Distribution of commensal rodents in rain-fed and irrigated areas of Swat district, Khyber Pakhtunkhwa, Pakistan / Distribuição de roedores comensais em áreas irrigadas e chuvosas do distrito de Swat, Khyber Pakhtunkhwa, Paquistão

Distribution pattern and relative abundance of the agricultural rodent pests of rain-fed and irrigated areas of district Swat Khyber Pakhtunkhwa, Pakistan were recorded from April 2011 to November 2013 using wire mesh live traps. A total of 350 rodents (269 Rattus rattus and 81 Mus musculus) were captured under 2268 trap nights (trap success: 0.15). Regression of daily captures on cumulative captures revealed an estimate of 350 rodents from all the sampled structures with an average of 21.8 rodents per crop field. House rats (R. rattus; 76.8% of captures) were numerically dominant in almost all types of agricultural fields, and were significantly different from the mice (Mus musculus; 23.1% of captures). Both species were found together in some fields. The sex ratio revealed that males outnumbered the females in both of the reported species.

O padrão de distribuição e a abundância relativa de pragas de roedores agrícolas nas áreas irrigadas e irrigadas do distrito Swat Khyber Pakhtunkhwa, Paquistão foram registrados de abril de 2011 a novembro de 2013 usando armadilhas vivas de malha de arame. Um total de 350 roedores (269 Rattus rattus e 81 Mus musculus) foram capturados em 2268 noites de armadilha (sucesso da armadilha: 0,15). A regressão das capturas diárias em capturas cumulativas revelou uma estimativa de 350 roedores de todas as estruturas amostradas, com uma média de 21,8 roedores por campo agrícola. Os ratos domésticos (R. rattus; 76,8% das capturas) foram numericamente dominantes em quase todos os tipos de campos agrícolas e foram significativamente diferentes dos camundongos (Mus musculus; 23,1% das capturas). Ambas as espécies foram encontradas juntas em alguns campos. A proporção de sexo revelou que os machos superaram as fêmeas em ambas as espécies relatadas.

Distribution of commensal rodents insome shops of three districts in Malakand region, Pakistan / Distribuição de roedores comensais em algumas lojas de três distritos na região de Malakand, Paquistão

Using wire mesh live traps distribution pattern of the Rattus rattus and Mus musculus in different shops of three districts of Malakand region, Pakistan were recorded from September 2014 to October 2015. Over all 103 rodents (Rattus rattus 86 and Mus musculus 17) were caught during in 0.04 trap success (2448 trap nights). Regression of daily captures on cumulative captures revealed an estimate of 103 rodents from all the sampled structures with an average of 3.55 rodents per shop. R. rattus; 83.4% of captures were numerically dominant in almost all types of shops sampled, and were significantly different than Mus musculus; 16.5% of captures. Both species were found together in some shops while they were mostly trapped from the separate shops. Male rodents outnumbered the females.

Usando o padrão de distribuição de armadilhas vivas de malha de arame do Rattus rattus e Mus musculus em diferentes lojas de três distritos da região de Malakand, o Paquistão foi registrado de setembro de 2014 a outubro de 2015. No total, 103 roedores (Rattus rattus 86 e Mus musculus 17) foram pegos durante em 0,04 armadilha de sucesso (2448 noites de armadilha). A regressão das capturas diárias em capturas cumulativas revelou uma estimativa de 103 roedores de todas as estruturas amostradas, com uma média de 3,55 roedores por loja. R. rattus; 83,4% das capturas foram numericamente dominantes em quase todos os tipos de lojas da amostra e foram significativamente diferentes do Mus musculus; 16,5% das capturas. Ambas as espécies foram encontradas juntas em algumas lojas, enquanto estavam na maior parte presas em lojas separadas. Os roedores machos eram mais numerosos do que as fêmeas.

Respiratory development in burrowing rodents: Effect of perinatal hypercapnia.

