[show abstract][hide abstract] ABSTRACT: Dehydroepiandrosterone (DHEA) and its sulfate, DHEAS, are the most abundant steroid hormones in primates, providing a large reservoir of precursors for the production of androgens. DHEAS levels decline with age in adult humans and nonhuman primates, prompting its consideration as a biomarker of senescence. However, the mechanisms responsible for this age-related decrease and its relationship to reproduction remain elusive. This research investigated DHEAS concentrations in fecal samples in order to determine age-related changes in captive Japanese macaques, as well as to assess the possible influence of seasonality. The subjects were 25 female Japanese macaques (2 weeks to 14 years-old) housed outdoors in social groups at the Primate Research Institute. We collected three fecal samples from each animal during the breeding season (October to December) and three additional samples from adult females during the non-breeding season (May to June). The hormonal concentrations were determined using enzyme immunoassay. DHEAS concentration was negatively correlated with age, but we did not find a significant difference between breeding and non-breeding seasons. Neonatal macaques had the highest DHEAS concentrations of all age groups. We suggest that elevated neonatal DHEAS is possibly a residue from fetal adrenal secretion and that, as in humans, it might assist in neurobiological development.
General and Comparative Endocrinology 06/2013; · 2.82 Impact Factor
[show abstract][hide abstract] ABSTRACT: In principle, conservation planning relies on long-term data; in reality, conservation decisions are apt to be based upon limited data and short-range goals. For the koala (Phascolarctos cinereus), frequently reliance is made on the assumption that indirect signs can be used to indicate behavioural preferences, such as diet choice. We examined the relationship between the use of trees by koalas and the presence of scats beneath those trees. Tree use was associated with scat presence on 49% of occasions when koalas were radio-tracked in both central Queensland (n = 10 koalas) and south-east Queensland (n = 5 koalas), increasing to 77% of occasions when trees were rechecked the following day. Koala densities were correlated with scat abundance at sites with koala density between ~0.2 and 0.6 koalas per hectare. Our results confirm that scat searches are imprecise indicators of tree use by koalas, but demonstrate that these searches can be used, with caveats, to estimate koala population densities. We discuss how errors in estimating or applying predictive model parameters can bias estimates of occupancy and show how a failure to validate adequately the assumptions used in modelling and mapping can undermine the power of the products to direct rational conservation and management efforts.
[show abstract][hide abstract] ABSTRACT: Sexual selection is often characterized by polygynous breeding systems, size dimorphism, and skewed operational sex ratios.
Koalas are sexually dimorphic in multiple domains, yet are absent from the literature on sexual selection and the structure
of their mating system is unclear. We provide the first documentation of the strength of sexual selection in koalas by using
microsatellite markers to identify sires. We combine the genetic data with morphological data in order to assess the role
of body size in regulating reproductive output. During our 4-year study, 37% of males were identified as possible sires. Males
were significantly larger than females, with sires heavier than non-sires. Male body mass correlated with annual reproductive
output, with Crow’s Index of Opportunity for Selection revealing that variation in male reproductive success was threefold
higher than that of females. Since it appears that male koalas rarely engage in physical confrontations over access to females,
size dimorphism could be based upon non-agonistic competition and/or female mate choice. We propose that size dimorphism in
koalas evolved as a consequence of endurance rivalry promoting vocal sexual advertisements that attract females. We suggest
that female choice is a key mediator of male reproductive output.
