University of Oulu

von Seth, J., van der Valk, T., Lord, E. et al. Genomic trajectories of a near-extinction event in the Chatham Island black robin. BMC Genomics 23, 747 (2022).

Genomic trajectories of a near-extinction event in the Chatham Island black robin

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Author: von Seth, Johanna1,2,3; van der Valk, Tom1,2; Lord, Edana1,2,3;
Organizations: 1Centre for Palaeogenetics, Svante Arrhenius Väg 20C, 106 91, Stockholm, Sweden
2Department of Bioinformatics and Genetics, Swedish Museum of Natural History, Stockholm, Sweden
3Department of Zoology, Stockholm University, 106 91, Stockholm, Sweden
4Department of Biology, Lund University, Ecology Building, 223 62, Lund, Sweden
5Ecology and Genetics Research Unit, University of Oulu, 90014, Oulu, Finland
6Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, 17121, Solna, Sweden
7Department of Anatomy, University of Otago, Dunedin, 9054, New Zealand
8Coastal People Southern Skies Centre of Research Excellence, University of Otago, PO Box 56, Dunedin, 9054, Aotearoa, New Zealand
9Department of Zoology, University of Otago, Dunedin, 9054, New Zealand
10School of Biological Sciences, University of Canterbury, Christchurch, 8140, New Zealand
11Department of Conservation, Biodiversity Group, Auckland, New Zealand
12Department of Conservation, Science and Capability, Christchurch, New Zealand
13School of Agricultural, Environmental and Veterinary Sciences and Gulbali Institute, Charles Sturt University, PO Box 789, Albury, NSW, Australia
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 1.7 MB)
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Language: English
Published: Springer Nature, 2022
Publish Date: 2022-11-21


Background: Understanding the micro-­evolutionary response of populations to demographic declines is a major goal in evolutionary and conservation biology. In small populations, genetic drift can lead to an accumulation of deleterious mutations, which will increase the risk of extinction. However, demographic recovery can still occur after extreme declines, suggesting that natural selection may purge deleterious mutations, even in extremely small populations. The Chatham Island black robin (Petroica traversi) is arguably the most inbred bird species in the world. It avoided imminent extinction in the early 1980s and after a remarkable recovery from a single pair, a second population was established and the two extant populations have evolved in complete isolation since then. Here, we analysed 52 modern and historical genomes to examine the genomic consequences of this extreme bottleneck and the subsequent translocation.

Results: We found evidence for two-fold decline in heterozygosity and three- to four-fold increase in inbreeding in modern genomes. Moreover, there was partial support for temporal reduction in total load for detrimental variation. In contrast, compared to historical genomes, modern genomes showed a significantly higher realised load, reflecting the temporal increase in inbreeding. Furthermore, the translocation induced only small changes in the frequency of deleterious alleles, with the majority of detrimental variation being shared between the two populations.

Conclusions: Our results highlight the dynamics of mutational load in a species that recovered from the brink of extinction, and show rather limited temporal changes in mutational load. We hypothesise that ancestral purging may have been facilitated by population fragmentation and isolation on several islands for thousands of generations and may have already reduced much of the highly deleterious load well before human arrival and introduction of pests to the archipelago. The majority of fixed deleterious variation was shared between the modern populations, but translocation of individuals with low mutational load could possibly mitigate further fixation of high-frequency deleterious variation.

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Series: BMC genomics
ISSN: 1471-2164
ISSN-E: 1471-2164
ISSN-L: 1471-2164
Volume: 23
Article number: 747
DOI: 10.1186/s12864-022-08963-1
Type of Publication: A1 Journal article – refereed
Field of Science: 1181 Ecology, evolutionary biology
Funding: Open access funding provided by Stockholm University. N.D. was funded by the Swiss National Science Foundation (Postdoc Mobility grant P300PA_177845), Carl Tryggers Foundation (Grant CTS 19: 257) and University of Otago Research Grant 2017. B.C.R. acknowledge University of Otago Research Grant 2017 and Performance based research funding from the Department of Zoology, University of Otago. J.v.S. and L.D. acknowledge support from FORMAS (grant 2015–676). L.D. and E.L. acknowledge funding from FORMAS (2018–01640) and the Bolin Centre for Climate Research. M.M. acknowledges funding from the Brian Mason Scientific and Technical Trust and the Mohamed bin Zayed Species Conservation Fund for Black robin research on Hokorereoro in 2014/15.
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