Dipodomys Spectabilis Research Articles

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, P AVP) 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 P AVP and plasma osmolality (P OSM) 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°) and fed a dry grain diet, P OSM and P AVP averaged 308.6 ± 0.7 mosmol/kg H 2O and 6.0 ± 0.7 pg/ml (2.2 ± 0.2 μU/ml), respectively (means ± SE). In separate groups of animals subjected to 48, 96, 144, or 192 hr of dehydration, P OSM and P AVP increased in a parallel linear manner with time to maxima of 329.7 ± 2.4 mosmol/kg H 2O and 68.8 ± 4.4 pg/ml (24.9 ± 1.6 μU/ml), respectively, at 192 hr of dehydration. Thus, a highly correlated and significant relationship between P OSM and P AVP ( r 2 = 0.941, P < 0.001) exists in dehydrated kangaroo rats, quantitatively defined by the linear regression equation P AVP (pg/ml) = 2.99 (P OSM − 306.4), with an apparent osmotic threshold for AVP release at a P OSM of 306.4 mosmol/kg H 2O. In comparison with previous radioimmunoassay studies on the osmotic regulation of P AVP in various mammalian species, the present studies indicate that (1) during normal hydration, the kangaroo rat maintains an elevated P OSM and a basal P AVP that is two- to threefold higher than that of the laboratory rat or other mammalian species; and (2) during dehydration, the kangaroo rat exhibits a markedly elevated osmotic sensitivity for AVP release and an enhanced capacity to increase and maintain P AVP for prolonged periods of time, achieving P AVP two- to threefold higher than the laboratory rat (a nondesert rodent of similar body mass).

Territorial defense in the bannertail kangaroo rat (Dipodomys spectabilis): footdrumming and visual threats

Footdrumming and visual displays associated with territorial defense in the bannertail kangaroo rat (Dipodomys spectabilis) were studied in the field in Arizona. We predicted that foot-drumming functioned like bird song in territorial advertisement. Rats were tested in their territories for their responses to the presentation of four different stimuli: a playback of airborne footdrumming patterns (audio); a stuffed and mounted kangaroo rat in an aggressive posture (visual); a combination of both (audio-visual); and a playback of cricket stridulation as a control. Kangaroo rats investigated all experimental stimuli equally by becoming alert, approaching, and retreating (Fig. 2). Rats, therefore, seemed to assess the amount of threat and footdrummed at higher rates and sooner in response to the more threatening visual stumulus of a stuffed rat than to the apparently less threatening ones of a airborne footdrumming playback or cricket stridulation (Fig. 1). We conclude that rats footdrum at long ranges to repel a potential intruder and also at close ranges when territories are threatened by a persistent intruder. Chase and attack, as in territorial birds, are the final lines of defense.

Sandbathing as a territorial scent-mark in the bannertail kangaroo rat, Dipodomys spectabilis

Sandbathing by the bannertail kangaroo rat, Dipodomys spectabilis, was studied in the laboratory and field to determine its possible function as a territorial scent-mark. Rats were tested for their responses to body oil and dorsal gland scents from familiar and unfamiliar rats and to the sandbathing sites of rats in different hormonal conditions. Field evidence showed that adult and juvenile rats of both sexes sandbathed at similar rates in their territories. Rats recognized scents of different conspecifics from body oils and dorsal gland secretions. The sandbathing marks of intact males, castrated males, oestrous females and non-oestrous females were equally attractive to rats in reproductive and non-reproductive conditions. Sandbathing scents apparently do not communicate information on reproductive status in this species. Rats sandbathe to scent-mark their territories and may use the scents to distinguish familiar neighbours from unfamiliar conspecifics. Neighbour recognition is probably important in maintaining the territorial social organization of D. spectabilis.

Spatial organization of a desert rodent community: food addition and species removal.

