Wild Rodents Research Articles

Detection of divergent Orthohantavirus tulaense provides insight into wide host range and viral evolutionary patterns

Orthohantavirus tulaense (TULV) is a member of the orthohantavirus genus and distributed in Europe and Asia. To shed light on TULV epidemiology and evolution, we trapped wild rodents from eastern Turkiye and found 15 TULV positive rodents. Sequencing and phylogenetic analyses confirmed the presence of diverse TULV strains. Global phylogenetic characterization suggested 5 distinct TULV lineages. Global phylogeographic reconstruction estimated different rooting times for each three segments, a potential ancestor location in Eastern Black Sea region, and strongly supported phylogeographic structure with 11 clusters. Dispersal velocity of TULV was estimated to be much faster than some other orthohantaviruses. Eastern Black Sea seemed to have lineages evolving faster and genetically closer to proto-Tula virus. Host switching estimates suggested potential switching events from Microtus arvalis to M. obscurus to M. irani with host-dependent sub-clustering within geographic clusters and suggested substantial evidence for no clear virus jumps from M. arvalis to M. irani.

Prolactin locally mediates follicular atresia in hyperprolactinemic vizcachas (Rodentia, Chinchillidae)

Infertility in hyperprolactinemic females is attributed to the dysregulation of GnRH release, subsequently affecting gonadotropin levels, and ultimately leading to anovulation. However, in addition to the hypothalamus, prolactin receptor (PRLR) is expressed in ovaries as well, suggesting potential local effects of PRL in cases of hyperprolactinemia. We have developed an experimental model of sulpiride (SPD)-induced hyperprolactinemia using a wild rodent, the plains vizcacha, and studied the implications of pharmacological PRL levels on folliculogenesis and steroid production. Ovaries of SPD females showed a striking number of atretic follicles along with a reduction in the collective number of viable follicles leading to a higher atretic/viable follicle ratio compared to that of control females (CTL) (P < 0.05). In terms of sensitivity to the hormonal environment, SPD ovaries substantially changed their potential responsiveness to pituitary PRL, as evidenced by the three-fold increase in PRLR expression alongside heightened expression of both gonadotropic receptors in comparison to CTL ovaries (P < 0.05). Circulating estradiol (E2) values doubled post-treatment in the SPD females, which also showed higher expressions of aromatase and 17β-hydroxysteroid dehydrogenase, along with both E2 receptors, ERα and ERβ than the CTL group (P < 0.05). Our findings strongly suggest that hyperprolactinemia-dependent dysregulation of ovarian function can be explained at least partially, by PRL direct actions facilitated by the heightened expression of PRLR in follicles and corpora lutea. Possibly these PRL actions synergize with those triggered by gonadotropic hormones ultimately leading to alteration of the steroidogenic pathway, folliculogenesis disruption and increased atresia.

Historical Assessment and Mapping of Human Plague, Kazakhstan, 1926-2003.

Understanding Kazakhstan's plague history is crucial for early warning and effective health disaster management. We used descriptive-analytical methods to analyze spatial data for human cases in natural plague foci in Kazakhstan during 1926-2003. The findings revealed 565 human cases across 82 outbreaks in Almaty (32.22%), Aktobe (1.59%), Atyrau (4.42%), Mangystau (21.24%), and Kyzylorda (40.53%) oblasts. Before antibiotic drugs were introduced in 1947-1948, major plague outbreaks occurred in 1926, 1929, 1945, 1947, and 1948, constituting 80.7% of human transmission. Plague spread through flea bites, camel handling, wild animal contact, aerosol transmissions, and rodent bites. Patients were up to 86 years of age; 49.9% were male and 50.1% female. Pulmonary cases were reported most frequently (72.4%), and person-to-person infection occurred at an incidence rate of 0.29 cases/10,000 population. Risk increased with human expansion into natural plague foci areas. Swift diagnosis and treatment are essential for curbing plague outbreaks in Kazakhstan.

