Schrankiana are gastrointestinal parasites of anurans, distributed throughout Central and South America. Schrankiana formosula and Schrankiana inconspicata are some of the most commonly reported species parasitising anurans from Brazil, and the morphological differences between them are unclear. In the present study, we redescribed S. formosula based on a re-examination of type series and newly collected material from the frog Leptodactylus pentadactylus in the state of Amapá, Brazil. Additionally, we re-examined the type series of S. inconspicata, and propose it as a junior synonym of S. formosula. We provide detailed morphological and morphometric data with intraspecific variation analyses and new molecular data for S. formosula. In the present phylogeny, S. formosula formed a well-supported clade with Raillietnema sp. and Labeonema synodontisi. Based on molecular phylogenetic analyses and some morphological similarities, our findings support the hypothesis that Schrankiana is a member of the family Cosmocercidae, not Atractidae. Additionally, we provide the first ultrastructural descriptions of S. formosula, and establish the species' phylogenetic position from the Cosmocercidae.

Cave biodiversity and ecosystems are underexplored. To guide conservation needs for visitor management, we surveyed the 2,158 m long Danial Cave in northern Iran for vertebrate fauna. We identified four mammalian and two amphibian species in the cave: the greater horseshoe bat Rhinolophus ferrumequinum, Blasius's horseshoe bat Rhinolophus blasii, the lesser mouse-eared myotis Myotis blythii, the Hyrcanian field mouse Apodemus hyrcanicus, the Hyrcanian wood frog Rana pseudodalmatina and the Eurasian marsh frog Pelophylax ridibundus. Considering the increasing tourism pressures at Danial Cave, information on cave fauna is imperative for the conservation management of unique and endemic cave species.

The aquatic and terrestrial clades of species of Trypanosoma could provide insight into the evolutionary history of the genus, as well as complementary information for biomedical studies of medically and economically important species of Trypanosoma. The ecological interactions and phylogeny of aquatic trypanosomes are currently not well-understood, mostly due to their complex life cycles and a deficiency of data. The species of Trypanosoma from African anuran hosts are of the least understood taxa in the genus. Trypanosomes were collected from South African frogs and subjected to morphological and phylogenetic analyses. This study redescribes Trypanosoma (Trypanosoma) nelspruitense Laveran, 1904 and Trypanosoma (Haematomonas) grandicolor Pienaar, 1962, with morphological and molecular data. The present study aims to create a platform for further future research on African anuran trypanosomes.

The genus Megalobatrachonema is a rare group of nematode parasites within Ascaridida. The systematic status of Megalobatrachonema in the superfamily Cosmocercoidea (Ascaridida) has long been controversial. The relationship of Megalobatrachonema and Chabaudgolvania remains unsolved. In the present study, a new species of Megalobatrachonema, M. hainanensis sp. nov., was described based on specimens collected in Amolops hainanensis (Boulenger) and Hylarana spinulosa (Smith) (Amphibia: Anura) from Hainan Island, China. The large ribosomal DNA (28S) and internal transcribed spacer (ITS1-5.8S-ITS2) were also sequenced for molecular identification and phylogenetic study. Phylogenetic analyses using maximum likelihood (ML) inference and Bayesian inference (BI) based on 28S and ITS1 sequence data, respectively, supported that Megalobatrachonema is a member of the family Kathlaniidae. In addition, the genetic comparison and phylogenetic results based on ITS1 sequence data also supported that the genus Chabaudgolvania should be considered as a synonym of Megalobatrachonema.

Southern California has experienced widespread amphibian declines since the 1960s. One species, the Vulnerable California red-legged frog Rana draytonii, is now considered to be extirpated from most of southern California. In February 2017 a population of R. draytonii was discovered in the southern foothills of the San Bernardino Mountains of Riverside County, California, near the edge of the species’ historical distribution. This population belongs to an mtDNA lineage that was presumed to be extirpated within the USA but is still extant in Baja California, Mexico. This discovery increases the potential for future, evolutionarily informed translocations within the southern portion of this species’ range in California.

With amphibians declining globally, conservation breeding and reintroduction programmes are increasingly important management tools. Here we examine whether these conservation initiatives are targeting species at the greatest risk of extinction. We compared conservation needs of species involved in conservation breeding programmes to those of their closest relatives not involved in such programmes, using eight variables related to immediate and future extinction risk. We found that species in breeding programmes were more likely to be threatened and were equally range-restricted and specialized as their closest relatives not being bred for conservation purposes. This suggests that in contrast to patterns reported for zoo holdings more generally, these conservation initiatives target species of conservation priority in the short and medium term.

