Phylogenetic relationships, population connectivity, and development of genetic assignment testing in Buller's Albatross (Thalassarche bulleri ssp.)
Authors:   , Wold Jana 
Published: November 2021

<p>The Diomedeidae (Albatrosses) family is comprised of 22 recognised species, 13 are of high conservation concern because they are experiencing population declines. The taxonomy of albatrosses has always been problematic, which makes it difficult to estimate the number and size of breeding groups within a species. The Northern Buller’s Albatross (Thalassarche bulleri platei) and Southern Buller’s Albatross (Thalassarche bulleri bulleri) (Robertson & Nunn 1998; Turbott 1990) were recognised as separate species until 2006. A review of morphological data provided a basis for defining them as one species (Thalassarche bulleri); a result that was supported by international conservation agreements. However, there was no genetic data available at the time to corroborate the taxonomic change. The species status of Buller’s Albatross ssp. is an important issue because they are consistently recorded in the top five observed seabird interactions with commercial fishing vessels within New Zealand's Exclusive Economic Zone. Despite their prevalence in fisheries interactions, the relative impact of commercial fishing activity on northern and southern populations is unknown. Incidental mortality of albatrosses in commercial fisheries is recognised as a primary source of population disturbance.  The overall goal of this thesis research was to investigate the genetic differences between the two sub-species of Buller’s Albatross. DNA was isolated from blood samples collected from a total of 73 birds from two Northern Buller’s Albatross colonies (n = 26) and two Southern Buller’s Albatross colonies (n = 47). The degree of genetic differentiation between the Northern and Southern taxa was estimated using DNA sequences from a 221 bp fragment of the mitochondrial control region, Domain II (CRII). The genetic differentiation between regional colony groups was high (pairwise ΦST = 0.621, p < 0.00001). Two haplogroups were identified within Northern Buller’s Albatross, while Southern Buller’s Albatross samples composed a single haplogroup. An analysis of molecular variance did not find any significant population structuring at the colony level. All individuals sampled from fisheries bycatch (n = 97) were assigned with maximum probability to either Northern (n = 19) or Southern Buller’s Albatross (n = 78; P = 1.00). The DNA sequences differences found in the mitochondrial control region can be used to assign provenance of T. bulleri ssp. samples, which will be a useful conservation management tool.  In addition, a genome wide set of markers was obtained using a Genotyping by Sequencing approach. DNA was digested using restriction enzymes, fragments were labeled adaptor sequences, and shotgun sequenced on an Illumina platform by AgResearch. The Stacks pipeline was used to filter the sequences and obtain a set of single nucleotide polymorphism (SNP) markers across the genome. Estimates of genetic diversity and gene flow were conducted for 26 319 putative loci comprised of 54,061 single nucleotide polymorphisms. Estimates of genetic diversity were consistent across datasets with both taxa exhibiting similar levels of nucleotide diversity (Northern π ≈ 0.002 – 0.004; Southern π ≈ 0.002 – 0.003). However, estimates of genetic differentiation increased slightly as filtering protocols became increasingly restrictive (FST ≈ 0.019 – 0.048). This low level of differentiation was supported by admixture analyses, which identified two distinct ‘clusters’, one corresponding to T. b. platei and the second to T. b. bulleri. The results of this research demonstrate that Northern and Southern Buller’s Albatrosses are two genetically distinct groups.</p>