Sex determination occurs early in development for most animals, at which time sex is fixed for life. Many teleost fishes, however, exhibit remarkable sexual plasticity throughout their life history, ranging from multiple morphs within a sex to functional adult sex reversal. To understand the development and evolution of adult sex reversal, I examined behavioral, endocrine, and genetic contributions to the regulation of functional sex in adult animals, using the bluebanded goby (Lythrypnus dalli) as an experimental model. This species was found to be equally capable of sexual transitions from female to male (protogyny) as from male to female (protandry). Throughout adult life, sexual phenotype is determined by social status, an emergent property of agonistic behavioral interactions that follows a relatively simple social convention: if dominant become or remain male, or if subordinate, become or remain female. The translation of social status into a change in sexual phenotype in the protogynous direction requires a rapid drop in circulating estrogens and an increase in the gonadal expression of a testis differentiating gene dmrt1. Steroid hormones do not play a significant role in modulating status, but the androgen 11-ketotestosterone does positively correlate with the expression of paternal behavior. Taken together, these findings suggest an evolutionary mechanism in sexually plastic species that has linked the conserved molecular cascades of sexual differentiation to a novel signal that varies over life history, social status, thereby allowing for lifelong phenotypic plasticity.

The dissertation thesis focuses on predator ecology in artificial water bodies. Paper I deals with the importance of chemical cues for predator-prey interactions in an aquatic environment. Here, I demonstrate that the ability to detect chemical cues represents a survival benefit for prey species. Paper II points out gillnet methodological bias, which may have subsequent repercussions in field evaluation of a predator's presence and assessment of larger fish abundance in general. Papers III and IV focus on asp Leuciscus aspius spawning grounds. In Paper III, I demonstrate how males maximize their spawning chances by early arrival and in Paper IV, I evaluate the predation pressure of asp prey, Alburnus alburnus, directed on asp eggs.

This thesis presents two studies where natural and sexual selection have interacted to evolve sexual behaviours. The thesis uses mathematical modelling to understand how these forces have caused each behaviour to evolve. This is useful because the results allow for reflection on the potential role of sexual selection in adaptation of these species to a changing environment. The first study is of early male arrival to spring breeding grounds in migratory avian species, this is termed protandry. The study explores the main hypotheses for avian protandry and then tests the susceptibility of each hypothesis to changing environment. The second study is of convenience polyandry in species where there is conflict over mating rate. Females have multiple strategies to avoid harassive males but strategies vary in cost and success rate; she must balance her strategy use to minimise her fitness depreciation. The study identifies the main factors that cause convenience polyandry to evolve and paves the way for future studies to investigate if sexual selection over resistance strategy provides these species a future advantage in adaptation to a changing environment.

In this thesis, I combined field observations and lab experiments to explore the ecological significance of floral signals in a North American wildflower, Penstemon digitalis. More specifically, to determine the potential mechanisms driving selection on floral scent, I studied how scent mediates interactions with pollinators and antagonists by (1) observing spatiotemporal variation in scent emission (2), floral volatile ability to suppress microbes (3) the honest advertisement of nectar, and (4) if scent could aid pollinator learning by reinforcing visual signals. Scent sampling of flower development, flower tissues, rewards and inflorescence day/night emission, revealed a complexity in floral scent composition and emission that could reflect several ecological functions. The floral bouquet of P. digitalis was strongest when flowers opened, primarily emitted from flower nectaries and was strongest during the day when pollinators are most active, suggesting a role in plant-pollinator interactions. Because linalool was one of the few floral compounds found in nectar where microbe growth can degrade the pollinator reward, I studied its role in plant-microbe interactions. Bacteria strains isolated from floral and vegetative tissues were exposed to varying concentrations of nectar volatiles: linalool and methyl nicotinate. Linalool inhibited bacteria growth rate from all tissue origins whereas methyl nicotinate had little effect, suggesting that microbes could drive selection on linalool emission strength.    To determine the extent that linalool could honestly signal nectar availability, linalool-nectar associations were measured for inflorescences and flowers. Linalool predicted inflorescence nectar availability but not flower, exposing a limit to its honesty. Pollinator Bombus impatiens could use linalool as a foraging signal at varying concentrations, suggesting linalool could be learned and used to choose the most rewarding plants.    Measurement and comparison of signal-reward associations for both olfactory and visual signals/cues of P. digitalis displays found display size and linalool honest indicators of nectar. Lab behaviour experiments showed multiple signals correlated with reward could increase bumblebee foraging efficiency and promote learning, providing an explanation for why floral displays are complex and consist of multiple signals.    Together my results show that an integrated approach is required to understand the mechanisms driving the evolution of the floral phenotype.

