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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Which is the costlier sex? : Sexual dimorphism and resource allocation in a dioecious herb, Silene dioica

Åkerlund, Elisabet January 2011 (has links)
Life-history theory proposes that different activities, such as growth, maintenance and reproduction compete for limited resources and therefore, life-history traits are bound together by physiological trade-offs. In dioecious species, females are assumed to invest a higher amount of resources in reproduction in comparison with males and this higher investment in reproduction is then assumed to have numerous consequences for the expression of other life-history traits. Some recent papers have, however, suggested that although common, this investment pattern may not be the case in all dioecious plant species. One notable exception is Silene latifolia. Therefore, I examined whether the male sex could be investing more in reproduction than females in a closely related Silene species, Silene dioica. This study was carried out on three islands in the Skeppsvik Archipelago, Umeå, where I examined possible differences between the sexes in different life history traits. On each island, 20 patches were laid out in two different successional zones. In each patch, flowering date was recorded and stem diameter, length and width of cauline leaves, flower diameter, and number of open flowers on male and female plants was measured. At the end of the study, flowering stems were collected and thereafter dried so they could be weighed to estimate biomass allocated to male and female vegetative and reproductive structures. The hypothesis that males of S. dioica should have a higher reproductive cost seemed to be confirmed since males started flowering earlier, produced more and larger flowers, produced smaller and fewer leaves and thinner stems. The males also allocated a greater proportion of their total biomass to reproductive parts and as a consequence, had a higher sink to source ratio. This study has shown that there are exceptions to the "rule" of females having a higher cost of reproduction and when doing research on dioecious species, it is important not to assume that only one and the same sex has the higher investment in reproduction in all species. This higher cost may have consequences for survival and reproductive fitness and can select for differences in other ecological traits, such as phenology, growth, chemical composition and morphology, which could in turn affect the competitive ability and the susceptibility to herbivores and pathogens.
2

A HYDRODYNAMICS APPROACH TO THE EVOLUTION OF MULTICELLULARITY: FLAGELLAR MOTILITY AND THE EVOLUTION OF GERM-SOMA DIFFERENTIATION IN VOLVOCALEAN GREEN ALGAE

Solari, Cristian Alejandro January 2005 (has links)
The fitness of any evolutionary unit can be understood in terms of its two basic components: fecundity and viability. The trade-offs between these fitness components drive the evolution of a variety of life-history traits in extant multicellular lineages. Here, I show evidence that the evolution of germ-soma separation and the emergence of individuality at a higher level during the unicellular-multicellular transition are also consequences of these trade-offs. The transition from unicellular to larger multicellular organisms has benefits, costs, and requirements. I argue that germ-soma separation evolved as a means to counteract the increasing costs and requirements of larger multicellular colonies. Volvocalean green algae are uniquely suited for studying this transition since they range from unicells to undifferentiated colonies, to multicellular individuals with complete germ-soma separation. In these flagellated organisms, the increase in cell specialization observed as colony size increases can be explained in terms of increased requirements for self-propulsion and to avoid sinking. The collective flagellar beating also serves to enhance molecular transport of nutrients and wastes. Standard hydrodynamic measurements and concepts are used to analyze motility (self-propulsion) and its consequences for different degrees of cell specialization in the Volvocales as colony size increases. This approach is used to calculate the physical hydrodynamic limits on motility to the spheroid colony design. To test the importance of collective flagellar beating on nutrient uptake, the effect of advective dynamics on the productivity of large colonies is quantified. I conclude first, that when colony size exceeds a threshold, a specialized and sterile soma must evolve, and the somatic to reproductive cell ratio must increase as colony size increases to keep colonies buoyant and motile. Second, larger colonies have higher motility capabilities with increased germ-soma specialization due to an enhancement of colony design. Third, advection has a significant effect on the productivity of large colonies. And fourth, there are clear trade-offs between investing in reproduction, increasing colony size (i.e. colony radius), and motility. This work shows that the evolution of cell specialization is the expected outcome of reducing the cost of reproduction in order to realize the benefits associated with increasing size.
3

