Thomas Breithaupt

The importance of the lateral line in nocturnal predation of piscivorous catfish

SUMMARY In a previous study we showed that nocturnal piscivorous catfish track the wake left by a swimming prey fish to locate it, following past locations to detect the present location of the prey. In a wake there are hydrodynamic as well as chemical signatures that both contain information on location and suitability of the prey. In order to determine how these two wake stimuli are utilised in prey tracking, we conducted experiments in catfish in which either the lateral line or the external gustation was ablated. We found that a functional lateral line is indispensable for following the wake of swimming prey. The frequency of attack and capture was greatly diminished and the attacks that did occur were considerably delayed when the lateral line was ablated. In contrast, catfish with ablated external taste still followed the wakes of their prey prior to attacking, albeit their attacks were delayed. The external taste sense, which was reported earlier to be necessary for finding stationary (dead) food, seems to play a minor role in the localisation of moving prey. Our finding suggests that an important function of the lateral line is to mediate wake-tracking in predatory fish.

Chemical communication in crustaceans

PART I. INTRODUCTORY SECTION 1. M. Thiel & T. Breithaupt: Chemical Communication in Crustaceans: research challenges for the 21st century 2. T. D. Wyatt: Pheromones and behavior PART II. GENERAL OVERVIEW OF SIGNAL CHARACTERISTICS AND RECEPTION 3. M. E. Hay: Crustaceans as powerful models in aquatic chemical ecology 4. M. J. Weissburg: Waterborne chemical communication: stimulus dispersal dynamics and orientation strategies in crustaceans 5. M. A. R. Koehl: Hydrodynamics of sniffing by crustaceans 6. E. Hallberg & M. Skog: Chemosensory sensilla in crustaceans 7. M. Schmidt & D. Mellon: Neuronal processing of chemical information in crustaceans 8. B. S. Hansson, S. Harzsch, M. Knaden and M. Stensmyr: The neural and behavioral basis of chemical communication in terrestrial crustaceans PART III. CHEMICAL COMMUNICATION AND BEHAVIOR 9. J. Yen & Lasley: Chemical communication between copepods: finding the mate in a fluid environment 10. M. Thiel: Chemical communication in peracarid crustaceans 11. K. Mead & R. Caldwell: Mantis Shrimps: olfactory apparatus and chemosensory behavior 12. J. Aggio & C. D. Derby: Chemical communication in lobsters 13. T. Breithaupt: Chemical communication in crayfish 14. R.T. Bauer: Chemical communication in decapod shrimps: the influence of mating and social systems on the relative importance of olfactory and contact pheromones 15. F. Gherardi & E. Tricarico: Chemical ecology and social behavior of Anomura 16. J. H. Christy & D. Rittschoff: Deception in visual and chemical communication in crustaceans 17. E. A. Hebets & A. Rundus: Chemical communication in a multimodal context 18. B. A. Hazlett: Chemical cues and reducing the risk of predation PART IV. TOWARDS IDENTIFICATION OF CHEMICAL SIGNALS 19. J. Hardege & J. Terschak: Identification of crustacean sex pheromones 20. M. Kamio & C. D. Derby: Approaches to a molecular identification of sex pheromones in blue crabs 21. E. S. Chang: The crustacean endocrine system and pleiotropic chemical messengers 22. A.S. Clare: Towards a characterization of the chemical cue to barnacle gregariousness 23. T. Snell: Contact chemoreception and its role in zooplankton mate recognition 24. Y. W. Chung-Davidson, M. Huertas & W. Li: A review of research in fish pheromones PART V. APPLIED ASPECTS: 25. A. Barki, C. Jones & I. Karplus.: Chemical communication and aquaculture of decapod crustaceans: needs, problems and possible solutions 26. K. H. Olsen: Effects of pollutants on olfactory mediated behaviors in fish and crustaceans 27. T. C. Baker: Insect pheromones: useful lessons for crustacean pheromone programs?

Chemical Communication in Crayfish

Crayfish are a species rich group of large decapod crustaceans that inhabit freshwater environments. Having served as important models for the study of the neural and hormonal control of behavior crayfish were among the first crustacean taxa that were reported to use sex pheromones. Decades of research on crayfish chemical communication have, after initial controversies, now generated a comprehensive picture of the role of pheromones in resolving combats and in initiating sexual interactions. Moreover, the structures involved in chemical signal emission and reception have been identified in most cases. Urine, released in the head region, conveys the chemical messages and is directed via water movements such as gill currents or maxilliped generated currents to the receiver. Chemo-receptors on the first antennae were shown – in most cases – to be responsible for pheromone detection. Urinary signals reduce the duration of aggressive interactions and are crucial for the development of a linear dominance hierarchy. The social hierarchy is based on chemical recognition of the dominance status between combatants. Males are more active than females in initiating reproductive interactions. They recognize a female sex pheromone contained in the urine pulses that females release during the initial aggressive bout preceding mating. Female assessment of male quality is multimodal, involving tactile, visual, and in some cases also chemical cues. The recent development of context-specific and less ambiguous bioassays will facilitate the future purification of the molecules that mediate sexual receptivity and social status in crayfish. These pheromones could be valuable for application in the control of alien invasive crayfish species that cause environmental damage.

