26 research outputs found
Endocrine correlates of social development in the spotted hyaena Crocuta crocuta (Erxleben)
Thesis (DPhil)--University of Pretoria, 1990.Zoology and EntomologyDPhilUnrestricte
FEMALE COMPETITION AND THE ROLE OF TESTOSTERONE IN A POLYGYNOUS SYSTEM
Testosterone plays an important role in male competitive ability, and it may play a similar function in females. Female-female competition for resources is often associated with high testosterone, both within females and in comparison to males. Positive associations between testosterone and competition are most likely to be seen in systems with high female-female competition. Resource defense polygyny may be one such system since females congregate on high-quality nutrient sources, leading to substantial opportunities for interference competition. I studied female Grantâs gazelle (Nanger granti), a classic resource defense polygynous species, to investigate female competition and its relationship to testosterone. I found substantial evidence for competition between females. Females frequently engaged in agonistic behavior, on average initiating over two agonistic bouts per hour, and higher-ranking females initiated more agonism than lower-ranking females. Testosterone appeared to play an important role in competitive ability. Immunoreactive fecal testosterone metabolites (fT) were strongly positively correlated to both dominance rank and number of agonistic bouts initiated per hour, but only agonism was associated with fT when dominance and agonism were accounted for simultaneously. Females had similar fT concentrations as males. fT was positively associated with immunoreactive fecal glucocorticoid metabolites (fGCM), and this relationship was not due to associations between dominance and fGCM. Month also influenced testosterone physiology. Females had lower fT during a drought than after rains had begun. In addition, fT increased more from August to November in high-ranking females than in low-ranking females. My results suggest that female-female competition may be substantial in resource defense polygynous systems. Testosterone might play an important role in mediating competitive ability in females, but it was also associated with higher glucocorticoid secretion. Future studies on females would be well served to investigate the consequences of testosterone secretion and how they relate to female competition
Adaptation, Exaptation, and Constraint: A Hormonal Perspective
We approach conceptual issues in evolutionary biology from an endocrinological perspective, noting that single hormones typically act on several target tissues and thereby mediate suites of correlated phenotypic traits. When several components of such a suite are beneficial, an important evolutionary question is whether all are adaptations or some are exaptations. The answer may depend on whether the traits arose in response to selection on variation in systemic levels of the hormone on variation in responsiveness of target tissues to invariant levels of the hormone. If the former, selection probably acted directly on fewer than all traits; beneficial traits arising indirectly would be exaptations. In contrast, multiple beneficial traits that arose out of independent changes in targetâtissue sensitivity to invariant hormone levels could all be adaptations. Knowledge of specific hormonal mechanisms as well as of historical selective regimes will be necessary to draw such distinctions. Endocrine constraints on evolution can be studied experimentally by applying hormones systemically and measuring interdependent responses of beneficial and detrimental traits to selection (phenotypic engineering with hormones). Supposing that alteration of one trait in isolation would enhance fitness, cases in which the net effect of endocrine alteration of multiple traits is to depress fitness provide evidence for constraints. We briefly report results of recent studies employing hormonal manipulations, stressing our own work on the darkâeyed junco (Junco hyemalis: Emberizidae)
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Social and endocrine correlates of immune function in meerkats: implications for the immunocompetence handicap hypothesis.
