Hybridization between escaped domestic and wild American mink (Neovison vison)

The release of domesticated organisms into natural populations may adversely affect these populations through predation, resource competition, and the introduction of disease. Additionally, the potential for hybridization between wild and domestic conspecifics is of great concern because it can alter the evolutionary integrity of the affected populations. Wild American mink (Neovison vison) populations may be threatened not only by competition for resources with domestic mink originating from farms, but by breeding with such escapees. Using 10 microsatellite loci, we genotyped mink from Ontario, Canada, sampled from two farms, two putatively mixed populations in regions surrounding the mink farms, and two wild populations with no recent history of mink farming. Using individual-based Bayesian population assignment, we identified four population clusters, including one wild, and three domestic populations. The latter were not clustered by farm but rather by distinct line-bred colour phases. Population clustering also identified domestic and hybrid mink in the free-ranging populations. Nearly two-thirds of the mink sampled in the two putatively mixed populations (78% and 43%) were either farm escapees or descendants of escapees. Principal components analysis of allele frequencies supported our Bayesian assignment results. The power of our assignment test was assessed using simulated hybrid genotypes which suggested that our overall correct classification rate was 96.2%. The overwhelming presence of domestic animals and their hybridization with mink in natural populations is of great concern for the future sustainability of wild mink populations.

Ranavirus: past, present and future

Emerging infectious diseases are a significant threat to global biodiversity. While historically overlooked, a group of iridoviruses in the genus Ranavirus has been responsible for die-offs in captive and wild amphibian, reptile and fish populations around the globe over the past two decades. In order to share contemporary information on ranaviruses and identify critical research directions, the First International Symposium on Ranaviruses was held in July 2011 in Minneapolis, MN, USA. Twenty-three scientists and veterinarians from nine countries examined the ecology and evolution of ranavirus-host interactions, potential reservoirs, transmission dynamics, as well as immunological and histopathological responses to infection. In addition, speakers discussed possible mechanisms for die-offs, and conservation strategies to control outbreaks.

Microsatellite marker data suggest sex-biased dispersal in the common frog Rana temporaria

Despite being important models in ecological, evolutionary and conservation biology research, very little is known about the dispersal in anuran amphibians, and juvenile dispersal in particular. Using microsatellite data, we assessed signatures of sex-biased migration in the common frog (Rana temporaria) in Scandinavia. Significant heterozygosity deficiency (FIS) and lower assignment value (mAIc) among females suggest that dispersal in R. temporaria is female biased. Also variance of assignment (vAIc), estimated separately for the two sexes, was consistent with this inference, although the difference was not statistically significant. Possible proximate and ultimate explanations for female-biased dispersal in amphibians are discussed.

Genetic variability predicts common frog (Rana temporaria) size at metamorphosis in the wild

We investigated associations between genetic variability and two fitness-related traits--size and age at metamorphosis--in two subartic populations of the common frog, Rana temporaria. We found that metamorphic size was positively correlated with individual heterozygosity (as estimated using eight microsatellite loci) and that maternal heterozygosity also explained a significant amount of variation in this trait. In contrast, age at metamorphosis was only explained by environmental factors. Since size at metamorphosis is positively correlated with fitness in amphibians, these results suggest that genetic variability may be an important component of individual fitness in common frogs. The environmental variation underlying timing of metamorphosis may indicate that strong selection pressure on this trait in the Nordic environment is likely to override genetic effects.

Isolation and characterization of polymorphic microsatellite loci in muskrat, Ondatra zibethicus

We describe the isolation and characterization of 12 highly polymorphic microsatellite loci for the muskrat, Ondatra zibethicus. Microsatellite markers from three other rodent species were cross-amplified in muskrat and one of them was polymorphic. We observed moderate to high levels of genetic variability in these 13 polymorphic loci (five to 22 alleles per locus) with observed heterozygosity ranging from 0.48 to 0.96. These markers will be useful for further studies on population genetic structure in muskrat and potentially in other rodent species.

Phylogenetic analysis of Hyalella colonization in lakes recovering from acidification and metal contamination

The freshwater amphipod Hyalella azteca (Saussure, 1858) is common throughout North America and is a popular organism for toxicity tests and assessment of an ecosystem’s health. However, recent studies suggest that this “species” may actually be a number of closely related species, possibly with distinct habitat requirements. The region in and around Sudbury, Ontario, has many lakes recovering from acidification and metal contamination with Hyalella slowly recolonizing the area. Analyzing mitochondrial cytochrome c oxidase I (COI) sequences, we find two major groups of Hyalella: one group associated with recolonization of the central, historically more contaminated set of lakes and a second group associated with the more distant, less impacted, lakes. Morphologically, these inner city amphipods are significantly larger than those observed in lakes farther away from the city. This study may provide a foundation for a better understanding of Hyalella species complex, as well as colonization routes, toxicological sensitivities, habitat requirements, and dispersal capabilities.