Generality of the Terminal Investment Hypothesis: Effects of Extrinsic Mortality and Resource Availability on Age-Related Reproductive Investment

Jones, Allystair 01 December 2014 (has links) (PDF)
A central question in life history theory is, what combination of traits and behaviors will lead to the highest reproductive success throughout a lifetime. The trade-off between current and future reproduction is central to the lifetime reproductive success of an organism. If there is a cost to reproduction, then allocation of energy to current reproduction will come at a cost to future reproduction. We expect young individuals to favor future reproduction over current reproduction and that balance shifts to current reproduction as they age (i.e. terminal investment hypothesis). However, how this transition from an emphasis on future reproduction to emphasis on current reproduction changes throughout a lifetime should depend on environmental factors like mortality and resource availability. We test for the generality of terminal investment across three species of poecilliid fishes in a range of environments. We found evidence of terminal investment in all three species in both high and low mortality environments and high and low resource availability environments. In general, high mortality or high resource availability tended to result in a decreased slope of the relationship between reproductive allocation and body size. Terminal investment appears to be general, even though there was an effect of high mortality and resource availability, it was not sufficient to completely preclude terminal investment.
4

Latitudinal Variation in Lifetime Survival and Reproduction in a Burying Beetle

Laidlaw, Clinton T. 01 March 2015 (has links) (PDF)
Temperature variation experienced across a latitudinal range is tied to changes in lifespan and life history across multiple taxa. Two patterns of adaptation to latitudinal temperature variation have been documented – counter-gradient (or co-gradient) variation, and local adaptation. To determine how natural selection has shaped life history variation in a burying beetle, Nicrophorus orbicollis, we quantified lifetime patterns of reproduction in two populations that represent the geographic and temperature extremes occupied by the species. Lifetime reproduction was quantified at two temperatures that represented conditions typical for each population. Burying beetles from different extremes of their geographic range show considerable variation in lifetime survival and reproduction at different temperatures. Patterns are generally consistent with the local adaptation hypothesis. However, at the higher temperature both populations have lower and equal numbers of offspring over a lifetime. High temperatures may create a constraint on offspring production because of the increased cost of maintaining the food source against bacterial decomposition. This temperature constraint on reproductive success may partially explain the absence of burying beetles from tropical environments, and may predict reductions in latitudinal range as global climate change proceeds.
5

Variation in Resource Utilization and Cost of Reproduction for Two Burying Beetle Species

Meyers, Peter J 01 December 2014 (has links) (PDF)
The cost of reproduction hypothesis suggests that allocation into current reproduction constrains future reproduction. How organisms accrue reproductive costs may differ between species and with varying levels of resource quality. Burying beetles are model organisms for testing for the cost of reproduction because of their unique natural history; beetles utilize small vertebrate carcasses for reproduction and they and their offspring feed exclusively on these discrete resources. Burying beetles also can utilize a large range of carcass sizes for reproduction. We tested for the cost of reproduction in two species of burying beetles, Nicrophorus marginatus and Nicrophorus guttula found in Central Utah by breeding beetles on a range of carcass sizes (5g, 10g, 20g, 30g, 40g, and 50g carcasses). We also used a manipulation experiment to force beetles into over-allocating energy into reproduction to assess reproductive costs. For both species, reproduction was costly, with beetles suffering reduced lifespan and reduced lifetime fecundity with increased resource quality. Both species also showed clear signs of senescence, having reduced brood size and lower efficiency as individuals aged. Females did not show indications of terminal investment in terms of female mass change, unlike the previously studied Nicrophorus orbicollis, which gained less mass after each reproductive attempt as it aged. Nicrophorus marginatus consistently outperformed N. guttula in terms of total number of offspring produced for all carcass sizes. Nicrophorus guttula populations may continue to persist with N. marginatus by exploiting a less desirable but more abundant resource.
6

