Effets de l'hypoxie d'altitude sur le développement embryonnaire et les performances juvéniles chez la couleuvre vipérine, Natrix maura, dans le contexte actuel du changement climatique

Le changement climatique pourrait entrainer, d'ici 2100, une hausse de la température moyenne à la surface de la Terre de 1°C à 6.5°C par rapport à la température moyenne estimée entre 1986 et 2005. Cela est susceptible d'augmenter le risque d'extinction des espèces, de modifier leur aire de répartition, en impactant la phénologie de reproduction et de migration des organismes, entraînant un changement des schémas de biodiversité à l'échelle mondiale. Les ectothermes, dont l'ensemble des traits physiologiques et comportementaux sont dépendants des températures environnementales, vont d'autant plus être affectés par le changement climatique et devront migrer vers des zones thermiques plus favorables, comme les zones de haute altitude. Cependant, en altitude, la diminution de la pression partielle de l'air réduit la quantité d'oxygène disponible. Cette nouvelle contrainte environnementale, l'hypoxie d'altitude, pourrait limiter leurs chances de coloniser ces milieux. Cette thèse cherche à mettre en évidence les réponses physiologiques à l'hypoxie d'altitude chez la Couleuvre vipérine, Natrix maura, une colonisatrice historique qui subit une expansion de gamme vers le haut, et à définir sa capacité à utiliser les espaces montagnards comme refuge face au changement climatique. Les objectifs sont, d'abord mesurer les effets de l'hypoxie d'altitude et de l'interaction qu'elle peut avoir avec la température sur le développement par l'intermédiaire du suivi de l'activité métabolique embryonnaire et des taux de développement. Puis, d'observer la persistance potentielle de ces effets sur les performances et le métabolisme des juvéniles. Les résultats de ces travaux suggèrent que, chez la Couleuvre vipérine, les réponses physiologiques plastiques des embryons à l'hypoxie de haute-altitude pourraient faciliter l'expansion de l'aire de répartition altitudinale à travers le maintien des phénotypes corporels et des performances physiques des juvéniles.By 2100, climate change could lead to an increase in the average temperature on the Earth's surface of 1°C to 6.5°C compared to the average temperature estimated between 1986 and 2005. This is likely to increase the risk of species extinction or change species ranges by impacting the reproductive phenology and the migration of organisms, leading to a change in biodiversity patterns on a global level. Ectotherms, whose set of physiological and behavioural traits are dependent on environmental temperatures, will be further affected by climate change and will have to migrate to more favourable thermal zones, such as to high altitude. However, at higher altitudes, the decrease in the partial pressure of the air reduces the availability of oxygen. This new environmental constraint, high-elevation hypoxia, could limit organisms' chances of colonizing these environments. This thesis seeks to highlight the physiological responses to high-elevation hypoxia in the Viperine snake, Natrix maura, a historical colonizer currently undergoing an upward range expansion, and to define its capacity to use mountain areas as a refuge in the context of climate change. The objectives are, in the first instance, to measure the effects of high-elevation hypoxia and the interaction it may have with temperature on development through monitoring embryonic metabolic activity and development rates. The second objective is to observe the potential persistence of these effects on the performance and metabolism of juveniles. The results of this work suggest that, in the Viperine Snake, the plastic physiological responses of embryos to high-elevation hypoxia could facilitate the expansion of the altitudinal range through the maintenance of body phenotypes and physical performance of juveniles

Multiple glacial refugia and contemporary dispersal shape the genetic structure of an endemic amphibian from the Pyrenees

Historical factors (colonization scenarios, demographic oscillations) and contemporary processes (population connectivity, current population size) largely contribute to shaping species’ present-day genetic diversity and structure. In this study, we use a combination of mitochondrial and nuclear DNA markers to understand the role of Quaternary climatic oscillations and present-day gene flow dynamics in determining the genetic diversity and structure of the newt Calotriton asper (Al. Dugès, 1852), endemic to the Pyrenees. Mitochondrial DNA did not show a clear phylogeographic pattern and presented low levels of variation. In contrast, microsatellites revealed five major genetic lineages with admixture patterns at their boundaries. Approximate Bayesian computation analyses and linear models indicated that the five lineages likely underwent separate evolutionary histories and can be tracked back to distinct glacial refugia. Lineage differentiation started around the Last Glacial Maximum at three focal areas (western, central and eastern Pyrenees) and extended through the end of the Last Glacial Period in the central Pyrenees, where it led to the formation of two more lineages. Our data revealed no evidence of recent dispersal between lineages, whereas borders likely represent zones of secondary contact following expansion from multiple refugia. Finally, we did not find genetic evidence of sex-biased dispersal. This work highlights the importance of integrating past evolutionary processes and present-day gene flow and dispersal dynamics, together with multilocus approaches, to gain insights into what shaped the current genetic attributes of amphibians living in montane habitats.info:eu-repo/semantics/publishedVersio

