Fine-Scale Population Structure and Contrasting Connectivity in Remnant Populations of the Alpine Tree Frog

The alpine tree frog ( Litoria verreauxii alpina ) persists in small remnant populations following severe declines associated with Batrachochytrium dendrobatidis ( Bd ), yet the genetic consequences of long-term persistence under endemic disease remain poorly resolved, limiting management of genetic diversity and connectivity. We used genome-wide SNP data to evaluate genetic diversity, effective population size, population structure, and connectivity across remnant populations in Victoria and New South Wales, including recent resampling of several New South Wales sites. Populations showed strong fine-scale genetic structure, with pairwise F _ST values ranging from 0.036 to 0.326. Victorian populations were highly differentiated despite short geographic distances, whereas New South Wales populations retained greater connectivity across broader spatial scales. Effective population sizes were generally low across the range, with most populations below 200, and all populations showed positive F _IS values. In New South Wales, resistance surface modelling identified slope as the dominant predictor of connectivity, with waterways potentially serving as population connectors, roads acting as near-barrier features, and topographic position exerting secondary effects. Together, these results indicate that remnant populations of L. v. alpina are characterized by strong isolation, reduced effective size, and region-specific differences in connectivity, all of which increase vulnerability to ongoing genetic erosion. Our findings highlight the value of population genomics for identifying hidden conservation risk in disease-impacted amphibians. Management should prioritize corridor protection, prevention of further fragmentation, and repeated genomic monitoring to maintain long-term adaptive potential.