Chaetodipus Penicillatus Research Articles

Gut Microbial Ecology of Five Species of Sympatric Desert Rodents in Relation to Herbivorous and Insectivorous Feeding Strategies.

The gut microbial communities of mammals provide numerous benefits to their hosts. However, given the recent development of the microbiome field, we still lack a thorough understanding of the variety of ecological and evolutionary factors that structure these communities across species. Metabarcoding is a powerful technique that allows for multiple microbial ecology questions to be investigated simultaneously. Here, we employed DNA metabarcoding techniques, predictive metagenomics, and culture-dependent techniques to inventory the gut microbial communities of several species of rodent collected from the same environment that employ different natural feeding strategies [granivorous pocket mice (Chaetodipus penicillatus); granivorous kangaroo rats (Dipodomys merriami); herbivorous woodrats (Neotoma albigula); omnivorous cactus mice (Peromyscus eremicus); and insectivorous grasshopper mice (Onychomys torridus)]. Of particular interest were shifts in gut microbial communities in rodent species with herbivorous and insectivorous diets, given the high amounts of indigestible fibers and chitinous exoskeleton in these diets, respectively. We found that herbivorous woodrats harbored the greatest microbial diversity. Granivorous pocket mice and kangaroo rats had the highest abundances of the genus Ruminococcus and highest predicted abundances of genes related to the digestion of fiber, representing potential adaptations in these species to the fiber content of seeds and the limitations to digestion given their small body size. Insectivorous grasshopper mice exhibited the greatest inter-individual variation in the membership of their microbiomes, and also exhibited the highest predicted abundances of chitin-degrading genes. Culture-based approaches identified 178 microbial isolates (primarily Bacillus and Enterococcus), with some capable of degrading cellulose and chitin. We observed several instances of strain-level diversity in these metabolic capabilities across isolates, somewhat highlighting the limitations and hidden diversity underlying DNA metabarcoding techniques. However, these methods offer power in allowing the investigation of several questions concurrently, thus enhancing our understanding of gut microbial ecology.

Small mammal assemblage composition and habitat associations across an elevational gradient in southern California

AbstractElevational gradients coincide with expansive climatic gradients and diverse plant and animal communities. We evaluated the small mammal assemblages in eight distinct vegetation types across an elevational gradient in southern California, the Deep Canyon Transect, to determine how assemblage composition changes across the gradient and to identify species with similar habitat associations. Livetrapping efforts (4,800 trap-nights) yielded 1,097 captures of 713 individuals, representing 14 heteromyid and cricetid species. Heteromyids dominated the six lower-elevation vegetation types (< 1,300 m a.s.l.), whereas cricetids dominated the upper end of the gradient. Richness and diversity exhibited bimodal responses to elevation, which do not conform to mid-domain effect null predictions. Canonical correspondence analysis revealed that 75% of the variation in small mammal abundances was explainable by habitat characteristics, and cluster analysis grouped small mammals into three ecologically distinct groups based on their habitat associations. One contained only Chaetodipus penicillatus, while the others were comprised of low- and high-elevation species, respectively. The low-elevation species exhibit unusual levels of sympatry (and syntopy) among closely related species of pocket mice (Chaetodipus). Further efforts should investigate the mechanisms of coexistence for Chaetodipus species with nearly identical associations and seasonal effects on richness and diversity. Repeated surveys of entire gradients such as the Deep Canyon Transect will help refine our understanding of temporal dynamics of community assemblage and diversity.

