Stéphane Sourice

Nitrate affects courting and breathing but not escape performance in adult newts

The increasing spread of contaminants in the environment affects the behaviour of individuals and can be predicted to modify population characteristics in the long run. It is thus crucial to investigate the effect of contaminants on fitness-related traits. Nitrate is a major pollutant that disrupts oxygen fixation and steroid metabolism and is expected to affect adult behaviour. In water breeding newts, reduced oxygen supply may increase predation risk by elevating surfacing rate and limiting the capacity to evade a predator. It may also reduce mating success by altering sexual behaviour. We assessed the effect of nitrate on fitness-related behavioural traits in male palmate newts Lissotriton helveticus. We measured courtship and breathing during sexual encounters and escape performance in exposed and non-exposed adults. Unexpectedly, exposed males courted females more often than control males. Body size and breathing rate were also positively related in control males but not in exposed males. Results only partially support the hypothesis of oxygen transfer disruption. Alternatively, exposed males seem to compensate their reduced olfactory attractiveness by decreasing surfacing and increasing courtship frequency. Surprisingly, nitrate did not affect escape performance possibly because anaerobic respiration supplies most of energy during unsustainable activity. Nitrate exposure altered time budget in exposed adults and shifted behavioural trade-offs between competing activities like breathing and courting. Ecological and evolutionary consequences, driven by changes on predation risk or sexual selection regimes, can be expected. This study calls for more attention on amphibian adult stages and the evolutionary response of populations in contaminated environments.

A new PCR-RFLP-based method for an easier systematic affiliation of European water frogs

We describe a non‐invasive, PCR‐RFLP‐based method that allows reliable determination of the European water frog species Pelophylax lessonae and Pelophylax ridibundus and the hybrid form Pelophylax esculentus. Maximum‐likelihood analysis of ITS2 sequences revealed two robust monophyletic clades corresponding to water frogs of the P. lessonae and P. ridibundus groups. Three restriction enzymes (KpnI, HaeII, and SmaI) were used to digest three conserved ITS2 domains. Taxonomic identification was unambiguous; the three restriction enzymes gave the same results. A French reference sample was identified using allozyme electrophoresis. Our PCR‐RFLP method confirmed circa 83% of identification of the allozyme method. We conclude that the difference between identifications was caused by introgression.

Vigilance in a solitary marsupial, the common wombat (Vombatus ursinus)

We studied vigilance activity in a wild population of the common wombat (Vombatus ursinus), a large, solitary, burrow-using, marsupial prey species in which individuals tolerate the presence of conspecifics within their home range. For the first time, we report postures and rates of vigilance in common wombats; our results show a limited repertoire of vigilant postures and low overall rates of vigilance. Because few studies of birds and mammals that have reported the effect of distance to conspecifics on the vigilance of focal animals have considered solitary prey species, we tested this effect in wombats. Our results show that a model including distance to cover and distance to the nearest conspecific, but not time of day, best explained the variation in the proportion of time that focal individuals spent in vigilance. Individual vigilance decreased when distance to cover increased. Vigilance of wombats increased when there was a conspecific within a radius of 70 m of the focal individual. In addition, we tested whether pairs of nearby wombats scanned independently of one another, coordinated their activity in non-overlapping bouts of vigilance or synchronised their bouts of vigilance. Wombats in close proximity exhibited independent bouts of individual vigilant and foraging activity. Thus, in this solitary species, our results support the assumption that individuals scan independently of each other.

Mate preference, species recognition and multimodal communication in heterogeneous environments

Mate selection in heterogeneous sensory environments may be challenging. Assessing the suitability of potential partners may be compromised if individual characteristics cannot be assessed reliably across all encountered conditions. The problem is particularly acute in a species recognition context if matings with heterospecific partners yield lower fitness than matings with conspecific partners of low quality. Multimodal communication may circumvent this problem by transmitting redundant information on several channels that are not affected by the same degradation processes (Backup hypothesis). We addressed this issue in two hybridizing newts (Lissotriton helveticus and L. vulgaris) for which visual species recognition is disrupted in water stained by humic acids, a common family of compounds produced by decaying vegetation. Because these species also use olfaction for sexual communication, we predicted that species recognition was maintained in stained water when olfactory information was available. Results did not support the prediction of the backup hypothesis. Species recognition was observed in the clear water treatment only, and the olfactory channel seemed to carry only limited additional information. Two mechanisms may account for the small contribution of olfaction to species recognition. (1) Females may have a lower sensory capacity to discriminate between olfactory than between visual signals. (2) Divergence between olfactory signals may be lower than divergence between visual signals. Resorting to multimodal communication does not seem to allow efficient discrimination across all environmental conditions. Therefore, we predict that hybridization rate would vary between habitats depending on water color.