Revisiting the fear of snakes in children: the role of aposematic signalling

International audienceWhy humans fear snakes is an old, yet unresolved debate. Its innate origin from evolutionary causes is debated against the powerful influence early experience, culture, media and religion may have on people’s aversion to snakes. Here we show that the aversion to snakes in human beings may have been mistaken for an aversion to aposematic signals that are commonly displayed by snakes. A total of 635 children were asked to rate single item images as “nice” or “mean”. Snakes, pets and smiley emoticon items were not rated as “mean” unless they displayed subtle aposematic signals in the form of triangular (rather than round) shapes. Another 722 children were shown images featuring two items and asked which item was “nice” and which item was “mean”. This context dependent comparison triggered even sharper responses to aposematic signals. We hypothesise that early primates evolved an aversion for aposematic signals in the form of potentially harmful triangular shapes such as teeth, claws or spikes, not for snakes per se. Further, we hypothesise that this adaptation was in turn exploited by snakes in their anti-predatory threat display as a triangular head or dorsal zig-zag pattern, and is currently the basis for efficient international road-danger signalling

Lizards at the Peak: Physiological Plasticity Does Not Maintain Performance in Lizards Transplanted to High Altitude

International audienceWarming climates are facilitating the range expansion of many taxa to habitats that were formerly thermally inhospitable, including to higher latitudes and elevations. The potential for such colonization, however, varies widely among taxa. Because environmental factors may interact to affect colonization potential, an understanding of underlying physiological and behavioral mechanisms is necessary to predict how species will respond to potentially suitable habitats. For example, temperature and oxygen availability will interact to shape physiological and performance traits. Our model species, the wall lizard, Podarcis muralis, is a widely distributed ectotherm that continues to expand its range in Europe despite being limited by cold temperatures at high elevations and latitudes. To test the potential for organisms to expand to warming high-altitude environments, we conducted a transplant experiment to quantify the within-individual effects of high-altitude hypoxia on physiological and performance traits. Transplanted lizards maintained individual differences in physiological traits related to oxygen capacity and metabolism (hemoglobin concentration , hematocrit, and peak postexhaustion metabolic rate), as well as performance traits tied to fitness (sprint speed and running endurance). Although lizards altered blood biochemistry to increase oxygen-carrying capacity, their performance was reduced at high altitude. Furthermore, lizards at high altitude suffered a rapid loss of body condition over the 6-wk experiment , suggesting an energetic cost to hypoxia. Taken together, this demonstrates a limited potential for within-individual plasticity to facilitate colonization of novel high-altitude environments

High Temperatures Limit Developmental Resilience to High-Elevation Hypoxia in the Snake \u3ci\u3eNatrix maura\u3c/i\u3e (Squamata: Colubridae)

Climate change is generating range shifts in many organisms, notably along the altitudinal gradient. However, moving up in altitude exposes organisms to lower oxygen availability, which may negatively affect development and fitness, especially at high temperatures. To test this possibility in a potentially upward-colonizing species, we artificially incubated developing embryos of the viperine snake Natrix maura Linnaeus 1758, using a split-clutch design, in conditions of extreme high elevation or low elevation at two ecologically-relevant incubation temperatures (24 and 32 °C). Embryos at low and extreme high elevations incubated at cool temperatures did not differ in development time, hatchling phenotype or locomotor performance. However, at the warmer incubation temperature and at extreme high elevation, hatching success was reduced. Further, embryonic heart rates were lower, incubation duration longer and juveniles born smaller. Nonetheless, snakes in this treatment were faster swimmers than siblings in other treatment groups, suggesting a developmental trade-off between size and performance. Constraints on development may be offset by the maintenance of important performance metrics, thus suggesting that early life-history stages will not prevent the successful colonization of high-elevation habitat even under the dual limitations of reduced oxygen and increased temperature