KeywordsKoalas–Sexual selection–Size dimorphism–Reproductive success–Mate choice–Microsatellite DNA
Behavioral Ecology and Sociobiology 01/2011; 65(6):1229-1235. · 2.75 Impact Factor
[show abstract][hide abstract] ABSTRACT: Ecological factors have a pervasive impact on animal population sizes and the structure of their social systems. In a number of ungulate species, predator pressure exerts a major influence on group size. Given that giraffe (Giraffa camelopardalis) live in an extremely flexible social system, and that breeding is nonseasonal, they are an ideal species for examining how ecological variables contribute to fluctuations in herd size. We present an analysis of 34 years of data on a population of Thornicroft’s giraffe (G. c. thornicrofti Lydekker 1911) that reveal how herd size changes with season and habitat. Sex differences in herd size were apparent, with bulls often travelling as singletons, whereas cows were generally observed with conspecifics. Herds were larger during the wet than dry season, but herd size changed in a parallel fashion across habitats. Giraffe herds were smaller in woodland and thicket areas than in open habitats, regardless of season. We suggest that the regular fluctuations in herd size among giraffe indicate a fission/fusion social system embedded within a larger social community. We conclude that changes in herd size among giraffe reflect a dynamic process regulated by individuals adjusting the number of associates based upon an interaction of foraging, reproductive, social and antipredator strategies.RésuméLes facteurs écologiques ont un effet généralisé sur la taille des populations animales et sur la structure de leurs systèmes sociaux. Chez un certain nombre d’espèces d’ongulés, la pression des prédateurs exerce une influence majeure sur la taille des groupes. Étant donné que la girafe Giraffa camelopardalis vit dans un système social extrêmement flexible, et que la reproduction n’y est pas saisonnière, c’est une espèce idéale pour examiner comment des variables écologiques contribuent aux fluctuations de la taille de la harde. Nous présentons une analyse couvrant 34 années de données sur une population de girafes de Thornicroft, G. c. thornicrofti Lyddeker 1911, qui révèle comment la taille de la harde change avec les saisons et l’habitat. La différence des sexes dans la taille des hardes était visible, les mâles voyageant souvent en solitaires alors que les femelles étaient généralement observées avec des congénères. Les hardes étaient plus grandes en saison des pluies qu’en saison sèche, mais la taille des hardes changeait, dans le même temps, selon les habitats. Les hardes de girafes étaient plus petites en forêt et dans les zones arbustives que dans les habitats ouverts, quelle que soit la saison. Nous suggérons que, chez les girafes, la taille des hardes indique une fission/fusion du système social ancré dans une communauté sociale plus large. Nous concluons que les changements de taille de hardes chez les girafes reflètent un processus dynamique régulé par des individus qui ajustent le nombre de leurs associés selon une interaction des stratégies alimentaires, reproductives, sociales et défensives contre les prédateurs.
[show abstract][hide abstract] ABSTRACT: A recurrent issue confronted by zoos is the extent to which animals living ex situ have life history profiles representative of those living in situ. The lengthy lifespan of African elephants hinders collecting proper comparative data, but enough information has been published to conduct preliminary analyses comparing the developmental profile of zoo and wild African elephants on their first day of life. We show that calves born in a zoo stand and walk on their own for the first time at the same age as those born in the wild. Calves born in the zoo take a little longer until first successful nursing, but the difference in age between wild and zoo is not statistically significant. Male and female calves born in zoos develop at the same pace, with data insufficient to compare with wild-born calves. We conclude maternal parity has an effect on the age of first nursing, but not on first standing or walking, because the initiation of suckling requires coordination between two animals. We suggest that available evidence indicates that calves born in the wild and in zoos develop at comparable rates.
[show abstract][hide abstract] ABSTRACT: Koalas specialize on Eucalyptus leaves, but also feed selectively. Food choice is not random, but depends on various factors that are not well understood, although most research has focused on the role of secondary plant compounds. We studied the feeding choices of four adult male koalas housed at the San Diego Zoo. All subjects had a choice of nine types of Eucalyptus leaves over the eight-week study. The most preferred species was E. camuldulensis, but individual males exhibited different feeding preferences. We conclude that food selectivity among koalas is probably due to multiple factors, rather than only a consequence of secondary plant chemicals. A combination of intrinsic factors, such as developmental trajectory and reproductive state, as well as extrinsic factors, such as leaf chemical fingerprint and moisture, probably interact to shape koala foraging preferences. Koalas forage almost exclusively on Eucalyptus species, but have evolved an adaptive flexibility, enabling them to exploit various Eucalyptus species.