Monoecy, the production of distinct male and female flowers on the same plant, is an important, though little studied, sexual strategy in the rainforest understory. This study of a monoecious plant discovered a cue to induce flowering, explored the interplay of gender constraint vs. plasticity in a natural population, and tested possible causes of gender in two laboratory experiments. An experiment in the lab found that reduced photoperiod for three weeks is an unambiguous cue for flowering. The remarkably long inductive period is followed by a long and variable period of floral initiation. This results in only partial synchronization of flowering among plants in a patch, which enhances mating opportunities in this protandrous plant. Inflorescence architecture is highly constrained, and ideally produces a phenotypic gender (proportion female) of about 0.5. However, in the forest at Las Cruces, Costa Rica, most plants were less female than predicted, mostly through abortion of female buds. Plants showed gender plasticity between and within years. Large plants produced more flowers and were more female in gender, and less variable in gender, than small plants. Reproduction was poorly correlated with environmental resource availability, measured as canopy openness, soil moisture, pH, and soil phosphorus, ammonium and nitrate. Phenotypic selection analysis on seed production suggests an optimal gender of 50-60% female, yet plasticity to be less female than this optimum, and in particular to express only male function, has been maintained. In a factorial experiment in the lab, high light or high nitrogen caused plants to produce more flowers and to be proportionally more female, and larger in weight, than low light or nitrogen. The effects of light and nitrogen on reproduction, plant size, and leaf greenness suggest an energy based determination of gender. Gender may be mostly influenced by plant size, but sometimes also opportunistically by environment. Inoculation with mycorrhizas caused plants to be less female in gender, and smaller in weight, than plants that were not inoculated. This suggests a net cost of mycorrhizas under experimental conditions, and supports the emerging view of the mycorrhizal symbiosis as not necessarily mutualistic under all circumstances.

Doctor of Philosophy (PhD) / A renewed focus on generalised pollinator systems has inspired a conceptual framework which highlights that spatial and temporal interactions among plants and their assemblage of pollinators can vary across the individual, population, regional and species levels. Pollination is clearly a dynamic interaction, varying in the number and interdependence of participants and the strength of the outcome of the interaction. Therefore, the role of variation in pollination is fundamental for understanding ecological dynamics of plant populations and is a major factor in the evolution and maintenance of generalised and specialised pollination systems. My study centred on these basic concepts by addressing the following questions: (1) How variable are pollinators in a generalised pollination system? To what degree do insect visitation rates and assemblage composition vary spatially among populations and temporally among flowering seasons? (2) How does variation in pollinators affect plant reproductive success? I chose to do this using a model system, Trachymene incisa subsp. incisa (Apiaceae), which is a widespread Australian herbaceous species with simple white flowers grouped into umbels that attract a high diversity of insect visitors. The Apiaceae are considered to be highly generalist in terms of pollination, due to their simple and uniform floral display and easily accessible floral rewards. Three populations of T. incisa located between 70 km and 210 km apart were studied over 2-3 years. The few studies investigating spatial and temporal variation simultaneously over geographic and yearly/seasonal scales indicate that there is a trend for more spatial than temporal variation in pollinators of generalist-pollinated plants. My study showed both spatial and temporal variation in assemblage composition among all populations and variation in insect visitation rates, in the form of a significant population by year interaction. However, removing ants from the analyses to restrict the assemblage to flying insects and the most likely pollinators, resulted in a significant difference in overall visitation rate between years but no difference in assemblage composition between the Myall Lakes and Tomago populations. These results indicate more temporal than spatial variation in the flying insect visitor assemblage of T. incisa. Foraging behaviour provides another source of variation in plant-pollinator interactions. Trachymene incisa exhibits umbels that function as either male or female at any one time and offer different floral rewards in each phase. For successful pollination, pollinators must