Les défis posés par des facteurs biotiques – les interactions avec des compétiteurs, des parasites, etc. – jouent un rôle important dans l’évolution des populations, mais sont souvent difficiles à étudier. Dans cette étude, nous avons utilisé le système biologique Artemia dans les salins d’Aigues-Mortes, France, pour étudier le caractère et l’évolution de plusieurs interactions interspécifiques. Le système est particulièrement bien adapté à cette recherche : il est simple, contenant deux espèces d’Artemia, trois parasites fortement prévalents (un helminthe et deux microsporidies), et des microbiota variés ; et beaucoup des interactions du système ont été nouvellement établies, car une des espèces d’Artemia est invasive. Nous avons étudié deux types d’interactions. Premièrement, la présence et l’évolution de l’interférence reproductive entre les espèces native et invasive d’Artemia. Nous avons trouvé que l’espèce invasive, qui est sexuée, subit une interférence sévère en allocation des sexes en présence de l’espèce native et asexuée, mais pas d’interférence en gardiennage de partenaire. Deuxièmement, l’évolution de la spécialisation de deux parasites microsporidiennes qui infectent les espèces d’Artemia. En nous basant sur des données de terrain, des infections expérimentales, et de l’évolution expérimentale, nous avons investigué l’état, les causes, et les conséquences de la spécialisation des microsporidies. Les résultats démontrent que les microsporidies sont spécialisées dans l’utilisation d’une des espèces d’hôte, même si elles sont capables de compléter leur cycle de vie dans chacun des deux hôtes. Cette spécialisation paraît être imposée par les outils précis nécessaires à l’exploitation de chaque hôte ; dans les hôtes non-spécialistes, ils provoquaient de l’exploitation sous-optimale, de la virulence maladaptative, et de l’immunopathologie. En général, ces études suggèrent que les facteurs biotiques imposent des pressions de sélection fortes sur Artemia, auxquelles elles ne peuvent pas toujours répondre facilement. L’importance des facteurs biotiques dans un système qui est autrement dominé par des conditions abiotiques extrêmes souligne l’importance des interactions interspécifiques dans l’évolution. / The challenges posed by biotic factors – interactions with competitors, parasites, etc. – play a large role in the evolution of populations, but are generally difficult to study. In this work, we used the Artemia system in the hypersaline salterns of Aigues-Mortes, France, to study the character and evolution of several interspecific interactions. The system is eminently suited to such studies: it is simple, containing two Artemia species, three highly prevalent parasites (one helminth and two microsporidians), and various microbiota; and many of its interactions are newly-established, because one of the Artemia species is invasive. We studied two types of interactions. First, the presence and evolution of reproductive interference between the native and invasive Artemia species. We found that the invasive Artemia species, which is sexual, undergoes severe interference in sex allocation when in the presence of the native, asexual Artemia, but no interference in mate guarding. Second, the evolution of parasite specialization in two microsporidian parasites infecting the Artemia species. Using field data, experimental infections, and experimental evolution, we investigated the state, causes, and consequences of specialization in the microsporidians. Results consistently indicated that the microsporidians are specialized for one host species, despite being able to complete their life cycle in either host. This specialization appears to be imposed by the precise toolkits needed to exploit each host species; in the non-specialized hosts, these triggered suboptimal exploitation, maladaptive virulence, and immunopathology. Overall, these studies suggest that the biotic factors acting on Artemia impose strong selection pressures, to which they cannot always respond easily. The importance of biotic factors in a system which is otherwise dominated by extreme abiotic conditions underlines the importance of species interactions in shaping evolution.

California's almond industry, valued at $2.3 billion per year, depends on the pollinator services of honey bees, although pollination by other insects, mainly solitary wild bees, is being investigated as an alternative because of recent declines in the number of honey bee colonies. Our objective is to model the movements of honey bees and determine the conditions under which they will forage in less favorable areas of a tree and its surroundings when other pollinators are present. We hypothesize that foraging in less favorable areas leads to increased movement between trees and increased cross pollination between varieties which is required for successful nut production. We use the Shigesada-Kawasaki-Teramoto model (1979) which describes the density of two species in a two-dimensional environment of variable favorableness with respect to intrinsic diffusions and intra- and interspecific interactions of species. The model is applied to almond pollination by honey bees and other pollinators with environmental favorableness based on the distribution of flowers in trees. Using the spectral-Galerkin method in a rectangular domain, we numerically approximated the two-dimensional nonlinear parabolic partial differential system arising in the model. When cross-diffusion or interspecific effects of other pollinators was high, honey bees foraged in less favorable areas of the tree. High cross-diffusion also resulted in increased activity in honey bees in terms of accelerations, decelerations, and changes in direction, indicating rapid redistribution of densities to an equilibrium state. Empirical analysis of the number of honey bees and other visitors in two-minute intervals to almond trees shows a negative relationship, indicating cross-diffusion effects in nature with the potential to increase movement to a different tree with a more favorable environment, potentially increasing nut production.

