Microsatellite marker data suggest sex-biased dispersal in the common frog Rana temporaria

Despite being important models in ecological, evolutionary and conservation biology research, very little is known about the dispersal in anuran amphibians, and juvenile dispersal in particular. Using microsatellite data, we assessed signatures of sex-biased migration in the common frog (Rana temporaria) in Scandinavia. Significant heterozygosity deficiency (FIS) and lower assignment value (mAIc) among females suggest that dispersal in R. temporaria is female biased. Also variance of assignment (vAIc), estimated separately for the two sexes, was consistent with this inference, although the difference was not statistically significant. Possible proximate and ultimate explanations for female-biased dispersal in amphibians are discussed.     

Polymorphic microsatellite DNA loci identified in the common frog (Rana temporaria,Amphibia, Ranidae)

We developed seven microsatellite loci in the common frog, Rana temporaria. There were between 2 and 27 alleles per locus and the expected heterozygosities ranged from 0.28 to 0.96 in a sample of frogs collected in the French Alps. Adding these seven markers to the 15 previously available microsatellite loci for this species should facilitate studies of genetic structure of Rana temporaria populations at a fine geographical scale.     

Molecular characterization of major histocompatibility complex class II alleles in the common frog, Rana temporaria

Major histocompatibility complex (MHC) class II genes, which play a major role in the immune system response, are some of the most polymorphic genes in vertebrates. We developed polymerase chain reaction primers for part of the second exon of an expressed MHC class II gene in the common frog, Rana temporaria. We genotyped this locus in five frog populations in southeast England and detected eight alleles in 215 individuals. Five or six alleles were detected in each population with a maximum of two alleles per individual, indicating that only a single locus was amplified. We also inferred the possible existence of a null allele. There were 23 variable nucleotide sites (out of 136) and 13 variable amino acid sites (out of 44), many of which corresponded to amino acids involved in antigen recognition. We detected a significant excess of nonsynonymous substitutions at antigen binding sites, indicating that this gene is under positive selection. The level of variation we found was similar to that in other amphibian MHC class II loci, such as those in Bombina bombina, Xenopus laevis and Ambystoma tigrinum.     

Isolation and characterization of 145 polymorphic microsatellite loci for the common frog (Rana temporaria)

We describe primers and polymerase chain reaction conditions to amplify 145 di‐, tri‐ and tetranucleotide microsatellite loci from the common frog (Rana temporaria), a species commonly used as a model in ecological and evolutionary research. Primers were tested on 46 individuals from two Fennoscandian populations and yielded an average of six to nine alleles per locus (range = 1–30) depending on the population. Average observed heterozygosities in the two populations were 0.16 (range = 0–0.91) and 0.36 (range = 0–1).     

Sex reversal and primary sex ratios in the common frog (Rana temporaria)

Sex reversal has been suggested to have profound implications for the evolution of sex chromosomes and population dynamics in ectotherms. Occasional sex reversal of genetic males has been hypothesized to prevent the evolutionary decay of nonrecombining Y chromosomes caused by the accumulation of deleterious mutations. At the same time, sex reversals can have a negative effect on population growth rate. Here, we studied phenotypic and genotypic sex in the common frog (Rana temporaria) in a subarctic environment, where strongly female‐biased sex ratios have raised the possibility of frequent sex reversals. We developed two novel sex‐linked microsatellite markers for the species and used them with a third, existing marker and a Bayesian modelling approach to study the occurrence of sex reversal and to determine primary sex ratios in egg clutches. Our results show that a significant proportion (0.09, 95% credible interval: 0.04–0.18) of adults that were genetically female expressed the male phenotype, but there was no evidence of sex reversal of genetic males that is required for counteracting the degeneration of Y chromosome. The primary sex ratios were mostly equal, but three clutches consisted only of genetic females and three others had a significant female bias. Reproduction of the sex‐reversed genetic females appears to create all‐female clutches potentially skewing the population level adult sex‐ratio consistent with field observations. However, based on a simulation model, such a bias is expected to be small and transient and thus does not fully explain the observed female‐bias in the field.     

