Genus Sigmodon Research Articles

Microbial community structure and composition is associated with host species and sex in Sigmodon cotton rats

BackgroundThe cotton rat (genus Sigmodon) is an essential small animal model for the study of human infectious disease and viral therapeutic development. However, the impact of the host microbiome on infection outcomes has not been explored in this model, partly due to the lack of a comprehensive characterization of microbial communities across different cotton rat species. Understanding the dynamics of their microbiome could significantly help to better understand its role when modeling viral infections in this animal model.ResultsWe examined the bacterial communities of the gut and three external sites (skin, ear, and nose) of two inbred species of cotton rats commonly used in research (S. hispidus and S. fulviventer) by using 16S rRNA gene sequencing, constituting the first comprehensive characterization of the cotton rat microbiome. We showed that S. fulviventer maintained higher alpha diversity and richness than S. hispidus at external sites (skin, ear, nose), but there were no differentially abundant genera. However, S. fulviventer and S. hispidus had distinct fecal microbiomes composed of several significantly differentially abundant genera. Whole metagenomic shotgun sequencing of fecal samples identified species-level differences between S. hispidus and S. fulviventer, as well as different metabolic pathway functions as a result of differential host microbiome contributions. Furthermore, the microbiome composition of the external sites showed significant sex-based differences while fecal communities were not largely different.ConclusionsOur study shows that host genetic background potentially exerts homeostatic pressures, resulting in distinct microbiomes for two different inbred cotton rat species. Because of the numerous studies that have uncovered strong relationships between host microbiome, viral infection outcomes, and immune responses, our findings represent a strong contribution for understanding the impact of different microbial communities on viral pathogenesis. Furthermore, we provide novel cotton rat microbiome data as a springboard to uncover the full therapeutic potential of the microbiome against viral infections.

Taxonomy, diet and geographical provenance of fossil species of Sigmodon from west central Mexico during the late Pleistocene

The information of diet, habitat and geographic location of animals obtained from fossil deposits is important to understand the environmental changes of a place that occurred through time. Most of the paleoecological research in Mexico is centered on large mammal taxa. A minimal research effort is allocated to small vertebrates which due to their relative brief longevity and small territories, provide fine-scale paleoenvironmental information. In the present work, the occlusal morphology of the first molar was analyzed, as well as the dental microwear marks and the 87Sr/86Sr isotopic ratio in fossil and extant relatives of the genus Sigmodon from La Cinta-Portalitos locality, situated on the northern portion of the Cuitzeo Basin, central western Mexico. Goals included determining species richness within Sigmodon, as well as dietary behavior and geographic origin. Based on the comparison of the occlusal morphology of fossils and modern teeth, three fossil species were distinguished: S. hispidus, S. leucotis and S. alleni. Microwear patterns showed that S. hispidus population could be associated to a grazer diet, inhabiting open areas, similar to the extant populations. The species S. leucotis exhibited a microwear signature associated to a grazer diet as well, and S. alleni revealed a fruit–grass–insect feeding behavior. Finally, in the case of S. hispidus, the 87Sr/86Sr isotopic signature proved to be like that of the bedrock, so the S. hispidus population was local and a suitable indicator of paleoenvironmental conditions of La Cinta-Portalitos.

Comparative post-natal growth in five species of the genus Sigmodon . I. External morphological character relationships

A comparative study of five species of cotton rats ( Sigmodon ) was carried out to diagnose similarities and differences in external morphology. These animals (a total of 610 individuals) were descendants of wild cotton rats from various localities in Mexico. The growth rate of body dimensions can be divided into three categories: from 1 to 40 days there is a rapid increase in length in all body dimensions; from 41 to 100 days the increase is moderate and from 101 days to adulthood (200-400 days) there is practically no growth. Regarding size, the five species can be divided into three groups: S. hispidus was represented by a population sample having large measurements and was the largest cotton rat studied. Sigmodon alleni and S. fulviventer were smaller and showed parallel growth rates. Sigmodon leucotis and S. ochrognathus were the smallest and showed similar patterns of growth. The differences found indicate that S. leucotis and S. ochrognathus are perhaps more remote from the supposed parent stock (presumably resembling S. hispidus ). Sigmodon alleni and S. fulviventer , on the other hand, appear similar to S. hispidus in morphological development and thereby more closely related. When comparing morphological characteristics with the preferred habitats of the species, it was found that, whereas the three larger species prefer deep soils and abundant grass or shrub cover, the smaller and shorter-tailed species ( S. leucotis and S. ochrognathus ) live usually on shallow rocky soils on sparselyvegetated slopes, suggesting survival patterns.