Burrowing rodents have a blunted hypercapnic ventilatory response compared to non-burrowing rodents, but semi-fossorial ground squirrels and hamsters are not born with this blunted response when raised in room conditions. This study examined the hypercapnic ventilatory response of rats, hamsters, and ground squirrels raised in burrow-like hypercapnia (∼3 % CO2) through development (embryonic day 16-18 to postnatal day 30) to determine if chronic hypercapnia exerts any effect on the developing and adult semi-fossorial response. Chronic hypercapnia attenuated the ventilatory response to 5 % CO2 by 60 % (rats), 150 % (hamsters), and 70 % (squirrels) in newborns when compared to newborns raised in normal conditions. When raised in burrow conditions, squirrels and hamsters reached the blunted adult response ∼8-12 days sooner in development than their room air counterparts, while burrow-reared rats maintained a consistently blunted response until removal from chronic hypercapnia. Our study revealed no lasting effect of chronic hypercarbia on the ventilatory responses to CO2 in burrowing rodents, but rather a change in the developmental profile such that the blunted adult response was reached earlier in development.

How to Make a Rodent Giant: Genomic Basis and Tradeoffs of Gigantism in the Capybara, the World's Largest Rodent.

Gigantism results when one lineage within a clade evolves extremely large body size relative to its small-bodied ancestors, a common phenomenon in animals. Theory predicts that the evolution of giants should be constrained by two tradeoffs. First, because body size is negatively correlated with population size, purifying selection is expected to be less efficient in species of large body size, leading to increased mutational load. Second, gigantism is achieved through generating a higher number of cells along with higher rates of cell proliferation, thus increasing the likelihood of cancer. To explore the genetic basis of gigantism in rodents and uncover genomic signatures of gigantism-related tradeoffs, we assembled a draft genome of the capybara (Hydrochoerus hydrochaeris), the world's largest living rodent. We found that the genome-wide ratio of nonsynonymous to synonymous mutations (ω) is elevated in the capybara relative to other rodents, likely caused by a generation-time effect and consistent with a nearly neutral model of molecular evolution. A genome-wide scan for adaptive protein evolution in the capybara highlighted several genes controlling postnatal bone growth regulation and musculoskeletal development, which are relevant to anatomical and developmental modifications for an increase in overall body size. Capybara-specific gene-family expansions included a putative novel anticancer adaptation that involves T-cell-mediated tumor suppression, offering a potential resolution to the increased cancer risk in this lineage. Our comparative genomic results uncovered the signature of an intragenomic conflict where the evolution of gigantism in the capybara involved selection on genes and pathways that are directly linked to cancer.

Importance of the lactation period in developmental programming in rodents.

Lactation is a critical period during which maternal nutritional and environmental challenges affect milk composition and, therefore, organ differentiation, structure, and function in offspring during the early postnatal period. Evidence to date shows that lactation is a vulnerable time during which transient insults can have lasting effects, resulting in altered health outcomes in offspring in adult life. Despite the importance of the developmental programming that occurs during this plastic period of neonatal life, there are few comprehensive reviews of the multiple challenges-especially to the dam-during lactation. This review presents milk data from rodent studies involving maternal nutritional challenges and offspring outcome data from studies involving maternal manipulations during lactation. Among the topics addressed are maternal nutritional challenges and the effects of litter size and artificial rearing on offspring metabolism and neural and endocrine outcomes. The lactation period is an opportunity to correct certain functional deficits resulting from prenatal challenges to the fetus, but, if not personalized, can also lead to undesirable outcomes related to catch up-growth and overnutrition.

Developmental environment influences activity levels in a montane rodent, Phyllotis xanthopygus.

Ambient temperature and thermal variability play a crucial role in diverse aspects of organisms' biology. In the current context of climate change, it is critical to understand how temperature impacts traits that could affect fitness. In Phyllotis xanthopygus, a small altricial rodent inhabiting an altitudinal gradient in the Andes Mountains of Argentina, the behavioral response to temperature varies between populations from different altitudes. Animals from high altitude (cold environment) reduce their activity rate at high temperatures, in contrast to animals from low altitude (relatively warmer environment). The goal of this study was to unveil the mechanism underlying such intraspecific behavioral variability in P. xanthopygus. We characterized activity rates under different thermal treatments both for wild-reared and lab-reared animals. As we expected, the intraspecific variability shown by animals raised at different altitudes in the field disappeared in animals raised under homogenous conditions in the laboratory. Our results are indicative of ontogenetic plasticity in P. xanthopygus and suggest that the behavioral versatility of adult individuals to deal with thermal challenges is shaped by the range of environmental conditions experienced during their early life. This adds to the list of features that modulate the biological performance of individuals and could influence the relative vulnerability of populations inhabiting different elevations under the global disturbance of climate change.

