Juvenile Richardson's Ground Research Articles

Gone girl: Richardson's ground squirrel offspring and neighbours are resilient to female removal.

Within matrilineal societies, the presence of mothers and female kin can greatly enhance survival and reproductive success owing to kin-biased alarm calling, cooperation in territory defence, protection from infanticidal conspecifics, joint care of young and enhanced access to resources. The removal of mothers by predators or disease is expected to increase the stress experienced by offspring via activation of their hypothalamic-pituitary-adrenal axis, increasing circulating glucocorticoids and reducing offspring survival and reproductive success. Yet, few studies have removed mothers in the post-weaning period to examine the assumed physiological and fitness consequences associated with these mortality events. We examined how the loss of a mother affects juvenile Richardson's ground squirrels' (Urocitellus richardsonii) faecal glucocorticoid metabolites and their survival. Given that neighbours are often close kin, we further hypothesized that conspecific removal would similarly diminish the fitness of neighbouring individuals. Upon removing the mother, we detected no impact on offspring or neighbouring conspecific faecal glucocorticoid metabolites in the removal year, or on overwinter survival in the following year. Furthermore, no impact on neighbour reproductive success was detected. Given the high predation rates of ground squirrels in wild populations, resilience to a changing social environment would prove adaptive for both surviving kin and non-kin.

Central distribution of oxytocin and vasopressin 1a receptors in juvenile Richardson's ground squirrels.

Oxytocin and vasopressin are well-conserved peptides important to the regulation of numerous aspects of social behavior, including sociality. Research exploring the distribution of the receptors for oxytocin (Oxtr) and for vasopressin (Avpr1a) in mammals has revealed associations between receptor distribution, sociality, and species' mating systems. Given that sociality and gregariousness can be tightly linked to reproduction, these nonapeptides unsurprisingly support affiliative behaviors that are important for mating and offspring care. We localized these receptors in juvenile Richardson's ground squirrel brains to determine whether distribution patterns of Oxtr and Avpr1a that are associated with promiscuous mating systems differ in rodents that also exhibit non-reproductive affiliation. These squirrels are social, colonial, and engage in nepotistic alarm calling behavior and affiliation outside of a reproductive context. Juveniles are the most affiliative age-class and are non-reproductive; making them ideal for examining these associations. We found that juveniles had dense Oxtr binding in the dentate gyrus of the hippocampus, amygdala, lateral septum, bed nucleus of the stria terminalis and medial geniculate nucleus. Juveniles had low to modest levels of Avpr1a binding in the medial preoptic area, olfactory bulbs, nucleus accumbens, superior colliculus, and inferior colliculus. We noted Oxtr and Avpr1a binding in the social behavior neural network (SBNN), further supporting a role of these nonapeptides in modulating social behavior across taxa. Oxtr and Avpr1a binding was also present in brain regions important to auditory processing that have known projections to the SBNN. We speculate that these neural substrates may be where these nonapeptides regulatecommunication.

Adult Richardson's Ground Squirrels (Spermophilus richardsonii) Ignore Rate Changes in Juvenile Alarm Calls: Age-Differential Response Urgency Perception?

Juvenile Richardson's ground squirrels (RGS; Spermophilus richardsonii) communicate response urgency by modulating the rate of syllable production in repetitive alarm calls, although longer call bouts do not promote more pronounced or longer-lasting (tonic) vigilance in juvenile call recipients. We exposed free-living adult RGS to playbacks of alarm calls differing in rate and length to determine whether adult receivers respond to the same alarm parameters as juveniles. Adult squirrels did not respond differentially to differences in call rate or length, suggesting that adult RGS do not attend to call rate as do juveniles. This difference in response may be attributable to a developmental change in the perceptual mechanisms by which individuals extract information regarding response urgency, but could also be a product of adult receivers devaluing information encoded in alarm calls emitted by relatively inexperienced juvenile signalers.

The squirrel that cried wolf: reliability detection by juvenile Richardson's ground squirrels ( Spermophilus richardsonii )

Where alarm signals function to warn others of the presence of threat, variation is likely to exist in the reliability of alarm signalers. Some signalers, with too low a threshold of excitation, will issue false alarms and should be ignored if potential alarm recipients are to maximize energy gains. We exposed juvenile Richardson's ground squirrels to reliable signalers, whose alarm calls were paired with the presentation of a predator model, and unreliable signalers, whose alarm calls were played when no potential predator was present. Call recipients discriminated among individual alarm callers, and reduced responsiveness to callers that had been unreliable. Thus, like primates, squirrels are capable of forming a concept of reliability by associating an individual's identity with that individual's past performance.

