Ecological genomics of high altitude adaptation in Rufous-collared sparrows (Zonotrichia capensis)

Adaptation is among the most prominent subjects in evolutionary biology. Despite its ubiquity in nature, many details of how adaptation occurs in natural populations remain poorly understood. Of particular interest are the genes and biochemical pathways that underlie adaptive phenotypes and how plasticity in these systems contributes to adaptive evolution. In this dissertation, I address these questions by investigating the molecular genetic basis of high-altitude adaptation in the Rufous-collared Sparrow (Zonotrichia capensis), a species with a broad altitudinal distribution in the Andes. First, I examined the role that variable selection pressures along elevational gradients play in the population genetic structure of Z. capensis. I found that mitochondrial gene flow was severely reduced along elevational transects relative to latitudinal control transects. Nuclear gene flow, however, was not affected by the elevational gradient. These results suggest that natural selection constrains mitochondrial gene flow along elevational gradients. The mitonuclear discrepancy was consistent with local adaptation of mitochondrial haplotypes, highlighting the importance of metabolic pathways in high-altitude adaptation in Z. capensis. Second, I used a newly developed genomic tool, a zebra finch (Taeniopygia guttata) cDNA microarray, to measure variation in genome-wide patterns of gene expression between high- and low-elevation populations of Z. capensis. I found that nearly 200 genes, many of which were involved in metabolic processes, were differentially expressed when individuals were sampled at their native altitudes. A common garden experiment demonstrated substantial plasticity in gene expression, and these results suggest that plasticity in the biochemical pathways that underpin cold and hypoxia compensation in Z. capensis may mechanistically contribute to enabling its broad altitudinal distribution. Finally, I examined geographic variation in metabolic gene expression along an elevational gradient. Although metabolic adjustments are often involved in thermal stress response and temperature decreases linearly with elevation in the Andes, expression of metabolic genes was non-linearly related to elevation. These results suggest a decoupling of metabolic gene expression and local temperature regimes. This decoupling may have several explanations, but the most plausible seem to be related to either physiological tradeoffs between thermal stress and hypoxia compensation, or genetically encoded expression differences

Migration-selection balance and local adaptation of mitochondrial haplotypes in Rufous-Collared Sparrows (Zonotrichia Capensis) along an elevational gradient

Variable selection pressures across heterogeneous landscapes can lead to local adaptation of populations. The extent of local adaptation depends on the interplay between natural selection and gene flow, but the nature of this relationship is complex. Gene flow can constrain local adaptation by eroding differentiation driven by natural selection, or local adaptation can itself constrain gene flow through selection against maladapted immigrants. Here we test for evidence that natural selection constrains gene flow among populations of a widespread passerine bird (Zonotrichia capensis) that are distributed along an elevational gradient in the Peruvian Andes. Using multilocus sequences and microsatellites screened in 142 individuals collected along a series of replicate transects, we found that mitochondrial gene flow was significantly reduced along elevational transects relative to latitudinal control transects. Nuclear gene flow, however, was not similarly reduced. Clines in mitochondrial haplotype frequency were strongly associated with transitions in environmental variables along the elevational transects, but this association was not observed for the nuclear markers. These results suggest that natural selection constrains mitochondrial gene flow along elevational gradients and that the mitonuclear discrepancy may be due to local adaptation of mitochondrial haplotypes. © 2009 The Society for the Study of Evolution

Gestating at altitude: How do maternal physiology and evolutionary adaptation influence fetal growth?

Lowland mammals, including humans, experience an increased risk for fetal growth restriction (FGR) at high altitudes. FGR is associated with a range of adverse lifetime risks, including lower infant survival. Maternal physiology, such as cardiopulmonary function and nutrient provisioning, has been hypothesized to play an important role in driving altitude-dependent FGR, but strong associations between specific aspects of maternal physiology and FGR at altitude have been difficult to establish. One approach has been to study populations adapted to altitude; highland populations of humans, sheep, and deer mice (Peromyscus maniculatus) mitigate altitude-induced reductions in fetal growth and may thus offer insight into the relevant underlying physiology. We assessed the relationship between measures of maternal physiology and fetal growth outcomes using deer mice derived from highland-adapted and lowland populations that gestated under normoxia or hypobaric hypoxia. At late pregnancy, we measured fetal mass along with an array of physiological measures from dams (e.g., body and organ masses, and blood hematocrit and glucose). Using linear modeling, we assessed the relationships between maternal physiology and fetal growth phenotypes. To investigate the possibility that fetal growth is a function of many incremental changes in physiology, we compressed dimensionality of the maternal physiology data using PCA and then used the reduced dimensions in a linear modeling framework. The results from our study will add to our broader understanding of how maternal physiology shapes fetal growth, and they will help expand our understanding of the physiological systems that contribute to altitude adaptation across mammals

