Variation in oxytocin is related to variation in affiliative behavior in monogamous, pairbonded tamarins.

Oxytocin plays an important role in monogamous pairbonded female voles, but not in polygamous voles. Here we examined a socially monogamous cooperatively breeding primate where both sexes share in parental care and territory defense for within species variation in behavior and female and male oxytocin levels in 14 pairs of cotton-top tamarins (Saguinus oedipus). In order to obtain a stable chronic assessment of hormones and behavior, we observed behavior and collected urinary hormonal samples across the tamarins' 3-week ovulatory cycle. We found similar levels of urinary oxytocin in both sexes. However, basal urinary oxytocin levels varied 10-fold across pairs and pair-mates displayed similar oxytocin levels. Affiliative behavior (contact, grooming, sex) also varied greatly across the sample and explained more than half the variance in pair oxytocin levels. The variables accounting for variation in oxytocin levels differed by sex. Mutual contact and grooming explained most of the variance in female oxytocin levels, whereas sexual behavior explained most of the variance in male oxytocin levels. The initiation of contact by males and solicitation of sex by females were related to increased levels of oxytocin in both. This study demonstrates within-species variation in oxytocin that is directly related to levels of affiliative and sexual behavior. However, different behavioral mechanisms influence oxytocin levels in males and females and a strong pair relationship (as indexed by high levels of oxytocin) may require the activation of appropriate mechanisms for both sexes.

Changes in prolactin and glucocorticoid levels in cotton-top tamarin fathers during their mate's pregnancy: the effect of infants and paternal experience.

We have previously shown that paternally experienced cotton-top tamarin fathers (Saguinus oedipus) had significant increases in prolactin and glucocorticoids at the midpoint of their mate's pregnancy, whereas less experienced fathers showed prolactin increases only the month before offspring birth [Ziegler & Snowdon, Hormones & Behavior 38:159-167, 2000; Ziegler et al., Hormones & Behavior 45:84-92, 2004]. These results could be owing to differing paternal experience or from paternal care given to previous offspring. To test the relative role of infant cues and paternal experience in these hormonal changes, we paired four paternally experienced tamarin fathers with a novel, primiparous female and monitored hormone levels during their first pregnancy together. No fathers showed the significant mid-pregnancy increase in prolactin seen previously. However, all fathers showed increases in cortisol and significant peaks of corticosterone in mid-pregnancy. The increase in corticosterone was consistent with previous data occurring in each male during the same week or the week following the urinary cortisol increase shown by his mate. These data may suggest that the elevated mid-gestation prolactin seen previously in experienced males may be owing to the presence of offspring from the previous set of infants. In contrast, increased cortisol and corticosterone occurred independently of infant cues and may be related to previous paternal experience. We therefore conclude that both offspring presence and paternal experience contribute to the hormonal changes seen in experienced cotton-top tamarin fathers during their mate's pregnancy.

Validation of urinary cortisol as an indicator of hypothalamic-pituitary-adrenal function in the bearded emperor tamarin (Saguinus imperator subgrisescens).

The use of cortisol levels as a measure of stress is often complicated by the use of invasive techniques that may increase hypothalamic-pituitary-adrenal (HPA) axis activity during sample collection. The goal of this study was to collect samples noninvasively and validate an enzyme-immunoassay (EIA) for the measurement of cortisol in urine to quantify HPA axis activity in the bearded emperor tamarin (Saguinus imperator subgrisescens). Urine samples were collected from trained subjects between 0700 and 0730 hr during a 1-month period, and were pooled for immunological validation. We validated the assay immunologically by demonstrating specificity, accuracy, precision, and sensitivity. For biological validation of the assay, we showed that levels of urinary cortisol (in samples collected between 0700 and 1700 hr) varied significantly across the day. Cortisol concentration was lowest at 0700 hr, increased to a mid-morning peak (0900 hr), and declined across the remainder of the day in a typical mammalian circadian pattern. We thus demonstrate that urinary cortisol can be used to quantify HPA activity in S.i. subgrisescens.

Responsiveness of expectant male cotton-top tamarins, Saguinus oedipus, to mate's pregnancy.

