Conservation genetics and disease status of an Endangered Population of tusked frogs (Limnodynastidae: Adelotus brevis) in eastern Australia

A population of tusked frogs (Adelotus brevis) occurring in the New England Tablelands (NET) and Nandewar (NAN) (NET/NAN) bioregions experienced drastic historical declines. The declines were most likely caused by the amphibian chytrid fungus (Batrachochytrium dendrobatidis, Bd) and resulted in the population being listed as Endangered. Few extant populations have been documented in the 25 years since listing, and the current status of the population is unknown. We conducted targeted surveys across three breeding seasons (2022–2024), focusing on abundance, distribution, and population health. Genetic material and Bd swab samples were collected from 13 tusked frogs at two sites, and three individuals (21%) tested positive for Bd. Genomic analyses indicated relatively low genetic diversity, with observed heterozygosity lower than expected, and positive inbreeding coefficients across sampled populations. Population structure analyses identified two major genetic clusters of tusked frogs across New South Wales (NSW) and recovered additional finer-scale substructure in southern NSW. However, the NET/NAN population clustered with geographically adjacent populations rather than form a distinct genetic unit. Our surveys confirm that the NET/NAN population persists at the western and upper elevational limits of the species’ range. Continued surveys are required to elucidate the threat posed by small population sizes, low genetic diversity and Bd, and to determine the full spatial extent of the Endangered Population via scientific surveys and citizen science.