Population Collapse of the Spidery Wattle (Acacia araneosa) During Late Holocene Aridification: Genomic Evidence for Critically Endangered Status.

Authors

Brittany P Hogben, Andrew J Lowe, Chelsea Hampel, Lars Littmann, Martin O'Leary, James B Dorey, Colette Blyth

Published in

Ecology and evolution. Volume 16. Issue 7. Pages e73959. Epub Jul 10, 2026.

Abstract

Protection and restoration of ecosystems, ceasing human-induced extinctions and maintaining genetic diversity are key goals for the Global Biodiversity Framework. Molecular techniques can provide empirical data to understand all these goals and provide actionable conservation advice. Acacia araneosa, an endangered aridland shrub, has a restricted distribution in South Australia where it coexists sympatrically with the widespread Acacia rivalis. Evidence of hybridisation between the two challenges the A. araneosa species concept. Here, we examine the genetic distinctness between the two species and use a genomic approach to estimate population genetic structure and historical population size. We used SNP data to quantify species boundaries, population structure, demography, kinship and genetic diversity within and between populations of both A. araneosa and A. rivalis. We found that while A. araneosa and A. rivalis hybridise to produce F1 hybrids, further backcrossing and gene flow are limited, suggesting that a post-zygotic breeding barrier may exist and that the two species are distinct. Genetic structure within A. araneosa suggests limited gene flow between the two remaining populations occurring within its small range. Our results also reveal a major reduction in effective population size (Ne) in recent times, dropping from ~49,000 to ~51 (-99.9%) over the last 3200 years, coinciding with widespread climatic drying across southern Australia. Paleoclimatic data over the last 3000 years in arid Australia are uncertain; hence, we provide novel empirical support for continued drying in this region using molecular techniques. We recommend that A. araneosa be listed as Critically Endangered on the IUCN Red List, and that the remaining populations are actively conserved and managed to maintain (and ideally increase) population size and genetic diversity.

PMID:
42437094
Bibliographic data and abstract were imported from PubMed on 12 Jul 2026.

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