Zoology - Theses

Permanent URI for this collection

Search Results

Now showing 1 - 2 of 2
  • Item
    Thumbnail Image
    The evolution and ecology of the Gadopsis marmoratus complex
    Sanger, Andrew Colin ( 1986)
    The Family Gadopsidae is the only family of fishes in South-eastern Australia which is both endemic to this region, and strictly confined to fresh water. Although several species of Gadopsis have been proposed, prior to the commencement of this study only one species, G. marmoratus Richardson, was formally recognised. This species was known to exhibit considerable geographic variation in morphology, colouration patterns, and size; and it had been suggested that the taxonomy of the genus was in need of review. This study is an attempt to: (i) determine the number of species in the, G. marmoratus complex; (ii) assess the relationships between G. marmoratus and any additional taxa in the complex; (iii) Formulate a biogeographic hypothesis to account for the geographic distributions and phylogenetic relationships of the taxa in the G. marmoratus complex; and, (iv) examine ecological characteristics of a population of Gadopsis from each side of the Great Dividing Range in Victoria. Analysis of meristic variation revealed that two sympatric taxa of Gadopsis were present in north-eastern Victoria. No evidence of hybridization between these taxa was found. The two taxa have different numbers of spines in the dorsal fin, and the specific status of the taxon with only two spines in the fin was recognised by the formal description of G. bispinosus Sanger. By adoption of an evolutionary species concept, and using univariate and multivariate statistical analyses of meristic variation, it was shown that G. marmoratus was comprised of two divergent taxa. It was proposed that these taxa be recognised as separate species, and for the purposes of this study are referred to as northern G. marmoratus and southern G. marmoratus. Multivariate statistical analyses of morphometric variation supported the proposal to recognise northern G. marmoratus and southern G. marmoratus as separate species. Electrophoretic analysis of protein variation also supported the recognition of northern G. marmoratus and southern G. marmoratus, and confirmed that hybridization was not occurring between G. bispinosus and northern G. marmoratus. The level of genetic divergence between northern G. marmoratus and southern G. marmoratus was less than that between both of these taxa and G. bispinosus. This result was interpreted to indicate a close phylogenetic relationship between northern G. marmoratus and southern G. marmoratus, and supported the relationships suggested by the phenetic analysis of meristic and morphometric variation. A biogeographic hypothesis to explain the geographic distributions and phylogenetic relationships of the three taxa was proposed. The ancestry of the Family Gadopsidae has been the subject of some dispute, and the alternative views on this subject were critically reviewed. Support was found for a basal percoid relationship for the family, and this result suggested that Gadopsis may have been of Gondwanan origin. The freshwater life-cycle of all the members of the family was interpreted as further support for a freshwater origin for Gadopsis. Several ecological characteristics of a population of G. bispinosus from the King Parrot Creek and G. marmoratus from the Yarra River system were compared. Gadopsis bispinosus in the King Parrot Creek is a small, lightly-built, short-lived species compared to G. marmoratus from the Yarra River system. The two species were found to have similar reproductive biologies. The discovery of additional species of Gadopsis has created the need for further examination of the evolution and ecology of the G. marmoratus complex, and suggestions for such further study are included at the end of this study.
  • Item
    Thumbnail Image
    Ecological studies of barnacles in temperate mangrove forests
    Nateekanjanalarp, Suvaluck ( 1997)
    I have examined the horizontal distribution and abundance of Elminius covertus across three zones, landward, middle and seaward, of mangrove forests at Rhyll, Phillip Island, Victoria during 1995-1997. In the seaward zone of the forest, the vertical abundance of E. covertus between 0-15 cm from the bottom was also investigated. To determine what processes affect these horizontal and vertical patterns, presettlement, settlement and recruitment of E. covertus have been examined. The horizontal distribution of adults reflected the horizontal pattern of recruitment and settlement. The horizontal pattern of settlement was determined by larval supply and larval behaviour. Post-settlement factors had little influence on this pattern. Consequently, the horizontal pattern of adults were ultimately explained by patterns of larval supply and larval behaviour. The distribution of adults on pneumatophores reflected the vertical pattern of recruitment, but contrasted with the vertical pattern of settlement. Variability in the vertical distribution of settlers reflects larval settling behaviour not larval availability and the vertical pattern of recruits and adults is determined by post-settlement mortality. The patterns of settlement of E. covertus on seedlings of Avicennia marina in the seaward zone of the forest were also documented, with the greatest density of barnacles found on the stem, followed by the lower-leaf and upper-leaf surfaces. No further studies were undertaken to test what processes determine this pattern. The presence of E. covertus produced no negative effects on the survival and growth of seedlings of A. marina. Seedling survival appears to depend on other factors, such as, intermittent smothering by drift algae, seagrasses, and sediment as well as unfavourable climatic conditions, especially low temperatures and strong winds and currents.