Bacula of Dipodomys ordii compactus and Dipodomys elator.
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Energy metabolism and body water turnover rates of two species of free-living kangaroo rats, Dipodomys merriami and Dipodomys microps.
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Animals↗
Eimeria chihuahuaensis sp.n. and other coccidia from Dipodomys spp. in El Paso County, Texas.
Dipodomys merriami Mearns and Dipodomys ordi Woodhouse were surveyed for coccidia in El Paso County, Texas. Infections with Eimeria chobotari, Eimeria dipodomysis and Eimeria balphae were 24.8%, 4.4%, and 11%, respectively, for D. ordi. Dipodomys merriami had an infection level of 23.8% with E. chobotari. Four animals concurrently harbored E. chobotari and E. balphae or E. dipodomysis or a new species Eimeria chihuahuaensis. Male and female host infection levels were not significantly different. The new species is described and photographs of 3 previously described Eimeria from Dipodomys are presented.
Animals↗
Species-specific footdrumming in kangaroo rats: Dipodomys ingens, D. deserti, D. spectabilis
Footdrumming was compared in three allopatric species of kangaroo rat, Dipodomysfrom three habitats. Analysis of footdrumming recordings revealed species-specific patterns of drumming ranging from single thumps to individual footdrumming signatures. The desert kangaroo rat, D. desertidrums single thumps spaced 0.25-0.30 s apart that are sometimes introduced with a short footroll. The giant kangaroo rat, D. ingensdrums long footrolls that can average over 100 drums at 18 drums/s. The banner-tailed kangaroo rat, D. spectabilisdrums three to 38 footdrums in a footroll combined into sequences of two to 12 footrolls at a rate of 17 drums/s. In playback tests, all three species stood in alert postures and entered the burrow in response to footdrumming of their own and the other species. The rats also responded in species-specific ways. Dipodomys spectabilisdrummed to its own species' footdrumming, but not to playbacks of the single drums of D. desertiInstead of footdrumming to playbacks of its own species, D. deserti approached the speaker more frequently than did either of the other two species. Dipodomys ingens footdrummed equally to all footdrumming playbacks. The species' differences reflect differences in social tolerance and spacing. Dipodomys deserti rarely engages in footdrumming exchanges and chases visitors from the burrow. Dipodomys spectabilis engages in frequent footdrumming exchanges and some chases, and D. ingens seems to tolerate close neighbours and footdrums periodically.Copyright 1997 The Association for the Study of Animal Behaviour1997The Association for the Study of Animal Behaviour
Journal Article↗
An anatomical study of the brains of Dipodomys (Mammalia: Rodentia: Heteromyidae).
Whole brains and Nissl-stained serial sections of 3 species of kangaroo rat (Dipodomys spectabilis, D. ordii, D. merriami) were compared for interspecific differences. Neuroanatomical variations were conservative in nature. Examination of the cerebellum revealed possible differences in locomotion and ecology. Dipodomys ordii exhibited more neurological evidence for increased specialization of the hindlimbs, while D. merriami had the least differentiated cerebellar surface, thereby suggesting more stereotyped movements of the hindlimbs. Dipodomys spectabilis had abilities that lie somewhere between those of D. ordii and D. merriami. Stereological analysis demonstrated little difference in the percent of total brain volume comprising the telencephalon, diencephalon, cerebellum, and brain stem; and it revealed the relative position of the cranial nerve nuclei.
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An analysis of sandbathing and grooming in the kangaroo rat (Dipodomys merriami).
The sandbathing and grooming behaviour of ten kangaroo rats (Dipodomys merriami) were recorded on sand and woodchip substrates after periods of 0, 1, 5 and 10 days without sand. Sandbathing is restricted to the sandy substrate. Grooming occurs on both, but with a higher frequency on sand. Increases in both grooming and sandbathing occur with increasing sand deprivation, but the temporal patterning does not change. D. merriami tends to alternate sandbathing components in contrast to other Dipodomys species. Lipid on the pelage increases noticeably with sand deprivation and decreases during a sandbathing bout; sand appears to be removed from the pelage by shaking and grooming. These findings suggest a three-process system for care of the body surface.
Adaptation, Physiological↗
Genomic analysis of differentiation and demography of the formerly conspecific agile (Dipodomys agilis) and Dulzura (D. simulans) kangaroo rats.