A dual death/survival role of autophagy in the adult ovary of Lagostomus maximus (Mammalia- Rodentia).

Follicular atresia is a cell death event that occurs in the great majority of follicles before ovulation in the mature mammalian ovary. Germ cell loss has been mainly associated to apoptosis although autophagy also seems to be at play. Aimed to increase our understanding on the possible cooperating role of autophagy and apoptosis in follicular atresia and/or follicular survival, we analyzed both programmed cell death mechanisms in a rodent model, the South American plains vizcacha, Lagostomus maximus. Female vizcacha shows highly suppressed apoptosis-dependent follicular atresia in the adult ovary, with continuous folliculogenesis and massive polyovulation. This strategy of massive ovulation requires a permanent remodeling of the ovarian architecture to maintain the availability of quiescent primordial follicles throughout the individual's reproductive lifespan. We report here our analysis of autophagy (BECN1, LAMP1 and LC3B-I/II) and apoptosis (BCL2 and ACTIVE CASPASE-3) markers which revealed interactive behaviors between both processes, with autophagy promoting survival or cell death depending on the ovarian structure. Strong BECN1, LC3B-II and LAMP1 staining was observed in atretic follicles and degenerating corpora lutea that also expressed nuclear ACTIVE CASPASE-3. Healthy follicles showed a slight expression of autophagy proteins but a strong expression of BCL2 and no detectable ACTIVE CASPASE-3. Transmission electron microscopy revealed a high formation of autophagosomes, autolysosomes and lysosomes in atretic follicles and degenerating corpora lutea and a low number of autophagic vesicles in normal follicles. The co-expression of LC3B-BECN1, LC3B-LAMP1 and LC3B-ACTIVE CASPASE-3 was only detected in atretic follicles and degenerating corpora lutea, while co-expression of BCL2-BECN1 was only observed in normal follicles. We propose that autophagy could act as a mechanism to eliminate altered follicles and remnant corpora lutea providing the necessary space for maturation of primordial follicles that continuously enter the growing follicular pool to sustain massive ovulation.

Effect of rodent density on tick and tick-borne pathogen populations: consequences for infectious disease risk.

BACKGROUND: Rodents are considered to contribute strongly to the risk of tick-borne diseases by feeding Ixodes ricinus larvae and by acting as amplifying hosts for pathogens. Here, we tested to what extent these two processes depend on rodent density, and for which pathogen species rodents synergistically contribute to the local disease risk, i.e. the density of infected nymphs (DIN). METHODS: In a natural woodland, we manipulated rodent densities in plots of 2500 m2 by either supplementing a critical food source (acorns) or by removing rodents during two years. Untreated plots were used as controls. Collected nymphs and rodent ear biopsies were tested for the presence of seven tick-borne microorganisms. Linear models were used to capture associations between rodents, nymphs, and pathogens. RESULTS: Investigation of data from all plots, irrespective of the treatment, revealed a strong positive association between rodent density and nymphal density, nymphal infection prevalence (NIP) with Borrelia afzelii and Neoehrlichia mikurensis, and hence DIN's of these pathogens in the following year. The NIP, but not the DIN, of the bird-associated Borrelia garinii, decreased with increasing rodent density. The NIPs of Borrelia miyamotoi and Rickettsia helvetica were independent of rodent density, and increasing rodent density moderately increased the DINs. In addition, NIPs of Babesia microti and Spiroplasma ixodetis decreased with increasing rodent density, which had a non-linear association with DINs of these microorganisms. CONCLUSIONS: A positive density dependence for all rodent- and tick-associated tick-borne pathogens was found, despite the observation that some of them decreased in prevalence. The effects on the DINs were variable among microorganisms, more than likely due to contrasts in their biology (including transmission modes, host specificity and transmission efficiency). The strongest associations were found in rodent-associated pathogens that most heavily rely on horizontal transmission. Our results draw attention to the importance of considering transmission mode of a pathogen while developing preventative measures to successfully reduce the burden of disease.