[show abstract][hide abstract] ABSTRACT: Knowledge of the reproductive life history of giraffe in the wild is sparse. Giraffe have two fairly unusual reproductive patterns among large mammals: they can become pregnant while lactating, and calf mortality is extremely high. Longitudinal records are largely absent, so tracking reproductive parameters tends to combine information from captive and field studies. In this study, we examine longitudinal data obtained over a 33-year period in one population of Thornicroft’s giraffe in order to chart their reproductive careers. We found that age at first parturition was 6.4 years, or slightly later than in captivity. Giraffe bred throughout the year, with cows producing offspring on average every 677.7 days. About half of the calves died before one year of age, but death of a calf did not reduce interbirth interval. We conclude that the lifetime reproductive success of giraffe is more dependent on longevity and calf survivorship than on reproductive rate.RésuméLa connaissance de la biologie reproductive de la girafe dans la nature est lacunaire. La girafe présente deux schémas de reproduction plutôt inhabituels chez les grands mammifères : elles peuvent être fécondées tout en allaitant, et la mortalité du jeune est extrêmement élevée. On manque cruellement de rapports longitudinaux, c’est pourquoi la recherche des paramètres de la reproduction a tendance à combiner les informations provenant d’études réalisées en captivité et sur le terrain. Dans ce rapport, nous examinons les données longitudinales recueillies sur une période de 33 ans dans une population de girafes de Thornicroft afin de dresser le tableau de leur carrière reproductive. Nous avons découvert que l’âge de la première parturition était de 6,4 ans, ou légèrement plus tard en captivité. Les girafes se reproduisent toute l’année, et les femelles mettent bas en moyenne tous les 677,7 jours. Près de la moitié des jeunes meurent avant l’âge d’un an, mais la mort du jeune ne réduit pas l’intervalle entre deux naissances. Nous concluons que la réussite de la vie reproductive d’une girafe dépend davantage de sa longévité et de la survie des jeunes que du taux de reproduction.
[show abstract][hide abstract] ABSTRACT: Patas monkeys (Erythrocebus patas) have aquamarine-coloured scrota, but data are unavailable regarding the potential connection between changes in scrotal coloration and testicular function. In the rhesus monkey (Macaca mulatta), seasonality of mating is accompanied by an intensification of red colour of the scrotum and a doubling of testicle size. A one-year study of male patas monkeys was undertaken in order to examine potential seasonal correlates of testicular function and scrotal colour. Increases in testosterone concentrations and testicular volume occurred during the mating season in adult males, but scrotal colour was fairly uniform throughout the year. Neither age, body weight, nor health influenced scrotal colour. These findings contradict the suggestion that the sex skin of seasonally breeding primates will become more intense during the mating season as a result of elevations in steroid hormone levels. Evidence from field studies in Africa suggest that the colour is part of a constellation of traits involved in male competition for mates.
