Land cover mediates predator effects on urban deer mouse abundance

High-altitude environments present a significant challenge to endotherms, where hypoxia can constrain aerobic metabolism but low temperatures amplify the metabolic demands for thermogenesis. Circulatory O2 delivery is essential for supporting aerobic metabolism, but it is unclear whether functional changes in cardiac mitochondria help high-altitude natives cope with cold hypoxia. We examined this issue in deer mice (Peromyscus maniculatus). Mice from populations native to high altitude and low altitude were born and raised in captivity, and adults from each population were acclimated to warm (25°C) normoxia or cold (5°C) hypoxia (∼12kPa O2). Mitochondrial respiration, reactive oxygen species (ROS) generation, metabolic and antioxidant enzyme activities, and oxidative stress markers were measured in left and right ventricle tissues. Respiratory capacities for oxidative phosphorylation and electron transport were similar between populations and unaffected by acclimation environment, as were activities of citrate synthase and cytochrome oxidase. However, lactate dehydrogenase activity increased in cold hypoxia and was greater in high-altitude mice than in low-altitude mice, probably to augment capacities for lactate oxidation. Mitochondrial ROS generation was lower in high-altitude mice, as measured both ex vivo in ventricle tissues and in vivo using MitoB. This was at least partly due to increased intra-mitochondrial ROS consumption, because population differences in mitochondrial ROS emission were abolished by auranofin (a thioredoxin reductase inhibitor). Consistent with these differences, high-altitude mice had less lipid peroxidation and protein carbonylation in ventricle tissue. These findings suggest that high-altitude adaptation has augmented mitochondrial ROS consumption pathways to support cardiac function in cold hypoxia. KEY POINTS: Deer mice native to high altitude somehow overcome the dual challenge of hypoxia, which constrains aerobic metabolism, and low temperatures, which increase demands for thermogenesis. We observed two key functional changes in cardiac mitochondria that probably help high-altitude mice overcome these challenges. High-altitude mice had increased lactate dehydrogenase activity in left and right ventricles to enhance the capacity for lactate oxidation. High-altitude mice exhibited lower mitochondrial reactive oxygen species (ROS) generation, probably due to enhanced intra-mitochondrial ROS consumption, and less oxidative stress. These results suggest that evolved changes in cardiac ROS management help overcome the challenges at high altitude.

Novel environments can induce fitness-reducing responses (i.e., maladaptive plasticity) that should be eliminated by selection via genetic compensation. Across an environmental gradient, genetic compensation may result in a cryptic form of trait variation known as countergradient variation, in which genetic changes oppose environmental effects on trait expression. We combined lab and field data to quantify maladaptive hematological responses to hypoxia and cold in deer mice (Peromyscus maniculatus) across their ∼4,000 m elevational range. In laboratory-raised mice native to low elevations, individuals increased their hemoglobin concentration and hematocrit in response to simulated high-elevation, a response that is maladaptive if unmitigated. In contrast, deer mice from high elevation increased hematocrit and hemoglobin to a lesser degree, consistent with genetic compensation. Unlike the predictions under complete genetic compensation, we observed a positive slope between hematological traits and elevation in the field, although this slope was lower than that observed in lowlanders in the lab. Our results suggest that deer mice have attenuated maladaptive hematological responses to high-elevation via genetic compensation that is incomplete, which has led to weak countergradient variation. We suggest this phenomenon is the result of a balance between positive selection for increased oxygen carrying capacity and antagonistic selection against elevated blood viscosity.

