Recipient Organization
UNIVERSITY OF CALIFORNIA, DAVIS
410 MRAK HALL
DAVIS,CA 95616-8671
Performing Department
Entomology and Nematology
Non Technical Summary
This project supports the mission of the Agricultural Experiment Station by addressing the Hatch Act area(s) of: plant and animal production, protection, and health. Natural, restored, and agricultural wetlands (e.g., rice fields) throughout California and the U.S.A. support natural resources such as aquatic macroinvertebrates and their predators, including waterfowl, fishes, reptiles and amphibians. These taxa provide recreational opportunities such as bird watching, hunting, fishing, and the general enjoyment of wildlife sightings. Wetland managers and natural resource agencies need to know how to manage wetlands so that they support robust food webs and preserve declining species, without causing problems such as high numbers of mosquitoes, low dissolved oxygen, or supporting harmful invasive animals. My research group is addressing several pressing issues in wetland management. 1. We will test the effects on larval mosquitoes of copper sulfate, which is used to control pests including algae in rice agriculture. We will use mosquitoes as indicators of possible effects on other insects, and also to understand if treated fields are less likely to require mosquito abatement. 2. Wetlands typically contain a mixture of sown and natural plants which produce detritus, and these help fuel the macroinvertebrates supporting higher trophic levels. However, the effects of different kinds of plant detritus on the food web are poorly understood. We hypothesize that for sustained wetland productivity it may be best to have a mix of emergent vegetation (e.g., tules and cattails), and low-growing, terrestrial plants (e.g., sea purslane, fat hen). Emergent vegetation may produce litter providing sustained nutrient release, whereas drowned terrestrial plants may yield a rapid pulse of nutrients that, although stimulating production, could create an initial high oxygen demand. 3. Central Valley wetlands support California's threatened giant garter snake (Thamnophis gigas) but also invasive bullfrogs (Lithobates catesbeianus). Bullfrogs serve as prey when small, but can consume young snakes when large. We will assess the positive and negative impacts of bullfrogs on the threatened giant garter snake. This will enable us to recommend whether, and what sizes, of bullfrogs might need to be culled from giant garter snake habitat in order to foster recovery of the snake.
Animal Health Component
25%
Research Effort Categories
Basic
75%
Applied
25%
Developmental
(N/A)
Goals / Objectives
Goal associated with study 1: Quantify the concentrations of copper sulfate that produce lethal and behavioral effects on Culex pipiens and Cx tarsalis mosquito larvae. Milestones are: A. Quantification of LD 10 and LD 50 levels of chronic copper sulfate exposure for Cx. pipiens and Cx tarsalis mosquitoes. B. Determination of what concentrations of copper sulfate cause changes in larval mosquito swimming behavior, and discover whether copper exposure affects mosquito neurology via assays of acetylcholinesterase. D. Discovery of whether copper exposure affects the expression of olfaction genes in mosquitoes. E. Production of a publication on each of these areas of new knowledge. E. Completion of Nermeen Raffat Amer's dissertation. Goal associated with study 2: Determine how decomposition patterns of plant functional groups affects secondary productivity of invertebrates. Milestones: A. Quantify nutrient content and release patterns during decomposition of common dominant plants of seasonal wetlands in the Suisun marsh. B. Measure associated effects on invertebrate productivity and water quality. C. Using survey data, produce a model of how wetland plant community structure affects productivity of invertebrates. D. Production of a publication on each of these areas of new knowledge. E. Completion of Katherine Hostetler's senior research thesis. F. Completion of Kyle Phillip's dissertation. Goal associated with Study 3: Discover which size classes of bullfrogs can consume giant garter snakes, and which sizes of bullfrogs are preferred prey of the giant garter snakes. Milestones: A. Determination of sizes of giant garter snakes that are vulnerable to bullfrog predation, and determination of sizes of bullfrogs on which the snakes can feed effectively. B. Produce a model of reciprocal predation that is parameterized for giant garter snakes and bullfrogs, but adaptable to other systems with intraguild predation. C. Describe giant garter snake behavioral interactions with bullfrog prey, including effects of bullfrog stage and size on its anti-predator behavior. E. Production of a publication on each of these areas of new knowledge. E. Completion of senior theses by Jenny Viera and Sam Yuen. F. Completion of Richard Kim's dissertation.
