Regilla Tadpoles Research Articles

Host Jump of an Exotic Fish Rhabdovirus into a New Class of Animals Poses a Disease Threat to Amphibians.

Spring viremia of carp virus (SVCV) is a rhabdovirus that primarily infects cyprinid finfishes and causes a disease notifiable to the World Organization for Animal Health. Amphibians, which are sympatric with cyprinids in freshwater ecosystems, are considered non-permissive hosts of rhabdoviruses. The potential host range expansion of SVCV in an atypical host species was evaluated by testing the susceptibility of amphibians native to the Pacific Northwest. Larval long-toed salamanders Ambystoma macrodactylum and Pacific tree frog Pseudacris regilla tadpoles were exposed to SVCV strains from genotypes Ia, Ib, Ic, or Id by either intraperitoneal injection, immersion, or cohabitation with virus-infected koi Cyprinus rubrofuscus. Cumulative mortality was 100% for salamanders injected with SVCV, 98-100% for tadpoles exposed to virus via immersion, and 0-100% for tadpoles cohabited with SVCV-infected koi. Many of the animals that died exhibited clinical signs of disease and SVCV RNA was found by in situ hybridization in tissue sections of immersion-exposed tadpoles, particularly in the cells of the gastrointestinal tract and liver. SVCV was also detected by plaque assay and RT-qPCR testing in both amphibian species regardless of the virus exposure method, and viable virus was detected up to 28 days after initial exposure. Recovery of infectious virus from naïve tadpoles cohabited with SVCV-infected koi further demonstrated that SVCV transmission can occur between classes of ectothermic vertebrates. Collectively, these results indicated that SVCV, a fish rhabdovirus, can be transmitted to and cause lethal disease in two amphibian species. Therefore, members of all five of the major vertebrate groups (mammals, birds, reptiles, fish, and amphibians) appear to be vulnerable to rhabdovirus infections. Future research studying potential spillover and spillback infections of aquatic rhabdoviruses between foreign and domestic amphibian and fish species will provide insights into the stressors driving novel interclass virus transmission events.

Tooth row variation in tadpoles of Dendropsophus labialis (Anura: Hylidae: Dendropsophini) and the evolution of oral morphology in the genus

Labial tooth row variation was assessed in Dendropsophus labialis tadpoles from the Cordillera Oriental in Colombia. The presence of a second anterior labial tooth row was detected, showing thus a labial tooth row formula of 2/2. This second anterior tooth row was present in a substantial number of individuals, suggesting that the observed variation is not unusual. This variation contradicts earlier reports about the number of labial tooth rows in this species, whose labial tooth row formula has been reported as 1/2 without variation. A novel ontogenetic pattern of tooth row addition was detected, differing from earlier observations made on Pseudacris regilla tadpoles in terms of tooth row appearance order. The taxonomic implications for these data are discussed along with the evolution of oral morphologies in the genus.

Pseudacris regilla tadpole density differentially affects periphyton and macrophytes in a California vernal pool community

Biotic interactions between herbivores and primary producers are believed to play a major role in determining community composition of many ecological communities. How differences in herbivore abundance alter the relative importance of these interactions is not well understood, especially in seasonal wetland systems. This study investigated the effects of varying Pseudacris regilla (pacific chorus frog) larval densities on California vernal pool aquatic communities. It was hypothesized that with increasing tadpole density, macrophyte percent cover, biomass, diversity, and richness would decrease; while algae and zooplankton abundance, biomass and richness increase. The experimental mesocosm design consisted of five tadpole density treatments, and was arranged in a 5×5 randomized block design. Each density treatment was replicated five times. Macrophytes, algae and invertebrates were identified to the lowest possible taxonomic unit, and the biomasses of each community were quantified. Treatment effects were determined using both multivariate and univariate analysis of variance techniques. To detect differences in community composition, multivariate ordination analyses (ANOSIM, SIMPER, NMDS) were conducted. Increasing densities of P. regilla tadpoles had significant effects on the vernal pool macrophyte community. Plant diversity, species richness, biomass, and percent cover were all negatively affected by increasing tadpole densities. Macrophyte community structure was also found to be significantly different in the presence of tadpoles due to the fact that Downingia bicornuta, Ranunculus aquatilis, and Gratiola ebracteata were predominately isolated to mesocosms were P. regilla was absent. In addition, periphyton biomass was shown to be facilitated by increasing tadpole densities in the lower treatment ranges. Aquatic macroinvertebrates and phytoplankton communities, on the other hand, were not significantly affected by increasing tadpole densities. This study demonstrates the influence of P. regilla larvae on the primary producers within California vernal pool systems. Understanding the effects of these abundant consumers, and the mechanisms that drive the importance of their direct and indirect effects are essential for the conservation of vernal pools and the threatened species associated with them.

