Influence of season, age, sex, and time of day on the endocrine profile of the common bottlenose dolphin (Tursiops truncatus).

Understanding baseline hormone levels, the magnitude of intra-individual variability, and their variation as a function of life history is difficult in toothed whales (e.g. dolphins and porpoises) because of the effects of capture stress. To determine the endocrine profile of the common bottlenose dolphin (Tursiops truncatus) as a function of season, time of day (TOD), age, sex, and reproductive status, blood corticosteroids, thyroid hormones, and catecholamines were repeatedly measured in a managed-care population exposed to ambient light and water temperatures of San Diego Bay. Additionally, fecal hormone metabolites were assessed for cortisol, aldosterone, and triiodothyronine. Samples were collected at two to four-week intervals over a period of two years, and multiple times within a day at monthly intervals over a year. Samples were collected through the voluntary participation of the dolphins in the blood draws and fecal collections in order to avoid the effects of handling stress. All serum hormones except aldosterone significantly varied with season and all serum hormones except total thyroxine significantly varied as a function of TOD. Fecal glucocorticoid metabolites significantly correlated with circulating cortisol levels, and there was a significant seasonal effect on triiodothyronine fecal metabolites. Strong seasonal effects demonstrated complex interactions with age and sex suggesting that contextual information is critical to interpreting differences in endocrine profiles. Strong circadian patterns further suggest that sampling design is important to the interpretation of blood or fecal collections, particularly since diurnal changes in some serum hormone levels are similar to the magnitude of seasonal differences. Despite potential impacts of feeding schedules on diurnal patterns, managed care populations can provide important insights into seasonal and age-related endocrine changes in toothed whales.

Validation and application of noninvasive glucocorticoid and thyroid hormone measures in free-ranging Hawaiian monk seals.

We validate fecal glucocorticoid (GC) and thyroid (T3) hormone metabolite measures in the Critically Endangered Hawaiian monk seal for the first time, and examine variation in the concentrations of these hormones in individuals across the species' range. We test hypotheses that monk seals from declining subpopulations have relatively high GCs and low T3 on average suggesting impacts of food limitation, and that this hormone pattern is more apparent in immature animals compared to adults, as food limitation is specifically indicated as a principal cause of poor body condition and survival of juvenile monk seals. We opportunistically sampled scat from 84 individually identifiable monk seals during the 2010 breeding season from two geographic regions, the main Hawaiian Islands (MHI) and the Northwestern Hawaiian Islands (NWHI). The MHI subpopulation of monk seals is growing, whereas subpopulations at many sites in the NWHI are in decline. Best fit general linear models predicting variation in GCs and T3 (examined separately) were similar (after accounting for significantly elevated hormone concentrations associated with molt and possibly lactation); both included sample date, region, and monk seal age as predictors. GC concentrations were significantly lower in MHI versus NWHI monk seals and decreased as the breeding season progressed. T3 concentrations were significantly lower in immature monk seals compared to adults. GC and T3 concentrations were positively correlated at 4 NWHI sites; prey may be adequate for physiological growth or maintenance at these sites but relatively stressful to acquire. GCs were highest at French Frigate Shoals, (a NWHI site) while T3 was relatively low here, indicating a possible signal of food limitation. GCs were lowest in the MHI. Disturbance associated with living near a high human population in the MHI appears to impact monk seal physiology less than other stressors encountered in the remote and highly protected NWHI where human presence is extremely low.

Glucocorticosteroid concentrations in feces and hair of captive caribou and reindeer following adrenocorticotropic hormone challenge.

Climate change and industrial development are contributing to synchronous declines in Rangifer populations across the Arctic. Chronic stress has been implicated as a proximate factor associated with decline in free-ranging populations, but its role in Rangifer is unspecified. Analysis of glucocorticosteroid (GC) concentration in feces, and more recently in hair, is a non-invasive method for monitoring stress in wildlife. Adrenocorticotropic hormone (ACTH) released from the pituitary gland stimulates GC release from the adrenals and can be administered to reflect adrenal activation. In this study, we assessed concentrations of GC metabolites in feces and cortisol in hair of Alaskan caribou (Rangifer tarandus granti) and reindeer (R. t. tarandus) following ACTH treatment. We predicted that ACTH challenge would increase concentrations of fecal GCs, but not hair cortisol because steroid deposited into the hair shaft occurs over an extended period of time (months) and is likely insensitive to acute adrenal stimulation. Adult caribou (n=10; mean age, 6.5 years old) exhibited a peak increase in fecal GCs 8h following a 2 IU/kg dose of ACTH compared to pre-injection concentrations. In contrast, sub-adult reindeer (n=10, 0.8 years old) elicited a diminished response to the same dose. Quadrupling the dose (8 IU/kg) prolonged the fecal GC response in female reindeer, but male reindeer were unresponsive. Hair cortisol was unaffected by a single ACTH challenge. Further investigation is required to ascertain whether subspecific differences in adrenal sensitivity are attributed to age or sex differences, or historical selective pressures from semi-domestication and/or sedentary life cycle in reindeer.

