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Tyson Research Center |
Summer 2005 Fellows at Tyson:
Photos: Tyson Orientation 5-17-05; Canoe trip 8-2-05; Misc. photos
(For Summer 2006 Fellows page, click here.)
Projects:
(including abstracts, posters, and photos)
Julia Buck; Carla Fresquez;
Stephanie Gallitano;
Daniel Oppenheimer; Molly Sobotka
(posters are from HHMI 2005 Symposium Program, Sat. Sept. 10, 2005)
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"OVIPOSITION SITE SELECTION IN RESPONSE TO AQUATIC PREDATION AND INSECTICIDES: IMPLICATIONS FOR AMPHIBIAN CONSERVATION" Julia Buck, James Vonesh. Biology Department, Washington University, St. Louis, MO. |
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Abstract: Many amphibians preferentially select ponds without predators and competitors for reproduction. If pesticides negatively impact aquatic predators or competitors of amphibians, amphibians could perceive contaminated habitats as being more suitable for their eggs than uncontaminated habitats. In this “ecological trap” scenario, pesticides could have a larger impact on amphibian populations than in the absence of oviposition habitat selection, because eggs are concentrated in contaminated sites. Alternatively, if amphibians can detect pesticides, they may avoid laying their eggs in contaminated habitats. In this scenario, the most important conservation concern may not be the direct toxic effects of pesticides, but rather habitat loss, since contaminated ponds are no longer perceived as suitable habitat. In this study we examine oviposition site selection by the gray treefrog, Hyla chrysoscelis, in response to aquatic predators and the insecticide carbaryl. First, we conducted a 2 x 3 factorial experiment in which presence or absence of carbaryl (Sevin™) was crossed with presence or absence of caged (i.e., non-lethal) predators, a crayfish (Orconectes punctimanus) or salamander larvae (Ambystoma maculatum ). Each treatment was replicated 10 times in an array of 60 plastic wading pools (300 L) spaced 0.5 m apart arranged around ponds at Tyson Research Center . Pools were filled with water and inoculated with leaf litter, zooplankton and cat food in order to establish a basic aquatic food web. Based on previous studies, initial carbaryl concentrations were established at 7 mg/L. Gray treefrogs naturally recruited to these artificial ponds. Pools were monitored and eggs were removed and counted daily. Treefrogs exhibited no preference with respect to aquatic predators but significantly preferred (by more than 3 times) non-carbaryl pools. In a second experiment, we examined the mechanism by which gray treefrogs were able to detect carbaryl. To test whether the frogs directly detected carbaryl or detected it indirectly through its effects on the aquatic food web, we manipulated presence of carbaryl in the absence of the aquatic food web established above. Both treatments were replicated 10 times. We found that even in the absence of trophic structure, frogs strongly preferred non-contaminated pools, suggesting they directly detect carbaryl or its breakdown products. Natural ponds are often widely separated in the landscape and costs of avoiding non-optimal breeding sites may be high. In a final experiment, we examined oviposition site selection in response to the presence or absence of carbaryl when pools are isolated. Both treatments were replicated 10 times in pools spaced > 100 m from each other or any natural ponds. The overall number of eggs deposited in these isolated pools was much lower than in the experiments above. As a result our statistical power to detect oviposition site selection was low. However, the pattern of oviposition was similar to the first two experiments. On average non-carbaryl pools received twice as many eggs as carbaryl pools. Collectively, these three experiments show that gray treefrogs strongly prefer pools with no history of carbaryl contamination, that they appear to respond to the chemical or its byproducts directly, and that this preference persists even in the absence of alternative breeding habitats. Thus, when considering the conservation implications of pesticide run-off for aquatic animals, one needs to consider not only the potential direct toxic effects but also habitat selection in response to contamination. |
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"Alliaria petiolata (Garlic Mustard) decreases fitness of native plants through reduction in mycorrhizal fungi symbiont colonization" Carla Fresquez , Laura Beaton, and Tiffany Knight. Department of Biology, Washington University , St. Louis , MO |
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Abstract: Garlic mustard, Alliaria petiolata, an invasive biennial is currently invading the understory of many North American temperate forests and displacing native understory vegetation. Garlic mustard, unlike native plants, is allelopathic. In laboratory experiments, allelopathic chemicals from garlic mustard were shown to kill mycorrhizal fungi. Reduced mycorrhizal colonization has been shown to lower fitness of native plants. We hypothesized that garlic mustard would reduce the abundance of these soil mutualists in the field, and as a result indirectly decrease the fitness of native plants. Our study is the first to examine allelopathic effects of garlic mustard as a mechanisms that allows their invasion success in the field. In our field observations and greenhouse experiment, we show that garlic mustard drastically reduces the mycorrhizal colonization of native plants. Because native plants rely on these soil mutualists, garlic mustard indirectly reduces the fitness of native plants. We have demonstrated a previously undocumented mechanism by which garlic mustard can compete with native plant species. Garlic mustard’s ability to alter the soil microbe community may explain its invasion success. We suggest that restoration of invaded communities may require not only removal of garlic mustard, but also inoculation of mycorrhizal fungi. |
