Increased forest growth in response to rising atmospheric concentrations of CO2 may mitigate a portion of fossil fuel emissions, especially if carbon is sequestered in longlived biomass or soil pools. Greater carbon uptake under elevated atmospheric [CO2] in forested ecosystems may facilitate the production of small diameter (i.e. “fine”) roots used for nutrient acquisition. Increased fine-root production in forested ecosystems may affect soil carbon storage and nitrogen cycling because fine roots live and die in the span of a year. My dissertation research took advantage of a long-term, on-going Free-Air CO2-Enrichment experiment in a sweetgum (Liquidambar styraciflua L.) forest stand at Oak Ridge National Laboratory to investigate the causes and consequences of increased fine-root production under elevated [CO2]. To examine the premise that N limitation was the cause of increased fine-root production in the CO2-enriched sweetgum stand, I fertilized plots in an adjacent sweetgum plantation with 200 kg ha-1 of N as urea. The relative C flux to wood production that I observed in the fertilized treatment is consistent with the premise that increased root production in the adjacent FACE experiment is in response to N limitation. To examine the consequencesof increased fine-root production under elevated [CO2], I: (1) quantified fine-root biomass and N inputs at several soil depths using a long-term minirhizotron data set combined with continuous, root-specific measurements of root mass per unit length and [N], and (2) allowed fine roots grown under current and elevated [CO2] to decompose in a common garden experiment by modifying existing litterbag methodology. I found that C and N inputs via root mortality were doubled under elevated [CO2], and half of the inputs were below 30 cm soil depth. However, CO2-enrichment had no effect on fine-root chemistry or decomposition rate, and therefore more root detritus may be incorporated into long-lived soil organic matter under elevated [CO2]. Quantification of the effects of elevated CO2 on the fate of a greater quantity of fine-root detritus, especially at depth in the soil, will provide critical information needed for predicting processes such as long-term soil C storage and N cycling in response to environmental change.

Phenotypic correlations between traits are thought to reflect genetic correlations. However, traits related to a central function, like reproduction, need not all be genetically correlated. Identifying genetic correlations between behavioral traits can help identify the evolutionary relationship between different behaviors, as well as provide initial information on the number of genes involved in behavioral variation and the rates and direction of evolution. This body of work describes the phenotypic and genetic relationship between mating traits in the parasitoid wasp genus Nasonia. Chapters 2 and 3 describe behavioral differences among the three species of Nasonia. Two of the species, N. vitripennis and N. giraulti, show extreme differences for several behavioral traits. Nasonia vitripennis females mate almost exclusively after emergence from the host puparium and show a strong propensity to remate, and males of this species show strong site fidelity after emergence. Conversely, N. giraulti females mate almost exclusively inside the host (called within-host mating; WHM), show a low frequency of remating, and males show no site fidelity and disperse after emergence. The third species, N. longicornis, is similar to N. vitripennis for male site fidelity, but shows between line variation for WHM and female remating. I used the between line variation to create divergent recombinant inbred lines (RILs), 24 of which were screened for ten different behavioral traits (Chapter 4), including WHM, male site fidelity, remating, components of male courtship, and male and female developmental traits. Three behaviors were genetically correlated; WHM was positively correltated with remating frequency and remating frequency was negatively correlated with male courtship duration. The relationship between WHM and remating frequency could not be explained in terms of timing of female receptivity. However, remating frequency was directly correlated with when females became sexually receptive as early female receptivity was found in lines with high remating frequencies. I also address the evolution of these behaviors in an ecological context (Chapter 5). WHM is thought to have evolved as a byproduct of selection against hybridization in nature, and the ecological distribution of Nasonia,a both within nests and host pupae, is consistent with this hypothesis.

Biological invasions threaten biodiversity, and understanding the factors that influence a community’s susceptibility to invasion informs both management of invasive species and conservation of biodiversity. The biotic resistance hypothesis postulates that communities with greater number of competitors, predators and/or pathogens will resist biological invasions. The underlying mechanism of biotic resistance, in the realm of competition, is that in species-rich communities harbor fewer open niches for introduced species to colonize therefore decreasing the probability of invasion. My dissertation research evaluated the role of native species diversity, as well as other biotic, abiotic and landscape factors shaping exotic species richness at multiple spatial scales in an old-field ecosystem. I found that old-field communities with greater native diversity are more invasible, having greater exotic richness, at multiple spatial scales. Additionally, I investigated the role of native species diversity, biotic and abiotic factors shaping patterns of abundance by an invasive species, Lespedeza cuneata, at multiple spatial scales. Lespedeza is a rank one invasive species in several U.S. states including Tennessee due to its potential ecological impacts. I found Lespedeza abundance to be negatively associated with the abundance of dominant species, as well as with the abundance of other N-fixing species (mostly native to North America). I then conducted two field experiments which addressed the role of dominant taxa identity, in particular, the genera Solidago and Verbesina affecting old-field community structure and invasibility by Lespedeza (i.e. establishment). The second experiment investigated the role of resource availability structuring an old-field community and early establishment by Lespedeza. Overall, my findings suggest that native species diversity, abiotic and landscape factors influence multiple spatial scales.

