Population genetics of a successful invader: the marsh frog Rana ridibunda in Britain

We investigated the genetic outcome of successful invasion by an alien species, the marsh frog Rana ridibunda, in Britain. Twelve adults translocated from Hungary into Kent (Romney) in 1935 resulted rapidly in a large localized population. A further successful translocation in 1973 from Romney to Sussex (Lewes), together with other range extensions, provided an opportunity to test bottleneck effects during colonization events. Romney and Lewes frogs had similar genetic diversities to those in Hungary at 14 random amplified polymorphic DNA marker (RAPD) and five microsatellite loci. The introduced populations were, however, differentiated genetically from each other and from a reference population in Hungary. Fitness assessments (larval growth and survival) revealed no differences between the Lewes and Romney populations. Despite starting with few founders, significant bottleneck effects on R. ridibunda in Britain were therefore undetectable, presumably because population expansions were rapid immediately after the translocations.     

Endohelminth fauna of the marsh frog Rana ridibunda from Lake Hazar, Turkey

In this study, 236 marsh frogs Rana ridibunda collected from Lake Hazar (Elazig, Turkey) at 15 d intervals between March 2001 and February 2002 were examined for endohelminths; of these, 148 (62.71%) frogs were found to be infected with helminths. In total, 9 helminth species (3 trematodes, 5 nematodes and 1 acanthocephalan) were identified. We observed Gorgoderina vitelliloba (prevalence 2.97%) in the urinary bladder, Haematoloechus variegatus (4.66%) and Rhabdias bufonis (8.90%) in the lung, Pleurogenoides medians (1.69%), Oswaldocruzia filiformis (3.81 %) and Acanthocephalus ranae (26.27 %) in the small intestine, Neoxysomatium brevicaudatum (16.95%) and Cosmocercoides sp. (3.39%) in the large intestine, and Eustrongylides excisus (14.41%) in the body cavity and on,the stomach. No helminth was found in the spleen, kidney, gall bladder, liver, heart or muscle. Of the 9 helminth species identified, Acanthocephalus ranae (26.27 %) had the highest prevalence and abundance and Oswaldocruzia filiformis (8.33+/-4.09) had the highest mean intensity.     

Biochemical variability and genetic differentiation of marsh frog Rana ridibunda Pall. populations]

Marsh frog populations of Rana ridibunda s. lato from the Ukraine, Caucasus, Turkmenistan and Tadzhikistan have been analyzed genetically by 31 isozyme gene loci. The genetic distance between populations from Tadzhikistan on the one hand, and other regions, on the other hand is D-0.269, that assumes evolutionary divergence at the species level. The presence of fixed allelic substitutions between two populations from Tadzhikistan by five gene loci (Aat-S, Ldh-B, Alb, Es-5) supposes genetic heterogeneity of species in this region. Peculiarities of allozyme variation of this species are discussed.     

Season dependent response of the Marsh frog (Rana ridibunda) to cadmium exposure

Cadmium toxicity related to cysteine metabolism and glutathione levels in several tissues of the Marsh frog (Rana ridibunda) collected in late spring were investigated after exposure to 80 mg CdCl2 L(-1) for 168 h. The results were compared to those obtained in a previous experiment carried out in autumn. The most striking changes involved the brain which could not maintain a proper glutathione level and the testes in which neither GSH nor sulfane sulfur levels recovered. Substantial damage is expected in the presence of Cd which decreases the antioxidant status of these tissues. It seems that in spring, frogs had lesser tolerance for Cd in comparison with frogs in autumn. This may be caused by the transition to aerobic respiration after hibernation.     

Distribution of prolactin receptor in frog (Rana ridibunda) dorsal skin during hibernation

The role of prolactin in the regulation of frog skin functions is still unclear particularly during environmental changes. In this study, prolactin receptor (PRLR) was detected in active and hibernating frog dorsal skin using immunohistochemical method. PRLR immunoreactivity in active frogs was observed in the epidermis, in the secretory epithelium of granular glands and the secretory channel cells of the glands. Myoepithelial cells of granular glands that started accumulating secretory material or those with a full lumen were PRLR immunoreactive, while some myoepithelial cells of empty granular glands were negative for PRLR. In hibernating frogs, this immunoreactivity was observed in the same regions; however, immunoreactivity was more intense than that in active frogs. PCNA was employed for detection of proliferative activity of PRL in the dorsal skin, and immunoreactivity was detected in the nuclei of a few epidermis cells and in the duct of glands of active frogs. The number of immunoreactive nuclei in these regions increased in hibernating and in prolactin injected groups. We conclude that prolactin provides morphological and functional integrity of skin stimulating the proliferation and regulating the function of granular glands and plays an important role in the adaptation of amphibians to the long winter period.     

