Low neutral and immunogenetic diversity in northern fringe populations of the green toad Bufotes viridis: implications for conservation

Abstract

Genetic variation is often lower at high latitudes, which may compromise the adaptability and hence survival of organisms. Here we show that genetic variability is negatively correlated with northern latitude in European green toads (Bufotes viridis). The result holds true for both putatively neutral microsatellite variation and supposedly adaptive MHC Class IIB variation. In particular, our findings have bearing on the conservation status of this species in Sweden, on the northern limit of its distribution where local populations are small and fragmented. These genetically impoverished populations are closely related to other populations found around the Baltic Sea basin. The low neutral and adaptive variation in these fringe populations compared to population at central ranges confirms a pattern shared across all other amphibians so far studied. In Sweden, the situation of green toads is of concern as the remaining populations may not have the evolutionary potential to cope with present and future environmental challenges.

Piecing the barcoding puzzle of Palearctic water frogs (Pelophylax) sheds light on amphibian biogeography and global invasions

“…While most water frog populations with a foreign genetic signature have a human‐mediated origin, our results also call for cautious interpretations in a few cases. First, rather than multiple translocations, postglacial expansions could have also naturally carried kurtmuelleri mtDNA and nuclear haplotypes over Central and Northern Europe (Kolenda et al., 2017; Litvinchuk et al., 2020), as seen in some anurans of Balkan origin (e.g., Bufotes viridis , Höglund et al., 2022). This scenario is possible given that P. ridibundus ridibundus and P. ridibundus kurtmuelleri seem to represent shallow refugial lineages of the same biological species (Papežík et al., 2023) that remain highly similar at the genomic scale (Dubey, Lavanchy, et al., 2019) and may thus hybridize without reproductive barriers.…”

“…While most water frog populations with a foreign genetic signature have a human-mediated origin, our results also call for cautious interpretations in a few cases. First, rather than multiple translocations, postglacial expansions could have also naturally carried kurtmuelleri mtDNA and nuclear haplotypes over Central and Northern Europe (Kolenda et al, 2017;Litvinchuk et al, 2020), as seen in some anurans of Balkan origin (e.g., Bufotes viridis, Höglund et al, 2022).…”

Body size mediates latitudinal population differences in the response to chytrid fungus infection in two amphibians

“…Firstly, due to post-glacial colonization patterns northern populations often harbor less genetic variation (Hewitt 2000 ). In many amphibians, this is true also for immunogenetic variation in major histocompatibility (MHC) genes (Zeisset and Beebee 2014 ; Cortázar-Chinarro et al 2017 , 2022 ; Höglund et al 2022 ), which is associated with Bd resistance (Savage and Zamudio 2011 ; Savage et al 2018 ; Kosch et al 2019 ). Furthermore, pathogen species richness and abundance are significant predictors of adaptive MHC variation (Wang et al 2017 ).…”

A Unified Approach to Analysis of Body Condition in Green Toads

“…For comparisons of results among populations and seasons in the same population, using the SMI with a standard coefficient appears to be the best approach. In studies monitoring green toads, which are of great concern for conservationists in many European countries [ 47 ], we propose to calculate the SMI with our ‘green toad coefficient’ (with the formula: mi = m × (60/L) 3 , where mi is the (scaled) mass index (SMI), m is the individual mass, and L is the SVL in mm). Of course, researchers may have good reasons to adopt a different exponent if the data indicate another scaling relationship intheir study populations.…”