Parasite transmission in complex communities: Predators and alternative hosts alter pathogenic infections in amphibians

While often studied in isolation, host-parasite interactions are typically embedded within complex communities. Other community members, including predators and alternative hosts, can therefore alter parasite transmission (e.g., the dilution effect), yet few studies have experimentally evaluated more than one such mechanism. Here, we used data from natural wetlands to design experiments investigating how alternative hosts and predators of parasites mediate trematode (Ribeiroia ondatrae) infection in a focal amphibian host (Pseudacris regilla). In short-term predation bioassays involving mollusks, zooplankton, fish, larval insects, or newts, four of seven tested species removed 62-93% of infectious stages. In transmission experiments, damselfly nymphs (predators) and newt larvae (alternative hosts) reduced infection in P. regilla tadpoles by -50%, whereas mosquitofish (potential predators and alternative hosts) did not significantly influence transmission. Additional bioassays indicated that predators consumed parasites even in the presence of alternative prey. In natural wetlands, newts had similar infection intensities as P. regilla, suggesting that they commonly function as alternative hosts despite their unpalatability to downstream hosts, whereas mosquitofish had substantially lower infection intensities and are unlikely to function as hosts. These results underscore the importance of studying host-parasite interactions in complex communities and of broadly linking research on predation, biodiversity loss, and infectious diseases.

Effects of environmentally relevant concentrations of endosulfan, azinphosmethyl, and diazinon on Great Basin spadefoot (Spea intermontana) and Pacific treefrog (Pseudacris regilla)

We conducted dose-response exposures to compare the lethality of endosulfan, diazinon, and azinphosmethyl in the early-life stages of the Great Basin spadefoot (Spea intermontana) and the Pacific treefrog (Pseudacris regilla). Our experiment occurred in two 8-d phases: one, with developing embryos, and two, with Gosner Stage 27 tadpoles. Pesticide concentrations were representative of field-measured concentrations (60 ng/L of endosulfan, 50 ng/L of azinphosmethyl, and 350 ng/L of diazinon), in the same geographic areas where these species occur in British Columbia. Although the concentrations met the requirements for federal water quality guidelines, we observed mortalities, deformities, and other sublethal effects. Phase 1 consisted of exposing Gosner Stage 10 embryos in the pesticide solutions for a total of 8 d. Significant mortality of S. intermontana began posthatch in the highest lethal concentrations of the commercial formulations of endosulfan (Thiodan; LC20(8d)=2,672.7 ng/L) and diazinon (LC20(8d)>175,000 ng/L). Phase 2 compared behavior, morphology, and survival of captive-reared tadpoles exposed to the same 8-d experimental regime as the embryo experiment. Endosulfan induced significant effects on behavior and morphology of P. regilla and significantly reduced survivorship of S. intermontana (LC20(8d)=77.1 ng/L). Abnormal behavior and excitability was observed in both species, with P. regilla tadpoles being more sensitive. At 60,000 ng/L endosulfan, P. regilla also lost pigmentation and exhibited abnormal tail morphology.

