Showing papers by "Richard K. Zimmer published in 2000"

Chemical signaling processes in the marine environment

Abstract: Understanding the mechanisms by which environmental chemical signals, chemical defenses, and other chemical agents mediate various life-history processes can lead to important insights about the forces driving the ecology and evolution of marine systems. For chemical signals released into the environment, establishing the principles that mediate chemical production and transport is critical for interpreting biological responses to these stimuli within appropriate natural, historical contexts. Recent technological advancements provide outstanding opportunities for new discoveries, thus allowing quantification of interactions between hydrodynamic, chemical, and biological factors at numerous spatial and temporal scales. Past work on chemically mediated processes involving organisms and their environment have emphasized habitat colonization by larvae and trophic relationships. Future research priorities should include these topics as well as courtship and mating, fertilization, competition, symbiosis, and mi...

Physical constraints on ecological processes: a field test of odor‐mediated foraging

Abstract: The physicochemical environment can strongly constrain the outcome of ecological interactions such as predation, mating, and competition. This is especially true of processes mediated by the sense of olfaction, because wind and water currents control the dispersal of odor signals and act as ancillary cues during odor plume following. In the field, we examined how variations in the physical and chemical properties of odor plumes would alter the foraging behavior of the blue crab Callinectes sapidus, a common predator/ scavenger in tidal marsh creeks in the southeastern United States. We video-recorded re- sponses of naturally foraging crabs to odor plumes of varying composition and odor release rate (characteristic of clams of differing size). During each trial we presented crabs with an experimental plume that was a mixture of fluorescein-dyed seawater and clam mantle fluid, oyster mantle fluid, or a suite of amino acids, and a control plume which consisted of dyed seawater only. In addition to manipulating the chemical composition and odor release rate of the plume, we allowed flow speed to vary naturally with the tide. We tested for effects of odor composition, odor release rate, and flow speed on the success (i.e., finding the target) and efficiency (i.e., search path direction) of blue crab foraging. Mantle fluid solutions and wounded prey items elicited active search and upstream walking, while control and amino acid solutions had no effect on crab behavior. Odors released at a low rate (either low volume flow or low concentration) elicited fewer responses from crabs, and the resulting search was less efficient and less successful than responses to odors released at higher rates. Ambient current speed also affected both search success and efficiency. There was a decline in search success when current speed in the tidal channel was below 1 cm/s; search success remained constantly high, however, when current speed was above this threshold. Search efficiency was directly proportional to ambient current speeds. Such relationships between hydrodynamic and chemical properties of the environ- ment and foraging success and efficiency suggest that variation in the physicochemical environment can influence the detectability of prey and strategies employed by foragers. These results extend beyond the foraging of marine crustaceans into other olfactory- mediated interactions and habitats.

Developmental dimorphism and expression of chemosensory-mediated behavior: habitat selection by a specialist marine herbivore.

Abstract: Developmental dimorphisms provide an opportunity to compare sensory systems and behavior patterns between different forms of a single species. Alternative morphs differing in dispersal ability often show behavioral differences that mediate life-history trade-offs. We measured the behavioral responses of both long-lived, feeding larvae and short-lived, non-feeding larvae of the specialist marine herbivore Alderia modesta during habitat selection. Larvae immediately responded to waterborne cues from the adult host algae by increasing their turning rate, by changing their swimming speed in the water and by moving in rapid hops or spiraling along the bottom. These behavior patterns retained larvae in areas where the dissolved cue was initially perceived, and prolonged exposure to the cue increased the percentage of larvae that initiated metamorphosis. Despite their differences in life span and trophic mode, both larval morphs displayed similar behavior patterns when stimulated by the waterborne cue. Long-lived larvae had a stronger response, however, suggesting that settlement behavior may offset the costs of a prolonged larval life. This is the first study to examine the effects of dimorphic development on chemosensory-mediated behavior.

Larval settlement: chemical markers for tracing production, transport, and distribution of a waterborne cue

Abstract: Dissolved chemical signals mediate many ecological interactions in the marine environ- ment, but little is known about how rates of production and distribution of waterborne cues affect life- history processes in the field. Larvae of the specialist marine herbivore Alderia modesta settle and metamorphose in response to complex carbohydrates produced exclusively by the adult host alga Vaucheria longicaulis, but the natural cue cannot be detected in sea water by current methods of ana- lytical chemistry. The simple carbohydrates mannitol and glucose, which are highly concentrated in V. longicaulis tissue, were tested as possible markers for the settlement cue in laboratory and field experiments. In production experiments, both mannitol and glucose were released by patches of the algae and accumulated in the surrounding water over time, as did bioactivity due to the settlement cue. Pore water trapped within patches of V. longicaulis during low tides contained high concentra- tions of mannitol and glucose, and induced a high level of larval metamorphosis even at a 1:5 dilu- tion. The bioactive pore water was released from algal patches into overlying water following immer- sion by a flood tide; water collected above the surface of V. longicaulis induced significant metamorphosis and changes in larval swimming behavior. Glucose content was significantly corre- lated with bioactivity in water collected above algal mats throughout the first 30 min of a flood tide, and also 2 h later, during the peak of a high tide. Mannitol and glucose concentrations were high in sea water above the center of an algal patch, but diminished rapidly at the edges and outside of the patch. Pore water collected from mats of the co-occurring alga Enteromorpha clathrata did not induce metamorphosis or changes in larval swimming behavior, and contained only background levels of the markers. The combined results show that mannitol and glucose are indeed released and transported along with complex carbohydrates from V. longicaulis, and can be used to define patterns of distrib- ution of the dissolved settlement cue on both spatial and temporal scales. Ecologically, the data sug- gest that settlement rates of larvae of A. modesta may vary widely during a tidal cycle, as a function of the release and subsequent hydrodynamic transport of waterborne cues from the host alga.