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Counter-gradient variation in thermoregulation in a widespread chilean lizard
Whether thermoregulation behaviour is evolutionary rigid or in the contrary evolutionary labile has been a long-standing controversy in the field of thermal biology. In squamate reptiles, including terrestrial lizard species, comparative evidence from the literature suggests that some thermal biology traits may vary adaptively across species but only a handful of studies have found significant variation in thermoregulation behaviour among populations within the same species, for example along an altitudinal gradient. In this article, we investigate geographic variation in thermoregulation behaviour between the range margins of the distribution of the widespread Liolaemus pictus lizard in Chile. The genus Liolaemus is highly diversified in South America, with more than 200 recognized species, and its thermal biology has been extensively characterized during the last decade. We compared the thermoregulation behaviour of lizards from two populations located at the warm and one population located at the cold range margin during two years, and manipulated thermal conditions in the laboratory during one year to test if the geographic variation could be due to thermal acclimation. To our surprise, we found that lizards from the cold margin preferred higher body temperatures and were as effective thermoregulators as lizards from the warm margin. We propose that this pattern is caused by "counter-gradient temperature" variation where there is strong selection for a faster life cycle in the less thermally suitable habitats from the cold margin. We compare our results with those published in the literature on Liolaemus lizards and demonstrate that more thermally challenging environments select for a higher thermoregulation effort and a more effective thermoregulation. Altogether, these data confirm that thermoregulation behaviour is evolutionary labile within and between species of Liolaemus lizards. This conclusion will be of wide interest to those interested in thermal biology of lizards and the evolution of thermoregulation behaviours.
 
 
Chaiten population

 Summary

 

• Variation in thermoregulation behavior between range margins is rarely investigated
• Liolaemus lizards from the cold margin preferred higher body temperatures
• Thermal acclimation may contribute to this counter-gradient temperature variation
• Selection for faster life cycle in a colder environment may explain the geographic variation.

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New tools for population viability analyses
 
 Oenothera glaziovianaSince three decades, the toolbox of biologists to assess conservation status of endangered species and take actions to improve their long-term viability includes the very popular matrix population models. For this range of models where populations are divided into discrete stages, a solid mathematical framework is available (e.g., Caswell Matrix population models 2001). In addition, softwares such as RAMAS or demogR allow to implement these models in real ecological situations. Unfortunately, not all populations of plants and animals can be divided into discrete categories without loss of significant biological information because individuals often differ for continuous traits such as body size, body condition or growth potential. Continuously structured populations can be described using integral projection models (IPMs), a mathematical framework first introduced by Stephen Ellner and collaborators (Easterling et al. Ecology 2000) and now more and more popular among population ecologists (Coulson Oikos 2012). Although the IPM is efficient with small data sets (Ramula et al. Journal of Applied Ecology 2009), it has not yet been used for real life population viability analyses. In this article, we present for the first time population viability analyses of animal and plant species using the stochastic IPM recently developed by Vindenes and collaborators (Ecology 2011). We show how to construct the stochastic IPM, demonstrate how to calculate and decompose deterministic and stochastic components of the population growth rate, and show results of sensitivity analyses. In addition, we compare results of a diffusion approximation with individual based simulations.
 
 
Photograph: Populations of Oenothera glazioviana, an evening primrose with a semelparous reproduction and size-structured populations were modelled in this study (photograph by Bernd Sauerwein on Wiki Commons)
 
Last Updated ( jeudi, 08 décembre 2016 )
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Plasticity in breeding phenology is not consistent across populations
Puy Mary population
 
 
Recent studies have identified so-called universal ecological consequences of climate warming, especially an advanced breeding and non-breeding phenology in many populations of plants and animals. In seasonal environments, among species variation in the extent of plasticity of phenology can generate temporal mistmatch between trophic level, where for example predators have higher energetic demands when preys are scarce in the environment. Until recently, however, we knew little about intra-specific variation in breeding phenology, which may vary across populations due to differences in selection or constraints. In a recent study, we combined data from more than 10 years of detailed monitoring of the breeding phenology in 11 populations of common lizards across the Massif Central. Our data demonstrate unambiguously that breeding phenology responds more to climate warming in some populations than in others. Contrary to some predictions from evolutionary theory, plasticity was stronger in warmer and less variable climates.
 
Picture: The Puy Mary population is characterised by cold and less variable climate conditions during gestation. This population is predicted to exhibit flat plasticity of the breeding phenology. Photograph: J.-F. Le Galliard.
 
 
 
 
Last Updated ( vendredi, 26 février 2016 )
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Ecosystem service provision: new perspectives from network theory
 
 
Quintessence: ecological network figure
The ecosystem services (EcoS) concept is being used increasingly to attach values to natural systems and the multiple benefits they provide to human societies. Ecosystem processes or functions only become EcoS if they are shown to have social and/or economic value. This should assure an explicit connection between the natural and social sciences, but EcoS approaches have been criticized for retaining little natural science. Preserving the natural, ecological science context within EcoS research is challenging because the multiple disciplines involved have very different traditions and vocabularies (common-language challenge) and span many organizational levels and temporal and spatial scales (scale challenge) that define the relevant interacting entities (interaction challenge). We propose a network-based approach to transcend these discipline challenges and place the natural science context at the heart of EcoS research.
 
 
 
Bohan, D. and the QUINTESSENCE consortium. 2016. Networking our way to better Ecossystem Service provision. Trends in Ecology and Evolution 31(2):105-115.
Last Updated ( vendredi, 26 février 2016 )
 
The UV reflective throat of male common lizards plays the role of a badge of status
According to the badge of status hypothesis, adult males of many vertebrate species exhibit, perceive and use ultraviolet (UV) colouration during aggressive interactions to settle territorial conflicts. Previous experimental studies of this question included protocols that cancel UV reflectance well below natural variability and can seldom be used to draw conclusions about inter-individual variability. In addition, they often did not test for important factors known to influence aggressive interactions, and none have controlled for effects of resident-intruder status. In addition, mechanisms ensuring the honesty of UV signals are hotly debated today because strong evidences of condition-dependent UV signals are still too rare. In this study, we investigated for the first time if UV signals interact with prior residency and familiarity to influence conflict resolution among males during the mating season. We used an experimental protocol where we decreased UV reflectance within its natural range in adult male common lizards (Zootoca vivipara). Males of this species display a bright UV colour patch on their throat that they expose to conspecifics during behavioural conflicts. We measured reflectance of wild males and quantified behavioural interactions during repeated resident-intruder encounters where UV reflectance was alternatively reduced or not in both rivals in a full factorial design. We further asked whether UV throat reflectance correlates with morphology, physiology and blood parasite load to distinguish between conventional and condition-dependent signalling. Our results show that UV manipulation predicts contest outcomes and aggressive behaviours when opponents are not familiar. Moreover, we demonstrate for the first time that effects of UV manipulation persist when opponents are familiar. However, we found no evidence supporting the hypothesis of condition-dependence of the expression of UV colours. Altogether, this suggests that UV reflectance acts as an arbitrary or conventional signal, which mediates the outcome of male-male competition in common lizards.
 
Digital visible (top) and UV (bottom) black-and-white photographs of a common lizard male (left) and female (right) - (c) Mélissa Martin, CNRS
 Digital photograph of lizard
 
 
 
Last Updated ( lundi, 09 novembre 2015 )
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