The gut microbiome is increasingly recognized as a key mediator of social behavior and division of labor in eusocial insects. In some species, trophallactic interactions facilitate nutrient exchange between larvae and adults, creating social interdependency. However, the role of gut bacterial symbionts in this process remains unclear. Here, we investigated the relative contributions of host identity, environment, and trophallactic interactions to gut microbiome assembly in two social wasp species, Vespa orientalis and Vespula germanica, using a cross-fostering, common garden experiment. Newly emerged workers and early-instar larvae were reciprocally exchanged and reared under controlled conditions. High-throughput 16S rRNA gene sequencing and functional inference revealed limited variation across treatments in worker gut communities, mainly shaped by shared environment, indicating stability and environmental dominance. Conversely, larval gut microbiomes were highly plastic, influenced by both larval species and the identity of their nursing workers, highlighting the impact of social interactions. Functional profiles reflected caste-specific roles: workers harbored microbiomes enriched for antimicrobial and detoxification pathways, while larvae microbiomes were enriched in metabolic functions for protein digestion and development. These findings demonstrate that metabolic division of labor in eusocial wasps is supported by life stage-specific microbial communities and functions and maintained by social interactions, positioning the gut microbiome as a key contributor to the maintenance of eusociality.

Many reptiles inhabit deserts where extreme heat and aridity make it imperative to minimize evaporative water loss (EWL) in order to maintain a water balance. We compared the EWL of desert versus Mediterranean snakes and the content and composition of their epidermal lipids, which form the primary barrier against evaporation. We obtained shed skins from two farm‐grown species (a desert specialist viper Echis coloratus and its Mediterranean relative Daboia palaestinae ), and from 17 captive snake species of both Mediterranean and desert origins, kept under identical conditions. Total EWL was measured in live snakes using flow‐through respirometry. Cutaneous EWL was approximated in vitro through the shed skin, and epidermal lipids were quantified following extraction in n ‐hexane and identified using ultraperformance liquid chromatography–mass spectrometry (UPLC‐MS). Total EWL in vivo was 50% higher in Mediterranean than in desert species. In winter, in vitro EWL was 67% higher in Mediterranean than in desert species, and this difference rose to 178% in summer. EWL in vitro was negatively correlated with skin lipid content, and accordingly, desert species had twice the skin lipid content, but only in the summer. Seasonal differences were significant in the multi‐species comparison, and not between the farm‐grown Echis and Daboia . UPLC‐MS confirmed equal quantities of total lipids between the two viper species. However, the abundance of fatty acids was 84% higher in the desert specialist Echis , and these were, on average, ~1 double bond more saturated. There was no difference in ceramide abundance, but ceramide carbon chains were ~1 carbon atom longer in Echis . This lipid profile favours a more compact and stable lipid barrier structure, which improves the skin's resistance to evaporation. Our results show that snake epidermal lipid content and composition vary between biomes and seasons, enabling desert species to maintain water balance under the harsh heat and dryness conditions by limiting water loss. More broadly, this work highlights how fundamental biochemical traits can underlie major ecological differences, and how animals can benefit from these differences and adapt to thrive in extreme conditions. Read the free Plain Language Summary for this article on the Journal blog.

Cellulose and chitin are the two most abundant polysaccharides on Earth. To digest these structural carbohydrates, herbivorous and omnivorous insects typically rely on cellulases, while insectivorous species often express chitinases. The American cockroach (Periplaneta americana), an extreme generalist omnivore, is known to thrive on a variety of diets. However, little is known about its ability to metabolize structural polysaccharides such as cellulose and chitin. In this study, we fed cockroaches 13C-labeled cellulose and chitin to assess their metabolic capacity and the tissue-level allocation of these polysaccharides across sexes and life stages. Our results show that P. americana metabolized chitin at a significantly higher rate than cellulose and incorporated only chitin-derived carbon into body tissues, with clear sex-and life stage-specific patterns: nymphs allocated more chitin-derived carbon to their muscles, while females incorporated more into the fat body and reproductive tissues. These results provide in vivo evidence of P. americana's capacity to metabolize both cellulose and chitin but also reveal a strong preference for chitin utilization under carbohydrate-rich conditions. This study contributes to our understanding of nutrient allocation strategies in generalist insects and offers evolutionary insight into the digestive capabilities of Blattodea, shedding light on their adaptive strategies for utilizing a wide range of dietary materials.