Field Response of Tadpoles to Conspecific and Heterospecific Alarm

AbstractMany organisms use chemical cues from a variety of sources to mediate predator avoidance. Response to heterospecific alarm cues has been demonstrated for tadpoles within but not among taxa and alarm response behavior has seldom been examined under field conditions. This study examined the response of three sympatric amphibian larvae and predaceous larval Dytiscus sp. (diving beetle) to damage‐release signals in natural ponds by using capture rates from treated funnel traps as an index of larval behavior. Hyla regilla (Pacific tree frog) tadpoles avoided traps treated with either crushed conspecifics or with Rana aurora (red‐legged frog) tadpoles but the larger ranids and Ambystoma macrodactylum (long‐toed salamander) did not respond to either treatment. H. regilla tadpoles were likely susceptible to any potential predators of ranid tadpoles in these ponds and this result is consistent with the hypothesis that a response to heterospecific alarm occurs in sympatric prey with shared predators.

Predator-Mediated Selection on Burst Swimming Performance in Tadpoles of the Pacific Tree Frog, Pseudacris regilla

Two experimental approaches were used to determine if burst swimming speed in Pseudacris regilla tadpoles is subject to selection by predatory garter snakes, Thamnophis sirtalis. In eight out of 10 experiments in seminatural arenas, fast tadpoles survived snake predation more often than expected (P < 0.01). In videotaped encounters, tadpoles that escaped attacks swam 1.68 times as fast (P < 0.0001) and nearly four times as evasively (P < 0. 05) as those that were captured. Burst swimming speed is clearly important to success at escaping snakes in experimental arenas and, given widespread snake predation on tadpoles, is probably subject to predator-mediated selection in nature.

Comparative toxicity of Guthion and Guthion 2S to Xenopus laevis and Pseudacris regilla tadpoles

Comparative toxicity of Guthion and Guthion 2S to Xenopus laevis and Pseudacris regilla tadpoles

Impacts of mosquitofish (Gambusia affinis) predation on plankton communities

An investigation of the effects of mosquitofish (Gambusia affinis) predation was conducted in 12 experimental ponds in southern California over a period of 10 months.Gambusia essentially eliminatedDaphnia pulex andCeriodaphnia sp. populations, reducedDiaptomus pallidus andKeratella quadrata populations, had little impact onCyclops vernalis, and caused large increases inK. cochlearis, Polyarthra sp.,Synchaeta sp., andTrichocerca spp. populations and in total phytoplankton.Gambusia caused a decrease in the PIE (probability of interspecific encounter) of the planktonic crustaceans and an increase in the PIE of the planktonic rotifers. Hemiptera, such as neustonicMicrovelia sp. and nektonicBuenoa sp. andNotonecta sp., andHyla regilla tadpoles were absent from fish ponds but sometimes abundant in control ponds.Gambusia caused higher pH and oxygen levels, presumably via its effect on the phytoplankton. The impact ofGambusia on the pond ecosystems was less in winter, when fish numbers and feeding rates were low, than in summer. Results of other fish-plankton studies are summarized in tabular form. A model is proposed to account for variation in the calanoid/cyclopoid ratio; evidence is summarized suggesting that in general calanoids are more susceptible to predation by predaceous zooplankters while cyclopoids are more susceptible to fish predation. Some parallels are drawn between the effects ofGambusia predation and those of insecticide treatments.

The effects of five organophosphorus insecticides on thermal stress in tadpoles of the Pacific tree frog, Hyla regilla

Three week old tadpoles of Hyla regilla were exposed to the insecticides temephos, fenthion, methyl parathion, chlorpyrifos, and malathion for 24 h at concentrations less than and at field applied rates as recommended for mosquito control in California. The thermal tolerance was significantly lowered by all chemicals and concentrations tested. Chlorpyrifos and methyl parathion were the most active compounds tested whereas malathion was the least toxic to H regilla tadpoles. Activity was depressed, in comparison to control tadpoles, by the chemicals methyl parathion (100 ppb) and malathion (500 ppb).

