Female Ground Squirrels Research Articles

Development of an homologous radioimmunoassay for secreted prolactin from the California ground squirrel (Spermophilus beecheyi).

A sensitive homologous radioimmunoassay was developed for secreted prolactin from the California ground squirrel (Spermophilus beecheyi). S. beecheyi plasma and pituitary extracts displaced 125I-labeled S. beecheyi prolactin in a parallel manner with S. beecheyi prolactin (sbPRL). Mean minimum sensitivity of the assay was 0.21 ng/ml, and mean intra- and interassay coefficients of variation were 4.1% and 14.5%, respectively. The assay was used to measure basal prolactin concentrations in male and female ground squirrels at various stages of their annual reproductive cycles. Mean concentrations in nonpregnant, nonlactating young females, pregnant females, and lactating females were 1.63, 11.35, and 10.86 ng/ml, respectively. Mean concentrations in nonreproductive and breeding males were 1.50 and 9.81 ng/ml, respectively. Finally, the assay was used to evaluate cross-reactivity between sbPRL and prolactins and growth hormones from other rodent species. Of the tested hormones, only hamster prolactin showed any cross-reactivity with sbPRL (about 0.03%).

A Bush Dog (Speothos venaticus) Pack in the Eastern Llanos of Colombia

MCLEAN, I. G., AND A. J. TOWNS. 1981. Differences in weight changes and the annual cycle of male and female Arctic ground squirrels. Arctic, 34: 249-254. MICHENER, G. R. 1979. Spatial relationships and social organization of adult Richardson's ground squirrels. Canadian J. Zool., 57:125-139. ? 1983. Kin identification, matriarchies, and the evolution of sociality in ground-dwelling sciurids. Pp. 528-572, in Recent advances in the study of mammalian behavior (J. F. Eisenberg and D. F. Kleiman, eds.). Spec. Publ., Amer. Soc. Mamm., 7:1-753. ? 1984. Age, sex, and species differences in the annual cycles of ground-dwelling sciurids: implications for sociality. Pp. 81-107, in Biology of ground-dwelling squirrels: annual cycles, behavioral ecology, and sociality (J. 0. Murie and G. R. Michener, eds.). University of Nebraska Press, Lincoln, 459 pp. MURIE, J. O., AND M. A. HARRIS. 1978. Territoriality and dominance in male Columbian ground squirrels (Spermophilus columbianus). Canadian J. Zool., 56:2402-2412. OWINGS, D. H., M. BORCHERT, AND R. VIRGINIA. 1977. The behaviour of California ground squirrels. Anim. Behav., 25:221-230. SHERMAN, P. W. 1980. The limits of ground squirrel nepotism. Pp. 504-544, in Sociobiology: beyond nature/nuture? (G. W. Barlow, and J. Silverberg, eds.). Westview Press, Boulder, Colorado, 627 pp. . 1981. Reproductive competition and infanticide in Belding's ground squirrels and other organisms. Pp. 311-331, in Natural selection and social behavior: recent research and new theory (R. D. Alexander and D. W. Tinkle, eds.). Chiron Press, New York, 532 pp. SILVERMAN, D. L. 1981. The behavioral ecology of the thirteen-lined ground squirrel (Spermophilus tridecemlineatus). Unpubl. M.S. thesis, Univ. Michigan, Ann Arbor, 45 pp. STORER, T. I., F. C. EVANS, AND R. G. PALMER. 1944. Some rodent populations in the Sierra Nevada of California. Ecol. Monogr., 14:165-192. STROUD, D. C. 1983. Seasonal activity, demography, dispersal, and a population simulation model of the California ground squirrel, Spermophilus beecheyi. Unpubl. Ph.D. dissert., Univ. California, Davis, 149 pp. TOMICH, P. Q. 1962. The annual cycle of the California ground squirrel, Citellus beecheyi. Univ. California Publ. Zool., 65:213-282.

Circannual variations in circadian rhythms of ground squirrels.

There was a circannual rhythm in the times of activity onset (psi o) and activity termination (psi T) and in the duration of the active phase (alpha) in female ground squirrels (Spermophilus lateralis) maintained in a light-dark (LD) 14:10 photoperiod for 22 mo. Activity onset occurred 2.3 h after light onset in the 4 mo before estrus, 0.5 h before light onset during the month encompassing estrus, and progressively later during each of the ensuing 4 mo. Termination of activity occurred later during the month of estrus than in the 4 mo preceding estrus; alpha nearly doubled during the month of estrus and decreased gradually over the next 3 mo. The psi o and psi T remained entrained to the daily illumination cycle, but the phase angles of activity onset and offset and the duration of the active phase varied seasonally and recurred with a circannual period of 9-11 mo. The LD 14:10 photoperiod entrained the circadian activity rhythm throughout the year; however, circannual variations in activity as well as in estrus and body mass were not entrained by this photoperiod but free-ran with periods of less than 12 mo.

