Craig W. Steele

Organization of Chemically Activated Food Search Behavior in Procambarus clarkii Girard and Orconectes rusticus Girard Crayfishes

The feeding responses of decapod crustaceans to chemical stimuli have most often been evaluated in terms of one defining act, ignoring the organization of the behavior. To gain greater insight into foraging behavior, we considered the organization of food-search behavior in evaluating the responses of two species of crayfishes to a feeding stimulant. We also examined the effects of food deprivation on the behavioral organization and whether a behavioral dichotomy exists between food search and feeding behavior in these species. Individual crayfish of the species Procambarus clarkii and Orconectes rusticus were presented with infusions of a feeding stimulant consisting of a supernatant leachate of 100 ml water and 1 g of fish flakes. The stimulant was injected with a syringe and small-bore plastic infusion tubing into the center of a behavioral arena 25 cm square and 15 cm deep. Total injection time was 20 s. Experimental groups were presented with either the full-strength leachate (100%) or one of five dilutions: 75%, 50%, 25%, 10%, or 0% (controls) of full-strength. The feeding stimulant was presented either the day after the crayfish were fed or after one week of food deprivation. We analyzed three components of food-search behavior--detection, probing (near-field search), and locomotion (far-field, or distant, search)--recording the order of occurrence and the latency time to initiation for each behavior. When presented with the stimulus following regular feeding, both species responded to concentrations {ge}50% full-strength with probing behavior (near-field search) prior to locomotion, and to concentrations <50% full-strength with locomotion prior to, or even in the absence of, probing. Detection always occurred first. These results indicate that chemical stimuli preferentially activate distant food search in both species and that a behavioral dichotomy exists between food search and feeding behavior. One week of food deprivation had no effect on the organization of food-search behavior in P. clarkii; however, groups of unfed O. rusticus presented with 25% and 10% full-strength concentrations probed prior to locomotion, indicating a change in behavioral organization.

COVER-SEEKING BEHAVIOR AND SHELTER USE BY JUVENILE AND ADULT CRAYFISH, PROCAMBARUS CLARKII: POTENTIAL IMPORTANCE IN SPECIES INVASION

Cover-seeking behavior of juvenile and adult crayfish, Procambarus clarkii, was examined in relation to the importance of darkness (shadow) and thigmotactic cues. Crayfish were observed individually in small aquaria 5 times per day, with at least 30 min between observations, for a 3-day period. Their positions were recorded as either within or outside shelter(s) provided. Experiment Ia presented crayfish with a choice between a clear thigmotactic shelter or open area. Adults were observed in the open area significantly more than in the shelter. Juveniles were also observed in the open area more often, but the difference was not statistically significant. Experiment Ib presented crayfish with a choice between a dark thigmotactic shelter and open area. Adults were observed more often in the open area, but the difference was not statistically significant. Juveniles were observed in the dark thigmotactic shelter significantly more often than in the open area. In Experiment II, crayfish were given a simultaneous choice among a clear thigmotactic shelter, a dark thigmotactic shelter, and open area. Adults were observed in both open area and dark thigmotactic shelter significantly more often than in the clear thigmotactic shelter. Juveniles were observed in the dark thigmotactic shelter significantly more often than in the open area and were never observed in the clear shelter. For Experiment III, crayfish were given a simultaneous choice among a dark reduced-thigmotactic shelter, a clear thigmotactic shelter, and open area. Adults chose the dark reduced-thigmotactic shelter significantly more often than the clear thigmotactic shelter, but not significantly more often than the open area. Juveniles chose the dark reduced-thigmotactic shelter significantly more often than either the open area or the clear thigmotactic shelter. Experiment IV gave crayfish a choice among a dark reduced-thigmotactic shelter, a dark thigmotactic shelter, and open area. Adults chose the dark reduced-thigmotactic shelter significantly more often. Juveniles chose the dark thigmotactic shelter significantly more often than the dark reduced-thigmotactic shelter, but not significantly more often than the open area. Darkness appears to be the controlling factor in the cover-seeking behavior of both juvenile and adult P. clarkii. The preferential use of larger shelters by adult P clarkii could reduce the limiting effects of shelter availability and might reduce competition for shelter between adults and juveniles, increasing juvenile recruitment. Differences observed in shelter use between adult crayfishes, P. clarkii and 0. rusticus, which prefer the same shelter as juveniles, may give P. clarkii an advantage over 0. rusticus in a species invasion.