Project Methods
Study 1: Effects of copper on mosquito larvae. Our student leader is Nermeen Raffat, collaborators are Dr. Richard Connon and the University of Cairo (funded by the Egyptian Cultural Ministry). We will use colonized Culex pipiens and Cx. tarsalis larvae from the Sacramento-Yolo or San Joaquin County mosquito abatement districts. We will test these `susceptible' strains that have been unexposed to pesticides for generations as is standard for toxicological work, and also use mosquitoes reared from field-collected eggs for better estimates of field mortality. We will rear mosquitoes at 25±0.5°C and ~80% humidity, with 18:6 h day/night cycle. Larvae live in enamel trays filled with ~1 L reconstituted deionized water (RDiW). Their diet is in the proportions of 5 g fish food, 5 g alfalfa, ½ g yeast and ½ g beef liver. Adults live in 30 X 30 X 30 cm cages. Adults feed on 10% sugar solution. After 4 days, we feed females with heparinized sheep blood (Hemostat Laboratories, Dixon, CA). We provided oviposition cups filled with RDiW water in each cage to receive eggs. Test concentrations are: 0, 125, 250, 500 and 1000 ug CuSO4 L-1 (QA/QC by the Interdisciplinary Center for Plasma Mass Spectrometry, UC Davis). Five replicates per concentration will contain 100 ml of CuSO4 solution and 10 1st instar larvae in a food-grade plastic cup. We will refresh 90% of the solution every 48 h. We will record stage and mortality daily, removing dead larvae. Other mosquitoes reared at these concentrations will be sent to the Connon lab for RNA analysis of olfactory gene expression (collaborator methods are beyond this proposal's scope). We will video 25 3rd instar individuals reared in the copper solutions , with and without predation cues. We prepare cues by crushing five 4th instar Cx. pipiens larvae and diluting the paste in 5 mL RDiW . To this we add `predator water' in which we reared individual dragonfly larvae in cups of ~50 mL water. Dragonflies will be provided mosquitoes as prey for 10 d before water collection. Culex will be starved 24 h before trials to standardize hunger. Larvae will be added to 5 cm petri dishes, acclimate for 3 min, then be recorded for 5 min using a Panasonic CCTV camera. Ethovision XT 6.1 Software will aide video analysis to determine distance moved and velocity. Data analysis is via parametric general linear models or non-parametric methods. We will calculate LD 50 and LD 10 of copper sulfate and determine if it affects Culex movement, whether the response to predation cues depends on exposure, and whether copper affects olfactory gene expression. Study 2. Effects of wetland plant detritus on productivity. Mesocosm experiments and wetland surveys will enable us to understand the role of plant detritus in secondary production of invertebrates. Kyle Phillips is our Ph.D. student study leader and his co-advisor Dr. John Durand is collaborating (study funded by Dept. of Water Resources). Field studies will employ existing remote-sensed vegetation maps, ground-truthing of vegetation, and field measurements of secondary production in wetlands encompassing a gradient of perennial emergent-dominated wetlands to annual terrestrial-dominated forbs. Mesocosm trials will test effects of material from wetland plant species on invertebrate production. We collected and oven-dry above-ground plants from three emergent taxa (tules, cattails, and common reed) and three terrestrial taxa (sea purslane, fat hen, and Russian thistle) from wetlands in Suisun marsh, and will add other taxa in future. Mesocosms are 35 buckets containing 7 L of field water, filtered through 50 micrometer mesh to remove zooplankton, with RO water added as needed to maintain volume. They are temperature-buffered in wading pools in a greenhouse. Treatments will have 5 replicates each. A leaf pack in each bucket will hold 3 g of plant material (approximate dry mass found in an equivalent area of wetland). We will measure temperature and water quality 3X per week. Detritus will incubate for 11 days prior to zooplankton addition, to allow litter degradation to spur algal growth. On day 12 we will add a standardized aliquot of field-collected zooplankton, preserving samples to determine initial community structure. Zooplankton will grow for 12 days and we will collect subsamples 2-3 times. Leftover detritus will be analyzed for C, N and P using a C:H:N analyzer, plus mass spectrometry methods for phosphorus. Zooplankton will be identified and enumerated. We will construct nested linear mixed models to test effects of plant functional group on zooplankton biomass. Plant species are nested factors within plant functional groups. Water-quality parameters are fixed effects (temperature, dissolved oxygen, or DO, chlorophyll a, DOC). AIC and BIC will inform model selection. We will use Non Metric Dimensional Scaling to assess differences in zooplankton community structure among treatments and map parameters associated with differences in community structure. We will survey > 20 managed wetlands in Suisun Marsh, working with the Suisun Resource Conservation District and duck clubs to access wetlands. We will estimate % cover of plant functional groups using data from the CA Dept. of Fish and Wildlife Veg CAMP program. Estimates will be ground-truthed with late summer surveys, quantifying above-ground vegetation in 8 x 8m plots placed at five random locations per wetland. Samples of plant species will be dried to describe the relationship between cover and biomass. We will collect data on wetland size, water control structures, and wetland management. MiniDOT loggers will monitor DO and temperature. We will sample invertebrates via 15 m zooplankton tows (30cm diameter 150um mesh net) from five sites per wetland in spring, as close together in time as feasible. We will collect 1 m sweep net samples of macroinvertebrates at each site. We will sample water quality for major nutrients, Chl a, salinity and conductivity. We will estimate biomass of plant samples using ash-free dry-mass, and identify and count invertebrates to calculate densities. We will build hierarchical linear mixed models to test effects of wetland plant composition in field sites on invertebrate density. Using Veg CAMP data, we will construct a spatially explicit model to produce a predicted map of zooplankton densities across wetlands in Suisun Marsh. Study 3. Effects of invasive bullfrogs on threatened giant garter snakes. Our graduate student study leader is Richard Kim; he is co-advised by Dr. Marissa Baskett, and Dr. Brian Halstead (U.S.G.S.) is collaborating (project funded by U.S.G.S. and the Jastro Endowment; IACUC protocol 21173). In mesocosm trials, snakes will be presented with three size categories of bullfrogs as prey; one each of a newly metamorphosed bullfrog, and frogs that are either ~20% of snake gape size or ~60%. Mesocosms are 1.8 m d cattle watering tanks filled to 30 cm with well water, which have resting platforms for animals and artificial vegetation for cover. Animals acclimatize in partitioned areas before trials. Feeding trials are videotaped for later analysis. Because the snake is a Threatened Species we won't directly study bullfrog choice of snake size. Instead, study leader Rich Kim has identified data sets of bullfrog gut contents, from which he is extracting information on the sizes and species of snake predation events and comparing these with bullfrog sizes. We will use these data and existing and newly generated snake and frog population data, to parameterize models of snake and frog size-dependent predation and population dynamics. Bullfrog and giant garter snake population dynamics data are being collected as separate mark-release-recapture projects by Mr. Kim and the U.S. Geological Survey. Results of these models will inform bullfrog management in the threatened snake's habitat.