Primary data associated with Gangloff et al. 2018

Provides experimental data on lizard (Podarcis muralis) morphometrics, physiology, and performance. Used for all analyses in manuscript except sprint speed

Sprint speed data associated with Gangloff et al. 2018

Provides experimental data on lizard (Podarcis muralis) sprint speed

Transplanting gravid lizards to high elevation alters maternal and embryonic oxygen physiology, but not reproductive success or hatchling phenotype

International audienceIncreased global temperatures have opened previously inhospitable habitats, such as at higher elevations. However, the reduction of oxygen partial pressure with increase in elevation represents an important physiological constraint that may limit colonization of such habitats, even if the thermal niche is appropriate. To test the mechanisms underlying the response to ecologically-relevant levels of hypoxia, we performed a translocation experiment with the common wall lizard (Podarcis muralis), a widespread European lizard amenable to establishing populations outside its natural range. We investigated the impacts of hypoxia on the oxygen physiology and reproductive output of gravid common wall lizards and the subsequent development and morphology of their offspring. Lowland females transplanted to high elevations increased their haematocrit and haemoglobin concentration within days and maintained routine metabolism compared to lizards kept at native elevations. However, transplanted lizards suffered from increased reactive oxygen metabolite production near the oviposition date, suggesting a cost of reproduction at high elevation. Transplanted females and females native to different elevations did not differ in reproductive output (clutch size, egg mass, relative clutch mass, or embryonic stage at oviposition) or in post-oviposition body condition. Developing embryos reduced heart rates and prolonged incubation times at high elevations within the native range and at extreme high elevations beyond the current range, but this reduced oxygen availability did not affect metabolic rate, hatching success, or hatchling size. These results suggest that this opportunistic colonizer is capable of successfully responding to novel environmental constraints in these important life-history stages

Yolk removal generates hatching asynchrony in snake eggs

International audienceHatching synchrony is wide-spread amongst egg-laying species and is thought to enhance offspring survival, notably by diluting predation risks. Turtle and snake eggs were shown to achieve synchronous hatching by altering development rates (where less advanced eggs may accelerate development) or by hatching prematurely (where underdeveloped embryos hatch concurrently with full-term embryos). In Natricine snakes, smaller eggs tend to slow down metabolism throughout incubation in order to hatch synchronously with larger eggs. To explore the underlying mechanism of this phenomenon we experimentally manipulated six clutches, where half of the eggs were reduced in mass by removing 7.2% of yolk, and half were used as the control. The former experienced higher heart rates throughout the incubation period, hatched earlier and produced smaller hatchlings than the latter. This study supports the idea that developmental rates are related to egg mass in snake eggs and demonstrates that the relationship can be influenced by removing yolk after egg-laying. The shift in heart rates however occurred in the opposite direction to expected, with higher heart rates in yolk-removed eggs resulting in earlier hatching rather than lower heart rates resulting in synchronous hatching, warranting further research on the topic

Pattern matters: Snakes exhibiting triangular and diamond-shaped skin patterns modulate electrophysiological activity in human visual cortex

International audienceThe neural and perceptual mechanisms that support the efficient visual detection of snakes in humans are still not fully understood. According to the Snake Detection Theory, selection pressures posed by snakes on early primates have shaped the development of the visual system. Previous studies in humans have investigated early visual electrophysiological activity in response to snake images vs. various alternative dangerous or non-dangerous stimuli. These studies have shown that the Early Posterior Negativity (EPN) component is selectively elicited by snake or snake-like images. Recent findings yielded the complementary/alternative hypothesis that early humans (and possibly other primates) evolved an aversion especially for potentially harmful triangular shapes, such as teeth, claws or spikes. In the present study we investigated the effect of triangular and diamond-shaped patterns in snake skins on the ERP correlates of visual processing in humans. In the first experiment, we employed pictures of snakes displaying either triangular/diamond-shaped patterns or no particular pattern on their skins, and pictures of frogs as control. Participants observed a random visual presentation of these pictures. Consistent with previous studies, snakes elicited an enhanced negativity between 225 and 300 ms (EPN) compared to frogs. However, snakes featuring triangular/diamond-shaped patterns on their skin produced an enhanced EPN compared to the snakes that did not display such patterns. In a second experiment we used pictures displaying only skin patterns of snakes and frogs. Results from the second experiment confirmed the results of the first experiment, suggesting that triangular snake-skin patterns modulate the activity in human visual cortex. Taken together, our results constitute an important contribution to the snake detection theory