Avaliação do estresse oxidativo em cérebro de ratas reprodutoras ao longo do envelhecimento

Heemann, Fernanda Maciel January 2015 (has links)
A reprodução é uma fase crítica e exigente na vida dos animais. Nos mamíferos, as fêmeas costumam investir muito mais no cuidado parental do que os machos e a lactação é o período mais exigente em termos energéticos da vida da fêmea. Aqui, testamos se o estresse oxidativo é uma consequência da reprodução em ratas Wistar. Foram avaliadas as atividades da glutationa peroxidase, glutationa S-transferase, superóxido dismutase, o consumo de peróxido de hidrogênio, carbonilação de proteínas, peroxidação lipídica, níveis de nitrito e nitrato, glutationa total, níveis de vitamina C, bem como os níveis de estradiol no tecido cerebral em 3 , 6, 12, e 24 meses de idade. Os animais foram agrupados de acordo com a experiência reprodutiva: reprodutores ou não reprodutores. A maioria dos parâmetros estudados mostrou uma diferença entre animais não reprodutores e reprodutores de 12 e 24 meses. Aos 24 meses de idade animais reprodutores apresentaram maior atividade de superóxido dismutase, consumo de peróxido de hidrogênio, glutationa peroxidase e carbonilação de proteínas do que os animais não reprodutores. Aos 6 meses de idade, durante o período que representaria o pico da atividade reprodutiva, animais não reprodutores apresentaram níveis mais altos de malondealdeído. Em animais não reprodutores aos 12 meses de idade observou-se níveis mais altos de estrogênio, vitamina C, consumo de peróxido de hidrogênio e atividades de superóxido dismutase e glutationa peroxidase em relação aos animais reprodutores. Demonstramos que o processo de envelhecimento induz a uma elevação no dano oxidativo e também nas defesas antioxidantes em cérebro de ratas reprodutoras, sendo de alguma forma, a reprodução um processo custoso. Este estudo mostra que existe um forte potencial para a investigação do custo reprodutivo e estresse oxidativo. / Reproduction is a critical and demanding phase of the animals’ life. In mammals, females usually invest much more in parental care than males and lactation is the most energetically demanding period of a female’s life. In this work, we tested whether oxidative stress is a consequence of reproduction in female Wistar rats. We evaluated the activities of glutathione peroxidase, glutathione S-transferase, superoxide dismutase, consumption of hydrogen peroxide, protein carbonylation, lipid peroxidation, nitrite and nitrate levels, total glutathione, vitamin C levels, as well as sex hormone levels in brain tissue at 3, 6, 12, and 24 months of age. Animals were grouped according to reproductive experience: breeders or non-breeders. The parameters studied showed a difference between non-breeders and breeders animals at 12 and 24 months. At 24 months of age breeders animals showed higher superoxide dismutase activity, consumption of hydrogen peroxide, glutathione peroxidase and carbonyl level than non-breeders animals. At 6 months of age, during the period that represents peak reproductive activity, non-breeders animals showed higher levels of malondialdehyde. In non-breeders animals at 12 months of age we observed a higher level of estrogen, vitamin C, consumption of hydrogen peroxide, superoxide dismutase and glutathione peroxidase activities than breeders animals. Finally, we demonstrated that the aging process causes higher oxidative damage and higher antioxidant defenses in brain of breeders female rats, being the reproduction process costly somehow. This study shows that there is strong potential for research linking the cost of reproduction and oxidative stress.
7

Telomere length compensation mechanisms as players in longevity and stress adaptation of insects

SÁBOVÁ, Michala January 2017 (has links)
Telomeres are nucleoprotein structures at the ends of eukaryotic chromosomes that are important for genome stability and integrity. They are shortened with each cell cycle and during organismal aging. Although the most common telomere length compensation mechanism is the activity of a special reverse transcriptase, telomerase, in Drosophila telomeres are maintained by the retrotransposition of telomeric elements. In mammals, telomere length and telomerase activity can be influenced by lifestyle and the environmental conditions. This thesis is focused on activity of telomere length maintenance mechanism in insects in relation to aging and stress response.
8

