Ecological and hormonal correlates of antipredator behavior in adult Belding’s ground squirrels (Spermophilus beldingi)

The influence of white adipose tissue on sexual maturation was investigated in captive-born male Belding's ground squirrels (Spermophilus beldingi). Juveniles were given abundant food during the summer and by fall achieved prehibernation body masses approximating those of sexually mature males. Immediately before being placed in a cold room (5–8 °C, constant darkness) for a 7-month hibernation period, fat was surgically removed (lipectomy) or left intact (sham lipectomy). The following spring, paired testes mass, serum testosterone, and spermatogenesis were monitored, mating tests were conducted, and body fat levels were determined. All three physiological indicators of reproductive status were significantly higher in sham-lipectomized than in lipectomized males, only sham-lipectomized males inseminated females, and body fat levels were significantly higher in sham-lipectomized than in lipectomized males. Thus, sexual maturation was accelerated in male Belding's ground squirrels by providing juveniles abundant food so they achieved body masses typical of adults; body fat was essential for accelerated development. In nature, males may forego reproductive development until they can acquire adequate fat stores to survive hibernation and activate their reproductive system and until they gain social experience important in male–male competition for mates.

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Seasonal effects of food provisioning on body fat, insulin, and corticosterone in free-living juvenile Belding's ground squirrels (Spermophilus beldingi)

Canadian Journal of Zoology ◽

10.1139/z01-222 ◽

2002 ◽

Vol 80 (2) ◽

pp. 366-371 ◽

Cited By ~ 8

Author(s):

Scott Nunes ◽

Eva-Maria Muecke ◽

Kay E Holekamp

Keyword(s):

Body Fat ◽

Plasma Insulin ◽

Plasma Concentrations ◽

Plasma Corticosterone ◽

Ground Squirrels ◽

Seasonal Effects ◽

Free Living ◽

Active Season ◽

Extra Food ◽

Spermophilus Beldingi

We evaluated the relationship between body fat and the metabolic hormones insulin and corticosterone in free-living juvenile Belding's ground squirrels (Spermophilus beldingi). Some free-living juveniles were provisioned with extra food high in fat and calories, and unprovisioned juveniles were used as controls. Body fat (as a percentage of body mass) of squirrels was regularly evaluated using non-invasive methods. Blood samples were also regularly collected from juveniles and assayed for plasma concentrations of insulin and corticosterone. Provisioned juveniles were fatter than unprovisioned juveniles during most of the active season, but differences in body fat disappeared near the end of summer as juveniles began fattening for hibernation. Thus, our data indicate that although body fat may fluctuate with energy availability early in the active season, it is regulated at precise levels as squirrels prepare for winter. Plasma corticosterone concentrations did not differ between provisioned and unprovisioned juveniles. However, plasma insulin concentrations were greater in provisioned than in unprovisioned juveniles early in the summer. Differences in insulin concentrations disappeared later in the active season, just prior to the disappearance of differences in body fat. Moreover, plasma insulin concentrations were significantly correlated with subsequent changes in body fat. Thus, our data suggest a link between insulin and seasonal regulation of body fat in juvenile S. beldingi.

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Ketone body metabolism in a ground squirrel during hibernation and fasting

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1985.249.4.r462 ◽

1985 ◽

Vol 249 (4) ◽

pp. R462-R470 ◽

Cited By ~ 22

Author(s):

B. L. Krilowicz

Keyword(s):

Energy Source ◽

Glucose Uptake ◽

Ground Squirrel ◽

Ketone Body ◽

Glucose Utilization ◽

Ground Squirrels ◽

Body Protein ◽

Muscle Tissues ◽

Spermophilus Beldingi

Hibernating Belding's ground squirrels (Spermophilus beldingi) are ketotic relative to fed nonhibernators. Muscles from torpid individuals, when incubated in media containing physiological concentrations of glucose and ketone, show reduced uptake of glucose in the presence of ketone. The magnitude of the reduction is dependent on ketone concentration and reaches 60% in heart and 100% in pectoralis at 1.4 mM ketone. Fasted squirrels are also ketotic. However, ketone does not reduce glucose uptake in muscles from fed or fasted animals. Glucose utilization by muscles decreases during a long-term fast, but the reduction is independent of ketone. Thus both a long-term fast and hibernation lead to changes in muscle tissues that decrease their reliance on glucose as an energy source. Ketosis leads to glucose sparing during hibernation, whereas muscle glucose utilization is decreased independently of ketone during a fast. The glucose sparing achieved in both hibernation and fasting leads to conservation of body protein, the major source of gluconeogenic precursors in fasting mammals.

