Mammals are excellent biomonitors for pollutants such as trace elements; however, there is a lack of studies on this subject in wild mammals across Latin America. This review provides a comprehensive and updated overview of the current state and trends in mammalian toxicology, offering an integrative regional perspective. A systematic literature review was conducted, identifying and synthesizing data on date of publication, country of study, analyzed pollutants, taxonomic group and trophic guild involved, biological matrix used, analytical techniques, and sample origin. Publications show a constant increase in their number and diversity. However, research remains concentrated in high-biodiversity or polluted areas within large countries such as Brazil, Mexico, and Argentina, leading to significant geographical biases. At present, the most frequently analyzed elements have been Hg, Pb, and Cd, reflecting their relevance as environmental pollutants generated from extractive industries and fossil fuel combustion. Aquatic carnivores are highly susceptible to bioaccumulation, making the order Cetacea and the piscivorous trophic guild the most studied groups, underscoring their well-documented issue of mercury contamination in aquatic ecosystems. On the other hand, terrestrial mammals remain comparatively understudied. Due to their central role in metabolic pathways and detoxification of contaminants, liver and kidney have been the most analyzed matrices. Atomic absorption spectrometry has been the most frequent quantification technique, favored for its suitable cost-benefit balance. Future research should incorporate non-invasive techniques and reevaluate the importance of scientific collections, as they offer valuable historical baselines for ecotoxicological studies. We strongly recommend prioritizing further research in mammal species populations living in urban areas and mining regions, to better understand and mitigate the ecological impacts of metal pollution in these threatened ecosystems.
Phenotypic variation in bats reflects the combined influence of environmental and evolutionary factors. Body size often responds to thermal gradients (Bergmann’s rule), whereas cranial and mandibular morphology are often associated with evolutionary history and diet, which are further shaped by resource seasonality. Corynorhinus mexicanus, an endemic bat of Mexico’s temperate forests, was analyzed to assess if environmental factors, evolutionary history, and their interaction influence forearm size and cranial and mandibular shape. Linear mixed models were fitted using forearm measurements and principal components derived from environmental variables, incorporating previously documented intraspecific lineages. Models were compared under annual and monthly temperature variation, accounting for reproductive timing and sex-specific energetic investment. Cranial and mandibular variation were examined using a two-dimensional geometric morphometric protocol to assess the influence of lineage and environmental seasonality as a proxy for dietary composition. Forearm length did not differ between lineages in females but did in males, with those from the Sierra Madre Occidental lineage being smaller. In both sexes, body size followed Bergmann’s rule. Cranial differences between lineages were restricted to the lateral view of the braincase and the ventral view of the rostrum. Overall, cranial variation appeared to be primarily driven by evolutionary history, whereas forearm size reflected a combined influence of evolutionary and environmental factors. Maximum temperatures during the reproductive period influenced forearm length in males, while minimum temperatures affected females. Finally, we highlighted the importance of considering temporal extent and environmental resolution in eco-evolutionary studies.
Recent studies have demonstrated that the Andean sigmodontine rodent Abrothrix andina (Sigmodontinae, Abrotrichini) is neither widespread nor a senior synonym of several nominal taxa (i.e., dolichonyx, cinnamomea, jucundus, gossei, and polius) described from Argentina, Chile, and Peru since the 19th century. However, a comprehensive taxonomic and nomenclatural reassessment requires the examination of type material. Here, we address this by analyzing topotypic specimens collected from three Andean localities near Santiago de Chile (Chile), the type locality of A. andina. Cytochrome b sequences from these specimens cluster within Abrothrix olivacea. These results support treating Abrothrix andina (Philippi in Philippi & Landbeck, 1858) as a junior synonym of Abrothrix olivacea (Waterhouse, 1837). Additionally, the nominal form Abrothrix gossei (Thomas, 1920) warrants recognition as a distinct species of Abrothrix, sister to A. olivacea. Although this study appears to complete the taxonomic reassessment of A. andina, a remote possibility remains that its holotype, currently lost, represents a still-unsampled Andean highland population, now extinct or extremely rare due to climate change.