Fecal triiodothyronine and thyroxine concentrations change in response to thyroid stimulation in Steller sea lions (Eumetopias jubatus).

Variation in concentrations of thyroid hormones shed in feces may help to identify physiological states of animals, but the efficacy of the technique needs to be validated for each species. We determined whether a known physiological alteration to thyroid hormone production was reflected in hormone concentrations in the feces of Steller sea lions (Eumetopias jubatus). We quantified variation of triiodothyronine (T3) and thyroxine (T4) concentrations in feces following two intramuscular injections of thyrotropin (thyroid-stimulating hormone, TSH) at 24h intervals in four captive female sea lions. We found fecal T3 concentrations increased 18-57% over concentrations measured in the baseline sample collected closest to the time of the first TSH injection (p=0.03) and 1-75% over the mean baseline concentration (p=0.12) for each animal of all samples collected prior to injections. Peak T3 concentrations were greater than the upper bound of the baseline 95% confidence interval for three animals. The peak T3 response occurred 48h post-injection in three animals and 71h in the fourth. Post-injection T4 concentrations did not differ between the baseline sample collected closest to the time of the first TSH injection (p=0.29) or the mean baseline concentration (p=0.23) for each animal. These results indicate that induced physiological alterations to circulating thyroid hormone concentrations can be adequately detected through analyses of fecal T3 concentrations and that the technique may provide a means of non-invasively detecting metabolic changes in Steller sea lions.

Long-term impacts of poaching on relatedness, stress physiology, and reproductive output of adult female african elephants.

Widespread poaching prior to the 1989 ivory ban greatly altered the demographic structure of matrilineal African elephant (Loxodonta africana) family groups in many populations by decreasing the number of old, adult females. We assessed the long-term impacts of poaching by investigating genetic, physiological, and reproductive correlates of a disturbed social structure resulting from heavy poaching of an African elephant population in Mikumi National Park, Tanzania, prior to 1989. We examined fecal glucocorticoid levels and reproductive output among 218 adult female elephants from 109 groups differing in size, age structure, and average genetic relatedness over 25 months from 2003 to 2005. The distribution in group size has changed little since 1989, but the number of families with tusked old matriarchs has increased by 14.2%. Females from groups that lacked an old matriarch, first-order adult relatives, and strong social bonds had significantly higher fecal glucocorticoid values than those from groups with these features (all females R(2)= 0.31; females in multiadult groups R(2)= 0.46). Females that frequented isolated areas with historically high poaching risk had higher fecal glucocorticoid values than those in low poaching risk areas. Females with weak bonds and low group relatedness had significantly lower reproductive output (R(2)[U]=0.21). Females from disrupted groups, defined as having observed average group relatedness 1 SD below the expected mean for a simulated unpoached family, had significantly lower reproductive output than females from intact groups, despite many being in their reproductive prime. These results suggest that long-term negative impacts from poaching of old, related matriarchs have persisted among adult female elephants 1.5 decades after the 1989 ivory ban was implemented.

Isolation of DNA from small amounts of elephant ivory: Sampling the cementum with total demineralization extraction.

