Esculenta Populations Research Articles

Genetic diversity of a Phascolosoma esculenta population following stock enhancement in Yueqing Bay, East China Sea

Responsible stock enhancement should aim to restore a population while ensuring uninterrupted genetic characteristics of the species. In this study, five pairs of screened microsatellite primers were used to analyze genetic diversity in a wild population (YS, before release), released population (FL), and recaptured population (HB, after release) of Phascolosoma esculenta to assess the impact of stock enhancement in Yueqing Bay. Microsatellite analysis revealed that the average numbers of alleles (Na) for the YS, FL, and HB of P. esculenta were 4.40, 5.40, and 5.40, respectively. The average effective numbers of alleles (Ne) were 2.11, 2.07, and 2.24, respectively. The average observed heterozygosity (Ho) was 0.312, 0.340, and 0.305, respectively, while the average expected heterozygosity (He) was 0.489, 0.465, and 0.496, respectively. The average polymorphic information content (PIC) was 0.425, 0.409, and 0.434, respectively. Analysis of Molecular Variance (AMOVA) revealed that most of the genetic variation was within populations. The genetic differentiation index (FST) values between the three populations were all less than 0.05. The three populations of P. esculenta all had moderate genetic diversity and there was minimal genetic differentiation between the populations, suggesting that the released P. esculenta were suitable for stock enhancement and that the current stock enhancement practices in Yueqing Bay have had no negative impact on the genetic diversity of P. esculenta.

Seasonal and Spatial Distribution Characteristics of Sepia esculenta in the East China Sea Region: Transfer of the Central Distribution from 29° N to 28° N.

The golden cuttlefish (Sepia esculenta) is an important cephalopod species with a lifespan of approximately one year. The species plays a crucial role in marine ecological support services and is commercially valuable in fisheries. In the seas around China, this species has emerged as the main target for cuttlefish fisheries, replacing Sepiella maindroni since the 1990s. Variations in oceanographic conditions associated with global warming could significantly impact the temporal-spatial distribution of the species. In this study, we performed bottom trawling surveys with four cruises during 2018-2019 in the East China Sea region to determine the current resource status and seasonal-spatial variations in S. esculenta. We found that the average individual weight (AIW) values were 4.87 and 519.00 g/ind at stations located at 30.50° N, 124.00° E and 30.50° N, 124.50° E, respectively, with the aggregation of larvae and parent groups in spring. The species was not distributed north of 32.00° N in summer. The catch per unit effort by weight (CPUEw) value decreased in the order of 2772.50→2575.20→503.29→124.36 g/h, corresponding to latitudes of 34.50° N→34.00° N→33.50° N→32.50° N 121.50° E in autumn. The most suitable fishing areas were the south of the East China Sea region in spring; the south of the East China Sea region extending to the center and outer parts of the East China Sea region in summer; the south of the Yellow Sea close to the Haizhou Bay fishing ground and the forbidden fishing line region of the Lusi and Dasha fishing grounds in autumn; and the south and center of the East China Sea region in winter. The most suitable sea bottom temperature (SBT) values from spring to winter were 14.76-20.53 °C, 19.54-22.98 °C, 11.79-17.64 °C, and 16.94-20.36 °C, respectively. The most suitable sea bottom salinity (SBS) values were 31.53-34.80‱ in spring, 32.95-34.68‱ in summer, 31.51-34.77‱ in autumn, and 33.82-34.51‱ in winter. We concluded the following: (1) the southern and northern areas of the East China Sea region are spawning and nursery grounds, respectively, in spring; (2) the central distribution is located at a latitude of 28.00° N in autumn and winter; and (3) the southern area of the Yangtze River to the north is a spawning ground in spring, and the areas located at 29.00-34.50° N, 124.00-124.50° E, and 28.00-30.50° N, 125.50-126.50° E are nursery grounds. The results of this study provide useful guidance for appropriate fisheries management, thereby avoiding a collapse in the S. esculenta population, which has been experienced in other species in this area.