Social status can mediate effects on the immune system, with profound consequences for individual health; nevertheless, most investigators of status-related disparities in free-ranging animals have used faecal parasite burdens to proxy immune function in the males of male-dominant species. We instead use direct measures of innate immune function (complement and natural antibodies) to examine status-related immunocompetence in both sexes of a female-dominant species. The meerkat is a unique model for such a study because it is a cooperatively breeding species in which status-related differences are extreme, evident in reproductive skew, morphology, behaviour, communication and physiology, including that dominant females naturally express the greatest total androgen (androstenedione plus testosterone) concentrations. We found that, relative to subordinates, dominant animals had reduced serum bacteria-killing abilities; also, relative to subordinate females, dominant females had reduced haemolytic complement activities. Irrespective of an individual's sex or social status, androstenedione concentrations (but not body condition, age or reproductive activity) negatively predicted concurrent immunocompetence. Thus, dominant meerkats of both sexes are immunocompromised. Moreover, in female meerkats, androstenedione perhaps acting directly or via local conversion, may exert a double-edged effect of promoting dominance and reproductive success at the cost of increased parasitism and reduced immune function. Given the prominent signalling of dominance in female meerkats, these findings may relate to the immunocompetence handicap hypothesis (ICHH); however, our data would suggest that the endocrine mechanism underlying the ICHH need not be mediated solely by testosterone and might explain trade-offs in females, as well as in males
Evidence For A Potential Role Of Estrogen In The Penis: Detection Of Estrogen Receptor-A And -B Messenger Ribonucleic Acid And Protein
Body tissues are traditionally classified as estrogen targets based on both the response to the hormone and the presence of estrogen receptors (ERs). We undertook the study on expression of ERff and ERb in the penis to identify compartments/cells responsive to estrogen, using immunohistochemistry, Western blotting, in situ hybridization, and RT-PCR analyses. Expressions of ERa and ERb in the rat penis were age dependent at both mRNA and protein levels, with the most intense signals being observed during the perinatal period and declining thereafter with age. Initial signals (fetal d 17) of ERff were localized to the mesenchyme and subepithelial stroma and later (postnatal d 2) to the corpus spongiosus, corpus cavernosus, and urethral epithelia. ERb was initially detected by postnatal d 2 and was localized diffusely in corpus spongiosus and cavernosus in immature rats. In the adult, both ERs were concentrated largely to the urethral epithelia and vascular and neuronal structures. The present study provides the first evidence for ER expression in the penis. Thus, our data add the penis to the list of estrogen-responsive tissues in males and provide a base and insight for future studies aimed at investigating a functional role of estrogen in the penis, especially in development
Social and endocrine correlates of immune function in meerkats : implications for the immunocompetence
Social status can mediate effects on the immune system, with
profound consequences for individual health; nevertheless,
most investigators of status-related disparities in freeranging
animals have used faecal parasite burdens to
proxy immune function in the males of male-dominant
species. We instead use direct measures of innate immune
function (complement and natural antibodies) to examine
status-related immunocompetence in both sexes of a femaledominant
species. The meerkat is a unique model for such
a study because it is a cooperatively breeding species in
which status-related differences are extreme, evident in
reproductive skew, morphology, behaviour, communication
and physiology, including that dominant females naturally
express the greatest total androgen (androstenedione
plus testosterone) concentrations. We found that, relative
to subordinates, dominant animals had reduced serum
bacteria-killing abilities; also, relative to subordinate females,
dominant females had reduced haemolytic complement
