Location of satellite DNAs in the chromosomes of the kangaroo rat (Dipodomys ordii)

The location of satellite DNA sequences in metaphase chromosomes has been studied in the kangaroo rat by the in situ hybridization technique, staining techniques and phase contrast microscopy. The HS- satellite DNA is located at the kinetochores of all but three chromosome pairs. The HD satellite is located predominantly in the short arms of the chromosomes containing HS- and in the kinetochores of chromosome pairs that lack HS-. The regions that contain the satellite DNA sequences can also be identified by the Giemsa staining technique, and can be visualized with phase contrast microscopy or following Feulgen staining of fixed chromosome preparations.     

Fractionation and characterization of satellite DNAs of the kangaroo rat (Dipodomys ordii)

Nuclear DNA from liver cells of the kangaroo rat species Dipodomysordii was fractionated and characterized with the aid of buoyant density gradients in neutral and alkaline CsCl and in Ag⁺-Cs₂SO₄. More than one-half of the DNA was present in three density satellites, a greater proportion than in any other species yet reported; the purified satellite DNAs were denser than principal DNA. All satellite fractions revealed sharp isopycnic bands and narrow denaturation profiles. Two had identical buoyant densities but differed substantially in T_m, base composition, and reassociation kinetics. In alkaline CsCl all three satellites, as well as a shoulder of intermediate repetitive DNA on the heavy side of the principal band, revealed unique strand densities. The most highly repetitive satellite was unusually rich in (G + C) and contained 6.7% of 5-methylcytosine. A survey of internal organs and spermatozoa of an adult male revealed no significant differences in distribution of the satellites among tissues.     

The endogenous stages of Eimeria utahensis (Protozoa: Eimeriidae) in the kangaroo rat, Dipodomys ordii

The endogenous life cycle of Eimeria utahensis is described from experimentally infected kangaroo rats, Dipodomys ordii. The endogenous asexual cycle consisted of 4 generations of meronts. First-generation meronts were concentrated in the anterior third of the small intestine. The succeeding generations of meronts and the sexual stages were concentrated in the middle third of the small intestine. First-generation meronts had a mean diameter of 9.7 micrometer and contained 12 to 16 merozoites. Second-generation meronts had a mean diameter of 8.0 micrometer and contained 12 to 16 merozoites and a residual body. Third-generation meronts had a mean diameter of 12.4 micrometer and contained 4 to 8 merozoites. Fourth-generation meronts had a mean diameter of 8.6 micrometer and contained 16 to 24 merozoites. Young gamonts were located in epithelial cells of the crypts of the small intestine. Shortly after the parasites entered the epithelial cells, the infected cells became displaced into the lamina propria, and most of the mature gamonts were in this location. The nuclei of host cells containing young sexual stages became greatly elongated and flattened. A few young gamonts were seen in cells in which the host cell nuclei were dividing. During development, nuclei of microgamonts became arranged on the periphery of numerous compartments. Only one type of wall-forming body could be distinguished in the macrogamonts.     

Analysis of the frequency of sister chromatid exchange in different regions of chromosomes of the kangaroo rat (Dipodomys ordii)

The frequency of sister chromatid exchanges (SCEs) has been determined for C band and non-C band regions of chromosomes of the kangaroo rat after staining with the fluorescence plus giemsa (FPG) technique. After one complete round of DNA synthesis in the presence of bromodeoxyuridine (BrdU) staining of the C band regions revealed simple or complex asymmetries between chromatids. After two complete rounds of DNA synthesis in the presence of BrdU harlequin chromosomes were observed. Analysis of the distribution of SCE in chromosomes at their 1st and 2nd mitosis showed that relatively few exchanges occur within C band regions, although the frequency of SCEs is high at the junction between C band and non-C band chromosome regions.     

Search for lunar periodicity in the bannertail kangaroo rat (Dipodomys spectabilis)

Abstract

The endogenous activity cycle of the nocturnal bannertail kangaroo rat was investigated. Although bannertail activity is a function of the lunar day as well as the solar day, all ten subjects exhibited free‐running activity periods of solar‐day length; there was no evidence of an endogenous lunar‐day cycle. Animals were provided with a burrow system and a small pseudo‐desert, a laboratory facility in which animal activity data closely resembled measurements taken in the field. Several analytical techniques for quantifying the data were utilized, and one, the mean interval of activity, is recommended to other investigators.     

