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Slow motion extinction: inbreeding, introgression, and loss in the critically endangered mangrove finch (Camarhynchus heliobates)

Abstract

The critically endangered mangrove finch is now limited to one small population on the west coast of Isabela Island in the Galápagos, but 100 years ago multiple populations were found on the islands of Isabela and Fernandina. By accessing genetic datasets through museum sampling, we are able to put current levels of genetic diversity and hybridization with congenerics into a historical context for enhanced conservation. In this study, we compared neutral genetic diversity of the now extinct Fernandina population to historical and current diversity of the Isabela population using 14 microsatellite markers. We found that current genetic diversity of the last remnant population (~80–100 individuals) is far below levels 100 years ago, with only about half of the allelic diversity retained. Current genetic diversity is close to levels in the Fernandina population that went extinct by the 1970s. Bottleneck analysis did not show a strong signature of recent decline, and instead implies that this species may have consistently had low population sizes with wide fluctuations. Hybridization with congeneric woodpecker finches was found in the modern Isabela population, implying that some individuals within the few remaining breeding pairs are finding mates with woodpecker finches. Within the context of historical low population sizes and wide fluctuations, current conservation efforts may help the mangrove finch face current extinction threats and avoid the fate of the Fernandina population. However, this historically small lineage will likely continue to face challenges associated with small specialist species surrounded by a widely-distributed sister lineage producing viable hybrids.

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Acknowledgments

We thank the Galápagos National Park Directorate, the Charles Darwin Research Station, and the California Academy of Sciences. This research was supported by Darwin Initiative (15-005, EIDP0031, 162/12/018), Save our Species (2011A-023), Galápagos Conservancy (002-2015) and International Community Foundation with a grant awarded by The Leona M. and Harry B. Helmsley Charitable Trust (20160098), Galápagos Conservation Trust (CT14-171), the Mohammed Bin Zayed Species Conservation Fund (14259510), Durrell Wildlife Conservation Trust, the National Science Foundation (DEB-0317687), the Frankfurt Zoological Society (FZS 1224/97), Swiss Association of Friends of the Galápagos Islands, and the Max Planck Society. We thank Andrew Clack for assisting in ancient DNA techniques, Bart Kempenaers for providing materials and facility access at Max Planck for genotyping, and Peter and Rosemary Grant who initiated the work on the mangrove finch and have, over the years, helped and advised on the project. Research was carried out under IACUC protocol (12-04-09-01) and with approval for ethical research from Galápagos National Park. This publication is contribution number 2139 of the Charles Darwin Foundation for the Galápagos Islands.

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Correspondence to Lucinda P. Lawson.

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Lawson, L.P., Fessl, B., Hernán Vargas, F. et al. Slow motion extinction: inbreeding, introgression, and loss in the critically endangered mangrove finch (Camarhynchus heliobates). Conserv Genet 18, 159–170 (2017). https://doi.org/10.1007/s10592-016-0890-x

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Keywords

  • Ancient DNA
  • Bottleneck
  • Camarhynchus pallidus
  • Darwin’s finches
  • Galápagos
  • Hybrids