Genotyping ivory samples can determine the geographic origin of poached ivory as well as the legality of ivory being sold in ivory markets. We conducted a series of experiments to determine where the DNA is most concentrated in ivory samples and how best to increase DNA yield from groups of samples likely to vary in DNA concentration. We examined variation in DNA amplification success from: the layer(s) of the tusk (cementum and/or dentine) being extracted, demineralization temperature and time, and the concentration of eluates. Since demineralization of the pulverized sample produces a pellet and supernatant, we also assessed DNA amplification success from the pellet, the supernatant, their combination, as well as variation in the respective amounts used for extraction. Our results show that the outer cementum layer of the tusk contains the highest concentration of DNA and should be separated and used exclusively as the source material of ivory processed for extraction, when available. Utilizing the combined demineralized lysate improves extraction efficiency, as does increasing demineralization time to 3 or more days, conducted at 4°C. The most significant improvements occurred for low template DNA ivory samples followed by medium quality samples. Amplification success of high quality samples was not affected by these changes. Application of this optimized method to 3068 ivory samples resulted in 81.2% of samples being confirmed for both alleles at a minimum of 10 out of 16 microsatellite loci, which is our threshold for inclusion in DNA assignment analyses.

CONSERVATION. Genetic assignment of large seizures of elephant ivory reveals Africa's major poaching hotspots.

Poaching of elephants is now occurring at rates that threaten African populations with extinction. Identifying the number and location of Africa's major poaching hotspots may assist efforts to end poaching and facilitate recovery of elephant populations. We genetically assign origin to 28 large ivory seizures (≥0.5 metric tons) made between 1996 and 2014, also testing assignment accuracy. Results suggest that the major poaching hotspots in Africa may be currently concentrated in as few as two areas. Increasing law enforcement in these two hotspots could help curtail future elephant losses across Africa and disrupt this organized transnational crime.

Psychosocial stress as a cause of infertility.

An adaptive model for the evolution of reproductive failure predicted psychosocial stress to increase as anatomic causes of infertility decrease. The nonanatomic infertility group in our study reported greater psychosocial stress than intermediate (P < 0.008) or anatomic groups (P < 0.0005). Controls, women with nonanatomic etiologies who were not attempting pregnancy, also reported higher psychosocial stress than the anatomic group (P < 0.007). Results are consistent with the hypothesis that psychosocial distress contributes significantly to the etiology of some forms of infertility.

Infertility, abortion, and biotechnology : When it's not nice to fool mother nature.

Patterns of reproductive failure described in humans and other mammals suggest that reproductive failure may in many instances be the result of adaptations evolved to suppress reproduction under temporarily harsh conditions. By suppressing reproduction under such conditions, females are able to conserve their time and energy for reproductive opportunities in which reproduction is most likely to succeed. Such adaptations have been particularly important for female mammals, given (a) the amount of time and energy that reproduction requires, and (b) the degree to which reproductive conditions can vary.The existence of conscious and unconscious mechanisms to suppress reproduction under poor conditions has several implications for obstetric/gynecologic practices. Two implications are discussed with reference to biotechnological advancements in our ability to facilitate conceptions and manage problem pregnancies: (a) potential dangers of sophisticated technologies overriding natural fertility controls; and (b) the need for greater appreciation of the association between psychosocial stress and reproductive failure in the treatment of reproductive problems. Implications for elective abortion practices are discussed as well.

Psychosocial stress and infertility : Cause or effect?

Experimental, theoretical, psychological, and economic barriers have caused physicians to rely on biomedical treatments for infertility at the exclusion of more environmentally oriented ones (e.g., psychosocial stress therapy). An evolutionary model is described for the origin of reproductive failure, suggesting why mammals evolved to be reproductively responsive to the environment and why psychosocial stress should have an especially strong impact on fertility problems. A study of the causal role of psychosocial stress in infertility is then summarized. The paper concludes with implications for future directions for the treatment of infertility and related human reproductive problems.

Reproductive control in wild baboons measured by fecal steroids.

Measurements of reproductive hormones (progestins and estrogens) excreted in feces were used to discriminate between 25 conceptive and 76 nonconceptive (including undetected early abortion) cycles of free-ranging yellow baboons at Mikumi National Park, Tanzania. Conceptive cycles had significantly higher luteal-phase progestin and estrogen concentrations than nonconceptive cycles as early as Day 4 postovulation. However, mean early luteal-phase progestin concentrations in conceptive cycles were lower when conception occurred during ecologically optimal vs. suboptimal times, and among females of high compared to low dominance rank. Mean estrogen concentrations in conceptive cycles showed the opposite dominance rank pattern: mean luteal-phase estrogen concentrations were higher in conceptive cycles of high-compared to low-ranking females. None of these relations existed for nonconceptive cycles. These data suggest that successful implantation is facilitated by relatively high early luteal-phase progestin and estrogen concentrations. However, long-term environmental cues predicting the probability of offspring survival appear to influence the amount of progesterone required for successful implantation; progesterone concentrations necessary to facilitate successful implantation are higher during suboptimal seasons or among females of low dominance rank-cues that also suggest that offspring survival conditions are relatively poor. This may act as a reproductive filter, restricting conception to females whose immediate condition (e.g., low social stress and good physical health) enables them to compensate physiologically and behaviorally for effects associated with these relatively harsh offspring survival conditions.