activities. Irrespective of an individualâs sex or social status, androstenedione concentrations (but not body condition, age or reproductive activity) negatively
predicted concurrent immunocompetence. Thus, dominant meerkats of both sexes are
immunocompromised. Moreover, in female meerkats, androstenedione perhaps acting directly
or via local conversion, may exert a double-edged effect of promoting dominance and reproductive
success at the cost of increased parasitism and reduced immune function. Given the prominent
signalling of dominance in female meerkats, these findings may relate to the immunocompetence
handicap hypothesis (ICHH); however, our data would suggest that the endocrine mechanism
underlying the ICHH need not be mediated solely by testosterone and might explain trade-offs in
females, as well as in males.This work was supported by the National Science Foundation (IOS-1021633 to C.M.D. and IOS-1601685 to
C.M.D. and K.N.S.) and the Duke University Graduate School (Judy C. Woodruff Fellowship, Fred and Barbara
Sutherland Fellowship and Katherine Goodman Stern Fellowship to K.N.S.). Vehicle costs in the field were supported
by Duke University (research funds to C.M.D.). We relied on records of individual life histories and access to a field
site maintained by the KalahariMeerkat Project (KMP). During the span of this study, the KMP was supported by the
European Research Council (Research grant no. 294494 to T.H.C.-B.), the University of Cambridge, the University of
Zurich, the Mammal Research Institute at the University of Pretoria and Duke University.http://rsos.royalsocietypublishing.orgam2019Mammal Research Institut
Proximate and ultimate drivers of breeding-group choice and reproductive success in male spotted hyenas (Crocuta crocuta)
In group-living species, the choice of the breeding group and the social rank in the hierarchy of the group strongly influence an individualâs fitness. Yet the causes and consequences of variation in breeding-group choice and dispersal propensity, and the proximate mechanisms through which social rank influences an individualâs ability to access mates and reproduce remain poorly understood. This thesis has three main aims: (i) identify the drivers of the coexistence of dispersal and philopatry among males in the spotted hyena (Crocuta crocuta), a large, group-living carnivore; (ii) assess whether and how social rank and social and physiological constraints influence reproductive investment and success in male hyenas; (iii) improve the applicability of non-invasive hormone concentration measurements. The thesis combines long-term data on the behaviour, physiology, survival and reproductive success of male spotted hyenas with demographic data from all eight social groups of a free-ranging hyena population in Tanzania. In Chapter 3, I show that philopatric male and dispersers are of similar phenotypic quality, follow the same process and apply the same rules to choose and settle in a breeding group, and have similar survival and reproductive success. I also show that social rank is a strong determinant of male access to mates and reproductive success in spotted hyenas. Philopatric males gain reproductive benefits associated with their high social rank and these benefits increase the propensity of males to choose their natal group as a breeding group. The results demonstrate that the distribution of breeding females across natal and nonnatal groups is an important determinant of dispersal patterns and of the coexistence of philopatry and dispersal in male spotted hyenas. In Chapter 4, I develop a novel method to standardise hormone metabolite concentration measurements when substantial changes in the accuracy of an immunoassay occur. The method is based on repeated assaying of a small number of samples and restores the comparability of the measurements. The method constitutes an effective alternative to the often impracticable re-assaying of complete sample sets. In Chapter 5, I show that males with a high social rank are less constrained by physiological stress than low-ranking males, owing to their greater opportunities to express dominance and enjoy the buffering effect of social bonds. This allows high-ranking males, including philopatric males, to allocate more time than low-ranking males to fitness-enhancing social and sexual activities, and to focus their sexual investment on females of high reproductive value. These results are consistent with the results of Chapter 3 and