IntroductionThe white-footed deermouse Peromyscus leucopus is a primary reservoir for theagents of Lyme disease and other zoonoses in North America and manifests infection tolerance for thebacteria, protozoa, and viruses it hosts. In previous in vivo studies, P. leucopusand Mus musculus differed in the degree of sickness and profiles of biomarkers after exposure to a bacterial lipopolysaccharide, a TLR4 agonist. MethodsAs an approach for assessing immunity of mammals in nature and for longitudinal studies of colonyanimals in the laboratory, we evaluated primary dermal fibroblast cultures of P. leucopus and M. musculus in their short-term responses to a TLR2 agonist lipopeptide using bulk and single-cell RNA-seq. ResultsBy single-cell RNA-seq, cultures of both species comprised at least two types of fibroblasts,which were further differentiated in their responses to TLR agonists. With continued passage, themouse cell population lost viability, while the deermouse cell population spontaneously transformedinto a cell line stably maintained under standard conditions. Bulk RNA-seq revealed distinctiveprofiles for deermouse and mouse cells in arginine metabolism gene expression, high baselinetranscription of the antioxidant transcription factor Nfe2l2 (Nrf2) in deermouse fibroblasts, andthe transcription of the aging-associated cytokine interleukin-11 in agonist-treated mouse fibroblasts but not deermouse fibroblasts. In the cultures of both species, there was increased transcription of several types of endogenous retrovirus (ERV) and transposable elements (TEs) after exposure to the agonist. The transcribed ERV/TE sequences in M. musculus cells were generally longer in length and had greater potential for translation than sequences in treated P. leucopus cells. DiscussionThe results indicate the feasibility of this in vitro model for both laboratory- andfield-based studies, and that inherent differences between deer mice and mice incell-autonomous innate immune responses and ERV/TE activation can be demonstrated in dermal fibroblasts as well as the animals themselves.

In India, the sambardeer (Rusa unicolor), barking deer ( Muntiacus muntjak), spotted deer (Axis axis), and Indian mouse deer (Moschiola indica, Artiodactyla: Tragulidae) are widely distributed. Deer are often poached for bush meat, skin, antlers and other purposes. The mitochondrial genome is essential for species identification and understanding evolutionary relationships. Therefore, sequencing the complete mitochondrial genome of deer species is vital for rapid species identification and conservation efforts. This study aimed to sequence the complete mitochondrial genomes of spotted and sambar deer using Next-Generation Sequencing technology. The results revealed the size of the complete mitochondrial genome (mt-DNA) of spotted deer (16,351 bp) and sambar deer (16,476 bp), respectively. Each mt-DNA encompassed 37 genes viz 13 Protein coding genes (PCGs), 22 tRNA, 2 rRNA, and a control region. The comparative analysis of mitochondrial nucleotide composition between Axis and Rusa species revealed closely similar ratios of A + T and G + C. Two complementary approaches (Maximum Likelihood and Bayesian Inference) were used to understand the phylogenetic relationship among Cervidae. The results indicated that the A. axis consistently formed a well-supported clade with bootstrap values of 100 and posterior probabilities of 1.000, which were closely related to A. porcinus and formed a sister group. R. unicolor, both trees showed strong support for its placement within a clade that included Rusa species and R. unicolor subspecies. The divergence times estimation analysis exhibited that the A. axis and A. porcinus divergence occurred around 3.38 MYA, suggesting a split during the late Miocene to early Pliocene. The clade containing R. unicolor (including R. unicolor subspecies) diverged approximately 3.7 MYA. These results suggested a relatively recent divergence, indicating ongoing speciation events within this group. In summary, our findings provide a new perspective on understanding Axis and Rusa species, which will not only be beneficial for species conservation but also open up new possibilities for forensic analysis.Supplementary InformationThe online version contains supplementary material available at 10.1038/s41598-025-24310-2.

Animals have evolved behavioral variation to adapt to distinct environmental features. The expansion of neuron number is a potential neural mechanism underlying this behavioral adaptation. Corticospinal neurons (CSNs) are a classic example: an expansion in the corticospinal system in the primate lineage has been hypothesized to underlie their exceptional dexterity. However, the role of CSN number in behavior has been difficult to assess due to the large evolutionary distance between primates and less dexterous taxa with fewer CSNs. Here, we use deer mice (Peromyscus maniculatus) to overcome this challenge. We compared two closely related subspecies of deer mice: forest mice, which evolved dexterous climbing to support a semi-arboreal lifestyle, and prairie mice, which are less dexterous. We find that forest mice have about two-fold larger corticospinal tracts (CSTs) driven by an increase in CSN number in secondary motor and sensory cortical areas (M2 and S2). Furthermore, in a reach-to-grasp test of dexterity, forest mice display higher success and greater grasping flexibility, using multiple grasp types. In contrast, prairie mice use a stereotyped scooping motion, consistent with the idea that an increase in CSN number supports more dexterous movement. High-throughput neural recordings during this task revealed a difference in the timing of neural activity between forest and prairie mice in M2, but not in primary motor cortex (M1): in forest mice, the peak of activity was shifted towards the time of grasp. Forest mice also outperform their prairie counterparts on an ecologically relevant climbing task, where they spend more time upright crossing a thin rod, move faster, and right themselves more quickly when they fall, suggesting a general increase in motor dexterity not restricted to hand use. To assess whether the increase in CSN number contributes to observed behavioral adaptations, we generated forest-prairie F2 hybrid animals with shuffled genomes, neural features, and behavior. We find that the F2 hybrids with larger CSTs perform better on the rod crossing task, suggesting that expansion of the CS system likely supports the adaptive increase in climbing dexterity in forest mice. Together, our work establishes the forest-prairie deer mouse system as a novel model to investigate the role of neuron number expansion, and CSNs in particular, in dexterous movement.