visit both male and female umbels during a foraging trip. Insects showed both preferences and non-preferences for umbel phases in natural patches where the gender ratio was male biased. In contrast, insects showed no bias in visitation during a foraging trip or in time spent foraging on male and female umbels in experimental arrays where the gender ratio was equal. Pollinator assemblages consisting of a mixture of different pollinator types coupled with temporal variation in the assemblages of populations among years maintains generalisation at the population/local level. In addition, spatial variation in assemblages among populations maintains generalisation at the species level. Fire alters pollination in T. incisa by shifting the flowering season and reducing the abundance of flying insects. Therefore, fire plays an important role in maintaining spatial and temporal variation in this fire-prone system. Although insect pollinators are important in determining the mating opportunities of 90% of flowering plant species worldwide, few studies have looked at the effects of variation in pollinator assemblages on plant reproductive success and mating. In T. incisa, high insect visitation rates do not guarantee high plant reproductive success, indicating that the quality of visit is more important than the rate of visitation. This is shown by comparing the Agnes Banks and Myall Lakes populations in 2003: Agnes Banks received the highest visitation rate from an assemblage dominated by ants but produced the lowest reproductive output, and Myall Lakes received the lowest visitation rate by an assemblage dominated by a native bee and produced the highest seedling emergence. Interestingly, populations with different assemblage composition can produce similar percentage seed set per umbel. However, similar percentage seed set did not result in similar percentage seedling emergence. Differences among years in reproductive output (total seed production) were due to differences in umbel production (reproductive effort) and proportion of umbels with seeds, and not seed set per umbel. Trachymene incisa is self-compatible and suffers weak to intermediate levels of inbreeding depression through early stages of the life cycle when seeds are self-pollinated and biparentally inbred. Floral phenology, in the form of synchronous protandry, plays an important role in avoiding self-pollination within umbels and reducing the chance of geitonogamous pollination between umbels on the same plant. Although pollinators can increase the rate of inbreeding in T. incisa by foraging on both male and female phase umbels on the same plant or closely related plants, most consecutive insect movements were between plants not located adjacent to each other. This indicates that inbreeding is mostly avoided and that T. incisa is a predominantly outcrossing species, although further genetic analyses are required to confirm this hypothesis. A new conceptual understanding has emerged from the key empirical results in the study of this model generalised pollination system. The large differences among populations and between years indicate that populations are not equally serviced by pollinators and are not equally generalist. Insect visitation rates varied significantly throughout the day, highlighting that sampling of pollinators at one time will result in an inaccurate estimate and usually underestimate the degree of generalisation. The visitor assemblage is not equivalent to the pollinator assemblage, although non-pollinating floral visitors are likely to influence the overall effectiveness of the pollinator assemblage. Given the high degree of variation in both the number of pollinator species and number of pollinator types, I have constructed a model which includes the degree of ecological and functional specialisation of a plant species on pollinators and the variation encountered across different levels of plant organisation. This model describes the ecological or current state of plant species and their pollinators, as well as presenting the patterns of generalisation across a range of populations, which is critical for understanding the evolution and maintenance of the system. In-depth examination of pollination systems is required in order to understand the range of strategies utilised by plants and their pollinators, and I advocate a complete floral visitor assemblage approach to future studies in pollination ecology. In particular, future studies should focus on the role of introduced pollinators in altering generalised plant-pollinator systems and the contribution of non-pollinating floral visitors to pollinator assemblage effectiveness. Comparative studies involving plants with highly conserved floral displays, such as those in the genus Trachymene and in the Apiaceae, will be useful for investigating the dynamics of generalised pollination systems across a range of widespread and restricted species.