Quantitative Analysis of the Timing of Development of the Cerebellum and Precerebellar Nuclei in Monotremes, Metatherians, Rodents, and Humans.

We have used a quantitative statistical approach to compare the pace of development in the cerebellum and precerebellar systems relative to body size in monotremes and metatherians with that in eutherians (rodents and humans). Embryos, fetuses, and early postnatal mammals were scored on whether key structural events had been reached in the development of the cerebellum itself (CC-corpus cerebelli; 10 milestones), or the pontine and inferior olivary precerebellar nuclear groups (PC; 4 milestones). We found that many early cerebellar and precerebellar milestones (e.g., formation of Purkinje cell layer and deep cerebellar nuclei) were reached at a smaller absolute body length in both metatherians and eutherians together, compared to monotremes. Some later milestones (e.g., formation of the external granular layer and primary fissuration) were reached at a smaller body length in metatherians than eutherians. When the analysis was performed with proportional body length expressed as a natural log-transformed ratio of length at birth, milestones were reached at a much smaller proportional body length in rodents and humans than in the metatherians or monotremes. The findings are consistent with the slower pace of metabolic activity and embryonic development in monotremes. They also indicate slightly advanced maturation of some early features of the cerebellum in some metatherians (i.e., early cerebellar development in dasyurids relative to body size), but do not support the notion of an accelerated development of the cerebellum to cope with the demands of early birth. Anat Rec, 2019. © 2019 American Association for Anatomy Anat Rec, 303:1998-2013, 2020. © 2019 American Association for Anatomy.

Mechanisms of Hantavirus Transmission in Oligoryzomys longicaudatus.

The cricetid rodent Oligoryzomys longicaudatus is the species host of Andes virus (ANDV) which causes hantavirus pulmonary syndrome in southern Argentina and Chile. Population density, behavioral interactions, and spacing patterns are factors that affect viral transmission among wild rodents. We predict that the highest prevalence of hantavirus antibody positive would be found among wounded, reproductive males and that, at high population densities, wounded, reproductive males would be dispersers rather than resident individuals. The study was conducted seasonally from October (spring) 2011 to October (spring) 2013 in a shrubland habitat of Cholila, Argentina. During each trapping session, we classified captured O. longicaudatus as resident or disperser individuals, estimated population density, and recorded wounds as an indicator of aggression among individuals. We obtained blood samples from each individual for serological testing. We used generalized linear models to test the statistical significance of association between antibody prevalence, and sex, resident/dispersal status, wounds and trapping session. The highest proportion of seropositive O. longicaudatus individuals was among wounded reproductive males during periods of the greatest population density, and the characteristics of seroconverted individuals support that transmission is horizontal through male intrasexual competition. A positive association between dispersing individuals and hantavirus antibody was detected at high population density. Our study design allowed us to obtain data on a large number of individuals that are seroconverted, enabling a better understanding of the ecology and epidemiology of the ANDV host system.

Hantavirus host assemblages and human disease in the Atlantic Forest.

