The mangrove genus Avicennia (Avicenniaceae) in Australia

Duke, Norman Clive (1988) The mangrove genus Avicennia (Avicenniaceae) in Australia. PhD thesis, James Cook University.

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Abstract

In Australia, New Guinea and the southwestern Pacific five species are recognised in Avicennia L. Four are redescribed in view of their Indo-Malesian counterparts, A. alba Bl., A. marina (Forsk.) Vierh., A. officinalis L., A. rumphiana Hallier f. (=A. lanata Ridl.), and one, A. integra N.C. Duke, was recently described as endemic to Australia. For A. marina, three varieties are proposed based on mrphological, phenological and genetic patterns. A systematic treatment provides a key, descriptions and synonymy, as well as notes on floral phenology, distribution and ecology. Morphological attributes were assessed using multivariate techniques. Interspecific differences were defined from herbarium specimens of flowers, fruit and leaves. No intermediates or potential hybrids were observed between the five species. Intraspecific assessment of A. marina used extensive field collections and found that morphological variation was related to regional and localised environmental factors, including temperature, rainfall, intertidal position and upriver range. Major differences were also observed within individuals, as shown in sun and shade leaves. In the past, much confusion surrounded the use of leaf size and shape in specific descriptions. Leafing and reproductive phenologies of A. marina were assessed using litter fall collections from around Australia. The results reveal major trends in leaf fall, flowering and fruit maturation related to latitude. These trends are highly significant and are indicative of a lesser importance of localised factors, such as rainfall, evapotranspiration, salinity, topography and nutrient availability. Possible causal factors related to latitude, including photoperiod and temperature, were investigated using correlative evaluation of simple models, similar to those used in crop studies. One model was highly predictive, explaining 92% of variance in total reproductive cycle duration and timing. In this model, initiation of the reproductive cycle occurs when daylength exceeds 12 hours (long days), and subsequent rates of development to fruit maturation are controlled by air temperature. Temperature appears to effect reproductive development by increasing growth rates by a factor of two or three, for each 10°C rise. The importance of this relationship and the model are discussed with a view to (1) predicting the timing of phenoevents in other years and regions, and, (2) understanding distributional limitations. Isozyme variation in four species, A. alba, A. germinans (L.) Steam, A. Integra and A. marina was assessed using electrophoretic techniques. Interspecific comparisons of banding mobilities revealed high levels of genetic dissimilarity. Some genetic interpretation was possible in three species, and a more detailed study of A. marina found important geographical patterns in allele frequencies. Collections were made throughout Australasia including ten Australian sites, and one each from New Zealand, Malaysia and Thailand. Allozyme genotypes were interpreted at twelve loci in five enzyme systems (aconitase, diaphorase, malate dehydrogenase, phosphoglucomutase and 6-phosphogluconate dehydrogenase). Comparisons with other Avicennia species were made using the same five enzyme systems, and three additional ones (aspartate aminotransferase, leucine aminopeptidase and peroxidase). Variation in respective allelic phenotypes were consistent with the notion that A. marina sensu law (including A. marina, A. eucalyptifolia and A. balanophora) was one polymorphic species. As such, unique alleles in any population were rare, heterozygotes were mostly found at Hardy-Weinberg equilibrium expectations (F=0; signifying that the taxon is random breeding), and there were no appreciable cross correlations of genotypes between loci. Intra-populational assessment of several sites indicated high levels of outcrossing (t=0.90). Based on the findings from morphological and electrophoretic studies, Australasian populations were divided into three varieties: A. marina var. australasica (Walp.) Moldenke [=var. resinifera (Forst.) Bakh.], a south-eastern variety ranging from Adelaide (SA) to Rockhampton (Qld), including New Zealand; A. marina var. eucalyptifolia (Val.) N.C. Duke comb. nov., in north-eastern and northern Australia; and, A. marina var. marina, in south-western Australia and Asia (Malaysia and Thailand). These varieties occur in sympatry in their respective contact zones in Australia, where they display no barriers to genetic intergradation. This situation, however, appears to have been maintained over an extremely long time, because of the biogeographical implications of var. australasica in New Zealand and Australia.

Item ID: 24104
Item Type: Thesis (PhD)
Keywords: flowering seasons; fruiting; hybrids; leaf litter; mangroves; morphology; Avicennia; taxonomy
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Date Deposited: 11 Dec 2012 07:37
FoR Codes: 06 BIOLOGICAL SCIENCES > 0603 Evolutionary Biology > 060310 Plant Systematics and Taxonomy @ 100%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960805 Flora, Fauna and Biodiversity at Regional or Larger Scales @ 100%
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