| Advisor : | ELSA CLELAND | ||
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| Abstract Title : | Climate change effects on soil microbial communities: Altered precipitation and invasion in a chaparral system | ||
| Abstract : | Environmental changes, including climate change and invasion by exotic species, threaten ecosystem stability and biodiversity worldwide. Regionally, Southern California is predicted to be disproportionately affected by climate change, and in particular long-term drought is predicted during the coming century. Moreover, the Southern California area is also threatened by high rates of invasion by exotic species. However, it is unclear how altered precipitation regimes coupled with changing community composition will affect soil microbial dynamics. To test this, we performed a wet-up and litter-addition experiment on soils collected following a 2-year rainfall manipulation where plots were subjected to low, ambient, or high rainfall. High and low water pulse treatments were applied to soils over eight weeks in combination with litter additions from two native and two exotic species found at the site. In general, microbial activity was higher for soils receiving a large moisture pulse than for soils receiving a low moisture pulse highlighting that decomposition is often moisture limited in arid and semiarid systems. Microbial activity was higher for soils with exotic litter additions than for soils with native litter additions. Exotic species at the site have more labile litter than natives and stimulated activity as indicated by microbial respiration throughout and microbial biomass at the conclusion of the experiment. Soils originating from different field rainfall treatments showed no difference in respiration responses to a moisture event. Microbial communities may be more responsive to current conditions rather than retaining legacy effects of precipitation regimes. These results show that altered rainfall regimes in combination with invasion by exotic species are capable of altering belowground processes as indicated by differences in microbial respiration. | ||
| Advisor : | DAVID HOLWAY | ||
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| Abstract Title : | Argentine ant invasion reduces diversity in mutualist and parasitoid guilds | ||
| Abstract : | Linepithema humile, the Argentine ant, is an invasive species that aggressively displaces native ants and forms mutualisms with honeydew-producing aphids, exchanging protection from parasitoid wasps for the sugary fluid. In California, the Argentine ant is most abundant in riparian woodlands bordering perennial streams which resemble its preferred habitat in Argentina. This study aims to determine if the Argentine ant differs from native ants in tending intensity and how its invasion affects diversity of aphids and higher trophic levels. Contrary to predictions based on the aggressive nature of the Argentine ant, we found no evidence that the invader allocated more ant foragers to aphid tending than native ant species. While aphid diversity declined in response to Argentine ant invasion, higher trophic levels may be less affected by changes in ant assemblages. This may indicate that wasp parasitoids are able to feed on more than one species of aphid host, showing a resilience to invasion which the aphids lacked. The spreading invasion of L. humile can affect both ant and non-ant arthropod species and has the potential to change the composition and functioning of riparian ecosystems across southern California as a whole. As research improves understanding of these interactions, we may be able to better preserve biodiversity as our planet continues to change. | ||
| Advisor : | JAMES NIEH | ||
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| Abstract Title : | Drinking Dirty Water: Why do honey bees (Apis mellifera) collect agricultural water and urban runoff? | ||
| Abstract : | Since scientists began noticing the major decline of honey bee populations in 2006, known as the colony collapse disorder (CCD), research has linked the cause to a variety of factors including mites, fungus, pathogens, and pesticides. Although there have been a lot of emphasis put on pesticide transmission through nectar and pollen foraging, there have not been much attention put towards pesticide transmission through water foraging. This study aims to establish an understanding to why honey bees prefer to collect contaminated water over pure water by using the Proboscis Extension Response (PER) test to examine individual salt concentrations preferences. We also took samples of water from sources where honey bees drink water from and analyzed its contents to what in present in the sources honey bees naturally drink out of. Our study found that honey bees prefer NaCl and MgCl2 concentrations at 1.5% while they tend to avoid high concentrations of KCl and Na2HPO4. | ||
| Advisor : | LIN CHAO | ||
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| Abstract Title : | Using CellProfiler as an Alternative to Other Methods in Collecting Data Related to the Study of Bacterial Aging | ||
| Abstract : | Current research on aging processes in E. coli has led to the hypothesis that mother cells partition the non-genetic damage they acquire over their lifetime unequally among their daughter cells, with the new pole daughter inheriting less damage than the old pole daughter. This partitioning is thought to improve the chances of survival of certain damage-light bacterial lineages in the face of harsh environments. An attempt to collect data on this partitioning process has been made in which GFP production is induced in E. coli and followed through the growth of a colony. The relative amounts of fluorescence between new and old pole daughter cells should provide information to help support or reject the above hypothesis. In this study, fluorescence data was collected using free image analysis software, CellProfiler. The results of this study were analyzed both individually and compared to data previously collected by less efficient methods. The data collected here strongly agree with previously collected data, both in overall relative fluorescence results and in correlation of individual data points, indicating that the method used in this study can be an efficient alternative to previous methods, both in finding evidence for the above hypothesis and in similar applications. | ||