Genetic Diversity and Genetic Structure of Phascolosoma esculenta Populations in Southeastern China Based on 16S rRNA Gene Sequences

Here, we investigated the population genetic structure and genetic diversity of the endemic Chinese oceanic sipuncula Phascolosoma esculenta by using partial mitochondrial DNA 16S rRNA sequences. In total, 80 samples were collected from Xiangshan, Wenling, Ningde, and Zhanjiang, which are four muddy intertidal zones of southeastern China. Results showed that of the 80 16S rRNA gene fragments, 5 were 1010 bp in length, 73 were 1011 bp in length, and 2 were 1012 bp in length. The A+T content (67.7%) was signifi cantly higher than the C+G content (32.3%), thus exhibiting obvious AT biases. In addition, 27 different haplotypes were defi ned by 33 polymorphic sites, giving an overall haplotype diversity of 0.908 and a nucleotide diversity of 0.00247. The topological structure of the haplotype neighbor-joining tree was extremely simple, without any obvious geographical structures within the four groupings. The genetic distances among populations ranged from 0.0022 to 0.0031, and those within populations ranged from 0.002 to 0.0028. The results of AMOVA revealed a low level of genetic differentiation among the four populations. A neutral test and mismatch analysis indicated a recent population expansion for P. esculenta.

Mating Types of Ustilago esculenta Infecting Zizania latifolia Cultivars in Japan Are Biased towards MAT-2 and MAT-3.

Zizania latifolia cultivars infected by the endophytic fungus Ustilago esculenta develop an edible stem gall. Stem gall development varies among cultivars and individuals and may be affected by the strain of U. esculenta. To isolate haploids from two Z. latifolia cultivars in our paddy fields, Shirakawa and Ittenkou, we herein performed the sporadic isolation of U. esculenta strains from stem gall tissue, a PCR-based assessment of the mating type, and in vitro mating experiments. As a result, we obtained heterogametic strains of MAT-2 and MAT-3 as well as MAT-2, but not MAT-3, haploid strains. Another isolation method, in which we examined poorly growing small clusters of sporidia derived from teliospores, succeeded in isolating a MAT-3 haploid strain. We also identified the mating types of 10 U. esculenta strains collected as genetic resources from different areas in Japan. All strains, except for one MAT-1 haploid strain, were classified as MAT-2 haploid strains or heterogametic strains of MAT-2 and MAT-3. The isolated strains of MAT-1, MAT-2, and MAT-3 mated with each other to produce hyphae. Collectively, these results indicate that the mating types of U. esculenta infecting Z. latifolia cultivars in Japan are biased towards MAT-2 and MAT-3 and that U. esculenta populations in these Japanese cultivars may be characterized by the low isolation efficiency of the MAT-3 haploid.

Whole genome population structure of North Atlantic kelp confirms high-latitude glacial refugia.

Coastal refugia during the Last Glacial Maximum (~21,000 years ago) have been hypothesized at high latitudes in the North Atlantic, suggesting marine populations persisted through cycles of glaciation and are potentially adapted to local environments. Here, whole-genome sequencing was used to test whether North Atlantic marine coastal populations of the kelp Alaria esculenta survived in the area of southwestern Greenland during the Last Glacial Maximum. We present the first annotated genome for A. esculenta and call variant positions in 54 individuals from populations in Atlantic Canada, Greenland, Faroe Islands, Norway and Ireland. Differentiation across populations was reflected in ~1.9 million single nucleotide polymorphisms, which further revealed mixed ancestry in the Faroe Islands individuals between putative Greenlandic and European lineages. Time-calibrated organellar phylogenies suggested Greenlandic populations were established during the last interglacial period more than 100,000 years ago, and that the Faroe Islands population was probably established following the Last Glacial Maximum. Patterns in population statistics, including nucleotide diversity, minor allele frequencies, heterozygosity and linkage disequilibrium decay, nonetheless suggested glaciation reduced Canadian Atlantic and Greenlandic populations to small effective sizes during the most recent glaciation. Functional differentiation was further reflected in exon read coverage, which revealed expansions unique to Greenland in 337 exons representing 162 genes, and a modest degree of exon loss (103 exons from 56 genes). Altogether, our genomic results provide strong evidence that A. esculenta populations were resilient to past climatic fluctuations related to glaciations and that high-latitude populations are potentially already adapted to local conditions as a result.