SHORT COMMUNICATION: Importance of adequate shelters for crayfishes maintained in aquaria

In short term experiments with different combinations of shelter types and sizes, shadow is the primary factor influencing shelter-seeking behaviour of both juvenile and non-breeding adult Orconectes rusticus and Procambarus clarkii

Effects of Sublethal Exposure to Cadmium on Shelter-Seeking Behavior of Juvenile Orconectes rusticus (Girard) Crayfish

Sublethal behavioral effect of heavy metals on crayfishes may adversely effect their survival in the environment. They may experience increased predation due to changes in their ability to remain in or under shelter. The effect of sublethal cadmium exposure on the ability of juvenile Orconectes rusticus crayfish to remain in shelter was evaluated. Four different treatment groups were used: a control group not exposed to cadmium, and three experimental groups exposed to 1, 2 ,or 3 mg Cd/L for 7 days. Crayfish were placed, individually, into small glass aquaria containing 3 L of laboratory water, with continuous aeration. Each crayfish was provided with a dark, thigmotactic shelter. Cadmium was introduced into the aquaria on days 1 and 4 to establish and maintain the nominal concentration. On days 5 through 7, observations were taken on each crayfish five times per day, with a minimum of 30 minutes between observations. The locations of the animals were recorded as in cover or in the open area of an aquarium. Repeated measures ANOVA was used to examine the effects of sublethal exposure to cadmium on shelter use by the juveniles.

Effects of sublethal lead exposure on the behaviours of green frog (rana clamitans), bullfrog (rana catesbiana) and American toad (bufo americanus) tadpoles

We examined the effects of sublethal exposure to lead (Pb) on avoidance‐preference responses, locomotor activity, discriminate learning, and retention (memory) of green frog (Rana clami‐tans) and bullfrog (Rana catesbeiana) tadpoles, and on avoidance‐preference responses of American toad (Bufo americanus) tadpoles. Sublethal exposure to Pb inhibited both acquisition and retention of discriminate avoidance learning in green frog and bullfrog tadpoles. Green frog and bullfrog tadpoles used in learning acquisition tests were exposed to 0 or 750 μg Pbl‐1for 144h; those used in retention tests were similarly exposed for 120 h. Lead‐exposed and control animals were conditioned to associate illumination (Conditioned Stimulus) with shock (Unconditioned Stimulus) in an aquatic shocking apparatus. Learning acquisition tests showed greater mean response times and fewer avoidances for Pb‐exposed tadpoles. Retention tests also showed greater mean response times, but no avoidances for Pb‐exposed animals. Sublethal expo...

Perspectives in Avoidance-Preference Bioassays

Although behavioral endpoints are used in hazard assessment, establishment of water quality criteria and assessment of a contaminant`s hazard to aquatic life rely primarily on standard acute and chronic toxicity tests. Sublethal effects of pollutants should, however, be of major concern because more organisms experience sublethal rather than acutely or chronically lethal exposures of contaminants. The avoidance-preference approach to behavioral bioassays is very useful in screening pollutants for which the mechanisms of perception or response are largely unknown. The underlying philosophy of these studies is that an animal which perceives a chemical can be attracted or repulsed by it. No response is frequently assumed to indicate lack of perception. All three responses have broad ecological implications. The authors discuss the conditions required for performing avoidance-preference bioassays, as well as their sensitivities, advantages, and limitations. In this regard, a comparative approach is used in examining the results of avoidance-preference bioassays with zebrafish in two different apparatuses. Finally, they compare the results of avoidance-preference studies with other measures of the behavioral toxicity of lead to tadpoles.

Behavioral Assessment of Aquatic Pollutants

Animal behavior is the link between organisms and their environment and is critical for biological adaptation. Despite many studies demonstrating the sensitivity and utility of behavioral endpoints in bioassays assessing potential pollutant effects in aquatic ecosystems, behavioral toxicity testing has not, historically, been included routinely in assessments of aquatic toxicity and subsequent environmental policy formulation. The results of behavioral risk assessments may allow behavioral toxicologists to demonstrate that a chemical is not merely a potential hazard, but that it elicits a functional change in an animal. In this regard, the behavioral toxicologist is on stronger ground than toxicologists recommending action based on isolated, non-functional changes such as acute or chronic mortality. Such sublethal pollutant effects should be of major interest and concern to individuals formulating environmental policies and water quality criteria because many more aquatic organisms encounter sublethal rather than acutely or chronically lethal concentrations of pollutants in nature.

