Twelth Annual Biology Student Colloquium

Friday, March 30, Room 116 Supple Science Building, time TBA.

List of presenters and abstracts:

In 2005, a team of researchers from Cornell University announced the “rediscovery” of the Ivory-billed Woodpecker (Campephilus principalis) in eastern Arkansas. Evidence supporting this claim included “double raps” recorded by autonomous recording units (ARUs) in White River National Wildlife Refuge. Similar evidence from the Choctawhatchee River of northwestern Florida was presented the following year. I co-authored a manuscript presenting data comparing double raps produced by wing collisions from an aerial Gadwall (Anas strepera) flock to double raps recorded by ARUs in Arkansas. Similarities in amplitude ratios, peak-to-peak times between raps, and auditory quality between double raps from ARU recordings and our Gadwall flock recording illustrate the ability of flying ducks to produce sounds easily mistaken for the territorial drums of Campephilus woodpeckers. ARU double raps suggesting the presence of an Ivory-billed Woodpecker(s) in a region where wintering waterfowl is abundant should be carefully considered in the continued search for this species.

Speciation is a product of the evolution of reproductive isolation between divergent lineages. This reproductive isolation is accomplished by various pre- and postzygotic isolating mechanisms which may not be “complete,” but act in concert to prevent gene flow between species. Prezygotic isolation has been studied extensively in few plant species, including the Louisiana irises. It is apparent that habitat divergence, reproductive asynchrony, and pollinator syndromes are not successful in the prevention of hybridization between species of this complex. I examined the fitness of Iris brevicaulis, I. fulva, F(1), and backcross hybrids in order to determine the strength and relative “importance” of postzygotic isolation in this species pair. Hybrids exhibited a range of fitness values. The mean fitness value for each backcross population was either equal to the parental values or higher than one parental mean. This suggests that reproductive isolation in this system is primarily attributed to pre-zygotic isolating mechanisms.

Michele A. Gaston
Mentor/Research Advisor: Dr. Michael R. J. Forstner

Prior investigations into the variation of advertisement calls of male Acris crepitans in Texas have demonstrated that significant spectral and temporal variation exists across the range of this species in the state, and suggest that this variation follows an east-west cline. This study sought to determine if clinal variation in call characteristics can be detected at a fine geographic scale and whether variation in morphological characters follows a similar geographic pattern. Spectral and temporal aspects of advertisement calls were analyzed from three adjacent river basins in central Texas. Morphological data were collected for most of the individuals recorded for acoustic analysis. Analysis of variance returned significant results for a number of behavioral and morphological characters, with some exhibiting the previously reported clinal pattern. Distributions of some characters were bimodal across the range sampled and within geographically discrete sample sites, suggesting disruptive selection on certain traits. Multivariate methods were applied to further explore patterns of covariation among behavioral and morphological characters and their geographic distribution. Results are interpreted in the context of theories regarding species-specific mating signals and in light of ongoing uncertainties about the subspecific groupings within this species.

Mercury (Hg) contamination of aquatic ecosystems is a widespread environmental problem in North America and the world. High levels of Hg, especially its organic form (methylmercury) can cause chronic health problems, even leading to death. Thus, determining the extent of Hg contamination and understanding the influence of factors which facilitate Hg contamination is fundamental to the amelioration of Hg environmental contamination. Once deposited in aquatic environments, inorganic Hg can be converted to methylmercury (MeHg) and ingestion of MeHg contaminated food items is often the main pathway for MeHg uptake. Small-bodied prey fish which forage on periphyton and aquatic invertebrates are important in the transfer of Hg to larger piscivorous fish and wildlife. Small-bodied prey fish that dominate the Rio Grande fish assemblage consistently exceed EPA wildlife Hg consumption criteria (>77 ppb) which suggests potential Hg contamination issues for the lower Rio Grande drainage. Preliminary assessment of spatial patterns suggest that there may be substantial variation in the contamination of Hg in Rio Grande drainage food webs related to abiotic conditions which favor Hg bioaccumulation. MeHg will bioaccumulates in tissues, leading to MeHg biomagnification in food webs. Therefore, large predatory fish, and piscivorous birds and mammals at the top aquatic and aquatic-linked terrestrial food webs can accumulate high concentrations of MeHg in tissues. My study examines fish, insect and sediment Hg concentration along the Lower Rio Grande, Texas and its tributaries in order to examine: (1) whether or not Hg concentration in Rio Grande fishes exhibit spatial variation, (2) if Hg concentration is comparable in functionally similar fishes (i.e., same trophic level), and (3) detect whether or not there are any patterns of Hg distribution related to abiotic and/or biotic factors that influence Hg bioaccumulation and biomagnification in food webs. Preliminary data finds that small-bodied likely-piscivorus fish (Astyanax mexicanus) exceed EPA wildlife criteria when averaged across all sites (181.7 ppb (SD ± 133.7), whereas small-bodied invertivores, such as cyprinids (Notropis sp. and Cyprinella sp.), have MeHg concentrations of 139.1 ppb (SD ± 83.2) and 81.7 ppb (SD ± 69.7), respectively.

