Bufo Hemiophrys Research Articles

Ranavirus Amplification in Low-Diversity Amphibian Communities.

In an era where emerging infectious diseases are a serious threat to biodiversity, epidemiological patterns need to be identified, particularly the complex mechanisms driving the dynamics of multi-host pathogens in natural communities. Many amphibian species have faced unprecedented population declines associated with diseases. Yet, specific processes shaping host-pathogen relationships within and among communities for amphibian pathogens such as ranaviruses (RV) remain poorly understood. To address this gap, we conducted a comprehensive study of RV in low-diversity amphibian communities in north-western Canada to assess the effects of biotic factors (species identity, species richness, abundance) and abiotic factors (conductivity, pH) on the pathogen prevalence and viral loads. Across 2 years and 18 sites, with communities of up to three hosts (wood frog, Rana sylvatica; boreal chorus frog, Pseudacris maculata; Canadian toad, Anaxyrus hemiophrys), we observed that RV prevalence nearly doubled with each additional species in a community, suggesting an amplification effect in aquatic, as well as terrestrial life-history stages. Infection intensity among infected wood frogs and boreal chorus frogs also significantly increased with an increase in species richness. Interestingly, we did not observe any effects of host abundance or abiotic factors, highlighting the importance of including host identity and species richness when investigating multi-host pathogens. Ultimately, only such a comprehensive approach can improve our understanding of complex and often highly context-dependent host-pathogen interactions.

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.

Multiscale Occupancy Patterns of Anurans in Prairie Wetlands

Abstract: Habitat loss and degradation appear to be the primary drivers of amphibian declines. Given the losses of native prairie and prairie wetlands, it is essential to understand the habitat conditions that support amphibian species in remaining prairie ecosystems. In this study, we combine wetland surveys, geographic information systems (GIS), and hierarchical statistical modeling to assess anuran occupancy relationships with wetland and landscape factors. We surveyed 141 wetlands with repeated sampling for amphibian breeding activity (calling, eggs, tadpoles, metamorphs) in the Sheyenne National Grasslands—one of the largest contiguous prairies on the North American continent. Overall we observed evidence of seven amphibian species breeding in the Sheyenne National Grasslands. Species with ubiquitous distributions (Boreal Chorus Frogs) or species that occurred infrequently (Canadian Toads and Great Plains Toads) had little variance in occupancy. However, Northern Leopard Frogs, Wood Frogs, and Gray T...

Oscillation of an Anuran Hybrid Zone: Morphological Evidence Spanning 50 Years

BackgroundThe hybrid zone between the primarily forest-dwelling American toad, Anaxyrus americanus, and the prairie-adapted Canadian toad, A. hemiophrys, in southeastern Manitoba is known to have shifted its position during the past 50 years. Hybrid zones are areas of interbreeding between species and their movement across a landscape should reflect their underlying dynamics and environmental change. However, empirical demonstrations of hybrid zone movements over long periods of time are rare. This hybrid zone is dominated by individuals of intermediate morphology and genetic composition. We sought to determine if it had continued to move and if that movement was associated with shifts in habitat, as predicted.Methodology/Principle FindingsWe used variation in the toads’ most diagnostic morphological feature, the separation between their interorbital cranial crests, to determine the geographic position of the hybrid zone center at four times between 1960 and 2009 using maximum likelihood methods. The hybrid zone center moved west by 38 km over 19 years and then east again by 10 km over the succeeding 29 years. The position of the hybrid zone did not track either the direction or the magnitude of movement of the forest-prairie habitat transition over the same time period.Conclusions/SignificanceThis is the first reported evidence of oscillation in the position of a hybrid zone. The back and forth movement indicates that neither species maintains a selective advantage over the other in the long term. However, the movement of the hybrid zone was not bounded by the breadth of the habitat transition. Its oscillation suggests that the hybrid zone is better described as being elastically tethered to the habitat transition.

