Chemical detection of sex and condition in the crayfishOrconectes virilis

Individual crayfish (Orconectes virilis) were tested for responses to water containing conspecific individuals of several sex-status categories. Isolated males did not react to self water but did show aggressive postures while isolated, nonself male water was introduced. Males' responses to female water was different from responses to male water. Water from aggressing males elicited fewer agonistic postures and more neutral postures. Females showed little difference in response to waters from different categories of conspecifics.     

Behavioral responses of crayfish (Orconectes virilis andOrconectes rusticus) to chemical feeding stimulants

We conducted two experiments to assess how chemical stimuli affect feeding behavior, grooming, and walking in the crayfishesOrconectes virilis andOrconectes rusticus. In the first experiment,O. virilis was tested with 29 amino acids; in the second experiment,0. rusticus was tested with 12 amino acids, 13 additional single compounds, and two six-compound mixtures. InO. virilis, the following amino acids, in order of potency, elicited feeding movements:l-isoleucine, glycine, hydroxy-l-proline,l-glutamate,l-valine, and B-alanine. Grooming increased in response tol-phenylalanine,l-tryptophan,l-tyrosine,l-leucine,l-methionine, and D-aspartate. InO. rusticus, both mixtures and the following single compounds, in order of potency, elicited feeding movements: cellobiose, sucrose, glycine, maltose, glycogen, nicotinic acid methyl ester, putrescine, andl-glutamate. Grooming increased in response to putrescine only, and walking increased in response to glycogen only. The responsiveness of these crayfishes to a wide variety of chemicals may reflect the omnivorous foraging habits of these crustaceans.     

Disturbance pheromones in the crayfishOrconectes virilis

The reactions of individual crayfish to the introduction of waters from tanks containing other individuals were recorded to test for the release of chemicals by stressed crayfish. FemaleOrconectes virilis and maleO. rusticus did not show responses to stressed crayfish. MaleO. virilis responded differently to undisturbed and disturbed male crayfish (conspecific and heterospecific). Responses to waters from tanks which contained disturbed individuals were similar whether the source of disturbance was aggressive, predatory, or thermal. Chemical(s) involved appear to persist for at least one hour at room temperature.     

Crayfish feeding responses to zebra mussels depend on microorganisms and learning

Three species of crayfish (Orconectes virilis, O. rusticus, andCambarus robustus) were tested for feeding responses to potential food odors from mollusks (either zebra mussels,Dreissena polymorpha, or native gastropods). In all three crayfish species, feeding responses to odor cues were shown only by individuals experienced with feeding on a prey type. Individuals exposed to just the smell of prey organisms did not show feeding responses, indicating the role of associative learning in diet breadth. Establishment of a learned association took more than one feeding experience but once established lasted more than three weeks. When microbial enzymatic degradation of food protein was eliminated, either by UV radiation or microfiltration, feeding responses were eliminated even for crayfish experienced with a prey type.     

Source and nature of disturbance-chemical system in crayfish

The responses of crayfish to water from aquaria containing either undisturbed or disturbed animals were observed. The crayfishOrconectes propinquus andO. rusticus showed no response to disturbed-conspecific water. Individuals ofO. virilis respond not only to disturbed crayfish but to other taxa (the leechMacrobdella decora, the darterEtheostoma exile, and rock bassAmbloplites rupestris), but not to the painted turtleChrsymes picta. Additional tests indicated partial responses byO. virilis to ammonium and to a chemical or chemicals released from the green gland of crayfish. Ablation experiments indicated the antennules as the site of reception of the chemicals. Additional behavioral tests indicated that detection of the disturbance chemical(s) results in the crayfish showing low-level alert for more than 15 min, once an initial priming period has passed.     

Ester components of aggregation pheromone ofDrosophila virilis (Diptera: Drosophilidae)

The male-produced aggregation pheromone ofDrosophila virilis was found to contain five ester components, in addition to a previously identified hydrocarbon, (Z)-10-heneicosene (Z10–21). The five esters were: the methyl, ethyl, and 1-methylethyl (isopropyl) esters of 2-methyl-(E)-2-butenoic (tiglic) acid and the methyl and ethyl esters of hexanoic acid. The esters were not detected in females. Each ester was active by itself in laboratory bioassay tests, and each increased the number of flies responding toZ10–21 ca. 4–5 times. In comparisons among the five esters at 10 ng per compound, ethyl tiglate was the most active, and methyl tiglate, the least. No mixture of esters was found to be significantly more active than ethyl tiglate alone. In a doseresponse study, bioassay activity increased with dose for both ethyl tiglate andZ10–21. Newly emerged males did not have detectable levels of the esters. All five esters increased as sexual maturity was approached. Ethyl tiglate and ethyl hexanoate were the most abundant in mature males, usually over 15 ng per individual. Ratios among the esters were variable. Male flies also contained an as yet unidentified attractant(s) still more polar than the esters, which was synergistic with the esters and hydrocarbon. Food odors also synergized the synthetic compounds.     