Stress and reproductive failure: an evolutionary approach with applications to premature labor.

This article takes an evolutionary approach to the study of reproductive failure, drawing attention to the importance of reproductive failure among mammals as a means of timing reproduction in response to a variable environment. These concepts also apply to the diagnosis and treatment of prematurity, because before the advent of modern medicine most premature births probably constituted failed reproduction. Problems in the diagnosis and treatment of reproductive failure are described, with specific parallels drawn between the diagnoses and treatments of infertility and prematurity.

Reproductive suppression among female mammals: implications for biomedicine and sexual selection theory.

Female mammals experience a very high and often unappreciated rate of reproductive failure. Among human pregnancies alone, over 50 per cent fail between conception and parturition, and the majority of these failures are unexplained. These findings present important problems for evolutionary theory as well as for health care practices. This paper addresses these high rates of reproductive failure among mammals, by extending the work of a number of evolutionary biologists regarding the reproductive consequences of environmental adversity. The basic model upon which we elaborate, termed the Reproductive Suppression Model, argues that females can optimize their lifetime reproductive success by suppressing reproduction when future conditions for the survival of offspring are likely to be sufficiently better than present ones as to exceed the costs of the suppression itself. These costs are a function of reproductive time lost and the direct phenotypic effects of the suppression itself. To evaluate the benefits and costs of suppression, the following types of cues should be assessed: the female's physical and mental health, her stage of reproduction, the physical and genetic status of her offspring, and the external conditions at the time of birth. We also examine various issues of social suppression, whereby the conditions for survival of offspring are a function of the reproduction and support of other group members. Under such conditions, some females may be able to improve current conditions for reproduction by suppressing the reproduction of others. Field data from our own work are presented, describing socially mediated reproductive competition among continuously breeding female yellow baboons and among female hoary marmots. Social suppression in other mammals is also evaluated, including that in human beings, and we conclude with some implications of the Reproductive Suppression Model for sexual selection theory regarding female-female reproductive competition, as well as human health care.

Lifetime reproductive success, longevity, and reproductive life history of female yellow baboons (Papio cynocephalus) of Mikumi National Park, Tanzania.

The relationship between longevity and lifetime reproductive success (LRS) was studied in free-ranging female baboons of Mikumi National Park, Tanzania. A severe population decline occurred between the 12th and 20th years of the study. The total sample consisted of 72 females born and reaching adulthood before the start of the population decline. There were 27 females who were adult at the start of the study and 45 who became adult within the 12 years prior to the decline. The subjects were studied until all 72 were dead and all of their offspring were either dead or at least six years old; this took 24 years. The relationship of longevity to LRS was statistically significant for the total sample and for both sub-samples, with 70% of the total variance in LRS accounted for by longevity. Longevity was linked to LRS via a chain of statistically significant relationships: The longer the life span, the longer the reproductive life; the longer the reproductive life, the more offspring produced; the more offspring produced, the higher the LRS. Mean LRS, life span, and reproductive longevity all differed between the two sub-samples. Since the sub-samples were time-linked to a population decline affecting longevity, either sub-sample separately would fail to reflect the broader picture. This illustrates the importance of appreciable sample sizes from long-term studies in helping understand the dynamics between life history estimates and ecological conditions in variable environments.

Rapid extraction of faecal steroids for measuring reproductive cyclicity and early pregnancy in free-ranging yellow baboons (Papio cynocephalus cynocephalus).