The Trypanosoma cruzi clade represents one of the most complex and ecologically diverse assemblages of mammalian trypanosomes. Although the group’s human pathogenic member T. cruzi is best known as the etiological agent of Chagas disease, its evolutionary origins remain debated. Two main hypotheses attempt to explain the diversification of the T. cruzi clade: the supercontinent hypothesis, which proposes an ancient co-diversification with South American marsupials, and the bat-seeding hypothesis, which suggests a more recent origin through host-switching from bat trypanosomes. Here, we combined parasite and host phylogenies with global-fit cophylogenetic analyses to evaluate whether mammalian diversification has influenced the evolutionary history of the T. cruzi clade. Using PACo and ParaFit, we detected a weak but statistically significant global correspondence between mammal and trypanosome phylogenies. This correspondence was primarily associated with bat-trypanosome relationships, whereas associations involving non-bat mammals showed limited phylogenetic concordance. Together, these findings suggest that mammalian diversification may have influenced trypanosome evolution across multiple evolutionary contexts and timescales.
Global biodiversity loss is accelerating, driven by multiple factors, including climate change. Protected areas are a cornerstone of conservation strategies; however, their effectiveness is often constrained by limited climate-resilience planning and taxonomic biases that often overlook ecologically important but non-charismatic groups, such as rodents. We analyzed rodent species richness in the Sierra Madre Oriental, Mexico, evaluating conservation effectiveness within protected areas (which cover 29% of the region) under climate change scenarios. Potential species richness for 85 rodent species was estimated using ensemble species distribution models under current conditions and future climate scenarios (RCP4.5 and RCP8.5) for projections to 2030, 2050, and 2070. Temporal trends in potential species richness were evaluated by Mann-Kendall trend test. Additional comparisons included bioclimatic corridors and functional groups (generalists and specialists). Results suggest that protected areas currently encompass all modeled rodent species in the Sierra Madre Oriental (excluding Dipodomys spectabilis, Geomys personatus and Sigmodon mascotensis), however, they do not fully overlap with areas of highest species richness, which are located in the southern Sierra Madre Oriental. Also, an overall decline in high-richness areas by 2070, particularly under the RCP8.5 scenario, where species losses in some protected areas could reach up to 35 species. Although generalist species exhibit relative stability, an overall decreasing trend in species richness is expected in most protected areas, with significant compositional changes projected for specialist species. Notably, bioclimatic corridors were found to host species currently absent from protected areas and to support the same proportion of species classified as at risk. Implementing climate-smart strategies, such as establishing and reinforcing bioclimatic corridors to improve connectivity, is recommended to mitigate biodiversity loss and enhance conservation resilience in the Sierra Madre Oriental.
Tequila or magueyero bats (i.e., the genus Leptonycteris) play a very important role as pollinators in most Mexican and southern US ecosystems, which is why they have recently been given greater attention. Female members of Leptonycteris nivalis populations exhibit migratory behavior associated with nectar consumption and pollination of ecologically important Agave species in Mexico, and with their reproductive events. Such migratory behavior makes them susceptible to the consequences of climate change. In this study, we explored how the distribution and the adaptive potential of L. nivalis may be affected by possible global warming scenarios. We obtained samples from six locations across the distribution of L. nivalis. Using parallel massive-sequencing techniques, we obtained 13,112 filtered SNPs (single-nucleotide polymorphisms). Just two of these SNPs were associated with a climatic variable, but we detected associations between heterozygosity and climate change in two sites. Models of future distribution under climate change indicated a reduction in climatic stable areas favorable to this bat’s presence. Our results will support the implementation of protection strategies for bats and the ecosystems they inhabit, which are the most representative in Mexico. Also, it is very important to maintain connectivity between the localities and refuges occupied by the magueyero bat, as well as to maintain populations within areas of greatest thermodynamic stability, where the most favorable conditions for bat presence are predicted. Based on our analysis, we believe the species has the potential to withstand changes in temperature and precipitation patterns, which may support its conservation.
Chorotypes are groups of species that share a similar distribution within a study area. Their identification depends on the geographic units and the taxa analyzed. For the terrestrial Mexican mammals, identification of chorotypes has not been explored yet. Our objectives are (1) to identify chorotypes for the species of terrestrial Mexican mammals using two different datasets (Map of Life [MOL] and International Union for Conservation of Nature [IUCN]), (2) to compare the results using biogeographic provinces, and (3) to discuss the relevance of the chorotypes for ecological regionalization. More than 400 species of mammals were used to identify 33 chorotypes in four different analyses: MOL and IUCN with the whole Chihuahuan province, and MOL and IUCN splitting it into Northern and Southern Chihuahuan. For the 33 chorotypes, one was recovered in all analyses, one was shared by three analyses, seven were shared by two, and 24 were unique for one. We demonstrate the importance of the use of different datasets of geographic distribution of mammals, as well as pre-defined units of analyses, and their influence on the results of a chorotype analysis. Most of the chorotypes identified the mixture of Nearctic and Neotropical biotas in the Mexican territory, but more interestingly, the affinity of ecological patterns of lowland and highland areas.