Land Ethic? What Land Ethic?

Just over 60 years ago, Aldo Leopold argued for a ‘land ethic,’ a self-imposed limitation on the degree to which a person modifies the landscape, in order to protect overall ecosystem quality. Leopold’s ‘The land ethic’ is the last essay in his book A sand county almanac (A. Leopold, 1949). Leopold ‘describes the development of an ethic of environmental protection’ (Blackburn, 1994), and notes that people were already ‘separated from the land by, innumerable physical gadgets’ (A. Leopold, 1949, p. 261). In the land ethic, Leopold proposes an extension of traditional ethics (which regulates behavior among humans), to include a respect for the biotic community. He expresses this ethic of environmental protection as thus: ‘A thing is right when it tends to preserve the integrity, stability, and beauty of the biotic community. It is wrong when it tends otherwise’ (A. Leopold, 1949, p. 262). Blackburn (1994) echoes Leopold’s philosophy in expressing the connection among ethics, science, and decision-making in protecting the environment. Leopold’s theme is still relevant today (Blackburn, 1994; Callicot, 1996; Walck & Strong, 2001; A.C. Leopold, 2004; Leopold Center for Sustainable Agriculture, 2006). In the words of Walck and Strong (2001), Leopold’s land ethic ‘provides a useful conceptual framework for interpreting environmental histories, which in turn may be used to plan more effective land use policies for the future,’ and, according to A.C. Leopold (2004), ‘the land ethic has been a major paradigm for ethical and environmental thinking’ since its publication. Because there is little industry or farming on public lands, the land ethic that Leopold proposes is mainly applicable to the attitude that private landowners should have toward the environment. However, nuclear power plants, whether built on private, public–private, or public lands are typified by considerable government involvement, not least the desire to develop alternative energies to save the environment and protect the general public from detriments associated with coal-fired electricity-generating plants. The issues of radioactive waste storage and accidental release of radioactive gases aside, nuclear power can be a double-edged ‘savior,’ as evidenced by Chernobyl and the

Linear intermolt growth in Americamysis bahia (Molenock 1969) (Mysida, Mysidae)

ABSTRACT Two phases of allometry, prepubertal, and pubertal, are evident in A. bahia, equally dividing the first six instars. Coefficients of variation of the sizes of individuals’ abdomens, carapaces, and standard lengths significantly decrease in intermolt four, suggesting a synchronization of the size at which individuals enter the pubertal phase. Growth in standard length is best expressed over the first six post-larval instars by a quadratic equation, but within instars 85%, or more, of the expansion occurs linearly during the intermolt period, with only about 15% occurring during ecdysis. Estimations of carapace:abdomen allometry indicate an average ratio of 1:1.97 during the intermolt and 1:1.68 during ecdysis. The average molt:intermolt ratio in the carapace expansion is 1:3.16, and in the abdomen, 1:3.71, indicating that proportional growth between the carapace and the abdomen is continuous during both the intermolt and molt phases, but occur at different rates and proportions during the two periods.

An analysis of avoidance generalization and food preference transitivity in goldfish, Carassius auratus

To examine the effect of novelty in food selection by fishes, goldfish were trained by feeding them on red or green food pellets. Individual fish and fish in shoals of two, three, and five were then given a choice between equal numbers of familiar pellets and novel (yellow) pellets. In experimental groups, the yellow pellets were soaked in 15% quinine hydrochloride to make them unpalatable. Fish were next presented with equal numbers of familiar and a second novel pellet. It was expected that fish would generalize from their experience with the unpalatable pellets and demonstrate avoidance to sampling a second novel food item. However, as groups, neither controls nor experimentals were reluctant to sample the second novel pellets. Also, fish did not eat significantly more familiar than novel pellets when both were palatable. A third set of experiments examined food preference transitivity in which each pellet type was presented alone and in three pair-wise combinations to individual fish. Although red and yellow pellets were preferred over green, they were preferred equally, indicating an absence of transitivity in pellet choice and, perhaps, a “preference” for a mixture of red and yellow pellets.