Erica L. Wildy

Shifts in Life History as a Response to Predation in Western Toads (Bufo boreas)

Larval western toads (Bufo boreas) are known to exhibit antipredator behavior in response to both chemical alarm cues released from injured conspecifics and chemical cues of predatory invertebrates. In this study, we tested whether long-term exposure to predator and alarm cues resulted in an adaptive shift in life history characteristics of the toads. We raised groups of tadpoles in the presence of: (1) predatory backswimmers (Notonecta spp.) that were fed toad tadpoles, (2) nonpredatory water boatman (Corixidae), and (3) chemical alarm cues of injured conspecifics. Tadpoles raised in the presence of both chemical alarm cues and cues of predators fed tadpoles metamorphosed in significantly shorter time than those raised in the presence of the nonpredator control. Reducing time taken to reach metamorphosis would reduce exposure to aquatic predators. There was no difference among treatments in the size at metamorphosis. Our results suggest that this shift in metamorphic characteristics may represent a facultative alteration in life history.

The effects of food level and conspecific density on biting and cannibalism in larval long-toed salamanders, Ambystoma macrodactylum

Previous studies have examined abiotic and biotic factors that facilitate agonistic behavior. For larval amphibians, food availability and conspecific density have been suggested as important factors influencing intraspecific aggression and cannibalism. In this study, we examined the separate and combined effects of food availability and density on the agonistic behavior and life history of larval long-toed salamanders, Ambystoma macrodactylum. We designed a 2×2 factorial experiment in which larvae were raised with either a high or low density of conspecifics and fed either a high or low level of food. For each treatment, we quantified the amount of group size variation, biting, and cannibalism occurring. Additionally, we examined survival to, time to and size at metamorphosis for all larvae. Results indicated that differences in both density and food level influenced all three life history traits measured. Moreover, differences in food level at which larvae were reared resulted in higher within-group size variation and heightened intraspecific biting while both density and food level contributed to increased cannibalism. We suggest that increased hunger levels and an uneven size structure promoted biting among larvae in the low food treatments. Moreover, these factors combined with a higher encounter rate with conspecifics in the high density treatments may have prompted larger individuals to seek an alternative food source in the form of smaller conspecifics.

Avoidance Response of Juvenile Pacific Treefrogs to Chemical Cues of Introduced Predatory Bullfrogs

Bullfrogs (Rana catesbeiana), native to eastern North America, were introduced into Oregon in the 1930s. Bullfrogs are highly efficient predators that are known to eat a variety of prey including other amphibians. In laboratory experiments, we investigated whether juvenile Pacific treefrogs (Hyla regilla) recognize adult bullfrogs as a predatory threat. The ability of prey animals to acquire recognition of an introduced predator has important implications for survival of the prey. We found that treefrogs from a population that co-occurred with bullfrogs showed a strong avoidance of chemical cues of bullfrogs. In contrast, treefrogs from a population that did not co-occur with bullfrogs, did not respond to the bullfrog cues. Additional experiments showed that both populations of treefrogs use chemical cues to mediate predation risk. Treefrogs from both populations avoided chemical alarm cues from injured conspecifics.

Avoidance response of a terrestrial salamander (Ambystoma macrodactylum) to chemical alarm cues

Organisms from a wide variety of taxonomic groups possess chemical alarm cues that are important in mediating predator avoidance. However, little is known about the presence of such alarm cues in most amphibians, and in particular terrestrial salamanders. In this study we tested whether adult long-toed salamanders (Ambystoma macrodactylum) showed an avoidance response to stimuli from injured conspecifics. Avoidance of stimuli from injured conspecifics could represent avoidance of a chemical alarm cue or, alternatively, avoidance of a territorial pheromone or conspecific predator odor. Consequently, we also tested whether salamanders avoided stimuli from noninjured conspecifics. Salamanders avoided stimuli from injured but not from noninjured conspecifics. Therefore, we concluded that the response to injured conspecifics represents avoidance of a chemical alarm cue and not avoidance of a territorial pheromone or predator cue. This is the first clear demonstration of chemical alarm signaling by a terrestrial amphibian and the first report of chemical alarm signaling in an ambystomatid salamander. By avoiding an area containing stimuli from injured conspecifics, long-toed salamanders may lower their risk of predation by avoiding areas where predators are foraging.

