Batrachochytrium dendrobatidis is the chytridiomycete fungus which has been implicated in global amphibian declines and numerous species extinctions. Here, we show that introduced North American bullfrogs ( Rana catesbeiana ) consistently carry this emerging pathogenic fungus. We detected infections by this fungus on introduced bullfrogs from seven of eight countries using both PCR and microscopic techniques. Only native bullfrogs from eastern Canada and introduced bullfrogs from Japan showed no sign of infection. The bullfrog is the most commonly farmed amphibian, and escapes and subsequent establishment of feral populations regularly occur. These factors taken together with our study suggest that the global threat of B. dendrobatidis disease transmission posed by bullfrogs is significant.

Invasive species control is now a conservation priority in many parts of the world. Demographic modeling using population matrix models is a useful tool in the design of these control efforts as it identifies the life stages with the strongest influence on population dynamics. As a case in point, American bullfrogs (Rana catesbeiana) have been introduced around the world and have negative effects on native fauna. We studied demography of four populations on southern Vancouver Island, Canada, using field observations and capture-mark-recapture methods to estimate survival, growth, and fecundity. The life cycle of these introduced bullfrogs progressed in yearly increments through the following stages: eggs/small tadpoles, first-year tadpoles, second-year tadpoles, metamorphs/juveniles, and adults. Some bullfrog tadpoles were able to skip the second-year tadpole stage and metamorphosed one year after hatching. With tadpole survival estimates from the literature and field estimates of the remaining parameters we constructed a matrix population model. Prospective demographic perturbation analysis showed that bullfrog population growth rate () was most influenced by the proportion of tadpoles metamorphosing early (tadpole development rate), and by early postmetamorphic survival rates. Most current control efforts for bullfrogs have focused on removing tadpoles and breeding adults, and our modeling suggests that these efforts may not be optimal. Partial removal of tadpoles may lead to higher tadpole survival and development rates and higher postmetamorphic survival due to decreased density-dependent competition. Removal of adults leads to higher survival of early metamorphic stages through reduced cannibalism. Our modeling suggests that culling of metamorphs in fall is the most effective method of decreasing bullfrog population growth rate. Our study shows how demographic information can be used to maximize the efficacy of control efforts, and our results are likely directly applicable to other invasive species with complex life cycles.

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Minimally invasive sampling (MIS) is widespread in wildlife studies; however, its utility for massively parallel DNA sequencing (MPS) is limited. Poor sample quality and contamination by exogenous DNA can make MIS challenging to use with modern genotyping‐by‐sequencing approaches, which have been traditionally developed for high‐quality DNA sources. Given that MIS is often more appropriate in many contexts, there is a need to make such samples practical for harnessing MPS. Here, we test the ability for Genotyping‐in‐Thousands by sequencing (GT‐seq), a multiplex amplicon sequencing approach, to effectively genotype minimally invasive cloacal DNA samples collected from the Western Rattlesnake (Crotalus oreganus), a threatened species in British Columbia, Canada. As there was no previous genetic information for this species, an optimized panel of 362 SNPs was selected for use with GT‐seq from a de novo restriction site‐associated DNA sequencing (RADseq) assembly. Comparisons of genotypes generated within and among RADseq and GT‐seq for the same individuals found low rates of genotyping error (GT‐seq: 0.50%; RADseq: 0.80%) and discordance (2.57%), the latter likely due to the different genotype calling models employed. GT‐seq mean genotype discordance between blood and cloacal swab samples collected from the same individuals was also minimal (1.37%). Estimates of population diversity parameters were similar across GT‐seq and RADseq data sets, as were inferred patterns of population structure. Overall, GT‐seq can be effectively applied to low‐quality DNA samples, minimizing the inefficiencies presented by exogenous DNA typically found in minimally invasive samples and continuing the expansion of molecular ecology and conservation genetics in the genomics era.

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