Jeremy F. Dahl

Cyclic perineal swelling during the intermenstrual intervals of captive female pygmy chimpanzees (Pan paniscus)

The perineal swelling cycle and intermenstrual interval of pygmy chimpanzees ( Pan paniscus ) have not been well documented, and it is not clear that cither characteristic differs from those of common chimpanzees ( P. troglodytes ). Consequently, adult females in a breeding colony of P. paniscus were monitored for menses over four and one-half years, and the perineal swelling cycles were detailed for half that period. To test the hypothesis that there are no differences between the species of Pan in reproductive cyclicity of captive females, the results were compared with data collected from 22 captive P. troglodytes over an eight-year period by W. C. Young and R. M. Yerkes. The average duration of the intermenstrual interval of 49 days ( n =23; S.E.=2·9) for adult P. paniscus differed from an average of 34–36 days for adult P. troglodytes , but was similar to the 50-day interval of adolescent P. troglodytes . The pattern of the swelling cycle was different from any cycles exhibited by adult or adolescent P. troglodytes ; following the first sign of detumescence, the swelling retained significant tumescence for an average of 12 days. By altering slightly the definitions of each swelling phase, the durations of the phases subsequent to abrupt detumescence were found to resemble either the adult or the adolescent postswelling phases of P. troglodytes . Adult female P. paniscus exhibit marked swelling for approximately 75% of the intermenstrual interval in comparison to about 50% or less of the intervals exhibited by P. troglodytes . It follows that female P. paniscus are sexually attractive to males for a greater portion of the time, which may contribute to the differences in social organization reported for the two species in the wild. Aspects of the similarity in cyclicity between adult P. paniscus and adolescent P. troglodytes are congruous with interspecific morphometric analyses and the comparative anatomy of the female external genitalia, suggesting that some characteristics of P. paniscus may be neotenous with respect to P. troglodytes but not all distinctions can be accounted for by neoteny alone. The structural resemblance between the sexual swelling of female chimpanzees and the buttocks of human females suggests that female Australopithecinae may have been continuously attractive to males.

Genetic Influence on the Expression of Hand Preferences in Chimpanzees (Pan Troglodytes): Evidence in Support of the Right-Shift Theory and Developmental Instability

Genetic mechanisms have been proposed to explain the pervasive representation of right-handedness in humans, whereas random, nongenetic factors have been posited to explain the lack of population-level right-handedness in nonhuman primates. We report evidence that hand preferences in chimpanzees are heritable, even among related individuals raised in different environments. Furthermore, we report that the degree of heritability is modified by factors associated with developmental instability, notably, offspring parity. The data are interpreted to reconcile both genetic models for handedness and hypotheses suggesting that developmental instability influences variation in handedness.

Perineal swelling during pregnancy in common chimpanzees and puerperal pathology

Abstract: Perineal swelling during pregnancy in captive common chimpanzees (Pan troglodytes) was studied to examine if the swelling pattern is consistent with known fluctuations in estrogens and progesterone and to test associations between reduced swelling and pathological outcome. Analyses of swelling during 107 pregnancies with a variety of outcomes revealed that a majority of swelling patterns fit an endocrinological model closely, but that a small minority (6.6%) from low parity mothers had exaggerated and extended swelling, suggesting an altered sensitivity of the swelling to steroids. Disregarding this extreme minority, swelling was found to be significantly reduced from that of normal outcome pregnancies for sub‐groups with varying degrees of maternal incompetence, neonatal fatality, and stillbirth. This reduction was most marked for pregnancies in nursery‐reared mothers. Given the validity of the correspondence between swelling patterns and steroid concentrations, lower estrogen concentrations are implicated in the etiology of the puerperal pathologies seen. That steroid hormone concentrations during pregnancy may influence maternal behavior in apes provides a clue to the etiology of post‐partum depression in women.

Birth Order and Hand Preference in Chimpanzees (Pan troglodytes): Implications for Pathological Models of Handedness in Humans

The effect of birth order on hand preference was assessed in a sample of 154 captive-born chimpanzees. Subjects were classified as first, middle, or latter born using 2 classification criteria based on their birth order. Hand preference was measured using a task that elicited coordinated bimanual actions. Significant birth-order effects were found for both classification criteria, with first- and latter-born subjects exhibiting a lesser degree of right-handedness compared with middle-born subjects. These data suggest that biological rather than sociological factors play a greater role in explaining the observed birth-order effects on hand preference in humans.

Size and Form of the Penis in Orang-Utans

Size and form of the external penis, or pars libera, was documented for 17 living orangutans ( Pongo pygmaeus ) of varying age. The pars libera was much longer than previously represented in comparative analyses, and most were filiform (as in Pan ), but form and color was variable: 1) a partially or completely demarcated glans-like structure (as in Gorilla ) was present in a few subjects; 2) epidermal specializations of the pars distalis had either a hinge-like or flap-like form and might be homologous to the keratinized spines seen in other species; 3) the pars libera was not a uniform pink in all cases as the pars medialis often was black or purple. Comparisons of the length of the pars libera relative to size of females across the great apes and humans ( Homo ) reveals that the pars libera of Pan is much longer than that of Homo which is longer than but similar to that of Pongo , which is much longer than that of Gorilla . Relative to size of males, however, Homo have pars libera that are twice as long as those of Pongo . Similarities and differences in penile structure between Pongo , which has a non-gregarious (dispersed) mating system, and Pan (with a multimale system) may be understood in relation to the form of the female genitalia; this is consistent with the notion that sexual selection by female choice may be an ultimate cause of sexual characteristics of hominoids. Hypotheses about causation, however, require scrutiny with a more complete dataset from living subjects.