Description and Life Cycle of Glypthelmins hyloreus sp. n. (Digenea: Plagiorchiidae)

Adults live in the intestine of the Pacific tree frog, Hyla regilla. Sporocysts in the pond snail, Lymnaea stagnalis, produce gymnocephalous cercariae with continuous dorsal and ventral caudal fins. Cercariae escape the snail, enter H. regilla tadpoles via the nares, and reach the coelom. There they develop as motile unencysted metacercariae which then enter and mature in the frog's intestine only after metamorphosis. Glypthelmins hyloreus most closely resembles G. pennsylvaniensis but has vitellaria which extend farther posteriorly, a larger seminal receptacle and cirrus sac, cercariae with fin folds and without stylet, and unencysted metacercariae. Separating the species of Glypthelmins on the basis of adult morphology alone is considered unsatisfactory. During a survey of Oregon amphibia for trematode infections, a plagiorchiid species was found in the intestine of the Pacific tree frog, Hyla regilla Baird and Girard. This fluke resembles other species of Glypthelmins but because of differences in morphology and life cycle it is here designated as a new species, Glypthelmins hyloreus. The taxonomy of Glypthelmins and related genera has been in confusion for many years. Stafford (1900) described Distomum quietum for which he later (1905) erected the genus Glypthelmins. Thereafter, species assigned and reassigned to this genus and the systematic position of the genus itself have posed the taxonomic difficulties which Byrd and Maples (1963) discussed in revising the genus Glypthelmins. Later, Nasir (1966) reduced Margeana Cort, 1919; Choledocystus Pereira and Cuocolo, 1941; Reynoldstrema Cheng, 1959; and Repandum Byrd and Maples, 1963 to synonymy with Glypthelmins in which he considered 20 species as valid. Leigh (1937, 1946) and Rankin (1944) independently determined the life cycle of Glypthelmins quieta. Xiphidiocercariae with caudal fins develop in species of Physa, emerge and encyst in the skin of various frogs. Metacercariae shed with the skin are ingested by the frog and develop to adults in the intestine. Cheng (1961) reported essentially the same life cycle for his Glypthelmins pennsylvaniensis except that Helisoma trivolvis Say is the intermediate host, and the cercaria lacks a caudal

Resistance to X-irradiation by embryonic cells of the limb-buds of tadpoles.

Both total-body irradiation and shielding of the trunk were used to study the effects of x irradiation from 1000 to 30000 r upon the limb-buds of Bufo boreas and Hyla regilla tadpoles. The object was to test the view that the younger the cells the more sensitive they are to irradiation. The answer is negative. If there is any special susceptibility of these undifferentiated cells it should appear at levels far below the 30000 r maximum employed. A sharp distinction is made between the very susceptible mitotic cells and the resistant non-dividing embryonic cells that have been accumulated in such numbers that they may rapidly differentiate into the characteristic limb tissues under the stimulus of the thyroid hormone. Many irradiated ectoderm cells were changed to form bizarre excrescences but were not destroyed. Unicellular cuthneous gland cells continued to arise even after the heaviest irradiation. Irradiated tadpoles with hind limb-buds from 0.6 mm down to 0.2 mm length were unable to develop normal limbs. This capacity was propontional to the number of non-dividing embryonic cells stored at the time of irradiation. Irradiation of 5000, equal degree but the rapidity was greatest in the cases of higher dosage. Not only did thesemore » levels of irradiation fail to destroy the non-dividing embryonic cells but they did not effect their pre-deterrmined specificity nor modify their capacity for subsequent differentiation and growth. Exposure to a thyroxin solution caused the hind limb-buds without visible differentiation of cells to grow from a length of 0.8 or 0.9 mm or 1.0 mm at the time of irradiation to a length of as much as 5.0 mm in the course of 7 days. Development of thigh, shank, ankle, and toes was complete. Microscopic studies showed characteristic tissues such as cartilage, connective tissue, and muscle, developed to a comparable degree in control and irradiated specimens. (auth)« less