From 1977 through 1983 we conducted experiments on a desert rodent community where supplemental seeds were added or certain rodent species and ants were removed from 0.25-ha fenced plots in a Chihuahuan Desert site in southeastern Arizona, USA. In this paper we examine the patterns of microhabitat use relative to vegetative cover by 11 rodent species. The results show that: i) removal of the largest seed-eating species, Dipodomys spectabilis, produced the most pervasive and dramatic shifts in microhabitat use by the remaining rodent species; ii) adding seeds or removing ants had little effect on the spatial use of microhabitats by rodents in this community; and iii) non-granivores were just as likely as granivores to shift microhabitat use when other granivores were removed. We believe these results indicate that both food and foraging microsites are limited but the relegation of subdominant species to lesspreferred microhabitats by the large Dipodomys spectabilis is the major factor underlying the spatial organization of this community. Results also demonstrate that strong interactions among species increase the probability that pathways of indirect interactions through intermediary species are important; these complex linkages may include species that overlap little in food preferences.

Terverticillate penicillia isolated from underground seed caches and cheek pouches of banner-tailed kangaroo rats (Dipodomys spectabilis)

Terverticillate penicillia were important colonists of the underground seed caches and the external cheek pouches of the banner-tailed kangaroo rat (Dipodomys spectabilis) from the North American desert. Two taxa representing the dominant Penicillium populations are described as new varieties of well-known ubiquitous species. Penicillium chrysogenum var. dipodomyis var.nov. produces the antibiotic penicillin but does not produce mycotoxins (PR-toxin and roquefortine C) known from P. chrysogenum. The new variety is further distinguished by having rough-walled stipes. Penicillium aurantiogriseum var. neoechinulatum var.nov. isolates produce penicillic acid, viridicatin, and cyclopenin, metabolites with antibiotic properties, but not the potent nephrotoxins xanthomegnin and viomellein or tremorgenic mycotoxins (e.g., penitrem A). The variety is also distinguished by conspicuously rough-walled conidia. Three additional new varieties which do not produce mycotoxins normally associated with their species are also reported: P. griseofulvum var. dipodomyicola var.nov. produced the antibiotically active compounds patulin and griseofulvin but not cyclopiazonic acid and roquefortine C; P. glandicola var. mononematosa var.nov. and P. glandicola var. confertum var.nov. did not produce roquefortine C, penitrem A, or patulin. Infrequently isolated strains of the species P. viridicatum and P. griseofulvum duplicated the mycotoxin profiles of the cultures ex type. It is suggested that the evolution of seed-caching behaviour in D. spectabilis may have guided the selection of less-toxic terverticillate penicillia as colonists in rodent seed caches.

Footdrumming and other anti-predator responses in the bannertail kangaroo rat (Dipodomys spectabilis)

Anti-predator behaviors of the bannertail kangaroo rat (Dipodomys spectabilis) toward snake predators were investigated. We induced responses by presenting a live (tethered) snake and an inflatable snake decoy to rats of known ages and sex in their territories. Comparisons of behaviors during spontaneous activity (baseline), naturally occurring snake-rat interactions, and experimental procedures further clarified anti-predator behaviors. The tethered snake immediately induced high rates of footdrumming (the repeated striking of the hind feet on the ground) in all rats (n=24) (Table 2), and individuals of both sexes and all ages footdrummed significantly more at the tethered snake than at the decoy. Other antipredator behaviors included alert postures, jumpback, kicking sand and avoidance. Juvenile rats exhibited more avoidance behavior and alert postures than adults and footdrummed at the decoy only if they experienced the snake first. We conclude that footdrumming functions as an individual alarm signal against predation by snakes in D. spectabilis. The drumming probably informs a snake that it has been detected and may cause it to leave. Because rats did not footdrum in response to aerial predators (owls), we suggest that kangaroo rats use different anti-predator strategies that depend on the kind of threat and the type of predator.