Morphometric and DNA investigations into European water frogs (Rana kl. esculenta Synklepton (Anura, Ranidae)) from different population systems

The population specific variability of diploid and triploid R. kl. esculenta individuals was investigated by means of morphometric methods (canonical discriminant analysis, UPGMA cluster analysis) and DNA fingerprinting. As a result of the morphometric investigations, as well as of the DNA investigations, a clear separation of single populations was possible. However, no correlations between the morphometry and different population systems could be recognized. Clear morphometric differences could be seen between diploid ♀♀ and ♂♂ and triploid ♀♀ on the one hand, and triploid ♂♂ on the other. While the diploid ♀♀ and ♂♂ and the triploid ♀♀ were located in the intermediate area between the parental species R. lessonae and R. ridibunda according to their morphometric parameters, the triploid ♂♂ showed a great overlap with R. lessonae. Up to now, this phenomenon has not been explained. The first results of the DNA investigations provided further hints at the high inter-individual and population-specific variability of R. kl. esculenta. R. kl. esculenta individuals of the R. lessonae/esculenta population Toter See could be distinguished from conspecific individuals of the R. ridibunda/esculenta-♀♀ population Alte Oder according to their fingerprint patterns. Moreover, in the R. lessonae / esculenta population, the fingerprints or the diploid R. kl. esculenta-♀♀ and the investigated R. lessonae-♀ were very similar. Furthermore, in this population, many R. kl. esculenta genotypes resemble R. lessonae in their morphometric features. This finding suggests the occurrence of recombination in R. kl. esculenta. In general, every population seems to have its own genetic background. A classification of water-frog populations according to population systems is only possible under certain conditions.

Food Habit of Rana (Pelophylax) kl. esculenta Females in a New Recorded E-System Population from a Forested Habitat in North-Western Romania

This is the first record of a green frog Rana (Pelophylax) kl. esculenta population from the E-system in the north-western part of Romania. From April to July 2005 we analysed the trophic spectrum of 84 Rana kl. esculenta females, extracting and identifying a total number of 801 prey items. Beside animal preys, plant materials and remains of shed skin were identified in the stomach contents. We did not find any Rana kl. esculenta individuals with empty stomachs. The importance of different animal prey categories varied in certain periods of the study. In the stomach contents collected in July we identified 2 adult amphibians. The analysed Rana kl. esculenta individuals forage mainly on land. The abundance of aquatic preys was higher only at the first sampling event.

DNA content in erythrocyte nuclei of water frogs from a pure Rana esculenta population in Dębki (Gdańsk district, Poland)

Rana esculenta is a hybridogenetic hybrid between Rana ridibunda and Rana lessonae. Usually the hybrids, among which diploid and triploid individuals of both sexes were described, live in mixed populations with one of the parental species (L-E or R-E systems). The hybrids also form pure esculenta-esculenta populations (E-E system). 114 individuals from the Baltic Sea region were collected in 1990–1991 and 1998-1999. Blood smears were taken and erythrocyte areas were measured. The erythrocyte area ranged from 318.27 μm2 to 571.82 μ2 and two peaks could be distinguished: 370 μ2 and 460–490 μ2. The smears were then stained according to the Feulgen method and the DNA amount per nucleus was determined by measuring the integrated optical density of the nucleus area. The correlation between erythrocyte size and DNA content was relatively high (0.82). Nevertheless, in some cases the erythrocyte size was not a good indicator of DNA content. Specimens had various DNA content and they formed two distinct groups: one with higher and one with lower DNA content. However, we were not able to discriminate the expected two classes of diploid and triploid individuals. The results indicated that the problem of ploidy is complicated, and we cannot rule out the existence of aneuploids or mosaics among hybrids. The problem needs to be elucidated in combination with other methods, especially because it allows measuring the ploidy level in great number of animals without killing them and thus seems to be very useful for population studies.

Hemiclonal reproduction slows down the speed of Muller's ratchet in the hybridogenetic frog Rana esculenta

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 x L matings. Intraspecific E x 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.

Variation in Sex Ratio and Evolutionary Rate of Hemiclonal Rana esculenta Populations

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 (α), 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.

