Diurnal Ground Squirrel Research Articles

Rodent burrow network dynamics under human-induced landscape transformation from desert to steppe in Kalmykian rangelands.

Rodents play an important role in rangelands through the engineering of extensive burrow systems, which provides key habitats for many animal and plant species. We have analyzed the long-term variation in the abundance and distribution of rodent burrows in grazing ecosystems of southern Russia (Kalmykia) under the landscape change from desert to steppe caused by the drastic reduction of livestock after the collapse of the USSR in the early 1990s. We conducted burrow surveys in the "desert" (1980) and "steppe" (2017) periods on 19 3-km transects. We found considerable changes in burrow abundance and distribution, as well as evidence of desert habitat fragmentation and isolation caused by the expansion of tall-grass communities. Burrows of the open-dwelling diurnal ground squirrel (Spermophilus pygmaeus), the dominant and the keystone species during the "desert" period, almost completely disappeared from the rodent burrow network by 2017, indicating significant habitat loss. In contrast, the burrows of the folivorous social vole (Microtus socialis) which was rare in the 1980s, became abundant and ubiquitously distributed. The burrow density of the desert-dwelling psammophilous midday gerbil (Meriones meridianus) decreased, while the distances between occupied patches increased, indicating desert habitat fragmentation and loss of population connectivity. Burrows of the folivorous tamarisk gerbils (M. tamariscinus) were recorded only sporadically in both 1980 and 2017. The observed changes in the rodent burrow network, the key component of grazing ecosystems, correlate with rodent species ecology and can have long-term and important consequences for ecosystem functioning.

Changes in neuropeptide Y immunoreactivity and transcript levels in circadian system structures of the diurnal rodent, the thirteen-lined ground squirrel

The intergeniculate leaflet (IGL) and its neuropeptide Y (NPY) projection to the main circadian clock, the suprachiasmatic nucleus (SCN), have been the focus of extensive research conducted, for the most part, on nocturnal rodent species. However, a variety of anatomical and physiological differences between the circadian system of diurnal and nocturnal species have been reported. These differences led us to question whether the role of NPY in the circadian system of the diurnal ground squirrel differs from that in nocturnal rodents. We used semi-quantitative immunohistochemistry to analyze NPY content in SCN terminals of squirrels sacrificed at specific times of the day and compared the data to previous published results from the rat. Additionally, IGL NPY mRNA was quantified using real-time PCR to determine if varying NPY immunoreactivity (-ir) levels could be the result of changes in peptide transcription. Our results demonstrate that NPY-ir levels in the ground squirrel SCN peak during the middle of the night unlike what is observed in the rat. Cell counts of NPY-ir neurons in the IGL revealed a pattern of variation 6 h out of phase compared to what was observed in the SCN. NPY mRNA levels showed only one sharp increase in the middle of the night, coinciding with increases in NPY-ir levels observed in the SCN. Differences in the pattern of fluctuation of NPY in the SCN between the rat and squirrel suggest that this peptide may serve distinct roles in the circadian system of diurnal and nocturnal species. Our data provide the first evidence of the relationship between transcript and peptide levels in the circadian system of a diurnal species.

Diffuse light increases metabolic activity in the lateral geniculate nucleus, visual cortex, and superior colliculus of the cone-dominated ground squirrel visual system

Ground squirrels were monocularly exposed to either steady- or flashing-diffuse light for 45 min following an injection of 14C 2-deoxyglucose (2-DG). Autoradiographic analysis indicated greater metabolic activity in the lateral geniculate nucleus, visual cortex and superior colliculus (SC) of the hemisphere lying contralateral to and receiving input from the diffusely stimulated eye (covered by a white mask), than in the corresponding regions of the other hemisphere receiving input from the occluded eye (black mask). The diffuse light results for the cortex and colliculus of the diurnal ground squirrel are different from those for the nocturnal rat. In the rat visual cortex, there is no difference between metabolic activity under conditions of diffuse light (steady or flashing) and under darkness. In the rat SC, although flashing-diffuse light increases metabolic activity (as is the case for the squirrel), steady-diffuse light decreases it to a level below that which occurs in darkness. The cortex and colliculus differences in 2-DG response to diffuse light between the ground squirrel and rat were attributed to differences in the operations of their respective cone- and rod-dominated visual systems.

Immunocytochemical characterization of the suprachiasmatic nucleus and the intergeniculate leaflet in the diurnal ground squirrel, Spermophilus lateralis

The suprachiasmatic nucleus (SCN) and the intergeniculate leaflet (IGL) are retinorecipient structures that play important roles in the expression of circadian rhythmicity. We examined these two structures in a diurnal ground squirrel, Spermophilus lateralis, using i immunohistochemical techniques, and cholera toxin-bound horseradish peroxidase. A number of immunoreactive substances are distributed within the ground squirrel SCN in a pattern similar to that reported in many other mammals. These include vasopressin, vasoactive intestinal polypeptide, serotonin, neuropeptide Y (NPY), and glial fibrillary acidic protein. The squirrel SCN differs from that of most other species examined to date in two respects. First, a dense cluster of cells containing immunoreactive l-enkephalin ( l-ENK-IR) is observed in the center of the SCN. Second, there is a contralateral, but no ipsilateral, projection from the retina to the SCN. In the lateral geniculate region there is a substantial region that contains NPY-immunoreactive cells and receives a bilateral retinal projection. This region is assumed to be homologous with the IGL described in other mammals. Cells containing l-ENK-IR are distributed throughout the LGN in groups that overlap, but which have a distinctly different distribution than the more extensive groups of NPY-IR cells.