Patterns of Chromosomal Evolution in Sigmodon, Evidence from Whole Chromosome Paints

Of the superfamily Muroidea (31 genera, 1578 species), the Sigmodontinae (74 genera, 377 species) is the second largest subfamily in number of species and represents a significant radiation of rodent biodiversity. Only 2 of the 74 genera are found in both North and South America (Sigmodon and Oryzomys) and the remainder are exclusively from South America. In recent molecular studies, the genus Sigmodon (Cricetidae, Sigmodontinae) has been considered sister to many other South American Sigmodontines [Steppan et al., 2004]. We examine the chromosomal evolution of 9 species of Sigmodon utilizing chromosomal paints isolated from S. hispidus, proposed to be similar to the ancestral karyotype [Elder, 1980]. Utilizing a phylogenetic hypothesis of a molecular phylogeny of Sigmodon [Henson and Bradley, 2009], we mapped shared chromosomal rearrangements of taxa on a molecular tree to estimate the evolutionary position of each rearrangement. For several species (S. hirsutus, S. leucotis, S. ochrognathus, S. peruanus, and S. toltecus), the karyotype accumulated few or no changes, but in three species (S. arizonae, S. fulviventer, and S. mascotensis) numerous karyotype rearrangements were observed. These rearrangements involved heterochromatic additions, centric fusions, tandem fusions, pericentric inversions, as well as the addition of interstitial DNA not identified by chromosome paints or C-banding. The hypothesis that the ancestral karyotype for this complex had a diploid number of 52, a fundamental number of 52, and a G-band pattern of which most, if not all are similar to that present in modern day S. hispidus fails to be rejected. This hypothesis remains viable as an explanation of chromosomal evolution in Sigmodontine rodents.

Molecular systematics of the genus Sigmodon: results from mitochondrial and nuclear gene sequences

Phylogenetic relationships within the genus Sigmodon Say and Ord, 1825 were examined using sequence data from multiple gene regions, including exon 1 of the nuclear-encoded interphotoreceptor retinoid binding protein, intron 7 of the nuclear beta-fibrinogen gene, and the mitochondrial cytochrome b gene from 27 individuals representing 11 species of Sigmodon. Nuclear genes were analyzed independently, combined with each other, and combined with the mitochondrial data. Topologies were constructed using parsimony and Bayesian methods, with nodal support provided by bootstrap and posterior probability values. All analyses recovered four independent clades (I-IV), each representing unique species groups: hispidus, fulviventer, peruanus, and alstoni. The analyses from the combined data also provided support for relationships previously proposed within those species groups.

A new species ofHypocristata(Nematoda, Trichostrongylina, Heligmosomoidea) a parasite ofSigmodon hispidus(Cricetidae, Sigmodontinae) from Venezuela

Description of Hypocristata tercera n. sp. (Heligmonellidae, Nippostrongylinae) a parasite of the small intestine of Sigmodon hispidus (Rodent, Sigmodontinae) from Venezuela. Two other species were described in the genus, both from Colombia and parasitic in Sigmodontinae. H. thomosomysi Durette-Desset, 1970, a parasite of Thomasomys sp. has about the same number of cuticular ridges at mid-body but differs by ridges having chitinoid struts, a caudal bursa pattern of type 2-2-1 (vs 1-3-1). H. anguillula Durette-Desset, 1970, a parasite of Sigmodontomys alfari (= Nectomys alfari) has the same caudal bursa pattern (type 1-3-1) but differs by the presence of ridges at mid-body in both sexes (absent at that level in H. tercera) and by ridges having chitinoid struts in female. This is the first report of the genus Hypocristata Durette-Desset, 1971 in Venezuela and in the genus Sigmodon (Sigmodontinae).

Preliminary Correlation of Florida and Central Great Plains Pliocene and Pleistocene Mammalian Local Faunas Based on Rodent Biostratigraphy

A preliminary attempt is made to correlate the late Pliocene and Pleistocene mammalian local faunas of peninsular Florida with those of the central Great Plains. Critical taxa among the rodents are the cotton rats, genus Sigmodon, and the arvicolids, especially Ondatra and Microtus. The dense rodent fossil record and accompanying radiometric dates of the Meade Basin of southwestern Kansas provide a chronological template for North American rodent faunas, and suggest that mammalian local faunas from the late Blancan Haile 15A through Rancholabrean of Florida may be fit into five of Martin’s Great Plains rodent zones.