[show abstract][hide abstract] ABSTRACT: Reproductive effort should negatively correlate with reproductive value, yielding a pattern of increased effort with age. According to the terminal investment hypothesis, females near the end of their reproductive life span should devote more resources to reproduction than those near the start of their reproductive careers. We tested predictions of the terminal investment hypothesis by evaluating 38 years of reproductive life-history data collected from Nile lechwe (Kobus megaceros), an ungulate species living at San Diego Zoo's Wild Animal Park. The maximum reproductive success of Nile lechwe matched predictions of models of lifetime reproductive effort, with the relative mass of newborn calves providing an accurate indicator of the costs of reproduction. Newborn mass was significantly correlated with maternal age, and neonatal males tended to be heavier than neonatal females. Older dams were more likely to produce sons than daughters, dams that produced sons were more likely to die than were dams tha
Journal of Mammalogy 01/2009; 90(1):40-46. · 2.31 Impact Factor
[show abstract][hide abstract] ABSTRACT: Female primates endure great costs during pregnancy and lactation. Some studies have been conducted on exploring these; however, information on how maternal condition before conception influences maternal postpartum recuperation and infant development are not well known, especially in primipares. This 2-year investigation explored how maternal condition, maternal foraging time and alert time, and infants' time on nipple influenced postpartum recovery of primiparous rhesus macaques, as well as their infant's development during the first 3 months postpartum. The study was conducted on 11 female rhesus macaques (Macaca mulatta) living at the Caribbean Primate Research Center, Sabana Seca Field Station, Puerto Rico. Infant survivorship and development were not influenced by maternal age at first parturition or by the infants' time on the nipple. Infant development and maternal recovery were influenced by maternal condition before conception. Older primipares demonstrated greater postpartum recuperation. Maternal postpartum recuperation was not influenced by maternal feeding time or time the infant spent on the nipple. Maternal recuperation was negatively correlated with increased vigilance (alert time).
American Journal of Primatology 08/2008; 70(11):1047-54. · 2.46 Impact Factor
[show abstract][hide abstract] ABSTRACT: Giraffe herds have been characterized as random associations of individuals, but recent evidence suggests giraffe have a more complex social structure. The authors formulated 3 hypotheses designed to evaluate whether a herd of captive giraffe (Giraffa camelopardalis) associated randomly or patterned their behavior and proximity in a manner indicative of social relationships. Affiliative interaction, proximity, and nearest neighbors for 6 captive female giraffe living in a large outdoor enclosure were analyzed, and all three measures were nonrandomly distributed, indicating female giraffe had social preferences. Furthermore, preferences were consistent across measures and time, suggesting that adult female giraffe maintain relationships. Mother-daughter pairs and pairs with large age differences between members interacted and associated most often. The social structure of this captive herd is influenced by social relationships between individual adult females, and the social behavior of individual females should be examined more closely in the wild.
Journal of Comparative Psychology 03/2007; 121(1):46-53. · 1.89 Impact Factor
[show abstract][hide abstract] ABSTRACT: When mammalian social groups exceed their optimal size, they often tend to split. In view of the potential evolutionary benefits, it should be more advantageous for animals to stay with kin, rather than nonkin, during such fission events. In the present study, the spontaneous fission of two social groups, R and S, of rhesus macaques living on Cayo Santiago, Puerto Rico, provided the opportunity to compare the kinship structure of the corresponding parent and daughter groups, using information on both maternal and paternal relatedness. In both instances, maternal half-siblings and pairs of animals from the same family were significantly more prevalent in the fission products than in the parent group. During the split of group R, significantly more paternal half-siblings stayed in the remnants of the parent group than joined the seceding group. Our findings are compatible with previous behavioural studies demonstrating that female primates bias their social behaviour more to maternal than to paternal kin, but that both types of half-siblings prefer each other more than unrelated animals. It remains to be clarified by future research, however, whether the observed co-segregation of paternal half-sibs in our study reflects active choice or is a by-product of the group-specific kin structures, prior to fission.
[show abstract][hide abstract] ABSTRACT: Female distribution exerts a major impact on male mating tactics. Giraffe cows have a reproductive cycle, and a social system, that should favor a male roaming reproductive tactic. We conducted a 2-year study of female Rothschild's giraffe (G. c. rothschildi) reproductive endocrinology in order to characterize attributes of the reproductive cycle and investigate how female endocrine and behavioral cues influence mating activity. We used non-invasive fecal steroid methods to determine reproductive state among females residing in a herd in a large outdoor enclosure. We found that females had an estrous cycle of 14.7 days and that they regularly had multiple ovarian cycles prior to conception. Adult males were more likely to associate with, and sexually investigate, females when they were cycling than when they were either pregnant or acyclic. During the estrous cycle, male-female proximity and sociosexual behavior were more pronounced during the probable fertile phase than the rest of the cycle. Sexual activity between giraffe coincided with the periovulatory period, with male interest in females peaking during the fertile window in the absence of proceptive behavior by females. We conclude that males detect reliable cues revealing female reproductive status and partition their reproductive effort in response to such cues. We propose that male giraffe adopt a roaming reproductive strategy with their large size, enabling them to search for and mate guard fertile females while minimizing metabolic costs.