Genomic insights into adaptation to high-altitude environments

Elucidating the molecular genetic basis of adaptive traits is a central goal of evolutionary genetics. The cold, hypoxic conditions of high-altitude habitats impose severe metabolic demands on endothermic vertebrates, and understanding how high-altitude endotherms cope with the combined effects of hypoxia and cold can provide important insights into the process of adaptive evolution. The physiological responses to high-altitude stress have been the subject of over a century of research, and recent advances in genomic technologies have opened up exciting opportunities to explore the molecular genetic basis of adaptive physiological traits. Here, we review recent literature on the use of genomic approaches to study adaptation to high-altitude hypoxia in terrestrial vertebrates, and explore opportunities provided by newly developed technologies to address unanswered questions in high-altitude adaptation at a genomic scale. © 2012 Macmillan Publishers Limited All rights reserved

Robust output feedback sampling control based on second order sliding mode

International audienceThis paper proposes a new second order sliding mode output feedback controller. This latter is developped in the case of finite sampling frequency and is using only output information in order to ensure desired trajectory tracking with high accuracy in a finite time in spite of uncertainties and perturbations. This new strategy is evaluated in simulations on an academic example

Contributions of phenotypic plasticity to differences in thermogenic performance between highland and lowland deer mice

Small mammals face especially severe thermoregulatory challenges at high altitude because the reduced O2 availability constrains the capacity for aerobic thermogenesis. Adaptive enhancement of thermogenic performance under hypoxic conditions may be achieved via physiological adjustments that occur within the lifetime of individuals (phenotypic plasticity) and/or genetically based changes that occur across generations, but their relative contributions to performance differences between highland and lowland natives are unclear. Here, we examined potentially evolved differences in thermogenic performance between populations of deer mice (Peromyscus maniculatus) that are native to different altitudes. The purpose of the study was to assess the contribution of phenotypic plasticity to population differences in thermogenic performance under hypoxia. We used a common-garden deacclimation experiment to demonstrate that highland deer mice have enhanced thermogenic capacities under hypoxia, and that performance differences between highland and lowland mice persist when individuals are born and reared under common-garden conditions, suggesting that differences in thermogenic capacity have a genetic basis. Conversely, population differences in thermogenic endurance appear to be entirely attributable to physiological plasticity during adulthood. These combined results reveal distinct sources of phenotypic plasticity for different aspects of thermogenic performance, and suggest that thermogenic capacity and endurance may have different mechanistic underpinnings. Includes Supplementary material

Nanostructuration de films nanocomposites amidon / argent et amidon / argent / montmorillonites par procédé de « chimie verte » : influence des voies de génération des nanoparticules métalliques sur la structure et les propriétés de transport

The present work reports a strategy involving the preparation of silver nanoparticles in a biodegradable polymer stemming from either an ex situ or an in situ method, using in both cases a completely green chemistry process. The influence of the reducing agent concentration and the silver nanoparticles generation route is investigated on the structure, the morphology and the properties of the nanocomposite films. In both routes, silver nanoparticles with a diameter below 30 nm were highlighted in the nanocomposite films. For all nanocomposite films, no modification on the crystalline structure of the starch matrix is observed in the presence of silver. The in situ generation route allowed to obtain the smallest silver nanoparticles with a diameter below 10 nm. Crystalline silver nanoparticles were obtained only from the in situ generation route at the temperature of 85°C. The introduction of montmorillonites in both generation routes was also studied. The decrease of the water sorption and the improvement of water and oxygen barrier properties were found to be not dependent on the reducing agent concentration but mainly on the presence of the crystalline structure of the silver nanoparticles. Thus, significant enhancement of the barrier properties were finally obtained for the in situ nanocomposite films thanks to an efficient interaction between the crystalline silver nanoparticles and the starch matrixDes films nanocomposites amidon / argent ont été préparés par deux voies de génération vertes de nanoparticules d'argent. La première voie, dite ex situ, consiste à préparer tout d'abord une solution colloïdale d'argent qui est ensuite redispersée dans une matrice amidon plastifiée glycérol. Les nanoparticules d'argent colloïdales sont synthétisées en solution aqueuse par réduction du nitrate d'argent par du glucose en présence d'amidon stabilisant. La seconde voie, dite in situ, consiste à disperser le nitrate d'argent dans le film amidon plastifié et le réduire directement dans le film par traitement thermique en présence ou non de réducteur. L'influence du taux de glucose réducteur, du temps de synthèse et de la température a été étudiée en termes de taille, distribution de taille et dispersion des nanoparticules d'argent dans les films nanocomposites ex situ et in situ. Tout en gardant des paramètres de procédé comparables, les deux voies de nanostructuration des films amidon/argent ont également été comparées en termes de structure, de propriétés thermiques et de transport. Enfin, l'incorporation de charges montmorillonites a également été étudiée dans les deux voies de génération des nanoparticules métalliques. L'ensemble des travaux a permis de valider les deux voies de génération vertes menant à des nanoparticules d'argent dispersées de manière homogène et de tailles moyennes inférieures à 30 nm. La voie in situ à 85°C se distingue par des nanoparticules d'argent cristallines et de très petites tailles (inférieures à 10 nm) avec une interface amidon/argent cohésive particulière qui permettent d'améliorer les propriétés barrières aux gaz et à l'eau avec une diminution de perméabilité observée jusqu'à 90