Social bonds between unrelated females increase reproductive success in feral horses

In many mammals, females form close social bonds with members of their group, usually between kin. Studies of social bonds and their fitness benefits have not been investigated outside primates, and are confounded by the relatedness between individuals in primate groups. Bonds may arise from kin selection and inclusive fitness rather than through direct benefits of association. However, female equids live in long-term social groups with unrelated members. We present 4 years of behavioral data, which demonstrate that social integration between unrelated females increases both foal birth rates and survival, independent of maternal habitat quality, social group type, dominance status, and age. Also, we show that such social integration reduces harassment by males. Consequently, social integration has strong direct fitness consequences between nonrelatives, suggesting that social bonds can evolve based on these direct benefits alone. Our results support recent studies highlighting the importance of direct benefits in maintaining cooperative behavior, while controlling for the confounding influence of kinship.     

Genetic diversity and reproductive success in mandrills (Mandrillus sphinx)

Recent studies of wild animal populations have shown that estimators of neutral genetic diversity, such as mean heterozygosity, are often correlated with various fitness traits, such as survival, disease susceptibility, or reproductive success. We used two estimators of genetic diversity to explore the relationship between heterozygosity and reproductive success in male and female mandrills (Mandrillus sphinx) living in a semifree ranging setting in Gabon. Because social rank is known to influence reproductive success in both sexes, we also examined the correlation between genetic diversity and social rank in females, and acquisition of alpha status in males, as well as length of alpha male tenure. We found that heterozygous individuals showed greater reproductive success, with both females and males producing more offspring. However, heterozygosity influenced reproductive success only in dominant males, not in subordinates. Neither the acquisition of alpha status in males, nor social rank in females, was significantly correlated with heterozygosity, although more heterozygous alpha males showed longer tenure than homozygous ones. We also tested whether the benefits of greater genetic diversity were due mainly to a genome-wide effect of inbreeding depression or to heterosis at one or a few loci. Multilocus effects best explained the correlation between heterozygosity and reproductive success and tenure, indicating the occurrence of inbreeding depression in this mandrill colony.     

Familiar neighbors enhance breeding success in birds.

We tested the hypothesis that long-term familiarity with neighbors is advantageous by determining whether male red-winged blackbirds (Agelaius phoeniceus) breeding adjacent to familiar neighbors have better reproductive success than other males. Using data gathered during a 10-yr study of breeding success, we found that males with familiar neighbors fledged, on average, significantly more offspring annually than males without familiar neighbors. We also found that the same males, breeding in different years on the same territories, had significantly larger harems in the years they had familiar neighbors. Improved reproductive success was due to the males' abilities to attract more females to nest in their territories. Alternative hypotheses to explain the positive relationship between familiar neighbors and breeding success were not supported by our data. Relatively high reproductive success for breeders with long-term neighbors may provide a basis for the evolution of cooperative behavior in this and other species.     

Warfare and reproductive success in a tribal population

Intergroup conflict is a persistent feature of many human societies yet little is known about why individuals participate when doing so imposes a mortality risk. To evaluate whether participation in warfare is associated with reproductive benefits, we present data on participation in small-scale livestock raids among the Nyangatom, a group of nomadic pastoralists in East Africa. Nyangatom marriages require the exchange of a significant amount of bridewealth in the form of livestock. Raids are usually intended to capture livestock, which raises the question of whether and how these livestock are converted into reproductive opportunities. Over the short term, raiders do not have a greater number of wives or children than nonraiders. However, elders who were identified as prolific raiders in their youth have more wives and children than other elders. Raiders were not more likely to come from families with fewer older maternal sisters or a greater number of older maternal brothers. Our results suggest that in this cultural context raiding provides opportunities for increased reproductive success over the lifetime.The causes of warfare in small-scale societies continue to be debated. Most anthropological explanations have focused on causes that ignore the individual benefits warriors sometimes receive for participation (1, 2). However, evolutionary anthropologists have commonly argued that warriors may receive fitness benefits that ultimately motivate their participation (3–7). This hypothesis has a contentious history, in part because of concerns that a positive association between warfare and reproductive success may suggest biological proclivities to engage in violence (8, 9). Although such a relationship would be unsurprising in other mammalian species with similar patterns of lethal intergroup relations (10, 11), the fact that humans also have the capacity for sustained peaceful relations between groups has sometimes been interpreted as suggesting that warfare has a different function than intergroup conflict in other species (12–14).Field data on the relationship between participation in small-scale warfare and reproductive success remain extremely sparse. Chagnon found that, among the Yanomamo of Venezuela, men who participated in killing an enemy and were then designated with a culturally specific label of unokai had greater reproductive success than non-unokais (3). By contrast, data on raids from the Waorani, an Ecuadorian group of horticulturalists, found that more zealous warriors had decreased reproductive success (15), whereas a study of killers vs. nonkillers among the Ache of Paraguay found that the children of men who had killed had greater child survivorship (16). Because these latter two studies did not differentiate between intra- and intergroup killings, their significance is unclear for understanding whether participation in intergroup warfare is generally associated with greater reproductive success. Therefore, the extent to which men in small-scale societies tend to benefit reproductively from their participation in war remains unresolved.Here we investigate whether participation in simple warfare is associated with increased reproductive success among the Nyangatom, an East African pastoralist society. We measure a warrior’s reproductive success by the number of his wives and children. We also examine whether participation in warfare is a means for individuals to overcome constraints on marriage opportunities created by their natal family composition. In this ethnographic context, men who have older maternal brothers or few maternal sisters are expected to have reduced access to bridewealth, resulting in increased reproductive competition. In groups similar to the Nyangatom, reproductive competition, including that provided by family composition, has been hypothesized to motivate participation in raiding as a means to improve reproductive prospects (17, 18). We then attempt to identify the likely pathways by which reproductive success may be affected by participation in raids focusing on access to bridewealth provided from successful raids.     