| Advisor : | THERESE MARKOW | ||
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| Abstract Title : | The Biodiversity of Arthropods in Organ Pipe (Stenocereus thurberi) Cacti in the Sonoran Desert | ||
| Abstract : | Biodiversity varies across different habitats and microhabitats throughout the world due to ecological relationships between individual species and their environments. Of particular interest to my lab is the biodiversity of arthropods living in the necrotic tissue of various cactus species in the Sonoran Desert. In our study we collected five samples of rotting tissue from two cactus species (Stenocereus thurberi and Pachycereus pringlei) in various locations in the Sonoran Desert in Baja California Sur, Mexico. My study focused on the diversity of the two organ pipe (Stenocereus thurberi) samples. I sorted and identified a total of 356 arthropod specimens, which included mostly beetles (Coleoptera), but also flies (Diptera), earwigs (Dermaptera), ants (Hymenoptera), true bugs (Heteroptera), springtails (Collembola) spiders (Araneae), mites (Acari), and pseudoscorpions (Pseudoscorpiones). Morphospecies data were used to estimate species richness of the samples in the program EstimateS. Many of the arthropod species overlapped between the two samples, but there were also some unique species in each sample. All of the arthropod species found in the organ pipe tissue also occurred in other samples, suggesting that these arthropods do not strongly associate with the organ pipe cactus. Based on these observations and on the results from the EstimateS program, I found that the species richness is lower in the organ pipe samples relative to the other cactus species sampled. | ||
| Advisor : | MAXI RICHMOND | ||
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| Abstract Title : | Arthropod Species Diversity within Cardon Cacti in the Sonoran Desert | ||
| Abstract : | When cactus tissue becomes necrotic it serves as a feeding and breeding site for a range of different desert arthropods. However, the species richness of the arthropods inhabiting this unique niche is relatively understudied. For our study, samples from rotten cactus tissue belonging to species of cardon (Pachycereus pringlei) and organ pipe (Stenocereus thurberi) were collected from the Sonoran Desert. The focus of my project was to sort and identify specimens from the three samples of cardon cacti collected in Baja California Sur, Mexico. A total of 589 arthropods from 93 species were collected from the cardon cacti. Beetles (Coleoptera) were the most prominent arthropods collected, particularly those belonging to the families Staphylinidae, Histeride, and Nitidulidae. Other common arthropods were true bugs (Heteroptera), flies (Diptera), and mites (Acari). Species richness estimates were calculated for the two separate species of cacti, and variation within and between cacti species was analyzed. Through an analysis of the arthropod diversity found within these cacti, we can establish a better understanding of the role of the necrotic cactus niche with regard to arthropods. | ||
| Advisor : | STUART SANDIN | ||
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| Abstract Title : | Does Size Matter? Prey Size Selectivity of Spotted Sand Bass (Paralabrax Maculofasciatus) | ||
| Abstract : | The size-efficiency hypothesis suggests that animals should choose the largest prey item available. Most piscivorous fishes are strongly size-selective. Because swimming speed increases with fish body size, however, larger prey items become harder to catch, so as piscivores grow larger they continue to include a range of prey items sizes in their diet. However, many studies have not explicitly controlled for prey escape behaviors, which affect predation decisions. Here, we tested the size-efficiency hypothesis using the spotted sand bass, Paralabrax maculatofasciatus, as a model predator and California market squid, Loligo opalescens, as a model prey. In over 15 experimental trials, we offered spotted sand bass "large" and "small" sizes of squid, explicitly controlling for other factors, such as prey escape behavior, that would otherwise influence foraging decisions. Our results indicate that spotted sand bass did not exhibit a statistically significant size preference, but did prefer certain areas of the experimental tank. This suggests that prey size may not be the most important factor affecting foraging decisions in this species. | ||
| Advisor : | JAMES NIEH, PHD | ||
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| Abstract Title : | Activating honey bee immunity against the widespread pathogen, Nosema ceranae. | ||
| Abstract : | Honey bees (Apis mellifera) serve as pollinators for $15-20 billion of agricultural crops each year in the U.S., most importantly almonds, apples, and melons. The recent decline in honey bee health has placed great stress on agricultural production and can be at least partially attributed to infection by the fungal pathogen Nosema ceranae. Previous studies suggested that N. ceranae could only infect adult honey bees. However, by using controlled in vitro rearing conditions, we show that N. ceranae can infect honey bee larvae. In this study, we fed three-day-old honey bee larvae a single dose of 0, 10,000, or 40,000 N. ceranae spores per bee. We recorded mortality of adult bees that were kept in cages, and after their deaths as adults, we counted N. ceranae spores in their midguts. We found significantly elevated spore counts in bees that were fed N. ceranae. Additionally, bees fed 40,000 spores had significantly decreased lifespans compared to uninfected control bees. We have now begun to investigate ways to protect honey bees from N. ceranae infection by activating honey bee immunity. Specifically, this paper focuses on exposing bees to probiotic bacteria, which can activate immune genes and lead to increased abaecin production. We test the hypothesis that probiotic bacteria can increase the ability of adult honey bees to fight off N. ceranae infection. | ||