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This study highlights the ecological significance of Rana esculenta as a key bioindicator species, essential for assessing environmental health and understanding the impacts of habitat degradation. The research examines the developmental stages of Rana esculenta tadpoles under controlled laboratory conditions, with a specific focus on crucial environmental factors such as temperature, water quality, and food availability. Eggs were collected from two sites in Romania and maintained in environments that closely simulated natural conditions. Over a seven-week observation period, important milestones were recorded in limb formation, organ maturation, and behavioural changes, providing detailed insights into the influence of environmental conditions on tadpole development. Results indicate that optimal temperature, between 20 and 23°C, along with high water quality, were vital for successful metamorphosis. By day 53, the majority of tadpoles had fully transitioned into juvenile frogs, displaying characteristic adult morphology of Rana esculenta. The findings underscore the critical role of maintaining healthy aquatic habitats, as poor water quality or limited food availability can negatively impact the survival and growth of tadpoles. This research contributes valuable data for conservation efforts, shedding light on the specific ecological requirements for Rana esculenta and emphasizing the species' sensitivity to environmental changes. Moreover, the study reinforces the broader role of amphibians as bioindicators, with their developmental success serving as an indicator of ecosystem health. As amphibians respond acutely to pollution, climate shifts, and habitat alterations, monitoring species like Rana esculenta can aid in detecting environmental stressors early. Ultimately, these findings support informed conservation strategies and the sustainable management of natural habitats, helping to preserve biodiversity and the overall health of ecosystems. [ABSTRACT FROM AUTHOR]

Interactions were studied among juvenile narrow-claw crayfish, Astacus leptodactylus (Eschscholtz), and common water frog, Rana esculenta (L.), tadpoles and common blue damselfly, Enallagma cyathigerum (Charpentier), larvae during rearing under controlled conditions. Interactions among the species studied had a positive impact on the survival of the crayfish, but the differences were not statistically significant (P ≥ 0.5). The juvenile crayfish attacked and consumed the frog tadpoles and damselflies, but the juvenile crayfish very rarely fell prey to them. Only in the initial stage of life and during molting did larval damselflies prey upon juvenile crayfish. After 30 days of the experiment the interaction between crayfish-tadpoles and crayfish-larval damselflies was not noted to have had a statistically significant (P ≥ 0.05) impact on crayfish growth. Juvenile crayfish aggression toward tadpoles and larval damselflies was often offset by the loss of even both chelipeds. In the crayfish-larval damselfly interaction the loss of both chelipeds was three-fold more common than it was in the crayfish-tadpole interaction; however, these differences were not statistically significant (P ≥ 0.5). The effect of intraspecific interaction (crayfish-crayfish) was more a threat in terms of mortality from cannibalism than were interspecific interactions (crayfish-tadpole and crayfish-larval damselfly).

The mechanical performances of the vertebrate skeletal muscle during isometric and isotonic contractions are interfaced with the corresponding energy consumptions to define the coupling between mechanical and biochemical steps in the myosin-actin energy transduction cycle. The analysis is extended to a simplified synthetic nanomachine in which eight HMM molecules purified from fast mammalian skeletal muscle are brought to interact with an actin filament in the presence of 2 mM ATP, to assess the emergent properties of a minimum number of motors working in ensemble without the effects of both the higher hierarchical levels of striated muscle organization and other sarcomeric, regulatory and cytoskeleton proteins. A three-state model of myosin-actin interaction is able to predict the known relationships between energetics and transient and steady-state mechanical properties of fast skeletal muscle either in vivo or in vitro only under the assumption that during shortening a myosin motor can interact with two actin sites during one ATP hydrolysis cycle. Implementation of the molecular details of the model should be achieved by exploiting kinetic and structural constraints present in the transients elicited by stepwise perturbations in length or force superimposed on the isometric contraction.