The pitfalls of extrapolation in conservation: movements and habitat use of a threatened toad are different in the boreal forest

AbstractWidely distributed species often vary geographically in their ecology. Thus, results of studies done in one part of their range cannot necessarily be extrapolated readily to populations elsewhere. This problem is particularly important for threatened species whose ecology has been studied in a few disconnected locations. The Canadian toad Bufo (Anaxyrus) hemiophrys occupies a large geographic range in western North America, but most studies of its ecology have been done in the prairies, where the species is considered to be closely associated with aquatic habitats. However, B. hemiophrys also occurs in boreal forest, where it faces threats from logging activities, especially if it uses upland habitats far from ponds and lakes. We radio‐tracked 29 toads in the boreal forest of northern Alberta, Canada to determine their patterns of movement and habitat use. Most movements between fixes were <50 m, but toads sometimes made longer movements exceeding 100 m. Over time, however, these short‐term movements combined into large‐scale directional movements that were highly variable among toads in both tortuosity and timing, but which generally took toads into upland forested habitats. Putative hibernacula also were located in upland sites. However, despite this terrestriality, toads still were associated with wetlands, using them significantly more often than would be expected based on their proportionate areal contribution to the landscape. Nonetheless, use of upland sites and long‐distance terrestrial movements differentiate this population of B. hemiophrys from those studied in prairie environments. Conservation plans based on what we know about the species elsewhere therefore would be inappropriate in this region. Management often requires site‐specific information, which can be obtained only from natural‐history studies of the populations in question.

Myiasis by Lucilia silvarum (Calliphoridae) in Amphibian Species in Boreal Alberta, Canada

We report myiasis by Lucilia silvarum with an overall prevalence of 0.9% in amphibian populations in boreal Alberta. In the period 1998--1999, we documented L. silvarum infestations in wild populations of wood frog (Rana sylvatica), boreal chorus frog (Pseudacris maculata), boreal toad (Bufo boreas boreas), and Canadian toad (B. hemiophrys). We believe this is the first record of this parasite from boreal and Canadian toads. Almost all previous records of L. silvarum parasitism in North America indicate that myiasis is fatal to an anuran host. Here, we provide the first record of adult individuals from 2 species (wood frog and boreal toad) surviving infestations. Although we actively captured and examined amphibians in Alberta from 1996 to 2006, we only found parasitism in 1998 and 1999. This is the most northerly record of anuran infestations by this parasite.

Indirect effects of fish winterkills on amphibian populations in boreal lakes

We exploited fish winterkills in small, boreal Alberta lakes to determine if anuran amphibians respond to large but natural changes in fish densities. Eight large declines in fish abundance occurred in seven lakes over a 5 year period, while major increases in fish abundance, reflecting recovery after winterkill, were recorded 5 times. Summer pitfall trapping of young-of-the-year (YOY) Wood Frogs (Rana sylvatica LeConte, 1825) and Boreal (Bufo boreas boreas Baird and Girard, 1852) and Canadian (Bufo hemiophrys Cope, 1886) toads indicated that frog abundance responded consistently to such large changes in fish abundance, but especially if fish communities were dominated by small-bodied species (sticklebacks and minnows). As well, changes in YOY Wood Frog and fish abundance were negatively correlated; YOY Wood Frogs were as much as 7.7 times more abundant after winterkills than in non-winterkill years. These increases in metamorphs did not result from an increased immigration of breeding adults to winterkill lakes, suggesting instead that larval survival was greater. Higher abundance of YOY Wood Frogs and toads was associated with smaller body size at metamorphosis. Despite this apparent reduction in individual growth, abundance of juvenile frogs remained significantly elevated 1 year after winterkill. In contrast to Wood Frogs, YOY toads tended to respond positively to recoveries of small-fish populations. Because anuran amphibians can respond to fish winterkill, and because winterkill is a frequent natural disturbance, small fish-bearing lakes can serve as important breeding habitat for amphibians in Alberta's boreal forest.

Life-history variation among populations of Canadian Toads in Alberta, Canada

Development of appropriate conservation plans relies on life-history information and how life-history traits vary across populations of a species. Such data are lacking for many amphibians, including the Canadian Toad (Bufo hemiophrys Cope, 1886). Here we use skeletochronology to estimate size at age, growth rates, age at maturity, and longevity of toads from nine populations along a latitudinal gradient in Alberta, Canada. Size of individual toads within each year class was highly variable, but age and size (measured as snout-to-urostyle length) were significantly related for almost all populations. The largest individuals were found in the southern-most population, while the smallest toads were found in three populations from the middle of the latitudinal range studied. Growth rates were highest in the southern-most population and lowest at the three populations with relatively small individuals. Maximum age was from 7 to 12 years for the populations sampled. The oldest individuals were found in populations in the middle of the latitudinal range sampled; toads in these populations were smaller than those in all other populations. Age at maturity was 1 year old for males and 2 years old for females in most populations. This study shows that some life-history traits exhibit significant variation between Canadian Toad populations, suggesting that effective conservation of this species will need to include population or area-specific management.

