Climate dependent heating efficiency in the common lizard

Regulation of body temperature is crucial for optimizing physiological performance in ectotherms but imposes constraints in time and energy. Time and energy spent thermoregulating can be reduced through behavioral (e.g., basking adjustments) or biophysical (e.g., heating rate physiology) means. In a heterogeneous environment, we expect thermoregulation costs to vary according to local, climatic conditions and therefore to drive the evolution of both behavioral and biophysical thermoregulation. To date, there are limited data showing that thermal physiological adjustments have a direct relationship to climatic conditions. In this study, we explored the effect of environmental conditions on heating rates in the common lizard (Zootoca vivipara). We sampled lizards from 10 populations in the Massif Central Mountain range of France and measured whether differences in heating rates of individuals correlated with phenotypic traits (i.e., body condition and dorsal darkness) or abiotic factors (temperature and rainfall). Our results show that heat gain is faster for lizards with a higher body condition, but also for individuals from habitats with higher amount of precipitation. Altogether, they demonstrate that environmentally induced constraints can shape biophysical aspects of thermoregulation.     

A food web perspective on large herbivore community limitation

The exceptional diversity of large mammals in African savannas provides an ideal opportunity to explore the relative importance of top‐down and bottom‐up controls of large terrestrial herbivore communities. Recent work has emphasized the role of herbivore and carnivore body size in shaping these trophic relationships. However, the lack of across‐ecosystem comparisons using a common methodology prohibits general conclusions. Here we used published data on primary production, herbivore and carnivore densities and diets to estimate the consumption fluxes between three trophic levels in four African savanna ecosystems. Our food web approach suggests that the body size distribution within and across trophic levels has a strong influence on the strength of top‐down control of herbivores by carnivores and on consumption fluxes within ecosystems, as predicted by theoretical food web models. We generalize findings from the Serengeti ecosystem that suggest herbivore species below 150 kg are more likely to be limited by predation. We also emphasize the key functional role played by the largest species at each trophic level. The abundance of the largest herbivore species largely governs the consumption of primary production in resident communities. Similarly, predator guilds in which the largest carnivore species represent a larger share of carnivore biomass are likely to exert a stronger top‐down impact on herbivores. Our study shows how a food web approach allows integrating current knowledge and offers a powerful framework to better understand the functioning of ecosystems.     

Maternal exposure to predator scents: offspring phenotypic adjustment and dispersal

Predation is a strong selective pressure generating morphological, physiological and behavioural responses in organisms. As predation risk is often higher during juvenile stages, antipredator defences expressed early in life are paramount to survival. Maternal effects are an efficient pathway to produce such defences. We investigated whether maternal exposure to predator cues during gestation affected juvenile morphology, behaviour and dispersal in common lizards (Zootoca vivipara). We exposed 21 gravid females to saurophagous snake cues for one month while 21 females remained unexposed (i.e. control). We measured body size, preferred temperature and activity level for each neonate, and released them into semi-natural enclosures connected to corridors in order to measure dispersal. Offspring from exposed mothers grew longer tails, selected lower temperatures and dispersed thrice more than offspring from unexposed mothers. Because both tail autotomy and altered thermoregulatory behaviour are common antipredator tactics in lizards, these results suggest that mothers adjusted offspring phenotype to risky natal environments (tail length) or increased risk avoidance (dispersal). Although maternal effects can be passive consequences of maternal stress, our results strongly militate for them to be an adaptive antipredator response that may increase offspring survival prospects.     

Costs of dispersal

Dispersal costs can be classified into energetic, time, risk and opportunity costs and may be levied directly or deferred during departure, transfer and settlement. They may equally be incurred during life stages before the actual dispersal event through investments in special morphologies. Because costs will eventually determine the performance of dispersing individuals and the evolution of dispersal, we here provide an extensive review on the different cost types that occur during dispersal in a wide array of organisms, ranging from micro‐organisms to plants, invertebrates and vertebrates. In general, costs of transfer have been more widely documented in actively dispersing organisms, in contrast to a greater focus on costs during departure and settlement in plants and animals with a passive transfer phase. Costs related to the development of specific dispersal attributes appear to be much more prominent than previously accepted. Because costs induce trade‐offs, they give rise to covariation between dispersal and other life‐history traits at different scales of organismal organisation. The consequences of (i) the presence and magnitude of different costs during different phases of the dispersal process, and (ii) their internal organisation through covariation with other life‐history traits, are synthesised with respect to potential consequences for species conservation and the need for development of a new generation of spatial simulation models.     

Matching habitat choice causes directed gene flow: a neglected dimension in evolution and ecology

Gene flow among populations is typically thought to be antagonistic to population differentiation and local adaptation. However, this assumes that dispersing individuals disperse randomly with respect to their ability to use the environment. Yet dispersing individuals often sample and compare environments and settle in those environments that best match their phenotype, causing directed gene flow, which can in fact promote population differentiation and adaptation. We refer to this process as "matching habitat choice." Although this process has been acknowledged by several researchers, no synthesis or perspective on its potentially widespread importance exists. Here we synthesize empirical and theoretical studies, and offer a new perspective that matching habitat choice can have significant effects on important and controversial topics. We discuss the potential implications of matching habitat choice for the degree and rate of local adaptation, the evolution of niche width, adaptive peak shifts, speciation in the presence of gene flow, and on our view and interpretation of measures of natural selection. Because of its potential importance for such a wide range of topics, we call for heightened empirical and theoretical attention for this neglected dimension in evolutionary and ecological studies.     