La communication est essentielle à de nombreuses fonctions vitales en permettant le transfert d’information entre les individus via des signaux. Alors que les fonctions de ces signaux ainsi que les contraintes à leur propagation ont été intensivement étudiées, leur évolution a majoritairement été envisagée à travers le prisme de la dyade constituée par l’émetteur du signal et le récepteur du signal. Pourtant les signaux sont toujours émis au sein de communautés sensorielles et de nombreuses interactions interspécifiques conditionnent les pressions de sélections qui les affectent. Dans cette thèse je me suis intéressé aux liens entre différentes composantes de la composition des communautés et l'évolution du chant et de la couleur chez les oiseaux. Tirant partie des conditions particulières retrouvées dans les îles océaniques, j'ai étudié comment les changements de richesse spécifique, densité de conspécifique et présence de prédateur étaient susceptibles de modifier les comportements de communication et les caractéristiques des signaux émis. Cette approche écologique de l'évolution des signaux est nécessaire pour comprendre leur évolution au sein de communautés sensorielles. Elle m’a permis de mettre en évidence le rôle potentiellement majeur des interférences acoustiques sur la niche sensorielle des espèces ainsi que celui de la prédation sur les changements de coloration en milieu insulaire. Dans le dernier chapitre de cette thèse, je me suis intéressé à un phénomène complémentaire en étudiant les liens entre l’extravagance des signaux et la dynamique des populations au sein des communautés aviaires. Cette thèse produit des éléments forts pour affirmer que la composition des communautés détermine une part des pressions évolutives conditionnant la communication mais qu’à l'inverse, les liens entre caractéristiques des signaux et la composition des communautés sont complexes et difficile à déterminer. / Communication efficiency is related with many essential functions determining the fitness of individuals. Mating signals leads to reproductive isolation, and hence to speciation and a huge amount of studies focused on their evolution. However signals are shaped by environmental properties including the composition of signalling community but this have been understudied. Here, I examined the link between different components of communities’ composition and the evolution of two mating signals: song and coloration in birds. Taking advantage of the particular conditions found in oceanic islands, I studied how species richness, conspecific density, and predator presence were likely to alter communication behaviors and the peculiarities of the transmitted signal. In doing so, I adopted an ecological approach of communication study which I believed to be necessary to understand the evolution of signal within sensory spaces. In the last chapter of this thesis, I focused on a complementary phenomenon by studying how such signals can be deleterious for species decreasing the life expectancy of populations. Overall, this thesis produces additional evidence that the composition of communities partly determines evolutionary pressures conditioning the communication and that conversely, signal characteristic can affect the composition of the communities by determining the viability of certain populations.

This thesis investigates the impact of avian malaria (Haemosporidia) parasites on the outcome of interspecific competition between two closely related bird species, pied (Ficedula hypoleuca) and collared (F. albicollis) flycatchers. I further investigated how variation in timing of breeding, life history strategies and immune competence genes (MHC genes) modulate the fitness effects of malaria parasites in one of the two species i.e. collared flycatchers. Collared flycatchers colonized the Baltic island Öland in the late 1950-ties and has since then been expanding their breeding range while competitively excluding pied flycatchers from the favourable habitats (deciduous forests). I investigated the underlying mechanisms behind this exclusion by combining detailed long-term breeding data with modern molecular genetic techniques identifying both the presence/absence and lineage specificity of haemosporidian blood parasites. I found that the rapid decline of pied flycatchers can be explained by the combined effects of competition over nestling sites, hybridization and haemosporidian infections. Haemosporidian infections have a negative impact on survival of pied flycatcher females but no detectable effect on collared flycatchers’ longevity or reproductive success. This may be due to the fact that collared flycatchers carry (and are potentially exposed to) a higher diversity of parasites than pied flycatchers, which in turn may select for a higher diversity of MHC genes and hence a better overall protection from the negative impact of parasites. Indeed, functional MHC diversity correlates negatively with malaria prevalence among collared flycatchers from Gotland. Moreover, I found that both, malaria infection intensity and immunoglobulin level influences how infected collared flycatchers respond to increased nestling food-demands. The latter results mean that there is variation in allocation strategies (i.e. in resource allocation between reproductive effort and immune competence) within the collared flycatcher population. Hence, this population has the ability to respond to novel selection pressures in terms of optimal allocation of resources into immune functions. In summary, my results show that local parasites may facilitate the expansion of a new colonizer. This is important in the context of global climate change that will probably increase the colonization rate of southern species and lead to novel host-parasite interactions.

