Brian A. Hazlett

EFFECTS OF INTERSPECIFIC COMPETITION ON FITNESS OF THE HERMIT CRAB CLIBANARIUS TRICOLOR

Clibanarius tricolor overlaps strongly in shell utilization with the other common species of intertidal hermit crabs found in the Florida Keys. Laboratory observations indicated C. tricolor can dominate Clibanarius antillenisis in shell fights, while Calcinus tibicen dominates C. tricolor. In micro-areas of sympatry with C. antillensis, C. tricolors shell fit is better and egg production parameters not affected when compared to adjacent areas where only C. tricolor occurs. Sympatry with Calcinus tibicen results in a poorer shell fit, a smaller shell size for a given size crab, a smaller mean size of crab, and a disruption of the relationship between clutch size and crab size:shell weight ratio. A strong effect of shell species on the probability of Y Y being ovigerous was noted. It is suggested that the ecological separation which characterizes these species over most of their ranges was an evolutionary response, in part, to the effects of interspecific shell competition.

Examination of the Agonistic Behaviour of the Crayfish Orconectes Virilis By Character Analysis

The agonistic behavior of the crayfish Orconectes virilis was observed in the laboratory, with attention to the effects of size, past experience, and displays. Character analysis was utilized to quantify the relative importance of these three factors. I) In short fights, larger animals and animals which had won previous fights had a decided advantage. 2) In long fights, size and past experience seemed to have little influence on who would win. 3) Initiating an interaction gave an animal and advantage in short fights or when both were the same size. 4) Model presentations indicated that postures assumed during fights were effective visual stimuli and that the white areas on appendages are important components of displays. 5) The greatest reduction in uncertainty concerning which behavior pattern would occur at any time in a fight came from knowing the just previous act of the other crayfish. 6) The amount of information transmitted from one crayfish to another by displays increased during fights to a peak of 160 bits (53% uncertainty reduction) in the middle of fights. 7) Partitioning the data into long or short fights and into initiator-won or defender-won fights increased the apparent importance of inter-animal communication.

Alarm responses in the crayfishOrconectes virilis andOrconectes propinquus.

Individuals of two species of crayfish (Orconectes virilis andO. propinquus) were tested in the laboratory for responses to chemicals released from physically damaged conspecifics. Individuals ofO. propinquus did not show an alarm response to crushed conspecifics. Individuals ofO. virilis responded to a water-borne substance released from crushed conspecifics by assuming an intermediate posture and ceasing movement. Similar alarm responses were shown by individuals ofO. virilis to crushed congeneric individuals (O. propinquus), and these responses were not eliminated by either freeze-thawing the crayfish used to prepare the signal or by treating freshly crushed crayfish with the enzyme trypsin. Individuals ofO. virilis showed strong feeding responses to solutions prepared from frozen fish flesh but showed a mixture of alarm and feeding responses to freshly killed fish. These results indicate that the alarm substance used byO. virilis is widespread.

RESPONSES TO MULTIPLE CHEMICAL CUES BY THE CRAYFISH ORCONECTES VIRILIS

To investigate how organisms respond to multiple cues, the responses of the crayfish Orconectes virilis to natural chemical stimuli presented both one at a time and in combinations were recorded in the laboratory. Following the introduction of predator (snapping turtle) odours, individuals decreased the rate of non-locomotory movements compared to control levels. The addition of food odour resulted in an increase in movement as well as postural changes. When both signals were presented simultaneously, the level of food-elicited movements was reduced and the extent of inhibition of food-related responses depended upon the relative intensity of the two types of input. The behavioural effect of predator odour introduction lasted about two hours. When alarm odour and food odour were presented simultaneously, movements were reduced even more strongly than with the predator odour-food odour combination. Presentation of two signals associated with danger (alarm and predator odours) resulted in a significantly greater reduction of food odour-induced movement than for either danger signal by itself.

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.

Integration of multiple predator cues by the crayfish Orconectes propinquus

We examined the responses of individual crayfish (O. propinquus) to cues associated with predation risk in the laboratory. We presented visual and tactile cues either alone or in combination with conspecific alarm odour. The addition of alarm odour resulted in crayfish responding to a visual cue at a greater distance and with a stronger response in terms of distance retreated. Similarly, the frequency of response and the magnitude of the responses shown to a tactile cue were higher when alarm odour was added, but only at night. During the day, the addition of alarm odour did not affect the responses shown to tactile input. We then presented a dilution series of alarm odour solutions (100, 50, 10 and 1% strength) in combination with the visual stimulus. There were no differences in response parameters with chemical cues of different strength. We discuss the response patterns observed with regard to the ecology of O. propinguus compared with related species of crayfish.

Starvation, Energy Reserves, and Aggression in the Crayfish Orconectes Virilis (Hagen, 1870) (Decapoda, Cambaridae)

Der Einfluss von Nahrungsentzug auf das aggressive Verhalten des Krebses Orconectes virilis wurde im Labor untersucht. Nach einer Woche Nahrungsentzug kampften die Versuchstiere ofter und langer und gewannen ofter als Kontrolltiere. Nach zwei Wochen Hungern waren diese Unterschiede nicht mehr zu beobachten.

Behavioral Biology of the Crayfish Orconectes virilis I. Home Range

The movements of individual crayfish, Orconectes virilis, were followed by hand captures of marked animals for over a year. Considerable variability was found in both the total home-range length recorded for individuals and in the capture-to-capture movement (both ranged from zero to 308 m). The average of the capture-to-capture movements was 33 m; the mode was 0-5 m (crayfish found in same grid area). Males and females did not differ in size of home-range or capture-to-capture movement, but several aspects of the data indicate that males moved more. Size was significantly correlated with movement for females but not males. Animals frequently moved farther after a molt, and many animals moved into shallow, sandy areas around the time of a molt.

Responses of Cambarid Crayfish to Predator Odor

The responses of individuals of four sympatric species of cambarid crayfish to the introduction of the odor of a common predator, the snapping turtle Chelydra serpentina, were recorded in the laboratory. Adult Orconectes virilis spent significantly more time in a lowered posture and reduced the frequency of nonlocomotory movements following introduction of snapping turtle odor but showed no change in behavior upon introduction of the odor of painted turtle (Chrysemys picta). Recently released young O. virilis did not respond to snapping turtle odor initially but did so after turtle odor and conspecific alarm odor had been paired. Individuals of O. propinquus did not respond to snapping turtle odor. Initial tests with O. rusticus did not yield any response to snapping turtle odor but after experience with paired turtle and alarm odor, individuals showed a decrease in nonlocomotory movements when just snapping turtle odor was introduced. Individuals of Cambarus robustus spent less time in the lowered posture, less time in their burrow, and more frequently executed nonlocomotory movements, in response to snapping turtle odor. The differences in responses to the odor of a common predator are correlated with ecological differences among the crayfish species.

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.