Sigmodontines (Rodentia: Cricetidae), the most diverse extant radiation of Neotropical rodents (91 genera, 507 species), include only a small fraction of taxa exhibiting morphological and ecological specializations associated with a semiaquatic mode of life. These specializations are unevenly distributed within the subfamily, being largely restricted to Ichthyomyini and to a limited number of mostly large-bodied species within Oryzomyini. Here, we examine the taxonomic, phylogenetic, and geographic distribution of semiaquatic sigmodontines within a historical framework. Phylogenetic analyses and ancestral-state reconstructions indicate that amphibious habits evolved convergently in these two lineages from a terrestrial ancestor. The resulting patterns reveal a marked phylogenetic clustering and a pronounced geographic asymmetry, with semiaquatic forms largely absent from extensive lowland and southern freshwater systems. These patterns are consistent with a scenario in which ecological constraints and historical processes jointly shaped the current distribution of semiaquatic taxa. In particular, predation pressure within continental freshwater environments may have limited successful colonization by small mammals, while occupation of predator-poor habitats may have facilitated localized diversification. In addition, paleontological and biogeographic evidence suggests that semiaquatic sigmodontines were more diverse and geographically widespread in the past, with subsequent reductions in diversity. In this context, the contemporary scarcity of semiaquatic sigmodontine rodents can be interpreted as consistent with a combination of ecological filtering associated with freshwater habitats and historical reductions in diversity through extinction. Comparison with murid rodents suggests that continental freshwater environments may represent a challenging ecological domain for small muroids more broadly.
Genetic information represents an important dimension of biodiversity beyond species or ecosystems, and genetic sequences are essential for all themes in biodiversity research. Genetic data are not exempt from gaps and biases, particularly in the tropics. Even for well-studied groups like mammals, many species remain understudied, and the completeness of underlying metadata for existing sequences is largely unknown. We quantified genetic data availability for 548 species of Mexican land mammals in the NCBI Nucleotide database. We evaluated the status and completeness of metadata regarding dates, locations, and voucher information associated with sequences, noting endemic species. We located genetic data for 90% of species, including sequences for 77% of Mexican endemics. Availability was skewed, with most species having very few sequences. In our sample, 316 of 496 species (64%) had at least one record with location, date, and voucher information, yet metadata quality was highly variable, and most records lacked key spatiotemporal details. We identified highly biased coverage in nucleotide sequence availability and relatively poor metadata quality for Mexican land mammals. Despite decades of sampling, decreasing costs, and advances in museomics and sequencing, major gaps and disparities remain. At a time of open science and open data, we insist on a research culture where sampling, sequencing, and adequate metadata recording happen concurrently.
Los Mármoles National Park (state of Hidalgo) is one of the oldest protected natural areas in Mexico. Due to its geographical location, it contains both Nearctic and Neotropical species, although the mammal species inhabiting the area have been poorly studied. This information is required to establish conservation actions in the area, which is heavily affected by mining and illegal logging. We sampled mammals across nine non-consecutive years (2013-2018, 2021-2022, and 2025) and searched records in literature to produce the first updated checklist for Los Mármoles. We conducted 62 field trips of varying lengths (1 to 12 days). We used pitfall and Sherman traps, mist nets, camera traps, and scent stations to trap mammals. In addition, we conducted interviews with local people and obtained incidental records (e.g., observations, dead animals, tracks, excrement). We recorded 85 native mammal species, including 10 protected species and 15 endemic species to Mexico. Chiroptera, Carnivora, and Rodentia were the most well-represented groups with the highest number of species in this study, highlighting the presence of large carnivores, such as Ursus americanus and Panthera onca. We documented domestic and feral animals within the protected area. Although Los Mármoles is home to more than 50% of the state’s mammal species, it faces serious threats, such as mining, feral dogs, and livestock.
Genomics is the study of the genome’s structure, function, evolution and mapping, including gene interactions with each other and with the environment. Genomics is a tool that allows studying fine evolutionary processes in non-model mammals. These approximations provide valuable information regarding levels and distribution patterns of neutral and adaptive genetic variation. Additionally, genomics allows studying organisms responses to environmental changes and anthropogenic activities. This information has high potential applications in the development of management and conservation plans for threatened mammalian populations and species. The present work provides information so that the reader can understand and outline a mammal conservation genomics project. This is an introductory guide for the use of genomics in the study of mammals, with emphasis in the link between genomics and conservation biology. This guide explains some general aspects of the genomics approximation that allow studying mammals such as sequencing methodologies, reduced representation sequencing, mitogenomes, whole genome sequencing, low coverage whole genome sequencing, metagenomics and transcriptomics; including some examples of their applications in conservation. We conclude this document with some challenges and perspectives for the application of mammal conservation genomics.