Doctor of Philosophy (PhD) / A renewed focus on generalised pollinator systems has inspired a conceptual framework which highlights that spatial and temporal interactions among plants and their assemblage of pollinators can vary across the individual, population, regional and species levels. Pollination is clearly a dynamic interaction, varying in the number and interdependence of participants and the strength of the outcome of the interaction. Therefore, the role of variation in pollination is fundamental for understanding ecological dynamics of plant populations and is a major factor in the evolution and maintenance of generalised and specialised pollination systems. My study centred on these basic concepts by addressing the following questions: (1) How variable are pollinators in a generalised pollination system? To what degree do insect visitation rates and assemblage composition vary spatially among populations and temporally among flowering seasons? (2) How does variation in pollinators affect plant reproductive success? I chose to do this using a model system, Trachymene incisa subsp. incisa (Apiaceae), which is a widespread Australian herbaceous species with simple white flowers grouped into umbels that attract a high diversity of insect visitors. The Apiaceae are considered to be highly generalist in terms of pollination, due to their simple and uniform floral display and easily accessible floral rewards. Three populations of T. incisa located between 70 km and 210 km apart were studied over 2-3 years. The few studies investigating spatial and temporal variation simultaneously over geographic and yearly/seasonal scales indicate that there is a trend for more spatial than temporal variation in pollinators of generalist-pollinated plants. My study showed both spatial and temporal variation in assemblage composition among all populations and variation in insect visitation rates, in the form of a significant population by year interaction. However, removing ants from the analyses to restrict the assemblage to flying insects and the most likely pollinators, resulted in a significant difference in overall visitation rate between years but no difference in assemblage composition between the Myall Lakes and Tomago populations. These results indicate more temporal than spatial variation in the flying insect visitor assemblage of T. incisa. Foraging behaviour provides another source of variation in plant-pollinator interactions. Trachymene incisa exhibits umbels that function as either male or female at any one time and offer different floral rewards in each phase. For successful pollination, pollinators must visit both male and female umbels during a foraging trip. Insects showed both preferences and non-preferences for umbel phases in natural patches where the gender ratio was male biased. In contrast, insects showed no bias in visitation during a foraging trip or in time spent foraging on male and female umbels in experimental arrays where the gender ratio was equal. Pollinator assemblages consisting of a mixture of different pollinator types coupled with temporal variation in the assemblages of populations among years maintains generalisation at the population/local level. In addition, spatial variation in assemblages among populations maintains generalisation at the species level. Fire alters pollination in T. incisa by shifting the flowering season and reducing the abundance of flying insects. Therefore, fire plays an important role in maintaining spatial and temporal variation in this fire-prone system. Although insect pollinators are important in determining the mating opportunities of 90% of flowering plant species worldwide, few studies have looked at the effects of variation in pollinator assemblages on plant reproductive success and mating. In T. incisa, high insect visitation rates do not guarantee high plant reproductive success, indicating that the quality of visit is more important than the rate of visitation. This is shown by comparing the Agnes Banks and Myall Lakes populations in 2003: Agnes Banks received the highest visitation rate from an assemblage dominated by ants but produced the lowest reproductive output, and Myall Lakes received the lowest visitation rate by an assemblage dominated by a native bee and produced the highest seedling emergence. Interestingly, populations with different assemblage composition can produce similar percentage seed set per umbel. However, similar percentage seed set did not result in similar percentage seedling emergence. Differences among years in reproductive output (total seed production) were due to differences in umbel production (reproductive effort) and proportion of umbels with seeds, and not seed set per umbel. Trachymene incisa is self-compatible and suffers weak to intermediate levels of inbreeding depression through early stages of the life cycle when seeds are self-pollinated and biparentally inbred. Floral phenology, in the form of synchronous protandry, plays an important role in avoiding self-pollination within umbels and reducing the chance of geitonogamous pollination between umbels on the same plant. Although pollinators can increase the rate of inbreeding in T. incisa by foraging on both male and female phase umbels on the same plant or closely related plants, most consecutive insect movements were between plants not located adjacent to each other. This indicates that inbreeding is mostly avoided and that T. incisa is a predominantly outcrossing species, although further genetic analyses are required to confirm this hypothesis. A new conceptual understanding has emerged from the key empirical results in the study of this model generalised pollination system. The large differences among populations and between years indicate that populations are not equally serviced by pollinators and are not equally generalist. Insect visitation rates varied significantly throughout the day, highlighting that sampling of pollinators at one time will result in an inaccurate estimate and usually underestimate the degree of generalisation. The visitor assemblage is not equivalent to the pollinator assemblage, although non-pollinating floral visitors are likely to influence the overall effectiveness of the pollinator assemblage. Given the high degree of variation in both the number of pollinator species and number of pollinator types, I have constructed a model which includes the degree of ecological and functional specialisation of a plant species on pollinators and the variation encountered across different levels of plant organisation. This model describes the ecological or current state of plant species and their pollinators, as well as presenting the patterns of generalisation across a range of populations, which is critical for understanding the evolution and maintenance of the system. In-depth examination of pollination systems is required in order to understand the range of strategies utilised by plants and their pollinators, and I advocate a complete floral visitor assemblage approach to future studies in pollination ecology. In particular, future studies should focus on the role of introduced pollinators in altering generalised plant-pollinator systems and the contribution of non-pollinating floral visitors to pollinator assemblage effectiveness. Comparative studies involving plants with highly conserved floral displays, such as those in the genus Trachymene and in the Apiaceae, will be useful for investigating the dynamics of generalised pollination systems across a range of widespread and restricted species.

