No abstract

In many animal societies, dominant individuals monopolize reproduction, but the tactics they employ to achieve this are poorly understood. One possibility is that aggressive dominants render their subordinates infertile by inducing chronic physiological ''stress.'' However, this hypothesis has been discarded largely for cooperatively breeding species, where reproductive monopolies are often extreme. Here we provide strong support for the stressrelated suppression hypothesis in a cooperative mammal, the meerkat (Suricata suricatta). When pregnant, dominant females subject some subordinate females to escalating aggression, culminating in temporary evictions from the group. While evicted, subordinate females suffer chronic elevation of their glucocorticoid adrenal hormone levels, reproductive down-regulation (reduced pituitary sensitivity to gonadotropin-releasing hormone), reduced conception rates, and increased abortion rates. Rather than constantly harassing all subordinate females, dominants only become aggressive when pregnant themselves (when subordinate reproduction would otherwise conflict with their own) and target those females with whom reproductive conflict is most likely (older, pregnant, and more distantly related females). Our findings suggest that dominant female meerkats employ stressful evictions to suppress reproduction among their probable competitors, when attempting to breed themselves. Given the lack of evidence for stress-related suppression in other cooperative breeders to date, it is clear that social stress alone cannot account for the reproductive failure of subordinates across such societies. However, our findings raise the possibility that, in some cooperative breeders at least, dominants may employ stress-related suppression as a backup mechanism to guard against lapses in reproductive restraint by their subordinates.cooperative breeding ͉ dominant control ͉ physiological ͉ reproductive restraint ͉ reproductive skew

"Limited control" models of reproductive skew in cooperative societies suggest that the frequency of breeding by subordinates is determined by the outcome of power struggles with dominants. In contrast, "optimal skew" models suggest that dominants have full control of subordinate reproduction and allow subordinates to breed only when this serves to retain subordinates' assistance with rearing dominants' own litters. The results of our 7-year field study of cooperative meerkats, Suricata suricatta, support the predictions of limited control models and provide no indication that dominant females grant reproductive concessions to subordinates to retain their assistance with future breeding attempts.

African wild dogs (Ljcaon pictus) live in cooperative packs with a clear-cut dominance hierarchy in each sex. Reproduction is largely monopolized by the dominant male and female. Alpha females produced 76% of all litters in the Selous Game Reserve and 81% in Kruger National Park. Only 6-17% of subordinate females gave birth each year, compared to 82% of dominant females. In nonmating periods, subordinate females had higher estrogen levels and higher estrogen/progestin ratios than alpha females, apparently preventing ovulation. During mating periods, subordinate females had lower estrogen levels than dominants, mated less often, and were less aggressive. Subordinate males mated at low rates, wore less aggressive than dominants, and had lower testosterone levels. Beta males were similar to alpha males behavioraDy and hormonalry, suggesting that alpha males may share paternity with beta males. If paternity is more evenly shared than maternity, then subordinate males have a larger incentive than subordinate females to remain in the pack. Following this expectation, dispersal in Selous was female biased (49% versus 24% dispersing annually). Perhaps as a result of mortality associated with dispersal, the adult sex ratio was male biased, although the pup sex ratio was unbiased. In Kruger, neither dispersal nor the adult sex-ratio was biased. Reproductive suppression is widely thought to be caused by social stress in subordinates, but basal cortkosterone levels were higher in dominants than in subordinates.

No abstract

Biodiversity hotspots understandably attract considerable conservation attention. However, deserts are rarely viewed as conservation priority areas, due to their relatively low productivity, yet these systems are home to unique species, adapted to harsh and highly variable environments. While global attention has been focused on hotspots, the world's largest tropical desert, the Sahara, has suffered a catastrophic decline in megafauna. Of 14 large vertebrates that have historically occurred in the region, four are now extinct in the wild, including the iconic scimitar-horned oryx (Oryx dammah). The majority has disappeared from more than 90% of their Saharan range, including addax (Addax nasomaculatus), dama gazelle (Nanger dama) and Saharan cheetah (Acinonyx jubatus hecki) -all now on the brink of extinction. Greater conservation support and scientific attention for the region might have helped to avert these catastrophic declines. The Sahara serves as an example of a wider historical neglect of deserts and the human communities who depend on them. The scientific community can make an important contribution to conservation in deserts by establishing baseline information on biodiversity and developing new approaches to sustainable management of desert species and ecosystems. Such approaches must accommodate mobility of both people and wildlife so that they can use resources most efficiently in the face of low and unpredictable rainfall. This is needed to enable governments to deliver on their commitments to halt further degradation of deserts and to improve their status for both biodiversity conservation and human well-being. Only by so-doing will deserts be able to support resilient ecosystems and communities that are best able to adapt to climate change.

No abstract

Recent success propagating captive beluga has resulted from combined efforts by North American zoos and aquariums to manage disparate collections as a single population. This success has provided a tremendous opportunity to increase our understanding of beluga reproductive biology. Blood samples were collected on a weekly to biweekly basis from 23 female and 12 male beluga, ranging in age from 2-15 years, for analysis of serum progesterone (P) and testosterone (T), respectively. Peri-parturient observational data, including food intake, duration and signs of labor, and nursing patterns were collected from 15 days prepartum to 30 days postpartum during 21 births. Total body lengths and weights were collected from 10 captive-born beluga. For female beluga, the mean (7SD) age, body length, and weight at first conceptions were 9.172.8 years, 318.079.1 cm, and 519784 kg. Thirty-five luteal phases and 13 conceptions were detected from January-June, and 70% of luteal phases and 80% conceptions occurred from March-May. The mean luteal phase and total estrous cycle lengths were 30.076.5 days and 48.074.6 days, respectively. For male beluga, the mean age that males sired their first calf was 13.372.6 years. Compared to younger males (o8 years of age, 0.95 ng/ml), levels of T secretion in older males (48 years of age, 5.0 ng/ml) were elevated significantly only during the interval from January-April. Highest T concentrations (6.274.9 ng/ml) were recorded from January-March, whereas nadir concentrations (1.171.0 ng/ml) were detected from August-September. The mean gestation length was 475.0720.4 days (n ¼ 9). For parturition, the mean time from the first appearance of fluke or rostrum to delivery, delivery to placental passage, and delivery to nursing were 4.472.9 hr, 7.671.8 hr, and 43745 hr, respectively. All cows had decreased food intake on the day of delivery, with 44% having zero intake. Peak 24-hr nursing activity occurred 3.972.7 days post-partum. Growth (i.e., body weight and length) as a function of age were well described by the Gompertz model (r 2 ¼ 0.91, 0.93). Based on the model, growth in body weight and length were significantly greater in males compared to females. Predicted birth weight (88.9 kg) was similar for both sexes, however, and male calves were predicted to be shorter (154.3 cm) than female calves (160.7 cm). The results provide the first descriptions of captive beluga reproductive physiology, including endocrinology, peri-parturient behavior, growth, and reproductive maturity. This knowledge is important for helping to maintain genetically diverse, self-sustaining populations of captive beluga whales.