Male mating speed promote hybridization in the Rana lessonae–Rana esculenta waterfrog system

Hybridization is a widespread phenomenon in many vertebrate groups. Prezygotic isolating mechanisms, probably caused by selection against hybrids with reduced fitness, reduce the likelihood of such events. Although hybrid-reduced fitness relatively to parental species is common, hybridization can also be beneficial, and hybrids sometimes outperform the pure species type. In this study, we examined two potential processes, Hubbs’s principle and male–male competition, which could enhance hybridization in the waterfrog complex and thus explain the proportion of heterospecific pairs collected in a natural pond. Firstly, by collecting 791 frogs in the field to study pair and chorus composition, we showed that in a mixed Rana lessonae–Rana esculenta population, the scarcity of hybrid R. esculenta males did not account for the proportion of heterospecific pairs: indeed, when examining pairing composition in six different choruses, we found that hybrid males were always under-represented and that R. esculenta females were found paired with R. lessonae males. Secondly, we investigated experimentally whether or nor male–male competition mechanism could explain pair formation in waterfrogs. Our mating speed experiment highlights mechanisms that could explain heterospecific pairs in a context of promiscuous mating where scramble competition was intense. To measure the rapidity with which a male grasps a female, we placed males in a grid cage with a female, and the dynamics of pair formation was monitored. R. esculenta males showed a lower pairing success than R. lessonae males as a smaller proportion of them amplexed females, and more time was needed for them to get amplexed. Thus, a less adaptative mechanism than female mate choice may also explain the mating pattern observed in waterfrog species.

REPRODUCTION AND HYBRID LOAD IN ALL-HYBRID POPULATIONS OF RANA ESCULENTA WATER FROGS IN DENMARK

All-hybrid populations of the water frog, Rana esculenta, are exceptional in consisting of independently and to some extent sexually reproducing interspecific hybrids. In most of its range R. esculenta reproduces hemiclonally with one of the parental species, R. lessonae or R. ridibunda, but viable populations of diploid and triploid hybrids, in which no individuals of the parental species have been found, exist in the northern part of the range. We test the hypothesis that nonhybrids arise every year in these all-hybrid populations, but die during larval development. Microsatellite markers were used to determine the genotypes of adults and abnormal and healthy offspring in three all-hybrid populations of R. esculenta in Denmark. Of all eggs and larvae, 63% developed abnormally or died, with some being nonhybrid (genomes matching one of the parental species), many being aneuploid (with noninteger chromosome sets), a few being tetraploid, and many eggs possibly being unfertilized. The 37% surviving and apparently healthy froglets were all diploid or triploid hybrids. In all three populations, gametogenesis matched the pattern previously described for all-hybrid R. esculenta populations in which most triploid adults have two R. lessonae genomes. This pattern was surprising for the one population in which triploid adults had two R. ridibunda genomes, because here it leads to a deficiency of gametes with an R. lessonae genome and should compromise the stability of this population. We conclude that faulty gametogenesis and mating between frogs with incompatible gametes induce a significant hybrid load in all-hybrid populations of R. esculenta, and we discuss compensating advantages and potential evolutionary trajectories to reduce this hybrid load.

REPRODUCTION AND HYBRID LOAD IN ALL-HYBRID POPULATIONS OF RANA ESCULENTA WATER FROGS IN DENMARK

All-hybrid populations of the water frog, Rana esculenta, are exceptional in consisting of independently and to some extent sexually reproducing interspecific hybrids. In most of its range R. esculenta reproduces hemiclonally with one of the parental species, R. lessonae or R. ridibunda, but viable populations of diploid and triploid hybrids, in which no individuals of the parental species have been found, exist in the northern part of the range. We test the hypothesis that nonhybrids arise every year in these all-hybrid populations, but die during larval development. Microsatellite markers were used to determine the genotypes of adults and abnormal and healthy offspring in three all-hybrid populations of R. esculenta in Denmark. Of all eggs and larvae, 63% developed abnormally or died, with some being nonhybrid (genomes matching one of the parental species), many being aneuploid (with noninteger chromosome sets), a few being tetraploid, and many eggs possibly being unfertilized. The 37% surviving and apparently healthy froglets were all diploid or triploid hybrids. In all three populations, gametogenesis matched the pattern previously described for all-hybrid R. esculenta populations in which most triploid adults have two R. lessonae genomes. This pattern was surprising for the one population in which triploid adults had two R. ridibunda genomes, because here it leads to a deficiency of gametes with an R. lessonae genome and should compromise the stability of this population. We conclude that faulty gametogenesis and mating between frogs with incompatible gametes induce a significant hybrid load in all-hybrid populations of R. esculenta, and we discuss compensating advantages and potential evolutionary trajectories to reduce this hybrid load.