Auxin serves as one of the most important plant hormones that regulate plant growth and development. It regulates many aspects of plant growth such as apical dominance, lateral root elongation, branching, vascular differentiation, fruit development, and embryo development. How auxin regulates these processes at molecular level is not completely understood. To understand the mechanisms through which auxin acts we have collected a number of Arabidopsis mutants that are resistant to the auxinic herbicide picloram. Here we describe the characterization of two mutants, pic82 and pic83. Both mutants are resistant to picloram but sensitive to another auxinic chemical 2,4-D. Genetic characterization indicates that pic82 is a semi-dominant mutation. Our initial efforts to map pic83 indicate the mutant gene is located in chromosome 2 between SSLP markers F13M22 and T2P4. Current studies are underway to identify and clone the genes responsible for these mutations.

The objective of this research is to determine changes in gene expression levels between day and night in zebrafish eye using microarray technology. Sampling was performed at midday in light adapted fish and midnight in dark adapted fish with the midday sample used as a control. Results using triplicate samples reveal 313 genes which are differentially regulated under these two conditions (p value <0.05). Among these 313 genes, 56 showed a 2-fold or greater change expression with 21 up regulated in dark and 35 down regulated in dark. We selected 2 genes for further analysis. Among these genes we found that expression of zgc:92682 (codes for motor protein) was up-regulated 2-fold in the dark. In contrast, expression of the phosphodiesterase zgc:73310 was decreased more than 50% in dark. Gene expression will be further analyzed by quantitative PCR and in situ hybridization.

The phyto-hormone auxin is vital for the plant growth and development throughout its lifecycle. The most abundant natural auxin is Indole-3-acetic acid. At molecular level auxin can rapidly modulate the expression of auxin responsive genes by degrading a family of negative regulators named Aux/IAA proteins. Besides IAA, there are several naturally existing auxins as well as many synthetic auxins. While these chemicals with auxinic activities are structurally different, they exert similar effects on gene plant growth. Do all synthetic auxins function in the same signaling pathway? Our initial results suggest that at least upstream components of the signaling pathway/s may be unique for picloram, an auxinic herbicide. To identify new genes that are involved in picloram specific signaling, we screened 70,000 EMS mutagenized Arabidopsis seedlings. So far we have isolated 30 mutants. Among those, pic11 mutant is resistant to both Picloram and 2, 4-D. The most prominent feature of pic11 is the lack of lateral roots. pic11 seedlings produce no lateral roots on ATS or in response to 2, 4-D, and produce only few lateral roots in response to picloram. Further pic11 mutation produces a characteristic shoot phenotype that includes defects in leaf, inflorescence, and flower morphology. By using SSLP markers dominant pic11 mutation was mapped to Chromosome 5 north arm of Arabidopsis thaliana genome, and recently we identified the mutant gene as IAA28. Work is in progress to understand the function of IAA28 in auxin response in plants.

It is recognized that organisms can have important impacts on physical and chemical processes occurring in ecosystems. These so-called ecosystem-engineers are defined as organisms that directly and indirectly modify the availability of resource and maintain alter or create habitats. Ecosystems-engineers also have the ability to affect nutrient cycling, energy flows and trophic linkages. In the San Marcos River, armored catfishes in the family Loricariidae (Hypostomus sp.) were introduced to the river and now represent ~50% of the upper river ichthyomass. Hypostomus feed mainly on detritus and attached algae and redistribute large amounts of benthic sediment. The invasion of Hypostomus into the San Marcos River may affect periphyton and organic matter dynamics. In addition, the big claw river shrimp (Macrobrachium Carcinus) resides within the upper San Marcos River and is the largest freshwater shrimp in the United States (> 1 kg wet mass). Due to their substantial size and omnivorous foraging behavior, M. carcinus may play an important role in directly affecting organic matter and algal dynamics. To examine the ecosystem-engineering effects of Hypostomus and Macrobrachium on primary production, nutrient cycling, and ecosystem functioning, we conducted a replicated stream channel experiment consisting of a 2 x 2 factorial design (e.g., presence and absence of catfish cross-classified with the presence and absence of shrimp). Hypostomus significantly reduced periphyton biomass, while shrimp did not. Both catfish and shrimp reduced the accumulation of organic and inorganic matter in stream channels. These results suggest that armored catfish and shrimp exhibit different effects on the San Marcos River community, but they both may have large impacts on the organic matter dynamics of the San Marcos River.