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"HABITAT SELECTION AND SURVIVAL IN EARLY LIFE STAGES OF CULEX MOSQUITOES" Stephanie Gallitano and James Vonesh, Tyson Research Center , Dept. of Biology |
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Abstract: Past studies have demonstrated that some mosquitoes select habitats for egg-laying based on resources, competitors, and predation risk. We studied oviposition site selection of mosquitoes (Culex spp.) in response to larval predators. In the first experiment we examined oviposition responses to backswimmers (Notonecta undulata). We found that apparent habitat selection by Cx.restuans was most likely due to egg predation by free backswimmers. We then examined the relative vulnerability of Cx. restuans and Cx. pipiens to backswimmer predation. We found that Cx. restuans larvae were more vulnerable to backswimmers and that backswimmers consumed more Cx. restuans when given a choice. Finally, we examined oviposition responses to green sunfish (Lepomis cyanellus). We found that Cx. restuans avoided fish pools while Cx. pipiens showed no preference. These studies suggest differences in vulnerability to predators may help explain patterns of habitat site selection in Culex mosquitoes. Future experiments are planned to examine 1) oviposition site selection by Cx. pipiens in response to backswimmers and 2) larval vulnerability of both species to green sunfish predation. Understanding the ecology of Culex mosquitoes is important because these species are potential vectors for disease. |
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"TRAIT-DEPENDENT IMPACTS OF HABITAT FRAGMENTATION ON PREDATOR-PREY INTERACTIONS" Daniel Oppenheimer, Wade A. Ryberg, and Jonathan M. Chase |
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Abstract: Spatial heterogeneity impacts predator-prey interactions. Subdivided habitats can weaken these interactions by creating isolated refugia for prey. Habitat edges can strengthen these interactions by supporting predators able to forage in each habitat type comprising the edge (ecological trap). As fragmentation alters isolation and edge simultaneously, it therefore, may also alter predator-prey interactions. Additionally, as species respond to fragmentation in different ways, fragmentation may also alter community composition favoring traits of certain species over others. To explore the impacts of increasing edge and isolation on predator-prey interactions, we compared attack rates estimated from the functional responses of 2 species of predators within 3 different spatial treatments. To identify whether the impacts of these treatments were trait-dependent we used predators with different foraging strategies: ambush and active. Our results suggest that the shape and configuration of remaining habitat fragments potentially influences predator-prey interactions. We show that isolation weakened predator-prey interactions, while increasing edge strengthened predator-prey interactions. However, the shape and configuration of remaining habitat fragments impacted the two predators differently, altering active and not ambush predator foraging behavior. If these behavioral differences translate into numerical differences, then fragmentation could alter the composition of communities, favoring less-mobile ambush predators. |
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"Hatching Plasticity in Gray Tree Frogs in Response to the Presence of Predators" Molly Sobotka, James Vonesh, Tyson Research Center, Dept. of Biology |
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Poster pdf file under construction.. |
Abstract: Recent studies have shown that some amphibians can adaptively shift the timing of hatching in response to the presence of predators. Studies have shown that species can hatch early to escape egg predators or delay hatching until they reach larger sizes to decrease vulnerability to size-specific post-hatching predators. We examined the effect of cues from crayfish (Orconectes punctimanus), salamander larvae (Ambystoma maculatum), and small mouth bass fry (Micropterus dolomieu) on the timing and size at hatching of the grey tree frog (Hyla versicolor). Based on previous accounts, we expected that crayfish prey primarily on embryos and might induce accelerated hatching, salamander larvae prey on both embryos and tadpoles, and that bass prey primarily on tadpoles and might induce delayed hatching. We observed no effect of crayfish or salamanders on hatching phenotype. In contrast to our expectations, grey treefrogs embryos hatched smaller, not larger sizes in the presence of bass, even though experiments confirmed that hatchlings are more vulnerable than embryos to this predator. Follow-up experiments show that hatching larger provides little or no benefit to tadpoles exposed to bass predation. Thus, hatching early could be a generalized response to accelerate development, and thus reduce exposure time, to aquatic predation risk. |
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Above photographs by Washington University Faculty, Staff and Students, 2005
Copyright Washington University in St.Louis. Electronic images displayed courtesy of Washington University.
Unauthorized use of these images is not permitted.
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