The Galápagos marine iguana (Amblyrhynchus cristatus), the world's only marine lizard, feeds predominantly on algae. Owing to warming waters and reduced upwelling, algal abundance is reduced during El Niño events, causing high iguana mortality. During such periods, adult iguanas may shrink in size, a compelling phenomenon that has been suggested as an adaptation to reduce energetic needs. However, shifts in energy consumption have never been tested directly. We measured the body condition and metabolic rates of marine iguanas during an El Niño year and the subsequent neutral year. During El Niño, body mass relative to length was 17% lower, girth relative to length was 12% lower, and resting metabolic rates were 20% lower. This supports the hypothesis that marine iguanas partly offset the adverse effect of El Niño by an active response aimed at reducing their energy consumption, complementary to the energy-saving effect of body size reduction. Future ocean warming could force this endemic species to resort to such strategies increasingly often, and will likely exacerbate the already-high mortality rates caused by these events.

Aim: More species-rich communities are often assumed to contain more specialist species with narrower niches and smaller ranges. Stronger interspecific competition in species-rich communities is thought to be a key mechanism explaining these patterns. Yet, the relationship between richness and specialisation has so far only been studied for a few taxa, and characterising the effects of interspecific competition on species distributions is challenging. Here, we assess broad-scale relationships between niche breadth, range sizes and geographic exclusion along richness gradients of bats. Location: Eastern Mediterranean, Western Asia, and Central Asia. Taxon: Bats (Chiroptera). Methods: Based on a novel integrated species distribution modelling approach that combines occurrence information with expert range maps, we assessed how environmental niche breadth and range sizes varied with species richness. In addition, by contrasting species' potential and realised distributions in areas where species pairs overlap, we derived indicators of geographic exclusion to understand how potential interspecific competition is affecting range limits along richness gradients. Results and Main Conclusions: We found a nonlinear association between environmental niche breadth and richness, with the most specialised species occurring in species-poor regions and niche breadth peaking at intermediate richness. Despite a positive association of niche breadth and range sizes at the species level, range sizes in predicted bat communities declined continuously with species richness. In addition, patterns of geographic exclusion were linked to patterns of niche breadth, with species filling less of their potential range overlaps when overlapping species were more specialised. Our findings suggest that small range sizes in species-rich bat communities are better explained by the number of interacting species than by environmental specialisation or stronger exclusion between individual species. More broadly, we show how integrated distribution modelling approaches can shed new light on the interplay of species richness, specialisation and community structure, and caution against generalising relationships between richness and specialisation across taxa and geographies.

Maintaining the body's water balance is crucial for function and survival in all animals. Humidity conditions vary between different habitats and greatly affect an animal's evaporative water loss (EWL). Species inhabiting arid regions have adaptions to minimize water loss, which those adapted to life in humid regions may lack. Therefore, the physiology of species from different habitats could respond differentially to acute exposure to dry conditions. We measured the EWL and resting metabolic rates (RMRs) of 12 Israeli squamate species, from either mesic or xeric habitats, spanning four orders of magnitude in size. We treated the animals to dry and humid air simulating natural conditions (vapor pressure deficits 3 and 1 kPa, respectively) at an ecologically relevant temperature of 25°C. EWL rates were higher in dry air, and the effect was stronger in mesic species. EWL of mesic species in humid air is similar to EWL of xeric species in dry air, indicating similar EWL when tested under settings that match each species' natural conditions. In dry air, the RMR of small-bodied (<5 g) mesic species increased, whereas those of some small-bodied xeric species decreased. Small mesic species might be displaying stress from unnaturally dry conditions, whereas small xeric species possibly display an adaptation to minimize EWL by lowering RMR, thereby respiration rates. Physiological measurements are usually taken in dry air, and our results suggest previous experiments may contain a methodological bias. Future ecophysiological research needs to consider ambient humidity, by either varying experimental humidity to match natural conditions, or considering possible effects of humidity during analysis and interpretation of experiments and models.