Mortality of captive Canadian toads from Basidiobolus ranarum mycotic dermatitis.

Twenty-six adult free-ranging Canadian toads (Bufo hemiophrys) were collected from northeastern North Dakota (USA) during the last week of August 1994 and placed in captivity. During late December and January 1995, 21 Canadian toads died. Clinical signs included increased time sitting in water bowls, darkened dorsal skin, constant arching of their backs, and hyperemia and sloughing of ventral epidermis. The condition progressively worsened until death occurred within 5 to 7 days after onset of clinical disease. Mycotic dermatitis due to Basidiobolus ranarum was diagnosed in all toads and the fungus was isolated from 11 (52%) of 21 toads. Histology of the ventral skin and digits revealed numerous fungal spherules and occasional hyphae without significant inflammatory reaction. This condition clinically resembled red leg associated with Aeromonas hydrophila and many other bacterial organisms, and the diseases could be confused without appropriate diagnostic tests. This also is the first report of B. ranarum causing clinical disease in a toad species.

An observation of interspecific amplexus between Boreal, Bufo boreas, and Canadian, Bufo hemiophrys, toads with a range extension for Boreal Toad in central Alberta

An observation of interspecific amplexus between Boreal, Bufo boreas, and Canadian, Bufo hemiophrys, toads with a range extension for Boreal Toad in central Alberta

Experimental exposure of Canadian toads to Basidiobolus ranarum.

Experimental transmission of the fungus Basidiobolus ranarum was induced in two treatment groups of Canadian toads (Bufo hemiophrys) and caused a fatal mycotic dermatitis. Seven of 10 (70%) toads that had their ventral skin mildly abraded and exposed to B. ranarum developed hyperemia, and sloughing of their ventral skin and died. Toads with abraded ventral skin or exposure to infected skin also were affected statistically at a higher rate than those with abraded skin and exposure to pure cultures of B. ranarum inoculated into their water source. Of toads showing clinical disease, B. ranarum was identified by both impression smears and histology in all cases, but not from toads that appeared clinically healthy. The organism was cultured from 5 of 7 (71%) toads with clinical disease but not from any toad that appeared clinically healthy (n = 28). This study documents methods of experimental transmission of B. ranarum, an organism responsible for causing a mycotic dermatitis that is fatal to toads.

Helminths of the Canadian Toad, Bufo hemiophrys (Amphibia: Anura), from Alberta, Canada

Forty adult Bufo hemiophrys from Alberta, Canada, were examined for helminths. Four species were found: a trematode, Gorgoderina simplex, and 3 nematodes, Cosmocercoides variabilis, Oswaldocruzia pipiens, and Rhabdias americanus. Rhabdias americanus had the highest prevalence of helminths (73%); C. variabilis had the highest mean intensity (26+/-33 SD). Bufo hemiophrys represents a new host record for each species of helminth.

THE TAXONOMIC STATUS OF THE WYOMING TOAD, BUFO BAXTERI PORTER

The population of toads in southeastern Wyoming named Bufo hemiophrys baxteri by Porter in 1968 is presumed to be extinct in nature, except perhaps for released, captive-bred specimens. It is sufficiently distinct in several respects, and sufficiently isolated geographically from its nearest rela- tive, B. h. hemiophrys, that it should be regarded as a distinct species, forming a superspecies group with B. hemiophrys.

An endangered species, the Wyoming toad Bufo hemiophrys baxteri—The importance of an early warning system

A protection system developed under the Endangered Species Act gives endangered species economic and political importance. Extinction-prone species must be identified early so that recovery programmes will succeed and be less costly. A comparison of systems for identifying extinction-prone species using a recently listed species, the Wyoming toad Bufo hemiophrys baxteri indicates that they are primarily useful in cases where decisions must be made immediately and information is limited. The sequence of events leading to the identification of the Wyoming toad as endangered shows that it would be beneficial to establish systematic monitoring programmes to ensure early detection of a species' decline. However, an effective protection programme will ultimately require detailed knowledge of the natural history of species and a comprehensive natural area programme.