Several viruses from the genus Orthohantavirus are known to cause lethal disease in humans. Sigmodontinae rodents are the main hosts responsible for hantavirus transmission in the tropical forests, savannas, and wetlands of South America. These rodents can shed different hantaviruses, such as the lethal and emerging Araraquara orthohantavirus. Factors that drive variation in host populations may influence hantavirus transmission dynamics within and between populations. Landscape structure, and particularly areas with a predominance of agricultural land and forest remnants, is expected to influence the proportion of hantavirus rodent hosts in the Atlantic Forest rodent community. Here, we tested this using 283 Atlantic Forest rodent capture records and geographically weighted models that allow us to test if predictors vary spatially. We also assessed the correspondence between proportions of hantavirus hosts in rodent communities and a human vulnerability to hantavirus infection index across the entire Atlantic Forest biome. We found that hantavirus host proportions were more positively influenced by landscape diversity than by a particular habitat or agricultural matrix type. Local small mammal diversity also positively influenced known pathogenic hantavirus host proportions, indicating that a plasticity to habitat quality may be more important for these hosts than competition with native forest dwelling species. We found a consistent positive effect of sugarcane and tree plantation on the proportion of rodent hosts, whereas defaunation intensity did not correlate with the proportion of hosts of potentially pathogenic hantavirus genotypes in the community, indicating that non-defaunated areas can also be hotspots for hantavirus disease outbreaks. The spatial match between host hotspots and human disease vulnerability was 17%, while coldspots matched 20%. Overall, we discovered strong spatial and land use change influences on hantavirus hosts at the landscape level across the Atlantic Forest. Our findings suggest disease surveillance must be reinforced in the southern and southeastern regions of the biome where the highest predicted hantavirus host proportion and levels of vulnerability spatially match. Importantly, our analyses suggest there may be more complex rodent community dynamics and interactions with human disease than currently hypothesized.

Phylogenetic and Developmental Constraints Dictate the Number of Cusps on Molars in Rodents.

Mammal tooth morphology and function correlate strongly with dietary ecology, and convergence is a major feature of mammalian tooth evolution. Yet, function and ecology are insufficient to explain morphological diversification and convergence within mammalian molar evolution; suggesting that development and phylogeny also limit possible structural solutions to selective pressures. Here, I use in silico models and empirical studies of extant and fossil rodent teeth to identify morphogenetic rules that influence molar morphology. Because rodents are the most diverse group of mammals with corresponding dental disparity they represent an excellent system for investigating how genetic interactions limit morphology. I find that lower first molars are limited to a minimum of four cusps and a maximum of nine cusps. Multiple developmental pathways produce the same numbers of cusps, despite highly variable cusp morphologies, indicating the existence of limits on how morphological evolution can fill a morphospace defined by cusp numbers. These constraints are both developmental and phylogenetic in nature and the identification of their influence on rodent molar shape provides a framework for investigation of how tooth batteries evolved an array of functions despite fundamental structural limits. The data presented here increase predictability of cusp number and evolutionary outcomes of rodent cheek dentition.

Relationships Between Enamel Prism Decussation and Organization of the Ameloblast Layer in Rodent Incisors.

Rodent enamel microstructure has been extensively investigated, primarily on the basis of 2D electronic microscopy data. The nature and dynamics of the ameloblasts (the enamel-secreting cells) have also been well studied. However, critical issues still remain surrounding exactly how the ameloblasts produce the astonishing microstructural complexity of enamel, and how this subtle architecture evolved through time. In this article, we used a new methodology based on confocal laser microscopy to reconstruct the enamel microstructure of rodent incisors in three dimensions (3D) with the ameloblasts in situ. We proposed interpretations regarding the possible relationships between the workings of the ameloblasts and the resulting enamel prisms, especially how the phenomenon of decussation is generated. Finally, we were able to represent the two main types of modern rodent incisor microstructures (uniserial and multiserial decussations), as a set of parameters that have been entered into the 3D enamel simulation software Simulenam to generate 3D models that can be digitally manipulated. Associating 2D data of incisor enamel microstructure of fossil rodents and Simulenam, it was then possible to better understand how the various decussation parameters evolved through time and gave rise to the two modern microstructure types from the same ancestral type (pauciserial). This study also confirmed that rodent and artiodactyl enamel do not share the same mechanism of decussation formation. Anat Rec, 302:1195-1209, 2019. © 2018 Wiley Periodicals, Inc.

Spatial heterogeneity of hemorrhagic fever with renal syndrome is driven by environmental factors and rodent community composition.