Marine iguanas occasionally face severe food shortages because of algal dieback during El Ni & ntilde;o events. Research on their adaptations to these periods has highlighted their unique ability to shrink in body length, which reduces their energetic needs. Additional mechanisms, like sustaining lower body temperatures and metabolic rates, could potentially also lower energy consumption, but have never been examined. We measured 665 iguanas over an 11-year period including three El Ni & ntilde;o events, and examined how heart rates (a proxy for metabolic rates) and body temperatures change with sea-surface temperature oscillations (Oceanic Ni & ntilde;o Index, ONI). Heart rate (adjusting for body size, temperature, season, and study site) was negatively correlated with ONI and lower during El Ni & ntilde;o, whereas the adjusted body temperature did not correlate with ONI or differ between El Ni & ntilde;o and other periods. We therefore hypothesize that marine iguanas can depress their metabolic rates in response to the harsh conditions, an adaptation that is complementary to shrinking and may further enhance their survival through periods of limited food. Direct metabolic measurements are needed to test this hypothesis.

Camouflage and crypsis are key survival strategies for many animals, enabling them to evade predators or enhance their ability to ambush prey. For cryptic species, effective camouflage requires not only morphological adaptations but also behavioral tactics that ensure individuals select appropriate microhabitats. However, how polymorphic cryptic species match their phenotype to their environment remains poorly understood. In this study, we investigated the morphological and behavioral plasticity of the polymorphic mantis Sphodromantis viridis from Mediterranean and desert populations to determine whether habitat selection and coloration occur when nymphs are reared in the absence of environmental color. We reared naive individuals in color-neutral conditions and examined their morphology, development time, body length, and microhabitat preferences. Color in S. viridis is sex-linked, with males exhibiting higher proportions of brown coloration than females, and color change occurs unidirectionally from green to brown. Desert males displayed greater variance in body size and development time, forming two distinct morphs: one is smaller, greener, and matures before females, and another is larger, browner, and matures after females, suggesting alternative reproductive strategies. Neither nymphal nor adult coloration of naive mantids influenced color choice in controlled conditions. Our findings suggest that S. viridis nymphs showed ontogenetic color change in the absence of environmental cues, which may reflect evolutionary adaptations to seasonal changes: green in spring when the vegetation is still green and brown later on when annuals dry out. Further studies on background-dependent rearing conditions could clarify how experience influences microhabitat choice.

Pollen serves as a crucial source of protein and lipids for numerous insects. Despite the importance of pollen lipids for nutrient regulation in bees, the digestibility and absorption of different fatty acids (FAs) by bees remain poorly understood. We used 13C labeled fatty acids (FAs) to investigate the absorption and allocation of three common dietary FAs in pollen by bumble bees. Palmitic acid, the most common saturated FA in pollen, was poorly absorbed, even when supplied as tripalmitate, emulsified, or mixed in vegetable oil. In contrast, the essential linoleic acid was absorbed and allocated at the highest rate among the three FAs tested. Oleic acid, a non-essential monounsaturated FA, was absorbed and oxidized at lower rates than linoleic acid. Notably, a feeding rate experiment revealed that different fatty acids did not affect the consumption rate of pollen. This results suggests that the specific FA's absorption efficiency and allocation differ in bumble bees, impacting their utilization. These findings demonstrate the importance of considering the digestibility and absorption of different FAs. Furthermore, the study highlights the influence of pollen lipid composition on the nutritional content for pollinators and raises questions about the utilization of polyunsaturated FAs in insect metabolism.