Survival and metabolic responses to freezing by the water frog (Rana ridibunda)

We studied the ability of the marsh frog Rana ridibunda to survive freezing exposure and the associated subsequent metabolic variations. This species that typically overwinters under water tolerates the conversion of 55% of its body water into ice. This ice content is attained after a few hours (between 8 and 36 hours depending on the mass of the individual and the environmental temperature) but death occurs at greater than 58% ice. Freezing stimulated a significant increase in blood carnitine and trimethylamine levels (respectively 4.5+/-2.5 and 0.5+/-0.2 micromol.l(-1) for controls versus 27.0+/-18.9 and 3.6+/-4.1 micromol.l(-1) after thawing) but these increases had no significant effect on plasma osmolality which was unchanged between control and freeze exposed frogs (252.6+/-20.3 versus 240.2+/-25.0 mOsmol.l(-1), respectively). Freezing also induced a significant dehydration of heart, liver and muscles (respectively 4.2, 3.2 and 2.8%) but the observed levels are low compared to values found in highly freeze tolerant species. This species could be classified as "partially freeze tolerant" enduring the transformation of a significant part of its body water into ice but not the completion of the exotherm. The existence of freeze tolerance in an aquatic hibernator that does not accumulate cryoprotectant, exhibiting low organ dehydration after freezing and low hypoxia tolerance, raises the possibility that a tolerance of nearly 60% ice within the body is common among anurans.     

Characterization of the cDNA encoding proopiomelanocortin in the frog Rana ridibunda

In the amphibian pars intermedia, secretion of proopiomelanocortin (POMC)-derived peptides is controlled by multiple factors including classical neurotransmitters and neuropeptides. To pursue questions concerning the regulation of POMC gene expression in Rana ridibunda, we have isolated and characterized a full-length cDNA for frog POMC. A cDNA clone isolated from a frog pituitary library contains an open-reading frame of 780-bp that predicts a 260 amino acid POMC protein. The structure of frog POMC demonstrates considerable amino acid sequence similarity with POMC from other species. In particular, the sequence of alpha-melanotropin (alpha-MSH) is identical in frog and all mammalian species studied so far, while adrenocorticotropin (ACTH) and beta-endorphin exhibit 79% and 84% homology with their human counterpart. Frog POMC contains only one potential asparagine-linked N-glycosylation signal (Asn-Ser-Thr) within the gamma-MSH domain. The alpha-MSH sequence is C-terminally flanked by the Gly-Lys-Lys amidation signal while the joining peptide is not amidate.     

The ultrastructural characteristics of the motor neuron synaptic organization in the spinal cord of the frog Rana ridibunda

Electron microscopic studies on the spinal motor nuclei in amphibians indicate significant diversity in chemical synapses formed on motoneurones by axonal endings of supra- and intraspinal systems. High ultrastructural specialization was observed among axosomatic, axodendritic and axoaxonal synapses. Several types of axo-spine synapses and axodentritic synaptic complexes of the "glomerular" type were revealed. New data on ultrastructural peculiarities of chemical synapses presented in this paper, together with earlier detailed data on morphologically mixed and electrotonic synapses, increase our knowledge of evolutionary trends in synaptic organization of motoneurones in the spinal cord and suggest the existence of a complex mechanism of integration of synaptic influences in the spinal cord of lower vertebrates.     

Oxygen consumption of a terrestrial toad (Bufo viridis) and semi-aquatic frog (Rana ridibunda)

1. Oxygen consumption was measured before and after dehydration at different ambient temperatures (Ta) in the terrestrial toad Bufo viridis and the semi-aquatic frog Rana ridibunda. 2. The metabolic rates at Tas between 14 and 27 degrees C were almost the same for R. ridibunda and B. viridis. 3. The metabolic rate at higher Tas (between 27 and 36 degrees C) was higher in R. ridibunda than in B. viridis. This situation was found before and after dehydration. 4. A similar situation was found with CO2 production, which was higher at high Tas in R. ridibunda compared with B. viridis.     

Patterns of orientation behavior in marsh frogs (Rana ridibunda Pall.) of southern populations

The behavior of frogs from southern areas with an arid climate released during the reproductive period between their “home” pond and a less distant river is shown to be independent of weather conditions. The experiments were performed on frogs living near the village of Dosang, Astrakhan oblast. The frogs were released 60 to 150 m from their “home” breeding waterbody and 60 to 80 m from an “alien” waterbody. Four experiments were performed on 27 individuals. The movements of the frogs were traced by the method of “tracking by a thread.” The results revealed no preference in the frogs to return to their own breeding ponds, rather than to the nearby river. This behavior is peculiar to frogs of southern populations.     

