Biology subjects

Guillard, J.

Publications and source records attributed to Guillard, J..

8 recordsLinked to original sources

bioRxiv2026

Early life thermal plasticity and adaptive divergence among populations of Arctic charr (Salvelinus alpinus)

Climate warming alters the thermal environment experienced by ectotherms, whose physiological performance and fitness are constrained by temperature. Early life stages are often the temperature-sensitive phases of the life cycle, particularly in freshwater stenotherms such as the Arctic charr (Salvelinus alpinus). In this study, we used a common garden approach to compare the response and phenotypic plasticity of four charr populations to warmer conditions. These populations inhabit thermally contrasted lakes, including both native and introduced populations. We reared embryos at either an optimal (5{degrees}C) or a warmer (8.5{degrees}C) temperature. We tested adaptive divergence among populations in four traits (survival, incubation duration, body length and yolk sac volume) using Qst - Fst comparisons. We found that warmer temperature reduced body size, survival and incubation time, while thermal reaction norms differed among populations. Unexpectedly, populations originating from warmer environments did not consistently exhibit higher trait values under elevated temperatures. In contrast, the colder high-altitude population exhibited higher survival rates and lower yolk reserves for a given size under heat stress than the other populations. Our results highlight substantial variation among populations in responses to heat stress, emphasizing the complexity of predicting population responses to climate warming.

evolutionary biology↗

bioRxiv2025

Early-life temperature drives recruitment success in Eurasian perch (Perca fluviatilis) populations

Interannual fluctuations in the abundance of young-of-the-year (YOY) European perch (Perca fluviatilis) were studied in two large French peri-alpine lakes using a 12-year dataset of late summer hydroacoustic surveys. Previous research based on sampling over only a few years in localized areas or experimental systems has already highlighted the importance of temperature. However, these studies often considered only monthly or seasonal averages. In our study, we sought to understand the factors behind the significant annual fluctuations in perch stock and analysed 12 years of data at the ecosystem level. We used traditional thermal indices based on average values, as well as novel indices reflecting daily temperature fluctuations, which were derived from 36 years of in situ perch spawning data. Embryonic thermal conditions alone accounted for between 44% and 88% of the variation in YOY density across the lakes. An increase in temperature during the embryonic phase was beneficial, whereas significant daily variations had the opposite effect. In contrast, trophic factors and the adult stock did not exhibit consistent trends. Our study confirms previous findings using ecosystem-scale analyses, long-term data, and novel thermal indices, validating in natura the central role of spring thermal regimes in shaping recruitment and improving our understanding of recruitment variability under climate change.

ecology↗

bioRxiv2025

Nutrient availability-driven changes in extracellular matrix biochemical and mechanical properties regulate pancreatic cancer cell biology

The extracellular matrix (ECM) provides key biochemical and biomechanical cues that govern fundamental cellular processes, including growth and migration. ECM dysregulation and altered cell-matrix interactions are a driver of cancer progression, exemplified by pancreatic ductal adenocarcinoma (PDAC), where an abnormally dense, collagen-rich, and stiff ECM correlates with poor patient outcomes. The PDAC microenvironment is poorly perfused, resulting in altered nutrient availability, yet how this metabolic stress shapes the ECM and its biological activity remains poorly understood. Herein, we demonstrate that glutamine, a key amino acid depleted in poorly perfused PDAC regions, regulates the biochemical composition, mechanical properties, and biological activity of fibroblast-derived ECM. As glutamine availability increases, fibroblasts shift from producing a basement membrane-like ECM toward an interstitial, mature ECM enriched in fibrillar collagens. The ECM generated under glutamine-rich conditions is stiffer, which limits PDAC cell growth, while simultaneously, the elevated collagen I content promotes migration in a 3D spheroid model. Mechanistically, glutamine-dependent collagen I engages integrin 2 (ITGA2) to activate focal adhesion kinase signaling, driving PDAC cell migration independent of growth. In PDAC patients, glutamine stress inversely correlates with collagen expression in CAFs, with collagen I-ITGA2 as the most enriched ECM receptor interaction pair compared to the normal pancreas. These findings establish nutrient availability as a key regulator of ECM biology and offer new avenues to therapeutically intervene with dysregulated cell-matrix interactions in PDAC.

cell biology↗

bioRxiv2025

Environmental DNA (eDNA) sampling strategies influence estimates of freshwater fish eDNA concentrations.

Quantifying in-situ environmental DNA (eDNA) concentrations is increasingly used to infer fish abundance and biomass in freshwater ecosystems. While various sampling strategies (i.e. the combination of sample collection, eDNA preservation and extraction protocols) have been proposed to collect eDNA, little efforts have been undertaken to evaluate how these different strategies affect taxon-specific eDNA recovery and the subsequent estimates of in-situ eDNA concentrations. In this study, we compared a point (i.e. eDNA collection from relatively small and spatially separated water samples filtered using low capacity filter units) and a spatially integrated sampling strategy (i.e. eDNA collected from spatially integrated larger water volumes filtered using high capacity filter units) in two natural lakes. Through quantitative analyses of total DNA, total fish eDNA and species-specific eDNA, we assessed the performance of both strategies to infer in-situ eDNA concentrations. Our results showed that the integrated strategy led to a reduced recovery of fish eDNA and a subsequent underestimation of in-situ eDNA concentrations compared to the point sampling strategy. While the exact mechanisms underlying this pattern require further investigation, our findings highlight the importance of carefully selecting sampling strategies according to study objectives.

genetics↗

bioRxiv2025

A century of allopatry: plasticity and rapid selection shape phenotypic trait variability under contrasting environments.