In the last several decades, amphibian populations have been declining worldwide. Many factors have been linked to global amphibian decline, including habitat destruction, pollution, introduced species, global environmental changes, and emerging infectious diseases. Recent studies of amphibian skin infections were mainly focused on the presence of chytridiomycosis, neglecting other members of the frogs' skin communities. The diversity pattern of fungal dwellers on the skin of green frogs (Pelophylax esculentus complex) was investigated. A total of 100 adults were sampled from three localities in South Banat (northern Serbia) over three consecutive years and detected fungal dwellers were identified using light microscopy and ITS and BenA gene sequencing. Structures belonging to fungi and fungus-like organisms including a variety of spores and different mycelia types were documented in the biofilm formed on amphibian skin, and are classified into 10 groups. In total, 42 fungal isolates were identified to species, section, or genus level. The difference in mycobiota composition between sampling points (localities and green frog taxa) was documented. The highest number of fungal structures and isolates was recorded on the hybrid taxon P. esculentus and locality Stevanove ravnice. Parental species showed a markedly lower diversity than the hybrid taxon and were more similar in diversity patterns and were placed in the same homogenous group. The locality Stevanove ravnice exhibited more pronounced differences in diversity pattern than the other two localities and was placed in a distinct and separate homogenous group. Among the fungal isolates, the highest isolation frequency was documented for Alternaria alternata, Aspergillus sp. sect. Nigri, Epicoccum nigrum, Fusarium proliferatum, and Trichoderma atroviride. Among the documented species, dematiaceous fungi, causative agents of chromomycosis in amphibians, were also recorded in this research with high isolation frequency. Also, some rare fungal species such as Quambalaria cyanescens and Pseudoteniolina globosa are documented for the first time in this research as microbial inhabitants of amphibian skin., (© 2022. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Background: The ability to eliminate a parental genome from a eukaryotic germ cell is a phenomenon observed mostly in hybrid organisms displaying an alternative propagation to sexual reproduction. For most taxa, the underlying cellular pathways and timing of the elimination process is only poorly understood. In the water frog hybrid Pelophylax esculentus (parental taxa are P. ridibundus and P. lessonae) the only described mechanism assumes that one parental genome is excluded from the germline during metamorphosis and prior to meiosis, while only second genome enters meiosis after endoreduplication. Our study of hybrids from a P. ridibundus—P. esculentus-male populations known for its production of more types of gametes shows that hybridogenetic mechanism of genome elimination is not uniform. Results: Using comparative genomic hybridization (CGH) on mitotic and meiotic cell stages, we identified at least two pathways of meiotic mechanisms. One type of Pelophylax esculentus males provides supporting evidence of a premeiotic elimination of one parental genome. In several other males we record the presence of both parental genomes in the late phases of meiotic prophase I (diplotene) and metaphase I. Conclusion: Some P. esculentus males have no genome elimination from the germ line prior to meiosis. Considering previous cytological and experimental evidence for a formation of both ridibundus and lessonae sperm within a single P. esculentus individual, we propose a hypothesis that genome elimination from the germline can either be postponed to the meiotic stages or absent altogether in these hybrids. [ABSTRACT FROM AUTHOR]

This study investigates the changes in fatty acid profile of gamma irradiated frog legs (Rana esculenta)during cold (2°C) storage period. Instead of freezing the frog legs for a prolonged shelf life, gamma irradiated fresh frog legs can be used for consumer satisfaction, because consumers prefer fresh frog legs and are willing to pay more than for frozen in the European market. Frog legs were irradiated at doses of 0, 4, and 5 kGy using60Co sources. The main fatty acids of nonirradiated and irradiated frog legs (4 and 5 kGy) were palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1ω9), linoleic acid (C18:2ω6), and eicosatrienoic acid (C20: 3ω3, ETE). Low doses (4 and 5 kGy) of irradiation treatment had no effect on fatty acid components of frog legs compared to the nonirradiated ones (p> 0.05). The fatty acid composition of frog meat was characterized by its high linoleic acid content (17.1–21.4%). At the initial stage of the storage, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) levels of frog legs remained unchanged with low doses of irradiation (p< 0.05). These fatty acids decreased significantly in the irradiated group (p< 0.05) at the end of the storage period. However, there were no significant changes in nonirradiated frog legs after 10 days of storage. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate KCNQ1 K+ channel expression in the frog kidney of Rana esculenta. KCNQ1 K+ channel, also known as KvLQT1, is the pore forming a-subunit of the IKs K+ channel, a delayed rectifier voltage-gated K+ channel, which has an important role in water and salt transport in the kidney and gastrointestinal tract. The expression of KCNQ1 K+ channel along tubular epithelium differs from species to species. In the present study the expression of KCNQ1 K+ channel in the frog kidney has been demonstrated by immunohistochemistry. The presence of KCNQ1 K+ channel was demonstrated in the epithelial cells of distal convoluted tubule and collecting duct. However, the pattern of expression of KCNQ1 K+ channel differs between distal convoluted tubules and collecting duct. All epithelial cells of distal convoluted tubules revealed basolateral expression of KCNQ1 K+ channel. On the contrary, only the single cells of collecting duct, probably intercalated cells, showed diffuse cell surface staining with antibodies against KCNQ1 K+ channel. These findings suggest that KCNQ1 K+ channel has cell-specific roles in renal potassium ion transport.