The structural characteristics of dorsal guard hair were analyzed in twelve cricetid rodent species, including eleven peromyscine and one sigmodontine species, using optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Hairs were collected from the dorsal region of adult specimens, prepared according to standard protocols, and examined to describe cuticular and medullary morphology. Optical microscopy revealed irregular mosaic-scale patterns with interspecific variation in density and contour. SEM confirmed diagnostic differences in scale size and arrangement, while TEM revealed variation in internal medullary organization. The combined use of these techniques provided morphological criteria useful for taxonomic assessment, particularly at higher taxonomic levels and established a comparative methodological framework for mammalogical studies. Our findings highlight the value of multitechnique hair analysis for taxonomic identification and for understanding structural adaptations in Neotropical rodents.
Elevation is a natural gradient that shapes wildlife and vegetation communities. Therefore, spatial, climatic and ecological hypotheses have been proposed to describe the diversity of rodents in the altitudinal gradient. Our objective was to describe the biological diversity of rodents at three elevations in relation to microhabitat characteristics and seasonality. We captured rodents using Sherman traps in three altitudinal zones (1600, 1800, 2000 m.a.s.l.) during the dry and rainy season. We measured five microhabitat characteristics at each elevation. We compared the species diversity using coverage-based rarefaction and extrapolation curves and the composition of the rodent’s community using the similarity indices of Jaccard and Bray – Curtis. In addition, we identify the species that contributed most to the differences in the community. Through Generalized Linear Models (GLM) we evaluate 1) the rodent occurrence by elevation, seasonality and microhabitat characteristics and 2) the variation of microhabitat characteristics by elevation and seasonality. In 2100 night-trap effort we captured 200 individuals of nine species. The most abundant species was Peromyscus nudipes. We found that the species diversity decreases with elevation and in the dry season. In terms of species composition, the low elevation between seasons and the high elevation between seasons were more similar. However, when we analyze the abundance, the 2000 m elevation were more similar between seasons. Rodent occurrence depends on the elevation. Finally, the microhabitat characteristics vary by elevation and seasonality. In conclusion, at Cloudbridge Nature Reserve the elevation influences the diversity and the presence of rodents by changing the microhabitat characteristics. Therefore, sites with microhabitat characteristics that could provide protection against predators and potential food sources harbor more rodent diversity.
The Mayan small-eared shrew, Cryptotis mayensis, is endemic to the Yucatán Peninsula, with records from México, Belize, and Guatemala. For half a century, skull fragments from dozens of individuals found in pellets of the barn owl (Tyto furcata) in Guerrero, Mexico, previously identified as the Mayan shrew, have intrigued taxonomists and biogeographers. A previous robust analysis of current and fossil C. mayensis dentary samples, including those from Guerrero, showed a high morphometric similarity between them. Given that these owl pellet remains are located 1,000 km from the known distribution of C. mayensis in the Yucatán Peninsula, this has raised the hypothesis that they are not an isolated population of C. mayensis but rather an as-yet-undescribed species. By integrating new specimens of C. mayensis from the Yucatán Península and Guerrero, as well as Cryptotis lacandonensis, the sister species of C. mayensis, we reanalyzed the morphological attributes. In addition, we used paleodistribution estimates to investigate the possible isolation of the records previously referred to as C. mayensis in Guerrero, Mexico. Multivariate analyses of morphological data from the cranium and dentary revealed high similarity in size among the three samples analyzed, especially between C. mayensis sensu stricto and Cryptotis from Guerrero. Paleodistribution models suggest that the population of Guerrero has remained in long-term isolation from the populations of the Yucatan Peninsula due to a very large area with unsuitable conditions for the connectivity of the shrew population during the last glacial-interglacial cycle. It is possible that the Guerrero population is an independent lineage, despite its morphological similarity to C. mayensis sensu stricto; however, genetic evidence to confirm this is essential.