Allopatric isolation under contrasting environments can drive rapid phenotypic divergence, even over contemporary timescales. Rapid changes in morphology or physiology can allow organisms to adapt to biotic and abiotic characteristics of their habitats. While studying metabolism, growth and resources needs may allow to understand adaptation to several selective pressures, these traits are rarely jointly considered. We investigated morphological, growth, and metabolic divergence in two allopatric populations of Arctic charr (Salvelinus alpinus) sharing a common evolutionary origin but inhabiting contrasting environments. We combined field observations, common garden and quantitative genetic approaches to disentangle contributions of genetic divergence and plasticity to phenotypic variability. Wild adults differed in body shape and growth trajectories, potentially reflecting plasticity related to resource availability and temperature variations. Under common garden conditions, juveniles displayed inter-population differences in routine metabolic rate, its allometric scaling with body mass. These patterns suggest divergent selection on physiological traits. Despite low neutral genetic differentiation, phenotypic divergence unfolded in fewer than 100 years, suggesting that plasticity and selection can promote rapid multi-trait changes. These findings highlight that considering changes in physiological, growth and morphological traits can reveal the adaptive potential of small, isolated populations facing rapid environmental change.

evolutionary biology↗

bioRxiv2022

Automatic detection, identification and counting of anguilliform fish using in situ acoustic camera data: development of a cross-camera morphological analysis approach

Acoustic cameras are increasingly used in monitoring studies of diadromous fish populations, even though analyzing them is time-consuming. In complex in situ contexts, anguilliform fish may be especially difficult to identify automatically using acoustic camera data because the undulation of their body frequently results in fragmented targets. Our study aimed to develop a method based on a succession of computer vision techniques, in order to automatically detect, identify and count anguilliform fish using data from multiple models of acoustic cameras. Indeed, several models of cameras, owning specific technical characteristics, are used to monitor fish populations, causing major differences in the recorded data shapes and resolutions. The method was applied to two large datasets recorded at two distinct monitoring sites with populations of European eels with different length distributions. The method yielded promising results for large eels, with more than 75% of eels automatically identified successfully using datasets from ARIS and BlueView cameras. However, only 42% of eels shorter than 60 cm were detected, with the best model performances observed for detection ranges of 4-9 m. Although improvements are required to compensate for fish-length limitations, our cross-camera method is promising for automatically detecting and counting large eels in long-term monitoring studies in complex environments.

ecology↗

bioRxiv2022

A quantitative eDNA-based method to monitor fish spawning in lakes: application to European perch and whitefish

There is an urgent need to evaluate the effects of anthropogenic pressures and climatic change on fish populations dynamics. When monitored in lakes, the spawning of fish is generally assessed using traditional, mostly destructive or damaging, methods as gillnetting and collection of fertilized eggs. Over the last decade, environmental DNA (eDNA) based methods have been widely developed for the detection of aquatic species, offering a non-invasive alternative method to conventional biomonitoring tools. In particular, the emergence of new methods as the droplet digital PCR (ddPCR) offer the possibility to quantify an absolute eDNA signal in a very sensitive way and at a low cost. Here, we developed and implemented a quantitative eDNA method to monitor the spawning activity of two fish species, European perch and whitefish. ddPCR protocols were formalized based on existing and newly designed COI primers, and were applied during four spawning periods in lake Geneva. The results demonstrate the efficiency of eDNA coupled with ddPCR to identify the timing and duration of the spawning periods, as well as the peak of the spawning activity for the targeted species. In addition, the use of a control species (i.e., quantification of the eDNA signal of a fish that does not reproduce during the monitoring period) was shown to be relevant to clearly discriminate fluctuations of the eDNA signal associated to the spawning activity from the baseline eDNA signal. For future implementation, we recommend using an integrative sampling strategy (e.g., pooled samples for a give station) to smooth the local variability of the eDNA signal. These results show that we reached an operational level to use these non-invasive eDNA methods to monitor the spawning periods of these two fish species in large lakes.

ecology↗

bioRxiv2021

Influence of warming temperatures on coregonine embryogenesis within and among species

The greatest known global response of lakes to climate change has been an increase in water temperatures. The responses of many lake fishes to warming water temperatures are projected to be inadequate to counter the speed and magnitude of climate change. We experimentally evaluated the responses of embryos from a group of cold, stenothermic fishes (Salmonidae Coregoninae) to increased incubation temperatures. Study groups included cisco (Coregonus artedi) from lakes Superior and Ontario (USA), and vendace (C. albula) and European whitefish (C. lavaretus) from Lake Southern Konnevesi (Finland). Embryos from artificial crossings were incubated at water temperatures of 2.0, 4.5, 7.0, and 9.0{degrees}C, and their responses were quantified for developmental and morphological traits. Embryo survival, incubation period, and length-at- hatch were inversely related to incubation temperature whereas yolk-sac volume increased with incubation temperature within study groups. However, varying magnitudes of responses among study groups suggested differential levels of developmental plasticity to climate change. Differential levels of parental effects indicate genetic diversity may enable all study groups to adapt to cope with some degree of changing environmental conditions. Our results suggest that the coregonines sampled within and among systems may have a wide range of embryo responses to warming incubation conditions.

ecology↗