Playing to their evolutionary strengths; heteromyid rodents provide opposite snake evasion strategies in the face of known and novel snakes

We evaluated the response of two competing heteromyid rodents, Desert Pocket Mice (Chaetodipus penicillatus) and Merriam's Kangaroo Rat (Dipodomys merriami) towards risk from morphologically convergent snakes, the Sidewinder Rattlesnake (Crotalus cerastes), and the Saharan Horned Viper (Cerastes cerastes). The sidewinder and these rodents originated in the Mojave Desert and, thus, they share an evolutionary history. The Horned Viper originated in the Sahara and is an unknown and novel predator. Each snake poses a different risk for which the optimal strategy of the rodents will differ. The sidewinder belongs to a lineage that evolved heat sensing pits, allowing it to detect rodents on nights without ambient moon light, while the Horned Vipers lack this adaptation. We used Giving-up Densities as a measure of risk perception and compared their responses in relationship to microhabitat, moonlight, time and risk from other predators. Pocket mice feared both snakes and kangaroo rats acted in a relatively fearless manner. The differences between the rodents can be attributed to their snake-evasion adaptations. Kangaroo rats used their saltatorial agility which allows them to take risk while pocket mice climb out of harm's-way and enter torpor to reduce energetic costs when risk prevents foraging.

Temporal changes in species composition affect a ubiquitous species' use of habitat patches.

Across landscapes, shifts in species composition often co‐occur with shifts in structural or abiotic habitat features, making it difficult to disentangle the role of competitors and environment on assessments of patch quality. Using over two decades of rodent community data from a long‐term experiment, we show that a small, ubiquitous granivore (Chaetodipus penicillatus) shifted its use of different experimental treatments with the establishment of a novel competitor, C. baileyi. Shifts in residency, probability of movement between patches, and the arrival of new individuals in patches altered which treatment supported the highest abundances of C. penicillatus. Our results suggest that the establishment of a new species worsened the quality of the originally preferred treatment, likely by impacting resource availability. Paradoxically, the presence of the new species also increased C. penicillatus’ use of the less preferred treatment, potentially through shifts in the competitive network on those plots.

Can we predict the success of a parasite to colonise an invasive host?

To understand whether a parasite can exploit a novel invasive host species, we measured reproductive performance (number of eggs per female per day, egg size, development rate and size of new imagoes) of fleas from the Negev desert in Israel (two host generalists, Synosternus cleopatrae and Xenopsylla ramesis, and a host specialist, Parapulex chephrenis) when they exploited either a local murid host (Gerbillus andersoni, Meriones crassus and Acomys cahirinus) or two alien hosts (North American heteromyids, Chaetodipus penicillatus and Dipodomys merriami). We asked whether (1) reproductive performance of a flea differs between an alien and a characteristic hosts and (2) this difference is greater in a host specialist than in host generalists. The three fleas performed poorly on alien hosts as compared to local hosts, but the pattern of performance differed both among fleas and within fleas between alien hosts. The response to alien hosts did not depend on the degree of host specificity of a flea. We conclude that successful parasite colonisation of an invasive host is determined by some physiological, immunological and/or behavioural compatibility between a host and a parasite. This compatibility is unique for each host-parasite association, so that the success of a parasite to colonise an invasive host is unpredictable.

Anthropogenic water sources and the effects on Sonoran Desert small mammal communities.

Anthropogenic water sources (AWS) are developed water sources used as a management tool for desert wildlife species. Studies documenting the effects of AWS are often focused on game species; whereas, the effects on non-target wildlife are less understood. We used live trapping techniques to investigate rodent abundance, biomass, and diversity metrics near AWS and paired control sites; we sampled vegetation to determine rodent-habitat associations in the Sauceda Mountains of the Sonoran Desert in Arizona. A total of 370 individual mammals representing three genera and eight species were captured in 4,800 trap nights from winter 2011 to spring 2012. A multi-response permutation procedure was used to identify differences in small mammal community abundance and biomass by season and treatment. Rodent abundance, biomass, and richness were greater at AWS compared to control sites. Patterns of abundance and biomass were driven by the desert pocket mouse (Chaetodipus penicillatus) which was the most common capture and two times more numerous at AWS compared to controls. Vegetation characteristics, explored using principal components analysis, were similar between AWS and controls. Two species that prefer vegetation structure, Bailey’s pocket mouse (C. baileyi) and white-throated woodrat (Neotoma albigula), had greater abundances and biomass near AWS and were associated with habitat having high cactus density. Although small mammals do not drink free-water, perhaps higher abundances of some species of desert rodents at AWS could be related to artificial structure associated with construction or other resources. Compared to the 30-year average of precipitation for the area, the period of our study occurred during a dry winter. During dry periods, perhaps AWS provide resources to rodents related to moisture.