Field Observations of Male Competition and Mating in Merriam's and Bannertail Kangaroo Rats

Field Observations of Male Competition and Mating in Merriam's and Bannertail Kangaroo Rats

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.

Management of sterile and mouldy seeds by a desert rodent

Banner-tailed kangaroo rats ( Dipodomys spectabilis) are known to store large quantities of seeds in underground caches. Over 20 species of moulds have been found in the caches, and experiments have shown that the kangaroo rats prefer to ingest slightly mouldy seeds over non-mouldy and very mouldy seeds. Laboratory experiments were designed to test the hypothesis that these rodents manage seeds to promote an intermediate level of seed mouldiness. The experiments revealed that rodents tended to move sterile seeds to the highest humidities available. The same individuals moved seeds with the preferred level of mouldiness to humidities below the threshold for further mould growth. We interpret these activities as adaptive attempts to increase mould growth on sterile seeds and inhibit further growth on sufficiently mouldy seeds.

Survivorship in Philopatric and Dispersing Kangaroo Rats (Dipodomys Spectabilis)

I use long—term mark—recapture data for banner—tailed kangaroo rats (Dipodomys spectabilis) to assess survival of philopatric and dispersing individuals. Results for 147 juveniles indicate that individuals that acquired parental resources, in this case large complex burrow systems and food catches, were significantly more likely to survive to reproductive age than individuals that successfully dispersed but did not acquire parental resources. Survival of juveniles that left their natal burrows and moved to other burrows was independent of the distance moved, which suggests that familiarity with natal areas and proximity to relatives impart no survival advantage in this species. Of the 37 juveniles that acquired natal burrows, 5 males and 7 females did so after their mothers abandoned those burrows. The frequency of burrow abandonment by adult females was independent of maternal age, and survival of abandoning mothers did not differ significantly from that of nonabandoning females

Ecological and Mycological Characteristics of Caches in the Mounds of Dipodomys spectabilis

Banner-tailed kangaroo rats ( Dipodomys spectabilis ) are primarily granivorous and store large quantities of seeds in underground caches. We found that a majority of these caches occurred near 30 cm in depth or below 50 cm. Most caches were approximately one third of the distance from the mound center to the edge and were on the north or northwest side of the mounds. There was no obvious temporal relationships between use of seed and when they were gathered. Seeds stored early and late in a four-month period were significantly depleted after the four months while those stored during the middle of the experimental period, when native seeds were abundant, were not depleted. Mycological analyses of the caches revealed at least 23 species of fungi. Fungal colonists were more abundant and diverse in caches made in the middle of a four-month caching period than early or late in the period.

Seed preferences by desert rodents based on levels of mouldiness

Large species of kangaroo rats (family Heteromyidae) make extensive underground caches of seeds. During collection and storage, seeds become inoculated with fungal spores, most of which are common pernicious storage moulds in human agriculture systems. The moulds and their metabolites may be beneficial or detrimental, depending on the species of mould and the growth conditions. Feeding experiments were conducted to determine the preferences for mouldy seeds by Dipodomys spectabilis. Results showed that kangaroo rats prefer slightly mouldy seeds over very mouldy seeds, dry seeds, and unmouldy, imbibed seeds, apparently taking advantage of beneficial effects of moulds while avoiding the liabilities.

Territorial defense and advertisement by footdrumming in bannertail kangaroo rats (Dipodomys spectabilis) at high and low population densities

Behaviors associated with territorial defense of large dirt mounds by bannertail kangaroo rats (Dipodomys spectabilis) at high and low population densities are reported. Rats were observed for 640 h during three summers and one spring from 1980–1982 in SE Arizona.

Natal philopatry in bannertailed kangaroo rats

I describe prolonged retention of offspring in natal home ranges, or natal philopatry, in the bannertailed kangaroo rat Dipodomys spectabilis. Though weaning occurs at about one month of age, offspring shared natal burrows with their mothers for three to seven months, and 39% of surviving offspring remained within natal home ranges through reproductive maturity. Males as well as females were philopatric. Data on the availability of burrows and on patterns of resettlement suggest that natal philopatry in this species may be a means of providing juveniles with access to essential resources, in this case food caches and large complex burrow systems, that are not readily available outside natal home ranges.