We compared reproductive characteristics of the dendrobatid frog Colostethus trinitatis at the Tamana cave in the Central Range hills and at five forest stream sites in the Northern Range hills of Trinidad. There were significant differences between sites in adult female body size, intraovarian clutch size (in absolute terms and relative to body size) and the size of tadpoles carried by male frogs. Clutch sizes ranged from 6 to 13 in the Northern Range samples and from 12 to 26 at Tamana. Adult male body size was similar at all sites. Tadpoles carried by male C. trinitatis at Tamana were significantly smaller (mean length 14.2 mm) than those carried by males at the five Northern range sites (mean length 16.4–16.7 mm). The smallest clutches and largest tadpoles were found at Mount St Benedict, where there was evidence of size-selective predation on tadpoles by fish. Tamana, where clutches were large and tadpoles small, differed from the Northern Range sites in terms of the physical environment (cave vs forest) and the abundance of invertebrates. We discuss possible ultimate and proximate causes of the differences in clutch size and tadpole size, particularly size-selective predation and availability of food.

Isolated retinal rods of the frog consisting of the outer segment and the ellipsoid were patch-clamped and recorded in the whole-cell mode. The recording pipettes were filled with solutions of different composition in order to alter the cytoplasmic content of sodium, phosphate, and calcium ions, and guanine nucleotides. When a simple medium with potassium as the principal cation was used, the dark voltage slowly approached more negative values. This tendency of spontaneous hyperpolarization was reduced significantly when cGMP or GTP were present in the pipette medium. Sodium ions, on the other hand, clearly increased the speed of hyperpolarization. In the presence of sodium (20 mM), the stabilizing effect of GTP did not occur and that of cGMP was clearly diminished. Phosphate (20 mM) neutralized the sodium effect. High calcium levels (100 μM) did not measurably influence the time course of hyperpolarization. We conclude that the normal cytoplasmic sodium level in rods does not exceed 10 mM and that higher internal sodium concentrations interfere with the sodium–calcium exchange mechanism.

“Sustained” visual units, i.e. nonerasable (R1) and erasable (R2) units as commonly described, were recorded in the superficial layers of the rostral optic tectum of Rana esculenta and their neuronal activity (expressed as the mean firing frequency ) was quantitatively analyzed The mean value of the exponent α of the velocity function of the erasable R1 units was found to be 0.46 and the constant k to be about 24.7. The optimal stimulus diameter was equal to 2.6 deg. For the whole population of the erasable units, the exponent α was found to be between 0.36–0.75 (mean value ≈ 0.56, i.e. largely different from the values currently reported for such units) and was independent of the stimulus diameter (D = 0.6–6 deg). However, the constant k of the velocity function (range: 8.2–37.7) varied with D. Most of the erasable units (called “mixed R1-R2” units) therefore showed an R1-type velocity function with an exponent α ≈ 0.5 and a constant k ≈ 25 but reacted to other parameters as did “typical” R2 units: (i) their neuronal response was related to the stimulus diameter by a logarithmic function with a maximum obtained for D = 2.4 deg; and (ii) a variation of about 4–17% on either side of the average value of was observed, independent either of the stimulus velocity or of the diameter of the stimulus. Results are compared to known quantitative data, and the use of stimulus-response relationships as a tool for classification is discussed.

In the frog Xenopus laevis, the isthmotectal projection, which relays input from the ipsilateral eye, exhibits anatomical reorganization following surgical eye rotation performed during tadpole stages while the isthmotectal projection in the frog Rana pipiens fails to show reorganization. This plasticity has been shown to be dependent upon activation of the N-methyl-D-aspartate (NMDA) receptor located on tectal cell dendrites. The reorganization process in Xenopus is hypothesized to employ a Hebbian mechanism requiring correlated firing of ipsilateral and contralateral inputs to a given tectal cell; when an ipsilateral axon synapses onto a tectal cell that receives input from a contralateral axon with a matching receptive-field location, the correlation in activity triggers stabilization of the ipsilateral synapse. However, in neither Xenopus nor Rana do ipsilateral and contralateral inputs begin to fire simultaneously in response to a given visual stimulus; the ipsilateral input is delayed because it reaches the tectum indirectly, through a polysynaptic relay via the opposite tectum and nucleus isthmi. The objective of this experiment was to test whether there is a significant difference in this intertectal delay between Xenopus laevis and Rana pipiens in order to determine whether intertectal delay could be a contributing factor in this species-specific ability to exhibit visual plasticity. We have found that intertectal delay is 26.16 ms longer in Rana pipiens (36.53 ms) than in Xenopus laevis (10.37 ms).