Repetitive calls of juvenile Richardson's ground squirrels (Spermophilus richardsonii) communicate response urgency

Richardson's ground squirrels, Spermophilus richardsonii, produce both repetitive and non-repetitive antipredator calls. While many hypotheses have been advanced to explain non-repetitive calls, the function of repetitive calling has received relatively little attention. We presented juvenile Richardson's ground squirrels with a predator model at distances ranging from 1 to 8 m and recorded the subsequent repetitive calls on digital audiotape. The rate of calling was inversely correlated with the distance between the model and the caller, with distance explaining almost 24% of the variation in call rate. To determine whether call recipients use that information, we manipulated the intersyllable latency of a single repetitive call exemplar to form 3 test stimuli varying only in call rate. Across 16 Richardson's ground squirrel colonies to which these calls were broadcast, the proportion of squirrels assuming the highly vigilant, alert posture increased with the rate of the repetitive call presented. Hence, juvenile Richardson's ground squirrels appear to communicate the proximity and presumably the degree of threat posed by potential predators.

Repetitive calls of juvenile Richardson's ground squirrels (<i>Spermophilus richardsonii</i>) communicate response urgency

Repetitive calls of juvenile Richardson's ground squirrels (<i>Spermophilus richardsonii</i>) communicate response urgency

Juvenile Richardson's Ground Squirrels (Spermophilus richardsonii) Manifest Both Littermate and Neighbour/Stranger Discrimination

AbstractNewborn ground squirrels (Spermophilus spp.) are reared in isolation of individuals belonging to other litters. At or near weaning, they broaden their social interactions to encompass conspecifics other than littermates. In laboratory studies, juvenile ground squirrels commonly discriminate littermates from non‐littermates, but few studies have examined whether behavioural discrimination at that level persists under natural circumstances. Previous studies have also all but ignored the possibility of alternative levels of social discrimination augmenting or replacing the discrimination of littermates from non‐littermates. To examine those possibilities, I staged interactions in a neutral arena between littermate, neighbour and non‐neighbour (stranger) pairs of otherwise free‐living juvenile Richardson's ground squirrels (Spermophilus richardsonii).Littermates interacted more frequently than other pair types and showed the highest proportion of cohesive behaviour and the least agonism. Strangers interacted less frequently than all other pair types, showed the fewest recognitive contacts, and were the least cohesive and most agonistic. Neighbours interacted less than littermates, but more than strangers, and showed intermediate levels of cohesion and agonism. Neighbours also engaged in more recognitive contacts than strangers, but did not have fewer recognitive contacts than littermates. Defecation rates also differed among interactant types: littermates left the fewest scats in the arena, neighbours deposited an intermediate number and strangers defecated the most. My results substantiate those of earlier laboratory studies suggesting that the discrimination of littermates from neighbouring juveniles persists in the natural context. These data also extend those earlier findings by demonstrating that juveniles come to discriminate neighbours from strangers. Comparisons of the behaviour of related vs. unrelated neighbours reveal that neighbour/stranger discrimination is contingent upon differential familiarity. Simultaneous social discrimination at the levels documented could promote kin‐biased behaviour and cooperation among both related and unrelated neighbours.

Juvenile Richardson's ground squirrels,Spermophilus richardsonii, discriminate among individual alarm callers

