Mikkel Skovrind:
Phylogeography, demographic history and hybridization in belugas Delphinapterus leucas

Date: 14-06-2019    Supervisor: Eline D. Lorenzen

The aim of the thesis is to further our understanding of the population structure and demographic history of beluga whales in a range-wide context, using genomic data. The thesis includes an introduction, and four chapters written as draft manuscripts; Chapter 1 is in revision with Marine Fisheries Review, Chapter 2 has been published in Mitochondrial DNA Part B, Chapter 3 is a draft manuscript intended for Molecular Ecology and Chapter 4 is accepted for publication in Scientific Reports and will be published June 22th 2019.

Chapter 1 Circumpolar mtDNA population structure and variation in belugas: a review. In this manuscript we review the genetic studies of belugas published to date, and for the first time present a range-wide analysis of levels of mtDNA diversity and differentiation in beluga populations. Our analysis of 302 bp of overlapping mtDNA control region sequence includes 2,933 individuals spanning all 21 recognized beluga stocks, and represents 71 haplotypes defined by 16 variable sites. Results put the diversity and differentiation in a global perspective and highlights the limitations of short mtDNA fragments in beluga phylogeography.

Chapter 2 Mitochondrial genome divergence between beluga whales in Baffin Bay and the Sea of Okhotsk. This publication has the first comparison of two complete mitochondrial sequences from separate ends of the beluga range and their estimated divergence time. Despite the caveats of small sample size and simplified methodology, we estimate that the divergence of beluga clades is in the order of hundreds of thousands of years. The publication is available from: ( www.tandfonline.com/doi/full/10.1080/23802359.2017.1318686 ).

Chapter 3 Habitat fragmentation and secondary contact shape phylogeography and demographic history of belugas. In this manuscript, we analyse 2 nuclear genomes and 202 mitogenomes from 23 localities covering the entire beluga distribution, applying population genetics, bayesian phylogenetic and species distribution modeling analyses. Our results show that the earliest split within belugas happened around 750 kya with four lineages established before the start of the last glaciation, and that current population structure is largely a result of secondary contact of these old lineages. Further, our results show that the effective population size of belugas has increased six-fold since LGM and that the suitable habitat range has increased since LGM, with the winter area increasing 3-4 fold.

Chapter 4 Hybridization between two high Arctic cetaceans confirmed by genomic analysis. We present genome-wide DNA sequence data from a monodontid skull which from its intermediate morphology was hypothesized to be a beluga/narwhal hybrid. Using DNA retrieved from the skull and a reference genomic panel of each parental species, we show that the specimen is indeed a first-generation hybrid. Our analyses reveal that it was a male, with a narwhal mother. We also present stable isotope analysis of the beluga/narwhal hybrid. The data suggest a unique diet of the hybrid relative to either parental species. These results further our understanding of the interaction between belugas and narwhals, and underscore the importance of natural history collections in monitoring changes in biodiversity.