Biology - Saimiri

Question 1

Historically, how popular was the squirrel monkey in research? Today?

Answer 1

Historically most common NWM, today second to common marmoset.

Question 2

How much do adult squirrel monkeys weight? Is sexual dimorphism present?

Answer 2

Approx. 1 kg. Some sexual dimorphism, but not as distinct as OWM. Males are 25-30% heavier with larger, longer canine teeth.

Question 3

What is a distinguishing feature of older squirrel monkeys?

Answer 3

Females greater than 5 years old develop a black spot in the peri-auricular region. Males and young females have clear hair coats in this region.

Question 4

Describe the trade of squirrel monkeys starting in the 1960s.

Answer 4

Large numbers imported to US in 1960s. South American governments began banning export of indigenous primates in 1970s. Bolivian gov. banned exportation of S. boliviensis boliviensis in 1980s. Only S. boliviensis peruviensis available from wild in mid-1980s. Currently, limited numbers of S. sciureus sciureus also available.

Question 5

Where are squirrel monkeys sourced from today?

Answer 5

200-300 from wild. Captive breeding colony at Uni Texas MD Anderson. Pan American Health Organization and NIH through Peruvian Primatology Project provides small number of new world monkeys to NIH

Question 6

Describe historical and current squirrel monkey taxonomy.

Answer 6

Historically a single species (S. sciureus) with several geographically separated subspecies. Now five distinct species and eight subspecies.

Question 7

What is the most common phenotypic characteristic for species identification? How does hair coloration differ? How is Saimiri sciureus sciureus (Guyanese) different?

Answer 7

Shape of nonpigmented hair above eyes.
Gothic arch, gray-green agouti head = S. sciureus, oerstedii, ustus
Roman arch, black head = S. boliviensis and S. vanzolinii
Guyanese = Pigmented hair resembling an eyebrow in Gothic arch

Question 8

What is the diploid chromosome number of squirrel monkeys? How can karyotype help distinguish?

Answer 8

44. Vary. In number of acrocentric autosomes from 5 to 7.

Question 9

Why is identification of the particular squirrel monkey critical?

Answer 9

Susceptibility to natural and experimentally induced disease
Inbreeding leading to heterozygous inversion, which can result in nonviable gametes, with 50% of conceptions in hybrids nonviable
Confounding variable in research

Question 10

Where are squirrel monkeys found in the wild?

Answer 10

Amazon basin of South America and isolated populations in Panama and Costa Rica

Question 11

Describe squirrel monkeys in the wild.

Answer 11

Diurnal, arboreal. Inhabit most forest types. Highly flexible in environmental adaptation.

Question 12

What do groups look like in the wild?

Answer 12

Large multimale-multifemale troops, number from 25-75 animals. Adult females and males, offspring, and subadults

Question 13

When do squirrel monkeys reach sexual maturity?

Answer 13

Female: 2.5-3.5 years
Males: 3.5-5 years

Question 14

How does transfer of individuals between groups work?

Answer 14

Bolivian, Peruvian, and Guyanese - Low rate of female transfer, high rate of male
S. oerstedii - Males have strong bonds, females transfer from their natal groups at sexual maturity.

Question 15

Describe social interaction of squirrel monkeys.

Answer 15

Varies between species.
S. oerstedii: Integrate males into egalitarian groups, intergroup aggression low.
S. boliviensis: Females dominant, males on periphery, social aggression common between both sexes
S. sciureus: Intermediate. Males integrated, dominant with high level of male-male aggression

Question 16

What predators are squirrel monkeys susceptible to? What methods of protection/communication do they use?

Answer 16

Raptors and wild felids. System of vocal calls to alert of danger and communicate. Close association with Cebus, who has an extensive alarm call system.

Question 17

Besides vocal calls, what other forms of communication do squirrel monkeys use?

Answer 17

Postural displays and olfactory cues (urine washing most widely recognized, mark trails or communicate sexual reproductive info)

Question 18

Describe squirrel monkey breeding. How odes this occur physiologically?