SYSTEMATICS OF THE GENUS SIGMODON: DNA SEQUENCES FROM BETA-FIBRINOGEN AND CYTOCHROMEb

Abstract Nucleotide sequences from intron 7 of the beta-fibrinogen gene (Fgb-I7) were used to evaluate phylogenetic relationships among members of the genus Sigmodon. In addition, these sequences were combined with mitochondrial cytochrome-b sequences and analyzed from a total evidence perspective. Results from parsimony and Bayesian analyses indicated support for 3 species groups (alstoni, fulviventer, and hispidus). A sister relationship was depicted for S. alleni and S. hirsutus, followed by the addition of S. toltecus; however, little resolution was provided for relationships between other members of the hispidus species group.

THE PLIOCENE AND PLEISTOCENE HISTORY OF COTTON RATS IN THE MEADE BASIN OF SOUTHWESTERN KANSAS

The taxonomy and dental evolution of cotton rats, genus Sigmodon, from Pliocene and Pleistocene deposits in the Meade Basin of southwestern Kansas are examined. Prosigmodon is here subsumed under Sigmodon. Morphological and multivariate statistical analyses identify 3 Sigmodon lineages and 5 immigration events in the Meade Basin. The 1st immigration event occurred during the early Blancan and the latest during the Holocene. The analyses of dental characters indicate directional trends in almost all features, representing both size and shape. A comparison of information from the cotton rat fossil record with a recent molecular phylogeny suggests the molecular phylogeny has set the origin of modern cotton rat groups too early. North American species groups probably do not predate the late Pliocene.

MOLECULAR SYSTEMATICS OF THE GENUS SIGMODON (RODENTIA: MURIDAE): EVIDENCE FROM THE MITOCHONDRIAL CYTOCHROME-bGENE

Abstract Phylogenetic relationships of 11 species of cotton rats (Genus Sigmodon) were assessed using nucleotide variation in the mitochondrial cytochrome-b gene. Results of the phylogenetic analyses do not support the conventional composition of the Sigmodon hispidus and S. fulviventer species groups. Instead, 3 species groups are recognized: hispidus (S. alleni, S. arizonae, S. hirsutus, S. hispidus, S. mascotensis, S. ochrognathus, and S. toltecus), fulviventer (S. leucotis, S. fulviventer, and S. peruanus), and alstoni (S. alstoni). Sequence divergence values ranged from 8.7% to 21.2%, indicating that divergence events within the genus occurred approximately 2.5–5.6 × 106 years ago. Taxa comprising the alstoni and fulviventer groups appear to have evolved early, whereas members of the hispidus group evolved more recently. Molecular data reflect an early origin (7 × 106 years ago) and support the hypothesis that cotton rats may occupy a basal position among South American sigmodontines.

VARIATION IN DEVELOPMENTAL CONSTRAINTS IN SIGMODON.

Developmental constraints can be interpreted as factors of developmental origin responsible for covariation among measured variables. Several hypotheses have been proposed to link the possession of such constraints to subsequent evolution. Using confirmatory factor analysis, we compare developmental factors across selected taxa of cotton rats, genus Sigmodon. Three factors explain well the covariation among orofacial measurements: (1) responses to body size variation, (1) coordinated growth of traits of the occluding-tooth complex, and (3) responses to musculoskeletal interactions. Sigmodon taxa share these factors, but differ in the variance-covariance matrix of factors, and the unique variances of individual traits. Patterns of covariation among measurements of the neurocranial complex reflect responses to body size variation, and perhaps also responses to fetal brain growth. While there are no significant differences across taxa in factorpattern, variance-covariance matrix of factors, or unique variance of measured neurocranial variables, the neurocranium is only weakly constrained. We doubt that even the relatively stronger developmental constraints on the orofacial complex would prevent evolutionary divergence because differences in the variances and covariances of factors, and in levels of unique variance of individual traits can provide different opportunities for selection to act in different Sigmodon taxa.

Comparative male meiosis in seven species of cotton rats, genus Sigmodon.

A study of the male meiosis in seven species of cotton rats, genus Sigmodon, was carried out. The general course of meiosis in four species, S. hispidus, S. leucotis, S. ochrognathus, and S. alleni, is similar to that in other mammals studied. In pachynema, the sex bivalent is negatively heteropycnotic and tightly coiled to form the sex vesicle. In diakinesis, the sex bivalent is elongated and stains lightly. All of these species have a diploid number of 52, and 26 bivalents are seen in diakinesis. In the remaining three species, S. arizonae, S. mascotensis, and S. fulviventer, the sex bivalent is negatively heteropycnotic in pachynema with no indication of condensation. It would appear that the functional activity of the sex chromosomes in meiosis in these species is completed before pachynema. Diakinesis stages in S. arizonae (2n=22, 24) possess 11 or 12 bivalents; in S. fulviventer (2n=28, 29, or 30) 14 or 15 bivalents; and S. mascotensis (2n=28) 14 bivalents. Differences found in activity of the sex bivalent can be correlated with the two groups of Sigmodon established on the basis of diploid and fundamental numbers and represent another expression of the differences in genomes between the two groups.