Migratory carryover effects and endocrinological correlates of reproductive decisions and reproductive success in female albatrosses

Physiological mechanisms mediating carryover effects, wherein events or activities occurring in one season, habitat, or life-history stage affect important processes in subsequent life-history stages, are largely unknown. The mechanism most commonly invoked to explain carryover effects from migration centres on the acquisition and utilization of resources (e.g. body mass, or individual 'condition'). However, other mechanisms are plausible, e.g. trade-offs reflecting conflict or incompatibility between physiological regulatory systems required for different activities or life-history stages (migration vs. reproduction). Here we show that in female black-browed albatrosses (Thalassarche melanophris) the decision to reproduce or to defer reproduction, made prior to their arrival at breeding colonies after long-distance migration, is associated with condition-related (body mass, hematocrit, hemoglobin concentrations) and hormonal (progesterone, testosterone, estrogen-dependent yolk precursors) traits. In contrast, reproductive success showed little association with condition but showed significant associations with the steroidogenic processes underlying follicle development. Specifically, success was determined by reproductive readiness via differences in steroid hormones and hormone-dependent traits. Successful albatrosses were characterized by high progesterone and high estradiol-dependent yolk precursor levels, whereas failed albatrosses had high testosterone and low yolk precursor levels. Results are discussed with reference to migratory carryover effects and how these can differentially affect the physiologies influencing reproductive decisions and reproductive success.     

Personality and reproductive success in a high-fertility human population

The existence of interindividual differences in personality traits poses a challenge to evolutionary thinking. Although research on the ultimate consequences of personality differences in nonhuman animals has recently undergone a surge of interest, our understanding of whether and how personality influences reproductive decisions in humans has remained limited and informed primarily by modern societies with low mortality–fertility schedules. Taking an evolutionary approach, we use data from a contemporary polygynous high-fertility human population living in rural Senegal to investigate whether personality dimensions are associated with key life-history traits in humans, i.e., quantity and quality of offspring. We show that personality dimensions predict reproductive success differently in men and women in such societies and, in women, are associated with a trade-off between offspring quantity and quality. In women, neuroticism positively predicts the number of children, both between and within polygynous families. Furthermore, within the low social class, offspring quality (i.e., child nutritional status) decreases with a woman''s neuroticism, indicating a reproductive trade-off between offspring quantity and quality. Consistent with this, maximal fitness is achieved by women at an intermediate neuroticism level. In men, extraversion was found to be a strong predictor of high social class and polygyny, with extraverted men producing more offspring than their introverted counterparts. These results have implications for the consideration of alternative adaptive hypotheses in the current debate on the maintenance of personality differences and the role of individual factors in fertility patterns in contemporary humans.     