Abstract: Heterogeneity in immune defense effectors can benefit hosts encountering a variety of parasites and pathogens. Antimicrobial peptides (AMPs) are a diverse set of immune defense effectors in many amphibians, and are secreted from dermal granular glands to protect the skin from infection. Over 50 different skin peptides have been reported from the European water frog hybridogenic complex (Pelophylax esculentus complex), consisting of the hybrid P. esculentus, and the parent species Pelophylax lessonae and Pelophylax ridibundus. In central Europe the hybrid is sympatric with only P. lessonae, while in other areas all three species can co-occur. Amphibian immune defenses are likely under selective pressure from emerging pathogens such as the chytrid fungus Batrachochytrium dendrobatidis (Bd). To assess if hybridization affects immune defenses against Bd, we compared skin peptides of the three species in terms of (i) quantity, (ii) activity against Bd, (iii) repertoire, and (iv) stability. Hybrids secreted AMPs at higher quantities and with greater fungicidal activity compared to cohabiting P. lessonae. Compared to P. ridibundus, AMPs from hybrids were of similar quantity but slightly greater antifungal activity. Mass spectrometric analyses (MALDI-TOF) revealed that of all three species P. esculentus has the greatest peptide diversity, a repertoire inclusive of peptides occurring in either one or the other parent species. Measurements of degradation dynamics indicate that peptides remain relatively stable on the skin of all species for over an hour after induction of skin gland secretions. Our data demonstrate that the hybrid has more effective peptide defenses against Bd and a richer peptide repertoire than either parent species. Hybrid advantage in environments hosting virulent pathogens may contribute to disassortative mating preferences, and we suggest that AMP diversity may be analogous to major histocompatibility complex (MHC) heterozygosity by benefiting hosts encountering multiple parasites. [Copyright &y& Elsevier]

Abstract: The Harderian gland of Pelophylax esculentus (previously: Rana esculenta) shows seasonal secretory activity changes. Specifically, the secretory activity reaches a maximum during the hottest months, i.e., July and August, drops in September and slowly increases from October onwards. Expressions of P-CaMKII, P-ERK1 and P-Akt1 correlate well with gland secretory activity; i.e., they peak immediately before the hottest part of the year (maximum secretory activity). When the gland activity declines, kinase expressions drop and remain low until February. Experiments of thermal manipulation indicate that high temperature induces the activation of CaMKII, ERK1 and Akt1, and at low temperatures, Akt1 expression decreases. Experiments of chemical castration indicate that the Harderian gland of Cyproterone acetate-treated frogs shows lower Akt1 activity as compared to controls, but the CaMKII and ERK1 activities remain unchanged. Furthermore, in a period of resumed gland activity (October–December) we observed the highest expression of PCNA, a mitotic marker. Immediately after the proliferative phase, we found the highest expression of caspase 3, an enzyme that plays a key role in apoptosis. In combination, the results suggest the following: 1) CaMKII, ERK1, and Akt1 modulate the annual secretory activity of the frog Harderian gland; 2) CaMKII and ERK1 activities are regulated by temperature, whereas both temperature and testosterone likely play a central role in Akt1 regulation; and 3) proliferation and apoptosis occur to restore and balance, respectively, an adequate cell number, which is essential to gland function. [ABSTRACT FROM AUTHOR]