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Maternal influence on juvenile growth rates in Belding's ground squirrel (Spermophilus beldingi)

Canadian Journal of Zoology ◽

10.1139/z91-299 ◽

1991 ◽

Vol 69 (8) ◽

pp. 2140-2145 ◽

Cited By ~ 14

Author(s):

Stephen C. Trombulak

Keyword(s):

Body Mass ◽

Sierra Nevada ◽

Early Summer ◽

Ground Squirrels ◽

The Body ◽

Supplemental Food ◽

Sierra Nevada Mountains ◽

Extra Food ◽

Spermophilus Beldingi ◽

Reproductive Females

The influence of food acquisition by pregnant and lactating Belding's ground squirrels (Spermophilus beldingi) on the body mass and growth rate of their offspring was assessed in a free-ranging population. In late spring and early summer of 1985 and 1986, individual females in a population of Belding's ground squirrels in the Sierra Nevada Mountains of California were given 300–500 g of sunflower seeds daily at the entrances to their burrows. Juveniles born to mothers who received supplemental food emerged from natal burrows on average 28% heavier than did controls (73.0 vs. 57.1 g, P < 0.001) and maintained a greater body mass throughout the remainder of the summer (P < 0.01). Also, females had a nonsignificant tendency towards greater survivorship during their first winter (P = 0.09). Supplemental feeding had no effect on litter size or sex ratio of offspring, or on the mass of the mothers up to the time of weaning, indicating that extra food available in the spring to reproductive females is converted primarily, if not exclusively, into larger offspring. Because the lengths of gestation and lactation are relatively invariable, the greater body mass of emerging juveniles must result from faster growth prior to weaning.

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How Rearing History Affects Alarm-call Responses of Belding's Ground Squirrels (Spermophilus beldingi, Sciuridae)

Ethology ◽

10.1046/j.1439-0310.1999.00388.x ◽

1999 ◽

Vol 105 (3) ◽

pp. 207-222 ◽

Cited By ~ 12

Author(s):

Jill M. Mateo ◽

Warren G. Holmes

Keyword(s):

Alarm Call ◽

Ground Squirrels ◽

Spermophilus Beldingi

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SNAKE-DIRECTED ANTIPREDATOR BEHAVIOR OF ROCK SQUIRRELS (SPERMOPHILUS VARIEGATUS): POPULATION DIFFERENCES AND SNAKE-SPECIES DISCRIMINATION

Behaviour ◽

10.1163/156853901316924485 ◽

2001 ◽

Vol 138 (5) ◽

pp. 575-595 ◽

Cited By ~ 37

Author(s):

Matthew Rowe ◽

Donald Owings ◽

Diane McKernon ◽

Patricia Arrowood ◽

Richard Coss

Keyword(s):

Sexual Size Dimorphism ◽

Antipredator Behavior ◽

Ground Squirrels ◽

Urban Site ◽

Species Discrimination ◽

Population Differences ◽

Behavioral Differences ◽

Size Dimorphism ◽

Study Sites ◽

California Ground Squirrels

AbstractThe purposes of this study were: (1) to describe the snake-directed antipredator behavior of rock squirrels; (2) to assess whether rock squirrels distinguish nonvenomous gopher snakes from venomous rattlesnakes; (3) to compare antisnake behavior in a snake-rare urban site and a snake-abundant wilderness site as a means of assessing whether natural selection or experience has generated population differences in behavior; (4) to assess snake densities in the two study sites; (5) to compare the antisnake behavior of rock squirrels with that of their closest relatives, California ground squirrels (Spermophilus beecheyi), a species that appears to differ from rock squirrels in exhibiting marked sexual-size dimorphism; and (6) to gather additional data on sexual size dimorphism in these two ground squirrel species. We tethered nonvenomous gopher snakes (Pituophis melanoleucus) and venomous western diamondback rattlesnakes (Crotalus atrox) in the field near burrows of marked squirrels and videotaped the ensuing interactions. Rock squirrels from both urban and wilderness populations confronted snakes while waving their fluffed tails from side to side, throwing substrate at the snakes, and even attacking snakes on occasion. Survey data confirmed large differences in snake densities between the two sites. Squirrels from the snake-abundant wilderness site distinguished rattlesnakes from gopher snakes, but squirrels from the snake-rare urban site did not. Since these squirrels show similar evidence of selection from snakes, as revealed by their equivalent physiological resistance to rattlesnake venom, we attributed these behavioral differences to the effects of snake experience. Rock squirrel antisnake behavior was very similar to that of California ground squirrels. Where the two species' behavior was dissimilar, the differences may be due in part to the interspecies variation in sexual size dimorphism confirmed in this study, and to the greater number of rattlesnake species that rock squirrels encounter.

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