Effets des variations climatiques et de disponibilité alimentaire sur les réponses phénotypiques et démographiques d’un rongeur hibernant, l’écureuil terrestre du Columbia

The abiotic environment, including climate conditions, may affects organism in multiple ways: by modifying their behaviour or physiology in the short-term, by having long-term evolutionary consequences, or by modifying resources availability. The consideration of both punctual and long-term climate effects have rarely been assessed, especially regarding seasonal species. My PhD aimed to evaluate microclimate and resources (vegetation) effects on a hibernating and herbivorous mammal (Urocitellus columbianus) living in the Rocky Mountains and with a short active period. Thanks to a 30-years population monitoring, effects of climate and vegetation variations on individual behaviour and physiology, as well as demographic consequences (young and adult survival, reproductive success), were measured. Whereas this species seemed well adapted to short climate event (snow and rainfalls), responses to changes in climate, vegetation, and population density were observed on the long-term. Punctual and long-term climate change effects on individuals was described, and now the questions remain on what can be the links between resource availability, quality, and individual and population performance.L’environnement abiotique, notamment les conditions climatiques, affecte les organismes de multiples manières : sur le court terme en modifiant leur comportement ou physiologie, sur le long-terme en ayant des conséquences évolutives, ou encore à travers les modifications des ressources disponibles. La différenciation des effets des évènements ponctuels ou des tendances à long-terme est peu connue, en particulier chez les espèces saisonnières. L’objectif de la thèse est donc d’évaluer les effets du microclimat et des ressources (végétation) sur un mammifère hibernant principalement herbivore (Urocitellus columbianus), vivant dans les montagnes Rocheuses et dont la période d’activité est très courte. A l’aide d’un suivi individuel à long-terme (>30 ans), les effets des variations climatiques et végétales sur le comportement et la physiologie du stress des individus, et les conséquences sur la démographie (survie des jeunes et des adultes, succès de la reproduction) sont mesurés. Cette espèce semble plutôt bien adaptée à des courts évènements climatiques (chute de neige, forte pluie) pendant la période d’activité, mais répondent également aux variations climatiques locales et aux changements temporels de végétation et de densité de population. Ayant mis en évidence des effets climatiques ponctuels et à long-terme sur les individus, il reste à comprendre quels sont les liens précis entre la disponibilité et la qualité des ressources, et la performance des individus ou des populations

Down-regulating the stress axis: Living in the present while preparing for the future

International audienceThe measurement of glucocorticoid (GC) hormones provides us with a window into the stress physiology of vertebrates and the adaptative responses they use to cope with predictable and unpredictable changes in the environment. Baseline GCs inform us about the metabolic demands they are subject to at that point in their yearly life-history stage, whereas GC changes (often increases) in response to acute challenges inform us on their capacity to cope with more immediate environmental challenges. However, baseline GC levels and the kinetics of GC responses to acute stressors can vary substantially among and within species, depending on individual characteristics (age, sex, condition, life-history stage). In addition, a thorough understanding of the stress status of an animal requires moving beyond the measurement of GCs alone by focusing on downstream measures of metabolic activation, such as oxidative stress. Here, we evaluated the changes in blood cortisol and oxidative stress markers in wild adult Columbian ground squirrels (Urocitellus columbianus), following a 30-min capture-handling stress performed in mid-late June. Measurements were taken when males were post-reproductive and preparing for hibernation and adult females were weaning litters. We found three key results. First, the time-course of GC increase was markedly slower (by an order of magnitude) than what is currently reported in the literature for most species of mammals, birds and reptiles. Second, there were marked differences in the male and female response, linked to differences in life-history stage: females close to weaning had abolished GC responses, whereas post reproductive males did not. Third, there were mild to moderate increases in oxidative damage and decreases in oxidative defenses in response to our short term challenge, consistent with the idea that short-term acute metabolic activation may carry physiological costs. However, these changes were not correlated to the changes in GCs, a novel result suggesting a disconnect of hormonal stress response and oxidative damage

Measuring fitness and inferring natural selection from long-term field studies: different measures lead to nuanced conclusions

