Biology subjects

Ruthsatz, K.

Publications and source records attributed to Ruthsatz, K..

7 recordsLinked to original sources

bioRxiv2026

Microbiome plasticity, not gut morphology, is linked to amphibian larval performance under elevated temperatures and low food quality

In many ecosystems, anthropogenic warming is reshaping thermal regimes, leading to resource quality declines and imposing a dual constraint for ectotherms: elevated metabolic demand coupled with reduced assimilable energy. We tested whether plasticity in gut morphology and gut microbiome can buffer amphibian larvae against these concurrent stressors. Common frog (Rana temporaria) tadpoles were reared at two temperatures (18 vs. 24.5{degrees}C) crossed with three food-quality treatments (low, medium, high). We quantified growth and developmental rates, critical thermal limits (CTmax, CTmin), gut morphology (mass, relative length), and gut bacterial diversity and composition, together with predicted functional pathways. Warming accelerated growth and development and increased CTmax. Food quality increased growth and development, with temperature-dependent effects on developmental rate and CTmax. Gut mass declined at higher temperature and low-quality diets, but relative gut length showed only modest diet effects and no temperature dependence. Bacterial community composition and structure shifted with temperature and food quality. Predicted pathways suggest functional reconfiguration under warming and low food quality, consistent with sustaining energy acquisition and mitigating metabolic and oxidative stress. Together, these results implicate microbiome plasticity, rather than gut morphological plasticity, as a candidate mechanism supporting larval performance and heat-tolerance acclimation under warming and low food quality.

ecology↗

bioRxiv2026

Ontogenetic consequences of developmental temperature in amphibians: simultaneous gains in heat tolerance and cumulative costs to stress physiology

Heat tolerance is critical for ectotherms facing environmental temperature variability, yet how it varies across life stages, and whether trade-offs occur between temperature-induced developmental plasticity and heat tolerance, remain unclear, particularly in organisms undergoing metamorphosis which represent 95% of all animal species. We examined how early-life thermal conditions shape growth, development, survival, acclimation capacity, heat tolerance, and energy allocation across ontogeny in the African clawed frog (Xenopus laevis), reared at six constant temperatures (17-32{degrees}C). We tested whether higher developmental temperatures generate trade-offs between accelerated growth and heat tolerance, and the consequences for post-metamorphic resilience to extreme heat. Rearing at 32{degrees}C was lethal before metamorphosis. At non-lethal warm temperatures (17-29{degrees}C), larvae and juveniles simultaneously accelerated development, maintained growth, and enhanced heat tolerance. However, juveniles reared at 29{degrees}C showed reduced survival, elevated corticosterone responses to acute stress, and diminished acclimation capacity, indicating increased energetic demands and constrained metabolic flexibility. These findings show that amphibians can integrate developmental plasticity with plastic adjustments in heat tolerance, but that such strategies incur cumulative physiological costs. By adopting an across-life-stage approach, our study highlights energy-allocation constraints that may limit population persistence under climate warming in species with complex life cycles.

ecology↗

bioRxiv2025

Bringing the Lab to the Field: Validating Water-Borne Corticosterone as a Conservation Tool in Captive and Wild Amphibian Larvae

Assessing physiological condition in wild populations is important for understanding how environmental variation shapes organismal performance. Water-borne corticosterone (WB-CORT) sampling shows promise for studying amphibian stress physiology, but its ecological relevance and limitations require evaluation, particularly when methods developed under laboratory conditions are applied to wild individuals. Here, we evaluated WB-CORT sampling in common frog (Rana temporaria) larvae by comparing field-collected and laboratory-reared individuals. We examined whether origin influenced baseline physiological traits by modeling ontogenetic changes in WB-CORT and body mass, an integrative measure of growth. Across ontogeny, laboratory-reared larvae generally showed lower WB-CORT release and higher body mass than field-collected larvae, with distinct developmental trajectories in both traits. Next, we evaluated the sensitivity of WB-CORT and body mass to acute (48h) nitrate exposure, a widespread pollutant in amphibian breeding ponds. Nitrate treatment did not affect post-exposure WB-CORT release in either origin group. Field-collected larvae lost body mass across all treatments, including controls, whereas laboratory-reared larvae showed nitrate-specific mass loss only at 100 mg/L. Finally, we assessed whether total WB-CORT release reflected internal corticosterone by examining its relationship with tissue CORT concentrations. WB-CORT and tissue CORT were positively related in both groups, supporting WB-CORT as a minimally disruptive physiological measure under the conditions tested. Together, these findings show that WB-CORT captures biologically meaningful variation in internal corticosterone under the conditions tested, but did not detect a sustained response to the acute nitrate challenge. WB-CORT should therefore be viewed as a promising, context-dependent physiological indicator rather than a stand-alone stress biomarker.

ecology↗

bioRxiv2025

Growth but not corticosterone, oxidative stress or telomere length is negatively affected by microplastic exposure in a filter-feeding amphibian