Population divergence of developmental thermal optima in Swedish common frogs,Rana temporaria

Growth rate, like any other trait, should be under balancing selection in natural populations, with selection adjusting mean growth rate in a population in relation to its site‐specific costs and benefits. In the present study, we tested for differences in thermal growth optima between a northern and a southern region of Rana temporaria by rearing tadpoles in three different temperatures in the laboratory (10, 15 and 20 °C). Because of the rapid increase in post‐melt temperature at high latitudes, spawn and tadpoles from the northern region experience significantly higher minimum, mean and maximum temperature throughout the period of pre‐metamorph development. Frogs up north also enjoys a shorter breeding season and activity season overall. This suggests that growth and development should be maximized at a relatively higher temperature in the north as a result of directional selection. In accordance with this prediction we found that tadpoles from the northern region grew faster at relatively higher temperature than frogs in the south, whereas the opposite was true at relatively lower temperatures. North tadpoles also had a higher mortality and poorer physiological performance than south tadpoles at low temperatures. In summary, our results conclusively support the hypothesis that frogs in the north are adapted to relatively warmer developmental conditions than frogs in the south.     

A test of the effect of supplemental UV-B radiation on the common frog, Rana temporaria L., during embryonic development

The release of certain man-made chemicals has led to recurrent, seasonal destruction of ozone in the upper atmosphere, allowing more solar radiation in the UV-B waveband to reach the Earth. Consequently, many amphibians may suffer increased exposure to UV-B at various stages in their lives. Embryonic stages of species which spawn in the spring, in shallow, open water, are at high risk of increased exposure. We exposed newly fertilized eggs of one such species, Rana temporaria L., to sunlight with and without supplemental UV-B. We used outdoor arrays of lamps to simulate the increase in UV-B which might result from previously documented ozone depletion. From immediately after fertilization to when hatchlings began feeding, ambient solar UV-B, weighted for DNA-damaging potential, was supplemented by ≈ 81% in 1995 and 113% in 1996. These levels of supplementation approximated the increase in solar UV-B expected to result from losses of 21% and 25%, respectively, of the total amount of ozone in the atmospheric column, relative to pre-ozone-depletion values. We found no evidence that these additions of UV-B radiation increased the incidence of mortality or overt developmental abnormality among embryos. We stress the need for appropriate dosimetry in studies of effects of UV-B on organisms.     

Immunoreactive Tamm-Horsfall protein in the kidney and skin of the frog Rana temporaria

Summary Tamm-Horsfall protein (THP) is the main protein in normal human urine, and is found in the thick limb of the Loop of Henle in human kidney, and in other mammalian species. The skin of the frog, Rana temporaria, has similar physiological properties to this mammalian kidney tissue. In the present study, an immunohistological method involving an antibody to human THP was used to investigate the distribution of this distinctive protein in frog kidney and skin, and to compare its distribution with that found in the kidney tubules of rat and rabbit. THP-positive material was detected in the distal renal tubules and nephric duct of frogs, and was also located in the superificial epidermis of skin. It is suggested that its presence in amphibian skin is consistent with the hypothesis that THP is an important component of tissues that absorb sodium and chloride ions, but remain impermeable to water.     

Directionality of the pressure-difference receiver ears in the northern leopard frog, Rana pipiens pipiens

We studied the directional response of the coupled-eardrum system in the northern leopard frog, Rana pipiens pipiens. Eardrum behavior closely approximates a linear time-invariant system, with a highly correlated input–output relationship between the eardrum pressure difference and the eardrum velocity. Variations in the eardrum transfer function at frequencies below 800 Hz indicate the existence of an extratympanic sound transmission pathway which can interfere with eardrum motions. The eardrum velocity was shown to shift in phase as a function of sound incident angle, which was a direct result of the phase-shift of the eardrum pressure difference. We used two laser-Doppler vibrometers to measure the interaural vibration time difference (IVTD) and the interaural vibration amplitude difference (IVAD) between the motions of the two eardrums. The coupled-eardrum system enhanced the IVTD and IVAD by a factor of 3 and 3 dB, respectively, when compared to an isolated-eardrum system of the same size. Our findings are consistent with the time-delay sensitivity of other coupled-eardrum systems such as those found in crickets and flies.     

The superficial vascular hyaloid system in the eye of the frogs,Rana temporaria and Rana esculenta

Summary The angioarchitecture of the superficial vascular hyaloid system (membrana vasculosa retinae) of the frog eye was studied by means of scanning electron microscopy of vascular corrosion casts. The terminal vessels form a single-layered sheath intimately adjacent to the vitreal side of the avascular retina. The hyaloid system is subdivided by the ventral venous trunk into three central areas: the dorsal, the temporo-ventral, and the naso-ventral area. Toward the ora serrata, the hyaloid system is bordered by an arterial ring, and by nasal and temporal venous branches forming more or less complete hemicircles. A vascular zone composed of several tongue-like sectors establishes an inter-connection between the peripheral vascular rings and the central areas of the fundus. The arterial blood is supplied from the arterial ring. The drainage of the hyaloid system is provided via two routes: (1) the Y-shaped ventral trunk collects blood from the central areas, (2) the two peripheral venous branches drain the tongue-like sectors. The vessels within the dorsal area follow preferentially a dorso-ventral meridional direction. This densely capillarized territory corresponds in localization to the area centralis retinae. The ultrastructure of microvessels of the hyaloid system is characterized by features typical for capillaries of the central nervous system.     