Avaliação do estresse oxidativo em cérebro de ratas reprodutoras ao longo do envelhecimento

Heemann, Fernanda Maciel January 2015 (has links)
A reprodução é uma fase crítica e exigente na vida dos animais. Nos mamíferos, as fêmeas costumam investir muito mais no cuidado parental do que os machos e a lactação é o período mais exigente em termos energéticos da vida da fêmea. Aqui, testamos se o estresse oxidativo é uma consequência da reprodução em ratas Wistar. Foram avaliadas as atividades da glutationa peroxidase, glutationa S-transferase, superóxido dismutase, o consumo de peróxido de hidrogênio, carbonilação de proteínas, peroxidação lipídica, níveis de nitrito e nitrato, glutationa total, níveis de vitamina C, bem como os níveis de estradiol no tecido cerebral em 3 , 6, 12, e 24 meses de idade. Os animais foram agrupados de acordo com a experiência reprodutiva: reprodutores ou não reprodutores. A maioria dos parâmetros estudados mostrou uma diferença entre animais não reprodutores e reprodutores de 12 e 24 meses. Aos 24 meses de idade animais reprodutores apresentaram maior atividade de superóxido dismutase, consumo de peróxido de hidrogênio, glutationa peroxidase e carbonilação de proteínas do que os animais não reprodutores. Aos 6 meses de idade, durante o período que representaria o pico da atividade reprodutiva, animais não reprodutores apresentaram níveis mais altos de malondealdeído. Em animais não reprodutores aos 12 meses de idade observou-se níveis mais altos de estrogênio, vitamina C, consumo de peróxido de hidrogênio e atividades de superóxido dismutase e glutationa peroxidase em relação aos animais reprodutores. Demonstramos que o processo de envelhecimento induz a uma elevação no dano oxidativo e também nas defesas antioxidantes em cérebro de ratas reprodutoras, sendo de alguma forma, a reprodução um processo custoso. Este estudo mostra que existe um forte potencial para a investigação do custo reprodutivo e estresse oxidativo. / Reproduction is a critical and demanding phase of the animals’ life. In mammals, females usually invest much more in parental care than males and lactation is the most energetically demanding period of a female’s life. In this work, we tested whether oxidative stress is a consequence of reproduction in female Wistar rats. We evaluated the activities of glutathione peroxidase, glutathione S-transferase, superoxide dismutase, consumption of hydrogen peroxide, protein carbonylation, lipid peroxidation, nitrite and nitrate levels, total glutathione, vitamin C levels, as well as sex hormone levels in brain tissue at 3, 6, 12, and 24 months of age. Animals were grouped according to reproductive experience: breeders or non-breeders. The parameters studied showed a difference between non-breeders and breeders animals at 12 and 24 months. At 24 months of age breeders animals showed higher superoxide dismutase activity, consumption of hydrogen peroxide, glutathione peroxidase and carbonyl level than non-breeders animals. At 6 months of age, during the period that represents peak reproductive activity, non-breeders animals showed higher levels of malondialdehyde. In non-breeders animals at 12 months of age we observed a higher level of estrogen, vitamin C, consumption of hydrogen peroxide, superoxide dismutase and glutathione peroxidase activities than breeders animals. Finally, we demonstrated that the aging process causes higher oxidative damage and higher antioxidant defenses in brain of breeders female rats, being the reproduction process costly somehow. This study shows that there is strong potential for research linking the cost of reproduction and oxidative stress.
9

Avaliação do estresse oxidativo em cérebro de ratas reprodutoras ao longo do envelhecimento