The history of population size and migration patterns leaves its mark in the genetics of populations. We investigate the genetic structure of the edible frog, Pelophylax esculentus in the Danish archipelago and adjacent countries. This frog is of particular interest because it is a hybrid that, in this area, forms all-hybrid populations of diploid (LR) and triploid (LLR and LRR) genomotypes with no (or very few) adults of the parental species (LL and RR). This study is the first to cover the entire geographic range of Danish, Swedish and German all-hybrid populations, documenting their extent and providing a broad picture of their diversity of neutral genetic markers and genomotype proportions. With 18 microsatellite markers, we found that genetic diversity declines northwards in agreement with the glacial refuge and central-marginal hypotheses; however, populations on small and medium-sized islands are no less diverse than those on large islands and continental peninsulas. Isolation by distance exists across the archipelago with limited influence of fragmentation by brackish seawater. The extremely low genetic diversity in all-hybrid populations, compared with adjacent populations, may be responsible for the maintenance of their special breeding system. We also show large variation among ponds in proportions of LLR, LR and LRR genomotypes, but little geographic pattern in their distribution. Instead, we found relationships between the genomotype proportions and some of 15 habitat parameters monitored. Body size differences among LLR, LR and LRR further suggest ecological differences. [ABSTRACT FROM AUTHOR]

Central European water frog Pelophylax esculentus (formerly known as Rana esculenta) is a natural hybrid between P. lessonae and P. ridibundus. The hybrids reproduce by hybridogenesis and usually share populations with one of the parental species. Natural ridibundus-esculentus (R-E) mixed populations are rare. The population described herein is composed of 80% P. ridibundus and 20% P. esculentus represented by both sexes. We analyzed 159 adults and 228 juveniles. Age of adults collected from breeding sites ranged from 2 to 6 years in males and from 3 to 7 years in females of both taxa. The percentage of individuals older than 5 years was low. Average age of P. ridibundus was higher than that of P. esculentus. In P. ridibundus the average age of females was higher than that of males. In P. esculentus the difference between ages of females and males was not significant. Measurements of yearly radial growth of long bones revealed that the frogs grew intensively before reaching sexual maturity (3 years for females and 2 years for males). In the group of juveniles before I hibernation, P. esculentus were significantly bigger than P. ridibundus, however, there was no difference in body size between both taxa after I hibernation i.e., before the start of a new growth season. Mean LAG-1 diameters were significantly greater in adults P. ridibundus than in juveniles after I hibernation, but not in P. esculentus. [ABSTRACT FROM AUTHOR]

The immunolabelled structures for gamma-aminobutyric acid (GABA) and their topographic distributions in the pancreas of the frog Rana esculenta are described for the first time in light and electron microscopy. At light microscopic level, the immunoreaction was detected both in the islets of Langerhans and the nerve fibbers supplying the exocrine tissue. At submicroscopic level, this multifunctional amino acid was identified in cytosol, secretory granules matrix and nuclear chromatin of insulin (INS)-, stomatostatin (SOM)-, glucagon (GLUC)- and pancreatic polypeptide (PP)- producing cells. Other reactive sites for this amino acid included the zymogen granules, mitochondria and nuclei of acinar cells. The above results and their functional significances entirely supporting the concept of a good conservation of this amino acid during phylogeny are discussed in connection with the findings previously reported in human and mammalian organs. [ABSTRACT FROM AUTHOR]

Speciation via interspecific hybrids is very rare in animals, as compared to plants. Whereas most plants overcome the problem of meiosis between different chromosome sets by tetraploidization, animal hybrids often escape hybrid sterility by clonal reproduction. This comes at the expense of genetic diversity and the ability to purge deleterious mutations. However, here we show that all-hybrid populations of diploid (LR) and triploid (LLR and LRR) water frogs ( Pelophylax esculentus) have secondarily acquired sexual reproduction. First, in a crossing experiment analyzed with microsatellite markers, triploid hybrids of both sexes and genotypes (LLR and LRR) recombined their homospecific genomes. Second, the great majority of natural populations investigated had low multilocus linkage disequilibrium, indicating a high recombination rate. As predicted from mating system models, the L genome had constant, low levels of linkage disequilibrium, whereas linkage disequilibrium in the R genome showed a significant reduction with increasing proportion of recombining triploids. This direct evidence of sexual reproduction in P. esculentus calls for a change of the conventional view of hybridogens as clonally reproducing diploids. Rather, hybridogens can be independent sexually reproducing units with an evolutionary potential. [ABSTRACT FROM AUTHOR]