Sonoran Desert rodent abundance response to surface temperature derived from remote sensing

Nocturnal rodents play a key role in the Sonoran Desert ecosystem as consumers, prey and reservoirs of disease-yet rodent distribution remains poorly mapped. We use surface temperature extracted from the Landsat Thematic Mapper thermal infrared band to model rodent abundance obtained from trapping data at the Organ Pipe Cactus National Monument in southwest Arizona. We produce response curves that describe the effects of surface temperature on species abundance. Daytime surface temperature derived from images collected in June across thirty rodent trapping grids ranged from 318 K (45.0 °C) to 332 K (59.2 °C). Results show peak seasonal surface temperature splits high species abundances into two groups: Merriam's kangaroo rat, Arizona pocket mouse, desert pocket mouse and southern grasshopper mouse species prefer habitat characterized by higher surface temperatures; and white-throated wood rat, cactus mouse, rock pocket mouse and Bailey's pocket mouse species prefer habitat characterized by lower temperatures. Abundances for the high and low temperature habitat groupings correlate linearly with surface temperature (r = +0.66 and −0.75, respectively, p < 0.001). Surface temperature integrates multiple landscape characteristics (e.g. topography, vegetation cover and soil properties) that define the dominant habitats of ORPI rodents. These results prove that simple models can inform complex ecological processes.

Pleistocene Impacts on the Phylogeography of the Desert Pocket Mouse(Chaetodipus penicillatus)

The desert pocket mouse (Chaetodipus penicillatus) comprises 6 nominate subspecies that occupy warm, sandy desert-scrub habitats across the Mojave and Sonoran deserts. The most thorough morphological assessment within the species noted variable levels of distinctiveness, leading to uncertainty regarding the geographic distributions of subspecies. Subsequent genetic assessments using chromosomal, allozymic, and mitochondrial DNA (mtDNA) sequence data detected a general east–west divergence centered on the Colorado River, but few locations were included in these assessments. We investigated phylogeographic structure in C. penicillatus by sequencing regions of mtDNA for 220 individuals from 51 locations representing all continental subspecies. We identify 2 major monophyletic mtDNA lineages (clades) roughly centered in the Mojave and Sonoran deserts. These clades broadly overlap along the Lower Colorado River valley and adjacent desert regions across most of the range of C. p. penicillatus. Outside this zone of mtDNA clade overlap, Sonoran clade haplotypes occur in populations from across the range of C. p. pricei and extend to the northwestern edge of the Sonoran Desert within the southern range of C. p. angustirostris. Northern clade haplotypes occur in populations within the ranges of C. p. sohrinus and C. p. stephensi and in populations from the western Mojave Desert in the northern range of C. p. angustirostris. Based on rough estimates for rates of sequence evolution, divergence among the major clades appears to have occurred during the Pleistocene, but well before the latest glacial maximum. The secondary contact among the major clades appears to have some longevity, with little evidence of recent, postglacial range expansion. We develop ecological niche models (EMNs) for the major lineages of C. penicillatus, and project these models onto reconstructions of climatic conditions during the latest glacial maximum (LGM; 18,000–21,000 years ago). The ENMs for each clade indicate differences in predicted current geographic distributions as well as distributions during the LGM. Models for the LGM indicate broad retention of potential habitat within the area of contact among the major clades. Furthermore, the ENM for the Mojave clade in particular indicates retention of suitable habitat during the LGM in small isolated patches within northern areas, consistent with the haplotype network that supports the perspective that some populations from the Mojave clade were isolated within northern refugia during the last glacial period.