A rapid method was developed for extracting and assaying oestradiol and progesterone in faeces (n = 242) of female yellow baboons, free-living in Tanzania. Dose response studies generated slopes of 1.02 (r2 = 0.99) for oestradiol and 1.09 (r2 = 0.99) for progesterone, suggesting that this method accurately measured these steroids in faeces. Parallelism was proved by demonstrating that slopes produced from serially diluted samples were not different from those generated from standard curves (mean P value = 0.53 +/- 0.17 for oestradiol and 0.44 +/- 0.13 for progesterone). Faecal progesterone concentrations measured over several cycles in 2 females increased and decreased in correspondence to visual markers of the luteal phase (i.e. the period between sex-skin detumescence and menses), but the presumed preovulatory oestradiol peak was not observed consistently in all cycles. Progesterone profiles during early to midgestation in 3 females confirmed pregnancy by 25 days (14%) of gestation. Oestradiol profiles were more variable and were not indicative of pregnancy until 40 days (22%) of gestation. Radiolabel-infusion studies revealed that 32% of progesterone (n = 2) but only 11% of oestradiol (n = 2), was cleared through faeces. The latter findings may account for the greater variation observed in temporal oestradiol patterns during the baboon menstrual cycle and pregnancy. Compared with previous techniques, these new methods (i) save considerable time in assaying raw material and (ii) result in high extraction recoveries of faecal steroids (approximately 88% for oestradiol and 91% for progesterone). This approach may be particularly useful for studying physiological function and endocrine-environmental interrelationships in free-living primate species.

Excreted steroids in primate feces over the menstrual cycle and pregnancy.

Techniques were established for the extraction and measurement of 17 beta-estradiol (E2) and progestins (P4) from feces of Old World primates. Studies were conducted to show the sensitivity of these measures, means of preserving fecal samples in the field, effects of urinary contamination, and means to eliminate these effects. Our results show that excreted steroid measures can be used to distinguish between mid-follicular and luteal phases in the menstrual cycle, and to identify pregnancy by Day 20 of gestation; the steroid measures can also be used to identify ovulatory levels of E2 and to establish the length of the menstrual cycle. Urine was shown to contaminate the fecal sample and to confound the estimate of steroid levels in feces; prolonged storage (less than 6 h) was shown to change the steroid estimate. Both urinary contamination and storage-dependent changes were eliminated by the addition of ethanol to the sample. Preliminary results also suggest that effects of dietary fiber on steroid hormone levels are minimal when controlled quantitatively by adjusting for water content of the fecal sample. We conclude that these measurements of excreted steroids provide a valid, noninvasive measure of physiological state of the hypothalamic-pituitary-ovarian axis among free-ranging animals in the field.

Comparative aspects of steroid hormone metabolism and ovarian activity in felids, measured noninvasively in feces.

Noninvasive fecal assays were used to study steroid metabolism and ovarian activity in several felid species. Using the domestic cat (Felis catus) as model, the excretory products of injected [14C]estradiol (E2) and [14C]progesterone (P4) were determined. Within 2 days, 97.0 +/- 0.6% and 96.7 +/- 0.5% of recovered E2 and P4 radioactivity, respectively, was found in feces. E2 was excreted as unconjugated estradiol and estrone (40%) and as a non-enzyme-hydrolyzable conjugate (60%). P4 was excreted primarily as non-enzyme-hydrolyzable, conjugated metabolites (78%) and as unconjugated pregnenolone epimers. A simple method for extracting fecal steroid metabolites optimized extraction efficiencies of the E2 and P4 excretion products (90.1 +/- 0.8% and 87.2 +/- 1.4%, respectively). Analysis of HPLC fractions of extracted fecal samples from the radiolabel-injected domestic cats revealed that E2 immunoreactivity coincided primarily with the unconjugated metabolized [14C]E2 peak, whereas progestogen immunoreactivity coincided with a single conjugated epimer and multiple unconjugated pregnenolone epimers. After HPLC separation, similar immunoreactive E2 and P4 metabolite profiles were observed in the leopard cat (F. bengalensis), cheetah (Acinonyx jubatus), clouded leopard (Neofelis nebulosa), and snow leopard (Panthera uncia). Longitudinal analyses demonstrated that changes in fecal E2 and P4 metabolite concentrations reflected natural or artificially induced ovarian activity. For example, severalfold increases in E2 excretion were associated with overt estrus or exogenous gonadotropin treatment, and elevated fecal P4 metabolite concentrations occurred during pregnant and nonpregnant (pseudopregnant) luteal phases. Although overall concentrations were similar, the duration of elevated fecal P4 metabolites during pseudopregnancy was approximately half that observed during pregnancy. In summary, steroid metabolism mechanisms appear to be conserved among these physically diverse, taxonomically related species. Results indicate that this hormone-monitoring approach will be extremely useful for elucidating the hormonal regulatory mechanism associated with the reproductive cycle, pregnancy, and parturition of intractable and endangered felid species.