Auxin is a pivotal plant hormone that plays a major role in plant growth and development. While Indole-3-acetic acid (IAA) is the major natural auxin found in plants, there are many synthetic chemicals with auxinic activity. 1-Naphthylacetic acid(1-NAA), 2, 4-dichlorophenoxyacetic acid (2, 4-D) and Picloram are some examples for synthetic auxins. Of these 2, 4-D and picloram are commonly used as herbicides in agriculture. While both natural and synthetic chemicals exhibit similar effects on plants, these chemicals are structurally different. Whether these structurally different chemicals function through similar molecular mechanisms are not known. Initial work in our laboratory indicates that picloram may function differently form other commonly known auxins. To identify components that are specific for picloram, we are using a forward genetics approach with Arabidopsis mutants generated by Ethyl methanesulfonate (EMS).

The objective of the current research is to characterize an Arabidopsis mutant, pic54 that shows altered response to auxin and to locate and clone the mutant gene by map based cloning. pic54 shows growth and developmental defects such as lack of apical dominance, small siliques, altered positioning of siliques, small stature compared to wild type plants. Subsequent dose response experiments done on pic54 revealed that the mutant has a high resistance to 2, 4-D and a slight resistance to Picloram. By using the positional cloning technique the mutant gene was mapped to the north arm of chromosome V between the annotation units MRG7 and F21J6. Future research will focus on fine mapping of the mutant gene, molecular and functional characterization of the PIC54.

The present study was carried out to examine the chemopreventive effects of clotrimazole on the hamster cheek pouch carcinogenesis model. This model of oral carcinogenesis has been widely used in chemoprevention studies. Clotrimazole is a synthetic antimycotic drug that has been used for several decades to treat yeast and fungal infections. In recent years it has been confirmed to possess anticancer activities. Benzo[a]pyrene (B[a]P) is a ubiquitously distributed environmental carcinogen. Using B[a]P and a complete carcinogenesis protocol we have been able to produce pre-cancerous (leukoplakia-like) lesions at 16 weeks of treatment and squamous cell carcinomas at 20 weeks of treatment. These lesions are primarily endophytic and resemble those that develop in human oral mucosa.
In the present study we are examining the long-term chemopreventive effects of clotrimazole on the hamster cheek pouch carcinogenesis model. The right cheek pouch of each male Syrian Hamster was treated topically 3 times per week with 50mM clotrimazole followed 30 minutes later by 2% B[a]P. The animal were sacrificed at 32-weeks and the right cheek pouches were harvested for histological and immunohistochemical evaluation. Upon histological evaluation the lesions were classified as pre-cancerous lesions, carcinomas in situ, or squamous cell carcinomas. The clotrimazole treated animals showed a 30% reduction in pre-cancerous lesions, a 55% reduction in carcinomas in situ, and an 80% reduction in squamous cell carcinomas when compared to the B[a]P-treated positive control group. Immunohistochemistry was performed to visualize proliferation, p53 protein accumulation, and apoptosis. The results were quantified and the clotrimazole group had a 40%, 58%, and 58% reduction, respectively, compared to the positive control group.
These results indicate strong, dramatic chemopreventive activities carried out by the synthetic compound clotrimazole. Furthermore, this experiment demonstrated that clotrimazole is a potent inhibitor of squamous cell carcinomas in the oral mucosa of this hamster cheek pouch model.