Are North Atlantic Alaria esculenta and A. grandifolia (Alariaceae, Phaeophyceae) conspecific?

Alaria (Alariaceae, Phaeophyceae) is a common genus of kelps in the northern hemisphere. Fourteen species are currently recognized, of which three, Alaria esculenta (L.) Greville, A. pylaii (Bory de Saint-Vincent) Greville and A. grandifolia J. Agardh, are reported for the coldtemperate North Atlantic Ocean. Alaria esculenta, the type species described originally from the North Atlantic, exhibits a range of biogeographically correlated morphotypes suggesting the possibility of multiple species, subspecies or hybrids. In Ireland we discovered an A. esculenta population with unusually long stipes resembling the type specimen of A. grandifolia described from Spitsbergen by J. Agardh in 1872. These and other plants of A. esculenta from Ireland were compared with plants from Spitsbergen fitting the description of A. grandifolia, using sexual hybridization, relative growth rate measurements and DNA sequence comparisons. Complete interfertility was observed between the different isolates. Three nucleotide substi...

Are North Atlantic Alaria esculenta and A. grandifolia (Alariaceae, Phaeophyceae) conspecific?

Alaria (Alariaceae, Phaeophyceae) is a common genus of kelps in the northern hemisphere. Fourteen species are currently recognized, of which three, Alaria esculenta (L.) Greville, A. pylaii (Bory de Saint-Vincent) Greville and A. grandifolia J. Agardh, are reported for the coldtemperate North Atlantic Ocean. Alaria esculenta, the type species described originally from the North Atlantic, exhibits a range of biogeographically correlated morphotypes suggesting the possibility of multiple species, subspecies or hybrids. In Ireland we discovered an A. esculenta population with unusually long stipes resembling the type specimen of A. grandifolia described from Spitsbergen by J. Agardh in 1872. These and other plants of A. esculenta from Ireland were compared with plants from Spitsbergen fitting the description of A. grandifolia, using sexual hybridization, relative growth rate measurements and DNA sequence comparisons. Complete interfertility was observed between the different isolates. Three nucleotide substitutions (0·37%) were found in the rbcL and RuBisCo spacer of A. grandifolia, and two in the partial 18S rRNA gene and ITS1 sequences. The relative growth rate at 10 °C of an Irish self-cross was significantly lower than those of all the other crosses. Comparison of RuBisCo spacer sequences of the Spitsbergen A. grandifolia and six A. esculenta isolates showed that A. grandifolia was identical to A. esculenta from Halifax, Canada. The partial 18S rRNA gene and ITS1 sequence of A. grandifolia was identical to that of A. praelonga from Japan and differed by a single substitution from A. esculenta from Scotland and by two nucleotide substitutions from the isolate from Ireland. The intraspecific differences in A. esculenta, together with the hybridization and morphometric results, suggest that A. grandifolia is to be considered conspecific with A. esculenta, and that A. grandifolia is most probably a large deep-water morphological variant, subspecies or ecotype of A. esculenta.

DNA content in erythrocyte nuclei of water frogs from a pureRana esculenta population in Dębki (Gdańsk district, Poland)

DNA content in erythrocyte nuclei of water frogs from a pureRana esculenta population in Dębki (Gdańsk district, Poland)

The edible brown seaweed Alaria esculenta (Phaeophyceae, Laminariales): hybridization, growth and genetic comparisons of six Irish populations

Alaria esculenta populations from six differentgeographical locations on the Irish coast wereexamined for hybridization abilities, growth rates andgenetic make-up with a view towards identifying afast-growing strain suitable for aquaculture.Hybridization experiments under laboratory conditionswith the three most geographically dispersedpopulations showed that all cross combinations wereinterfertile, although differences were found insurvival, and in blade and hapteron morphology. Acomparison of relative growth rates showed significantdifferences amongst the self-crosses and hybrids. Thedata of the hybridization experiments and growth ratesunder laboratory conditions show that the bestpopulation for the purpose of seaweed aquaculture arethe Slea Head and Corbet Head self-crosses and theirhybrids. Genetic fingerprinting of the internaltranscribed spacer of the ribosomal DNA of five A. esculenta isolates from geographically separatedpopulations in Ireland revealed no restriction lengthpolymorphisms between the tested isolates and showthat the A. esculenta populations around theIrish coast are clearly genetically homogenous inrespect of the DNA region examined. The geneticanalysis, interfertility of the populations,morphology and growth rates are discussed with a viewto potential cultivation.