Ethanol, a natural by-product of sugar fermentation, can be found in various fruits and nectar. Although many animals routinely consume ethanol in low concentrations as part of their natural diets, its inherent toxicity can cause severe damage. Even species particularly well adapted to ethanol consumption face detrimental effects when exposed to concentrations above 4%. Here, we investigated the metabolism of ethanol and its impact on survival and behavior in the Oriental hornet ( Vespa orientalis ), a social wasp that naturally consumes ethanol. We show that chronic ethanol consumption, even at concentrations as high as 80%, had no impact on hornet mortality, construction behavior, or agonistic behavior. Using 13 C1 labeled ethanol, we show that hornets efficiently metabolized ingested ethanol and at a much higher rate than honey bees. The presence of multiple copies of the alcohol dehydrogenase (NADP+) gene in the Vespa genera suggests a potential mechanism for ethanol tolerance. These findings support the hypothesis that the mutualistic relationship between ethanol-producing organisms and vespid hosts may be at the origin of their remarkable capacity to utilize and metabolize ethanol.

Life under the shadow of war is full of anguish. While we mostly focus, rightfully and understandably, on the toll on human lives, armed conflicts also have far-reaching effects on biodiversity conservation (Conteh et al., 2017; Sousa et al., 2022). Wildlife populations can suffer from direct hits, habitat destruction, and exploitation by displaced people—all of which is exacerbated by declines in environmental funding and enforcement (reviewed in Gaynor et al., 2016; Hanson, 2018). Military activity is also full of sudden, unnaturally loud noises, potential stressors for wild animals (Shannon et al., 2016). Both domestic (Bowen, 2008) and wild animals (reviewed in Krausman et al., 1998) alter their behaviors in response to aircraft noise, gunshots, and fireworks. Physiological responses to noise, however, are less commonly studied; mammal heart rates have been shown to increase in response to military jet flyovers (Geist et al., 1985; MacArthur et al., 1979; Weisenberger et al., 1996), but few studies have been conducted on this phenomenon. In reptiles, even outside the context of war, fear and distress are difficult to gauge (Lambert et al., 2019), and research on their reaction to anthropogenic noise is minimal (Shannon et al., 2016). However, the lizard Aspidoscelis neotesselatus has shown stress responses in reaction to military jet flyovers, including higher blood ketone and corticosterone levels, and more time spent foraging afterward as compensation for lost energy (Kepas et al., 2023). Dubiner et al. (2023) recently reported evidence of a sharp increase in the respiration of a single individual blind snake Xerotyphlops syriacus during a 2021 rocket attack on Tel Aviv. Sadly, while conducting a long-term experiment on the physiology of geckos, the eruption of the war between Israel and Hamas allowed us to empirically test and quantify the real-time effects of repeated bombings on reptile metabolism. During the first month of the tragic Israel–Hamas war (ongoing since October 7, 2023), Hamas fired ~10,000 rockets into Israeli civilian areas, some of which (in 25 separate barrages) exploded or were intercepted not far from our university. On September 18, 2023, we had begun a long-term experiment on the physiology of the elegant short-fingered gecko (Gekkonidae: Stenodactylus sthenodactylus; Figure 1a). We caught seven geckos in Netanya (32.278° N, 34.835° E) under Permit 43032 from the Israel Nature and Parks Authority. The geckos were kept at Tel Aviv University in terraria with water ad libitum and fed with mealworms 6 and 3 days before each measurement. The metabolism of all individuals was recorded weekly (every Tuesday) at 28°C in cycles of 30 min every 4 h per individual, from noon to midnight. The metabolic chamber volume was 50 mL, through which dry air flowed at 50 mL/min into an LI-7000 CO2/H2O analyzer (LICOR, Lincoln, NE, USA). An empty identical chamber was automatically recorded between measurements as a reference. Geckos were fed and rehydrated when the experiment ended. We released the geckos to their