Research on palatability of bait for targeted control of Brandt's vole (Lasiopodomys brandtii) in typical steppes

Chemical control is still the primary means of controlling wild rodent pests in China's grasslands; however current rodenticides are broad-spectrum and pose a risk to several other grassland ecosystems. Improving the precision of grassland rodent pest control and reducing collateral damage to non-target animals is an urgent problem. One solution to this problem is to ensure that bait choices are preferred by specific rodent. However, most studies on the development of rodenticides have neglected bait choice. We focused on Brandt's voles (Lasiopodomys brandtii), the dominant rodent species in the typical steppes of China, in this study. By measuring the percentage of feeding amount (PFA) different baits in a cafeteria setting, we sought to test the palatability of different candidate baits. We found that one of our blend baits was as popular as the wheat bait among Brandt's voles under laboratory conditions. However, our blended bait was preferred to the wheat bait when rodenticide was added. Non-target animals Columba livia, Gallus domesticus, Ovis aries, and sympatric non-target rodents feed less on blended bait than on wheat. We also used field trials to test whether baits were removed by Brandt's voles or PFA of partially consumed baits. In the wild, the removal time and PFA of Brandt's voles for the rodenticide + blend bait were better than those for the rodenticide + wheat bait. Mixing the wheat baits with bromadiolone rodenticide made poisoned baits less attractive to prey species than unpoisoned baits; however, Brandt’s voles were more likely to take the tainted baits than the unpoisoned baits when bromadiolone was added to the blends. Our results suggested that blend bait with 80 % Allium polyrhizum+ 20 % Stipa krylovii was highly palatable to Brandt's voles, did not become less palatable when poisoned with rodenticide, and was less likely to be eaten by non-target species including Columba livia, Gallus domesticus, Cricetulus barabensis, Phodopus campbelli and Ovis aries. Thus, blend bait has the potential to improve the pest management of Brandt's voles in China.

First report of Hepatozoon and Lankesterella spp. infections in wild rodents from Pakistan, and their potential impact on blood parameters and oxidative stress markers in vital organs.

Pakistan is home to a rich rodent fauna, yet no investigations have been conducted on the presence of Haemogregarines in these animals, leaving their epidemiology and genetic diversity in this subtropical region unexplored. In this study, blood samples from four wild rodent species, Rattus (R.) rattus (n = 122), Mus (M.) musculus (n = 64), Rattus norvegicus (n = 57), and Dryomys nitedula (n = 1), were collected between May 2022 and July 2023 from three districts in Punjab and three in Khyber Pakhtunkhwa. PCR targeting a fragment of 600 base pairs from the 18S rDNA gene revealed a 2.86% (7/244) prevalence of Haemogregarines in the rodents. DNA sequencing and BLAST analysis confirmed the presence of Hepatozoon spp. and Lankesterella spp. in the blood samples. Phylogenetic analysis indicated genetic diversity in the Pakistani sequences, which clustered with sequences found in reptiles, amphibians, birds, and mammals from various countries. The prevalence of the parasite varied among rodent species, with R. rattus showing the highest infection rate, followed by R. norvegicus and M. musculus. Female rodents were more frequently infected than males. Infected R. rattus exhibited significant disruptions in white blood cells, red blood cells, and platelet counts. Oxidative stress markers indicated elevated superoxide dismutase in the kidney, catalase in the heart, and malondialdehyde in the liver and lungs of infected rodents compared to uninfected ones. This study is an important contribution towards science as it the first report of Haemogregarines and Lankesterella spp. infections among Pakistani rodents.

Seasonal shifts and land-use impact: unveiling the gut microbiomes of bank voles (Myodes glareolus) and common voles (Microtus arvalis).

Gut microbial diversity influences the health and vitality of the host, yet it is itself affected by internal and external factors, including land-use. The impact of land-use practices on wild rodents' gut microbiomes remains understudied, despite their abundance and potential as reservoirs for zoonotic pathogens. We examined the bacterial and fungal gut microbiomes of bank voles (Myodes glareolus) and common voles (Microtus arvalis) across grassland and forest habitats with varying land-use intensities and types. We collected rodents seasonally and used 16S rRNA and ITS amplicon sequencing for microbe identification. We found significant differences in alpha and beta diversities between the species, with M. arvalis exhibiting higher diversity. Seasonality emerged as a prominent factor influencing microbial diversity, with significant variations between sampling months. While land-use affects the gut microbiome, its impact is subordinate to seasonal variations. Differential abundance analysis underscores the dynamic nature of microbial composition, with seasonal changes playing a predominant role. Overall, our findings highlight the significant influence of seasonality on gut microbiome diversity and composition in wild rodents, reflecting dietary shifts associated with seasonal changes. Understanding the interplay between environmental factors and microbial communities in wild rodents enahnces our knowledge of ecosystem health and resilience, warranting further investigation.