Multi-tool diagnosis of an outbreak of ranavirosis in amphibian tadpoles in the Canadian boreal forest

Investigation of mortalities in isolated wild amphibian populations presents diagnostic difficulties that can hinder reaching a definitive diagnosis for the cause of death. Disease can only be diagnosed when pathogen presence (e.g. detection by PCR) is linked to tissue lesions (histopathology) in the host. We report a 2-site outbreak of ranavirosis in wild anuran tadpoles in the boreal forest of Wood Buffalo National Park, Canada, diagnosed by histologic and molecular techniques. Mortalities occurred in wood frog Rana sylvatica tadpoles and boreal chorus frog Pseudacris maculata tadpoles. Lack of mortality in sympatric Canadian toad Bufo (Anaxyrus) hemiophrys tadpoles suggested lower disease susceptibility in this species. In the former 2 species, ranavirosis was diagnosed based on consistent histopathology, immunohistochemistry (IHC), in situ hybridization (ISH), and quantitative PCR results. The most common histopathologic lesion present in wood and boreal chorus frog tadpoles was necrosis of the skin, oral mucosa, renal tubular epithelium, renal hematopoietic tissue, and branchial epithelium. Mild hepatic and pancreatic necrosis and rare intracytoplasmic inclusion bodies in hepatocytes were less common. Skeletal and connective tissues in budding limbs often had multifocal to coalescing necrosis and were intensely positive for ranavirus, with IHC staining even in areas where no obvious necrosis could be observed. Abundant IHC and ISH staining in actively growing tissues support a link between disease emergence and amphibian developmental stage. Our findings provide a definitive diagnosis of ranavirosis in free-living amphibians and highlight the effectiveness of multi-tool approaches to mortality investigation and elucidation of pathogenesis of ranavirosis in wild amphibians.

Water Pollution Increases the Risk of Chytridiomycosis in Mexican Amphibians

Chytridiomycosis is affecting amphibians worldwide, causing the decline and extinction of several amphibian populations. The disease is caused by the fungus Batrachochytrium dendrobatidis (Bd), a multihost pathogen living in freshwater habitats. While several environmental factors have been associated with the prevalence of Bd and its virulence, the effects of water quality on the pathogen are not clear yet. Some evidence suggests that water pollution may reduce amphibians' immune response and increase prevalence of Bd. To explore this hypothesis, we analyzed the relationship between water quality and the presence of Bd by using spatial data mining of 150 geolocations of Bd in amphibians from 9 families where Bd positive specimens have been previously reported, and water quality in 4,202 lentic and lotic water bodies in Mexico from 2010 to 2021. Our model showed that in the 3 main families where Bd was recorded, its presence is high in locations with low water quality, i.e., water polluted likely contaminated with urban and industrial waste. Using this model, we inferred areas suitable for Bd in Mexico; mainly in poorly studied areas along the gulf and on the pacific slope. We further argue that actions to reduce water pollution should become an integral part of public policies to prevent the spread of Bd and protect amphibians from this deadly pathogen.

An enigmatic mass mortality event of Blanding’s Turtles (Emydoidea blandingii) in a protected area

Mass mortality events (MMEs) can remove up to 90% of individuals in a population and are especially damaging to population viability of long-lived species with slow life histories. Our goal was to elucidate the cause(s) of a MME of 53 Blanding’s Turtles (Emydoidea blandingii (Holbrook, 1838)), a globally endangered species, in a protected area. We investigated disease, winter-kill, and depredation as potential causes of the mortality. The turtle carcasses lacked soft tissue to test for disease, so we examined tissue from co-occurring live Leopard Frogs (Lithobates pipiens (Schreber, 1782)) and found no evidence of ranavirus, indicating that the disease was not present at our study site. Water temperature and dissolved aquatic oxygen at known overwintering sites and sites which yielded carcasses did not differ, suggesting that winter-kill did not cause the MME. Carcass condition, comparisons with descriptions of turtle depredation events in the literature, and trail cameras paired with turtle decoys identified potential predators within the study site and suggested that mass depredation, enabled by low water levels and a concomitant reduction in aquatic habitat, was the most likely cause of mortality. Our study can inform conservation of the study population and the management of MMEs of long-lived species elsewhere.