Assessment of mercury concentrations in small mammals collected near Las Vegas, Nevada, USA

Mercury concentrations in liver and hair tissue were determined for five species of small mammals captured near Las Vegas, Nevada, USA. These data were then used to evaluate the suitability of using hair as a noninvasive technique for determining body burdens of mercury. A total of 104 small mammals were captured and analyzed; four main species were examined and included: Dipodomys merriami, Chaetodipus penicillatus, Peromyscus eremicus, and Neotoma lepida. Mean mercury concentrations were highest in N. lepida, followed by D. merriami, C. penicillatus, and P. eremicus respectively. Positive associations were found between hair and liver taken from D. merriami (r = 0.647) and C. penicillatus (r = 0.533) indicating that hair may be a suitable indicator of body burdens in these two species.

Chemosensory recognition by males of the Desert Pocket Mouse, Chaetodipus pencillatus to odors of various species of snakes

Studies were conducted to assess responses of the Desert Pocket Mouse Chaetodipus pencillatus, to chemosensory cues (treatment odors) associated with three naturally-occurring sympatric snake predators (Crotalus atrox, Pituophis melanoleucas, Elaphe guttata), and a snake that does not feed on mammals (Hypsiglena torquata), as well as an odorless control (water) and pungency control (cologne). Pocket mice were tested in a chamber where they were exposed to various treatments and their locomotor activity and defecation rate were recorded. Locomotor activity and defecation rates were significantly greater for mice exposed to odors associated with snake predators as compared to H. torquata or controls. There was no significant difference in responses of pocket mice to water or cologne treatments. Results suggest that because all test subjects had no prior experience with any of the snake species, their ability to detect and respond to odors associated with these predators must be innate.

Foraging under Multiple Costs: The Importance of Predation, Energetic, and Assessment Error Costs to a Desert Forager

We investigated spatial and temporal variation in the use of resource patches by Chaetodipus penicillatus by documenting changes in foraging activity over several seasons, under two moon phases, and in two resource patch types. In particular, we examined the influence of nocturnal illumination (a surrogate for predation risk) and ambient temperature on: (1) foraging effort (which is inversely proportional to the giving-up density, GUD), and (2) GUD equality, i.e. the ability of foragers to accurately assess patch quality by equalizing heterogeneous resource patches to the same GUD. There were significant positive relationships between foraging effort and relative GUD equality, ambient temperature and foraging effort, and ambient temperature and GUD equality. In contrast, despite having a strong effect at the beginning of our study, moonlight did not have a consistent or significant impact on foraging effort and GUD equality when analyzed over several seasons. Our results indicate that as energetic or predation costs decline, foraging effort rises, which in turn, leads to an increase in GUD equality and a reduction in assessment error costs. This increased harvesting equality is due to both enhanced functional harvest rates and increased accuracy of patch assessment by foragers as more time is spent within a patch. In addition, predation risk and energetic costs appeared to switch in relative importance in C. penicillatus over the course of several seasons. These results emphasize the importance of considering multiple foraging costs and their additive effects in studies of foraging and patch use.

The genus Geomylichus Fain (Acari: Listrophoridae) from Mexico, with descriptions of four new species

From heteromyid rodents collected on the Mexican Plateau, new and named species of Geomylichus Fain (Listrophoridae) were found. Commensal prevalence, intensity, mean intensity and microdistribution are given for each association. Four new species are described, each from a different subspecies or species of Chaetodipus Merriam (Heteromyidae): G (Geomylichus) nelsoni n. sp. from Chaetodipus nelsoni nelsoni (Merriam); G. (G.) durangoensis n. sp. from Chaetodipus nelsoni canescens (Merriam); G. (G.) penicillatus n. sp. from Chaetodipus penicillatus eremicus (Mearns); G (G.) hispidus n. sp. from Chaetodipus hispidus zacatecae (Osgood). Additionally, new host records and new range extensions for five namedspecies of Geomylichus from the Mexican Plateau are given.

