Antarctic ecosystem
Climate
Krill (Euphausia superba)
The enormous repetitive Antarctic krill genome reveals environmental adaptations and population insights
Summary
This study presents the first complete genome assembly of Antarctic krill, revealing a massive 48.01 billion base pair genome - the largest animal genome assembled to date. The enormous size results from extensive repetitive DNA sequences (92.45% of the genome), particularly jumping genes that copy themselves throughout the genome. The genome reveals molecular mechanisms underlying krill's adaptation to Antarctica's extreme seasonal environment, including expanded gene families for molting and energy processing, and a complete biological clock system. Population genetic analysis of 75 individuals from four Antarctic regions shows essentially one interconnected population with high gene flow, though subtle genetic differences exist due to environmental pressures on specific genes. Population history analysis indicates a major population bottleneck approximately 10 million years ago followed by expansion around 100,000 years ago, coinciding with major climate change events.
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Distribution of repetitive DNA content across the genome shown in non-overlapping 10 kilobase sections.Key Findings
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1. First complete Antarctic krill genome at 48.01 billion base pairs - the largest animal genome assembled to date.2
2. The genome is 92.45% repetitive sequences, with DNA jumping elements being the dominant component.3
3. Molecular structure of the biological clock system reveals adaptation to extreme polar light-dark cycles.4
4. Twenty-five significantly expanded gene families are related to molting and energy processing functions.5
5. Population analysis shows one interconnected population around Antarctica with high gene flow between regions.6
6. Environmental pressures were detected on 387 adaptive genetic variants across the genome.7
7. A population bottleneck occurred approximately 10 million years ago, followed by expansion around 100,000 years ago.8
8. Genetic diversity remains low despite large population size, illustrating a known evolutionary puzzle (Lewontin's paradox).Abstract
Antarctic krill (Euphausia superba) is Earth's most abundant wild animal, and its enormous biomass is vital to the Southern Ocean ecosystem. Here, we report a 48.01-Gb chromosome-level Antarctic krill genome, whose large genome size appears to have resulted from inter-genic transposable element expansions. Our assembly reveals the molecular architecture of the Antarctic krill circadian clock and uncovers expanded gene families associated with molting and energy metabolism, providing insights into adaptations to the cold and highly seasonal Antarctic environment. Population-level genome re-sequencing from four geographical sites around the Antarctic continent reveals no clear population structure but highlights natural selection associated with environmental variables. An apparent drastic reduction in krill population size 10 mya and a subsequent rebound 100 thousand years ago coincides with climate change events. Our findings uncover the genomic basis of Antarctic krill adaptations to the Southern Ocean and provide valuable resources for future Antarctic research.Published in
Cell
2023Authors
Shao, C., Sun, S., Liu, K., Wang, J., Li, S., Liu, Q., Deagle, B.E., Seim, I., Biscontin, A., Wang, Q., Liu, X., Kawaguchi, S., Liu, Y., Jarman, S., Wang, Y., Wang, H.-Y., Huang, G., Hu, J., Feng, B., De Pittà , C., Fan, G.Institutions
Yellow Sea Fisheries Research Institute, Chinese Academy of Fishery SciencesBGI-QingdaoUniversity of QueenslandUniversity of PadovaAustralian Antarctic DivisionCurtin UniversityAlfred Wegener Institute Helmholtz Centre for Polar and Marine Research
Methods
Biological sampling DataField
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