Demography and population genetic structure of the Australian sea lion, neophoca cinerea

Richard Campbell

Research output: ThesisDoctoral Thesis

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Abstract

The Australian sea lion, Neophoca cinerea, is Australia?s only endemic pinniped, and one of the rarest sea lions in the world. This species suffered localised extinction events, and a probable population decline during the commercial sealing era of the 18th to 20th centuries. This species also has a unique reproductive cycle and breeding system compared with all other pinnipeds. Unlike the usual annual, synchronous cycle, this species has a 17.5 month breeding cycle which is asynchronous across its range. Small groups of proximate colonies appear to breed synchronously, but otherwise the timing appears randomly distributed. It was proposed that this system is endogenously controlled and maintained by exclusive female natal site fidelity (Gales et al. 1994). This would have a discernible impact on the population genetic structure, and would be directly applicable to conservation management practices. Investigation of population genetic structure of the Australian sea lion using mtDNA and microsatellite markers revealed a highly subdivided population that showed strong patterns of sex-biased dispersal, and strong regional divisions. The level of female natal site fidelity was extreme, resulting in very high levels of genetic differentiation, unparalleled in other marine mammal populations. Significant divisions existed across both macro and micro geographic scales, with fixed differences occurring between colonies separated by as little as 20 kilometres. Strong phylogeographic patterning suggested that divisions between populations are of some antiquity. High levels of fixation in mtDNA markers among the many small colonies in Western Australia was attributed to the high rate of genetic drift in small populations, especially for these markers. Genetic subdivison, as measured by microsatellite markers, revealed a malebiased dispersal pattern. Levels of male dispersal were sufficient in overcoming the female natal site fidelity and rendering small groups of colonies effectively panmictic. However, the range of male dispersal was limited to approximately 200 kilometres and resulted in a regional population structure best defined by geographic distance. This level of subdivision was perhaps greater than expected given the dispersal capabilities of this species, and suggested that some behavioural processes may limit dispersal. Historical processes of extinction and colonisation are thought to have had a strong influence on the current pattern of population subdivision as well.
Original languageEnglish
QualificationDoctor of Philosophy
Publication statusUnpublished - 2003

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