The problem of malaria in the South, and in other parts of the United States as well, has demanded a considerable amount of research. The greater part of this work has been concerned with the control of the disease by the eradication of the anopheline mosquitoes, and much of such work recently has dealt with the ecological aspects of the problem. Such factors as temperature, humidity, larval food, plant associates, hydrogen-ion concentration of the water of larval breeding places, and many others have been considered. The effects of these various factors on the life and habits of the mosquitoes usually differ for the various species and often differ for a single species in different parts of its range. Since the life of an animal is never entirely governed by a single factor, but by a complex combination of interrelated factors, each area studied offers to some extent a condition peculiar to the location. In the following pages an attempt will be made, after the plotting of fluctuations in the seasonal abundance of the one common Anopheles of the region, Anopheles quadrimaculatus Say, to evaluate the various ecological factors involved in producing these fluctuations. It will be shown that the influence of some of these factors is of very local nature; that is, certain factors may operate in quite different manners and may be of decidedly different importance in a locality where a bayou is the main source of emerging mosquitoes, on the one hand, and in a nearby locality where flooded rice fields are the main source. This survey covered the period of time from March 1932 to January 1934. The area studied included the southern part of the city of Houston and immediate vicinity outside the city limits, and also a rice farming district 15 miles to the west of the city.

In the field of helminthology, the life cycle of an organism not only brings to light the ontogeny of the individual, but also indicates its phylogenetic relationship in the general scheme of taxonomy. By means of the work presented in this thesis leading to the completion of the life history of Monoecocestus sigmodontis, it is hoped that some further contribution has been made to our knowledge of the Anoplocephalidae and their host-parasite relationship. In addition to developmental studies of this tapeworm, we have endeavored to uncover evidence of resistance to infection with this parasite on the part of the definitive host, the cotton rat, Sigmodon hispidus.

Supportive breeding is currently being used in the management of threatened populations, but the effects of this management strategy remain relatively untested. The common house fly, Musca domestica, was used as a model to assess the relative effectiveness of supportive breeding strategies for endangered species management. Captive populations were subjected to one of two captive breeding treatments, and served as the source of migrants for "wild" populations, which received either 5% or 50% of their total census size from captive migrants each generation. One "wild" population treatment served as a control and received no migrants. Measures of fitness were assessed from each population for nine generations. Within the captive populations, analyses found highly significant declines in fitness across generations, with much higher total fitness in the equalized breeding strategy as compared to the structured breeding scheme. Captive population fitness did not prove to be a good predictor of "wild" population fitness after reintroduction, but the inbreeding co-efficient of the captive populations were found to be correlated with recipient "wild" population fitness. This suggests that captive breeding programs with goals of future reintroduction to the wild should focus on overall kinship as opposed to fitness levels and make every attempt to minimize the co-efficient of inbreeding within the captive population. "Wild" populations that received low levels of ideally bred captive migrants performed significantly better than control populations, which received no outside migration. No other "wild" population treatments were found to differ significantly from the control populations, which may be due in part to the small population sizes that limited the effects of selection and migration and strengthened the influence of factors such as genetic drift and inbreeding. It is likely that the constraints of small population size led to the control populations having the lowest overall fitness. Based on this study, it does not appear that sweeping generalizations can be made about the effects of migrant breeding treatment and level of migration on wild populations. Further research is warranted before supportive breeding programs are implemented for a broader range of threatened and endangered species.

The ability of subsurface microbial populations to degrade organic contaminants is affected by nutrient availability. A study was performed to measure the change in microbial ecology of a weathered JP-4 jet fuel contaminated site (Eglin Air Force Base, Florida) over the course of a nitrate-based treatment in terms of heterotrophs, JP-4 degraders, oligotrophs, biosurfactant producers, bioemulsifier producers, and predators. Microbial numbers increased and species diversity decreased in the nitrate-amended site significantly more than in background areas. The surfactant producing potential of native microbial communities decreased significantly with nitrate addition. Bioemulsification capacity of these communities was slightly lowered with addition of nitrate. Aerobic predators decreased over the course of the experiment, while microaerophilic predators increased significantly. Due to fluctuations in measured JP-4, no conclusions could be drawn about the success of nitrate addition as a remedial enhancement technique at this site.

The theory of kin selection is central to the understanding of social evolution. Recent theoretical work suggests a limitation on the action of kin selection in structured populations. The first such limit involves a specialized population structure, termed "budding viscosity," common to social insects, in which new groups are formed by fission with no individual dispersal. An argument based on the separation of kin selection dynamics into among and within group components suggests that kin selection cannot operate in this structure. However, stochastic computer simulations show that random variation among daughter groups can supply the needed among-groups variation and allow kin selection to proceed. The second limit on kin selection involves simple population viscosity, in which individuals disperse limited distances and so are related to their neighbors. Altruism toward neighbors, favored by kin selection, is opposed by local competition. Computer simulation confirms this limitation and shows that some form of specific kin recognition is required to favor the evolution of altruism by kin selection. All applications of kin selection require a measure of genetic relatedness; a computer program for calculating this statistic from genetic data on natural populations is described.