Microplastics (MPs) are of increasing global concern for species inhabiting aquatic habitats. However, the mechanisms behind animal responses to MPs need comprehensive exploration. Amphibians are the most threatened vertebrate group with most species having a complex life cycle, commonly with an aquatic larval stage. Here, we investigated whether exposure to an environmentally-relevant concentration of MPs affects the growth of filter-feeding larvae of the African clawed frog (Xenopus laevis), and the consequences for their stress physiology (corticosterone (CORT) levels), or health and ageing physiology (oxidative stress and telomere length). We conducted a 3x2 experiment with three levels of fibre exposure (fibres absent -control-, and MP and cellulose fibre treatments), and two stress levels (CORT absent -control-, and CORT present simulating a stressful condition). We observed a negative impact of MP exposure on larval growth; however, this did not alter the CORT levels, oxidative stress or telomere length. Our study shows that realistic concentrations of MPs is not enough to induce major alterations on the stress or health and ageing physiology of a filter-feeding amphibian. Whether compensatory growth responses during the post-metamorphic stages could lead to detrimental effects later in life should be explored in amphibians and other organisms with complex-life cycles.

evolutionary biology↗

bioRxiv2024

Living in a multi-stressor world: nitrate pollution and thermal stress interact to affect amphibian larvae

The interaction of widespread stressors such as nitrate pollution and increasing temperatures associated with climate change are likely to affect aquatic ectotherms such as amphibians. The metamorphic and physiological traits of amphibian larvae during the critical onset of metamorphosis are particularly susceptible to these stressors. We conducted a common-garden experiment using Rana temporaria larvae subjected to four constant acclimation temperatures (18, 22, 26, 28 {degrees}C) crossed with three environmentally relevant nitrate concentrations (0, 50, 100 mg x L-1) to investigate the interactive and individual effects of these stressors on metamorphic (i.e., growth and development) and physiological traits (i.e., metabolism and heat tolerance) at the onset of metamorphosis. Larvae exposed to elevated nitrate concentrations and thermal stress displayed increased metabolic rates but decreased developmental rate, highlighting interactive effects of these stressors. However, nitrate pollution alone had no effect on either metamorphic or physiological traits, suggesting that detoxification processes were sufficient to maintain homeostasis but not in combination with increased acclimation temperatures. Furthermore, larvae exposed to nitrate displayed diminished abilities to exhibit temperature-induced plasticity in metamorphosis timing and heat tolerance, as well as reduced acclimation capacity in metabolic rate and heat tolerance to higher temperatures. These results highlight the importance of considering the exposure to multiple stressors when investigating how natural populations respond to global change.

ecology↗

bioRxiv2024

Between a Warm Winter and a Cold Spell: Physiological Responses to Changing Winter Climate in Amphibians

Climate change is swiftly altering environmental winter conditions, leading to significant ecological impacts such as phenological shifts in many species. As a result, animals might face physiological mismatches due to longer or earlier activity periods and are at risk of being exposed to late spring freezes. Our study points for the first time to the complex physiological challenges that amphibians face as a result of changing thermal conditions due to winter climate change. We investigated the physiological responses to a period of warmer winter days and sudden spring freeze in the common toad (Bufo bufo) by acclimating them to 4{degrees}C or 8{degrees}C for 48 h or exposing them to 4{degrees}C or -2{degrees}C for 6 h, respectively. We assessed the daily energy demands, determined body condition and cold tolerance, explored the molecular responses to freezing through hepatic tissue transcriptome analysis, and measured blood glucose levels. Toads acclimated to higher temperatures showed a higher daily energy expenditure and a reduced cold tolerance suggesting faster depletion of energy stores and the loss of winter acclimation during warmer winters. Blood sugar levels were higher in frozen toads indicating the mobilization of cryoprotective glucose with freezing which was further supported by changed patterns in proteins related to glucose metabolism. Overall, our results emphasize that increased thermal variability incurs physiological costs that may reduce energy reserves and thus affect amphibian health and survival. This might pose a serious threat to breeding adults and may have subsequent effects at the population level.

ecology↗

bioRxiv2023

Acclimation Capacity to Global Warming of Amphibians and Freshwater Fishes: Drivers, Patterns, and Data Limitations

Amphibians and fishes play a central role in shaping the structure and function of freshwater environments. These organisms have a limited capacity to disperse across different habitats and the thermal buffer offered by freshwater systems is small. Understanding determinants and patterns of their physiological sensitivity across life history is, therefore, imperative to predicting the impacts of climate change in freshwater systems. Based on a systematic literature review including 345 experiments with 998 estimates on 96 amphibian (Anura/Caudata) and 93 freshwater fish species (Teleostei), we conducted a quantitative synthesis to explore phylogenetic, ontogenetic, and biogeographic (thermal adaptation) patterns in upper thermal tolerance (CTmax) and thermal acclimation capacity (Acclimation Response Ratio, ARR) as well as the influence of the methodology used to assess these thermal traits using a conditional inference tree analysis. We found globally consistent patterns in CTmax and ARR, with phylogeny (taxa/order), experimental methodology, climatic origin, and life stage as significant determinants of thermal traits. The analysis demonstrated that CTmax does not primarily depend on the climatic origin but on experimental acclimation temperature and duration, and life stage. Higher acclimation temperatures and longer acclimation times led to higher CTmax values, whereby Anuran larvae revealed a higher CTmax than older life stages. The ARR of freshwater fishes was more than twice that of amphibians. Differences in ARR between life stages were not significant. In addition to phylogenetic differences, we found that ARR also depended on acclimation duration, ramping rate, and adaptation to local temperature variability. However, the amount of data on early life stages is too small, methodologically inconsistent, and phylogenetically unbalanced to identify potential life cycle bottlenecks in thermal traits. We therefore propose methods to improve the robustness and comparability of CTmax/ARR data across species and life stages, which is crucial for the conservation of freshwater biodiversity under climate change.

ecology↗