Gaston-Denis Guex

• PhD
• Senior Researcher at University of Zurich

Hybridogenesis is a reproductive tool for sexual parasitism. Hybridogenetic hybrids use gametes from their sexual host for their own reproduction, but sexual species gain no benefit from such matings as their genome is later eliminated. Here, we examine the presence of sexual parasitism in water frogs through crossing experiments and genome-wide da...

Epidermal papillomas of alpine newts (Ichthyosaura alpestris) collected in the field (Germany, Austria) were studied by histology (LM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Papillomas were found on the head, the trunk and the tail, with the most and largest on the head of males. They protruded beyond the b...

Infecties bij amfi bieën in Nederland: Amphibiocystidium Amfi bieën hebben te maken met een groot aantal bedreigingen, waaronder ziektes. Chytridiomycose en Ranavirus zijn de bekendste, maar er zijn meer ziektes waar amfi bieën mee te maken hebben, waaronder Amphibiocystidium-infectie. Maar wat is dat, en hoe herken je het? Tariq Stark & Gaston-Den...

We combine multivariate ratio analysis (MRA) of body measurements and analyses of mitochondrial and nuclear data to examine the status of several species of European paper wasps (Polistes Latreille, 1802) closely related to P. gallicus. Our analyses unambiguously reveal the presence of a cryptic species in Europe, as two distinct species can be rec...

Concentrations of commonly used organochlorine pesticides (OCPs) were determined in tissues of 23 adult and 24 larval water frogs of two coexisting species (Rana lessonae and the hemiclonal hybrid R. esculenta) and in the water of their breeding pond in an agricultural zone in Umbria, central Italy, where increased occurrence of infectious diseases...

Variation patterns of allozymes and of ND3 haplotypes of mitochondrial DNA reveal a zone of genetic transition among western Palearctic water frogs extending across northeastern Greece and European Turkey. At the western end of the zone, allozymes characteristic of Central European frogs known as Pelophylax ridibundus predominate, whereas at the ea...

Habitats of the Blister beetle (Coleoptera: Meloidae) Sitaris muralis (Foerster, 1771) in Switzerland. – After only 5 habitats of Sitaris muralis had been published from Switzerland, 2 of them without evidence, we managed to establish at least 14 proven habitats so far due to both a survey and own observations. None of these habitats is supposed to...

RrS1-like sequences of water frogs (genus Pelophylax) display varied genomic organization, whereas the centromeric hybridization pattern reveals species-specific differences. Using fluorescent in situ hybridization, Pelophylax cf. bedriagae, Pelophylax kurtmuelleri, and Pelophylax ridibundus showed a hybridization signal at centromeres of chromosom...

Aim Our aims were to assess the phylogeographic patterns of genetic diversity in eastern Mediterranean water frogs and to estimate divergence times using different geological scenarios. We relate divergence times to past geological events and discuss the relevance of our data for the systematics of eastern Mediterranean water frogs. Location The ea...

Water frogs [genus Pelophylax (Rana)] that occur around the eastern Mediterranean Sea provide an opportunity to study early stages of speciation. The geography of the eastern Mediterranean region has changed dramatically since the Middle Miocene as a result of motions of adjoining lithospheric plates and regional-scale vertical crustal motions (upl...

Hemiclonal hybrids of Western Palearctic water frogs of the Rana esculenta complex transmit only one parental genome to their offspring without recombination (hybridogenesis). Such genomes are thus prone to accumulate deleterious mutations. The frog complex is unique among hybridogens in that hemiclonal hybrids occur in both sexes. This provides th...

A 5' truncated non-LTR CR1-like retrotransposon, named RanaCR1, was identified in the serum albumin intron-1 (SAI-1) of at least seven species of western Palearctic water frogs (WPWF). Based on sequence similarity of the carboxy-terminal region (CTR) of ORF2 and/or the highly conserved 3' untranslated region (3' UTR), RanaCR1-like elements occur al...

Interspecies transfer of mitochondrial (mt) DNA is a common phenomenon in plants, invertebrates and vertebrates, normally linked with hybridization of closely related species in zones of sympatry or parapatry. In central Europe, in an area north of 48 degrees N latitude and between 8 degrees and 22 degrees E longitude, western Palaearctic water fro...

Rana esculenta progeny from experimental crosses (using R. esculenta from natural lineages and F1Rana ridibunda × Rana lessonae), reared in artificial ponds and in cages immersed in natural breeding ponds, showed three different types of malformations reflecting developmental disturbances, each affecting few individuals overall. Giant tadpoles arre...