Juvenile western toads, Bufo boreas, avoid chemical cues of snakes fed juvenile, but not larval, conspecifics

Previous investigations have demonstrated the importance of predator diet in chemically mediated antipredator behaviour. However, there are few data on responses to life-stage-specific predator diets, which could be important for animals like amphibians that undergo metamorphosis and must respond to different suites of predators at different life-history stages. In laboratory choice tests, we investigated the chemically mediated avoidance response of juvenile western toads, Bufo boreas, to four different chemical stimuli: (1) live conspecific juveniles; (2) live earthworms; (3) snakes fed juvenile conspecifics; and (4) snakes fed larval conspecifics (tadpoles). Juvenile toads avoided chemical cues from snakes that had eaten juvenile conspecifics, but did not respond to the other three stimuli, including chemical cues from snakes fed larval conspecifics. In addition, the response to cues from snakes fed juveniles differed significantly from that of snakes fed larvae. To our knowledge, this is the first study to demonstrate the importance of diet in predator avoidance of juvenile anurans and the ability of juvenile toads to distinguish between chemical cues from predators that have consumed larval versus juvenile conspecifics. Copyright 2000 The Association for the Study of Animal Behaviour.

CANNIBALISM ENHANCES GROWTH IN LARVAL LONG-TOED SALAMANDERS, (AMBYSTOMA MACRODACTYLUM)

Intraspecific predation (=cannibalism) has been widely documented within numerous animal populations (Elgar and Crespi, 1992). Several studies have explored possible selective forces behind the existence of cannibalism, including reduction in competition, enhanced reproductive success, and better nutrition (Fox, 1975; Polis, 1981; Meffe and Crump, 1987; Elgar and Crespi, 1992). In amphibians, several studies have documented the occurrence of and mechanisms sur-

INFLUENCE OF ABIOTIC AND BIOTIC FACTORS ON AMPHIBIANS IN EPHEMERAL PONDS WITH SPECIAL REFERENCE TO LONG-TOED SALAMANDERS (AMBYSTOMA MACRODACTYLUM)

Animals living in ephemeral habitats are subjected to various abiotic and biotic selection pressures that may not be present to the same degree in permanent habitats. For example, pond drying can lead to increased predation and competition as resources become limited and temperature and water quality undergo drastic fluctuations. Amphibians provide an excellent model for studying factors associated with survival in temporary habitats. Aquatic amphibians developing in ephemeral habitats must find food, avoid predators, and cope with potentially great fluctuations in abiotic parameters under increasingly harsh conditions. In Oregon (U.S.A.), larval long-toed salamanders (Ambystoma macrodactylum) often inhabit temporary ponds that gradually dry during the summer. We have been studying several factors that may influence long-toed salamander behavior, growth, and survival in ephemeral montane ponds in the Cascade Range. These include biotic interactions focusing on cannibalism and predation, and abiotic factor...

Avoidance Response of Post-metamorphic Anurans to Cues of Injured Conspecifics and Predators

Despite the widespread occurrence of chemically mediated antipredator responses among larval anurans, little is known concerning whether anurans utilize chemical cues after metamorphosis. Larval western toads (Bufo boreas) and red-legged frogs (Rana aurora) both exhibit antipredator responses when exposed to alarm cues of injured conspecifics. There is some debate as to whether larval Cascades frogs (Rana cascadae) show a similar response. In this study, we documented that toads and red-legged frogs respond to cues of injured conspecifics after metamorphosis, while Cascades frogs do not The avoidance

Shifts in Life-History Traits as a Response to Cannibalism in Larval Long-Toed Salamanders (Ambystoma macrodactylum)

We examined the potential influence of cannibalism on life-history characteristics of larval long-toed salamanders (Ambystoma macrodactylum). Using a 2 × 2 factorial design, crossing morphology with diet, we exposed typical morph larvae to one of four types of stimulus animals: cannibal morphs fed a conspecific diet, cannibal morphs fed a heterospecific diet (i.e., Tubifex), typical morphs fed a conspecific diet, and typical morphs fed a heterospecific diet. Test larvae exposed to stimulus animals fed a conspecific diet exhibited a slower growth rate and an increase in the time taken to reach metamorphosis. These changes in life history likely represent a cost of antipredator behavior.

Embedding Multiple Literacies into STEM Curricula

In fall 2012, an interdisciplinary team of science, English, and library faculty embedded reading, writing, and information literacy strategies in Science, Technology, Engineering, and Mathematics (STEM) curricula as a first step in improving student learning and retention in science courses and aligning them with the Next Generation Science and Common Core State Standards. The authors present their reading, writing, and information literacy contributions, explaining the importance of introducing these concepts and strategies into science courses.