Sulfation plays a major role in regulating the activity of various neurosteroids, including pregnenolone and dehydroepiandrosterone. The present report describes the immunohistochemical distribution of two enzymes involved in the control of neurosteroid sulfation, hydroxysteroid sulfotransferase (HST) and unconjugated steroid enzyme sulfatase (STS), in the brain of the European green frog Rana esculenta during development. HST and STS immunoreactivity were detected from stage VIII-XII. At this early stage, HST-positive fibers were seen in the glomerular layer and the basal rhombencephalon. Subsequently, at stage XIII-XV, HST- and STS-immunoreactive fibers were vizualized in the accessory olfactory bulb. At stage XVI-XVIII, STS-positive cell bodies were observed in the periventricular region of the diencephalon. These observations indicate that the enzymes controlling sulfation of hydroxysteroids are expressed in the frog brain during development. [ABSTRACT FROM AUTHOR]

Abstract: Unexpectedly severe radiation damage, showing up through deformation of the saccule, was encountered during a synchrotron radiation high-resolution (700nm pixel size) tomographic observation of an inner ear, fixed in a formaldehyde solution, of the frog Rana esculenta. The visible displacement of the edge of the otoconia-filled part of the saccule amounted to about 100μm after an irradiation with 20.5keV X-ray photons corresponding to a dose of 1.5kGy for the protein matrix. The close-knit coexistence of organic and mineral components in the biological tissue may be linked to the dramatic increase of radiation dosage sensitivity. [Copyright &y& Elsevier]

The fatty acid profile and mineral composition (calcium, magnesium, sodium, phosphorus, potassium, iron, zinc, manganese, silicon, boron, cadmium, chromium, nickel, aluminium, copper, and lead) by Inductively Coupled Plasma-Atomic Emission Spectometry (ICP-AES) and the proximate composition of the body and legs of edible frog (Rana esculenta) were investigated. The fatty acids occurring in the highest proportions in both the body and leg of frogs were mystiric acid (C14:0, 1.13-2.30%), palmitic acid (C16:0, 19.76-23.23%), stearic acid (C18:0, 3.61-6.29%), palmitoleic acid (C16:1, 7.06-13.08%), oleic acid (C18:1n-9 cis, 10.83-16.71%), linoleic acid (C18:2n-6, 6.44-6.71%), γ-linolenic (C18:3n-6, 0.13-0.27%), linolenic (C18:3n-3, 2.32-3.37%), cis-11,14,17-eicosatrienoic acid (C20:3n-3, 4.71-7.72%), cis-5,8,11,14,17-eicosapentaenoic acid (C20:5n-3, 3.96-6.05%) and cis-4,7,10,13,16,19-docosahexaenoic acid (C22:6n-, 2.77-6.67%). Among the minerals determined, potassium was found to be highest, followed by phosphorus. Calcium, aluminium, cadmium, copper, lead, chromium, nickel, boron, silicon and zinc are found to be lower than the potential toxicity levels. [ABSTRACT FROM AUTHOR]

We examined the density of 2 endangered amphibians, natterjack toads (Bufo calamita) and yellow-bellied toads (Bombina variegata), in 150 breeding pools at each of 2 military training areas in the German state of Bavaria. We selected pools to ensure a wide range of observable ground disturbance resulting from military vehicular traffic during cross-country maneuvers. Both species exhibited significant affinity for pools with high levels of ground disturbance. Natterjack toads preferred pools with 80-100% ground disturbance; yellow-bellied toads preferentially occupied pools with 40-100% ground disturbance. Pools occupied by the target species were characterized by higher levels of bare ground and minimal vegetation. Among other observed amphibians, European edible frogs (Rana esculenta) preferred pools with ≤60% ground disturbance, less bare ground, more vegetative cover, and disturbance >2 years old. Common tree frogs (Hyla arborea), smooth newts (Triturus vulgaris), and alpine newts (T. alpestris) showed no preference for level of disturbance; densities were correlated to parameters apparently unrelated to disturbance. The habitat mosaic created by the heterogeneous nature of military training disturbance may help explain the high biodiversity that often characterizes military training areas. Preservation of native biodiversity is dependent on maintaining an appropriate disturbance regime that, in turn, maintains a habitat mosaic conducive to the presence of native species adapted to a broad disturbance-succession continuum. [ABSTRACT FROM AUTHOR]