European water frog hybrids Rana esculenta reproduce hemiclonally, by hybridogenesis: In the germ line they exclude the genome of the parental species Rana lessonae and produce haploid, unrecombined gametes with a genome of the parental species Rana ridibunda. These hybrids coexist with and depend as sexual parasites on the host parental species R....

European water frog hybrids Rana esculenta (R. ridibundaxR. lessonae) reproduce hemiclonally, by hybridogenesis: in the germ line they exclude the genome of one parental species and produce haploid gametes with an unrecombined genome of the other parental species. In the widespread L-E population system, both sexes of hybrids (E) coexist with R. le...

A family of interspersed repetitive elements, RlBamHI, with sequence similarity to the transposase of hAT DNA transposons, occurs in genomes of eight western Palaearctic water frog taxa and the brown frog Rana dalmatina, but was not detected in Xenopus laevis or Salamandra salamandra. RlBamHI elements are not tandemly arrayed, are dispersed across...

In central Europe, the hybridogenetic water frog Rana esculenta is a sexual parasite that only persists in the presence of the parental species, R. lessonae, with which it must mate in order to reproduce. R. esculenta is a superior larval competitor, and adult females are about three times more fecund than R. lessonae. This suggests that, in the ab...

-Spontaneous deleterious mutations are expected to accumulate through Muller's ratchet in clonally reproducing organisms and may lead to their extinction. We study deleterious mutations and their effects in a system of European frogs. Rana esculenta (RL), natural hybrids R. ridibunda (RR) X R. lessonae (LL), reproduce hemiclonally; both sexes exclu...

Genotypic variation at six of 67 microsatellite loci we developed from Rana ridibunda, containing di- or trinucleotide simplesequence repeats, confirms the value of microsatellites as an evolutionary genetic tool for studying western Palearctic water frogs, a model system characterized by clonal reproduction in natural hybrid lineages. R. ridibunda...

European water frog hybrids Rana esculenta (Rana ridibunda x Rana lessonae) reproduce hemiclonally, transmitting only their ridibunda genome to gametes. We compared fitness-related larval life-history traits of natural R. esculenta from Poland with those of the two sympatric parental species and of newly generated F1 hybrids. Compared with either p...

We tested for environmental factors that may lead to balancing selection and to the maintenance of a genetic polymorphism at the enzyme locus lactate dehydrogenase B (LDH-B) in the pool frog, Rana lessonae. We raised tadpoles individually in a factorial experiment in which we manipulated temperature, food level, and food quality. The only statistic...

Vertebrate animals reproducing without genetic recombination typically are hybrids, which have large ranges, are locally abundant, and live in disturbed or harsh habitats. This holds for the hemiclonal hybridogenetic frog Rana esculenta: it is widespread in Europe and commonly is found in disturbed habitats such as gravel pits. We hypothesize that...

Vertebrate animals reproducing without genetic recombination typically are hybrids, which have large ranges, are locally abundant, and live in disturbed or harsh habitats. This holds for the hemiclonal hybridogenetic frog Rana esculenta: it is widespread in Europe and commonly is found in disturbed habitats such as gravel pits. We hypothesize that...

Animal taxa of interspecies hybrid origin that have derived obligatory clonal reproductive modes leading to genealogical persistence demand clear, stable names as labels to refer to them. We recommend (1) that clonal hybrid taxa distinguished by the combination of parental genomes they contain be recognized; (2) that they be referred to, consistent...

Hybrid water frogs Rana esculenta reproduce by hybridogenesis: one parental genome (of Rana lessonae) is excluded in the germ line, the other (of Rana ridibunda) is clonally transmitted to haploid gametes. The two parental species differ in that the amount of centromeric heterochromatin revealed by differential staining is much higher in Rana ridib...

European water frog hybrids Rana esculenta (Rana ridibunda Rana lessonae) reproduce hemiclonally, transmitting only their ridibunda genome to gametes. We compared fitness-related larval life-history traits of natural R. esculenta from Poland with those of the two sympatric parental species and of newly generated F 1 hybrids. Compared with either pa...

The intrauterine nourishment of the viviparous alpine salamander, Salamandra atra, has been demonstrated to consist of two phases: oophagy - after hatching from the jelly membrane, the developing embryo ingests the remaining disintegrated, unfertilized egg mass. Epitheliophagy - a special cranial portion of the uterus wall, the zona trophica, is st...