may explain why philopatric males and high-ranking immigrants are particularly successful at siring offspring with females of high reproductive value. The thesis provides insights into (i) the role of demographic variability and the distribution of breeding partners in driving the evolution of dispersal and in shaping dispersal patterns within populations; (ii) the traits that underpin differences in competitive ability and reproductive performance between males of different social rank; and (iii) the role of social rank and of social and physiological constraints in shaping differences in life history and reproductive success among males in group-living species.Bei gruppenlebenden Arten wird die Fitness von Individuen stark durch die Wahl der Fortpflanzungsgruppe und den sozialen Rang in der Hierarchie der Gruppe beeinflusst. Die Ursachen und Folgen von Unterschieden in der Wahl der Fortpflanzungsgruppe und der Abwanderungsneigung sowie die Mechanismen, durch die der soziale Rang den Zugang zu Paarungspartnern und den Fortpflanzungserfolg beeinflusst, sind weitgehend unbekannt. Diese Arbeit hat drei Hauptziele: (i) Ursachen fĂŒr die Koexistenz von Abwanderung und Ortstreue (Philopatrie) bei MĂ€nnchen der TĂŒpfelhyĂ€ne (Crocuta crocuta), einem groĂen, gruppenlebenden Raubtier, zu identifizieren; (ii) den Einfluss des sozialen Ranges und sozialer und physiologischer Eigenschaften auf die Investitionen in die Fortpflanzung und den Fortpflanzungserfolg bei TĂŒpfelhyĂ€nen-MĂ€nnchen zu ermessen; (iii) die Anwendbarkeit von nicht-invasiven Hormonkonzentrationsmessungen zu verbessern. Die Arbeit verbindet Langzeitdaten ĂŒber das Verhalten, die Physiologie, das Ăberleben und den Fortpflanzungserfolg von TĂŒpfelhyĂ€nen-MĂ€nnchen mit demographischen Daten aus allen acht Clans einer freilebenden HyĂ€nenpopulation in Tansania. In Kapitel 3 zeige ich, dass abgewanderte und philopatrische TĂŒpfelhyĂ€nen-MĂ€nnchen von Ă€hnlicher phĂ€notypischer QualitĂ€t sind, die gleichen Prozesse und Regeln anwenden, um eine Fortpflanzungsgruppe auszuwĂ€hlen und sich darin niederzulassen, und Ă€hnliche Ăberlebenswahrscheinlichkeiten und Fortpflanzungserfolge haben. Ich zeige auch, dass der soziale Rang den Zugang zu Paarungspartnern und den Fortpflanzungserfolg beeinflusst, dass philopatrische MĂ€nnchen durch ihren hohen sozialen Rang einen hohen Fortpflanzungserfolg haben, und dass die Vorteile von Ortstreue die Wahrscheinlichkeit der MĂ€nnchen erhöht, ihre Geburtsgruppe als Fortpflanzungsgruppe auszuwĂ€hlen. Die Ergebnisse zeigen, dass die Anzahl der Paarungspartner in der Geburts- und anderen Gruppen das Abwanderungsverhalten und die AbwanderungshĂ€ufigkeit bestimmt und die Koexistenz von Abwanderung und Ortstreue bei TĂŒpfelhyĂ€nen-MĂ€nnchen begrĂŒndet. In Kapitel 4 entwickle ich eine neuartige Methode zur Standardisierung der Messung von Hormonmetabolitenkonzentrationen wenn wesentliche Ănderungen in der Messgenauigkeit eines Immunoassays auftreten. Das Verfahren basiert auf der bei jeder Messung wiederholten Analyse einer kleinen Anzahl von Proben und stellt die Vergleichbarkeit der Messungen her. Es ist eine effektive und effiziente Alternative zur oft undurchfĂŒhrbaren wiederholten Analyse aller Proben. In Kapitel 5 zeige ich, dass MĂ€nnchen mit einem hohen sozialen Rang mehr Möglichkeiten haben, Dominanz auszuĂŒben und von der Pufferwirkung sozialer Bindungen zu profitieren als MĂ€nnchen mit einem niedrigeren Rang. Hochrangige MĂ€nnchen werden dadurch weniger stark durch physiologischen Stress eingeschrĂ€nkt als tieferrangige MĂ€nnchen. Dies ermöglicht es hochrangigen MĂ€nnchen, einschlieĂlich philopatrischen MĂ€nnchen, mehr Zeit in fitnessfördernde soziale und sexuelle AktivitĂ€ten zu investieren als tiefer rangige MĂ€nnchen und besonders viel in Weibchen mit hohem Fortpflanzungswert zu investieren. Diese Ergebnisse stehen im Einklang mit den Ergebnissen von Kapitel 3 und können erklĂ€ren, warum philopatrische MĂ€nnchen und hochrangige Einwanderer besonders hĂ€ufig Nachkommen mit Weibchen von hohem Fortpflanzungswert zeugen. Die Arbeit liefert Einblicke in (i) die Rolle der demographischen VariabilitĂ€t und der Verteilung von Paarungspartnern fĂŒr die Evolution von Abwanderung und Philopatrie und die Entstehung von Abwanderungsmustern auf Populationsebene, (ii) Merkmale, die Unterschiede in der KonkurrenzfĂ€higkeit und der Investition in Fortpflanzung zwischen MĂ€nnchen unterschiedlichen sozialen Ranges verursachen, und (iii) die Rolle des sozialen Ranges und sozialer und physiologischer Eigenschaften bei der Entstehung von Unterschieden in der Lebensgeschichte und des Fortpflanzungserfolgs zwischen MĂ€nnchen bei gruppenlebenden Arten