Fighting behaviour and the role of urinary signals in dominance assessment of Norway lobsters, Nephrops norvegicus

Norway lobsters, Nephrops norvegicus, live on the bottom of the continental shelf where they construct and defend burrows. Little is known about their agonistic behaviour and potential mechanisms of dominance. This paper investigates fighting behaviour of size-matched male Norway lobsters with a particular emphasis on the role of urinary chemical signals in the assessment of dominance. Norway lobsters were paired in dyadic encounters on two consecutive days. A decrease in fight duration from first to second encounters indicates that N. norvegicus are able to maintain dominance in sequential contests. The main difference between the two encounters is in the behaviour of the loser. Losers strongly reduce their aggression level from first to second encounters. Olfactory sampling behaviour (antennule flicking) of eventual losers is higher than that of the winner indicating that the loser assesses chemical signals of the dominant male. When urine release is blocked for the second encounter, there is no difference in fight duration between first and second encounter. The results suggest that Norway lobsters develop lasting dominance relationships. The study also provides preliminary evidence that urine-borne chemical signals play an important role in mediating dominance.

The flow generated by an active olfactory system of the red swamp crayfish

SUMMARY Crayfish are nocturnal animals that mainly rely on their chemoreceptors to locate food. On a crayfish scale, chemical stimuli received from a distant source are dispersed by an ambient flow rather than molecular diffusion. When the flow is weak or absent, food searching can be facilitated by currents generated by the animal itself. Crayfish employ their anterior fan organs to produce a variety of flow patterns. Here we study the flow generated by Procambarus clarkii in response to odour stimulation. We found that while searching for food the crayfish generates one or two outward jets. These jets induce an inflow that draws odour to the crayfishs anterior chemoreceptors. We quantified velocity fields in the inflow region using Particle Image Velocimetry. The results show that the inflow velocity decreases proportionally to the inverse distance from the animal so that it takes about 100 s for an odour plume to reach the animals chemoreceptors from a distance of 10 cm. We compare the inflow generated by live crayfish with that produced by a mechanical model. The model consists of two nozzles and an inlet and provides two jets and a sink so that the overall mass flux is zero. Use of the model enabled us to analyze the inflow at various jet parameters. We show that variation of directions and relative intensities of the jets allows the direction of odour attraction to be changed. These results provide a rationale for biomimetic robot design. We discuss sensitivity and efficiency of such a robot.

Finding females: pheromone-guided reproductive tracking behavior by male Nereis succinea in the marine environment.

SUMMARY Pheromones trigger reproductive responses of many marine organisms, but little is known about how pheromones mediate mate-finding behavior in the marine environment. This paper investigates whether the tetrapeptide nereithione (cysteine-glutathione disulfide), known to be released by females of the polychaete Nereis succinea to trigger spawning in male N. succinea, can also be used at lower concentrations to guide males to the females. Low concentrations of pheromone elicited increased swim speed and turning left or right 84% of the time. Animals sometimes weaved back and forth, or in other cases swam straight along the trails an average of 8.1±1.2 cm before veering off. At higher concentrations, the males circled frequently, often encountering 10–20 cm of pheromone trail before swimming away. Male responses to nereithione were modeled by computer simulation, taking into account arousal of swim speed, activation of turning, speed of response and its decay, etc. In the model, low concentrations (<10–8 mol l–1) of pheromone significantly increased the number of encounters with the pheromone trail, an average following of simulated trails of 10.5±3.6 cm, and a significant increase in the frequency of encountering a virtual female on the trail (ANOVA, P<0.001). The model supports the hypothesis that a pheromone can have a dual function, with low concentration pheromone trails being used by male N. succinea to find females and increase their likelihood of mating whereas high concentrations of the same pheromone trigger the spawning behavior itself.