Habitat-Dependent Species Recognition in Hybridizing Newts

Many species breed in heterogeneous environments where conditions affecting signaling fidelity may vary. Species recognition may be impaired under particular environmental conditions enhancing the hybridization risk. We investigated the influence of habitat on species recognition efficiency in two hybridizing newts, Lissotriton vulgaris and L. helveticus. The former is considered to be an open habitat species where the two species are in sympatry, whereas the latter also breeds in forest ponds where dissolved humic acids attenuate wavelength transmission, especially in the UV range. Because UV sexual signalling occurs in L. vulgaris, we predicted that species recognition would be reduced in water stained by humic acids. We conducted two-choice preference tests in males and females in stained and clear water. Females of both species preferred the conspecific male in clear water but not in stained water. Males did not show species recognition in either treatment. In both newts, visual species recognition is likely to depend upon habitat. Resorting to chemical communication may offset the loss of visual information but the same environmental factors that affect the transmission of visual signal can also affect the transmission of chemical signals. This environmental disruption of species recognition may account for the general avoidance of forest ponds by L. vulgaris in sympatry with L. helveticus. Stochastic variations of visual conditions in ponds may also explain the ongoing hybridization between two long diverged species that exhibit many and well differentiated sexual ornaments, and more generally between taxa naturally experiencing strong variations of their sensory environment.

Habitat‐related variation in the plasticity of a UV‐sensitive photoreceptor over a small spatial scale in the palmate newt

Plastic phenotypes are expected to be favoured in heterogeneous environments compared with stable environments. Sensory systems are interesting to test this theory because they are costly to produce and support, and strong fitness costs are expected if they are not tuned to the local environment. Consistently, the visual system of several species changes with the conditions experienced during early development. However, there is little information on whether the amplitude of the change, that is the reaction norm, differs between visual environments. Given the rapid change of many ecosystems, especially eutrophication for aquatic habitats, it is crucial to determine down to which spatial scale, change in the reaction norm occurs. We addressed this issue by quantifying the between‐habitat variation in the expression of a UV‐sensitive opsin in a newt. In western France, this species breeds in ponds of small forest patches, where water filters out UV, and in agricultural ponds where UV transmission is variable. We raised larvae from both habitats with or without exposure to UV. Opsin expression was reduced in larvae from agricultural habitats when raised without UV, whereas it was low in larvae from forest ponds under all lighting conditions. Thus, the variation in the reaction norm of opsin expression was lower in stable filtering environments and higher in heterogeneous environments. Its variation occurred between habitats across a small spatial scale. We discuss the hypotheses for this pattern and for the maintenance of residual opsin expression in forest populations.

UV wavelengths experienced during development affect larval newt visual sensitivity and predation efficiency

We experimentally investigated the influence of developmental plasticity of ultraviolet (UV) visual sensitivity on predation efficiency of the larval smooth newt, Lissotriton vulgaris. We quantified expression of SWS1 opsin gene (UV-sensitive protein of photoreceptor cells) in the retinas of individuals who had developed in the presence (UV+) or absence (UV−) of UV light (developmental treatments), and tested their predation efficiency under UV+ and UV− light (testing treatments). We found that both SWS1 opsin expression and predation efficiency were significantly reduced in the UV− developmental group. Larvae in the UV− testing environment displayed consistently lower predation efficiency regardless of their developmental treatment. These results prove for the first time, we believe, functional UV vision and developmental plasticity of UV sensitivity in an amphibian at the larval stage. They also demonstrate that UV wavelengths enhance predation efficiency and suggest that the magnitude of the behavioural response depends on retinal properties induced by the developmental lighting environment.