Speciation in the Desert Pocket Mouse (Chaetodipus penicillatus Woodhouse)

Variation in mitochondrial DNA was studied across the range of Chaetodipus penicillatus . Sequence data from the COIII gene and restriction-enzyme analysis of a 2,150 base pair fragment indicated a significant genetic demarcation between samples assigned to C. p. pricei and those assigned to C. p. eremicus . Sequence and restriction data also show that populations assigned to C. p. eremicus share a common history not shared by populations assigned to C. p. pricei . These data are concordant with independent evidence from nuclear data of divergence among populations of C. penicillatus at protein and chromosomal levels. Furthermore, the overall pattern of phylogeographic population structure in C. penicillatus is consistent with an hypothesis of long-term isolation and divergence of Chihuahuan and Sonoran desertscrub biotas. We recommend that C. p. eremicus be recognized as a distinct species. The appropriate binomial for populations thus far examined from the Chihuahuan Desert is Chaetodipus eremicus .

Long‐Term Experimental Study of a Chihuahuan Desert Rodent Community: 13 Years of Competition

An experimental study of competition between kangaroo rats (Dipodomys spp.) and other sympatric desert rodents using exclosures with "semipermeable" fences has been continuously maintained at a site in the northern Chihuahuan Desert since 1977. A new set of experimental manipulations begun in 1988 at the same site repeated this study. As reported previously for this community, exclusion of three species of Dipodomys from both original and new experimental plots resulted in greater abundances of five species of small granivorous rodents (Chaetodipus penicillatus, Perognathus flavus, Peromyscus eremicus, P. maniculatus, Reithrodontomys megalotis) on these plots relative to controls. In contrast, there were no significant treatment effects on the abundances of insectivorous grasshopper mice (Onychomys spp.). The long time lag before the response by small granivores to Dipodomys removal observed in the original experiment was not repeated in the experiment begun in 1988. Long—term (10 yr) exclusion of kangaroo rats from experimental plots has resulted in changes in vegetative cover, particularly increased grassiness, on these plots relative to controls. We used the repetition of the Dipodomys exclusion experiment in 1988 to evaluate the importance of this potential indirect effect of kangaroo rats on other rodents in this community. By examining differences in rodent capture numbers on the original and new sets of Dipodomys exclusion plots, we could identify four species (C. penicillatus, Perognathus flavus, Peromyscus eremicus, P. maniculatus) whose responses to Kangaroo rat removal reflected direct competition from kangaroo rats, one species (R. megalotis) whose response reflected both direct and indirect (via vegetation changes and habitat selection) effects, and two species (Sigmodon hispidus, S. fulviventer) whose responses reflected only vegetation—mediated effects. The continuous presence of competition between small granivores and kangaroo rats over the 13—yr study despite large, specie—specific fluctuations in abundances suggests that competition is pervasive within this community.

New Host and Locality Records of Coccidia (Apicomplexa: Eimeriidae) from Rodents in the Southwestern and Western United States

One hundred forty-seven murid and heteromyid rodents were collected from various sites in the southwestern and western United States (Arizona, Colorado, New Mexico, Texas, and Utah) and Baja California Norte, Mexico, and their feces were examined for coccidial parasites. Of these, 53 (36%) were infected with at least 1 coccidian; 45 of 53 (85%) of the infected rodents harbored only 1 species of coccidian. Infected rodents included: 10 of 22 (45%) Neotoma albigula, 3 of 11 (27%) Neotoma floridana, 2 of 14 (14%) Neotoma lepida, 15 of 29 (52%) Neotoma micropus, 5 of 8 (63%) Peromyscus crinitis, 6 of 6 (100%) Peromyscus difficilis, 1 of 2 (50%) Peromyscus eremicus, 9 of 34 (26%) Sigmodon hispidis, and 2 of 3 (67%) Sigmodon ochrognathus; 4 Neotoma cinerea, 3 Neotoma devia, 3 Neotoma mexicana, 1 Peromyscus maniculatus, 1 Onychomys leucogaster, 1 Onychomys torridus, 3 Chaetodipus fallax, and 2 Chaetodipus penicillatus were negative. Although no new species was found, the following coccidians were identified from infected rodents: Eimeria albigulae from N. albigula, N. floridana, and N. micropus, Eimeria antonellii from N. albigula and N. micropus, Eimeria ladronensis from N. albigula, N. floridana, N. lepida, and N. micropus, Eimeria arizonensis and Eimeria lachrymalis from P. crinitis and P. difficilis, Eimeria lachrymalis from P. eremicus, Eimeria tuskeegensis from S. ochrognathus, and Eimeria roperi, Eimeria sigmodontis, Eimeria tuskeegensis, Eimeria webbae, and an unidentified species of Eimeria from S. hispidis. This report documents 12 new host and several distributional records for Eimeria species from murid rodents in Arizona, Texas, and Utah.