Spatial Arrangement of Odor Sources Modifies the Temporal Aspects of Crayfish Search Strategies

In natural habitats, animals encounter cues from multiple odor sources that may impact foraging decisions. Previous work has focused on orientation behavior to one food odor source, and does not distinguish between mechanosensory and chemosensory guidance of orientation. The present study investigated how the spatial distribution of two food cues affects crayfish orientation behavior. Crayfish, Orconectes virilis, were presented with odor sources that were separated in an artificial stream. Orientation behavior was filmed from above and digitized at a rate of 1 frame per sec. Electrochemical recordings were taken to characterize the odor plume, and an acoustic doppler velocimeter was used to characterize the hydrodynamic structure of the artificial stream. Temporal changes in odor plume structure were seen as a result of the positioning of the odor sources. Changes in the intermittency of the odor pulses as well as concentration, rise time, and slope of the pulse were observed. Time series analysis showed that the lower frequency signals of the dual odor source were higher in energy than the single 1X or single 2X sources. Crayfish altered orientation strategies when presented with different spatial arrangements of food cues. In particular, the temporal aspects of the orientation pattern were most altered by the differences in odor presentations. Crayfish responded with faster walking speeds as a function of distance to the odor source and exhibited more consistent turning angles. This correlates with temporal changes in odor structure, and indicates that the temporal pattern of odor stimulation may be driving the temporal pattern of behavior.     

Alarm pheromones from the marine opisthobranchNavanax inermis

When molested, the marine opisthobranchNavanax inermis secretes into its slime trail, a bright yellow mixture of three major compounds and several closely related minor substances. Collectively, these compounds induce an avoidance-alarm response in a trail-followingNavanax at the concentration limits of 1 × 10^–5 M. The three major compounds have been isolated and identified as 10-(3-pyridyl)-3E,5E,7E,9E-decatetraen-2-one (navenone A), 10-phenyl-3E,5E,7E,9E-decatetraen-2-one (navenone B) and 10-(4-hydroxyphenyl)-3E,5E,7E,9E-decatetraen-2-one (navenone C). The minor constituents of the mixture are proposed as the 3Z,5Z,7E,9E-isomers and the 3-methyl homologs of navenones A and B. The navenones appear to be produced in a specialized gland referred to in earlier studies as the yellow gland and to communicate the presence of predators within the species.     

Alarm response by a plethodontid salamander (Desmognathus ochrophaeus): Conspecific and heterospecific “Schreckstoff”

The detection of chemical alarm cues plays an important role for predator avoidance in many taxonomic groups, but little is known about the presence of such chemical cues in adult or caudate amphibians. We investigated the response (i.e., aversion or nonaversion) to chemical cues from damaged salamander skin and mealworms (Tenebrio molitor) in the plethodontid salamander,Desmognathus ochrophaeus. Avoidance responses were demonstrated to skin extracts of both conspecific and heterospecific salamanders. However, salamanders (D. ochrophaeus) did not avoid heated conspecific skin, fresh conspecific viscera, fresh mealworm, or freshPlethodon richmondi skin extracts. These results indicate that chemical alarm cues are: (1) present in the skin ofDesmognathus salamanders, (2) not present in mealworm or the viscera ofDesmognathus salamanders, and (3) denatured or deactivated by heating. These results also suggest that an avoidance response to chemical cues from damaged conspecifics has adaptive value in predator avoidance in terrestrial as well as aquatic vertebrates.     

Alarm pheromone of pentatomid bug,Erthesina fullo Thunberg (Hemiptera: Pentatomidae)

In the pentatomid bug,Erthesina fullo Thunberg, the odor of male metathoracic scent gland elicits an alarm response, making the male individuals of the same species alert and disperse; the alarm response of males is more obvious than that of females. Chemical composition of the glandular secretion was identified by gas chromatography and mass spectrometry data in comparison with authentic compounds. No sexual dimorphism exists in the glandular composition in this species. A total of 9 compounds [(E)-2-hexenal, (E)-4-keto-2-hexenal, (E)-2-hexenyl acetate,n-undecane,n-dodecane, (E)-2-decenal,n-tridecane, (E)-2-decenyl acetate, andn-pentadecane] are identified, among whichn-tridecane and (E)-4-keto-2-hexenal comprised nearly 70% of the total secretion in both females and males.     