Richardson's ground squirrels,Spermophilus richardsonii, issue vocal alarm responses to avian and terrestrial predators. Recipients of those calls presumably benefit from enhanced detection and subsequent avoidance of predators. If receivers of alarm calls differentiate among callers, they could use that information to tailor their behavioural response to the perceived level of threat. A neighbour's call may indicate more imminent danger than that of a non-neighbour; with individual recognition, recipients could adjust their response according to the reliability of the caller. I elicited and recorded alarm calls of juvenile Richardson's ground squirrels using an avian predator model. Series of five calls were then played back to focal juveniles in the field. Within each series, playbacks involved an initial ‘habituation series’ of four calls of either a neighbour or a non-neighbour. In ‘control’ series, the fifth call was from the same individual but differed from the four preceding it. In ‘experimental’ series, the fifth call was from a different individual than those played earlier. Juveniles showed greater vigilance in response to playbacks of neighbours’ calls relative to non-neighbours’ calls, but habituated rapidly to call playbacks, showing a significant decline in vigilance by the second call. In control series, a different call from the same individual did not significantly increase vigilance. In experimental series, a call from a different individual restored vigilance to a level similar to that recorded prior to habituation. These results suggest that juvenile Richardson's ground squirrels discriminate among callers and use that ability to respond differentially to alarm calls issued by neighbours and non-neighbours.

Fattening and fatty acid synthetase in juvenile richardson's ground squirrels

1. 1. Intraperitoneal white adipose tissue (WAT) first appeared in juvenile squirrels when they were 10–12 weeks old and had achieved about two thirds of adult lean body mass. 2. 2. Rate of fat deposition at age 12–16 weeks was about 6.5 g per week, similar to the rate in adults during their respective periods of prehibernatory fattening when expressed as fat deposited per 100 g of lean body mass. 3. 3. Upon emergence from the natal burrow there was little fatty acid synthetase (FAS) activity and most of that was in liver. At 14 weeks of age nearly all FAS activity was in WAT, suggesting WAT was the primary tissue of fatty acid synthesis. 4. 4. At a given age, there were no differences between sexes in FAS activity of liver, WAT, or brown adipose tissue (BAT).

The “hibernation induction trigger”: Specificity and validity of bioassay using the 13-lined ground squirrel

Even though the existence of the blood-borne “hibernation induction trigger” has been reported in the 13-lined ground squirrel, transfusion of plasma from hibernating rodents with other hibernating species as the recipients failed to induce the occurrence of summer hibernation. In order to verify whether the response to the “trigger” substance is species specific, the present study was carried out to compare the effect of plasma from hibernating Richardson's ground squirrels on the incidence of summer hibernation in both juvenile Richardson's and adult 13-lined ground squirrels. In two series of experiments, 13-lined ground squirrels entered hibernation quite readily independent of the treatment. The rate of occurrence of hibernation ranged from 78% after sham injection to 86% after warm saline, fresh summer active plasma, and fresh hibernating plasma, respectively. There were no differences in the number of hibernation bouts and the number of days in hibernation after each treatment. In contrast, none of the juvenile Richardson's ground squirrels entered hibernation after any of the treatments up to the end of the 8-week observation period. These results not only argue against the existence of blood-borne “trigger” substance, at least in the Richardson's ground squirrel, but also caution against the use of the 13-lined ground squirrel as a standard test animal for the bioassay of the “trigger” substance.

Brown and white adipose tissue in relation to age and sex in juvenile Richardson's ground squirrels

Deposits of brown and white adipose tissue were monitored from birth to hibernation in laboratory-born and field-caught juvenile Richardson's ground squirrels (Spermophilus richardsonii). The weight-specific mass of brown adipose tissue was low at birth and, except for a brief increase at 3 days, declined postnatally. Total mass of brown adipose tissue and its lipid content were also low at birth, but increased postnatally, up to hibernation. Brown adipose tissue probably plays a greater role in hibernation thermogenesis than in neonatal thermoregulation. Both total and weight-specific mass of white adipose tissue increased postnatally, with maximum values prior to hibernation. Laboratory-born squirrels were fatter than wild squirrels and acquired more fat for a given increase in body mass. Females, both laboratory-born and wild, were fatter than males, and likewise acquired more fat for a given increase in body mass. Although at entry into hibernation wild juvenile females weighed 20% less than juvenile males, we calculated that females had twice as much total body lipid (91.1 versus 45.8 g).

