UBC Theses and Dissertations
Learning from the past, examining the present and planning for the future : genetic approaches to the conservation of giant Galápagos tortoises Jensen, Evelyn Lise
Population genetics allows us to interpret the historical information contained in DNA, telling the story of population dynamics, demography and divergences, both recent and ancient, providing insights difficult or otherwise impossible to obtain. My PhD thesis research addresses fundamental questions in conservation genetics and demonstrates the utility of incorporating genetic information into conservation planning. Prioritizing taxa to receive conservation efforts is a difficult and contentious issue. Numerous methods have been proposed to rank taxa based on the importance of the phylogenetic diversity they contribute. However, all of these metrics share a flaw, in that complementarity among taxa is not taken into account when determining rankings. Here I propose a new method, I-HEDGE, which is an improvement on existing metrics as it integrates evolutionary isolation, probability of extinction and complementarity. Another area I address is that all too often the genetic impacts of conservation activities, including captive breeding and head-start programs, go unmonitored, which can result in losses of genetic diversity. The giant Galápagos tortoises endemic to Pinzón Island narrowly escaped extinction in the 20th century thanks to an intensive head-start program, now operating for 50 years. I evaluated two cohorts of the head-start program in detail using microsatellite markers to determine how representative they are of the extent and distribution of genetic variation in the wild population, which is one of the goals of the program. The cohorts were not representative of the sample of wild adults used for comparison, but the Pinzón tortoises appear to have retained a remarkable amount of genetic variation despite their near extinction. The genomic consequences of a rapid population decline and recovery, such as that experienced by the Pinzón tortoise, have rarely been empirically evaluated. This study system has the advantage of a large number of historical specimens collected in 1906, allowing a direct evaluation of genomic patterns pre- and post-decline. By estimating effective population sizes and patterns of diversity in the historical and contemporary populations, it became clear that despite their near extinction, the Pinzón tortoises have retained high levels of diversity thanks to their demographic history and quick recovery.
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