Chemical detection of conspecifics in the crayfishProcambarus clarkii: Role of antennules

Tests with female crayfish (Procambarus clarkii) confirm that conspecifics can be detected chemically. The subjects were more attentive in the presence of water from a stranger's tank than in the presence of water from their own tank. Animals with intact antennules performed this discrimination best, but animals with one intact inner ramus and one intact outer ramus also clearly responded. Conspecific chemical discrimination after loss of both inner or both outer rami was weak (trial 2) or absent (trial 1). The relevance of this outcome to previous conflicting reports on the use of antennules in sex and species discrimination in crayfish is discussed.     

Alarm substances of the stingless bee,Trigona silvestriana

2-Nonanol, 2-heptanol, octyl decanoate, and octyl octanoate were identified from the heads ofTrigona silvestriana workers. When presented at the nest, 2-nonanol, 2-heptanol, and the mixture of the four compounds elicited angular flights, landing, and buzzing of guard bees. Octyl octanoate elicited a weaker response. No response was given to octyl decanoate, to the ether solvent, or to the control volatile, vanillin.     

Ostariophysan Alarm Pheromones: Laboratory and Field Tests of the Functional Significance of Nitrogen Oxides

In laboratory and field-trapping studies, we exposed fathead minnows (Pimephales promelas) and finescale dace (Chrosomus neogaeus) to hypoxanthine-3-N-oxide and a suite of structurally and functionally similar compounds in order to determine if: (1) hypoxanthine-3-N-oxide functions as a chemical alarm signal in ostariophysan fishes and (2) the purine skeleton, a structural component, or the nitrogen oxide, a functional component, or both act as the molecular trigger in this chemical alarm signaling system. Minnows and dace exhibited significant antipredator responses when exposed to conspecific skin extract or hypoxanthine-3-N-oxide (increased shoaling and decreased area use) and the functionally similar pyridine-N-oxide (increased shoaling) but not to structurally similar molecules lacking a nitrogen oxide functional group or to a swordtail skin extract control. Field-trapping studies revealed similar results. Traps labeled with fathead minnows skin extract, hypoxanthine-3-N-oxide, or pyridine-N-oxide caught significantly fewer fish than did those labeled with distilled water. These data strongly suggest that the nitrogen oxide functional group acts as the chief molecular trigger in the Ostariophysan alarm pheromone system and that, contrary to previous research, hypoxanthine-3-N-oxide may be one of several possible molecules that function as a chemical alarm signal. Here we report the first example of a single functional group capable of eliciting a suite of behavioral responses.     

Laboratory experiments to determine if crayfish can communicate chemically in a flow-through system

The importance of chemical cues for transmitting information concerning sexual identity, agonistic state, and stress-related condition in the crayfishProcambarus clarkii (Girard) was examined in a flow-through system. Experiments tested the effects of conditioned water from stimulus tanks on the behavior of solitary male or female crayfish. Twenty males and 20 females were subjected to a random sequence of five treatments: unconditioned water (control), conditioned water flowing through tanks containing a solitary male or female, and conditioned water from tanks holding either two males or two females. Durations of the following behaviors were recorded: chelae up, chela(e) in baffle hole, chela waving, climbing, digging, grooming, gross body movement, and meral spread. Results indicated that crayfish chemically detected another animal within 0.25 m without additional visual or tactile stimuli; however, crayfish apparently did not communicate information on sexual identity, agonistic state, or stress condition, nor does this detection necessarily imply discrimination between stimuli from crayfish and other taxa (e.g., fish). Our conclusions are contrasted with the two previous reports on chemical communication in crayfish in which experimental animals were tested in static systems. We suggest that a temporal separation of molting and copulation and a long reproductive receptivity period for females (which would allow abundant intersexual encounters) could account for a lack of selective pressure to evolve long-distance sex pheromones.     

