Abstract
Small, isolated populations are often of conservation concern because of poor genetic health (i.e., genetic diversity and inbreeding). Genetic diversity decreases at a greater rate in small populations through processes such as genetic drift which can lead to loss of rare alleles. Inbreeding is more prevalent in small populations as inbred interactions become more difficult to avoid leading to increased homozygosity in offspring which can cause inbreeding depression through the expression of recessive deleterious alleles. Bottlenecks on these small, isolated populations can cause further loss of genetic diversity and an increase in inbred interactions, increasing the need for conservation action for the small, isolated populations. Limited conservation funding is not prioritized for taxonomically uncertain species regardless of assessment of genetic health.
The Lord Howe currawong (Strepera graculina crissalis) is a medium-sized passerine which is currently recognized as a subspecies of pied currawong (Strepera graculina). However, taxonomic uncertainty remains for Lord Howe currawong given the lack of gene flow from mainland pied currawong. Additionally, Lord Howe currawong are constrained to small population size due to the restricted habitat of Lord Howe Island. Further stress to the threatened Lord Howe currawong occurred in 2019 as a rodent eradication program was administered on Lord Howe Island with non-target primary and secondary poisoning effects on Lord Howe currawong. Given the information above this thesis investigates the phylogenetic affinities and genetic health of the Lord Howe currawong to inform appropriate conservation management.
The phylogenetic affinities and genetic health of Lord Howe currawong were assessed using genome-wide SNPs generated from genotyping-by-sequencing. Phylogenetic affinities of the currawong genus (Strepera) consisting of pied, grey, black, and Lord Howe currawong were assessed using 202,564 genome wide SNPs with Australian magpie (Gymnorhina tibicen) used as an outgroup for tree construction. Historical and contemporary effective population size (Ne) were assessed as an estimator of genetic health. Meanwhile, genetic health was assessed for Lord Howe currawong before and after rodent eradication using 6,635 Lord Howe currawong specific SNPs to determine the impact of rodent eradication using estimate of genetic diversity, relatedness, inbreeding, and population differentiation.
The phylogenetic affinities of Lord Howe currawong suggest they are a geneticallydistinct taxon with consensus across methods of tree construction. Historical estimates of Ne suggest the founding population of Lord Howe currawong had reduced genetic diversity relative to other mainland taxa, while contemporary estimates of Ne for Lord Howe currawong was small suggesting the possibility of short-term inbreeding. Genetic health of Lord Howe currawong before and after the rodent eradication found no immediate impact on genetic health, but that future negative genetic health consequences were possible if Lord Howe currawong are not managed properly given increased relatedness following the rodent eradication. Thus, this thesis highlights the importance of thorough genetic assessment of taxa for informing management practices.