International audienceMeasuring individual reproductive success in the wild is often achieved by counting the number of descendants produced by individuals. In seeking to understand how reproductive success can inform us about natural selection, however, we are faced with a conundrum. In terms of timing, what is the most relevant measure for examining selection? We might count the number of offspring born, surviving to the termination of parental care, surviving to adulthood, or only those surviving to themselves reproduce. Clearly, only the latter are passing on genes and traits to future generations, but this estimate may not always be available. So, are different estimates of fitness consistent? Do they provide us with similar inferences of selection on phenotypic traits? We examined these questions on a 29-year long-term study of individually monitored male and female Columbian ground squirrels (Urocitellus columbianus). We used the long-term data to calculate male and female fitness based on an annual measure of adult survival and the yearly production of offspring counted at the stages of birth, weaning, and yearling age. We then decomposed fitness into its constitutive elements including (1) adult survival to the next spring, and (2) the yearly production of offspring counted at the stages previously mentioned. We then compared fitness metrics to evaluate if they provided similar or contrasting information in the wild. Next, we used those fitness metrics to test for selection on the date of emergence from annual hibernation, a phenotypic trait previously shown to be highly variable, heritable, and associated with reproduction. Finally, we partitioned selection on emergence date into additive episodes of selection by looking at how selection changed from reproduction measured at birth, weaning and when offspring reached yearling age. Overall, fitness metrics were well correlated, but correlations weakened the further offspring were counted from birth. We generally found directional selection for earlier emergence dates both in males and females. The strength of selection depended o

Integrating microclimatic variation in phenological responses to climate change: a 28-year study in a hibernating mammal. Running head: Phenology and microclimate

International audienc

Integrating microclimatic variation in phenological responses to climate change: A 28-year study in a hibernating mammal

Phenological shifts associated with directional changes in climate, resulting in earlier spring activities, have been documented in several animal species. However, the extent to which species respond to overall climate change versus local climate variation is rarely studied. In addition, climate data are usually averaged over large spatial scales, even though local heterogeneity in habitats may be high, and species might be more susceptible to changes in local rather than global climate conditions. In this study, we examined the effects of spatiotemporal climate variation and climate change on the phenology of a hibernating mountain rodent, the Columbian ground squirrel (Urocitellus columbianus). Over 28 years of research (1992–2019), we studied the relationship between the microclimatic conditions experienced by adult and juvenile ground squirrels from four neighboring meadows, and their dates of emergence from hibernation. We used a microclimate model to calculate microclimate variables (local snow depth, soil temperature, air temperature, wind speed, and humidity) at an hourly scale, a 5-m spatial resolution, and at animal height on the study sites over 28 years. Emergence dates varied with age and sex, among years, as well as among and within meadows, with some areas averaging up to 10 days earlier emergence dates from hibernation than others. While emergence dates tended to be delayed throughout the study period, long-term temporal changes and interannual variability in emergence dates differed among meadows and depended on individual age and sex. Dates of hibernation emergence were correlated with local climate variables considered either during hibernation or during the preceding summer. Ground squirrels emerged earlier in years or at locations when/where snow melted earlier (years: all individuals excluding 2-year-old males, locations: yearlings and older females), and when the previous summer was less windy (≥3-year-old individuals) and more humid (2-year-old males). Two-year-old male ground squirrels also emerged later in locations where snow depth during winter was higher. Using a microclimate model allowed realistic predictions of phenological responses to climate, highlighting its potential for research on animal responses to abiotic change

Weathering the storm: Decreased activity and glucocorticoid levels in response to inclement weather in breeding Columbian ground squirrels

International audienceInclement weather can rapidly modify the thermal conditions experienced by animals, inducing changes in their behavior, body condition, and stress physiology, and affecting their survival and breeding success. For animals living in variable environments, the extent to which they have adapted to cope with inclement weather is not established, especially for hibernating species with a short active season that are constrained temporally to breed and store energy for subsequent hibernation. We examined behavioral (foraging activity) and physiological (body mass and fecal cortisol metabolites) responses of Columbian ground squirrels (Urocitellus columbianus), small hibernating rodents inhabiting open meadows in Rocky Mountains, to 3 events of inclement weather (two snow storms in May 2021 and May 2022, one heavy rainfall in June 2022). We found that individuals adapted to inclement weather conditions by (1) reducing above-ground activity, including foraging, (2) decreasing the mobilization of stored resources as indicated by a decrease in the activity of the hypothalamo-pituitary-adrenal (HPA) axis and lower fecal cortisol metabolites in the hours/days following periods of inclement weather; and (3) compensating through increased foraging and more local activity when favorable conditions resumed. As a result, body mass and growth did not decrease following short periods of inclement weather. Columbian ground squirrels were well-adapted to short periods of inclement weather, coping via modifications of their behavior and the activity of the HPA axis