Temperature and Humidity of Expired Air: Interspecific Comparisons and Significance for Loss of Respiratory Heat and Water from Endotherms

The temperature of expired air at the external nares of black-tailed prairie dogs (Cynomys ludovicianus) was measured at inspired (ambient) air temperatures of 25, 30, 35, and 40 C, and over a broad range of humidities at each temperature. Expired air temperature was positively related to inspired air temperature and humidity; comparisons with published data for banner-tail kangaroo rats (Dipodomys spectabilis), deer mice (Peromyscus maniculatus), house mice (Mus musculus), and Australian hopping mice (Notomys alexis) showed similarities and differences among coefficients of multiple linear regressions describing analogous relationships. Simulations for a hypothetical mammal suggested how differences in the recovery of respiratory heat and water in nasal passages, and the loss of respiratory heat and water from the nose, should be affected by different relationships between the temperature of expired air and the temperature and humidity of inspired air.

Experimental field evidence of interspecific aggression between two species of kangaroo rat (Dipodomys).

The competitive coexistence of heteromyid rodents has been primarily ascribed to differential utilization of resources such as microhabitats and seeds. An examination of the use of space by the kangaroo rat Dipodomys merriami indicates this species is aggressively subordinate to a larger species, Dipodomys spectabilis and is excluded from the larger species home range during the crtical fall harvesting season. These experiments suggest that interspecific aggression may be involved in the coexistence of these species. Additional evidence is presented that small scale spatial variations in resource productivity may promote the coexistence of these two species.

Impact of Burrowing Activity of the Bannertail Kangaroo Rat on Southern New Mexico Desert Rangelands

Impact of Burrowing Activity of the Bannertail Kangaroo Rat on Southern New Mexico Desert Rangelands

Clump size selection: A field test with two species of Dipodomys.

Seed distribution (clump size) selection has been proposed as a possible mechanism of resource subdivision for competing heteromyid rodent species. To test this hypothesis, field experiments were conducted over two years during both richer and sparser seasons of the year. None of the predictions derived from the hypothesis were supported by our results. Though some selectivity was displayed by both Dipodomys spectabilis and D. merriami, the patterns of selectivity did not match the expected patterns. Our results further indicate that clump selection may be influenced by variables other than the density of seeds within a clump. These results have led us to conclude that clump size selection is unlikely to play a role in the coexistence of different species of the genus Dipodomys.

The Status of Banner-Tailed Kangaroo Rats, Genus Dipodomys, from Central Mexico

The Status of Banner-Tailed Kangaroo Rats, Genus Dipodomys, from Central Mexico

Body dehydration in xeric adapted rodents: Does the renin—Angiotensin system play a role?

1. 1. Plasma and cerebrospinal fluid (CSF) angiotensin 2 (A2) levels, plasma Na + concentration, osmolality, and hematocrits were measured in desert and nondesert rodents during food and water deprivation induced dehydration. 2. 2. During food deprivation, polydipsia was observed in the xerophilous species ( Dipodomys spectabilis and Meriones unguiculatus), while decreased water consumption was evident in the mesically adapted species ( Rattus norvegicus). All species revealed reductions in intravascular volume during fasting with no change in plasma or CSF A2 levels. 3. 3. A five-fold elevation in plasma A2 was observed in water deprived rats while the desert rodents evidenced only slight elevations. There were no changes in CSF A2 concentrations in response to water deprivation. 4. 4. Plasma osmolality was chronically elevated during water deprivation in all species. 5. 5. The present findings question the importance of the renin-angiotensin system in the normal maintenance of body water balance by desert rodents subjected to dehydration challenges.