Description of Sarcocystis campestris sp. n. (Protozoa: Sarcocystidae): a parasite of the badger Taxidea taxus with experimental transmission to the Richardson's ground squirrel, Spermophilus richardsonii

Sarcocystis campestris sp. n. (Protozoa: Sarcocystidae) is an heteroxenous coccidium with badgers (Taxidea taxus) as natural and experimental definitive hosts and Richardson's ground squirrels (Spermophilus richardsonii) as experimental intermediate hosts. Free sporocysts (10.2 × 8.0 μm with a large, round sporocyst residuum consisting of a single refractile granule), obtained from intestinal scrapings of badgers (carcasses frozen 2 years at −20 °C), were orally administered to juvenile Richardson's ground squirrels. Acute fatal sarcocystosis developed in some squirrels at 11–13 days postinoculation (p.i.). Meronts (second generation) were present 9–12 days p.i. in the vascular endothelium of many tissues (especially the lungs). Cysts developed in skeletal muscle, contained metrocytes (7 × 5 μm) 30 days p.i., and beginning 46 days p.i., bradyzoites (12.0 × 3.5 μm) were present. Cysts were macroscopic as early as 258 days p.i. Squirrel carcasses containing cysts (76 days p.i.) of S. campestris sp. n. were fed to Sarcocystis-free badgers. The prepatent period was 9 days and the patent period at least 13 days. Both badgers were ill early in the patent period and passed unformed feces during the patent period. Free sporocysts were 10.2 × 8.0 μm and each had an elongate sporocyst residuum containing numerous small refractile granules.

Seasonally-related physiological and behavioural changes in captive Richardson's ground squirrels ( Spermophilus richardsoni)

1. 1. This study reveals the interrelationship among body weight, food intake and activity for a one-year period in two different year groups of captive juvenile Richardson's ground squirrels ( Spermophilus richardsoni) 2. 2. An increase in body weight during initial captivity and during the post-hibernation period related to an increase in food intake and in activity. 3. 3. High and constant body weights during the pre-hibernation seasons were associated with a “voluntary” reduction in food intake, a decline in standard metabolic rate and in activity. These changes occurred before changes in photoperiod and temperature. 4. 4. Hibernation occurred in most of the food-deprived animals but, except for one individual, not in animals provided with food ad libitum.

Photoperiod as an environmental cue for hibernation in juvenile Richardson's Ground Squirrels, Spermophilus richardsoni

Photoperiod as an environmental cue for hibernation in juvenile Richardson's Ground Squirrels, Spermophilus richardsoni

Comparison of body weights between captive and free-ranging juvenile Richardson's ground squirrels (Spermophilus richardsoni)

Body weights of free-ranging and captive juvenile Richardson's ground squirrels (Spermophilus richardsoni) were determined at regular intervals during the nonhibernating season. Animals in captivity gained weight at a faster rate and to a greater extent than those in their natural habitat. Attainment of maximum weights in captive ground squirrels was associated with a reduction in food intake and could not be related to food availability, a change in temperature, or in photoperiod.

Ontogeny of spatial relationships and social behaviour in juvenile Richardson's ground squirrels

The development of spatial and social patterns by juvenile Richardson's ground squirrels, from first emergence from the natal burrow to entry into hibernation, is described. Juveniles enter the aboveground population at [Formula: see text] weeks of age. During the next 4 weeks juveniles remain in close spatial proximity to family members with whom they engage in frequent amicable social interactions. Thereafter, juveniles become increasingly independent from the family unit, establishing their own spatially distinct core areas and exhibiting site-dependent dominance toward nonkin. Typically juveniles remain physically closer to and more amicable with littermates and mother than other conspecifics such that they compose kin clusters, the members of which are agonistic toward members of adjacent kin clusters. Daughters are more likely to continue to reside close to kin as adults than are sons. At 9–10 weeks of age juveniles exhibit the majority of spatial and social patterns characteristic of adults, and at 12 weeks they are behaviourally indistinguishable from adults. Similar rapid acquisition of adult patterns occurs in four other species of ground-dwelling sciurids that are also obligate hibernators and that breed immediately following emergence from their first hibernation.

Field observations on the social relationships between adult female and juvenile Richardson's ground squirrels

Field observations were conducted in southern Saskatchewan in 1969 and 1971. Adult female Richardson's ground squirrels and their own young engaged predominantly in nasal and cohesive contacts while adults and young from other litters engaged predominantly in agonistic contacts. Identification sometimes occurred at a distance based on the location and behavior of the other animal.Newly emerged juveniles remained close to the home burrow and engaged mainly in non-agonistic interactions with both their mothers and other adults. Not until juveniles were 6–7 weeks old and were familiar with the area used by the mother did they correctly identify adults regardless of where the interaction occurred.