Auxin is a major plant hormone that regulates many aspects of plant growth and development. Auxin controls plant growth by altering the expression of many genes. One family of auxin responsive genes is the SAURs (small auxin up-regulated RNAs). There are over 70 known genes that make up the SAUR gene family with some of its members sharing the same functions. Transcript levels of SAUR genes increase in response to auxin, but their role in auxin response in plants, however, still remains unclear. Recently it has been proposed that some SAUR proteins are involved in the Ca2+/calmodulin mediated processes in plant cells.
To investigate the functions of SAUR genes on plant growth and development, we use a reverse genetics approach. We have selected a group of SAUR genes for cloning and identification of their roles in plant development. The six SAUR genes that have been chosen are the following: At4g34750, At2g28085, At1g19840, At1g75590, At3g09870 and At5g10990. To track these SAUR proteins in plants, we clone each gene into pBluescript plasmid vector, and add a small protein tag known as myc. Then this myc-tagged version of SAUR gene is subcloned into a binary vector for transformation of Arabidopsis plants using Agrobacterium. Additionally, we plan to use RNAi technique to silence this family of SAUR genes to characterize their roles in Arabidopsis. The present study provides a foundation for the characterization of the SAUR gene family.

Mercury (Hg) is a pollutant of concern worldwide. Methylmercury (MeHg), an organic form, is a potent neurotoxin and has been linked to health epidemics in Japan, Iraq, Pakistan, and Guatemala. While these epidemics were caused by exposure through industrial and agricultural usage, Hg is naturally present in the environment at low levels and can be transformed into highly toxic MeHg through natural biological processes. Transformation of Hg to MeHg usually occurs in aquatic ecosystems, and humans are typically exposed through the consumption of fish which have bioaccumulated MeHg. Historically, a majority of research on Hg in lentic systems has been performed on lakes and reservoirs in temperate or boreal zones, with very different water chemistry and environmental conditions than those in the arid West and Southwest of the United States. Over the past 150 years there has been a 2- to 5- fold increase in the background level of Hg in the atmosphere, and even sites far removed from emission sources can be impacted. Amistad International Reservoir is spatially isolated from point source inputs of Hg and previous authors have suggested atmospheric input as the major source. Sediments from the reservoir were analyzed for total Hg, MeHg, chemical components, and bacteria known to methylate Hg. Additionally, two collections of largemouth bass (Micropterus salmoides) were utilized to assess the movement of Hg into the tissue of a popular sport fish. Results for total Hg suggest higher loading to the Rio Grande arm of the reservoir, while MeHg levels in the sediments appear to be somewhat higher in the Devils River Arm. Fish over the legal sport fishing size limit regularly exceed the USEPA consumption recommendation level of 0.3 mg/kg, and data from younger fish suggest that more Hg is accumulated in fish in the Devils River arm.

A clonal library was created using cDNA from nitrogen fixing bacteria from rhizosphere samples of the salt marsh grass, Spartina patens. Sequences with similarity to the ε-subclass of Proteobacteria represent a majority of the clones retrieved from these salt marshes sediments. Nitrogen fixing genes with close sequence similarity to members of the ε-subclass of Proteobacteria have not been described previously in salt marshes or in any other ecosystem. Both computer analyses of available sequences and testing of several different nitrogen fixing gene amplification protocols indicate that the amplification target site on the nitrogen fixation gene can limit detection of gene sequences corresponding to the ε-subclass of Proteobacteria. Gene amplification biases have likely contributed to the lack of reported sequences for the ε-subclass of Proteobacteria in previous salt marsh nitrogen fixing bacterial diversity estimates.

Drift fence sampling is a common technique applied to survey amphibian, reptile and small mammal populations. The objective of this study was to investigate the effectiveness of two common drift fence traps, pitfalls and single funnels, when compared with a new 1-way double funnel design. The 1-way double funnel is a typical single funnel with an additional funnel located within the trap. The second funnel effectively captures individuals twice. Once an individual is captured, the path of least resistance is always the interior section which makes escapes less likely. This new trap design should decrease the escape rate over standard trapping techniques and therefore increase drift fence sampling efficiency. Five 15 m linear drift fence arrays, constructed of aluminum flashing, were located within a 25 acre Guadalupe County property in central Texas. Traps were open for a total of 34 days between 15 September and 22 October 2007. Each array was run with a 1-way double funnel for the full 34 days. Pitfall traps were run for the first 19 days and were then switched out for single funnel traps for the remaining 15 days. To determine differences in capture rates between the new trap design and the typical traps, we used the program R to conduct paired t-tests for four categories: amphibians, reptiles, herptiles, and vertebrates. The 1-way double funnels caught significantly more individuals then single funnel traps for all categories. When compared with pitfall traps the 1-way double funnels caught significantly more for the reptile and vertebrate category. Results indicate 1-way double funnels appear to offer an improved trapping technique especially when compared with typical single funnel traps.