Heemann, Fernanda Maciel January 2015 (has links)
A reprodução é uma fase crítica e exigente na vida dos animais. Nos mamíferos, as fêmeas costumam investir muito mais no cuidado parental do que os machos e a lactação é o período mais exigente em termos energéticos da vida da fêmea. Aqui, testamos se o estresse oxidativo é uma consequência da reprodução em ratas Wistar. Foram avaliadas as atividades da glutationa peroxidase, glutationa S-transferase, superóxido dismutase, o consumo de peróxido de hidrogênio, carbonilação de proteínas, peroxidação lipídica, níveis de nitrito e nitrato, glutationa total, níveis de vitamina C, bem como os níveis de estradiol no tecido cerebral em 3 , 6, 12, e 24 meses de idade. Os animais foram agrupados de acordo com a experiência reprodutiva: reprodutores ou não reprodutores. A maioria dos parâmetros estudados mostrou uma diferença entre animais não reprodutores e reprodutores de 12 e 24 meses. Aos 24 meses de idade animais reprodutores apresentaram maior atividade de superóxido dismutase, consumo de peróxido de hidrogênio, glutationa peroxidase e carbonilação de proteínas do que os animais não reprodutores. Aos 6 meses de idade, durante o período que representaria o pico da atividade reprodutiva, animais não reprodutores apresentaram níveis mais altos de malondealdeído. Em animais não reprodutores aos 12 meses de idade observou-se níveis mais altos de estrogênio, vitamina C, consumo de peróxido de hidrogênio e atividades de superóxido dismutase e glutationa peroxidase em relação aos animais reprodutores. Demonstramos que o processo de envelhecimento induz a uma elevação no dano oxidativo e também nas defesas antioxidantes em cérebro de ratas reprodutoras, sendo de alguma forma, a reprodução um processo custoso. Este estudo mostra que existe um forte potencial para a investigação do custo reprodutivo e estresse oxidativo. / Reproduction is a critical and demanding phase of the animals’ life. In mammals, females usually invest much more in parental care than males and lactation is the most energetically demanding period of a female’s life. In this work, we tested whether oxidative stress is a consequence of reproduction in female Wistar rats. We evaluated the activities of glutathione peroxidase, glutathione S-transferase, superoxide dismutase, consumption of hydrogen peroxide, protein carbonylation, lipid peroxidation, nitrite and nitrate levels, total glutathione, vitamin C levels, as well as sex hormone levels in brain tissue at 3, 6, 12, and 24 months of age. Animals were grouped according to reproductive experience: breeders or non-breeders. The parameters studied showed a difference between non-breeders and breeders animals at 12 and 24 months. At 24 months of age breeders animals showed higher superoxide dismutase activity, consumption of hydrogen peroxide, glutathione peroxidase and carbonyl level than non-breeders animals. At 6 months of age, during the period that represents peak reproductive activity, non-breeders animals showed higher levels of malondialdehyde. In non-breeders animals at 12 months of age we observed a higher level of estrogen, vitamin C, consumption of hydrogen peroxide, superoxide dismutase and glutathione peroxidase activities than breeders animals. Finally, we demonstrated that the aging process causes higher oxidative damage and higher antioxidant defenses in brain of breeders female rats, being the reproduction process costly somehow. This study shows that there is strong potential for research linking the cost of reproduction and oxidative stress.
10

Stratégies de reproduction des femelles du kangourou géant (Macropus giganteus)