Les comportements de dispersion, c'est-À-Dire les mouvements conduisant à des flux de gènes dans l'espace, jouent un rôle majeur dans de nombreux processus écologiques et évolutifs. Les Gastéropodes terrestres sont des hermaphrodites simultanés dont le mouvement est extrêmement coûteux, une combinaison de traits très intéressante pour étudier les liens entre dispersion et autres traits d'histoire de vie. Dans le cadre de cette thèse, nous avons étudié (i) les relations complexes entre dispersion, croissance, reproduction mâle et femelle chez le petit-Gris Cornu aspersum, un escargot anthropophile, (ii) comment la dispersion et le comportement exploratoire de cette espèce varient en fonction de la compétition ressentie et de l'hétérogénéité environnementale, (iii) comment la propension à disperser coévolue avec d'autres traits à l'échelle interspécifique. Cornu aspersum passe par une phase subadulte mâle de durée variable avant de devenir adulte et hermaphrodite. Le comportement de dispersion s'exprime principalement pendant cette phase subadulte, et sa diminution chez les adultes est liée à l'accroissement de l'investissement dans la fonction femelle. Cette espèce disperse de façon très densité-Dépendante : les individus quittent les sites à haute densité et s'installent dans ceux peu peuplés, une stratégie qui facilite la colonisation et la persistance en environnements instables. La propension à explorer augmente en environnements urbains fragmentés, malgré les coûts plus élevés du mouvement. Au niveau interspécifique, dispersion et généralisme sont liés, ce qui rend les espèces spécialistes doublement vulnérables, mais facilite le succès des généralistes en milieux hétérogènes. Cette combinaison de traits a probablement joué un rôle majeur dans la colonisation de nombreux milieux anthropisés par cette espèce à travers le monde. / Dispersal behaviours, i.e. movements leading to gene flow in space, play a key role in many ecological and evolutionary processes. Terrestrial gastropods are simultaneous hermaphrodites and have an extremely high cost of locomotion, a seldom studied combination of traits which makes them very valuable to investigate the links between dispersal and other life-History traits. During this project, we investigated (i) the complex relationships and trade-Offs between dispersal behaviour, growth, male and female reproduction in the anthropophilous brown garden snail Cornu aspersum, (ii) how its dispersal and exploration vary as a function of competition and environmental heterogeneity, (iii) how dispersal ability coevolved with other traits at the interspecific level. This snail presents a male-Biased subadult phase of varying duration before reaching adulthood and hermaphroditism. Dispersal behavior was mostly expressed during this subadult stage, and its decrease in adults was linked to investment in the female function. Brown garden snail dispersal is highly density-Dependant: snails leave crowded sites and settle readily in low-Density patches, a strategy that facilitates colonization and persistence in spatio-Temporally variable environments. Their movement propensity increases in urban, fragmented habitats, despite the higher costs of movement. At the interspecific level, dispersal and ecological generalism are linked in a dispersal syndrome, which makes specialist species doubly vulnerable, but increases success odds of generalists in heterogeneous landscapes . This combination of traits is likely to have played a major role in the successful worldwide colonization of many anthropogenic landscapes by this species.