Hormones and Behavior 09/2006; 50(2):314-21. · 3.74 Impact Factor
[show abstract][hide abstract] ABSTRACT: Prior to 1985 tetanus was a major cause of mortality in the free-ranging colony of rhesus monkeys on Cayo Santiago, accounting for almost a quarter of annual deaths. In 1985 and 1986 all animals (except infants) received primary and booster doses, respectively, of tetanus toxoid. In subsequent years primary immunizations were given to all yearlings, and boosters were administered to all 2-year-old animals during the annual capture of the colony. The main objectives of the tetanus immunization program were to reduce the pain and suffering caused by tetanus infections and to decrease mortality in the colony. Other objectives were to evaluate the efficacy of the two-dose tetanus toxoid immunization protocol and to determine whether additional boosters might be required to provide adequate long-term protection against tetanus infections. The immediate effect of the mass immunization program was the elimination of clinical tetanus infections in the population and a 42.2% reduction in the overall mortality rate. Since the immunization program began, no cases of tetanus have been observed in the colony, except in two unimmunized infants, and it has not been necessary to give tertiary injections of tetanus toxoid to maintain protection against infection. A sample collected in 2004 of the original cohort of monkeys immunized in 1985 and 1986 showed that 93.3% (14/15) had protective tetanus antibody titers (>0.01 IU/ml) at the ages of 20-23 years, which is close to the life expectancy of the Cayo Santiago rhesus macaques. Two intramuscular doses of tetanus toxoid provided long-term, if not lifelong, protection against tetanus for rhesus monkeys living in a tropical clime where tetanus is enzootic and the risk of infection is great.
American Journal of Primatology 08/2006; 68(7):725-31. · 2.46 Impact Factor
[show abstract][hide abstract] ABSTRACT: Zoological institutions provide an environment conducive to studying proximate mechanisms influencing reproduction that can provide guidance to both field and captive settings seeking to manage their stock. Both national parks and zoos have space limitations that sometimes require the use of reversible contraception in order to reduce reproductive rate or limit specific individuals from reproducing. We designed a study to test the efficacy of a long-lasting contraceptive in female giraffe by monitoring reproductive endocrinology and behavior. We implanted two animals with the GnRH agonist deslorelin and monitored their endocrine status using fecal steroid analysis. We have previously validated an assay for fecal pregnanes and here we report our validation for fecal estrogens. Both sex steroid concentrations were suppressed in two females, although one female exhibited an immediate post-implantation positive feedback response. Sexual activity nearly disappeared in one animal, whereas the other showed regular sexual behavior. The contraceptive effect lasted for at least 472 d, and successfully suppressed estrous cyclicity in one female for >2 y. We conclude that deslorelin implants provide a minimally invasive means for long-term suppression of reproduction in female giraffe.
[show abstract][hide abstract] ABSTRACT: We analyzed 18 years of data collected from a breeding colony of captive koalas Phascolarctos cinereus in order to identify factors regulating mating success and to generate expectations about the behavioral ecology of wild koalas. Short-term mate fidelity was associated with reproductive success, but familiarity appeared to diminish reproductive output with time. Male body mass had no effect on reproductive success. Reproductive output was highest when males were slightly older than females. Survivorship of joeys was not dependent on either male or female age. We suggest that sexual selection regulates koala mating tactics primarily in the context of non-agonistic male competition. We hypothesize that field studies will reveal that females in the wild probably capitalize on the link between male vocal and olfactory advertisements and male age as a mechanism to foster positive assortative mating by age.