Amplitude of miniature potentials of motor neurons in the frog Rana ridibunda

Miniature synaptic potentials have been recorded from motoneurones of the isolated spinal cord of the frog Rana ridibunda. In normal Ringer's solution, their frequency varied from 5 to 50/sec, whereas their amplitude reached 2-5 mV. Only 50-300 microV (rarely 0.5-1.5 mV) potentials persisted when TTX was added to Ringer's solution and/or Ca was replaced by Mn. However, in Ca-free solution, TTX in combination with Mn did not decrease the amplitude of miniature potentials, provided the initial values varied within 50-300 microV. Noise fluctuations did not exceed 40-50 microV, and the ratio of the number of miniature potentials of 50 microV to the number of 50 microV noise potentials was about 10:1. The observed miniature potentials with an amplitude of 50-100 microV coincide with the quantal units calculated by other authors from statistical analysis of the unitary EPSPs evoked by primary afferents or by ventrolateral tract fibers.     

Liver regenerative potential of the lake frog Rana ridibunda after partial hepatectomy

A histomorphological study of the regenerating liver of Rana ridibunda, within 2 months after partial hepatectomy, shows that regenerative processes on the wound surface are slowly proceeding. Processes of reticular fiber reconstruction occurred in the composition of the basal membrane of liver sinusoids. A cytophotometric study shows that glandular cells in R. ridibunda liver are commonly tetraploid. The post-traumatic regeneration of the liver after partial hepatectomy involves activation of DNA synthesis in hepatocytes, leading to increase in their ploidy. Within the 1st month of regeneration, the mitotic index of hepatocytes substantially increased. Regeneration of glandular parenchyma of the liver is accompanied by a quantitative increase in binucleate hepatocytes, which is most highly expressed within 5-20 days after partial hepatectomy.     

Hepatic mixed function oxidase (MFO) activities during the seasonal life cycle of the frog,Rana temporaria

1. A single dose of DDT (5 mg/kg) did not affect the activities of hepatic mixed function oxidase (MFO) components in fed summer frogs, Rana temporaria.2. The activity of MFO system showed remarkable seasonal variation with its higher activity level during the summer period.The MFO activity tended to be lower in the females than in the males at the beginning of spawning time while at the end of the spawning the reverse tendency was observable.4. In frogs overwintered in laboratory the activity levels of MFOs were lower than in the frogs undergone a natural wintering. The activity levels in an immature female resembled those observable in mature males.     

Efferent neurons of the auditory center in the midbrain of the frog Rana ridibunda

Individual cells which produce projections from the torus semicircularis in the frog have been visualized after injection of horseradish peroxidase (HRP) to various thalamic and isthmal areas. Labeled toral cells were observed if HRP had been injected to the posterodorsal areas of the thalamus or to the isthmal areas where lateral lemniscus fibers and cells of the premature lateral lemniscal nucleus are situated. Medium and large size cells in the rostrolateral torus semicircularis were mainly labeled. Thalamic injections of the HRP produced more labeled cells in the lateral part of the magnocellular nucleus, whereas isthmal injections produced labeled cells mainly in the lateral part of the laminar nucleus. A few HRP containing cells were observed in the principal nucleus of the torus. Specificity of the neuronal organisation of the auditory pathway in amphibians is discussed.     

Distribution of atrial natriuretic factor-like immunoreactivity in the brain of the frog Rana ridibunda

The localization of atrial natriuretic factor (ANF)-like immunoreactivity in the central nervous system of the frog Rana ridibunda was examined by the indirect immunofluorescence technique, using an antiserum against synthetic ANF (Arg101-Tyr126). Immunoreactive cell bodies were principally found in the dorsal and medial pallium, the medial septal nucleus, the ventrolateral and anteroventral areas of the thalamus, the lateral forebrain bundle, the posterolateral thalamic nuclei, the preoptic nucleus, the dorsal infundibular nucleus, and the anteroventral tegmentum nucleus of the mesencephalon. Numerous cell bodies and a very dense fiber bundle were visualized in the interpeduncular nucleus. All the areas mentioned above contained a high density of immunoreactive fibers. In addition, the amygdala, the infundibular nucleus, the median eminence, and most of the areas of the mesencephalon contained a moderate number of ANF-positive nerve processes. In the frog pituitary, fibers and nerve terminals were found in the peripheral zone of the neural lobe. The intermediate and anterior lobes of the frog pituitary were totally devoid of ANF immunoreactivity. These results indicate that ANF-like material is widely distributed in the frog brain and that ANF may be involved in various brain functions including neuroendocrine regulations.