Microclimate, an inseparable part of ecology and biogeography

Abstract Microclimate science has developed into a global discipline. Microclimate science is increasingly used to understand and mitigate climate and biodiversity shifts. Here, we provide an overview of the current status of microclimate ecology and biogeography, and where this field is heading next. We showcase the recent advances in data acquisition, such as novel field sensors and remote sensing methods. We discuss microclimate modelling, mapping, and data processing, including accessibility of modelling tools, advantages of mechanistic and statistical modelling, and solutions for computational challenges that have pushed the state-of-the-art of the field. We highlight the latest research on interactions between microclimate and organisms, including how microclimate influences individuals, and through them populations, communities, and entire ecosystems and their processes. We also briefly discuss recent research on how organisms shape microclimate from the tropics to the poles. Microclimates are also important in ecosystem management under climate change. We showcase new research in microclimate management with examples from biodiversity conservation, forestry, and urban ecology. We discuss the importance of microrefugia in conservation and how to promote microclimate heterogeneity. We identify major knowledge gaps that need to be filled for further advancing microclimate methods, investigations, and applications. These gaps include spatiotemporal scaling of microclimate data, mismatches between macroclimate and microclimate in predicting responses of organisms to climate change, and the need for more evidence on the outcomes of microclimate management. &nbsp; Biosketch The authors are participants of the Microclimate Ecology and Biogeography conference held in Antwerp, Belgium in 2022. Together they collaboratively wrote this perspective paper that brings together 97 experts and their views on the recent advancements and knowledge gaps in terrestrial microclimate. The paper was coordinated by Julia Kemppinen, Jonas Lembrechts, Koenraad Van Meerbeek, and Pieter De Frenne, and writing different sections was led by Jofre Carnicer, Nathalie Chardon, Paul Kardol, Jonathan Lenoir, Daijun Liu, Ilya Maclean, Jan Pergl, Patrick Saccone, Rebecca Senior, Ting Shen, Sandra Słowińska, Vigdis Vandvik, and Jonathan von Oppen. For more details on authors statistics and how the work was organised, please see Supplementary information Figures S1-3.</p

Microclimate, an important part of ecology and biogeography

Brief introduction: What are microclimates and why are they important?: Microclimate science has developed into a global discipline. Microclimate science is increasingly used to understand and mitigate climate and biodiversity shifts. Here, we provide an overview of the current status of microclimate ecology and biogeography in terrestrial ecosystems, and where this field is heading next. Microclimate investigations in ecology and biogeography: We highlight the latest research on interactions between microclimates and organisms, including how microclimates influence individuals, and through them populations, communities and entire ecosystems and their processes. We also briefly discuss recent research on how organisms shape microclimates from the tropics to the poles. Microclimate applications in ecosystem management: Microclimates are also important in ecosystem management under climate change. We showcase new research in microclimate management with examples from biodiversity conservation, forestry and urban ecology. We discuss the importance of microrefugia in conservation and how to promote microclimate heterogeneity. Methods for microclimate science: We showcase the recent advances in data acquisition, such as novel field sensors and remote sensing methods. We discuss microclimate modelling, mapping and data processing, including accessibility of modelling tools, advantages of mechanistic and statistical modelling and solutions for computational challenges that have pushed the state‐of‐the‐art of the field. What's next?: We identify major knowledge gaps that need to be filled for further advancing microclimate investigations, applications and methods. These gaps include spatiotemporal scaling of microclimate data, mismatches between macroclimate and microclimate in predicting responses of organisms to climate change, and the need for more evidence on the outcomes of microclimate management