Populations that colonize islands experience novel selective pressures, fluctuations in size, and changes to their connectivity. Owing to their unique geographic setting, islands can function as natural laboratories in which to examine the interactions between demographic history and natural selection replicated across isolated populations. We used whole genome sequences of wild-caught deer mice (Peromyscus maniculatus) from two islands (Saturna and Pender) and one mainland location (Maple Ridge) in the Gulf Islands region of coastal British Columbia to investigate two primary determinants of genome-wide diversity: chromosomal inversions and non-equilibrium demographic history. We found that segregating inversions produce characteristic, large-scale distortions in allele frequencies and linkage disequilibrium that make it possible to identify and characterize them from short-read sequence data. Patterns of variation within and between karyotypes indicate that six inversion polymorphisms have been maintained by a shared history of balancing selection in both island and mainland populations. Whereas the estimated timing of contemporary population splits is consistent with the isolation of island populations from each other following the Last Glacial Maximum, ancestral island and mainland lineages are inferred to have diverged much earlier. These aspects of demographic history suggest that shared inversions existed long ago in a common ancestor or spread via limited gene flow between ancestral island and mainland lineages. Our results raise the possibility that inversions segregating among Gulf Islands populations are on similar evolutionary trajectories, providing a contrast to previous findings in mainland P. maniculatus and contributing to the emerging portrait of inversion evolution in this species.

Abstract In rodents, different selective pressures influence behavioural, physiological and life-history strategies between sexes. Anisogamy and the reproductive cost hypothesis suggests that differences in gamete size and trade-offs in reproduction are driving mechanisms of sex-specific reproductive strategy. However, relationships between behaviour and energetic investment in income-breeding rodents are not fully explored. We investigated behavioural and physiological traits in two rodent species from Algonquin Provincial Park, Canada using two standardized behavioural assays and faecal glucocorticoid metabolites (FGMs) as a proxy for movement and energetic stress. We hypothesized that sex differences in reproductive investment throughout a single breeding season would influence behavioural and physiological traits. We predicted that males would be more explorative and less docile than females due to increased risks associated with mate acquisition. We also predicted that FGMs would be greater in females compared to males due to the increased investment in the development and care of young. In contrast to our hypothesis, we observed some differences in behaviour between sexes in the opposite direction. Male deer mice ( Peromyscus maniculatus ) were more docile (mean difference = 0.312, 95% CI = [−0.24; 0.87], ), and male red-backed voles ( Clethrionomys gapperi ) were less explorative (mean difference =-73.8 s, 95% CI = [−127.5; −19.029], ) than female counterparts. There was also a high degree of within-individual variation in FGMs in both species. Between-individual variation was only observed in red-backed voles (26.7%), however neither species had a significant relationship between sex and FGMs. Our findings reveal some relationships between behaviour and physiology in income-breeding rodents.