Development of behavioural and physiological assays to assess discrimination of male and female odours in crayfish, Pacifastacus leniusculus

Summary Many aquatic organisms use chemical signals to coordinate courtship. However, relatively few water-borne pheromones have been identified. A key obstacle hindering progress in the purification of crustacean pheromones has been the development of reliable bioassays. This study focuses on developing novel bioassays to guide the purification of sex pheromones in signal crayfish, Pacifastacus leniusculus. We aimed to elicit specific sexual behaviours in male crayfish in response to female urine or conditioned water released from a female dummy. A physiological assay, based on male heartbeat recordings, was developed to assess if physiological tests could provide quicker and more sensitive responses than the behavioural assay. Males exposed to female urine showed significantly increased levels of specific mounting behaviours in comparison to male urine or control water. However, other sexual behaviours such as seizing, turning and spermatophore deposition were not observed. The physiological assay demonstrated that a rapid change in the heart rate of male crayfish could be induced through exposure to odour from conspecific female crayfish. Our study indicates male crayfish can discriminate between male and female odours. Physiological measures provide a quick assay for sensitivity to a substance whilst behavioural assays indicate its functional significance.

Sensory biology and behaviour of Nephrops norvegicus.

The Norway lobster is one of the most important commercial crustaceans in Europe. A detailed knowledge of the behaviour of this species is crucial in order to optimize fishery yields, improve sustainability of fisheries, and identify man-made environmental threats. Due to the cryptic life-style in burrows, the great depth and low-light condition of their habitat, studies of the behaviour of this species in its natural environment are challenging. Here, we first provide an overview of the sensory modalities (vision, chemoreception, and mechanoreception) of Nephrops norvegicus. We focus particularly on the role of the chemical and mechanical senses in eliciting and steering spatial orientation behaviours. We then concentrate on recent research in social behaviour and biological rhythms of Nephrops. A combination of laboratory approaches and newly developed tracking technologies has led to a better understanding of aggressive interactions, reproductive behaviours, activity cycles, and burrow-related behaviours. Gaps in our knowledge are identified and suggestions for future research are provided.

Chemical Communication in Crustaceans: Research Challenges for the Twenty-First Century

Chemical signals play an important role during various life stages of crustaceans. Settling of larvae, parent–offspring communication, mate finding, mate choice, aggressive contests, and dominance hierarchies are all mediated by chemical signals. Enormous advances have been made on understanding the function of chemical signals in crustaceans and we are on the doorstep of major advances in chemical characterization of pheromones. In many species urine is the carrier of chemical signals. Crustaceans control release and transfer direction of urine, but it is unknown whether crustacean senders can manipulate the composition of urineborne pheromones. Chemicals contained in the urine effectively convey information about conspecific properties such as sex, sexual receptivity, species identity, health status, motivation to fight, dominance, individual identity, and molt stage. In larger species (shrimp, crabs, lobsters, crayfish) signal delivery is often aided by self-generated fanning currents that flush chemicals towards receivers, which themselves might actively pull water towards their sensory structures. Antennal flicking also supports molecule exchange at the receptor level. Contact pheromones play a role in sex recognition in several crustacean taxa and in settlement of barnacles. Large crustacean species show little or no sexual dimorphism in receptor structures, but in smaller taxa, e.g. peracarids and copepods, males often have larger antennae than females. Whether differences in sexual roles have also resulted in sex-specific brain centers is not known at present. While pheromones play an important role in mate finding and species recognition, there are numerous examples from peracarids and copepods where males pursue or even form precopulatory pairs with females of closely related congeners. Differentiation of chemicals often appears to be insufficient to guarantee reproductive isolation. In many freshwater and coastal habitats, pollutants may also disrupt chemical communication in crustaceans, but the specific mechanisms of interference are not well understood. The chemical characterization of crustacean pheromones is viewed as a major step in improving our understanding of chemical communication. Knowing the chemical nature of pheromones in freshwater species will boost research on aquatic crustaceans. Interdisciplinary work between chemists (metabolomics), behavioral ecologists (bioassays), neurobiologists (chemoreception), and molecular biologists (genomics) promises to produce significant advances in our understanding of crustacean chemical communication during the coming decade.

Sensitivity of Crustaceans to Substrate-Borne Vibration

There is increasing interest in the responsiveness of crustaceans to vibrations, especially in the context of marine developments where techniques such as pile driving create strong vibrations that are readily transmitted through the seabed. Experiments were undertaken under controlled conditions to investigate the sensitivity of unconditioned crustaceans to substrate-borne vibration. The subjects were exposed to a range of frequencies and amplitudes using the staircase method of presentation to determine the thresholds of response. Behavior varied according to the strength of the stimuli and included bursts of movement and rapid bouts of movement.