Recreational human activities along waterways may influence the abundance of waterbirds. I investigated the possible impacts of recreational activity and vegetative characteristics on the relative abundance of waterbirds along a heavily used river, the San Marcos River, in central Texas. Abundance of waterbirds and human disturbance was estimated by conducting point counts for 20 minutes at 30 randomly determined locations along the San Marcos River. Measurement of riparian characteristics at representative transects along the San Marcos River system were conducted to examine correlations between certain vegetative and aquatic parameters and bird abundance using multi-variant statistics. A Principle Component Analysis test was run to analyze the difference between the three a priori sections of the river, divided by the amount of disturbance present, as well as variance partitioning, a test utilizing the Canonical Correspondence Analysis test. With only 2 percent of the explained variation in the location and abundance of waterbirds coming from human disturbance, out of 25 percent explained in total, its apparent that the birds may have habituated out of necessity and that the river vegetative composition is the major deciding factor in determining bird abundance.

Invasive species pose a critical threat to aquatic ecosystems in Texas, and can significantly impact ecosystem structure and functioning of lotic systems. Conversely, Texas waters contain a large number of threatened taxa, whose loss could potentially alter the biotic and abiotic environment. The invasive armored suckermouth catfish (Hypostomous sp.), imported from South America as aquarium fishes, reportedly established itself in central Texas as early as the 1960’s due to escapes and releases. Armored catfishes are distinctive from native North American catfishes in that they are covered ventrally by bony, armor-like plates and are highly efficient algavores, which has caused concern that Hypostomous sp. will replace native grazers. The big claw river shrimp, or Macrobrachium carcinus, a widely distributed species, is native to 11 river basins in Texas, including the San Marcos River. However, populations of M. carcinus have decreased significantly over the past several decades, and it is now listed as Threatened by the state of Texas. Because both Hypostomous sp. and M. carcinus are active benthic foragers, their movements may significantly alter sediment movements within lotic systems, or alter community composition.

I tested the hypothesis that M. carcinus and Hypstomous sp. modify the physical and biotic environment and alter ecosystem functioning by analyzing their individual and combined effects on detrital breakdown rates, insect biomass, sediment movement and sediment organic composition. This study was conducted in artificial stream system containing substrate mimicking natural conditions. Each channel contained one of four treatments: one M. carcinus, two Hypostomous sp., a combination of both, or no addition. Sediment movements were tracked via sediment traps, periphyton tiles were used to monitor primary productivity and leaf packs were used to assess insect biomass and detrital breakdown rates. Significant results were found for this experiment.

During the last 20 years significant declines in populations of amphibians have been observed worldwide. Although many factors such as habitat loss, environmental toxins, invasive species, and UV radiation have been implicated in declines, some of the blame for recent losses is given to the emerging infectious fungus Batrachochytrium dendrobatidis (Chytrid fungus). Although the pathogen has been detected in many US states, consequences of the occurrence of this pathogen in North America remain unclear. However, its presence is not well documented in Texas which provides habitat for several endemic and threatened amphibians. The aim of our study was to screen individuals of four threatened amphibians in Central Texas for Chytrid fungus. Using PCR-based analyses, Chytrid fungus was detected on endangered Jollyville (Eurycea tonkawae), Barton Spring (Eurycea sosorum) and San Marcos (Eurycea nana) salamanders, and also on Houston toad (Bufo houstonensis). While all analyses of salamanders were based on recently obtained samples, Houston toad samples covered a time range from year 2000 to 2006 with only the most recent samples being positive for Chytrid fungus. Sequence analysis of PCR products confirmed the detection of Chytrid fungus, and thus demonstrated the presence of this pathogen in populations of endangered species in Central Texas.

The purpose of this study was to assess the efficacy of academic background variables as predictors of students’ achievement in the entry-level biology courses at Texas State University-San Marcos. Participants in this study were 582 students enrolled in the two entry-level courses in the Fall 2007. Participants’ demographic data, pre-post tests’ scores and course final grades were considered as primary data sources. The study found that there is an increase in students’ scores from pre to post tests as expected and also increase in the higher level thinking skills. Further data analysis will explain if the achievement in the entry-level courses is associated with other variables such as students’ major, regular and AP science courses completed, work load and their high school GPA.