Helminths of sympatric populations of kangaroo rats (Dipodomys ordii) and grasshopper mice (Onychomys leucogaster) from the high plains of eastern New Mexico

During a 1-yr period 124 Dipodomys ordii and 92 Onychomys leucogaster were trapped from the same locality and were examined for helminths. Only 1 cestode species (Catenotaenia linsdalei) was recovered from D. ordii, whereas O. leucogaster was infected with 2 nematoda (Litomosoides carinii, Mastophorus muris), 2 cestoda (Hymenolepis citelli, and 1 unknown), and 1 acanthocephalan (Moniliformis clarki) species. All represent new host and distribution records.     

Spatial population structure in the banner-tailed kangaroo rat,Dipodomys spectabilis

I attempted to characterize spatial units of local dynamics and dispersal in banner-tailed kangaroo rats (Dipodomys spectabilis), to determine if spatial structure influenced population dynamics in the way predicted by current metapopulation models. D. spectabilis exhibited a hierarchical spatial structure. Local populations that appeared as discrete entities on a scale of kilometers were subdivided into clusters of mounds on a scale of meters. This structure, however, cannot be characyerized in terms of the discrete habitat patches envisioned by the metapopulation models. Occupied areas were statistically distinguishable from the surrounding matrix, but this difference was only quantitative. There were no discrete boundaries between occupied areas and the matrix. Habitat within occupied areas was heterogeneous, and occupied areas in different locations were statistically distinguishable from each other. High heterogeneity within occupied areas, and high contrast among them, make it difficult to define what is a suitable habitat patch for D. spectabilis. On a smaller spatial scale, there was significant aggregation of resident mounds within occupied areas. These aggregations, however, do not correspond to discrete habitat patches. Rather, they appear to result from an interaction between fine-scale habitat heterogeneity and limited dispersal due to natal philopatry and low adult vagility. These complications make it difficult to identify habitat patches independent of the species' distribution. For species like D. spectabilis that are patchily distributed but do not occupy discrete habitat patches, a patch occupancy approach does not seem appropriate for describing spatial structure. Hierarchical spatial structure underscores the need for a framework that incorporates multiple scales of spatial structure, rather than one that pre-imposes a single spatial scale as being important for population dynamics. A framework that (i) considers patchiness as a combination of both habitat heterogeneity, and life-history and behavioral characteristics, and (ii) incorporates hierarchical spatial structure, appears to be the most suitable for conceptualizing spatial dynamics of behaviorally complex vertebrates such as D. spectabilis.     

Elastic energy storage in the hopping of kangaroo rats (Dipodomys spectabilis)

Bipedal hopping of kangaroo rats has been studied by making force plate records and X-ray cinematograph films simultaneously. Calculations using the data so obtained, and
anatomical data, show that energy saving by elastic storage is much less important than
in kangaroos.     

Chromosomes of a cell line of Dipodomys panamintinus (kangaroo rat) a banding and autoradiographic study

The chromosomes of an established cell line of Dipodomys panamintinus have been characterised in terms of their C, G and Q banding patterns, and the distributions of silver grains in autoradiographs of chromosomes labelled in early or late S phase. No relationship could be established between C, G or Q banding regions of chromosomes and a particular S phase time of replication of the DNA in these banded regions. The implication of this result to the concept of heterochromatin is discussed.     

Scatter hoarding by kangaroo rats (Dipodomys merriami) and pilferage from their caches

We observed radio-implanted Merriam's kangaroo rats disposingof 10-g bonanzas of rolled oats in 48 trials in the field. Theprincipal determinant of the initial disposition of discoveredfood was apparently its distance from the day burrow: food foundwithin about 10m was mainly larder hoarded, whereas food encounteredfarther afield was usually dispersed immediately in shallowcaches. Cache sites were newly dug for the purpose and not reused;most caches were nearer the current day burrow than was thefood source, but a few were placed far from both the cacher'sday burrow and its habitual nocturnal range. An experiment withartificial caches indicated that security from discovery increaseswith spacing and with proximity to perennial shrubs. Nine kangaroorats cached dyed food, and fecal dye traces revealed extensivepilferage from five of them, by both conspecifics and otherrodent species. Limited evidence indicates that food encounterednearer home and initially larder hoarded was more secure frompilferage than food initially scattered, and yet kangaroo ratswere observed to scatter caches soon after initial larder hoarding.A kangaroo rat whose dyed stores escaped pilferage fed fromthem at intervals for at least 12 days. Even cachers who incurredpilferage made as much, or more, use of their caches as anythief, suggesting that scattering caches may be a defense againstcatastrophic losses.     

