Search

From the mid-19th century until the 1980's, frogs and toads provided important research models for many fundamental questions in visual neuroscience. In the present century, they have been largely neglected. Yet they are animals with highly developed vision, a complex retina built on the basic vertebrate plan, an accessible brain, and an experimentally useful behavioural repertoire. They also offer a rich diversity of species and life histories on a reasonably restricted physiological and evolutionary background. We suggest that important insights may be gained from revisiting classical questions in anurans with state-of-the-art methods. At the input to the system, this especially concerns the molecular evolution of visual pigments and photoreceptors, at the output, the relation between retinal signals, brain processing and behavioural decision-making.

International audience; Solar ultraviolet-B (UV-B) radiation can be harmful for developing amphibians. As the UV-B dose increases with altitude, it has been suggested that high-altitude populations may have an increased tolerance to high levels of UV-B radiation as compared to lowland populations. We tested this hypothesis with the common frog (Rana temporaria) by comparing populations from nine altitudes (from 333 to 2450 in above sea level). Eggs collected in the field were used for laboratory experiments, i.e., exposed to high levels of artificial UV-B radiation. Eggs were reared at 14 +/- 2 degrees C and exposed to UV treatments until hatching. Embryonic developmental rates increased strongly and linearly with increasing altitude, suggesting a genetic capacity for faster development in highland than lowland eggs. Body length at hatching varied significantly with UV-B treatments, being lower when eggs developed under direct UV-B exposure. Body length at hatching also increased as the altitude of populations increased, but UV-B exposure times were shorter as altitude of population increased. However, the body length difference between exposed and non-exposed individuals in each population decreased as altitude of populations increased, suggesting a costly effect of UV exposure on growth. Type of UV exposure did not influence the mean rates of embryonic mortality and deformity, but both mortality and deformity rates increased as the altitude of populations increased (while UV-B exposure duration decreased). The effect of UV-B on body length at hatching, mortality, and deformities suggests that the sensitivity to UV-B varied among populations along the altitudinal gradient. These results are discussed in evolutionary terms, specifically the potential of R. temporaria high-altitude populations to develop local genetic adaptation to high levels of UV-B. (c) 2008 Elsevier GmbH. All rights reserved.

International audience; In anuran competition over mates, disadvantaged (i.e., less competitive) males are generally known to be the smallest ones, but ages of those males have rarely been documented. In the context of a high level of male competition for mates, disadvantaged males were expected to use alternative mating tactics. To test for alternative tactics in a territorial toad (the spadefoot toad, Pelobates fuscus, Pelobatidae), daily breeding migration patterns were observed during 3 consecutive years. Relationships between migration pattern, operational sex ratio (OSR), and male's age (inferred from skeletochronological analysis), size, and mass were analysed. During 2 of the study years, OSRs were highly male-biased at the beginning of the breeding season and then gradually decreased when male numbers increased. Males with a low body condition index (CI) tend to arrive later and to lose relatively more mass than males with a higher CI. There was a negative relationship between percent mass loss per day and CI as well as length of stay in the breeding area, which suggests that a high energetic cost tactic was adopted by males with a higher CI. A negative relationship between length of stay and age was also observed. We conclude that based on competition for mates, male P. fuscus seem to adopt reproductive behaviour that differs according to body condition and age.

International audience; We describe the life-history traits (body size, age at maturity, longevity, and survivorship) of a terrestrial salamander, Mertensiella luschani, from a population living in the Mediterranean environment of southwestern Turkey. We used phalangeal skeletochronology to estimate the age of juveniles and adults. Lines of arrested growth, deposited during the winter cessation of bone growth, allowed us to estimate the age at maturity to be 3 years old in both sexes. Males attained a maximum age of 8, whereas females attained a maximum age of 10. Juveniles ranged from 1 to 3 years old. Males were smaller than females. Growth curves fitted to von Bertalanffy's equation revealed similar growth coefficients in adults and larger average maximum body lengths in males. Adult annual survivorship and adult life expectancy were 0.79 and 5.4 years, respectively. Knowledge of age, growth, and survivorship in this species under the constraints of a seasonal Mediterranean climate, and a comparison of similar traits in other salamandrid species, allow us to test predictions regarding optimal timing of growth and reproduction in these species.

International audience; River floodplains are disturbance-dominated landscapes where floods are major regulators of both aquatic and nearby terrestrial communities. Amphibians are common inhabitants of floodplains and their life cycle depends on both aquatic and terrestrial habitats. We focused on how different syntopic species of amphibians reacted to the environmental conditions of a large river floodplain. We examined life-history traits such as population age structure and growth in small- and large-bodied species of anurans and urodeles in the lower Danube River floodplain in Romania. Two newt species, Triturus vulgaris (small-bodied) and Triturus dobrogicus (large-bodied), and two anuran taxa, Bombina bombina (small-bodied) and the Rana esculenta complex (large-bodied), were included in the study. The ages of individuals estimated by skeletochronology varied from 3 to 5-6 years for T. vulgaris and from 2-3 to 4-5 years for T. dobrogicus. In the anurans, ages varied from 2 to 5 years in B. bombina and from 4 to 10 years in the R. esculenta complex. The numbers of breeding opportunities (i.e., the number of years the adults reproduce) are similar in both newt species (3), while growth rates and age at maturity differ between the large- and small-bodied species. In anurans, the number of breeding opportunities for the smallest species, B. bombina (4), is associated with a high growth rate and earlier maturation. In the larger R. esculenta complex, the higher number of breeding opportunities (7) is associated with a low growth rate and delayed maturation. The study of age distribution and associated parameters provides useful information on population life history. We discuss how age structure and growth of amphibian populations in large river floodplains can be used as indicators of environmental conditions.

International audience; Compared to other vertebrate groups, movement patterns and microhabitat use in amphibians has been little studied. The two goals of this study were (1) to compare two different methods of tracking amphibians (implantable transmitters and fluorescent pigments); and (2) to characterize movement patterns and habitat use in the nocturnal, fossorial spadefoot toad (Pelobates fuscus) A fluorescent pigment method was useful for microhabitat studies, as trails could be detected in all kinds of terrestrial habitats, even under wet conditions Using this method it was possible to trace complete nocturnal movement patterns (maximum distance moved 73 m). Implantable transmitters were particularly appropriate for fossorial species, such as Pelobatesfuscus. Diel home range and microhabitat preferences were more precisely defined using a combination of telemetry and pigments. In addition, the vertical component of habitat use could be assessed. The spadefoot toad was more likely to use areas of bare soil or short vegetation and seemed to avoid shrub-covered areas. Mean distance moved between two successive burrows was higher in females (22.9 m) than in males (12.9 m).