European common frog (Rana temporaria) recolonized Switzerland from multiple glacial refugia in northern Italy via trans‐ and circum‐Alpine routes

The high mountain ranges of Western Europe had a profound effect on the biotic recolonization of Europe from glacial refugia. The Alps present a particularly interesting case because they form an absolute barrier to dispersal for most taxa, obstructing recolonization from multiple refugia in northern Italy. Here, we investigate the effect of the European Alps on the phylogeographic history of the European common frog Rana temporaria. Based on partial cytochrome b and COXI sequences from Switzerland, we find two mitochondrial lineages roughly north and south of the Alpine ridge, with contact zones between them in eastern and western Switzerland. The northern haplogroup falls within the previously identified Western European haplogroup, while the southern haplogroup is unique to Switzerland. We find that the lineages diverged ~110 kya, at approximately the onset of the last glacial glaciation; this indicates that they are from different glacial refugia. Phylogenetic analyses suggest that the northern and southern haplogroups colonized Switzerland via trans‐ and circum‐Alpine routes from at least two separate refugia in northern Italy. Our results illustrate how a complex recolonization history of the central European Alps can arise from the semi‐permeable barrier created by high mountains.     

中国林蛙皮cDNA文库的构建

目的：为研究林蛙皮抗菌肽,筛选、克隆及表达相关抗菌功能基因,构建林蛙皮cDNA文库。方法：提取林蛙皮总RNA后,利用V—gene纯化试剂盒纯化mRNA,RT-PCR合成双链cDNA;取10ng／μLcDNA按照不同比例连接到入噬菌体载体,以选择最佳连接比例。结果：获得克隆总数为1．2×10^5的林蛙皮cDNA文库,重组率为99．4％。结论：所建立的cDNA文库可用于进一步筛选、克隆抗菌功能新基因。     

On the Development of the Eminentia Mediana of the Hypophysis in Rana temporaria, Studied in Normal, Hypophysectomized, and Thyroidectomized Tadpoles.

In the Rana temporaria tadpole, the part of the infundibular floor that eventually becomes the eminentia mediana is very thin throughout premetamorphosis; the supply of aminergic and neurosecretory nerves is poor, and the area is covered by a few fenestrated capillaries. The organ begins to thicken around mid-prometamorphosis owing to a marked invasion of nerves. At this stage it is also penetrated by capillaries and perivascular space extensions, which together form the neurovascular link structures. These become more pronounced during metamorphic climax, when the eminentia mediana attains the adult appearance. Development of the organ is arrested at the premetamorphic stage after thyroidectomy in the young premetamorphic tadpole. Removal of the adenohypophysial primordium from the embryo of the tailbud stage prevents the vascular—but not the neural—component of the eminentia from developing beyond the premetamorphic stage. By contrast, in the American Rana -species investigated the neural component also fails to develop after hypophysectomy.     

Thymic vascular system of the European common frog,Rana temporaria: a scanning electron-microscopic study of vascular casts

Vascular corrosion casts of the thymus of adult individuals of the European common frog, Rana temporaria, were analysed by scanning electron microscopy. The main arterial vessel, which is derived either from the temporal artery or from the auricular ramus, approaches the central territory of the gland and branches into twigs that, on penetrating the parenchyma, give rise to capillaries. Most of these capillaries run vertically towards the surface of the gland; they either join the superficial capillary plexus or follow this plexus for a variable distance and then run back towards the medulla, forming capillary loops. The former capillaries link with the extensive venous plexus composed of irregular meshes, whereas the latter capillaries join the venules at the cortico-medullary boundary and finally escape into collecting veins on the gland surface. The venous twigs, which join together near the gland, form the main thymic vein, which empties into the external jugular vein. The details of the thymic vasculature of the anuran amphibian, R. temporaria, are compared with those described in mammalian species, viz. the mouse, rat and guinea pig.