Karyotype variation within Pacific kangaroo rat Dipodomys agilis motivated its division in 1997 into the agile kangaroo rat (AKR, D. agilis, 2N = 62) in the north of its range in California, and Dulzura kangaroo rat (DKR, D. simulans, 2N = 60) to the south, with a suspected sympatric zone south of the San Gabriel and San Bernardino Mountains. This division was supported by our whole genome sequencing that sampled a ~120 km transect from north of the mountains to SW Riverside County. The taxa showed marked genetic differentiation, with no evidence of hybridization or sympatry. AKR was found at the southern edge of the mountains, precluding the mountain barrier driving isolation, suggesting ecological separation linked to habitat differences between the mountains and the arid area to the south. Adding four additional Dipodomys species, we estimated genetic divergence times in the genus back to ∼3.5 mya. AKR and DKR diverged from D. stephensi ∼1.7 mya, and from each other ∼0.5 mya, when their joint effective population size (Ne) was ~100,000. After separation, DKR's Ne declined to ~20,000, while AKR's was little changed. More recently their Ne converged at ~50,000. Runs of homozygosity were longer in AKR, indicating a smaller neighborhood size, which may have promoted the karyotype change; however, nucleotide diversity was higher in AKR, but both had levels typical for rodents, indicating neither experienced recent bottlenecks. These patterns provide a baseline for any future conservation efforts. More generally, this study shows how a detailed genomic study can resolve taxonomic and demographic questions among morphologically indistinguishable taxa.
Animals↗
Ultrastructure of pinealocytes of the kangaroo rat (Dipodomys ordi).
The ultrastructure of the pinealocytes of the wild-captured ord kangaroo rat (Dipodomys ordi) was examined. A homogeneous population of pinealocytes was present in the pineal gland of the kangaroo rat. The Golgi apparatus, granular endoplasmic reticulum, mitochondria, lysosomes, dense-core vesicles, vacuoles containing a flocculent material and lipid droplets were consistent components of the pinealocyte cytoplasm, whereas infrequently-observed organelles included centrioles, multivesicular bodies, subsurface cisternae, "synaptic" ribbons and cilia. The number of dense-core vesicles was relatively high and dense-core vesicles and vacuoles containing a flocculent material were present in the same cell. Although it has been recently suggested that two different secretory processes, i.e., neurosecretory-like (Golgi apparatus - dense-core vesicles) and ependymal-like (granular endoplasmic reticulum - vacuoles containing a flocculent material) may be involved in different regulatory mechanisms in the pinealocytes, the definitive answer to this is still far from clear. Therefore, the pineal gland of the kangaroo rat appears to be a good model for the study of the potential relationship between these two secretory processes, especially in respect to seasonal changes.
Animals↗
Satellite DNA and cytogenetic evolution. DNA quantity, satellite DNA and karyotypic variations in kangaroo rats (genus Dipodomys).
The genus Dipodomys (kangaroo rats) exhibits major interspecies variations in the proportions of highly reiterated satellite DNA sequences in the genome as well as in the chromosome number and the proportions of uni-armed and bi-armed chromosomes. For nearly all of the approximately 22 species of the genus and several subspecies, liver DNA was distributed in neutral CsCl buoyant density gradients into four fractions; principal DNA (1.698 g/ml), intermediate-density DNA (1.702 G/ML), MS satellite (1.707 g/ml) and HS (heavy satellites (1.713 g/ml). The total nuclear DNA content of diploid liver cells measured in eleven species by quantitative cytophotometry, ranged from 6.9 to 10.9 pg. These data were correlated with known features of the karotypes of individual species. The salient findings were: (1) that interspecies variations in diploid chromosome number cluster at 52-54, 60-64 and 70-72 (2) that high total nuclear DNA was associated with high chromosome number, and with relatively large amounts of satellite DNA (3) that a high ratio of HS satellites to intermediate-density DNA was generally correlated with a predominance of metacentric and submetacentric chromosomes (high fundamental number). The relationships of satellite DNA to karyotype structure reveal a new level of hierarchy in the genome that appears capable of exerting global control over environmental adaptation and the evolution of new species. This mechanism is consistent with recent hypotheses that changes in the macro-structure of the genome are more important than point mutations in facilitating the rapid phases of animal evolution.
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The sequence of the 3.3-kilobase repetitive element from Dipodomys ordii suggests a mechanism for its amplification and interspersion.