Photically responsive neurons in the hypothalamus of a diurnal ground squirrel

The suprachiasmatic nuclei (SCN) function as a circadian pacemaker. Entrainment to the external light-dark cycle is mediated by the retina which gives rise to both direct and indirect projections to the SCN. The hypothalamic targets of the retinohypothalamic tract (RHT) were investigated in thirteen-lined ground squirrels ( Spermophilus tridecemlineatus) following WGA-HRP injections. The results indicate that retinal fibers project to the entire SCN. Extracellular single-unit activity was recorded in and near the SCN of thiopental sodium anesthetized squirrels while the eyes were photically stimulated. A small population of hypothalamic cells were responsive to retinal illumination. About half of these cells were activated by light while the others were light-suppressed. The majority of these cells responded in a sustained way to light pulses. Light intensities of at least 1000 lux appeared necessary to induce a sustained response to light. No differences in light responsiveness were observed between visual cells inside and outside the SCN. The visual properties of SCN cells have previously been investigated in hamsters and rats, both nocturnal species. Hypothalamic cells in all 3 species were similar in that they showed predominantly sustained responses to retinal illumination. The diurnal squirrel differed from the other two species in that there was a higher proportion of photically suppressed cells in the squirrel, and in that higher light intensities were required to stimulate photically responsive neurons.

Standard Operative Temperatures and Thermal Energetics of the Antelope Ground Squirrel Ammospermophilus leucurus

We measured standard operative temperatures ($T_{es}$) for the diurnal ground squirrel Ammospermophilus leucurus in its Southern California desert habitat by using pelt-covered metal models of the animals. Values of $T_{es}$ were used to predict duration of periods of activity, microhabitat use, and energy costs of thermoregulation at various times of the year. For A. leucurus, $T_{es}$ (a direct measure of heat flow) specifies the thermal environment more realistically than any of the standard micrometeorological indices. In the hot season, $T_{es}$ in unshaded areas can be 30 C above the upper critical temperature ($T_{uc}$) of A. leucurus and 20 C above air temperature for much of the day. Under such conditions maximum tolerable periods of surface activity for A. leucurus are 7-9 min. Even in the shade, $T_{es}$ often exceeds $T_{uc}$, and the only available thermal refugia on hot days are in underground burrows. These findings strongly support the interpretation that the thermoregulatory strategy of A...

A comparative study of the visual system in the diurnal ground squirrel, Citellus tridecemlineatus tridecemlineatus and in the nocturnal guinea pig, Cavia cobaya.

A comparative study of the visual system in the diurnal ground squirrel, Citellus tridecemlineatus tridecemlineatus and in the nocturnal guinea pig, Cavia cobaya.

A STUDY OF THE LATERAL GENICULATE BODY IN THE DIURNAL GROUND SQUIRREL, CITELLUS TRIDECEMLINEATUS TRIDECEMLINEATUS AND IN THE NOCTURNAL GUINEA PIG.

AbstractThe ground squirrel, Citellus tridecemlineatus tridecemlineatus, is a strictly diurnal species and possesses a pure‐cone retina. The present work comprises the results of an investigation of the morphology and the histological structure of the lateral geniculate body of this interesting mammal. The lateral geniculate body of the nocturnal guinea pig was also investigated and a comparison of the two made.In both species, the lateral geniculate body comprises two nuclei: a smaller ventral and a larger dorsal. These nuclei are devoid of lamination — a feature presumably related to the absence of binocular vision in these animals. Only the dorsal nucleus projects to the cortex in both species.Measurements on 1,000 neurons in the dorsal nucleus of both species reveal that neuron population is uniform in size and that on the average the neurons of the guinea pig are a little smaller (ground squirrel, nucleus: 12.36 m̈; perikaryon: 16.70 m̈ and guinea pig, nucleus: 12 m̈; perikaryon: 15.82 m̈).The lateral geniculate body of the guinea pig is smaller than that of the ground squirrel. The dorsal nucleus in the latter species is estimated to contain 74,900 neurons. This is a large number and undoubtedly is related to the fact that the retina is pure‐cone with numerous ganglion cells and a large optic nerve.

The Relation of Oxygen Consumption to Temperature in Desert Rodents

No information is available on the effects of temperature upon the oxygen consumption of any desert rodent, although the Schmidt-Nielsens (1950 a ) have made measurements on several species at 25° C. in the course of their extensive investigations of water metabolism (1952). Accordingly, this study dealing with the Merriam and Panamint kangaroo rats ( Dipodomys merriami and D. panamintinus ) and with the antelope ground squirrel ( Citellus leucurus ) was undertaken. It attempts to define the zones of metabolic thermal neutrality for these desert animals, to analyse their metabolic responses to ambient temperatures above and below thermal neutrality, and to compare the temperature regulation of the nocturnal kangaroo rats, which do not meet the most intense desert heat, with that of the diurnal ground squirrel, which periodically encounters high air temperatures and intense solar radiation. This investigation was carried out during tenure of a U. S. Public Health Service Research Fellowship in the Department of Zoology, University of California, Los Angeles. I am grateful for the numerous courtesies extended by Dr. George A. Bartholomew in placing the facilities of his laboratory at my disposal. Materials and Methods .—Twenty-five Merriam kangaroo rats, 15 Panamint kangaroo rats, and 12 antelope ground squirrels were used in this study. All were captured during June and July, 1953, at Lovejoy Buttes, Los Angeles County, California, a site located near the western edge of the Mojave Desert. They were housed in glass terraria during their stay in the laboratory. Each terrarium had a sand-covered floor and was provided with a 16 oz. bottle made of brown glass, which afforded the animals a place of retreat. Cotton was available for nesting material. The antelope ground squirrels and Panamint kangaroo rats were housed individually. The more sociable Merriam kangaroo rats were placed several to a terrarium. Pood consisting of sunflower …