Hemorrhagic fever with renal syndrome (HFRS) is a rodent-borne disease caused mainly by two hantaviruses in China: Hantaan virus and Seoul virus. Environmental factors can significantly affect the risk of contracting hantavirus infections, primarily through their effects on rodent population dynamics and human-rodent contact. We aimed to clarify the environmental risk factors favoring rodent-to-human transmission to provide scientific evidence for developing effective HFRS prevention and control strategies. The 10-year (2006-2015) field surveillance data from the rodent hosts for hantavirus, the epidemiological and environmental data extracted from satellite images and meteorological stations, rodent-to-human transmission rates and impacts of the environment on rodent community composition were used to quantify the relationships among environmental factors, rodent species and HFRS occurrence. The study included 709 cases of HFRS. Rodent species in Chenzhou, a hantavirus hotspot, comprise mainly Rattus norvegicus, Mus musculus, R. flavipectus and some other species (R. losea and Microtus fortis calamorum). The rodent species played different roles across the various land types we examined, but all of them were associated with transmission risks. Some species were associated with HFRS occurrence risk in forest and water bodies. R. norvegicus and R. flavipectus were associated with risk of HFRS incidence in grassland, whereas M. musculus and R. flavipectus were associated with this risk in built-on land. The rodent community composition was also associated with environmental variability. The predictive risk models based on these significant factors were validated by a good-fit model, where: cultivated land was predicted to represent the highest risk for HFRS incidence, which accords with the statistics for HFRS cases in 2014-2015. The spatial heterogeneity of HFRS disease may be influenced by rodent community composition, which is associated with local environmental conditions. Therefore, future work should focus on preventing HFRS is moist, warm environments.

Long-Term Study of a Hantavirus Reservoir Population in an Urban Protected Area, Argentina.

Green spaces in urban areas can play a key role in protecting wildlife. However, the presence of wildlife in urban areas can lead to human health risks. Although the presence of the rodent species Oligoryzomys flavescens (hantavirus reservoir) has been recorded in cities of Argentina, its population dynamics in this type of habitat is still unknown. Here, we evaluated: (1) long-term spatial and temporal patterns of O. flavescens abundance and how these patterns were influenced by weather factors and (2) the seroprevalence of hantavirus and the identity of the viral lineage circulating in the population that inhabits the Costanera Sur Ecological Reserve, a protected area in the city of Buenos Aires. Genetic results confirmed that the pathogenic ANDES Central Lechiguanas virus is present in O. flavescens populations inhabiting this urban reserve. Abundance of O. flavescens showed interannual and seasonal fluctuations, with maximum values in winter and spring and minimum ones in summer and autumn. Summers with the highest abundances of O. flavescens were preceded by warmer winters, while winters with lower abundances were preceded by warmer summers. On the other hand, accumulated precipitations in the previous 6 months positively affected winter abundance. These results could help the authorities in charge of the green spaces of Buenos Aires to identify priority areas and times of the year for the implementation of preventive measures that minimize the contact of rodents with visitors. Such measures could be intensified when winters are warmer than normal, and summers are cooler and wetter than normal.

A Brief Guide to Studying Fear in Developing Rodents: Important Considerations and Common Pitfalls.

Development is a time of rapid change that sets the pathway to adult functioning across all aspects of physical and mental health. Developmental studies can therefore offer insight into the unique needs of individuals at different stages of normal development as well as the etiology of various disease states. The aim of this overview is to provide an introduction to the practical implementation of developmental studies in rats and mice, with an emphasis on the study of learned fear. We first discuss how developmental factors may influence experimental outcomes for any study. This is followed by a discussion of methodological issues to consider when conducting studies of developing rodents, highlighting examples from the literature on learned fear. Throughout, we offer some recommendations to guide researchers on best practice in developmental studies. © 2018 by John Wiley & Sons, Inc.

Oligodendrocyte morphology in the developing brain of the African giant rat (Cricetomys gambianus, Waterhouse): Histology, immunohistochemistry and electron microscopy.