Corticosterone manipulation reveals differences in hierarchical organization of multidimensional reproductive trade-offs in r-strategist and K-strategist females

Life history trade-offs are often hierarchical with decisions at one level affecting lower level trade-offs. We investigated trade-off structure in female side-blotched lizards (Uta stansburiana), which exhibit two evolved strategies: yellow-throated females are K-strategists and orange-throated are r-strategists. Corticosterone treatment was predicted to differentially organize these females' reproductive decisions. Corticosterone-treated yellow females suppressed reproduction but survived well, and augmented egg mass without decreasing clutch size. Conversely, corticosterone enhanced mortality and reproductive rates in orange females, and increased egg mass only after lengthy exposure. Corticosterone did not affect post-laying condition, suggesting that corticosterone increased egg mass through enhanced energy acquisition (income breeding). Corticosterone enhanced survival of lightweight females, but decreased survival of heavy females, introducing a foraging vs. predation trade-off. We conclude that rather than being a direct, functional relationship, observed trade-offs between offspring size and number represent evolved differences in hierarchical organization of multidimensional trade-offs, particularly in response to stress.     

Evolution of dispersal and life history strategies – <Emphasis Type="Italic">Tetrahymena</Emphasis> ciliates

Background  

Considerable attention has focused on how selection on dispersal and other core life-history strategies (reproductive effort, survival ability, colonization capacity) may lead to so-called dispersal syndromes. Studies on genetic variation in these syndromes within species could importantly increase our understanding of their evolution, by revealing whether traits co-vary across genetic lineages in the manner predicted by theoretical models, and by stimulating further hypotheses for experimental testing. Yet such studies remain scarce. Here we studied the ciliated protist Tetrahymena thermophila, a particularly interesting organism due to cells being able to transform into morphs differing dramatically in swim-speed. We investigated dispersal, morphological responses, reproductive performance, and survival in ten different clonal strains. Then, we examined whether life history traits co-varied in the manner classically predicted for ruderal species, examined the investment of different strains into short- and putative long-distance dispersal, while considering also the likely impact of semi-sociality (cell aggregation, secretion of 'growth factors') on dispersal strategies.     

Selection of physiological and metabolic adaptations to food deprivation in the Pyrenean newt Calotriton asper during cave colonisation

Food restriction is one of the major and most common constraints that subterranean animals face in their biotope. Cave-dwelling organisms thus have to cope with fasting periods that can extend from a month to a year. However, adaptive fasting resistance previously found in subterranean fauna has only been highlighted by direct comparisons with phylogenetically distant epigean organisms, which could severely impact conclusions. Here we report physiological and metabolic responses to 42 days of fasting followed by 10 days of refeeding in two populations (one subterranean and one epigean) of Calotriton asper. In the fed state (control), the hypogean population exhibited a hypometabolism together with higher glycogen (+ 25% in liver and muscles) and triglyceride stores (+ 50% in muscles). During the fasting period, cave individuals exhibited a 20% decrease in VO₂ whereas epigean individuals experienced no significant change. In addition, the energetic reserves always remained higher in the hypogean population. According to phylogenic and biogeographic data, cave colonization by this species dates back to less than 10,000 years, suggesting a rapid selection of adaptive traits related to fasting. This study strongly suggests that cave colonization induces a decrease in metabolism together with a higher capacity to accumulate energy reserves and therefore to withstand unpredictable fasting periods.     

Urbanisation effects on the functional diversity of avian agricultural communities

Urbanisation is affecting ecological communities worldwide. Despite the disproportionate impact on farmland over other habitats, the effect on farmland bird communities has been poorly studied. Considering the still-alarming conservation status of farmland birds, investigations into the effects of pressures such as urbanisation on those communities could be of great interest for their conservation. We studied the urbanisation effects on functional diversity using existing indices designed for the purpose of standardisation. This study uses a functional character measuring species habitat specialisation for indices calculation. A bird survey was conducted on 92 plots of 1 × 1 km chosen after stratification on the proportion of urban area and farmland habitat (either 0, 25, 50, 75%), with the focus on farmland habitat. Two aspects of urbanisation were studied: the intensity and the age of the urbanisation. Functional richness was found to decrease with urbanisation, while functional evenness and divergence increased in a nonlinear way. No significant difference was observed in functional richness and evenness with urbanisation age, however extreme ages of urbanisation (young and old) showed higher niche differentiation concerning specialisation. This implies less important resource competition for species and a more vulnerable state for the ecosystem. Using functional diversity indices based on specialisation allows a better insight in the consequences of urbanisation on diversity/ecosystem–community functioning, which is of crucial importance in the face of global changes.