Insights into tail-belting by wild mice encourages fresh perspectives on physiological mechanisms that safeguard mammal tissues from freezing

We investigated tail-belting (TB), the newly-discovered freeze avoidance behavior among wild rodents. When temperatures dropped to -6 °C, wild mice (Apodemus agrarius and Apodemus flavicollis) were observed curling their tails inward and positioning it on the back. A literature search suggested TB had never been documented, presumably because rodents, especially in the laboratory, are seldomly assayed under cold stress. Due to the infrequent occurrence of the behavior, we used infrared and thermal cameras to confirm observations. We also collected tail-skin samples to investigate whether any physiological mechanisms might co-occur with TB. If such mechanisms were found, they could inform wider debate involving freeze protection among mammals, and could potentially lead to understanding mammal susceptibility or resilience to sudden temperature changes such as those associated with climate change. Lastly, we scored behaviors by bank voles (Myodes glareolus) which unexpectedly visited chambers. Across four winters, we observed TB in both Apodemus species during subzero conditions, but bank voles never performed the behavior. We also confirmed that TB occurs as an adaptive reflex which warms the tail. From tissue samples, we found that free amino acids, peptides, and glycoproteins were significantly higher during cold-stress. Thus, TB may have been accompanied by the expression of cold-protective proteins which ostensibly enable the peripheral body parts of mammals to survive temperatures well below 0 °C. These findings should inspire new dialogue regarding the role of lipids in tissues of peripheral organs in mammals. By extension, our findings may lead to the discovery of a putative cryoprotection mechanism among mammals.

The Accessory Olfactory Bulb in Arvicola scherman: A Neuroanatomical Study in a Subterranean Mammal.

The accessory olfactory bulb (AOB) processes chemical signals crucial for species-specific socio-sexual behaviors. There is limited information about the AOB of wild rodents, and this study aims to characterize the neurochemical organization of the AOB in the fossorial water vole (Arvicola scherman), a subterranean Cricetidae rodent. We employed histological, immunohistochemical, and lectin-histochemical techniques. The AOB of these voles exhibits a distinct laminar organization, with prominent mitral cells and a dense population of periglomerular cells. Lectin histochemistry and G-protein immunohistochemistry confirmed the existence of an antero-posterior zonation. Immunohistochemical analysis demonstrated significant expression of PGP 9.5, suggesting its involvement in maintaining neuronal activity within the AOB. In contrast, the absence of SMI-32 labelling in the AOB, compared to its strong expression in the main olfactory bulb, highlights functional distinctions between these two olfactory subsystems. Calcium-binding proteins allowed the characterization of atypical sub-bulbar nuclei topographically related to the AOB. All these features suggest that the AOB of Arvicola scherman is adapted for enhanced processing of chemosensory signals, which may play a pivotal role in its subterranean lifestyle. Our results provide a foundation for future studies exploring the implications of these adaptations, including potential improvements in the management of these vole populations.

Hematophagous Ectoparasites1 of Wild and Synanthropic Rodents in Yucatan, Mexico

Hematophagous Ectoparasites1 of Wild and Synanthropic Rodents in Yucatan, Mexico

Application of a Sensitive Capture Sequencing Approach to Reservoir Surveillance Detects Novel Viruses in Zambian Wild Rodents.

We utilized a pan-viral capture sequencing assay, VirCapSeq-VERT, to assess viral diversity in rodents from the Eastern Province of Zambia as a model for pre-pandemic viral reservoir surveillance. We report rodent adeno-, parvo-, paramyxo-, and picornaviruses that represent novel species or isolates, including murine adenovirus 4, two additional species in the genus Chaphamaparvovirus, two paramyxoviruses distantly related to unclassified viruses in the genus Jeilongvirus, and the first Aichivirus A sequence identified from rodents in Africa. Our results emphasize the importance of rodents as a reservoir for potential zoonotic viruses.