original home range on November 7, 2023. Measurements were conducted under ethics permit number 23071423 from the TAU Ethics Committee. Five barrages that struck or were intercepted near our university coincided with respirometric measurements involving five of the seven geckos. We compared the metabolic rates recorded in response to the explosions to the same individuals' metabolic rate before and after the barrages using Expedata 1.9.20. Exact bombing times were retrieved from the National Emergency Portal (http://www.oref.org.il/12481-he/Pakar.aspx). Metabolic rates (log-transformed) were calculated from VCO2, assuming a respiratory quotient of 0.8. Gecko metabolic rates were, on average, 2.3 ± 0.3 times higher immediately after the explosions (averaged from the explosion to the end of the 30-min measurement) compared to 4 h prior (Tukey honestly significant difference [HSD]: n = 5; t = −8.3; padj = 0.004; Figure 1b). However, the metabolic rates during the 30 min immediately after the explosions were 1.6 times higher than 4 h after them. This difference was not statistically significant (Tukey HSD: n = 5; t = −3.7; padj = 0.062; Figure 1b; see Appendix S1: Table S1 for details). The strength of the response over time did not attenuate over the 4 weeks (ordinary least squares for change against date: slope = −0.03; R2 = 0.09; p = 0.52). We assume the increased metabolic costs indicate an acute stress response, initiated by the loud noise or vibrations from the explosions (Dubiner et al., 2023) and continuing, to a lesser degree, several hours after. Despite ranging from the Day 4 to Day 32 of the war, the geckos' response did not attenuate. In their terraria, geckos were exposed to all 25 barrages, not only the five occurring when their metabolic rates were measured. Some (but not all) mammals may habituate to military noise after prolonged exposure (Krausman et al., 1998), but our data suggest that for geckos the detrimental effects may last for as long as hostilities do. It is also worth noting that we recorded the responses inside a sheltered, windowless room with concrete walls. In the wild, animals are much more exposed and may be affected by explosions more strongly and across a larger area. A metabolic response of the magnitude we recorded could gradually deplete energy stores reserved for growth and reproduction, thereby decreasing fitness (Steyermark, 2002). It could also increase foraging times to compensate for the heightened demands of stress (Kepas et al., 2023), which can negatively impact lizard fitness and population stability (Sinervo et al., 2010). This would reduce the time allocated to other fitness-increasing activities, exposing animals to more hours at risk (e.g., predation), precisely when risks from military sources are already high (Gaynor et al., 2016; Hanson, 2018; Sousa et al., 2022). While the conservation consequences are probably minor for Least Concern populations and species such as S. sthenodactylus (Baha El Din et al., 2021), they may be quite high for rare or endemic species, many of which are distributed completely within the range of current or potential armed conflict (Hanson, 2018; Hanson et al., 2009). Some of these, which have limited distributions in areas heavily used by the army (e.g., Acanthodactylus beershebensis, Mediodactylus amictopholis; Bar et al., 2021), might actually face a risk to their populations from "everyday" military training and presence, rather than open war. Therefore, we call for armed forces to consider conservation issues when training, even if these are not prioritized when fighting. Finally, we greatly mourn the pain and loss caused to people in armed conflicts here and everywhere and hope that our results serve as a reminder that war can have devastating effects that extend far beyond what is easily noticed. Shahar Dubiner is funded by the Azrieli Graduate Studies Fellowship. We thank Adi Baram, Avigail Mitrani, Jonathan Ben-Simon, and Simon Jamison for their help in gecko collection and husbandry. We also wish to extend our thoughts to the people in Israel, Gaza, and Lebanon, who are still suffering in this tragic war. The authors declare no conflicts of interest. Appendix S1. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