Rare recombination in otherwise asexually reproducing organisms is known to beneficially influence the fitness in small populations. In most of the investigated organisms, asexual and rare sexual generations with recombination follow each other sequentially. Here we present a case where clonal reproduction and rare recombination occur simultaneously in the same population. The hybridogenetic water frog Rana esculenta (E), a hybrid between R. lessonae (L) and R. ridibunda (R) produces gametes that only contain the unaltered maternal R part of their genome. New generations of R. esculenta usually arise from E × L matings. Intraspecific E × E matings produce mostly inviable offspring, but in rare cases, female R. ridibunda arise from such matings which are capable of recombination. In the absence of conspecific males, these R females have to mate with E males, which results in further R females, or with L males, which produces new E lineages. This indirect mechanism reintroduces recombination into the otherwise clonally transmitted R genomes in R. esculenta populations. In this study, we show through Monte Carlo simulations that, in most cases, it is sufficient that only between 1 % and 10 % of mixed water frog populations consist of R females to prevent or significantly reduce the fixation and accumulation of deleterious mutations. [ABSTRACT FROM AUTHOR]

Frog relaxin (fRLX) belongs to the relaxin/insulin gene family present in the testis of Rana esculenta and is specifically expressed by Leydig cells. Since the expression of fRLX transcript changes during the reproductive cycle and is more abundant when circulating levels of androgens are relatively high, we investigated the effect(s) of testosterone and its antagonist (cyproterone acetate, CPA) on its expression pattern, in the testis of the frog Rana esculenta. Results from in vivo and in vitro experiments demonstrate that testosterone strongly induces a significant increase of fRLX mRNA expression in frog testes and, this effect is counteracted by CPA, supporting the existence of intratesticular (autocrine/paracrine) mechanisms of action. Interestingly, in both the control and testosterone-treated testes, fRLX mRNA expression was markedly decreased 24 h post-treatment, as compared to that measured at 2 h and 8 h post-treatment, suggesting that factor(s), other than testosterone, may act(s) in controlling its expression. In addition, RT-PCR analysis and in situ hybridization performed on frog testis injected with CPA for 15 days, on alternate days, showed a strong decrease of fRLX expression, suggesting that CPA counteracts the effect of testosterone on fRLX expression. Taken together our results strongly indicate that changes in the production, by the Leydig cells, of both testosterone and fRLX may represent a marker for the study of Leydig cell activity in the testis of the frog Rana esculenta. [ABSTRACT FROM AUTHOR]

In many plant and animal taxa mutation rates are higher in males than in females. As a result, the evolutionary speed of genes depends on how much time they spend in either sex. Usually, this time differs between genes located on sex chromosomes but not between those on autosomes. Here we present an unusual system with a partially sex-linked inheritance of autosomes: the hemiclonal frog Rana esculenta (E) which is originally a hybrid between the sexual species R. lessonae (L) and R. ridibunda (R). Rana esculenta excludes the L genome prior to meiosis, produces eggs or sperm containing an unrecombined R genome and restores hybridity by mating with R. lessonae (‘hybridogenesis’). Matings between L males and E females result in offspring with an even sex ratio, whereas the reverse combination produces only daughters. The extent of the resulting female bias and the proportion that R alleles have spent in either sex depend on the relative survival (b) and the relative reproductive contribution (a) of E males vs. E females. In this paper, we analyze mathematically how different combinations of a and b influence the sex ratio in R. esculenta populations and, combined with the male/female mutation rate ratio (a), the evolutionary rate of the clonally transmitted R genome. We find that this rate is higher than in an asexual population and lower than in a sexual one. Hence, clonal diversity through new mutations is more easily achievable than in purely asexual species. In contrast, the occurrence and accumulation of deleterious mutations is lower than in a comparable sexual species. We conclude that these intermediate mutation rates improve the ecological and evolutionary potential of hemiclonal organisms, and we draw attention to the implications for the use of microsatellites. [ABSTRACT FROM AUTHOR]