A panoramic view of the molecular epidemiology, evolution, and cross-species transmission of rosaviruses

Rosavirus is a newly discovered member of the family Picornaviridae that was initially detected in wild rodents and subsequently in children with diarrhoea. Nevertheless, there is a significant gap in our understanding of the geographical distribution, phylogenetic relationships, evolutionary patterns, and transmission of rosaviruses. To address these issues, we analysed 434 rodents and shrews from five different species that were collected in southern China. Using PCR screening of faecal samples, we detected rosaviruses in Norway rats (Rattus norvegicus) and identified two previously undocumented host species: tanezumi rats (Rattus tanezumi) and Asian house shrews (Suncus murinus). Rosaviruses were particularly common in these animals, with an overall prevalence rate of 32.49% (141/434). For genetic and evolutionary analyses, we selected six representative positive samples to amplify the complete genomes of rosaviruses. Bayesian phylogenetic analysis suggested that our sequences clustered within the genus Rosavirus, where genotype B sequences are the closest relatives. The elevated nonsynonymous-to-synonymous ratios observed in rosavirus B may be attributed to relaxed selection pressures driven by virus spillover events. On the basis of the available data, it is hypothesized that the genus Rosavirus may have originated from Norway rats around the year 1339. In summary, these findings provide valuable insights into the complex evolutionary history of rosaviruses and underscore the urgent need for ongoing surveillance of this virus.

Comprehensive Surveillance of Severe Fever with Thrombocytopenia Syndrome Virus in Patients with Acute Febrile Illness, Wild Rodents, and Trombiculid Larval Mites, Thailand.

Infection with severe fever with thrombocytopenia syndrome (Bandavirus dabieense) virus poses a substantial public health threat because of its high mortality rates and severe complications. The virus is prevalent in Asia, although data from Thailand are scarce. Our study confirmed the virus in 1.6% of acute febrile illness patients and specific antibodies in 3% of archived samples since 2015 in Thailand. Nationwide zoonotic surveillance identified the virus in 8 rodent species and 4 chigger genera. Our findings underscore the importance of raising awareness among healthcare providers and the general public about the symptoms, risks, and prevention strategies associated with severe fever with thrombocytopenia syndrome virus infection. Ongoing surveillance of the virus in human and animal populations is essential for monitoring its prevalence, distribution, and potential for emergence.

Brucella microti and Rodent-Borne Brucellosis: A Neglected Public Health Threat.

Brucellosis is one of the most important zoonoses worldwide, primarily affecting livestock but also posing a serious threat to public health. The major Brucella species are known to cause a feverish disease in humans with various clinical signs. These classical Brucella species are (re-)emerging, but also novel strains and species, some of them transmitted from rodents, can be associated with human infections. As a result of our review on rodent-borne brucellosis, we emphasise the need for more comprehensive surveillance of Brucella and especially Brucella microti in rodent populations and call for further research targeting the ecological persistence of rodent-associated Brucella species in the environment, their epizootic role in wild rodents and their virulence and pathogenicity for wildlife.

Field tests reveal acoustic variation of call types in a subterranean rodent, the Northern Mole Vole Ellobius talpinus

Abstract This study investigates acoustic variation of human-audible sonic (below 20 kHz) and human-inaudible ultrasonic (above 20 kHz) calls in a wild subterranean rodent, the Northern Mole Vole (Ellobius talpinus), under 3 call-eliciting tests conducted during captures for 1 day. The Contact-in-Tunnel Test modeled contacts of 2 individuals during digging earth in a burrow tunnel. The Restraint Test modeled restraint of an animal by a surrogate predator (human hand). The Release-to-Burrow Test modeled acoustic communication of many family members returned to their home burrow after their isolation for about 8 h, from morning to evening. We described 8 call types: 3 sonic, 3 ultrasonic, and 2 expanding from sonic to ultrasonic range of frequencies; 6 call types were described for the first time for this species. No relationship was found between acoustic parameters and proxies of body size (body mass and the width of 2 upper incisors). No sex differences were found in body size or the acoustic parameters. Different call types prevailed in different tests: wheeks and upsweeps were made during peaceful interactions; squeaks and squeals were related to animal discomfort during the Restraint Test; rasps were only made in Release-to-Burrow Tests when animals were plugging the burrow entrance; and variative calls did not show any relationship with type of test. Based on presence or absence of certain call types in the tests, we evaluate their potential communicative role in comparison with published data on vocal repertoires of other subterranean rodents.