AimSquamate fitness is affected by body temperature, which in turn is influenced by environmental temperatures and, in many species, by exposure to solar radiation. The biophysical drivers of body temperature have been widely studied, but we lack an integrative synthesis of actual body temperatures experienced in the field, and their relationships to environmental temperatures, across phylogeny, behaviour and climate.LocationGlobal (25 countries on six continents).TaxaSquamates (210 species, representing 25 families).MethodsWe measured the body temperatures of 20,231 individuals of squamates in the field while they were active. We examined how body temperatures vary with substrate and air temperatures across taxa, climates and behaviours (basking and diel activity).ResultsHeliothermic lizards had the highest body temperatures. Their body temperatures were the most weakly correlated with substrate and air temperatures. Body temperatures of non-heliothermic diurnal lizards were similar to heliotherms in relation to air temperature, but similar to nocturnal species in relation to substrate temperatures. The correlation of body temperature with air and substrate temperatures was stronger in diurnal snakes and non-heliothermic lizards than in heliotherms. Body-substrate and body-air temperature correlations varied with mean annual temperatures in all diurnal squamates, especially in heliotherms. Thermal relations vary with behaviour (heliothermy, nocturnality) in cold climates but converge towards the same relation in warm climates. Non-heliotherms and nocturnal species body temperatures are better explained by substrate temperature than by air temperature. Body temperature distributions become left-skewed in warmer-bodied species, especially in colder climates.Main ConclusionsSquamate body temperatures, their frequency distributions and their relation to environmental temperature, are globally influenced by behavioural and climatic factors. For all temperatures and climates, heliothermic species' body temperatures are consistently higher and more stable than in other species, but in regions with warmer climate these differences become less pronounced. A comparable variation was found in non-heliotherms, but in not nocturnal species whose body temperatures were similar to air and substrate irrespective of the macroclimatic context.

Social wasps exhibit a unique nutritional cycle in which adults feed larvae with prey, and larvae provide adults with larval secretions (LS). LS serves as a vital nutritional source for adults, contributing to the colony’s health and reproductive success. The LS nutrient composition has been previously reported in various wasp species, yet these analyses focused solely on worker-destined larvae, overlooking the potential caste designation effects on LS composition.Using metabolomics techniques, we analysed and compared the metabolite and nutrient composition in LS of queen- and worker-destined larvae of the Oriental hornet. We found that queen-destined LS (QLS) contain greater amounts of most metabolites, including amino acids, and smaller amounts of sugars compared to worker-destined LS (WLS). The amino acid-to-sugar ratio in QLS was approximately tenfold higher than in WLS. Thus, as the colony transitions from the production of workers to the production of reproductives, it gradually experiences a nutritional shift that may influence the behaviour and physiology of the adult nest population. This caste-specific metabolite profile and nutrient composition of LS reflect the differences in the diet and physiological requirements of worker- and queen-destined larvae and may play a critical role in caste determination in social wasps.

The scaling of the energetic cost of locomotion with body mass is well documented at the interspecific level. However, methodological restrictions limit our understanding of the scaling of flight metabolic rate (MR) in free-flying insects. This is particularly true at the intraspecific level, where variation in body mass and flight energetics may have direct consequences for the fitness of an individual. We applied a 13C stable isotope method to investigate the scaling of MR with body mass during free-flight in the beetle Batocera rufomaculata. This species exhibits large intraspecific variation in adult body mass as a consequence of the environmental conditions during larval growth. We show that the flight-MR scales with body mass to the power of 0.57, with smaller conspecifics possessing up to 2.3 fold higher mass-specific flight MR than larger ones. Whereas the scaling exponent of free-flight MR was found to be like that determined for tethered-flight, the energy expenditure during free-flight was more than 2.7 fold higher than for tethered-flight. The metabolic cost of flight should therefore be studied under free-flight conditions, a requirement now enabled by the 13C technique described herein for insect flight.