The Forkhead Box P2 (FOXP2) DNA binding protein is encoded by a highly conserved gene of the same name. Two normal copies of this gene are necessary for human language acquisition. A point mutation in the FOXP2 gene causes specific language impairment, a rare phenomenon for which the London KE family is a vivid example. Genetic studies show that the KE mutation is autosomal dominant with the homozygous condition lethal. A recent crystallographic study by Stroud et al. [Stroud J.C. et al., 2006. Structure 14, 159-166.] of the FOXP2 protein bound to its target DNA identified the DNA sequence and binding domains of the protein, and also showed that FOXP2 protein is a domain-swapped dimer in its natural state. Because of this unusual property, the FOXP2 protein may regulate expression of two genes simultaneously, genes that may be far apart in primary structure or even on different chromosomes. The goal of my study is to identify the target genes of the FOXP2 protein to discover the developmental cascade that leads to our ability to acquire speech and language, phenomena resulting from the uniquely human abilities of symbolic logic and abstract thought. I have chosen chromatin immunoprecipitation (ChIP) for isolating DNA bound by the FOXP2 protein in human neuroblastoma (SH-SY5Y) cells. A preliminary immunohistochemical study verified abundant presence of FOXP2 in these cells and validated the antibody to be used for ChIP. Necessary calibration and control runs have been performed to maximize chromatin shearing efficiency and DNA yield, which is key to future DNA sequencing. A positive control for human Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) is currently being used to standardize the immunoprecipitation procedure, which will be followed by experimental trials using the FOXP2 antibody. Once the target genes of the transcription factor are identified, a closer examination of their gene products may provide insight into the mechanisms of FOXP2-driven language development.

Regeneration in the central nervous system of teleost fish is well documented. A study using epifluorescence microscopy and laser scanning confocal microscopy was conducted to correlate regeneration stages of severed axons of the optic nerve in adult zebrafish (Danio rerio) with analysis of changes in gene expression in the retina. Optic nerve injury was performed on wild-type zebrafish which were then sacrificed at one day intervals for 10 days. 24 hours prior to sacrifice the injured eye was either injected with DiO or Gelfoam soaked in DiI neurotrace paste. Fish were dissected leaving the optic tectum, eyes, and optic nerve intact. Regenerating axons were visualized by epifluorescence and confocal microscopy. Preliminary results indicate after 3 days axons have crossed the lesion site and by 7 days have reached the optic tectum of the brain. This work supported by NSF 0615762 to DMG and an REP to JRK.

Light adaptation in most vertebrates occurs through adjustments in pupil diameter. Teleosts, however, have a fixed pupil size, so they rely on retinomotor movements to regulate the amount of light incident on the photoreceptors. Retinomotor movements include photoreceptor contraction and elongation as well as the aggregation and dispersion of membrane bound pigment granules located in the retinal pigment epithelium. Previous work in bluegill has shown that pigment granule dispersion can be induced using the neurotransmitter acetylcholine acting via muscarinic receptors and that dispersion can be inhibited by Modd receptor specific antagonists. In this study we demonstrate Modd receptor expression using Western Blot analysis with an anti M3 antibody and in situ hybridization using probes that target the five different subtypes of muscarinic receptors. Western Blot Analysis revealed a band at 75 kDa indicating a likely Modd receptor. This finding was corroborated with In situ hybridization of the different muscarinic receptor sequences. These results suggest that multiple muscarinic receptor subtypes are expressed in the fish retina, and lay the foundation for future studies to elucidate the role of muscarinic signaling pathways in the retina, especially as they pertain to light adaptation.

Anuradha Gunathilake
Mentor/Research Advisor: Dr. Nihal Dharmasiri

Auxins were the first plant hormones to be discovered. Indole acetic acid (IAA) is the major natural auxin found in plants. Auxins have long been used as growth regulators as well as herbicides in agriculture. Due to the importance in agro-industry, many synthetic chemicals with auxinic activities have been identified. Picloram and 2,4D are two such widely used synthetic auxins. These synthetic auxins are structurally different from IAA. However they exhibit somewhat similar effects on plants. This gives rise to the question whether all synthetic auxins function in the same signaling pathway using similar molecular mechanisms. Preliminary work done in our laboratory indicates that picloram may be functioning in a different manner to other known auxins. To isolate new genes in auxin signaling, we carried out a mutant screening in Arabidopsis. Here we describe initial characterization of one mutant named pic64.
pic64 is highly resistant to 2,4-D and slightly resistant to Picloram. Additionally, this mutant was defective in trichome development. To test whether these two characteristics, auxin resistance and trichome development, were caused by the same mutation we carried out a back cross. Results showed the two characteristics to be caused by two independent mutant genes. Two mutations were mapped to two separate loci in chromosome 3 of Arabidopsis thaliana. While pic64 is resistant to 2, 4-D, picloram and IAA, it is sensitive to another auxin, 1-NAA, suggesting that pic64 may define a gene involved in auxin transport. Work is in progress to isolate and characterize the mutant genes.