Effects of multiple mating on reproduction in female thirteen-lined ground squirrels

Effects of multiple mating on reproduction in female thirteen-lined ground squirrels

Recovery of white adipose tissue after lipectomy in female ground squirrels

Female golden-mantled ground squirrels were subjected to surgical removal of adipose tissue (lipectomy) at 4 months of age. Compensation for the 9.6% reduction in body mass effected by lipectomy was observed within 2 weeks and body mass did not differ between lipectomized and sham-lipectomized groups from that time to the conclusion of the experiment. At the time of the second peak in body mass, approximately 11 months postoperatively, lipectomized and sham-lipectomized groups did not differ with respect to total carcass lipid content, water content, or fat-free dry mass. Restoration of body mass after lipectomy did not involve measurable increases in food consumption. There was complete restoration of the retroperitoneal fat depot, but little if any recovery in the parametrial fat depot which was reduced in mass by 75% relative to that of the sham-lipectomized squirrels. Precise regulation of the adipose tissue mass is an important component of the annual cycle in energy balance of female squirrels.

Rapid recovery of body mass after surgical removal of adipose tissue in ground squirrels.

A substantial proportion of total adipose tissue mass was surgically removed from female ground squirrels during weight gain or weight loss phases of the circannual body weight cycle. Within 2 months of fat removal, squirrels had restored body mass to levels appropriate to the stage of the annual body weight cycle. These findings suggest that ground squirrels may use feedback from body lipids in controlling body weight.

The association of female kin in the arctic ground squirrel Spermophilus parryii

The association of kin in arctic ground squirrels (Spermophilus parryii) was studied near Haines Junction, Yukon Territory, during the summers of 1977, 1978, and 1979. Males dispersed in this population, thus only females were likely to live near relatives. Close female kin (sisters, mothers/daughters) had greater overlap of home ranges and interacted more amicably and less agonistically than did less closely related females. Closely related females clumped their young at emergence, whereas more distantly related females did not; there was little indication of clumping of pre-emerged young. The overlap of home ranges of distant relatives (known genetic relatives that had not associated in a natal burrow) was intermediate to that of close relatives and non-relatives. The types of interactions between distant relatives were more similar to those between non-relatives than between close relatives. I conclude that female arctic ground squirrels exhibit nepotism. Females may benefit from associations with relatives by sharing watching for predators once juveniles become conspicuous. Male arctic ground squirrels commit infanticide and several females may be more effective at protecting their young from infanticidal males than females living alone. I suggest that clumping of young by close relatives may provide a mechanism allowing distantly related females to identify each other.

Circannual cycles in golden-mantled ground squirrels: Experiments with food deprivation and effects of temperature on periodicity

Female golden-mantled ground squirrels,Spermophilus lateralis, kept in a cool room (9.5 °C), were food deprived and their hibernation thereby extended by 11 weeks on average compared to undeprived control animals in the same room. The deprived group was then refed. Despite their prolonged hibernation, peak weights and onset of hibernation in the subsequent season were only 2–4 weeks later than in the undeprived controls and this effect was only marginally significant. However, the periods of circannual cycles of both the deprived and undeprived groups in the cool room were significantly longer than those of another group of female ground squirrels kept in a warm room (21 °C). It is argued that warm temperatures are capable of terminating the winter phase of circannual cycles, namely that of hibernation and declining body weight. If animals are kept continuously in a cool environment this phase ends spontaneously. Even many weeks of food deprivation are only capable of extending this phase by a relatively small amount, if at all.

Responses to alarm calls by California ground squirrels: Effects of call structure and maternal status

1. The purposes of this study were to assess the response eliciting properties of five structural variants of the California ground squirrel alarm call system, and to compare the responsiveness of females with and without young to the vocalizations. Tape recordings of alarm calls and control sounds were played back in the field to adult female ground squirrels. The squirrels responded very little to control sounds. Following alarm calls, however, posture height and running increased; feeding, walking and non-locomotion movements decreased. None of the playbacks elicited vocalizations from the squirrels. 2. The four chatter-chat calls evoked patterns of response that were distinctly different from reactions to the whistle. The immediate running response to chatter-chats was followed quickly by upright posturing, which subsequently declined throughout the 3-min period following the call. Feeding was suppressed throughout the 3-min post-chatter-chat interval, but movement increased after initial inhibition. After the initial running response to whistles, walking was common and upright posturing was delayed until the second post-call minute. Feeding and nonlocomotion movement were initially suppressed but increased monotonically over time. We proposed that these differences were adaptively related to the fact that chatter-chats typically follow detection of terrestrial predators, whereas whistles usually signal flying raptors. 3. The responses to the four chatter-chat calls were graded in intensity, reaching higher levels in response to calls with more notes and lower noise content. The chat, a one-note call with high noise content, evoked the weakest reaction. We proposed that these two dimensions of calling (number of notes and noise content), in conjunction with several other semi-independent parameters, provide a sufficient diversity of signals to permit specification of the referent of the call (conspecific or predator) as well as the arousal level of the caller. 4. We hypothesized that kin selection was responsible for the greater responsiveness of parous than of nonparous females to the alarm calls, and we discussed some implications of this difference.