Gélin, Uriel January 2014 (has links)
Résumé : La reproduction entraîne des dépenses énergétiques importantes chez les femelles mammifères. Ces dépenses sont supposées diminuer l'énergie disponible pour d'autres traits positivement corrélés à l'aptitude phénotypique et augmenter les besoins d'alimentation. Toutefois, des différences individuelles dans la capacité d'acquisition et d'allocation peuvent masquer l'impact négatif de l'effort reproducteur. La manipulation expérimentale de l'effort reproducteur et le contrôle statistique des effets individuels sont deux approches puissantes et complémentaires mises en œuvre dans le cadre de mon étude afin de contrôler pour l'hétérogénéité individuelle. Elles ont permis de montrer clairement un coût de la reproduction chez le kangourou gris de l'Est (Macropus giganteus). Dans un premier temps, nous avons trouvé que le coût de la reproduction affectait le montant d'énergie alloué à certaines fonctions somatiques (CHAPITRE I). L'effort reproducteur diminuait le gain de masse et la croissance des jambes pour des intervalles de capture supérieurs à deux ans. Chez les femelles non manipulées, un effet négatif sur le gain de masse était aussi observable pour un intervalle inférieur à 3 ans. À l'échelle de deux événements successifs de reproduction, le gain de masse et dans une moindre mesure la croissance des bras, mais non des jambes diminuaient avec un effort reproducteur plus important à la précédente reproduction. Ensuite, nous avons démontré qu'il y avait un coût de la reproduction en terme de futur succès reproducteur (CHAPITRE II). Les individus dont l'effort reproducteur avait été diminué expérimentalement produisaient davantage de jeunes qui survivaient au stade 'LPY', âgés approximativement de 7 mois, que les femelles contrôles. Ils diminuaient également davantage leur taux de reproduction en allongeant l'intervalle entre les naissances, mais la survie au sevrage n'était pas affectée. Le CHAPITRE III montre que les femelles adaptaient leur comportement alimentaire en fonction de leur statut reproducteur. En comparaison avec les individus manipulés ou ayant perdu leur jeune, les femelles allaitantes augmentaient leur temps passé à s'alimenter durant la journée, l'intensité de leurs bouchées et de leur mastication sans impliquer de compromis avec la vigilance. Nous avons aussi découvert que la survie au sevrage du jeune précédent menait à une augmentation du taux de bouchées pour l'année en cours. Les CHAPITRES I et II ont mis en évidence l'effet non négligeable des différences individuelles sur la détection des coûts de la reproduction. En effet, en l'absence de manipulation expérimentale ou de contrôle statistique, aucun compromis n'était détecté autant en terme de croissance que de prochaine reproduction. Au contraire, des corrélations positives entre l'effort reproducteur et les autres traits ont été trouvées. Le CHAPITRE I suggérait notamment que cette variabilité du succès reproducteur était liée à l'hétérogénéité individuelle dans le gain de masse maternelle qui augmentait la survie du jeune. Dans le CHAPITRE II, une corrélation positive entre les probabilités d'avoir un 'LPY' lors de deux événements successifs de reproduction suggérait que certaines femelles étaient capables de mener à bien ou non leur reproduction, mais cela indépendamment de l'effort reproducteur précédent. Enfin dans le dernier CHAPITRE (III), l'effet aléatoire était significatif dans l'analyse de différents comportements d'alimentation, ce qui pourrait être lié aux différences de gain de masse des femelles présentées dans le CHAPITRE I. Certaines contraintes individuelles affectant le coût de la reproduction ont été identifiées. La masse et la condition corporelle augmentaient le succès reproducteur et diminuaient l'intervalle entre deux naissances successives (CHAPITRES I et II), mais contrairement à de précédentes études le comportement d'alimentation des femelles n'était pas affecté par leur masse (CHAPITRE III). L'âge des individus avait également une influence. Les jeunes femelles croissaient davantage, avaient aussi une prise alimentaire plus importante et subissaient un coût de reproduction supérieur. Ce dernier se traduisait par un taux d'échec plus élevé à la reproduction suivante si les jeunes femelles avaient eu un jeune l'année précédente (CHAPITRES I, II et III). Des contraintes environnementales fortes influençaient la reproduction des femelles. La croissance, le succès reproducteur, l'intervalle entre les naissances et les comportements d'alimentation variaient suivant le site et l'année d'étude. Le site du Promontory et l'année 2011 apparaissaient particulièrement limitants. En effet en 2011, le gain de masse et le succès reproducteur ont diminué et l'intervalle de naissance et la prise de nourriture pour les femelles allaitantes