Possible Extinction of the Wyoming Toad, Bufo hemiophrys baxteri

The Wyoming toad (Bufo hemiophrys baxteri) is a relictual subspecies confined to the Laramie Basin, Albany County, Wyoming. Since its discovery in south-eastern Wyoming, this subspecies has been known to occur only within a 2330 square kilometer area (Baxter and Meyer, 1982). The Wyoming toad was abundant in the 1950's and 1960's, but by the mid 1970's a drastic decline in population numbers had occurred (Baxter et al., 1982). An investigation in 1980 to determine the status of the Wyoming toad revealed a small population in a five square kilometer area (Van Kirk, 1980). In 1981 only one male and one female were observed during the breeding season (Baxter and Meyer, 1982). No toads were observed during a limited search in 1982. Until the discovery in 1983 of two juvenile specimens reported in this paper, no evidence of reproduction by this species had been observed since 1975.

Attempted avian predation by a Canadian Toad, Bufo americanus hemiophrys

Attempted avian predation by a Canadian Toad, Bufo americanus hemiophrys

A Natural Hybrid between the Toads Bufo hemiophrys and Bufo cognatus in Minnesota

A Natural Hybrid between the Toads Bufo hemiophrys and Bufo cognatus in Minnesota

Effects of Ionizing Radiation on Natural and Laboratory Populations of Manitoba Toads, Bufo hemiophrys

The ${\rm LD}_{50(30)}$ and ${\rm LD}_{50(60)}$ for adult male Bufo hemiophrys exposed to whole-body cesium-137 radiation in the laboratory was 2200 and 2000 R, respectively. Survival of toads expo...

Homing and Survival in the Manitoba Toad, Bufo Hemiophrys, in Minnesota

Homing to overwintering sites, spring emergence, and structure and density of a population of the Manitoba toad, Bufo hemiophrys, were studied in northwestern Minnesota from 1960 to 1967. Data were obtained on 15,837 individuals as they emerged from their wintering sites. Toads generally returned to the same Mima—type mound each fall, although individuals from various mounds were mixed in the breeding choruses and at the pond margins during summer. The high percentages of toads which homed to the wintering site correctly, ranging from 88 to 95%, indicate remarkable orientation capabilities. Toads committing an error when homing are much more likely to select a mound near their "home" mound, rather than a more distant one. Error rates were 10.2% for toads released as year—old juveniles and 2.9% for adults. Emergence occurs during a 5—6 week period, generally starting during the last few days of April. In general adult males emerged before adult females with juveniles emerging last. Deep frost in the soil delays the period of emergence. Population structure and density were determined mainly from toads wintering in four mounds. Yearly trends in juvenile numbers have been unanimously reflected by all four mounds. The 1966 population size, estimated by the Lincoln index, was 510 males, 1,276 females and 2,415 juveniles. Adult sex ratios varied from 33 to 38% males. The best estimate of the age structure of the total population at the time of breeding varied from 1.47 to 14.06 juveniles per adult. Survival of all toads from year to year ranged from 23.9% in 1963 to 44.4% in 1965. Juveniles had lower survival rates than adults, with the greatest mortality occurring in 1963 as the result of light snow and subsequent deep frost.

EVOLUTIONARY STATUS OF A RELICT POPULATION OF BUFO HEMIOPHRYS COPE.

The displacement of many populations during the Wisconsin glacial maximum and subsequent climatic changes have resulted in the fragmentation of ranges of many members of the North American fauna. One species so affected is the Dakota toad, Bufo hemiophrys Cope, which is an inhabitant of the northern plains with a wide distribution in central Canada and extreme northcentral United States. An ecological relict population of this species occurs about 500 miles to the south on the Laramie Plains of southeastern Wyoming (Fig. 1). The interruption of gene flow through geographical isolation is a major factor leading to the divergence of sister populations and eventual speciation, so the study of isolated populations may throw some light on the problem of the origin and age of species. The purpose of this study was to use several approaches to compare the Laramie population of the Dakota toad with those of the same kind occurring elsewhere in order to obtain data revealing the stage of speciation of the relict population.