Alarm response of the marine mud snail,Nassarius obsoletus: Specificity and behavioral priority

Nassarius obsoletus, N. vibex, andN. trivittatus were exposed to juices of conspecifics and taxonomically and ecologically related gastropod species. Conspecific juices caused the strongest alarm responses, while those from taxonomically related species (congeners) induced less pronounced responses. Juices from nonrelated species induced no alarm response with one notable exception, the strong alarm response ofN. trivittatus toUrosalpinx cinerea juices. Nonrelated gastropod species induced stronger feeding responses than more closely related species. The strongest feeding responses, however, were induced by juices from nongastropod mollusks. The apparent balance between feeding attraction to less related species and alarm response to more related species was further examined by manipulating the snails' diet. Starvation resulted in a great reduction of conspecific alarm responsiveness. Following the resumption of feeding, the original responsiveness was again observed. Although the alarm response is likely an antipredator device, conclusive evidence for its effectiveness in reducing predation is lacking. One of the predators ofNassarius obsoletus which may be responsible for maintenance of an alarm response is the green crab,Carcinus maenas.This paper is based in part upon a thesis submitted by D.S. to Boston University for the degree of Master of Arts.     

Chemical sex discrimination in the crayfishProcambarus clarkii: Role of antennules

Chemical sex discrimination of conspecifics by male and female crayfish (Procambarus clarkii) was tested. Intact female subjects were more attentive in the presence of stimulus water from males than from females and showed more aggressive postures in the presence of stimulus water from females than from males. Intact males showed more aggressive postures in the presence of stimulus water from males than from females. Females and males with only one inner antennule ramus and one outer ramus performed discrimination and localization almost as well as intact subjects. Subjects with only the two inner rami or only the two outer rami were disadvantaged in either responding to the stimuli or localizing them. The relevance of this outcome to previous conflicting reports on the use of antennules in sex discrimination in crayfish is discussed.     

Chemical and behavioral ecology of foraging in prairie rattlesnakes (Crotalus viridis viridis)

Free-ranging prairie rattlesnakes (Crotalus viridis viridis) exhibit lengthy vernal migrations upon emergence from winter hibernation. A series of laboratory experiments was designed to test hypotheses regarding the function and causation of vernal movements. Rattlesnakes obtained from Wyoming and Colorado populations were used. First, we hypothesized that the function of vernal movements is to locate small mammal prey. Second, we predicted that activeC. v. viridis use prey chemicals, as well as other cues, to decide whether or not rodents are present in an area. Third, we hypothesized that vernally active males would be more responsive to rodent prey and their odors than females, given observed differences in behavior in the field. Fourth, we predicted that rattlesnakes captured in Colorado would be more sensitive to prey odors than those obtained in Wyoming, because of disparate community structure and, hence, small mammal spatial distributions. As expected, snakes exhibited reduced activity, as well as certain other dependent measures reflecting predatory investigation, in arena zones containing either live rodents or their chemicals. However, responses to the latter were reduced in Wyoming rattlesnakes tested with chemicals from deer mice (Peromyscus maniculatus), relative to Colorado animals tested with chemicals obtained from house mice (Mus musculus). In contrast to patterns observed in nature, males and females exhibited almost no differences in overall responsiveness. Results are discussed in the context of simulation modeling and ongoing studies of prairie rattlesnake behavior.     

Influence of age and body size on alarm responses in a freshwater snail Pomacea canaliculata

A hypothesis that size selection of prey by predators elicits size-specific responses from prey was examined. Freshwater snails, Pomacea canaliculata, ages 1, 3, 7, 15, 30, or 60 days, were given an extract of 3-day-old snails, and 3-day-old snails were given extracts of snails of the other ages or eggs. Snails 15 days or younger crawled out of the water in response to the 3-day-old snail extract, but older ones did not. The 3-day-old snails responded to the extracts of snails of all examined ages, but not to the extract of eggs. Snails of four size classes, 3-days-old, small (shell lengths 8–12 mm), medium (13–20 mm), and large (>28 mm) were given extracts of snails of each of these four classes. The 3-day-old snails crawled out of the water in response to the extract of 3-day-old snails, but showed a lower or no response to other extracts. Larger snails buried themselves in the soil in response to the extract of snails of similar sizes. These responses are discussed in the context of the evolution of the snail's avoidance behavior in response to the size-dependent prey choice by the predator.     

Chemical detection of “self” and conspecifics by crayfish

Stimulus waters were used to examine behaviorally chemical communication in female crayfishProcambarus clarkii. Animals detected conspecifics. Response to stimulus water drawn from the animal's own tank, self water, mimicked either response to distilled water or response to water drawn from the tank of another animal. The response to self water depended on the relative concentration of substance(s) in self water stimuli to that of the same substance(s) in the test animal's tank.     

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.