Changes in serum sex steroid levels throughout the reproductive cycle of Bufo arenarum females

The changes in the serum levels of the sexual steroids estradiol-17beta (E(2)), testosterone (T), dihydrotestosterone (DHT), and progesterone (P) in Bufo arenarum females were determined by radioimmunoassay (RIA) during 3 consecutive cycles (1999-2001). The serum concentrations of T and DHT, which showed a close parallelism during the annual reproductive cycle, exhibited the highest levels during the preovulatory period, when oogenesis is advanced, while lowest serum levels of these hormones were found during the ovulatory period. The data obtained for E(2) showed a pattern contrary to that determined for androgens. The maximum E(2) concentrations detected in the early postovulatory period might be associated with vitellogenesis and follicular growth. Lowest E(2) concentrations were reached during the period in which B. arenarum undergoes its final hibernation stage. Serum P showed a peak during the preovulatoy period, related to the induction of nuclear maturation in full grown oocytes. A strong decrease in the levels of the circulating hormones was observed after ovariectomy. Our results showed that, out of the four hormones examined, T and DHT were the best indicators of ovarian and oviductal stage, as shown by the strong positive correlation found between androgen levels and organ weight, while E(2) showed a weak negative correlation with ovarian and oviductal weight.     

The reproductive cycle of the Tasmanian devil (Sarcophilus harrisii) and factors associated with reproductive success in captivity

Numbers of wild Tasmanian devils are declining as a result of the fatal, transmissible Devil Facial Tumor Disease. A captive insurance population program has been initiated but current captive breeding rates are sub-optimal and therefore the goal of this project was to increase our understanding of the estrous cycle of the devil and elucidate potential causes of failed male-female pairings. Temporal patterns of fecal progestagen and corticosterone metabolite concentrations were examined for females (n=41) in three categories of reproductive status (successful: viable young, n=20 estrous cycles; unsuccessful: paired with a male but no young confirmed, n=44 estrous cycles; non-mated: no access to a male during estrus, n=8 estrous cycles) but substantial differences were not found. Females were more likely to produce pouch young if pairing with the male extended into late proestrus (P<0.05), thereby decreasing the time between pairing and presumed ovulation. The interval between the end of proestrous elevation in progestagen metabolite concentrations and the beginning of the luteal phase was 7.6±2.3 days in successful females. The length of the luteal phase in successful females was 12.5±1.4 days which was not different from unsuccessful or non-mated females (P>0.05). Unsuccessful females had 1-3 estrous cycles within a single year. Successful females were predominantly wild-caught (17/19, 90%) and most produced young following the first estrous cycle of the season (18/20, 90%). Unsuccessful females were predominantly captive born (20/27, 74%) in this study. It is possible that a proportion of females that do not produce pouch young achieve conception but the timing of reproductive failure continues to be elusive in this species.     

Serum total and HDL cholesterols according to reproductive status in Japanese females

In order to observe variations according to reproductive status, serum total cholesterol (TC) and HDL cholesterol (HDL-C) were investigated in 153 pregnant, in 153 age-adjusted non-pregnant females, in 787 females aged 45-54 years living in a northern suburb of Tokyo, and in 150 12-year-old girls from a private junior high school in a southern suburb of Tokyo. Non-menstruating (non-menarcheal, postmenopausal) females had significantly higher TC and significantly lower HDL-C/TC than menstruating (menarcheal, premenopausal) females did in both the age groups of 12 and 45-54 years, although no significant difference of HDL-C was found between them. The menstruating females tended to be more overweight in Quetelet's index and had thicker skinfolds. Pregnant females at the eighth month of gestation revealed a significantly high value of both TC and HDL-C vs age-adjusted non-pregnant females, while at the fourth month of gestation only HDL-C was high.     

Life histories,blood revenge,and reproductive success among the Waorani of Ecuador

The Waorani may have the highest rate of homicide of any society known to anthropology. We interviewed 121 Waorani elders of both sexes to obtain genealogical information and recollections of raids in which they and their relatives participated. We also obtained complete raiding histories of 95 warriors. An analysis of the raiding histories, marital trajectories, and reproductive histories of these men reveals that more aggressive warriors have lower indices of reproductive success than their milder brethren. This result contrasts the findings of Chagnon [Chagnon N (1988) Science 239:985–992] for the Yanomamo. We suggest that the spacing of revenge raids may be involved in the explanation of why the consequences of aggressiveness differ between these 2 warlike lowland South American peoples.     