An introductory section provides a review for the role of bats as reservoirs of infectious diseases, and highlights the rationale for investigations of host life history, ecology, and evolution in regard to bat epizootiology. Chapter 1 presents field investigations of life history, ecology, body condition, and rabies virus neutralizing antibody seroprevalence in six natural colonies of Brazilian free-tailed bats from caves and bridge roosts in Texas. Chapter 2 presents a replicate field investigation of life history, ecology, body condition, and rabies virus neutralizing antibody seroprevalence in six natural colonies of Brazilian free tailed bats from bridges and bat house roosts in Florida and Georgia. Chapter 3 evaluates the relative influence of local and landscape factors on life history, ecology, body condition and rabies virus neutralizing antibody seroprevalence in Brazilian free-tailed bats in the southern United States. Chapter 4 describes the role of host population genetic structure in big brown bat rabies virus epizootiology, and describes comparative pathogenicity of two big brown bat rabies virus isolates across several captive experimental infection studies. The information presented has been used in the development of individual, population, and metapopulation models of rabies virus epizootiology in bats.

Patterns of geographic variation in body size and cell size have long fascinated biologists, and climatic variables have often been considered to explain such patterns. Environmental temperature can profoundly influence the phenotype, including body size. of ectotherms, and reptiles in particular. This dissertation presents four studies that examine how temperature shapes morphology on developmental and evolutionary timescales in the green anole lizard, Anolis carolinensis. The first three studies examined variation in and phenotypic plasticity of cell size and body size through laboratory experiments using eggs and juveniles from wild-caught females in five populations of A. carolinensis. The fourth study examined geographic variation in body size and cell size in 19 wild populations across the species range. Temperature-induced plasticity in cell size but not initial hatching size was demonstrated. However, subsequent differences in growth rates among juveniles reared in a common laboratory environment indicated a latent effect of incubation temperature on body size. Sampling of body size and red blood cell size from four eastern populations in the range suggested a latitudinal trend in body size and cell size. Rearing of offspring in a common environment indicated differences among populations in juvenile and, potentially, embryonic growth rates contributing to divergence in adult body size. Extended sampling of body size and cell size from 19 populations throughout the range, however, showed that inclusion of Florida populations heavily skewed geographic patterns because of the smaller body and cell size of anoles in the peninsular state. Exclusion of these populations revealed a negative relationship between latitude and both body size and muscle cell size, and no geographic trends in red blood cell size.

The purpose of this study was to investigate geographic and temporal diversification patterns in the barcheek darter species group. Specifically, my two questions were “Is there geographical structure of alleles or haplotypes within currently recognized species that is suggestive of unrecognized, or cryptic, species diversity within the clade?” (geographic diversification pattern) and “How old are inter- and intraspecific divergence events in the evolutionary history of the clade?” (temporal diversification pattern). A three gene dataset from 159 barcheek individuals of two mitochondrial coding regions, cyt b and ND2, along with a nuclear intron, S7, was analyzed using parsimony and Bayesian phylogentic methods to answer the first question. Divergence times were estimated using fossil calibration of this Bayesian phylogeny in order to answer the second question. Three barcheek species were found to have significant population structure suggestive of cryptic species diversity. E. basilare in particular was recovered as being comprised of five reciprocally monophyletic clades endemic to each of the major tributaries to the upper Caney Fork River. Inter- and intraspecific divergence events were found to be relatively old in the clade, nearly all pre-Pleistocene, with a crown node age estimated at 12.68 mya. These results are discussed in light of the present understanding of the tempo of diversification in the darter radiation.

Piperaceae is unique among Piperales because it is the only tetrasporic group in the order and a great deal of diversity in the ontogenetic trajectories of the female gametophyte is found in its genera. The evolutionary developmental origin of the sixteen-nucleate female gametophyte remains unclear in the family until now. In Piperaceae, Manekia has been identified as sister to Zippelia, and this clade is sister to core Piperaceae (Piper, Peperomia). This research is the first attempt to understand the development of the female gametophyte of Manekia naranjoana in order to provide critical data on the origin of tetrasporic development in the family. Several aspects of the floral biology and phenological events taking place in the ovary, the flower and the inflorescence were explored. Manekia has a tetrasporic, sixteen nuclei female gametophyte, that is being produced from a single archesporial cell. The egg apparatus is located at the micropylar end of the female gametophyte. It is constituted of three cells, two synergids and an egg. The central cell nuclei consist of two nuclei, one from the micropylar end and the other one from the chalazal one. The eleven remaining nuclei are arranged toward the chalazal pole of the female gametophyte, and sometimes fuse. This description corresponds mostly to the Drusa type. But Penaea type is also occasionally reported for first time in this study for the genus. Manekia and Zippelia share a similar structure of the female gametophyte with a total of 16 nuclei, and two nuclei in a central cell suggesting a triploid endosperm. The transition from monosporic to tetraporic female gametophyte development can be explained through the theory of modular construction and several kind modifications in the ontogenetic trajectories. Heterochronic and heterotopic changes, additions, and deletions in the development of the female gametophytes reflect evolutionary histories of the particular taxa implicated. A great deal of plasticity in terms of lack of polarity and nuclear fusion of antipodals was found in the chalazal module of the female gametophyte of Manekia.