One of the primary goals in conservation management is maintaining genetic variation in natural populations, specifically in threatened and endangered species. The aquatic beetle, Heterelmis comalensis (Coleoptera: Elmidae), is endemic to central Texas and listed as federally endangered. H. comalensis requires a habitat conservation plan based on variation within and among populations. Using molecular techniques, I analyzed the genetic variation within and among H. comalensis populations, as well as compared variation within and among this species to more common species, including H. vulnerata, H. glabra, and H. obesa, by sequencing individuals for both the COI and COII regions of mitochondrial DNA. MtDNA data was used to estimate haplotype frequencies within and among populations, and a maximum parsimony haplotype network was created. Results showed a significant amount of variation among H. comalensis populations compared to some of the more common species. This suggests that H. comalensis is not suffering the effects of genetic drift or inbreeding depression, and in fact may have large population sizes at some locations, with unique haplotypes in several populations. Finally, molecular analysis was used to delineate phylogenetic relationships among the Heterelmis populations in Texas. H. comalensis was shown to be monophyletic with high Bayesian Maximum Likelihood support, and is clearly differentiated from the more common species.

The introduction of exotic ruminants into Texas brought with it the potential for negative impacts on native ruminants. Though there has been much work describing food habits and displacement of species, no experimental work examined forces driving spatial interactions between white-tailed deer (Odocoileus virginianus) and exotic ruminants. This study compared habitat utilization between white-tailed deer and axis deer (Axis axis) using spatial and temporal controls. White-tailed deer were surveyed in two areas (12 km apart) from July – December 2006. The control site had white-tailed deer only and the treatment site had both axis and white-tailed deer. After the axis deer were removed, both areas were surveyed from July – December 2007 to assess possible changes in white-tailed deer habitat selection and distribution. Spatial locations were analyzed using program PRESENCE to correct for imperfect detection. Data were then analyzed using 95% confidence intervals of proportions to determine if the species were using specific habitat types consistent with their availability. During the first survey season white-tailed deer used wooded habitat to a lesser extent than available whereas during the second survey season they used wooded habitat to a significantly greater degree than its availability. During the two survey seasons habitat use by white-tailed deer in the control area did not change. This change in habitat use suggests that white-tailed deer were being displaced by axis deer. Presently, data on social interactions at supplemental feeders is being analyzed to understand the nature of the competitive displacement.

It is possible that both female and male mate choice have played a role in reproductive isolation when two closely related species are found sympatrically. If reproductive isolation is occurring, it is important to determine if it is asymmetrical such that one species prefers conspecifics more strongly than the other species. To do this, we examined two species of livebearing fish, Gambusia (G. affinis and G. geiseri) that occur in sympatry in parts of their geographic distributions. We studied actual male mate choice for conspecific vs heterospecific females of both species of males by recording gonopodal thrusts directed at each species of female. To assess female mate choice, we examined association time with a conspecific vs. a heterospecific male. Whether hybridization occurs is not clear, but given the maintenance of the two species sympatrically we predict some amount of reproductive isolation. In addition to gaining better understanding of the direction of evolution in these species, we also expect the results of this study to be important for understanding the impact of G. affinis, a widely introduced species, on endemic species of Gambusia.

Gall-former life cycle events are tied to host-plant phenology but may be altered by the effects of other herbivores on host plants. Here we describe variation in emergence and oviposition phenology and natural enemy exposure in the gall-former Belonocnema treatae, host specific to live oak, Quercus fusiformis, as a prelude to testing whether defoliation of the host-plant alters phenology of life cycle events. B. treatae alternates generations where an asexual generation developing within leaf galls follows a sexual generation developing within root galls. Up to 23 natural enemies attack leaf galls. Collections from 1995–2000 in Hays County, Texas, detected leaf gall emergence from October–December with mortality ?99%. In 2001 in adjacent Travis County, emergence was detected from January–March with reduced mortality (40–60%). Consequently, from November 2006–February 2007 galls were collected from 8 and 22 trees in Hays and Travis counties to estimate emergence phenology and mortality. A region-wide shift in emergence phenology was detected, and mortality ranged from 80–99%. Live oaks often experience defoliation by lepidopteran consuming initial leaf flush and deposited B. treatae eggs, resulting in a second flush. To determine if shifts in emergence are due to oviposition timing driven by defoliation, oviposition phenology and degree of defoliation were monitored from March–July 2007. Oviposition timing occurred later compared with historical records region-wide, while defoliation ranged from low to near complete. Correlations between degree of defoliation, emergence and oviposition phenology and mortality will be examined after the 2007–2008 emergence season. We hypothesize that (a) oviposition into the second leaf flush, resulting from defoliation, is responsible for emergence phenology shifts and (b) B. treatae on the second leaf flush are “out of phase” with natural enemies and experience reduced mortality. Experiments have been implemented to determine whether defoliation creates temporally separated “broods” potentially limiting gene flow among B. treatae populations.

