kulpara (0.69 and 0.74 respectively), and these values did not differ significantly from that of the Swan Reach population (0.71). Allelic diversity was slightly lower in the colonies on the Yorke Peninsula; but this was not statistically significant from the population in the Murraylands. Inbreeding was not detected in any population. Despite this, wombats from the Yorke Peninsula were found to be smaller in body morphology and have larger testes. These animals also had significantly lower ejaculate volumes, with greater numbers of sperm morphological abnormalities in the ejaculate. A trend for lower sperm concentration and sperm motility in wombats from the Yorke Peninsula was also observed. The lower seminal quality in Yorke Peninsula male wombats was not reflected in a reduction in the reproductive success of the population, with all three populations examined exhibiting a similar number of females with pouch young, and in late lactation. There was, however, an unequal sex ratio within the Urania population, with a lower number of adult females in the population during the breeding season. The results from this study suggest that colonies of southern hairy-nosed wombats on the Yorke Peninsula are in danger of localised extinction if not appropriately managed and conserved. Future study directions and possible management techniques are discussed in order to minimise localised extinctions and maintain the viability of southern hairy-nosed wombats on the Yorke Peninsula and throughout South Australia.
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    ItemOpen Access
    Molecular evolution of the carboxy terminal, the putative sperm-ZP binding site, of the zona pellucida 3 glycoprotein in old world murine rodents.
    (2007) Swann, Christine A.; Breed, William Godfrey; Cooper, Steven John Baynard; School of Medical Sciences : Anatomical Sciences
    In mammals, before fertilisation can occur, sperm have to bind to, and penetrate, the extracellular coat of the oocyte, the zona pellucida (ZP). In the laboratory mouse, which has been used as a model system for fertilization studies, sperm-ZP binding has been found to be mediated by a region near the carboxy terminal, encoded by exon 7 of the Zp3 gene. This region shows considerable interspecific sequence diversity in North American cricetid rodents, with some evidence of adaptive evolution, suggesting that this may contribute to species specific sperm-ZP binding. However, by contrast, in a preliminary study of three species of Australian murine rodents an identical protein sequence of the region encoded by exon 7 of Zp3 was found to be present. The aim of this present study was to determine the pattern of sequence diversity of this region in the most speciose subfamily of mammals, the murine rodents, and to obtain insight into the selective pressures involved in its evolution. For this, DNA was extracted from murine rodents of Africa, Eurasia, South-east Asia, New Guinea and Australia. The nucleotide and predicted amino acid sequence of exons 6 and 7 of Zp3 in 96 murine species from 14 divisions, as recently defined by Musser and Carleton (2005), was determined and compared. Generally, it was found that closely related species shared a highly similar ZP3 sequence. Maximum likelihood analyses of codon substitution models using representatives from 14 murine divisions, suggested that positive selection had occurred within only a few lineages at several different codon sites adjacent to, or within, the putative combining-site for sperm of ZP3. Positive selection was not evident when the analysis was restricted to the Australian taxa which showed low levels of both intra- and inter-generic sequence divergence. There was no good evidence that this region contributes to species specificity of sperm-ZP binding in these species. These findings thus suggest that the selective forces acting on the Zp3 exon 7 region during the evolution of the murine rodents have varied possibly due to a range of selective pressures not necessarily restricted to the prevention of hybridization. It seems unlikely, therefore, that the amino acid sequence of the exon 7 coding region contributes to species specificity of sperm-ZP binding within most of the lineages from this most speciose subfamily of eutherian mammals.