Agroecosystems produce insects in great abundance, with episodic irruptions in time, and patchy distributions in space. In the industrial scale agroecosystems of south-central Texas, millions of Brazilian free-tailed bats (Tadarida brasiliensis) consume these insect pests. In the past decade, growers in Texas have planted transgenic Bt (Bacillus thuringiensis) crops on a large scale, which may reduce populations of target insect species by up to 95%. To investigate potential impacts of this evolving agricultural landscape on insectivorous bats, I examined the response of foraging bats to emergences of insects from replicate Bt and non-Bt fields of corn and cotton in the Winter Garden region of south-central Texas. I quantified bat activity using ultrasonic detectors deployed simultaneously in Bt and non-Bt fields. I measured insect activity using pheromone traps and video imaging. Professional crop consultants scouted fields to determine dates of insect emergence. We recorded 92% more echolocation calls, 62% more AnaBat files, and 257% more feeding buzzes over agricultural fields during periods of local insect emergence. During these insect emergence periods, bat activity was correlated with the abundance of moths and negatively related to the distance between foraging sites and roosting sites. In general, Bt crops did not have a measurable impact on the activity of bats except at one site where moths were more abundant over non-Bt crops versus Bt crops. Foraging bats showed a delayed response to moth abundance, which is consistent with the hypothesis that roosts serve as information centers that enhance foraging efficiency. The ability of millions of bats to exploit localized patches of prey across a large area provides further evidence of their pest control service. This economically important pest control service extends beyond growers in Texas, as the populations of moths produced in agroecosystems in Texas influence agricultural production on a continental scale.

To assess changes in coccinellid communities subsequent to the introduction of two non-native species, Coccinella septempunctata and Harmonia axyridis, ladybird numbers were monitored over a 20 year period at Mt. Saint Helens, Washington and in three years between 1996 and 2004 in southwestern Virginia. Surveys conducted at Mt. Saint Helens included pre- and post- invasion years for both non-natives. At Mt. Saint Helens, C. septempunctata and H. axyridis both increased in abundance, accompanied by declining numbers of the native ladybird Adalia bipunctata at one of the two Washington sites and of the native ladybird Coccinella transversoguttata at both sites. Declines in these two native ladybirds are strongly correlated with increases in the two introduced species. Given the long study period at Mt. Saint Helens, the declines in these two natives appear to be real trends. Further research is required to determine if the introduced species have indeed been the direct cause of the declines, and to find the mechanisms of interactions. The arrival of C. septempunctata to Virginia predated the first year of this study likely by several years. Harmonia axyridis was detected in Virginia by 1993, three years prior to the first study year in this state. In Virginia, only one introduced species, H. axyridis, showed an increase during the study and this was at one site only. This increase was not accompanied by declines in native species. In fact, the native Coleomegilla maculata also increased at the site during this period. Lack of evidence for declines in native species in Virginia may simply indicate that native species were not affected by the two introduced species, or it may reflect lack of power in the data to detect changes. Alternatively, any changes to the ladybird community may have occurred prior to the start of this study.

Rare species with fragmented distributions often exhibit reduced levels of genetic diversity within populations. However, life history traits such as long lived perennial habit and outcrossing mating system, are associated with high levels of within species genetic variation being partitioned within populations. Schisandra glabra (Schisandraceae) is a rare basal angiosperm with a fragmented distribution across the southeastern US and in a disjunct population in cloudforest of Mexico. The species’ clonal reproduction by rhizomes, confounds the delineation of genetically distinct individuals in the field. The patterns of genetic diversity and clonality in 10 populations of S. glabra were investigated using AFLP markers. I found a surprising number of distinct genetic individuals in the two populations sampled on 3m grids, with 31 unique genotypes out of 42 samples at Wolfpen Creek, KY, and unique genotypes in all 48 samples from Panther Creek, GA. AMOVA of 237 individuals from 10 populations revealed that the largest portion of the genetic variation is found within populations (58.0%; P<0.0001), and 27.7% (P<0.0001) of the genetic variation is partitioned between the US and Mexico S. glabra populations. Population structure was also detected between the US and Mexico populations, but no structure was detected between the majority of the US populations. The genetic differentiation of the disjunct population in Mexico, may be the result of a Pliocene or Miocene vicariance hypothesized for many species with similar distributions. The high levels of genetic diversity found within populations are evidence of historical gene flow between the US populations, and the preservation of genetic diversity by the long lived species in its present fragmented distribution.