In situ and dot blot hybridization were used as tools to quantify growth of two Frankia strains inoculated alone or together into non-sterile soil microcosms with ground leaf litter of Alnus glutinosa as sole carbon (C) and nitrogen (N) sources. A significant increase in cell numbers and filament length was observed during the first 6 weeks after inoculation for strain Ag45/Mut15, both alone and in mixed culture with strain ArI3, followed by a decrease until the end of the study after 12 weeks. The number of filaments remained unchanged. In contrast, cell numbers and filament length of strain ArI3 were reduced significantly during the first 2 weeks and undetectable for the remainder of the study. These results were comparable to those obtained in sterile mineral medium amended with leaf litter of A. glutinosa, although reductions in cell numbers and filament length were less pronounced than in soil microcosms. In concomitant control studies without leaf litter amendments for both experimental setups, filaments of both strains could only be detected immediately after inoculation. These results were matched in all experimental setups by concomitant shifts in rRNA content of both strains, i.e., an immediate decline in rRNA content for strain ArI3 after inoculation, and an increase in rRNA content followed by a late decline during incubation for strain Ag45/Mut15. These results demonstrated that Frankia strain Ag45/Mut15 could grow saprophytically in soil with complex C and N sources such as leaf litter, while growth of strain ArI3 was not supported.

Bastrop County contains critical habitat for the endangered Texas endemic, Bufo houstonensis, the Houston toad. One factor known to impact Houston toad populations is drought. However, the factors during drought conditions that lead to decline or even loss of Houston toad populations remain unknown. In fact, few studies have sought to determine the proximate effects of drought on wildlife. One factor could be interruptions in food diversity or abundance. Arthropods are the primary food source for Houston toads and our recent severe drought years followed by the exceptionally wet spring and summer of 2007 provide an opportunity to evaluate effects on this critical food resource. Monthly sweep net surveys were repeated for 6 transect lines in Bastrop County from July 2006-July 2007. We identified arthropods to the family level and calculated the Shannon-Weiner diversity index and evenness for each sample. Drought indices for our sampling dates were plotted against evenness and abundance. We tried to determine whether arthropod evenness or abundance were related to rainfall. A decline in the food source diversity for Houston toads could represent one of the negative effects on this species resulting from drought. Our results indicated that evenness was not related to rainfall. Arthropod abundance seemed to be affected by rainfall but due to disturbance events and seasonality the strength of the relationship was unclear.

Increasing changes due to development along river systems of Texas concerns many biologists. Of particular concern are avian communities associated with these rivers. Obtaining reliable data about avian populations and communities on a local and broad scale is a constant challenge for applied biologists. Our objectives were: 1) assess avian community of the Blanco River Valley by occupancy modeling, 2) compare data on avian populations to data generated by landowners in the area, and 3) assess the feasibility of using landowner data for monitoring trends in avian populations across large areas. Presence–absence surveys were conducted three times during 2007-2008: spring, summer, and winter. Thirty survey points were sampled from 11 sites along the Blanco River and tributaries. Baseline vegetation was collected at each point and used to quantify habitat quality. Dominant species were Cedar Elm (Ulmus crassifolia) and pecan (Carya illinoinensis). Species richness for all seasons was 98, and landowner species richness was 73, with 40 species being unique to occupancy surveys. Data was analyzed in Presence 2.0. Common species such as Northern Cardinal and Carolina Wren had 100% occupancy and high probabilities of detection, and were detected on landowner surveys. Additionally, secretive species of concern like the Yellow-billed Cuckoo had high occupancy but very low detection probabilities, yet were recorded on landowner surveys. There was a 56% similarity in presence-absence and landowner surveys. The data supports that spring and summer surveys conducted by landowners can be a useful tool for biologists when used over a broad-scale and over time.