Gestational hypoxia reduces fetal growth and birth weight across mammals, including humans. Evolutionary adaptation to high-elevation hypoxia mitigates these negative effects, and identifying these protective mechanisms may offer insight into how environmental factors interact with gestational physiology to influence health outcomes. We know that gestational hypoxia modifies development of the placenta, which mediates maternal-fetal exchange, but little is known about how high-altitude adaptation interacts with this developmental plasticity to influence placental exchange capacity. We tested the hypothesis that hypoxia-dependent remodelling of the placental exchange surface is protective for fetal growth and thus will be exaggerated in highland-adapted individuals by using a model rodent system, the North American deer mouse. We acclimated lowland- and highland-ancestry deer mice to normoxia or hypoxia (12.3% O2) during gestation and found that lowland-ancestry deer mice expand their placenta and maternal blood spaces in the placenta in response to environmental hypoxia. Highland-ancestry deer mice produce even larger placentas and maternal blood spaces, suggesting that these hypoxia-driven responses may benefit fetal growth by increasing total exchange capacity. Notably, we also found that the fetal blood spaces in highland-ancestry placentas have increased perimeter (a proxy for surface area) per unit area occupied by blood. Similar changes to fetal vasculature have been observed in high-elevation-adapted human populations, which is suggestive of convergent adaptation. Our results demonstrate that the hypoxia-sensitive development of placental vasculature is remodelled by adaptation to environmental hypoxia and that some of these processes may be points for convergent adaptation across species despite distinct placental architectures. KEY POINTS: Evolutionary adaptation to high elevations provides protection against hypoxia-dependent fetal growth restriction. The placenta is a key determinant of fetal growth because it defines the total surface area available for nutrient and gas exchange between the gestational parent and offspring. We tested the hypothesis that evolutionary adaptation to high elevations protects fetal growth by increasing placental surface area for exchange using acclimation experiments in a model rodent system, the North American deer mouse. As we predicted, high-elevation ancestry increased the size of maternal blood spaces in the placenta, especially under gestational hypoxia; however, highland ancestry was also associated with narrower fetal blood spaces, which could increase exchange efficiency. The patterns observed in deer mice resemble developmental plasticity observed in placentas from humans with high-elevation ancestry, pointing to potential for convergent adaptation across species with distinct placental architectures.

Bacterial species within the mammalian gut microbiota exhibit considerable strain diversity associated with both geography and host genetic ancestry. However, because geography and host ancestry are typically confounded, disentangling their contributions to the diversification of gut bacterial strains has remained challenging. Here, we show through joint profiling of gut bacterial and mitochondrial genomes from wild-living populations of deer mice (Peromyscus maniculatus) sampled across the United States that isolation by distance (IBD) drives gut bacterial strain diversification independently of the effects of host ancestry. Analyses revealed significant IBD in 27 predominant gut bacterial species, including members of the Muribaculaceae and Lachnospiraceae, but limited evidence for co-inheritance of gut bacterial genomes with mitochondria during the diversification of extant mouse populations. Gut bacterial species capable of forming spores exhibited reduced IBD independently of phylogenetic history, indicating that adaptations facilitating bacterial dispersal can mitigate the geographic structuring of strain diversity. These results show that the diversification of gut bacterial strains within rodent species has been mediated by geographic separation of host populations rather than host genealogical divergence.

Populations that colonize islands experience novel selective pressures, fluctuations in size, and changes to their connectivity. Owing to their unique geographic setting, islands can function as natural laboratories in which to examine the interactions between demographic history and natural selection replicated across isolated populations. We used whole genome sequences of wild-caught deer mice (Peromyscus maniculatus) from two islands (Saturna and Pender) and one mainland location (Maple Ridge) in the Gulf Islands region of coastal British Columbia to investigate two primary determinants of genome-wide diversity: chromosomal inversions and non-equilibrium demographic history. We found that segregating inversions produce characteristic, large-scale distortions in allele frequencies and linkage disequilibrium that make it possible to identify and characterize them from short-read sequence data. Patterns of variation within and between karyotypes indicate that six inversion polymorphisms have been maintained by a shared history of balancing selection in both island and mainland populations. Whereas the estimated timing of contemporary population splits is consistent with the isolation of island populations from each other following the Last Glacial Maximum, ancestral island and mainland lineages are inferred to have diverged much earlier. These aspects of demographic history suggest that shared inversions existed long ago in a common ancestor or spread via limited gene flow between ancestral island and mainland lineages. Our results raise the possibility that inversions segregating among Gulf Islands populations are on similar evolutionary trajectories, providing a contrast to previous findings in mainland P. maniculatus and contributing to the emerging portrait of inversion evolution in this species.