Marker-Assisted Verification of Hybrids in Pearl Millet-Napiergrass (Pennisetum glaucum [L.] R. Br. x Pennisetum purpureum Schumach.). (December 2011) Charlie D. Dowling, III, B.S., College of Agriculture and Life Sciences Chair of Advisory Committee: Dr. Russell W. Jessup A high-biomass perennial grass that is directly seeded using existing farm equipment can reduce both planting and overall input costs. Three cytoplasmic male-sterile cms A-lines and four fertile genotypes of pearl millet (Pennisetum glaucum [L.] R. Br.) and one novel pearl millet selection from the Perennial Grass Breeding Program at Texas A&M University were selected to cross with napiergrass (Pennisetum purpureum Schumach.). The pearl millet parents were chosen based on characteristics such as basal tillering, plant height, and days to anthesis. Three napiergrass accessions from the Perennial Grass Breeding Program and the cultivar Merkeron were used as pollinators for these crosses. The cms and fertile pearl millet accessions produced full heads of seed when pollinated with napiergrass. There were a large range of seed sizes and weights for each hybrid family, and the seed were separated into four size classes. The weight differences from the largest to smallest class of seed varied by more than 30%. All of the seed classes germinated, and seed size, in this case, was completely unrelated to the ability to germinate. 100% germination was observed in five seed size classes for both PMN iv hybrids, and 90% germination was observed in three of the eight classes. Essentially all of the hybrid seed recovered from the original pearl millet x napiergrass crosses germinated, but all of the F 1 hybrids were sterile in that none of them produced viable seed. Flow cytometry could not be used to identify the hybrids because the DNA content of pearl millet and napiergrass were essentially the same even though distinct 2C and 4C peaks were seen from the diploid pearl millet. From the 58 EST-SSRs surveyed in the bulked segregate analysis, several were heterozygous dominant and many were homozygous dominant and hemizygous at its particular loci. Seven hemizygous EST-SSRs were identified for Merkeron, seven for PEPU09FL01, eight for PEPU09FL02, and six for PEPU09FL03. These markers are extremely valuable to any pearl millet x napiergrass hybridization program because they provide a means whereby the hybrids can be easily identified. Identification of hemizygous pearl millet markers will also assist in future DNA sequencing and also in a marker-assisted breeding program.

Ecology has been devoted to defining the content of a species’ environment. Defining the extent, or size, of a species’ environment is also pivotal to elucidating species-habitat relationships. More than a home range, this extent integrates an individual’s lifetime experiences with resources, competition, and predators. I theorised that a species’ habitat extent is identifiable from its characteristic spatial scale of habitat selection, which in turn is predicted by body size. I reviewed scale-dependent mammalian habitat selection studies and found that a characteristic scale was typically not identified, but identifiable. Of several ecological predictors tested, only body mass was a significant predictor of the relative size of a species’ characteristic habitat selection scale. Tests of existing data are confounded by differing approaches, so I empirically tested the scale-body mass hypothesis using a standardised survey of 12 sympatric terrestrial mammal species from the Canadian Rocky Mountains. For each species, support for habitat models varied across 20 scales tested. For six species, I found a characteristic selection scale, which was best predicted by species body mass in a quadratic relationship. Occurrence of large and small species was explained by habitat measured at large scales, whereas medium- sized species were explained by habitat measured at small scales. The relationship between body size and habitat selection scale is congruent with the textural-discontinuity hypothesis, and implies species’ evolutionary adaptation to landscape heterogeneity as the driver of scale-dependent habitat selection. I applied this principle to examine wolverine habitat selection, and found that anthropogenic fragmentation of the landscape influences that species’ occurrence in space at large spatial scales. Finally, I contended that the prevailing paradigm equating habitats to resources omits interspecific interactions that are key predictors of a species’ occurrences. I examined habitat selection of martens and fishers in terrestrial environments, and sea otters in marine coastal environments, and tested whether the presence of heterospecifics could explain spatial occurrence beyond landscape structure and resources. In both cases, the presence of heterospecifics explained species occurrence beyond simple resource selection. Interspecific interactions are key drivers of a species’ distribution in space; this is the spatial expression of the concepts of fundamental and realized niches. Body size interacts with landscape structure to determine the scale of a species’ response to its environment, and within this habitat extent, interspecific interactions affect the species’ pattern of occurrence and distribution. / Graduate

No description available.

No description available.

No description available.

No description available.