Floral nectar, a vital nutrition source for pollinators, contains diverse chemical compounds, including γ-Aminobutyric acid (GABA), a prevalent non-proteinogenic amino acid. While GABA's physiological role is known and well-studied, its ecological significance in plant-pollinator interactions remains unclear. Recent studies on GABA's effects on pollinators' preference, consumption, survival, physiology, and behavior show varying outcomes according to the species, indicating a complex relationship. GABA consumption impacts motor function and cognitive abilities, potentially influencing pollination efficiency. Future research addressing diverse concentrations, species, and behavioral aspects is crucial for comprehensively understanding GABA's ecological role in plant-pollinator interactions.

AbstractSquamates are adapted to thrive in extreme deserts thanks to, among other mechanisms, the water-conserving characteristics of their integument. Yet very small-bodied species, such as the fossorial desert thread snake Myriopholis macrorhyncha (∼1 g), face challenges because of their high relative surface area entailing high evaporative water loss. Fossorial snakes avoid dry periods by retreating underground, which can reach high humidity even in the desert habitat of M. macrorhyncha. We measured evaporative water loss of three individuals at 25°C and three different ecologically relevant humidity conditions. We found low water loss at 70% relative humidity (RH) compared to the high water loss in dry air (near 0% RH). Interestingly, we found apparent water absorption at 97% RH, confirmed by both respirometry and equivalent gains in body mass following this treatment. This suggests an adaptation allowing the snake to acquire water from the atmosphere during its retreat to subterranean burrows and ant nests. Coupled with other water-conserving strategies, such as discontinuous gas exchange to reduce respiratory water loss, this strategy could be crucial for survival in arid environments where water is scarce.

Dietary fatty acids (FAs) are essential macronutrients affecting animal fitness, growth, and development. While the degree of saturation of FAs usually determines the level of absorption and allocation within the body, the utilization of dietary FAs across the life stages of individuals remains unknown. We used three different 13 C labeled FAs, with a different saturation level (linoleic acid (18:2), oleic acid (18:1), and palmitic acid (16:0)), to investigate the absorption and allocation of dietary FAs across the life stages of the Oriental hornet. Our results show that only larvae utilized all tested FAs as metabolic fuel, with palmitic acid being oxidized at the highest rate. Oleic and palmitic acids were predominantly incorporated into larval tissues, while oleic acid dominated pupal tissues. In contrast, linoleic and oleic acids were predominantly incorporated into adult tissues. These findings highlight a life stage-dependent shift in certain FAs utilization, with palmitic acid mostly utilized in early stages and linoleic acid in adulthood, while oleic acid remained consistently utilized across all life stages. This study emphasizes the importance of considering FA saturation and life stage dynamics in understanding FA utilization patterns.

In winter, many reptiles have a period of inactivity ("brumation"). During brumation there is no energetic intake, therefore there would be an advantage to reducing energetic expenditure. The size of energetically costly organs, a major determinant of metabolic rate, is known to be flexible in many tetrapods. Seasonal plasticity of organ size could serve as both an energy-saving mechanism and a source of nutrients for brumating reptiles. We studied a population of an invasive gecko, Tarentola annularis, to test for seasonal changes in activity, metabolic rate, and mass of various organs. The observed period of inactivity was December-February. Standard metabolic rates during the activity season were 1.85 times higher than in brumating individuals. This may be attributed to decreased organ mass during winter: heart mass decreased by 37%, stomach mass by 25%, and liver mass by 69%. Interestingly, testes mass increased by 100% during winter, likely in preparation for the breeding season, suggesting that males prioritize breeding over other functions upon return to activity. The size of the kidneys and lungs remained constant. Organ atrophy occurred only after geckos reduced their activity, so we hypothesize that organ mass changes in response to (rather than in anticipation of) cold winter temperatures and the associated fasting. Degradation of visceral organs can maintain energy demands in times of low supply, and catabolism of the protein from these organs can serve as a source of both energy and water during brumation. These findings bring us closer to a mechanistic understanding of reptiles' physiological adaptations to environmental changes.