Oligodendrocyte and myelin-related studies have been pivotal in understanding disruption of central nervous system (CNS) myelin through injury, toxicological, pathological degeneration or genetic intervention. The African giant rat (AGR) has been postulated as an indigenous wild-type model within the African context. This work thus describes oligodendrocyte morphologies and myelin components of the developing African giant rat brain using histological, immunohistochemical and ultrastructural techniques. Five types, precursor-progenitor oligodendrocytes, pre-oligodendrocytes, immature oligodendrocytes, mature non-myelinating oligodendrocytes and mature myelinating oligodendrocytes, were identified. The first four types were observed in neonates while juvenile and adult AGR had predominantly mature myelinating oligodendrocytes with evidence of myelin sheath deposition. All cell types identified showed positive CNPase-positive immunosignalling across all age groups. This suggests CNPase as a suitable, sensitive and reliable biomarker for studying CNS neurodegenerative/demyelinating disorders in the AGR. This baseline study has given detailed insight into the morphology of oligodendrocytes and myelin in the AGR. It may be useful for anatomical studies and detection of alterations in neurocellular profile of oligodendrocytes and myelin in the AGR in real-life or in experimental models.

Spatial modeling of rat bites and prediction of rat infestation in Peshawar valley using binomial kriging with logistic regression.

In this study, we propose to develop a geostatistical computational framework to model the distribution of rat bite infestation of epidemic proportion in Peshawar valley, Pakistan. Two species Rattus norvegicus and Rattus rattus are suspected to spread the infestation. The framework combines strengths of maximum entropy algorithm and binomial kriging with logistic regression to spatially model the distribution of infestation and to determine the individual role of environmental predictors in modeling the distribution trends. Our results demonstrate the significance of a number of social and environmental factors in rat infestations such as (I) high human population density; (II) greater dispersal ability of rodents due to the availability of better connectivity routes such as roads, and (III) temperature and precipitation influencing rodent fecundity and life cycle.

An allometric analysis of sexual dimorphism in Ctenomys australis: integrating classic morphometry and functional performance in vivo.

The South American rodents of the genus Ctenomys (Rodentia, Hystricognathi), which use both forelimbs and incisors to dig, show strong, specialized morphological adaptations to living in the underground niche. In these rodents, the effectiveness of a bite - in this case the potential to inflict physical damage - mostly depends on the strength of the incisors (e.g. bending and torsion stresses) and the power of the masseteric muscle of the jaw. Ctenomys australis (the sand dune tuco-tuco) is a highly territorial subterranean rodent that builds large and exclusive burrow systems in coastal sand dunes found continuously along the Atlantic coast of the Buenos Aires province, Argentina. Incisors in this species are used both in agonistic encounters among congeners (i.e. reproductive or territorial intentions) as well as to dig and increase the size of their burrows daily (e.g. acquisition of plant material as food resources). We first characterized sexual dimorphism in cranial traits involved in aggressive interactions between males, analyzing ontogenetic trajectories of both sexes. We also analyzed some remarkable attributes of sexual dimorphism in subadult and adult individuals, the bending and torsion stresses and the bite performance in vivo, hypothesizing that males are able to apply comparatively stronger bite forces at their incisor tips than females, concordant with a broader mandible for the insertion of a powerful adductor musculature. Bite forces were measured in vivo in wild animals of both sexes using a strain gauge load cell force transducer. These individuals were also used to estimate the incisor area (CA), the 2nd moment of inertia of the incisors (I, or the bending strength to external forces), and the torsional strength of the incisor (J), all traits involved in the production of the force that can be withstood at the incisor tips. Ontogeny explained some sexual differences in the cranial traits of adults, expressed as (i) morphological changes related to body size variation, and (ii) morphological changes associated with differences in the slope of ontogenetic trajectories (regardless of body size variation). Recordings of in vivo bite forces were significantly higher in adult males than in females. These differences in bite forces were not associated with the sex itself, but the sexual dimorphism in body size. Although males did not show significantly higher allometric coefficients for I, J and CA than females, males still showed a strong sexual dimorphism in these traits due to body size variation. On the other hand, measurements of mandibular width - an estimator of the relative size of masseteric muscles - in vivo showed strong differences between sexes, suggesting higher force performance at the incisor tips for males. Overall, we observed that many attributes related to bite performance might have been molded by sexual selection, which implies differences in allometric coefficients from some morphological traits throughout ontogeny.