Sexual behavior of chimpanzees (Pan troglodytes): Male versus female regulation.

We investigated the sexual behavior of 13 chimpanzees (Pan troglodytes) in 2 types of pair test in order to clarify the interaction of social variables with female hormonal state. The frequency of copulation in tests in which the partners were freely accessible to each other was related to the males dominance over the female; copulation was less frequent and was related to social compatibility in tests in which the female controlled access. Copulation was related to female hormonal state in both types of test. The results demonstrate (a) an association between female hormonal state and sexual activity of chimpanzees, (b) the influence of social relationships on sexual interactions, and (c) the importance of focusing on female sexual behavior before copulation, rather than copulation per se, in research on sexual arousability of female primates.

Birth order and left-handedness revisited : some recent findings in chimpanzees (Pan troglodytes) and their implications for developmental and evolutionary models of human handedness

This paper examines the relationship between parity, pregnancy outcome, and handedness in a sample of captive chimpanzees (Pan troglodytes). The relation between parity, maternal age and positive or negative pregnancy outcome was assessed from life history data for 536 chimpanzees housed at the Yerkes Regional Primate Research Center. The incidences of negative pregnancy outcome (notably spontaneous abortions and stillbirths) were significantly higher in parities of 8 or higher compared to all other parities. In a sub-sample of 165 chimpanzees, the relation between parity, maternal age and handedness was assessed to determine whether left handedness may serve as a marker of prenatal pathology. These analyses indicated that left-handedness was more prevalent in 1st and 8 or higher parities compared to parities between 2 and 7, respectively. Possible prenatal hormonal and periparturitional factors are discussed as possible mechanisms for the observed findings.

Hormone levels and anogenital swelling of female chimpanzees as a function of estrogen dosage in a combined oral contraceptive

Abstract A combined oral contraceptive consisting of ethinyl estradiol (EE2) in three dosages (50, 100, and 400 μg) and norethindrone (0.5 mg) was given to female chimpanzees to determine the effect on endogenous sex hormone levels and anogenital swelling. Serum levels of EE2 increased with increasing dosages of EE2, estradiol decreased, and luteinizing hormone, progesterone and testosterone were maintained at approximately midfollicular phase levels. Urinary levels of EE2 glucuronide increased with the increasing dosages of EE2, whereas estrone and pregnanediol glucuronide were essentially undetectable. The cyclic increase in female anogenital swelling was abolished when the norethindrone was combined with 50 μg of EE2 and relatively constant and low levels of swelling were recorded. Relatively constant but successively higher levels of swelling were recorded when the norethindrone was combined with the higher dosages of EE2. These effects of oral contraceptives on female genital tissues are relevant to our laboratory studies of sexual behavior in chimpanzees given oral contraceptives and could also have some implications for women taking oral contraceptives.

Assisted Reproduction in the Great Apes

Assisted reproduction with great apes will be considered here as facilitated reproduction in order to include the experimental and clinical approaches related to fertility evaluation (including correction of infertility) and optimization of natural fertilization as well as the more invasive methods of reproduction enhancement associated with artificial insemination (AI), in vitro fertilization (IVF), gamete storage, and surgical intervention. Those techniques are only now becoming effectively applied to the great apes. In addition, the existing data pertaining to early termination of pregnancy, obstetrical intervention, and neonatal and infant mortality can provide valuable guidance regarding the development of strategies for assisted reproduction. Such strategies are, therefore, to be directed to initiation of pregnancy, maintenance of pregnancy, reduction of neonatal loss, provision of means for “normal” postnatal development, and arrangement for social conditions conducive to subsequent natural breeding and rearing of offspring.

Effects of an oral contraceptive on sexual behavior of chimpanzees (Pan troglodytes)

Behavioral and physiological effects of a combined oral contraceptive (OC) were studied in chimpanzees for comparative purposes related to (i) the ambiguity surrounding the effects of OCs on the sexuality of humans, (ii) the close biological relationship between chimpanzees and humans, especially with respect to endogenous sex hormones and sexual behavior, and (iii) the relatively greater behavioral sensitivity of the chimpanzee to changes in sex hormone levels such as those that accompany the use of OCs. Two different types of pair tests and detailed behavioral assessments were used to differentiate the hormonal effects of female behavior from social effects imposed by the male. Anogenital swelling and copulation were reduced during OC cycles, but the effect of the OC on copulation was directly related to the social and sexual relationship of the pair during natural cycles. The more compatible and more frequently copulating pairs in the natural cycles continued to copulate during the OC cycles, albeit at reduced rates, whereas the less compatible and less frequently copulating pairs ceased copulating altogether when the female received the OC. There was no independent effect of the OC on ejaculation per se. Both male and female sexual initiative were reduced in the OC cycles, but female responsiveness to male sexual solicitations and direct copulatory attempts were not affected. Data indicate that despite generally adverse effects of the OC on certain physiological and behavioral dimensions of sexuality, social factors ultimately determined the degree of response to the OC.(ABSTRACT TRUNCATED AT 250 WORDS)