Docosahexaenoic acid status in females of reproductive age with maple syrup urine disease

Individuals with maple syrup urine disease (MSUD) have impaired metabolism of branched-chain amino acids (BCAA) valine, isoleucine, and leucine. Life-long dietary therapy is recommended to restrict BCAA intake and thus prevent poor neurological outcomes and death. To maintain adequate nutritional status, the majority of protein and nutrients are derived from synthetic BCAA-free medical foods with variable fatty acid content. Given the restrictive diet and the importance of omega-3 fatty acids, particularly docosahexaenoic acid (DHA), in neurological development, this study evaluated the dietary and fatty acid status of females of reproductive age with MSUD attending a metabolic camp. Healthy controls of similar age and sex were selected from existing normal laboratory data. Total lipid fatty acid concentration in plasma and erythrocytes was analyzed using gas chromatography–mass spectroscopy. Participants with MSUD had normal to increased concentrations of plasma and erythrocyte alpha linolenic acid (ALA) but significantly lower concentrations of plasma and erythrocyte docosahexaenoic acid (DHA) as percent of total lipid fatty acids compared with controls (plasma DHA: MSUD 1.03 ± 0.35, controls 2.87 ± 1.08; P = 0.001; erythrocyte DHA: MSUD 2.58 ± 0.58, controls 3.66 ± 0.80; P = 0.011). Dietary records reflected negligible or no DHA intake over the 3-day period prior to the blood draw (range 0–2 mg). These results suggest females of reproductive age with MSUD have lower blood DHA concentrations than age-matched controls. In addition, the presence of ALA in medical foods and the background diet may not counter the lack of preformed DHA in the diet. The implications of these results warrant further investigation.     

Effects of corticosterone on the proportion of breeding females,reproductive output and yolk precursor levels

In this study we investigated the role of corticosterone (B) in regulating the proportion of laying females, timing of breeding, reproductive output (egg size and number), and yolk precursor levels in chronically B-treated female zebra finches (Taeniopygia guttata). Corticosterone treatment via silastic implant elevated plasma B to high physiological (stress-induced) levels (24.1 +/- 5.3 ng/ml at 7-days post-implantation). B-treated females had high plasma levels of very-low density lipoprotein (VLDL) but low levels of plasma vitellogenin 7-days post-implantation, suggesting that corticosterone inhibited yolk precusor production and perhaps shifted lipid metabolism away from production of yolk VLDL and towards production of generic (non-yolk) VLDL. Only 56% of B-treated females (n = 32) initiated laying, compared with 100% of sham-implanted females (n = 18). In females that did breed, corticosterone administration delayed the onset of egg laying: B-treated females initiated laying on average 14.5 +/- 0.5 days after pairing compared to 6.4 +/- 0.5 days in sham-implanted females. B-treated females that laid eggs had significantly higher plasma B levels at the 1st-egg stage (45.9+/-9.0 ng/ml) than did sham-implanted females (7.9+/-6.8 ng/ml). Despite this there was no difference in mean egg mass, clutch size, or egg composition in B-treated and sham-implanted females. These results are consistent with the idea that elevated corticosterone levels inhibit reproduction, but contrast with studies of other oviparous vertebrates (e.g., lizards) in relation to the role of corticosterone in regulating egg and clutch size.     

Genetic polymorphism of microsomal epoxide hydrolase enzyme gene in preeclamptic females

IntroductionMicrosomal epoxide hydrolase enzyme is involved in xenobiotics detoxification. It catalyzes the phase I hydrolysis of epoxides and plays a role in the detoxification processes and in the metabolism of endogenous and exogenous compounds. Preeclampsia, which is one of the most serious complications of pregnancy, may be due to an imbalance between these compounds, such as lipid peroxides and oxygen-free radicals and detoxifying and scavenging substances. Two variants of human epoxide hydrolase enzyme with different enzyme activity have been described; exon 3 polymorphism is associated with lower enzyme activity whereas exon 4 polymorphism is associated with higher activity. The authors tried to investigate the association between these genetic polymorphisms and preeclampsia.MethodThirty preeclamptic females together with 30 normal pregnant females as controls were included in the study. Genotyping for exons 3 and 4 of microsomal epoxide hydrolase enzyme was done by polymerase chain reaction–restriction fragment length polymorphism.ResultsThere was no statistical significant difference in the distribution of exon 3 genotype between cases and controls (P = 0.4); on the other hand, a highly statistical significant difference was found between cases and controls as regard exon 4 genotype (P = 0.002).ConclusionThere may be an association between epoxide hydrolase enzyme polymorphism and the risk of preeclampsia.     