BackgroundCryptosporidiosis is a leading cause of zoonotic illness. We aimed to describe cryptosporidiosis illnesses in Tennessee by species and molecular subtypes, and explore epidemiological risk factors.MethodsCryptosporidium is a reportable condition in Tennessee. Cases are investigated and molecular subtyping is performed. Collected data includes patient demographics, risk factors, laboratory results, and Cryptosporidium species and subtype. We described Tennessee residents with cryptosporidiosis during 2018–2023. To explore risk factors, we used binomial probabilities to compare exposure frequencies with the Foodborne Diseases Active Surveillance Network (FoodNet) Population Survey.ResultsDuring 2018–2023, Tennessee recorded 1174 cryptosporidiosis cases. Of those, 282 (24%) had species information and 214 (18%) had genotype information. Of 802 laboratory-confirmed cases without species information, 664 (83%) did not have a specimen submitted for molecular subtyping. Most frequently identified species were C. parvum (n = 183, 65%) and C. hominis (n = 60, 21%) with most frequently identified subtypes being C. parvum subtypes IIaA15G2R1 (n = 80) and IIaA15G2R2 (n = 15), and C. hominis subtype IfA12G1R5 (n = 15). C. felis (n = 8), C. ubiquitum (n = 5), C. meleagridis (n = 3), C. canis (n = 2), and C. deer mouse subtypes (n = 2) were also identified. Rates were higher for C. parvum in rural counties and C. hominis in urban counties. Persons with C. parvum infections more often reported contact with goats, cows, or sheep compared to the population (39% vs. 6%, P <.001). Persons with C. hominis infections more often reported contact with natural (22% vs. 9%, P =.003) and treated (32% vs. 12%, P <.001) water, and having contact with another person with diarrheal illness (28% vs. 15%, P =.013).ConclusionsMolecular cryptosporidiosis surveillance can facilitate more detailed understanding of cryptosporidiosis risk factors and prevention measures. To best use this tool, a greater proportion of specimens need to be submitted for molecular subtyping.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12879-025-11364-w.

Three distinct forms of Pneumocystis coexist in individuals of two species of deer mice (genus Peromyscus).

Sin Nombre virus (SNV) is the main causative agent of hantavirus cardiopulmonary syndrome (HCPS) in North America. SNV is transmitted via environmental biological aerosols (bioaerosols) produced by infected deer mice (Peromyscus maniculatus). It is similar to other viruses that have environmental transmission routes rather than a person-to-person transmission route, such as avian influenza (e.g., H5N1) and Lassa fever. Despite the lack of person-to-person transmission, these viruses cause a significant public health and economic burden. However, due to the lack of targeted pharmaceutical preventatives and therapeutics, the recommended approach to prevent SNV infections is to avoid locations that have a combination of low foot traffic, receive minimal natural sunlight, and where P. maniculatus may be found nesting. Consequently, gaining insight into the SNV bioaerosol decay profile is fundamental to the prevention of SNV infections. The Biological Aerosol Reaction Chamber (Bio-ARC) is a flow-through system designed to rapidly expose bioaerosols to environmental conditions (ozone, simulated solar radiation (SSR), humidity, and other gas phase species at stable temperatures) and determine the sensitivity of those particles to simulated ambient conditions. Using this system, we examined the bioaerosol stability of SNV. The virus was found to be susceptible to both simulated solar radiation and ozone under the tested conditions. Comparisons of decay between the virus aerosolized in residual media and in a mouse bedding matrix showed similar results. This study indicates that SNV aerosol particles are susceptible to inactivation by solar radiation and ozone, both of which could be implemented as effective control measures to prevent disease in locations where SNV is endemic.

Picture books have long been recognized as a valuable vehicle for language learning, offering the combination of visual and linguistic support, and despite the rise of digital media, they remain an essential resource for language learning. This study scrutinizes the relationship between verbal and visual texts in a picture book for meaning-making and explores the potential of a picture book for the teaching of English to young learners. This qualitative study uses two primary data sources: the Indonesian children’s picture book The Kind Mouse Deer and video-recorded teaching simulations from two elementary English teachers. The book was analyzed using the Multimodal Discourse Analysis (MDA) approach and the videos were analyzed using content analysis. The findings show that the book employs visual texts to repeat or complement the verbal elements. The complementarity of verbal and visual elements was found to be used by teachers to help young EFL learners understand the story in English. During the simulations, they also used a mix of Bahasa Indonesia and English, supplemented by facial expressions and gestures to convey meaning in terms of story plot and description of characters. Further research is needed to investigate classroom implementation, highlighting students’ engagement with picture books in developing their English proficiency.