We have examined the integrity of the blood-brain barrier during optic nerve regeneration in the frog Liloria (Hyla) moorei using rhodamine B-labeled bovine serum albumin (RBA). A transient localized breakdown of the blood-brain barrier was observed between 1 and 5 weeks after extracranial optic nerve crush. The zone of breakdown progressed along the experimental optic nerve, ascended the opposite optic tract, and swept rostro-caudally across the tectum contralateral to the crushed nerve. By 7 weeks, the blood-brain barrier was once again intact along the length of the optic pathway. In a concurrent series of frogs, regenerating optic axons were visualized by anterograde transport of horseradish peroxidase (HRP). At each stage examined, the region reached by the front of regenerating axons corresponded to that in which the blood-brain barrier had been shown to break down.

In contrast to the results after nerve crush, the blood-brain barrier remained intact along the length of the optic pathway following optic nerve ligation to prevent regeneration. We conclude that the breakdown of the blood-brain barrier which occurs during optic nerve regeneration in the frog is triggered by the regenerating axons.

We have previously reported that during optic nerve regeneration in the frog, 30–40% of retinal ganglion cells die, the loss being complete within 10 weeks. In the present study, we crushed the optic nerve, waited 10 weeks, and then recrushed the nerve at the same site. Retinae were examined 10 weeks later. We estimated ganglion cell numbers from cresyl-violet-stained wholemounts and found a fall of 53% compared to normals. The loss was significantly greater than the losses of 36% and 35%, respectively, in frogs which received a single optic nerve crush and were examined 10 or 20–24 weeks later. The results indicate that a second episode of ganglion cell death took place when the optic nerve regenerated a second time. We conclude that ganglion cells in the frog are not comprised of two subpopulations, only one of which intrinsically possesses the ability to regenerate.

During optic nerve regeneration in the frog, axons transiently grow along the opposite optic nerve forming a retino-retinal projection. In the present study, we crushed the left optic nerve in the frog Litoria (Hyla) moorei and later applied horseradish peroxidase (HRP) or diamidino yellow (DY) to the right optic nerve. In one series, retinae were examined 3 days after application of the tracer. The retino-retinal projection was found to be maximal at 5 weeks, fell significantly by 7 weeks, and returned to close-to-normal levels by 24 weeks. In a second series, we applied DY at 5 weeks as before but did not sacrifice the frogs until 7 weeks. Numbers of labeled ganglion cells were not significantly different from those frogs in the first series labeled and examined at 5 weeks. We conclude that ganglion cells giving rise to the retino-retinal projection had not died in appreciable numbers, presumably being sustained by collateral axons in the brain.

In the South African clawed-toed frog Xenopus laevis, visual experience plays a crucial role in the formation of matching binocular maps in the tectum. The ipsilateral eye's projection, relayed through the crossed isthmotectal projection, displays marked plasticity in response to altered visual input during a critical period of development. This plasticity and the events responsible for the end of the critical period are mediated by N-methyl-D-aspartate (NMDA) receptor function. We have previously reported that chronic blockade of tectal NMDA receptors with the NMDA antagonist 5-amino-phosphonovaleric acid (APV) prevents plasticity of the crossed isthmotectal projection during the critical period, while chronic treatment with NMDA restores this plasticity after the end of the critical period. These results raise the question of whether the effects on plasticity are due to changes in electrical responsiveness of the treated tissue. In this study, we have quantitatively assessed the actions of APV and NMDA on certain aspects of tectal cell activity in Xenopus during and after the critical period by recording the output of the nucleus isthmi cells that are activated by the tectum after three weeks of treatment. We have found that chronic APV treatment does not alter tectal output, as indicated by the firing of isthmotectal axons, during the critical period and that chronic NMDA treatment increases tectal output in postcritical period Xenopus. Tectal output does not differ between normal Xenopus during and after the end of the critical period.

These results indicate that the effect of APV on blocking isthmotectal plasticity is not due to a nonspecific inhibition of the segment of the retinotectal relay that activates the nucleus isthmi. The enhancement of tectal output in postcritical period Xenopus by chronic NMDA treatment may promote the effectiveness of NMDA in restoring isthmotectal plasticity after the end of the critical period, but the finding that tectal activity does not differ between normal Xenopus during and after the critical period implies that a reduction in tectal activity in not the cause of the loss of plasticity at the end of the critical period.