Anurans use a saltatorial (jumping) mode of locomotion. A jumping cycle can be divided into four sub-phases: propulsion, flight, landing and recovery. We studied the landing phase during locomotion in Rana esculenta by measuring the ground reaction forces during propulsion and landing over a range of distances. Landing performance affects locomotor ability in jumping frogs. Landing and recovery together take up one third of the locomotor cycle. Peak landing forces are on average almost three times larger than propulsive forces. The forelimbs appear to be fully extended when they make contact with the substrate and absorb the first impact peak. The height of this peak varies depending on arm positioning and jumping distance. Since the stiffness of the arms stays constant over the full jumping range, it is possible that this is a limiting factor in the ability of the forelimbs to work as dampers. A spring-dashpot model is used to model the effect of arm angle at touch down. Damping during landing is performed by placing the forelimbs at an optimal angle to cancel frictional forces effectively. [ABSTRACT FROM AUTHOR]

Batrachochytrium dendrobatidis (phylum Chytridiomycota, order Chytridiales) is the causative organism of chytridiomycosis in amphibians, a disease associated with their population decline worldwide. In this work, we report a cutaneous infection in water frogs of the Rana esculenta complex in agricultural areas of Umbria, central Italy. Histological, immunohistochemical, ultrastructural, and molecular analyses demonstrated for the first time the presence of the Batrachochytrium dendrobatidis in this complex; to date, no association between the presence of chytrid fungal infection and mortality has been found, to our knowledge. However, the presence of Batrachochytrium dendrobatidis infection in the water frogs of the Rana esculenta complex is of concern because the frogs could act as a reservoir species and contribute to the decline of less resistant species. [ABSTRACT FROM AUTHOR]

Frogs propel themselves by kicking water backwards using a synchronised extension of their hind limbs and webbed feet. To understand this propulsion process, we quantified the water movements and displacements resulting from swimming in the green frog Rana esculenta, applying digital particle image velocimetry (DPIV) to the frog's wake. The wake showed two vortex rings left behind by the two feet. The rings appeared to be elliptic in planform, urging for correction of the observed ring radii. The rings' long and short axes (average ratio 1.75:1) were about the same size as the length and width of the propelling frog foot and the ellipsoid mass of water accelerated with it. Average thrust forces were derived from the vortex rings, assuming all propulsive energy to be compiled in the rings. The calculated average forces (Fav=0.10±0.04 N) were in close agreement with our parallel study applying a momentum-impulse approach to water displacements during the leg extension phase. We did not find any support for previously assumed propulsion enhancement mechanisms. The feet do not clap together at the end of the power stroke and no ‘wedge-action’ jetting is observed. Each foot accelerates its own water mantle, ending up in a separate vortex ring without interference by the other leg. [ABSTRACT FROM AUTHOR]

Frogs are animals that are capable of locomotion in two physically different media, aquatic and terrestrial. A comparison of the kinematics of swimming frogs in a previous study revealed a difference in propulsive impulse between jumping and swimming. To explore this difference further, we determined the instantaneous forces during propulsion in swimming using an impulse-momentum approach based on DPIV flow data. The force profile obtained was compared with force profiles obtained from drag-thrust equilibrium of the centre of mass and with the force profiles generated during jumping. The new approach to quantifying the instantaneous forces during swimming was tested and proved to be a valid method for determining the external forces on the feet of swimming frogs. On the kinematic profiles of swimming, leg extension precedes propulsion. This means that it is not only the acceleration of water backwards that provides thrust, but also that the deceleration of water flowing towards the frog as a result of recovery accelerates the centre of mass prior to leg extension. The force profile obtained from the impulse-momentum approach exposed an overestimation of drag by 30% in the drag-thrust calculations. This means that the difference in impulse between jumping and swimming in frogs is even larger than previously stated. The difference between the force profiles, apart from a slightly higher peak force during jumping, lies mainly in a difference in shape. During swimming, maximal force is reached early in the extension phase, 20% into it, while during jumping, peak force is attained at 80% of the extension phase. This difference is caused by a difference in inter-limb coordination. [ABSTRACT FROM AUTHOR]