Metagenomic profiling of cecal microbiota and antibiotic resistome in rodents

The rodent gut microbiota is a known reservoir of antimicrobial resistance, yet the distribution of antibiotic resistance genes (ARGs) within rodent cecal microbial communities and the specific bacterial species harboring these ARGs remain largely underexplored. This study employed high-throughput sequencing of 122 samples from five distinct rodent species to comprehensively profile the diversity and distribution of ARGs and to identify the bacterial hosts of these genes. A gene catalog of the rodent cecal microbiome was constructed, comprising 22,757,369 non-redundant genes. Analysis of the microbial composition and diversity revealed that Bacillota and Bacteroidota were the dominant bacterial phyla across different rodent species, with significant variations in species composition among the rodents. In total, 3703 putative antimicrobial resistance protein-coding genes were identified, corresponding to 392 unique ARG types classified into 32 resistance classes. The most enriched ARGs in the rodent cecal microbiome were associated with multidrug resistance, followed by glycopeptide and elfamycin antibiotics. Procrustes analysis demonstrated a correlation between the structure of the microbial community and the resistome. Metagenomic assembly-based host tracking indicated that most ARG-carrying contigs originated from the bacterial family Oscillospiraceae. Additionally, 130 ARGs showed significant correlations with mobile genetic elements. These findings provide new insights into the cecal microbiota and the prevalence of ARGs across five rodent species. Future research on a wider range of wild rodent species carrying ARGs will further elucidate the mechanisms underlying the transmission of antimicrobial resistance.

The Agoutis: A Future Model for Ecologically Relevant Neuroscience and Physiology In Natura

ABSTRACTThe overarching goal of neurobiology is to understand how complex behaviors are generated by the nervous system. The behavior of each species, and the brain that controls it, is shaped by the historical and current state of the environment that they inhabit. This fact is juxtaposed with the reductionist approach of neuroscience that isolates animals from their natural environment. Understanding how brains evolved to orchestrate the myriads of natural behaviors an animal performs in response to its environment requires an integrative approach to neuroscience that considers ecology, ethology, and evolution. Current technological developments are leading us to an inflection point at which studying brain functions in the wild is now possible. Ecological studies on how the environment affects behavior of animals (i.e., hibernation, foraging, food hoarding, and nest building) have framed a plurality of questions to be answered mechanistically, and yet, only few studies have addressed the relationship between the environment and the brain's anatomy and physiology. Neuroscience needs new animal models that allow us to tackle such questions in the wild. Here, we propose a new animal model for wild neuroscience, the agouti (Dasyprocta spp.), a large wild rodent playing a critical seasonal role in the maintenance of the central and south American rainforest ecosystems. We focus on how a rodent model, like the agouti, will allow for the investigation of large‐scale brain dynamics during seasonal behaviors of ecological importance: scatter‐hoarding and retrieval. We describe agouti evolution, ecology, and physiology as well as neuro‐anatomical and neurophysiological studies, which have set the foundation for future neuroscience in natura. We suggest agoutis have the potential to be a groundbreaking model for wild neuroscience.

Detection, genetic diversity, and factors associated with infection by hemotropic mycoplasmas in rodent and marsupial populations in regions of the states of Rio de Janeiro and Parana, Brazil

Hemotropic mycoplasmas, also known as hemoplasmas, are found in several animal species around the world. New species and genotypes of mycoplasmas have been described recently but much more remains to be discovered, especially in wildlife. The objective of this study was to investigate the presence of hemotropic mycoplasmas and diversity of the 16S rDNA sequence fragment in populations of small nonflying mammals in regions with different phytophysiognomies in the states of Rio de Janeiro and Parana, Brazil, as well as to evaluate environmental and animal factors influencing infection rates. Of the 257 animals sampled, 33.8 % (n = 87) were considered positive by conventional PCR. Of the 230 samples from wild rodents (Cricetidae), 36.5 % (n = 84) amplified hemotropic mycoplasma DNA, followed by synanthropic rodents (Muridae) (12.5 %, n = 2/16), and marsupials (Didelphidae) (9.0 %, n = 1/11). The regions with the highest frequency of positivity were Ponta Grossa (46.5 %, n = 27/58) and Cruz Machado (46.1 %, n = 24/52), followed by Nova Friburgo (30.8 %, n = 33/107), and Lidianopolis (12.5 %, n = 5/40). Oligoryzomys had the highest rate of infection (78.5 %), statistically different from Oxymycterus spp. (40.0 %), Akodon spp. (27.0 %) and Sooretamys (8.3 %). Males had a higher prevalence of Mycoplasma spp., being 3.97 times more likely to be positive for hemoplasma than females. Phylogenetic analysis grouped the sequences from this study into two clades, A and E, together with other hemoplasma sequences previously detected in small wild and synanthropic rodents from Brazil, Hungary, and Japan. Haplotype network reveals exclusive haplotypes for wild and synanthropic rodents. Our study reveals considerable genetic diversity suggesting the circulation of at least two species among sequences from this study and highlights the importance of considering environmental and biological factors in the epidemiology of these infections in wild mammals.