DNA from the kangaroo rat, Dipodomys ordii, contains a 3.3-kb, highly repeated sequence that is interspersed throughout the genome in small tandem clusters. One 3.3-kb unit has been cloned into pBR322 and the nucleotide sequence determined. The clone used was shown to be representative of the bulk of such sequences found in the genomic DNA. The sequence contains 10 homologous subunits each ca. 260 bp in length. Comparison of these to one another yielded a 258-bp consensus sequence containing a 35-bp terminal inverted repeat. Two unique stretches also occur. One of these contains a region that could serve as a promoter for RNA polymerase III; the other contains a sequence related to the ARS sequences of yeast. It is proposed that an ancestral sequence similar to the consensus sequence was amplified to 10 or more units, and that, subsequently, two other sequences were inserted. The properties of these insertions may have led to the dispersal of the sequence throughout the genome.
Animals↗
Seismic communication between the burrows of kangaroo rats, Dipodomys spectabilis.
Banner-tailed kangaroo rats, Dipodomys spectabilis, footdrum to produce substrate-borne and airborne acoustic energy. Previous studies show that they communicate territorial ownership via airborne footdrumming signals. The research reported here used simulated footdrum patterns generated by an artificial 'thumper' to address the question of whether kangaroo rats communicate through seismic components of these acoustic signals. With microphones suspended in sealed burrows, we found that airborne sounds were attenuated by approximately 40 dB as they passed through the burrow wall into the burrow chamber. The substrate-borne vibrations from the thumper yielded sound approximately 40 dB greater in peak amplitude than the attenuated airborne sound. Thus, 99.9% of the peak power of the thumper was transmitted directly through the substrate into the burrow. The rats in sealed burrows timed their responses to playbacks of footdrums from the thumper and a loudspeaker so they did not initiate a drumming sequence during either the seismic or airborne signals. When these signals were masked by loud noise, the rats continued to drum to the seismic signal but drummed randomly during the airborne playback. These results suggest that the sealed burrow provides a quiet place in which D. spectabilis can listen for substrate-borne communications from conspecifics.
Acoustic Stimulation↗
Regulation of plasma antidiuretic hormone in the dehydrated kangaroo rat (Dipodomys spectabilis M.).
A sensitive and specific radioimmunoassay was used to measure plasma antidiuretic hormone (plasma arginine vasopressin, PAVP) concentrations in a conscious desert-adapted mammal, the banner-tailed kangaroo rat (Dipodomys spectabilis; 131 +/- 2.3 g body mass), during normal hydration and in response to progressive dehydration. Simultaneous measurements of PAVP and plasma osmolality (POSM) in these experiments permitted determination of the hypothalamo-neurohypophyseal system-osmoreceptor set point and sensitivity to extracellular hyperosmolality during dehydration. In normally hydrated kangaroo rats, acclimated to room temperature (20-24 degrees) and fed a dry grain diet, POSM and PAVP averaged 308.6 +/- 0.7 mosmol/kg H2O and 6.0 +/- 0.7 pg/ml (2.2 +/- 0.2 microU/ml), respectively (means +/- SE). In separate groups of animals subjected to 48, 96, 144, or 192 hr of dehydration, POSM and PAVP increased in a parallel linear manner with time to maxima of 329.7 +/- 2.4 mosmol/kg H2O and 68.8 +/- 4.4 pg/ml (24.9 +/- 1.6 microU/ml), respectively, at 192 hr of dehydration. Thus, a highly correlated and significant relationship between POSM and PAVP (r2 = 0.941, P less than 0.001) exists in dehydrated kangaroo rats, quantitatively defined by the linear regression equation PAVP (pg/ml) = 2.99 (POSM - 306.4), with an apparent osmotic threshold for AVP release at a POSM of 306.4 mosmol/kg H2O.(ABSTRACT TRUNCATED AT 250 WORDS)
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Lack of gonadal control of the dorsal gland and sandbathing in male and female bannertail kangaroo rats, (Dipodomys spectabilis).
Previous studies have demonstrated gonadal control of mammalian scent glands; castration leads to reduced scent-marking rates and smaller gland sizes. I investigated whether gonadal hormones control the size of the dorsal gland (a specialized sebaceous gland) and sandbathing as a scent-marking behavior in adult male and female bannertail kangaroo rats (Dipodomys spectabilis). Gland sizes of males and females were similar in all age classes, except adult males with larger body weights had proportionately larger glands than females. Male gland sizes declined 18% following castration but were not significantly smaller than those of intact males; females showed no change in dorsal gland size either as a result of ovariectomy or after estradiol benzoate implants. Sandbathing rates also did not decline as a result of gonadectomy. Rather, castrated males and overiectomized females sandbathed at higher frequencies than intact males and ovariectomized females with estradiol benzoate implants, respectively. Gonadal hormones apparently have little influence on the function of a specialized scent gland and may inhibit sandbathing as a scent-marking behavior in adult D. spectabilis.