ont augmenté (CHAPITRE I,II et III). Nous cherchions également à mettre au jour une allocation différentielle des mères suivant le sexe de leur jeune. Si le coût supérieur d'avoir un mâle par rapport à une femelle était évident quant aux taux de bouchées (CHAPITRE III), il s'est avéré plus difficile à détecter sur d'autres traits. À Anglesea, les jeunes mères avaient moins de probabilité d'avoir un jeune qui atteigne le stade 'LPY' après avoir eu un fils qu'une fille (CHAPITRE II). Toutefois, des résultats contraires à nos attentes ont été trouvés, du moins au premier abord, sur la croissance et le succès reproducteur subséquent. Ainsi, les femelles qui avaient eu une fille perdaient davantage de masse (CHAPITRE I) et avaient généralement une probabilité moindre de produire un jeune qui atteigne le stade 'LPY' ou qui soit sevré par la suite (CHAPITRE II). En revanche, l'intervalle de naissance n'était pas différent suivant le sexe du jeune alors qu'il était fortement affecté par le coût de la reproduction démontré grâce à la manipulation, invoquant une autre explication qu'un coût supérieur des filles par rapport aux fils. En effet, les femelles qui étaient en mauvaise condition corporelle gagnaient de la masse quand elles produisaient une fille, mais pas un fils (CHAPITRE I). De surcroît, les jeunes mères avaient moins de chances de sevrer un jeune à l'événement de reproduction suivant si elles avaient eu un fils plutôt qu'une fille, et le succès reproducteur des mères des fils n'était plus différent de celui des mères des filles dans les années plus difficiles (CHAPITRE II). Enfin, les mères des fils augmentaient la quantité de nourriture ingérée si elles avaient sevré un jeune l'année précédente, mais les mères des filles la diminuaient. Ces différents résultats suggéraient fortement qu'un ajustement du sexe-ratio était utilisé quand les ressources individuelles ou environnementales contraignaient davantage la reproduction. En conclusion, pour limiter le décalage entre les besoins énergétiques et la disponibilité en nourriture, les femelles chez le kangourou gris de l'Est pourraient modifier l'allocation de leurs ressources à la reproduction en reportant la prochaine mise bas et en produisant un jeune du sexe le moins coûteux en accord avec les contraintes individuelles et environnementales. Ces résultats soulignent l'importance d'études avec un suivi individuel sur plusieurs années afin de pouvoir comprendre la variabilité des stratégies de reproduction et leurs conséquences sur la dynamique des populations. // Abstract : Reproduction in living beings, particularly in female mammals that produce milk, is costly, potentially involving trade-offs with life-history traits if resources are limited and an increase in foraging effort. Individual differences may, however, hide the negative effects of this cost on life-history traits. I used two powerful and complementary approaches, to deal with individual heterogeneity: experimental manipulation of reproductive effort and statistical control of individual effect. Using both approaches, I investigated the effect of presence, size and sex of young on growth, subsequent reproduction and individual foraging behaviours of females. I used data of tagged free-ranging eastern grey kangaroos (Macropus giganteus) collected over six years at five study sites in Victoria, Australia. There was a clear cost of reproduction. Reproductive effort decreased mass gain and limb growth for inter-capture intervals greater than two years. Over two successive reproductive events, mass gain and arm growth were reduced but leg growth was independent of reproductive effort (CHAPTER II).In addition, survival to Large Pouch Young ('LPY') stage, about 7 months of age, was higher and birth rate lower in manipulated compared to control females but survival to weaning was not affected (CHAPTER III). CHAPTER IV shows that lactating females cope with current reproductive costs by increasing ivtime spent foraging as well as bite and chewing rates without decreasing vigilance comparedto non lactating ones. Bite rate was also greater for females that weaned a young at the previous reproductive event. My study supports reproductive cost hypothesis while showing substantial individual differences. To limit mismatch between energetic needs and resource availability, females of eastern grey kangaroo could modify resource allocation to reproduction by delaying birth date of subsequent young and producing the less costly sex according to individual and environmental constrains. My thesis shows the importance of experimental approach and individual monitoring over multiple years to understand the diversity of reproductive strategies and their consequences in evolutionary ecology and population dynamic.

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