The tectum of Xenopus frogs receives input from both eyes. The contralateral eye's projection reaches the tectum directly, via the optic nerve, and the ipsilateral eye's projection reaches the tectum indirectly, via the nucleus isthmi. Under normal conditions, the topography of the ipsilateral map relayed from the nucleus isthmi is in register with the topography of the retinotectal map from the contralateral eye. During development, the process of aligning the two maps is complicated by the dramatic changes in binocular overlap of the two eyes' visual fields which take place during late tadpole and juvenile stages. The goal of this study is to determine the branching patterns of contralaterally projecting isthmotectal axons before, during, and after the period of rapid eye migration.

Isthmotectal axons were filled by anterograde transport of horseradish peroxidase (HRP) from the nucleus isthmi. The results show that crossed isthmotectal axons enter the entire extent of the tectum before binocular overlap begins to increase. Therefore, binocular overlap is not necessary for the initial isthmotectal projection to span the tectum. The density of isthmotectal branches rises dramatically at the same time that the eyes begin to shift. During the period when eye migration is most rapid, many isthmotectal axons form arbors which resemble adult arbors but which extend over greater proportions of the tectal surface.

The axons appear to be directed toward appropriate mediolateral positions as they enter the tectum. Their trajectories are roughly rostocaudal, with relatively little change along the mediolateral dimension. These data, when combined with available physiological data, suggest that mediolateral order is initially established by vision-independent mechanisms but can be altered by vision-dependent mechanisms. Rostrocaudal order becomes discernable only at the time when binocular visual cues become available and appears to be established primarily on the basis of the activity of the retinotectal and isthmotectal axons.

The effects of cobalt ions on 502-nm rod- and 575-nm cone-driven components of the b-wave of the electroretinogram were studied in the isolated frog retina. Addition of 100–150 μM cobalt initially caused a suppression of rod-driven responses and an enhancement of cone-driven responses. In the continued presence of cobalt, however, the rod-driven responses gradually recovered and the cone-driven responses became suppressed. These concentrations of cobalt had no effect on the rod- and cone-driven mass receptor potentials which were isolated in the presence of 4 mM glutamate. At higher concentrations of cobalt (1 mM or greater), both rod- and cone-driven b-wave responses were eliminated and there was no recovery in the continued presence of cobalt. The results suggest that cobalt has markedly different, time-dependent effects on signal transmission from rods and cones to second-order cells.

Single frog rods consisting of the outer segment and the ellipsoid were investigated by the whole-cell patch-clamp technique. When the recording pipette was filled with a simple intracellular medium containing potassium as the principal cation, a slow increase in dark voltage (hyperpolarization) associated with a decay of the photoresponses was observed. The hyperpolarization started at a dark voltage of −27 ± 8 mV, followed an exponential course, and leveled out at −52 ± 6 mV. The time constant was proportional to the access resistance of the preparations. With a pipette medium containing a 0.5 or 1.0 μM cGMP, the initial dark voltage was shifted to more positive values and the tendency of hyperpolarization was clearly attenuated. Similar results were obtained with 1 mM GTP. The effects of GDP and of ATP were less significant. In experiments with 1 mM GTP plus 1 mM ATP, the dark voltage behaved as in experiments with only GTP. The stabilizing action of GTP was amplified by EGTA so that with 1 mM GTP plus 1 mM free EGTA the dark voltage was stable at a level of −15 mV. It is concluded that the preparations lose intracellular components such as cGMP and GTP by diffusion into the recording pipette and that the losses are prevented or reduced when the pipette medium contains these nucleotides in nearly physiological concentrations. For the internal transmitter cGMP, the results suggest that its free concentration does not exceed 1 μM.

The sensitivity of rod- and cone-driven responses was studied in the isolated frog retina during the period of rapid dark adaptation following a conditioning flash which bleached a negligible amount of visual pigment. Following a conditioning flash, cone-driven b-wave responses were first enhanced and then depressed. The time courses of the enhancement and subsequent depression of cone-drive responses varies greatly with the intensity and wavelength of the conditioning flash, but were identical when the conditioning' flashes were matched for equal excitation of 502 nm rods. These changes in cone-driven response sensitivity were correlated with the desensitization and recovery of rods following the conditioning flash. When signal transmission from rods to second-order cells was interrupted by the addition of L-glutamate, the conditioning flash did not produce the above-described enhancement and subsequent depression of long-wavelength receptor potential responses. The suppression of cone-driven response therefore appears to be due to a synaptically mediated influence from 502 nm rods which is maximal when the rods are in the dark-adapted state, with little or no contribution from 433 nm rods, and no involvement of the pigment epithelium.