Landscape genetics identifies barriers to Natterjack toad metapopulation dispersal

Abstract

Habitat fragmentation and loss reduce population size and connectivity, which imperils populations. Functional connectivity is key for species persistence in human-modified landscapes. To inform species conservation management, we investigated spatial genetic structure, gene flow and inferred dispersal between twelve breeding sites of the Natterjack toad (Bufo calamita); regionally Red-Listed as Endangered in Ireland. Spatial genetic structure was determined using both Bayesian and non-Bayesian clustering analysis of 13 polymorphic microsatellite loci genotyping 247 individuals. We tested the influence of geographic distance, climate, habitat, geographical features, and anthropogenic pressure on pairwise genetic distances between breeding sites using Isolation-by-distance and Isolation-by-resistance based on least-cost path and circuit theory models of functional connectivity. There was clear spatial structuring with genetic distances increasing with geographic distance. Gene flow was best explained by Isolation-by-resistance models with coniferous forestry plantations, bog, marsh, moor and heath, scrub, anthropogenic presence (Human Influence Index) and rivers (riparian density) identified as habitats with high resistance to gene flow while metapopulation connectivity was enhanced by coastal habitats (beaches, sand dunes and salt marshes) and coastal grassland. Despite substantial declines in census numbers over the past 15 years and its regional status as Endangered, the Natterjack toad population in Ireland retains high genetic diversity. If declines continue, maintaining habitat connectivity to prevent genetic erosion by management of coastal grasslands, pond construction and assisted migration through translocation will be increasingly important.

Quantifying uncertainty in inferences of landscape genetic resistance due to choice of individual‐based genetic distance metric

“…In addition, the question of whether inference based on population‐based approaches is less affected by the choice of genetic distance metric needs to be investigated. Furthermore, a ResistanceGA ‐based empirical study has recently suggested that convergence of the results obtained with different population‐based genetic distance metrics and AICc‐based model support improved when using a least‐cost path approach, rather than the current flow method implemented here, to calculate resistance distances (Reyne et al, 2023). The study was performed on natterjack toads ( Bufo camalita ) and further research will show whether this conclusion is generally valid or a result of the limited mobility of the study species.…”