Behavior of Spermophilus lateralis between Periods of Hibernation

A study of the behavior of golden-mantled ground squirrels, Spermophilus (= Citellus ) lateralis , during the period of activity between periods of winter-pattern hibernation revealed the following: (1) the average duration of the period of activity of 134 male and 170 female ground squirrels exhibiting the winter pattern of hibernating behavior was 11.0 and 10.3 hours (h), respectively; (2) continuous visual observations of behavior during 15 periods of activity revealed that the following approximate percentages of the period of activity were devoted to five patterns of behavior—hibernation posturing, 93.4 percent; bedding arrangement, 3.7 percent; grooming, 1.8 percent; exploratory behavior, 0.9 percent; feeding, 0.2 percent. No consistent pattern of behavior that could be correlated with the first activity upon arousal from hibernation or the last activity prior to induction was detected. Behavior pertaining to elimination or to the obtaining of food or water was not considered significant. None of the behavior observed suggested a functional relationship regarding the physiological causation for arousal from a period of hiberation.

THE OVARY OF THE 13-LINED GROUND SQUIRREL (CITELLUS TRIDECEMLINEATUS MITCHELL) AFTER ADRENALECTOMY

SUMMARY This paper gives an account of a re-investigation of the work of Groat (1943, 1944). It shows that, apart from animals dying from extraneous causes, the female ground squirrel in anoestrus, some 5 weeks after adrenalectomy, is in good condition, grows, prefers tap-water, and has electrolyte concentrations in blood and muscle similar to those of control animals. In the absence of the adrenals, new tissue appears in the ovaries and, more rarely, in extra-ovarian sites, and reasons are given for considering it to be adrenocortical both in form and function. The origin of this presumptive adrenocortical tissue and the implications of its formation are discussed.

Extended survival of adrenalectomized rats possessing ear- or spleen- grafted ovaries.

In most mammals removal of the adrenal glands results in deleterious changes leading to loss of body weight and terminating in death after a variable, usually brief, period of time. The female ground squirrel (Citellus tridecemlineatus) is apparently an exception to this rule since it lives for periods up to one yea.r following “adrenalectomy” (Groat, 1943). Its ovaries are altered to the extent that some ovarian cells are described as “adrenocortical-like” and it is this altered histology that is held to be accountable for increased survival. If an ovary is grafted to the ear of a castrate mouse or rat it becomes morphologically and functionary different from control ovaries in that it possesses thecal luteinization and it secretes an androgen (Hill, 1937a, 1937b; Deanesly, 1938). An ovary transplanted to the spleen of a rat becomes markedly luteinized, even to the point of luteoma format on, after a period of time (Biskind and Biskind, 1944).

Effects of estrogen on the genital tract and urethra of anestrous female ground squirrels

Effects of estrogen on the genital tract and urethra of anestrous female ground squirrels

THE BIOLOGICAL ASSAY OF THE MAMMOGENIC DUCT GROWTH FACTOR OF THE ANTERIOR PITUITARY1,2

IT HAS BEEN established that the ovarian hormones are ineffective in stimulating mammary gland growth in hypophysectomiz,ed male guinea pigs, mice and rats, and in female rabbits, cats, ground squirrels and guinea pigs (1, 2, 3, 4, 5,6, 7). That the pituitary was necessary for the action of estrogen upon the mammary gland was concluded by Selye et al. (8). Contrary results, however, have been reported by several investigators (9, 10). Ruinen (10), was unable to secure localised growth of mammary glands with estrogen painted on the skin. A large number of experiments always gave equal development of all glands. Injection of desiccated whole pituitary powder from non-pregnant sheep was ineffective in stimulating mammary gland growth in three hypophysectomiz; ed immature female guinea pigs (4). One hypophysectomised and one castrated male rat showed no mammary gland growth after 30 daily implants of normal adult rat pituitaries.

The reproductive cycle in the female ground squirrel, Citellus tridecemlineatus (Mitchill)

The reproductive cycle in the female ground squirrel, Citellus tridecemlineatus (Mitchill)