Museum genomics (museomics) provide powerful tools for detecting cryptic diversity in natural history collections, including previously undetected invasions. We analyzed genomic and morphological data from 75 Peromyscus specimens collected during the Channel Islands Biological Survey (1939-1941), a series of expeditions on the California Channel Islands spearheaded by the Natural History Museum of Los Angeles County (LACM). Most of these specimens were confirmed as native Channel Island deer mice (P. gambelii subspp.), but two specimens from San Clemente Island (SCL) were re-identified as P. truei, a species never reported before on the Channel Islands. Using study skins, complete mitogenomes, and low coverage whole-genome data, we confirmed these identifications, and our phylogenetic analyses determined that these P. truei individuals are closely related to California mainland populations. We also placed these species within the subfamily Neotominae, including the first mitogenome of a native Channel Island deer mouse. Additional morphological data reveal several more likely P. truei specimens, indicating the existence of a substantial populations of this species in 1939. Combined with the presence of other non-native rodents on San Clemente Island (Reithrodontomys megalotis and Microtus californicus), these findings suggest a possible co-introduction from San Diego County during the 1930s via hay shipments. Our results have important implications for conservation management on San Clemente Island, and potentially Santa Rosa Island, where some specimens appear phenotypically inconsistent with P. gambelii. This study highlights the value of molecular tools for reassessing historic collections, especially in dynamic systems subject to high levels of anthropogenic modification.
The genus Habromys includes seven species of rodents restricted to Mesoamerican cloud forests across the mountain systems of central and eastern Mexico and northern Central America. Previous studies have suggested that diversification within the genus largely shaped by vicariant scenarios in which range expansion was followed by isolation driven by habitat fragmentation. However, these hypotheses have not been formally evaluated within a time-calibrated framework using explicit model-based approaches. Here, we reconstructed the biogeographic history of Habromys using a time-calibrated phylogeny based on mitochondrial genes, previously used in published studies, and evaluated alternative parametric biogeographic models implemented in BioGeoBEARS. The DEC+j was the best-supported model explaining geographic range evolution, indicating that founder-event speciation and within-area cladogenesis (narrow and subset sympatry) were the most frequent processes shaping diversification, whereas vicariance and anagenetic dispersal/extinction were inferred as comparatively uncommon. Divergence-time estimates suggest that crown diversification in Habromys began during the Pliocene, whereas most interspecific divergences occurred during the middle Pleistocene. These patterns are consistent with a biogeographic history driven by climatic oscillations that periodically increased connectivity among cloud forest habitats and later promoted isolation in montane regions. Overall, our results support a scenario in which repeated colonization and isolation events associated with Pliocene–Pleistocene climatic fluctuations played a greater role than vicariant processes linked to mountain building.
Among the most common animal lifestyles, parasitism stands out, often occurring in groups that also include free-living organisms. Among metazoans, helminths and arthropods include a large number of parasitic species. The objective of the present study was to compile, update and list for the first time all nominal species of metazoans that infect and infest wild rodents, analyzing their geographic distribution, defining the state of the art, and suggesting possible avenues of research that will allow us to complete the knowledge of the group. A total of 3,909 records of metazoan parasites of 204 rodent species were obtained from the 32 states of Mexico. Estado de México (Mexico) and Oaxaca were the states with the greatest parasite richness. At a national level, this richness is composed of 70 nominal species of helminths, 204 of mites, 40 of anoplurans, 67 of chewing lice, and 136 species of fleas.
Well resolved phylogenetic relationships are fundamental to understanding species’ evolutionary history, but inferring robust phylogenies can be challenging. The mitochondrial genome has resulted a valuable resource to achieve higher phylogenetic resolution and support. The Commissarisis’s long-tongued bat (Glossophaga commissarisi) is a widely distributed nectar-feeding bat in the Americas, ranging from Mexico to Colombia and Peru. In this study, we sequenced and assembled the complete mitochondrial genome of the species to characterize its genomic structure, codon usage, and patterns of selection; and to determine its phylogenetic position within Phyllostomidae. We confirmed its phylogenetic position within the genus Glossophaga and the family Phyllostomidae. The mitogenome was a circular molecule with a total length of 16,648 bp, containing 13 protein-coding genes (PCGs), two ribosomal genes, 22 transfer RNA genes, and one D-loop or control region (CR). The overall nucleotide composition was A = 32.18%, T = 29.63%, C = 23.97%, and G = 14.22%, with A + T content = 61.81% and G + C content of 38.19%. The phylogenetic tree reconstructed using the 13 PCGs included 61 taxa and recovered G. commissarisi as a sister species of G. leachii and a fully-supported clade (bv = 100) containing the genus Glossophaga. Our study provides a crucial genomic resource for the study of these bats and demonstrates the utility of complete mitogenomes in achieving well-resolved phylogenies for rapidly diversifying mammalian groups.