Answer 18

Seasonal breeders. Hormonally-induced physiological changes during the breeding season, moving from periods or infertility or anestrus with low levels of circulating steroid hormones to fertility with high levels of hormones.

Question 19

When is the breeding season? Describe the ovulatory cycle during this time.

Answer 19

Approx. 3 months in duration, from Dec - March in the Northern Hemisphere. Consists of cluster of ovulatory cycles varying 6-12 day length.

Question 20

How long is gestation and the interbirth interval?

Answer 20

Gestation 150 days. Interbirth interval 1 year (S. oerstedii) to 2 years (S. boliviensis and S. sciureus)

Question 21

What hormones characterize the breeding season of female squirrel monkeys?

Answer 21

Elevations in estradiol and progesterone. Estradiol very high immediately post-mating.

Question 22

Do squirrel monkeys cycle in synchrony with others in the same social group? What does this complicate?

Answer 22

No. Complicates prediction of cyclic events within breeding groups.

Question 23

How can ovulation be verified? When does mating occur in relation to ovulation?

Answer 23

Laparoscopy or serial ovarian hormone determinations. All within 24 hours of ovulation.

Question 24

What physical and behavioral changes do male squirrel monkeys undergo during the breeding season? What hormone do these responses correlate positively with?

Answer 24

Enlargement of testes concomitant with spermatogenesis and gain 15% of body weight, primarily of upper torso (fatting). Behavior characterized by reduced aggression and increase in sexually related responses. Androstenedione

Question 25

Serum concentrations of what hormones can be used to diagnose pregnancy?

Answer 25

Estradiol, progesterone, and squirrel monkey chorionic gonadotropin. SMG increases after 30 days

Question 26

During gestation, what hormone stimulates the production of estrogens? When does this hormone peak? How does this compare to other primates?

Answer 26

Placental corticotropin-releasing hormone stimulates production of estrogens. CRH peaks at 45-70 day of gestation, similar to other NWM. Differs from humans and apes which show highest CRH levels just prior to parturition.

Question 27

Why are early abortions a serious problem in squirrel monkey breeding colonies? How often do early abortions occur? How are they recognized?

Answer 27

All females must conceive during narrow time span of strict seasonal breeding season. Those that abort may not have another opportunity to conceive. Early abortions often occult, occur in 25% of pregnancies. Diagnosed and followed by changes in circulating hormone levels.

Question 28

What is a contributing factor to reduced reproductive efficiency in squirrel monkeys?

Answer 28

Large fetal mass in comparison to maternal size. Infant weighs approx. 18% the size of nonpregnant dam. High incidence of dystocia and stillbirths.

Question 29

What season are squirrel monkeys usually born in? What time of day and how long is the birthing process? What is unique to squirrel monkeys?

Answer 29

Summer. Occurs at night with labor lasting 1-2 hours. Infant actively participates in delivery once shoulders are free.

Question 30

How much do infants weight at birth? Below what weight do infants usually not survive?

Answer 30

100 grams, typically don’t survive if weighing less than 80 grams.

Question 31

Describe infant behavior during the first 2 weeks of life, at one month of age, and when weaning occurs.

Answer 31

Spends first 2 weeks of life clinging to dorsum of dam and sleeping. At 1 month begins to move off dam. Weaning age varies with species; 4 months for S. oerstedii (also has shorter interbirth interval) and up to 18 months for S. boliviensis, but more typically 90-120 days.

Question 32

Do male squirrel monkeys participate in infant care? Who provides care in addition to the mother? When does this occur?

Answer 32

No. Juvenile and other adult females will provide allomaternal care. Usually begins within first 2 weeks of infant life and involves carrying, potentially nursing.

Question 33

Describe the infant care costs of Saimiri species?

Answer 33

One of the highest among small new world monkeys due to the carrying of a large infant relative to adult body size.