Locomotion has a clear ecological relevance for many animals. As animals need to move in order to escape from predators, find food, defend territories, etc., it is expected that locomotor performance might affect an individual's survival and reproduction. Clear links have also been found between an animal's performance and its morphology. A function analysis can unravel the underlying mechanistic facets of this link. Frogs are interesting model species because they add an extra element to this topic; they have to perform in two entirely different physical environments, particularly semi-aquatic species. However, no trade-off was found between jumping and swimming performance. Morphological correlates were found but, to understand causations, a thorough understanding of the mechanics of locomotion is required. When comparing the mechanics of jumping and swimming, the question arises of how to ensure a sound comparison. Ideally, some measure of 'effort' has to be added to the analysis. We suggest the use of the propulsive impulse. Unexpectedly, the impulse of swimming proved to be significantly smaller than the jumping impulses during locomotion in a semi-aquatic frog, Rana esculenta, even when maximal performance had been induced in both media. To verify our impulse calculations, we analysed the external forces during both locomotor modes. The forces during terrestrial locomotion can be measured directly using a force plate; determining the forces in water requires a more complex set-up. For that reason, we performed a DPIV (Digital Particle Image Velocimetry) analysis on the flow generated by swimming frogs. These experiments confirmed the results of our impulse calculations. [ABSTRACT FROM AUTHOR]

Rana esculenta is a hybrid between Rana lessonae (LL) and Rana ridibunda (RR), and hybrids may be diploid (LR) or triploid (LLR or LRR). Genotypes can be roughly determined from erythrocyte size and morphometry in adult frogs, but accurate genotyping requires more labourious methods. Here I demonstrate that both the L and R genomes have specific microsatellite alleles, and that genotype and ploidy can be accurately inferred from the quantitative ratio of PCR-amplified (polymerase chain reaction-amplified) genome-specific alleles. This method greatly facilitates genotyping in DNA studies of the R. esculenta complex and allows analysis of badly preserved samples and embryos. [ABSTRACT FROM AUTHOR]

Zymosan-induced peritoneal inflammation was inhibited by morphine co-injection in mice and fish but not in anuran amphibians. In present experiments, an in vitro migration of mouse, goldfish, and frog leukocytes to L15 medium, control serum (S) or zymosan-activated serum (ZAS) was recorded following cell preincubation with L15 or with agonists of mu, delta, or kappa opioid receptors (morphine, deltorphine, or U-50,488H, respectively). In all species, migration of control leukocytes was in the order ZAS>S>L15. Pretreatment with morphine or deltorphine (but not with U-50,488H) enhanced leukocyte migration to L15 and S in each species, while it inhibited migration of mouse and fish (but not frog) leukocytes to ZAS, phenomena reversed by specific antagonists of mu and delta opioid receptors (CTOP or naltrindole, respectively). It seems that final effects of opioids on cell migration are dependent on a species-specific balance between up- and down-regulation of leukocyte migration resulted from interplay between receptors for opioids and chemotactic factors. [Copyright &y& Elsevier]

The present study investigates the occurrence of Trk-like neurotrophin receptor proteins in the lizard and frog kidney. In lizard rare TrkB-like immunoreactive cells in intermediate and distal tubules were found. TrkC-like immunoreactive cells were numerous in collecting tubules and became less numerous in collecting ducts. No TrkC-like immunoreactivity was detected in the ureteric duct. In the frog, we observed numerous TrkC-like immunoreactive cells in collecting tubules and ducts while they were scattered among negative epithelial cells in the wolffian duct. TrkB- and TrkA-like immunoreactivity was never found. Western blot analysis demonstrated that the frog and lizard kidney contains TrkC-like protein; TrkB-like protein was present only in the lizard kidney. These results demonstrate for the first time the occurrence of Trk-like proteins in the kidney of amphibians and reptiles, and aid in the assessment of the role of Trk receptor-like proteins in the kidney physiology of vertebrates. [ABSTRACT FROM AUTHOR]