Effects of Day Length, Temperature, and Green Food on Testicular Development in a Desert Pocket Mouse Perognathus formosus

Coordination of reproductive condition in male pocket mice (Perognathus formosus) by environmental factors limits the season of reproduction to a time associated with the springtime peak in availability of dietary resources that are critical to reproduction. This optimal time for reproduction follows winter hibernation and precedes summer drought. Responsiveness of reproductive function to environmental influences was studied in male P. formosus of the Mojave Desert region by bringing freshly captured animals into the laboratory at different seasons and exposing them to a variety of experimental manipulations. Long days (16 h light/day) stimulated or maintained seasonal testicular function, whereas short days (8 h light/day) were nonstimulatory or inhibitory. However, because natural reproductive development begins while the mice hibernate underground in total darkness, it is not yet clear how day length might influence this pattern of reproductive development in nature. Reproductive development was great...

Influence of Photoperiod and Partial Contact on Estrus in the Desert Pocket Mouse, Perognathus penicillatus1

The effects of photoperiod and proximity of a male on the incidence of estrus were studied in the desert pocket mouse (Perognathus penicillatus). Groups of 8–20 females were maintained for two years in one of three photoperiods: (1) seasonally increasing and decreasing daylength; (2) constant long (16 h) daylength; (3) constant short (10 h) daylength. Within each photoperiod one half of the animals were housed singly, the other half were subjected to male stimulation by being housed with a male in a screen-divided cage. Unpaired mice in the seasonal photoperiod showed the expected annual cycle of a high frequency of estrus in spring and summer and quiescence in fall and winter. Constant photoperiod, either long or short, caused a disruption of this periodic behavior. The mice exhibited discrete periods of higher and lower estrous frequency of several months’ duration, which did not coincide with natural seasons and differed in timing between individual mice. Olfactory and possibly other stimulation by the constant proximity of a male led in screen-paired mice to an increased level of sexual activity. This increase was much more pronounced in animals maintained under a constant long or constant short photoperiod than in those under normal seasonal illumination. These results are consistent with the hypothesis that exposure to abnormal, constant photoperiods will cause, in the pocket mouse, an escape from the entrainment of the circannual gonadal rhythm by annual seasons and that the proximity of a male exerts an enhanced stimulation on their sexual activity under these conditions. These animals may therefore provide a good model for the study of the interaction of the two modes of stimulation and their effects on the neuroendocrine regulation of estrous behavior.

Karyotypic Variation in the Pocket Mouse,Perognathus PenicillatusWoodhouse (Rodentia-Heteromyidae)

SUMMARYThree karyotypic variants of six of the eight recognized subspecies of the Desert Pocket Mouse, Perognathus penicillatus Woodhouse, are described. All variants have a diploid number of 46, so differences present are of a non-Robertsonian nature. The mechanisms and direction of chromosomal change, evolutionary history, geographic distribution, and systematic status of the variants are discussed.

Partial Contact as a Stimulus to Laboratory Mating in the Desert Pocket Mouse, Perognathus penicillatus

Partial Contact as a Stimulus to Laboratory Mating in the Desert Pocket Mouse, Perognathus penicillatus

Yttrium localization in the desert pocket mouse Perognathus penicillatus.

Forty-eight hours after intraperitoneal mnjection of radioactive yttrium (Y/sup 91/) into the desert pocket mouse (Perognathus penicillatus) large quantitmes of the isotope were discovered in the kidney tissue. Teeth and bones also concentrated this element to a large extent. Very little isotope was found in either blood or muscle. (auth)