In the cotton-top tamarin, a primate where paternal care is critical to the survival of the offspring, we found that expectant fathers experienced multiple hormonal changes during their mate's pregnancy. Fathers that had experienced several previous births showed significant changes in urinary estrogens, androgens, prolactin and cortisol in the last 2 months before birth, whereas less-experienced fathers (LEF) did not. The female's midpregnancy rise in glucocorticoids was followed within 1-2 weeks by a peak of cortisol and corticosterone in her paired male in 70% of all males and 100% of all experienced males. Examination of behavioral interactions between the pairs did not reveal changes in rates of interactions between the experienced pairs over pregnancy. However, the less-experienced pairs had significantly higher levels of affiliative and sexual interactions. Therefore, behavioral communication between the pair did not appear to account for the hormonal changes occurring within the experienced fathers (EF). The midpregnancy rise of glucocorticoids in females may stimulate a glucocorticoid response in male tamarins and thereby activate other hormonal changes in males to prepare them for their parenting role.

Gonadal source of testosterone metabolites in urine of male cotton-top tamarin monkeys (Saguinus oedipus).

Examining gonadal function in the small excitable cotton-top tamarin monkey (Saguinus oedipus) requires noninvasive sampling techniques. Two studies were performed to identify the quantifiable urinary metabolites of testosterone in cotton-top tamarins and which of the measurable metabolites would best reflect a gonadal source of testosterone secretion. In the first study, we injected unlabeled testosterone i.m. in males at either 500-ng or 1-microg levels. Urine samples were analyzed for androgens and estrogens. Testosterone and dihydrotestosterone (DHT) increased significantly following the injections in test males but not in control males. No significant increases in androstenedione occurred. Mean levels of estradiol and estrone did not consistently increase during the 5 days following injection. In the second study, a gonadotropin-releasing hormone antagonist, Antide, was used to block LH stimulation of gonadal steroidogenesis. Males given Antide at either a 6 mg/kg dose or an 18 mg/kg dose showed significantly lower levels of urinary LH than controls. At the higher Antide dose, testosterone levels were significantly reduced during weeks 1 and 2 posttreatment, whereas DHT levels significantly declined during the 2nd week posttreatment. Estradiol levels were highly variable prior to treatment but decreased significantly following treatment, whereas estrone levels remained variable throughout. These results indicate that measurement of urinary testosterone and possibly DHT reflect gonadal function in male cotton-top tamarins. Other sources of urinary estrogens may occur for the male cotton-top tamarin, but these data suggest that a substantial part of urinary estradiol is from gonadal sources, whereas urinary estrone appears to be mainly from extragonadal sources.

Cyclic excretion of urinary oestrogens in female tamarins (Saguinus oedipus).

Urine was collected from 6 female cotton-top tamarins (Saguinus o. oedipus) and urinary oestrone and oestradiol concentrations were measured by radioimmunoassay. Oestrone was excreted at 50-fold higher concentrations than oestradiol. Five females showed patterns of regular oestrone cyclicity, with a mean peak-to-peak oestrone cycle of 23.6 +/- 1.2 days. Levels of oestradiol tended to vary with levels of oestrone excretion, but peaks were less pronounced and more variable. The sixth female, diagnosed as having 'wasting marmoset syndrome', had very low levels of excreted oestrogens, suggesting infertility. We suggest that urinary oestrone provides a good index to ovarian cyclicity in female cotton-top tamarins.

Urinary oestrogen excretion in the female cotton-topped tamarin (Saguinus oedipus oedipus).

Daily urinary oestrogen excretion was measured by radioimmunoassay in 6 adult female cotton-topped tamarins. Four females showed obvious cyclicity in oestrogen excretion and the mean cycle length for 10 complete cycles was 22.7 +/- 1.7 days with a range of 19-25 days. In 3 of the 6 females a dip-and-read test for blood in the urine gave positive readings which were distributed during trough and mid-cycle periods although females of this species are believed not to menstruate.

Comparison of urinary oestrogen excretion in South American primates.

Changes in the excretion of immunoreactive oestrogens and biologically active LH were assessed from measurements on small samples of urine collected from a capuchin, a tamarin, a spider monkey and a squirrel monkey. The hormone profiles were used to time matings of the capuchin and spider monkey; conception and pregnancy ensued. Detailed analysis of one urine sample from each female by using partition chromatography and reverse-phase high-pressure liquid chromatography showed that oestrone was more abundant than oestradiol-17 beta and oestriol combined, but the relative contribution of individual oestrogens to the total oestrogen complement differed. In the sample from the capuchin, an immunoreactive oestrogen slightly less polar than oestradiol appeared to be the most abundant urinary oestrogen.