Plains zebra (Equus quagga) adrenocortical activity increases during times of large aggregations in the Serengeti ecosystem
Adverse environmental stimuli (stressors) activate the hypothalamic-pituitary-adrenal axis and contribute to allostatic load. This study investigates the contribution of environmental stressors and life history stage to allostatic load in a migratory population of plains zebras (Equus quagga) in the Serengeti ecosystem, in Tanzania, which experiences large local variations in aggregation. We expected higher fGCM response to the environmental stressors of feeding competition, predation pressure and unpredictable social relationships in larger than in smaller aggregations, and in animals at energetically costly life history stages. As the study was conducted during the 2016 El Niño, we did not expect food quality of forage or a lack of water to strongly affect fGCM responses in the dry season. We measured fecal glucocorticoid metabolite (fGCM) concentrations using an enzyme immunoassay (EIA) targeting 11ÎČ-hydroxyetiocholanolone and validated its reliability in captive plains zebras. Our results revealed significantly higher fGCM concentrations 1) in large aggregations than in smaller groupings, and 2) in band stallions than in bachelor males. Concentrations of fGCM were not significantly higher in females at the energetically costly life stage of late pregnancy/lactation. The higher allostatic load of stallions associated with females, than bachelor males is likely caused by social stressors. In conclusion, migratory zebras have elevated allostatic loads in large aggregations that probably result from their combined responses to increased feeding competition, predation pressure and various social stressors. Further research is required to disentangle the contribution of these stressors to allostatic load in migratory populations.A grant from the Leibniz Gemeinschaft (SAW-2015-IZW-1 440) and the Leibniz Institute for Zoo and Wildlife Research.http://www.elsevier.com/locate/yhbeh2019-06-01hj2018Anatomy and PhysiologyMammal Research InstituteZoology and Entomolog
The Past Is Never Dead, It Isn't Even Past: Maternal Environment Affects Multiple Generations of Offspring via Hormone Provisioning
An animalâs phenotype may be shaped by its genes, but also reflects its own environment
and often that of its parents. Nongenetic parental effects are often mediated by steroid
hormones, and operate between parents and offspring through mechanisms that are well
described in vertebrate and non-vertebrate model systems. However, less is understood
about the strength and frequency of hormone mediated nongenetic parental effects across
more than one generation of descendants, and in nonmodel systems.
In Chapter 2, I report that variation in the ecdysteroid hormones (ESH) provided by
female house crickets (Acheta domesticus) to their eggs can be robustly, replicably
measured using an Enzyme Immunoassay technique.
In Chapter 3, I show that variation in the ESH that female A. domesticus deposit into their
eggs determines the early development rates of their offspring. I also show that variation
in the active forms of ESH provided by a female house cricket to her eggs derives
primarily from the quality of nutrition available to her mother and maternal grandmother,
regardless of genetic background, age at oviposition, or any contribution of ESH by her
mate.
In Chapter 4, I uncover a potential mechanism of generating delayed density dependence
by showing that female A. domesticus alter their ESH provisioning strategy in response to
social density.
In Chapter 5, I demonstrate that these effects are not limited to lab-raised species, but are
relevant to and present in at least two species of wild Gryllid (Gryllus veletis and G.
pennsylvanicus).
In sum, work reported here demonstrates the power of variable hormone provisioning by
mothers to their offspring. These findings highlight the importance of distinguishing
between phenotypic plasticity and genetic effects in observing field and laboratory
organisms across time and space.PHDEcology and Evolutionary BiologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/143928/1/crockerk_1.pd