Animals↗
Role of urine in coordinating reproduction in a desert rodent (Dipodomys merriami).
Detection of reproductive status from chemical signals in the urine of a desert rodent was examined. Intact and castrated male and estrous (induced) and nonestrous (ovariectomized) female Dipodomys merriami were tested for their preferences for various combinations of water and urine from intact males, estrous females, castrated males, and nonestrous females. Intact and castrated males were also tested for their responses to urine from females at different stages of the reproductive cycle: proestrus, estrus, and diestrus. Neither intact nor castrated males exhibited a preference for urine from females in any stage of the estrous cycle. Urine from intact males, however, was preferred by both intact males and estrous females. Urine from reproductively active males, rather than from estrous females, seems to contain information for coordinating reproduction in D. merriami.
Animals↗
Genomic structure and sequence variation of a 3.3-kb repeat DNA element of the kangaroo rat, Dipodomys ordii.
The genomic structure and sequence variation of a 3.3-kb repeat DNA element, representing 5% of the genome of the kangaroo rat Dipodomys ordii, has been investigated. Most of the repeats are arranged in tandem arrays of 50 kb or more. Thirteen randomly selected genomic clones have been mapped with twelve restriction enzymes. The frequency of sequence divergence in the genomic clones is 0.5%. The clone maps and the genomic structure studies have permitted the characterization of a number of variant members of the 3.3-kb repeat family. The genomic organization of the repeat resembles that for repeated DNAs found in large tandem arrays or satellites.
Animals↗
Spatial memory in the desert kangaroo rat (Dipodomys deserti).
Desert kangaroo rats (Dipodomys deserti) forage for seed distributed in patches in the desert environment and may remember patch locations. In Experiment 1, 7 desert kangaroo rats that had discovered the location of a plastic token in 1 box accurately dug for a token hidden in the same location in a 2nd identical box. Results of Experiment 2 indicated that the rats primarily remembered the spatial location of the token within the box in relation to extramaze objects and the walls of the experimental box. Female rats also remembered the chip's location in relation to objects inside the box, but males did not. Experiment 3 demonstrated that the rats' ability to locate the buried token did not depend on detection of the odor of the token. In the discussion I propose that spatial memory in kangaroo rats may have evolved as a result of an overall change in the ontogeny of the species rather than as a specialized adaptation for foraging efficiency.
Animals↗
Maternal presence and rearing condition affect responses to a live predator in kangaroo rats (Dipodomys heermanni arenae).
Experiment 1 compared the responses of wild-caught adult and captive-born adult and juvenile kangaroo rats (Dipodomys heermanni arenae) to a live snake. Wild-caught adult rats were less active and monitored the snake more than during a control condition; captive-born juvenile rats did not behave differently during snake and control tests. Snake-naive adult rats behaved more like the wild-caught adult rats, but not on all measures. In Experiment 2, pups were tested at 25 and 50 days of age in 4 conditions: no-snake control, alone with the snake, with a sibling and the snake, and with the mother and the snake. Pups did not behave differently during control and snake tests, but during tests with the mother, pups faced the snake less and followed the mother. Younger pups were more often near the mother than a sibling and followed the mother more when the snake was present. Development of defensive behavior may depend on both predator experience and maternal influence.
Age Factors↗
Fleas (Siphonaptera) infesting giant kangaroo rats (Dipodomys ingens) on the Elkhorn and Carrizo Plains, San Luis Obispo County, California.
The giant kangaroo rat, Dipodomys ingens (Merriam), has a limited distribution in the San Joaquin Valley, CA. Because of reductions in its geographic range, largely resulting from humans, the species was listed as an endangered species in 1980 by the California Fish and Game Commission. As part of a study of the community ecology of southern California endangered species, including D. ingens, we were able to make flea collections from the rats when they were trapped and marked for population studies. All but one of the fleas collected from the D. ingens in this study were Hoplopsyllus anomalus, a flea normally associated with ground squirrels (Sciuridae). It has been suggested that giant kangaroo rats fill the ground squirrel niche within their range. Our data indicate that this role includes a normal association with Hoplopsyllus anomalus.
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