Nationwide Survey of Vector-Borne Diseases in Rodents and Mites in Korea: Anaplasma, Ehrlichia, and Rickettsia.

Rodents are reservoirs for zoonotic pathogens, making it essential to study both rodents and their ectoparasites. In 2022 and 2023, we investigated the spatial distribution of rodents and their mites across Korea, focusing on three vector-borne diseases (VBDs): Anaplasma, Ehrlichia, and Rickettsia. A total of 835 wild rodents were collected from 16 locations, each consisting of five distinct environmental settings (mountains, waterways, reservoirs, fields, and paddy fields), with 20 traps per setting, totaling 100 Sherman live folding traps per site. Each rodent was identified using a taxonomic key, and post-mortem examinations led to the collection of 7971 mites (498 pools), followed by PCR analysis. Among the rodents, Anaplasma phagocytophilum was detected in 10.3%, Ehrlichia muris in 0.5%, Ehrlichia ruminantium in 0.2%, and Rickettsia raoultii in 2.9%. In mites, A. phagocytophilum was found in 8.8%, E. muris in 0.2%, R. raoultii in 0.2%, R. endosymbiont in 1.6%, and R. australis in 1.2%. This study marks the first detection of E. muris and R. raoultii in Korean rodents and the first global discovery of E. ruminantium in rodents. The detection of multiple pathogens in mites worldwide highlights the importance of continuous VBD monitoring to mitigate public health risks.

Wild rodent fleas carrying Bartonella and Rickettsia in an area endemic for vector-borne diseases from Argentina.

Vector-borne diseases account for nearly 20% of all globally recognised infectious diseases. Within the spectrum of flea-borne pathogens, Bartonella and Rickettsia bacteria are prominent, contributing to the emergence and resurgence of diseases on a global scale. This study investigates the presence of species of Bartonella and Rickettsia harboured by fleas collected from wild rodents in northwestern Argentina (NWA). A total of 28 fleas from three genera and seven species were assessed. DNA of Bartonella and Rickettsia spp. was found in 12 fleas (42.8%). Phylogenetic analysis of concatenated sequences of gltA and rpoB genes showed the presence of Bartonella quintana in eight fleas of two species, Craneopsylla minerva minerva and Polygenis acodontis. Phylogenetic analysis of concatenated sequences of gltA, ompA and ompB genes identified Rickettsia felis in ten fleas of five species, C. m. minerva, P. acodontis, Polygenis bohlsi bohlsi, Polygenis byturus and Tiamastus palpalis. These bacterial species mark the first report in all flea species studied. This study represents the first survey of flea-borne bacteria for NWA. The results provide information to address strategies for the control and prevention of bartonellosis and rickettsiosis that could have an impact on public health in one of the geographical areas of Argentina with the highest incidence of infections transmitted to humans by ectoparasites.

Ultradian rhythms of activity in a wild subterranean rodent.

Many animals adapt their activity patterns to the best environmental conditions using daily rhythms. African mole-rats are among the mammals that have become models for studying how these rhythms can be entrained by light or temperature in experimental laboratory studies. However, it is unclear whether they exhibit similar circadian rhythms in their natural lightless, subterranean environment. In this study, we used biologging to investigate the activity rhythms of wild, highveld mole-rats. We show that their activity cycle exhibited an ultradian rhythm with a length between 4 and 8 h. On an individual level, mole-rats displayed about five activity bouts per day, occurring at various times during the day and night. On a population level, activity peaked in the afternoon, coinciding with the peak in ambient temperature. Our research suggests that wild subterranean mammals, which experience reduced environmental variation, are unlikely to show clear circadian rhythmicity in activity patterns. Instead, activity periods are distributed over several bouts throughout the day and night, and activity coincides with the peak in daily temperature. We propose that ultradian rhythms in activity may be more common than previously thought and discuss how physiological processes may generate differences in periodicity between laboratory and wild populations.