In this thesis, I investigated how evolutionary forces and conservation action interact to shape
neutral and adaptive genetic variation within and among populations. To accomplish this, I
studied an island species, the Seychelles warbler (Acrocephalus sechellensis), with
microsatellite markers and major histocompatibility complex (MHC) genes as measures of
neutral and adaptive variation respectively. First, I used museum DNA and historical records to
reveal a recent bottleneck that provides context for the contemporary genetic variation
observed in this species. I then determined the impact of four translocations on genetic
diversity over two decades. I found that diversity does not differ significantly between islands
but the use of smaller founder sizes in two translocations has caused population divergence.
These results indicate that stochastic genetic capture is important in translocations and that
future assisted gene flow between populations may be necessary. As a tool for conservation
practitioners, I wrote a technical report of the most recent translocation - to Frégate Island -
detailing practicalities and outcomes to help inform future translocation policy. Using two
translocation events as experiments, I then tested whether MHC-based social mate choice acts
to maintain MHC diversity in the Seychelles warbler, finding that male age and heterozygosity,
but not MHC, predicted pairing success. Lastly, I investigated survival and reproductive
consequences of Ase-ua4, an MHC class I allele previously shown to confer a survival
advantage in the Seychelles warbler. I found widespread patterns of allele frequency increase
within cohorts consistent with the survival effect, but no overall increase in population allele
frequency over time. I investigated potential antagonistic reproductive mechanisms, but found
no clear evidence for why this allele is not driven towards fixation. Collectively, my results
provide an interesting case study of the evolutionary conservation approach, whilst providing
insight into the importance of maintaining genetic variation in natural populations