Progeny of water frog populations in central Poland

Abstract The authors discuss progenies of 18 watcr frog populations. Individuals with esculenta phenotype which arc hybridogenetic hybrids between Rana ridibunda and Rana lessonae are the most numerous frogs among the adults and progeny. Esculenta tadpoles began and finished their metamorphosis mostly as first, and in progeny with esculenta phenotype there were more females than males. In pure esculenta population most of progeny belonged to ridibunda phenotype and female sex. The froglets caught in August were larger on an average than those in October or after hibernation.

Evolutionary history of the hybridogenetic hybrid frog Rana esculenta as deduced from mtDNA analyses.

mtDNA of the hybridogenetic hybrid frog Rana esculenta from Switzerland, Austria, and Poland was compared to mtDNA of the parental species R. ridibunda and R. lessonae using electrophoretic analysis of restriction enzyme fragments. Two mtDNA phenotypes, with 3.4% sequence divergence, are present in R. lessonae: type C is found in Poland, and type D is found in Switzerland. Rana ridibunda from Poland has either of two mtDNA phenotypes: type A is the typical ridibunda mtDNA, and type B is a lessonae mitochondrial genome, introgressed into R. ridibunda, that differs from type C mtDNA of R. lessonae by only 0.3%. Each of the three lessonae genomes differs from A, the typical ridibunda mtDNA, by approximately 8%. All four types of mtDNA (A and B of R. ridibunda, C and D of R. lessonae) are found in R. esculenta. Of 62 R. esculenta from Poland, 58 had type C, three had type A, and one had type B mtDNA. All nine R. esculenta from Switzerland had type D mtDNA. All three R. esculenta from Austria, from a population in which males of R. esculenta are rare, had ridibunda mtDNA, two having type B and one having type A. Both field observations and studies of mating preference indicate that the primary hybridizations that produce R. esculenta are between R. ridibunda females and R. lessonae males; thereafter, R. esculenta lineages are usually maintained by matings of R. esculenta females with R. lessonae males. The presence of ridibunda mtDNA in the three R. esculenta sampled from Austria, its occasional presence in R. esculenta populations in Poland, and its absence from R. esculenta in Switzerland support both the direction of the original hybridization and the rarity of formation of new R. esculenta lineages. The preponderance of R. esculenta individuals with lessonae mtDNA in our samples from central Europe suggests that most lineages have gone through at least one mating between an R. lessonae female and an R. esculenta male. This reveals a greater reproductive role for R. esculenta males than their partial sterility and infrequent matings would suggest.

Plasma sex hormones and post-reproductive period in the green frog, Rana esculenta complex

The plasmatic profiles of androgens, estradiol, and progesterone, together with gonads and SSC modifications, have been followed, throughout the post-reproductive period in two Rana esculenta populations, inhabiting, respectively, a mountain poud (Colfiorito) and a sea level lagoon (Lesina). Testosterone and progesterone progressively decrease in the blood until July, while estradiol shows, in both sexes, an increase in the same month. Testosterone depletion accounts for thumb pad atrophy in the male and probably, in both sexes, for the summer interruption of sexual behavior. The estradiol increase could be linked to the induction of vitellogenin synthesis by the liver or, alternatively, could act through negative feed-back on the brain centers involved in GnRF synthesis and therefore it could be responsible for an inhibition of LH release and, in turn, of androgen synthesis/secretion by the gonads. The last function can be framed in the endocrine regulation of the so-called “refractory period” which interrupts the breeding during the summer. The hematic level of progesterone is higher during the ovulation period and this is consistent with the role assigned to the hormone, i.e., the induction of jelly release from oviductal glands. The hormonal trends in the blood of the two frog populations are very similar, although some differences exist in the levels of testosterone and progesterone.