Phylogenetics of Channel Island Deer Mice Based on the Cytochrome B Gene Sheds Light on Multiple Colonization Events and Supports Current Taxonomy

Leptospirosis is a global zoonotic disease affecting humans, wildlife, companion, and domestic animals. Incidental hosts can contract the disease directly or indirectly from asymptomatic reservoir hosts, most commonly small rodents. The Golden Syrian hamster is recognized as the dominant rodent model for acute leptospirosis because the animals are susceptible to many serovars and are used to maintain laboratory strains and test bacterin vaccine efficacy. However, hamsters are primarily used in survival-based studies, and investigations into host immune response and disease pathogenesis are limited. We found that Peromyscus leucopus white-footed deer mice are susceptible to acute leptospirosis, and thus might be an alternative rodent model. Furthermore, similar to hamsters, deer mice produce circulating foamy macrophages in response to Leptospira challenge. Deer mice exhibit differences in response to different serovars, clinical disease severity, kidney and liver lesions, and an overall sex effect, with male mice demonstrating more severe clinical signs and higher bacterial burden.

Island populations of small land vertebrates frequently exhibit insular gigantism, presenting with larger body sizes in comparison to mainland counterparts. While insular gigantism has been observed globally, the effects of biogeographic and ecological factors on body size in island systems are not well understood. Here, we examine the biogeographic and ecological associations of insular gigantism. Deer mice (Peromyscus maniculatus) were live trapped and body mass measured on six of the Gulf Islands and the nearby mainland of British Columbia, Canada. Biogeographic measures of land area and island distance from the mainland and the ecological measure of predator species richness were used in piecewise structural equation modelling to identify associations with insular gigantism. We found evidence of insular gigantism in the Gulf Islands system, with island mice having a larger mean body mass than mainland populations. Land area was positively associated with predator species richness, and predator species richness had a strong negative effect on deer mouse body mass, resulting in the observed pattern of insular gigantism. The concurrent analysis of biogeographic and ecological factors contributes to a better understanding of the evolution of insular gigantism in small vertebrates and its juxtaposition to the phenomenon of insular dwarfism of large vertebrates.

Education at the elementary school level plays a fundamental role in shaping students’ character and literacy skills during their golden age of growth. However, strengthening noble character and improving literacy, especially reading interest and comprehension of stories, still face challenges so that students do not feel bored. Facing this phenomenon, the synergy between Indonesia’s as a source of moral values and local wisdom, and digital comics as a visual medium that is popular and effective in attracting reading interest, offers great potential. The folktale “Mouse Deer, the Bear, and the Secret Forest” contains relevant moral messages, while digital comics can presnt it in an interactive and easily understandable format for students. This research aims to deeply examine the potential synergy between folktales (case study “Mouse Deer, Bear, and the Secret Forest” and digital comic learning as an effective stimulus in strengthening character education and improving literacy among elementary school students. Using a qualitative approach, this research will explore how the integration of these two media can be implemented and its impact on instilling character values through the moral messages in the story, as well as developing literacy skills through an engaging visual-verbal format for students. It is hoped that this learning model can be an innovative alternative solution in achieving the goals of character edutation and literacy in elementary schools.

The cold and hypoxic conditions at high altitude place high demands on the cardiovascular system to sustain circulatory O2 transport. High-altitude natives have evolved to overcome cold hypoxia, but the cardiovascular mechanisms involved remain poorly understood in most taxa. Here, we investigated the evolved changes in reflex control of cardiovascular function in deer mice (Peromyscus maniculatus) native to high altitude. High- and low-altitude populations of deer mice were each bred in captivity and then chronically acclimated to warm normoxia (25°C, ∼20 kPa O2) or cold hypoxia (5°C, 12 kPa O2) for 6-8 weeks. Cardiovascular function was measured in vivo using physiological telemeters, complemented by wire myography to examine vascular function ex vivo. High-altitude mice acclimated to cold hypoxia exhibited greater heart rates and were better able to maintain blood pressure in moderate and severe hypoxia, in association with less pronounced depression of metabolism and body temperature. High-altitude mice also exhibited greater baroreflex sensitivity than low-altitude mice across acclimation environments, as reflected by greater changes in heart rate and smaller changes in arterial blood pressure during pharmacological manipulations. Mesenteric arteries from each population exhibited similar ex vivo smooth muscle contractions in response to phenylephrine (α1-adrenoceptor agonist), and similar endothelium-dependent relaxation in response to acetylcholine, suggesting that evolved changes in the baroreflex arise from adjustments in autonomic control of the heart and/or other resistance vessels. These evolved changes in cardiovascular function and reflex control may be valuable for supporting high metabolic rates in the cold and hypoxic environment at high altitude.