Seasonal variation in various blood indices of the kangaroo rat, Dipodomys panamintinus

1. Various blood indices in the Panamint kangaroo rat revealed seasonal fluctuations. The red blood cell count during winter and summer averaged 7.2 +/- 1.0 X 10(6) and 9.2 +/- 0.2 X 10(6)/mm3 respectively. 2. The mean cell hemoglobin during winter and summer averaged 25 +/- 10.8 pg and 18.6 +/- 3.7 pg respectively. 3. These fluctuations may reveal a rapid rate of red blood cell destruction during winter in combination with a change in diet, concomitant to this, is an increase in mean cell hemoglobin of the surviving red blood cells.     

Adaptations for leaf eating in the great basin kangaroo rat,Dipodomys microps

Summary Dipodomys microps forages in saltbush (Atriplex confertifolia), gathering the leaves into its external check pouches and returning them to the burrow to be cached or eaten. The leaves are available throughout the year and contain 50–80% water. D. microps can survive on these leaves in the laboratory without other food or water, but it is unusual among kangaroo rats in that it quickly succumbs when placed on a diet of air-dried seeds without water or succulent plant material. Its mean urine concentration on the seed diet was 2827 mOsm/l, which is lower than any previously reported for the genus. On the other hand, D. merriami, which occurs with D. microps and is well known as a seed specialist, cannot survive on the saltbush leaves, although it is capable of living on a seed diet without water or green vegetation. D. microps is behaviorally and morphologically specialized for exploiting the unusual leaves of A. confertifolia. The leaves are higher in electrolyte content than the leaves of most plants; but the electrolytes, which are most highly concentrated on the leaf surfaces, apparently serve in the maintenance of water balance in the leaves. D. microps does not usually consume saltbush leaves in toto, but rather uses its unique, chisel-shaped lower incisors to shave off the outer tissue from both sides of the leaf, and then consumes the inner tissue. Sodium concentration with respect to water in the eaten tissue was only 3% that of the discarded shavings, and the specialized photosynthetic parenchyma which is eaten is high in starch content.The highly divergent dietary habits of D. microps should serve to minimize competition with its granivorous congeners. Some of the present limits to the geographic distribution of D. microps are a reflection of its reliance on the leaves of perennial shrubs throughout the year; but where its does occur, D. microps should be independent of the unpredictable availability of ephemeral annuals.     

The influence of seed apparency,nutrient content and chemical defenses on dietary preference in Dipodomys ordii

Summary Physical, nutritional and defensive qualities of seeds differ in the extent to which they influence granivore preference. In a study aimed to quantifying those differences, Ord's kangaroo rats (Dipodomys ordii) were found to prefer the seeds of just three of twenty-nine species: Cryptantha crassisepala, Oryzopsis hymenoides and Salsola kali. Oryzopsis hymenoides was most preferred during the early plant growth season (April–July); preference for S. kali peaked during late (August–November) and dormant (December–March) seasons; and greatest preference for C. crassisepala occurred during dormant and early seasons. Regression of forage ratios, averaged across seasons, against seed length, mass, abundance, patchiness, percent nitrogen, energy content, and chemical defenses showed seed length to be the most important predictor of seed preference. Seed length combined with nitrogen (protein) content and levels of two defensive compounds, saponins and non-protein amino acids, to account for 68% of the variation in seed preference. The importance of seed length rather than biomass indicated that there are limits to the ability of D. ordii to detect small seeds and that small size facilitated escape of dispersed seeds. Seasonality in preference suggested, however, that seed escape was encountered by predispersal harvesting of newly maturing seeds still on plants. Maximization of protein intake contradicted previously published observations, but presumably reflected low nitrogen availability. In addition to small size, the presence of saponins or non-protein amino acids in seeds was sufficient to negate the positive influence of higher protein content.