Methane emissions from flooded rice paddies are important contributors to the increasing atmospheric concentrations of methane, a potent greenhouse gas. With an increased need for rice agriculture to feed the growing global population, there is a need to develop methods that reduce methane emissions from rice paddies without adversely affecting grain yield. Two potential mitigation strategies were examined in this study: water management and cultivar choice. Previous studies indicate that floodwater management is a promising mitigation tool, with mid-season field drainage significantly reducing methane emissions. A variety of soil parameters, methane emissions, and soil porewater acetate concentrations were measured in outdoor pot and field water management studies. Acetate received particular consideration as it is a major precursor of methane formation within anaerobic soils. Field drainage caused rapid oxidation of the soil, with a sharp reduction in soil acetate concentrations, methane production, and methane emission rates. Evidence of drainage induced substrate depletion is presented as a possible mechanism responsible for the reduced methane production and emission after field drainage. Intervarietal differences in methane emission rates from rice have also been reported in previous studies. Methane emission rates and soil acetate concentrations were compared for a high emitting and a low emitting cultivar of rice. Significantly more soil acetate was present in the high emitting cultivar than the low emitting cultivar during the vegetative stage of plant growth. These results suggest that differences in methane emission between varieties of rice are the result of different methane production rates, not differences in methane transport processes. The different production rates are the result of differences in root carbon loss between the two cultivars. Neither of these strategies had an adverse effect on grain yield. The results strongly support the use of floodwater management and cultivar choice as methods to mitigate methane emissions from rice paddies.

Genetic data was obtained from a colony of Parachartergus colobopterus using DNA microsatellites. A colony cycle referred to as cyclical oligogyny is believed to account for the high relatedness in this polygynous species. The genetic data was analyzed to support the presence of cyclical oligogyny and determine some of the specific mechanisms behind it. Specifically, queen reduction, increasing reproductive dominance, sexual specialization by queens, and maternity of males (worker vs. queen) were examined. There was evidence for queen reduction occurring in this colony. To the contrary, no support was found for either increasing reproductive dominance or sexual specialization among the queens. It appears that the queens produced all of the males in this colony. This concurs with a worker preference for queen laying of the males that was seen in relatedness estimates.

I used sapling demographic data to investigate the relationship between shade tolerance and parameter estimates of a mortality-growth model and a height-diameter model. The study site is at Wier Woods, a mesic forest in southeast Texas. The results show that species order for probability of mortality at zero growth corresponds closely to the standard shade tolerance classification: the probability of mortality at zero growth decreases as shade tolerance rank increases. Also, the probability of mortality decreases rapidly as growth increases for shade-intolerant species, while showing little variation for shade-tolerant species. Therefore, this study provides strong support for the assertion that the mortality-growth relationship is a key life-history characteristic that determines shade tolerance. The results of a linear regression of height against DBH show that shade-intolerant species have steeper slopes than shade-tolerant species. This implies that a trade-off of photosynthate allocation between height growth and diameter growth may be an additional mechanism that influences shade tolerance.

Several transitions to higher levels of biological organization have punctuated the history of life. These transitions occur when cooperative alliances lead to the integration of non-identical partners into more complex wholes. Yet there is inevitable conflict within these cooperative alliances. In the following chapters I investigate reproductive conflicts of interest between cooperators within insect societies and chimeric multicellular organisms. In the first chapter I show that in the tropical wasp, Parachartergus colobopterus, workers use aggression toward totipotent, emerging females to influence the reproductive future of the latter. By doing this workers resolve conflict over who reproduces in accord with their collective interests. In the second chapter I show that environmental heterogeneity can affect the outcome of conflict between co-aggregating clonal lineages of Dictyostelium discoideum. This helps account for the coexistence of cheaters and victims in natural populations of D. discoideum.

Invasive species, fire suppression and nutrient deposition, as distinct disturbance factors, have altered Texas prairie communities. Arthropod diversity, abundance, and community composition may be modified by these factors either directly or by changes in plant community structure. Because arthropods provide essential ecosystem services and represent a large proportion of terrestrial biodiversity, understanding the responses of arthropod communities to disturbance is the central theme of this doctoral thesis. Land managers commonly utilize fire to control woody species encroachment into prairies and anthropogenic nutrient deposition increases plant productivity. The responses of arthropods to fire and fertilizer manipulations were examined. Fire maintained arthropod diversity by limiting woody plant cover. Path analysis indicated fertilization decreased arthropod diversity by promoting woody plant invasion. Direct negative effects of fire on the arthropod community were small compared to the indirect, positive effects. Arthropod abundance and species richness on the invasive species Chinese Tallow Tree (Sapium sebiferum) were compared to arthropods on three native tree species: Silver Maple (Acer saccharinum), Sycamore (Platanus occidentalis), and Sweetgum ( Liquidambar styraciflua). Although arthropod community composition differed on Sapium, species richness and abundance were similar to levels on native trees. Sapium experienced less chewing, fungal, and mining damage and supported relatively abundant predators and detritivores whilst there were relatively fewer herbivores. These observations are in accord with the Enemies Release Hypothesis that predicts low herbivore loads may contribute to Sapium's invasive success. When Sapium was compared to native plant dominated habitats, predators and detritivores were again relatively abundant while total arthropod diversity was comparatively low. This implies that Sapium has not acquired an insect fauna comparable to native plants in Texas. Insect assemblages on Sapium were examined along a geographical gradient, representing time since introduction. Sapium trees in Florida and Georgia (present longer) had higher insect loads compared to those in Louisiana and Texas (more recently introduced), but species richness did not differ. Herbivore and omnivore abundance and species richness were higher where Sapium has been present longer. This suggests that time since introduction is an important factor constraining herbivore diversity and abundance. Accumulation of herbivores may limit Sapium populations in the future.