女性神经性厌食症患者的瘦素水平及其在生殖功能调节中的作用

目的研究青年女性神经性厌食症(AN)患者血清瘦素水平与下丘脑-垂体-性腺(HPG)轴功能改变的相互关系。方法测定16例新诊断的女性神经性厌食症患者的身体组成成分、性激素、瘦素等水平,分析其与生殖功能间的相关性。其中4例患者接受了24 h血清瘦素节律的研究。经18周综合治疗后,再次评价AN患者身体组成成分、血清瘦素、性激素水平,并分析其与月经周期恢复的相互关系。另设26例年龄匹配的健康女性为正常对照。结果(1)16例AN患者均发生闭经,13例为继发性闭经,3例为原发性闭经,14例患者LH低于正常参考范围的下限(1．5 U／L),12例患者FSH低于正常参考范围的下限(4．6 U／L),其中5例患者FSH和LH低于0．01 U／L。(2)治疗前16例AN患者体重指数(BMI)、体脂、血清瘦素水平较正常对照组显著降低[分别为(13．6±3．5)kg／m2 vs(20．2±2．2)kg／m2;(16．14±1．99)％vs (23．20±2．64)％;(1．21±0．36)μg/L vs(7．70±4．15)μg／L,均P<0．01];AN组瘦素水平与BMI、体脂含量呈正相关(分别为r=0．526,P=0．015;r=0．628,P=0．003),调整BMI和体脂的影响后,AN组的血清瘦素水平仍显著低于正常对照组(P<0．01)。血清瘦素水平与年龄、体重、FSH、LH未见相关性。(3)24 h血清瘦素节律提示AN患者瘦素分泌曲线较正常人低平。(4)经18周治疗,11例患者体重上升>15％,瘦素水平较未治疗时显著上升(P<0．01),16例患者月经周期均未恢复。结论女性AN患者血瘦素水平较正常人群显著降低,并保持与BMI、体脂含量的相关性,经治疗后瘦素水平上升,但月经周期迟迟不能恢复。AN人群性腺功能低下可能与血瘦素水平的降低存在一定关系。     

Chronic stress in free-living European starlings reduces corticosterone concentrations and reproductive success

Chronic increases in stress hormones such as glucocorticoids are maladaptive, yet studies demonstrating a causal relationship among chronic stress, increases in glucocorticoid concentrations, and subsequent fitness costs in free-living animals are lacking. We experimentally induced chronic psychological stress in female European starlings (Sturnus vulgaris) by subjecting half of the females at our study site to a chronic stress protocol consisting of 4, 30 min stressors (loud radio, predator calls, a novel object, or predator decoys including a snake, rat, and owl) administered in random order daily for 8 days after clutch completion. Experimental females were captured at the end of the chronic stress protocol (9 days after the onset of the chronic stress protocol), and unstressed control females were captured at the same stage of the nesting cycle. Chronically stressed females had lower baseline corticosterone (CORT, the avian glucocorticoid) concentrations and lower reproductive success than unstressed females. Furthermore, surviving nestlings in experimentally stressed broods showed sensitization of the CORT response to acute stress, which is a physiological change that could persist to adulthood. Attenuation of baseline CORT concentrations in adult females is contrary to the general assumption that elevated CORT concentrations indicate stress, suggesting that more research is necessary before CORT concentrations can be used to accurately assess chronic stress in field studies.     

Fecal corticosterone concentrations and reproductive success in captive female southern white rhinoceros

Prolonged or frequent secretion of adrenal glucocorticoids in response to aversive stimuli can negatively impact reproduction. Because female southern white rhinoceros (Ceratotherium simum simum) reproduce poorly in captivity, we compared fecal corticosterone metabolite concentrations among parous, nulliparous, and adolescent females and examined social and physical aspects of the captive environment that might be related to differences in corticosterone metabolite concentrations. Aggression, dominance, sexual and play interactions, social group size and composition, enclosure size, and other housing characteristics were assessed though behavioral observations and review of historical and institution records. Concentrations of metabolized corticosterone in fecal samples were analyzed by enzyme immunoassay. The proportion of nulliparous females did not differ (p > 0.05) between subordinate and dominant animals, and subordinates did not have a higher mean fecal corticosterone concentration than dominants (p > 0.05). Of the behaviors examined, only the frequency of sexual play behaviors differed (p < 0.05) between dominants and subordinates. Average corticosterone concentrations differed (p < 0.05) across housing institutions but were not consistently elevated (p > 0.05) for females housed in most of the environmental conditions assessed. Housing with a female companion known from adolescence, however, tended to be associated (p = 0.06) with a lower mean corticosterone concentration than that when housing with a female companion introduced during adulthood or no female companion. Wild-caught females had a higher (p < 0.05) average corticosterone concentration than captive-born females. Average corticosterone concentration did not differ (p > 0.05) between acyclic and cycling, or nulliparous and parous females.