Biomedical subjects
Julia Ostner
Publications and source records attributed to Julia Ostner.
What Hanuman langur males know about female reproductive status.
In species with a high risk of infanticide, a conflict of interest exists between the sexes over the amount of paternity information that is available to males. While females are expected to keep males unaware of their reproductive status in order to confuse paternity, selection should favor those male traits that enhance the males' assessment of female status and consequently of paternity probability. In Hanuman langurs (Semnopithecus entellus), a species that is extremely vulnerable to infanticide, females have been shown to successfully conceal the exact timing of ovulation from males--perhaps because they exhibit no sexual swelling and mate during all reproductive phases, including gestation. Nevertheless, it remains unclear whether males have hitherto unrecognized information about females' reproductive condition on a broader level that could still enhance male reproductive success. We investigated male assessment of female reproductive states in a population of wild Hanuman langurs as indicated by changes in male behavior, such as rates of copulations, anogenital inspections, and consortships, in relation to different female receptive periods (pregnant, fertile-nonconceptional, and conceptional). Our data indicate that males were able to discern qualitatively distinct reproductive states. Males were more interested in fertile than pregnant females, as indicated by higher copulation rates. Based on consortships, males distinguished fertile from nonfertile phases, as well as fertile, nonconceptional receptive periods from conceptional ones. Hanuman langur males are thus not as unaware of female reproductive condition as previously thought, supporting the idea of an ongoing battle of the sexes over paternity information. However, granting some knowledge while at the same time concealing the exact day of ovulation may also reflect a pure female strategy of balancing paternity concentration with paternity confusion, which is the most likely strategy in this system with high infanticide risk and male defense of infants.
Intersexual dominance, masculinized genitals and prenatal steroids: comparative data from lemurid primates.
Masculinization of female genitalia and female intersexual dominance distinguish spotted hyenas (Crocuta crocuta) and Malagasy primates (Lemuriformes) from most other mammals. An unusual prenatal endocrine environment has been proposed to proximately underlie the development of these traits in hyenas. To examine whether female dominance and genital masculinization are similarly enhanced by the prenatal environment in lemurid primates, we measured androgen and estrogen excretion in pregnant wild redfronted lemurs (Eulemur fulvus rufus). Our results showed that estrogen levels during the second phase of gestation were much higher in females carrying a male fetus than in female-carrying mothers. This may indicate the onset of testicular activity in male fetuses, because androgens of fetal origin are aromatized to maternal estrogens. Levels of androgen excretion were similar in all mothers regardless of the fetus' sex, which may suggest that androgen-independent mechanisms also contribute to female masculinization. The much higher androgen/estrogen ratio in female-carrying mothers indicates that relative, rather than absolute, prenatal steroid concentrations may play a role in female masculinization.
Endocrine characterization of female reproductive status in wild redfronted lemurs (Eulemur fulvus rufus).
In order to characterize the endocrine changes associated with ovarian function and pregnancy in wild redfronted lemurs (Eulemur fulvus rufus), profiles of immunoreactive 5alpha-pregnane-3alpha-ol-20-one (5-P-3OH) and total estrogens (E(t)) in feces were generated during the breeding season and gestation. HPLC data confirmed the presence of high amounts of 5-P-3OH in the feces of redfronted lemurs and showed that estrone and estradiol-17beta were the major estrogens excreted into feces, with estrone predominating. Due to an extreme day-to-day variability in excretion of both hormones during the breeding season, estrus cycle characterization was not possible for the free-ranging females. Comparison with endocrine data from captive animals suggested that this might have been associated with a highly variable amount of undigested fecal matter in the feces of wild females. A gestation length of 121.3 days was calculated on the basis of the day of behavioral estrus and date of parturition. Hormonally, pregnancy could be reliably diagnosed from day 40-45 after conception, when fecal progestogen levels clearly increased above breeding season concentrations in all females. Levels gradually increased thereafter, with 15- to 35-fold elevated maximum levels being reached shortly before parturition. In contrast, the pattern of fecal estrogen excretion was strongly related to the sex of the fetus in utero, with only females carrying male infants showing elevated (25- to 50-fold) estrogen levels during the last third of gestation, while levels remained at low breeding season levels in female-carrying mothers. Thus, fecal estrogen measurements during the last 6-7 weeks of gestation allow fetal sex to be determined prenatally. By providing the first data on the reproductive endocrinology of E. fulvus, we have shown that fecal hormone analysis is a useful tool to monitor endocrine changes associated with pregnancy, while it appears to have certain limitations regarding the assessment of ovarian function.
Social thermoregulation in redfronted lemurs (Eulemur fulvus rufus).
Pronounced seasonality, with temperatures dropping as low as 5 degrees C during the dry season, has led to the hypothesis that Malagasy lemurs face cold stress and respond to this by inactivity and social thermoregulation, i.e. resting in tight body contact with conspecifics. Compared to anthropoids, lemur groups are comprised of an unusually high number of males, leading to an even or slightly male-biased adult sex ratio. According to one hypothesis, females may benefit from these surplus males in their groups if males huddle with females. The results of this study on redfronted lemurs (Eulemur fulvus rufus) in Kirindy Forest, Madagascar revealed that the animals indeed responded to cold ambient temperatures by increased inactivity and the formation of huddling groups. However, surplus males did not participate more frequently than expected in huddling groups with females and females do not, therefore, benefit from the high number of males in their groups by increased social thermoregulation.