Interactions Between the Cotton Rats, Sigmodon fulviventer and S. hispidus

Interactions between two sympatric species of cotton rat, Sigmodon fulviventer and S. hispidus, were studied for 1 year. Both species had similar ecological requirements and occurred in bunchgrass (Sporobolus wrightii) on the central plateau in Durango, Mexico. Demographic changes in S. hispidus populations following experimental removal of S. fulviventer, the numerically dominant animal, included: (1) higher population levels; (2) slightly higher survival rates; (3) slightly greater life expectancy; (4) occupation of areas formerly held by S. fulviventer; and (5) greater distances captured from individual centers of activity. These changes were attributed to S. hispidus immigrating into an unoccupied space in habitat common to both species and less opportunity for interspecific interactions following removal of S. fulviventer. A postexperimental trapping study 1 year later revealed that S. fulviventer had increased its populations to near preremoval levels and had reinvaded and reoccupied areas held by S. hispidus during the removal experiment. Correspondingly, the S. hispidus population had decreased and been displaced by S. fulviventer. It was concluded that both species were interacting in unmanipulated populations, but that the interactions were of a passive (avoidance) nature. These interspecific interactions may influence population regulation, habitat selection, geographical range-extending ability and evolution in both species. Although competitive interactions were not demonstrated, certain data suggested the possibility of some form of interspecific competition. At present, S. fulviventer appears to be the numerically and interactively dominant Sigmodon. INTRODUCTION Intersp-ecific interactions between closely related small mammals arem difficult to demonstrate and evaluate in field situations. Baker (1969) observed that when two species of grass-eating, runway-making rodents of the genus Sigmodon (cotton rats) live in the same area, one is generally abundant and the other less abundant. Such a situation existed in the desert-grassland ecotone of E-Central Durango, Mexico (240 38' N lat and 1030 42' W long). S. fulviventer Allen, usually abundant, and S. hispidus Say and Ord, usually uncommon, were resident in bunchgrass (Sporobolus wrightii) habitat. Hence, this area offered an excellent opportunity to study population dynamics and interactions of both species. Adults of S. fulviventer and S. hispidus in this part of Mexico have similar body weights and measurements but are easily distinguished by different hair colors and other characteristics (Baker, 1969). This study attempts to describe the numerical and spatial relationships between these cotton rats, and to demonstrate certain demographic changes which occur when sympatric populations of these 1 Present address: Department of Zoology and Entomology, Iowa State University, Ames 50010.

A New Species of Microtine from the Late Pliocene of Kansas

A new species of microtine, Pliophenacomys finneyi , is named on the basis of smaller crown height and shorter dentine tracts from the Fox Canyon local fauna of late Pliocene age. Pliophenacomys finneyi is considered to be ancestral to P. primaevus , which has a higher crown height and dentine tracts and is found in stratigraphically younger local faunas in the Great Plains area. We suggest that the absence of Pliophenacomys from the type locality of the Rexroad local fauna is due to its ecological replacement by the genus Sigmodon .

Comparative post-natal growth in five species of the genus Sigmodon. II. Cranial character relationships.

At birth, the catton rat skull is oval and the braincase continues to expand during the first 20 days to near the adult size. Subsequently with the development of the dorsal area and the extension of the bones at the base of the braincase, the rounded form is transformed into the typical long-snouted appearance of the adult. Skull measurements demonstrate the initial rapid expansion of the braincase and the subsequent extension of the rostrum. Adult skull size is attained within the first 100 days of life. Normally, during the first days after birth, height of the braincase is greater than the length of the post-palatal area. However, at 20 to 30 days growth in the latter is greatest and its dimensions surpass those of the former. In three species, Sigmodoll hispidru, Sigmodon alleni and Sigmodon ochrognathus , the rostral length exceeds the height of the braincase only after the animals are over 100 days old. At 40 days palatal and maxillary tooth-row lenglbs are ncar the maximum adult size, while tbe diastema is 50 to 67 percent (depending on the species). At birth the zygomatic arches are small but rapidly expand laterally in comparison with the slower-growing braincase. This process, together with the lengthening of the rostral region is related to weaning and the development of the masticatory and facial muscles. The change of growth from an accelerated phase (1 to 40 days) to a much slower rate seems correlated with attainment oi sexual maturity.

Genus Sigmodon

Genus Sigmodon