Excretion rates and metabolites of oestradiol and progesterone in baboon (Papio cynocephalus cynocephalus) faeces.

Two unanaesthetized female yellow baboons (Papio cynocephalus cynocephalus) were infused (i.v.) with [3H]oestradiol and two with [3H]progesterone, early in the follicular phases of their cycles. One month later, the two females infused with [3H]oestradiol were simultaneously infused with [14C]progesterone and [3H]dehydroepiandrosterone. All urine and faeces were collected for 96 h after infusion. The proportion of steroid excreted in faeces (versus urine) was 10.0% for oestradiol and 40% for progesterone. Peak excretion in urine occurred 4.5 h after infusion. Peak excretion in faeces occurred an average of 36.4 h after infusion, with remarkable consistency between steroids. Eighty per cent of faecal oestradiol and progesterone metabolites were excreted as free (rather than conjugated) steroids. Simply boiling (20 min) the dried faecal sample in 90% ethanol proved to be the most rapid and efficient means of extracting these steroid metabolites. High pressure liquid chromatography and immunoreactivity studies revealed that oestradiol was excreted in faeces as oestradiol (36%), oestrone (44%) and a conjugated metabolite that co-eluted with oestrone sulfate (20%). Progesterone was excreted as eight different free forms, only a minor portion of which was progesterone, and what appeared to be a conjugated metabolite that co-eluted with pregnanediol-glucuronide (20%). The free progesterone metabolites were identified by gas-chromatography-mass-spectrometry as epimers of 5-pregnane-3-diol and 5-pregnane-3-ol-one. These data suggest that currently available immunoassays for free oestradiol and oestrone should adequately characterize faecal oestrogen profiles in baboons. However, high variability in crossreactivities of various progesterone antisera to progesterone metabolites in baboons makes antiserum selection a more serious concern in attempts to quantify faecal progestogen dynamics.(ABSTRACT TRUNCATED AT 250 WORDS)

Excretory fate of estradiol and progesterone in the African elephant (Loxodonta africana) and patterns of fecal steroid concentrations throughout the estrous cycle.

We developed and validated a noninvasive method to quantify fecal estrogens and progestins as a tool for monitoring long-term ovarian activity in free-ranging African elephants. The lag times between iv injection of [(3)H]estradiol and [(14)C]progesterone and peak excretion of radioactivity in urine and feces were approximately 4 hr and 48 hr, respectively. The majority of progesterone metabolites recovered was excreted in feces (55%) versus urine (45%), whereas comparatively little of the recovered estradiol metabolites were excreted in feces (5%) compared to urine (95%). Intrasample variation in fecal hormone concentrations was extremely high but could be substantially reduced by extracting well-mixed fecal powder from freeze-dried samples, taken from the central or premixed portion of the wet sample. This method resulted in a close correspondence between matched serum and fecal progestins (mean correlation = 0.81, range 0.61-0.94) collected from five nonpregnant adult females over a 7-month period. Fecal estrogen profiles were more ambiguous, tending to overlap with those of fecal progestins. We conclude that analyses of fecal progestins can provide an effective, noninvasive means of characterizing ovarian activity in free-ranging African elephants.

Ageing and social rank effects on the reproductive system of free-ranging yellow baboons (Papio cynocephalus) at Mikumi National Park, Tanzania.

Ageing and social status effects on reproductive condition are examined in 106 wild female baboons from 1974 to 1997. The mean duration of each reproductive state (follicular and luteal phase components, pregnancy and lactation) was examined per female, using a repeated measures analysis of variance across each of four age classes (3-6, 7-10, 11-14, and 15-20+ year olds) and dominance rank quartiles. The sex-skin swelling portion of the follicular phase increased whereas the fully swollen portion decreased in duration with advancing age and with low dominance rank. The detumescing portion of the luteal phase increased with advancing age, being most pronounced in lowest ranking females. The number of cycles to conception decreased with age, with no dominance rank effect. However, owing to variation in lactation duration, the interbirth interval was unaffected by age but was shorter in high ranking females. The miscarriage rate was unaffected by age but increased as female rank declined. Age and rank effects became significantly more pronounced in response to a crash in the study population between 1987 and 1993. In conclusion, age- and rank-related reproductive changes in baboons, like those in humans, appear to represent attempts to compensate endocrinologically for accelerated ovarian atresia and increased environmental hardship.