Biodiversity

Arelys Astacio - Effects of Temperature on E. coli Diversity.  Mentor: Dr. M.H.H. Stevens, Botany.

Biodiversity increases as one approach the tropics, as compared to the high latitudes. Several theories explain that temperature is an important factor for this pattern. The objective of this experiment was to analyze E. coli cultures incubated on different temperatures, to compare the growth of the bacteria, and to determine if the temperature influences the evolution rates of E. coli. To test our hypothesis: If the greater temperatures could imply shorter generation time and higher rates of mutation (Rhode, 1992), then this causes an increases of E. coli speciation; we used long-term stationary phase of E. coli, incubated  in 37˚C  and 30˚C  and then in 37˚C  and 27˚C. MacConkey agar was use to inoculate the bacteria. The colonies were classified in red, dark pink, pink, light pink and white. The reason by which the colonies grow in different colors (phenotypes) is because they have a gene called rpoS that is responsible for the stress response and phenotypes. I expected that in 37˚C I would find more diversity than in 30˚C and in 27˚C. I found that in 37˚C and in 30˚C the cultures have the same diversity but 27˚C cultures have less diversity than 37˚C cultures.

Jennifer Burks - Feeding Rates by Harvestmen (Opiliones) on Aphids and their Associated Behaviors.  Mentor: Dr. Alan Cady, Zoology

Harvestmen (Arachnida: Opiliones) are generalist predators that prey on soft-bodied insects including aphids (Homoptera: Aphididae), which are common nuisances in greenhouses. Leiobunum nigripes is an abundant, highly active species of harvestmen found in North America. This study tested feeding rates and behaviors of L. nigripes on aphids present on eggplant leaves during 24 hours in a controlled setting. The experiment was separated into two parts. One examined how the presence of a single harvestman affected aphid numbers, while the second part inspected how interactions among pairs of harvestmen influenced their aphid consumption. The numbers of individual aphids (both dead and alive) were counted before and after exposure to harvestmen on control and experimental eggplant leaves. In addition, specific behaviors associated with harvestmen activities in the presence of aphids at the start of the 24 hour period were directly observed for 45-60 minutes. There was a trend for single harvestmen to consume more aphids than harvestmen pairs. Unlike single harvestmen, increased time-on-leaf for paired harvestmen led to increased aphid consumption. Single harvestmen spent more time exploring than paired harvestmen during the initial 60 minutes, however, this was reversed when measured across 24 hours. Finding that harvestmen will consume both live and dead aphids make them possible agents of biological control in greenhouses. Since little is known about harvestmen activity and their consumption of prey, the results of this study provide information important to greenhouse managers and augment our general knowledge about harvestmen behavior in two different contexts.

Jorge Lassus - Population genetics as revealed by microsatellites in Lampsilis reeviana in the Spring and South Fork Rivers, Arkansas.  Mentor: Dr. David Berg, Zoology.

The goal of this project is to understand the genetic variation within and among three populations of the freshwater mussel, Lampsilis reeviana (Arkansas Brokenray), in the South Fork and Spring rivers, both located in Arkansas.To achieve this goal, we will screen 12 microsatellite primer pairs that amplify L. reeviana DNA. Second, we will use successful primer loci to analyze gene frequencies and infer gene flow in and between populations of L. reeviana.  Hypothesis one is that primers that work for other Lampsilis species will work for L. reeviana.  Our hypothesis for the second objective is that genetic variation will be highest within populations of L. reeviana rather than among populations.   Nine of 12 primer pairs amplified L. reeviana DNA and eight of these were polymorphic loci.  For the first three loci analyzed, there was an average of 8 alleles per locus.  Our results for these three loci show that genetic variation within the population sites is high in this species while among population variation is low. This suggests that populations are highly affected by host fishes in these streams.

Angie Matthews – Genetic Assessment of the Hyalella Species Complex in desert springs of New Mexico and Texas.  Mentor: Dr. David Berg, Zoology.

 Freshwater ecosystems, such as those in the Chihuahuan desert springs of New Mexico and Texas, have high levels of understudied endemic species that may represent a greater percentage of global biodiversity than previously estimated. Previous studies in this area have begun looking at genetic diversity patterns in populations of several taxa in this region, including the amphipod Gammarus. In this study, we examine the patterns of diversity and divergence in another gammarid amphipod, Hyalella, by sequencing the COI (cytochrome oxidase I) gene in individuals from several isolated spring locations along the Pecos River. In phylogenetic analysis of sequence data, individuals from different locations cluster together on separate clades based on their degree of sequence similarity. Preliminary results show that there is significant genetic diversity within populations and that divergence among populations is based on geography. This pattern is similar to results for Gammarus. A thorough analysis of genetic diversity within this region could lead to the identification of cryptic species and aid in the development of conservation plans for the region.

Ashley Scioneaux - Qualitative Tannin Variation in Four Cross Types of Cottonwood.  Mentor: Dr. Ann Hagerman, Chemistry and Biochemistry.

Tannins are polyphenols in plants, and it is suggested that they provide protection from insects, infection, and large herbivores.  Previous research has demonstrated that within the Poplar genus (cottonwood) there is quantitative variation in condensed tannin levels within four different cross types.  The objectives of this study include:  modify a literature method for qualitative analysis of condensed tannins to accommodate frozen leaf material and compare the compositions between cross types (Fremont, narrowleaf, backcross, and F1) and individuals of the same cross type.  The hypotheses are:  the thiolysis method will successfully be adapted to frozen leaf tissue, the HPLC will accurately separate and identify each flavan-3-ol, there will be a >10% variation in composition between cross types, and <10% variation between individuals of the same cross type.    An appropriate method requiring only five-milligram samples was developed and high performance liquid chromatography (HPLC) was used to interpret the data.  The qualitative variation of each cross type sample was tested by analyzing the time and area of each terminal and extender present, such as catechin, epicatechin, gallocatechin, and epigallocatechin (all called flavan-3-ols).  A >10% difference between cross types and individuals of the same cross type was found.  The preliminary significance of this research shows that tannin quality is distributed more randomly across individuals of the same species than expected, which can lead to research on how plants produce tannins based on their ecosystems, climate, and other ecological processes.