David L. Macmillan

Crayfish Recognize the Faces of Fight Opponents

The capacity to associate stimuli underlies many cognitive abilities, including recognition, in humans and other animals. Vertebrates process different categories of information separately and then reassemble the distilled information for unique identification, storage and recall. Invertebrates have fewer neural networks and fewer neural processing options so study of their behavior may reveal underlying mechanisms still not fully understood for any animal. Some invertebrates form complex social colonies and are capable of visual memory–bees and wasps, for example. This ability would not be predicted in species that interact in random pairs without strong social cohesion; for example, crayfish. They have chemical memory but the extent to which they remember visual features is unknown. Here we demonstrate that the crayfish Cherax destructor is capable of visual recognition of individuals. The simplicity of their interactions allowed us to examine the behavior and some characteristics of the visual features involved. We showed that facial features are learned during face-to-face fights, that highly variable cues are used, that the type of variability is important, and that the learning is context-dependent. We also tested whether it is possible to engineer false identifications and for animals to distinguish between twin opponents.

Exploration in a T-Maze by the Crayfish Cherax destructor Suggests Bilateral Comparison of Antennal Tactile Information

Many crayfish species inhabit murky waters or have a crepuscular lifestyle, which forces them to rely on chemical and mechanical information rather than visual input. Information on how they use one form of mechanical information—tactile cues—to explore their local environment is limited. We observed the exploratory behavior of the crayfish Cherax destructor in a T-maze under red light. Animals moved forward along the long arm of the maze and then moved equally in one of two available directions. The arm chosen by one crayfish did not affect that selected by a second crayfish tested immediately after in an unwashed maze. Previous experience in the maze also did not affect the choice. We found, however, that crayfish with one antenna denervated or splinted back to the carapace turned more often toward the unaltered side. Our data support the hypothesis that crayfish bilaterally compare information from their antennae.

Specialisation of the venom gland proteome in predatory cone snails reveals functional diversification of the conotoxin biosynthetic pathway

Conotoxins, venom peptides from marine cone snails, diversify rapidly as speciation occurs. It has been suggested that each species can synthesize between 1000 and 1900 different toxins with little to no interspecies overlap. Conotoxins exhibit an unprecedented degree of post-translational modifications, the most common one being the formation of disulfide bonds. Despite the great diversity of structurally complex peptides, little is known about the glandular proteins responsible for their biosynthesis and maturation. Here, proteomic interrogations on the Conus venom gland led to the identification of novel glandular proteins of potential importance for toxin synthesis and secretion. A total of 161 and 157 proteins and protein isoforms were identified in the venom glands of Conus novaehollandiae and Conus victoriae, respectively. Interspecies differences in the venom gland proteomes were apparent. A large proportion of the proteins identified function in protein/peptide translation, folding, and protection events. Most intriguingly, however, we demonstrate the presence of a multitude of isoforms of protein disulfide isomerase (PDI), the enzyme catalyzing the formation and isomerization of the native disulfide bond. Investigating whether different PDI isoforms interact with distinct toxin families will greatly advance our knowledge on the generation of cone snail toxins and disulfide-rich peptides in general.

Multimodal individual recognition in the crayfish cherax destructor

There is some evidence that macrurans recognize each other as individuals. In freshwater crayfish there are conflicting reports and there is limited information about the sensory mechanisms involved. To determine the extent to which the crayfish Cherax destructor is capable of individual recognition, we performed experiments that familiarized animals with each other and then manipulated their recent success in dominance contests. Crayfish were more likely to win an encounter when paired against a familiar opponent than an unfamiliar one after the manipulation stage. In other experiments, animals were attracted to familiar conspecifics when only visual or chemical cues were present. This demonstrates that C. destructor is able to discriminate between a familiar and an unfamiliar opponent. The results highlight the complex nature of intraspecific communication in crayfish and suggest elements likely to be of importance in the social interactions of groups in the wild state.

Crustacean social behavioral changes in response to isolation.

Periods of isolation during which animals have no social contact are common in the design of behavioral experiments. They are used, for example, to test memory and recognition responses, or to ensure a baseline condition before experimental manipulations commence. We investigated the effect of isolation periods on the aggressive behavior of matched pairs of the crayfish Cherax destructor in two contexts. The first experiment tested the effects of a period of isolation between two encounters. The second experiment tested the effects of isolation before an encounter by pairing one crayfish from a communal living environment with another crayfish from an isolated one. Fight outcome and aggression levels were analyzed, resulting in three conclusions about the social biology of C. destructor. First, encounters between familiar opponents are influenced by the outcome of the familiarization fight for about 2 weeks. Second, the level of aggression and the outcome of an encounter are affected over different time frames. Third, individuals that are isolated before an encounter can be disadvantaged. These data suggest that isolation, or events that occur during periods of isolation, affect multiple elements of social behavior in C. destructor. This suggestion has implications for the interpretation of previous results and future studies in crustaceans and other taxa.

Feeding activity and the morphology of the digestive tract in stage-I phyllosoma larvae of the rock lobster Jasus edwardsii

First-stage phyllosoma larvae of the rock lobster Jasus edwardsii attached to and fed on larvae of the Tasmanian trumpeter fish, Latris lineata, when the two were placed together in an aerated, through-circulating, sea-water aquarium. Scanning electron micrographs of the mouthparts showed adaptations suitable for scraping and cutting soft substrata. Phyllosomas removed from the fish while feeding had pigment particles from the fish integument throughout their digestive tracts. The behaviour of these phyllosomas, swimming in a Petri dish, was recorded with a microscope and video system. The presence of the pigment particles made it possible to see the lumen of the gut diverticulae and parts of them undergoing regular contractions. Transmission electron micrographs of the gut showed that the parts of the gut that contracted in the video records have well developed muscle bands associated with them. The ultrastructure of the digestive tract is relatively uniform throughout and is lined by cells resembling the undifferentiated (E) cells of other scyllarid and palinurid larvae. Extensive folding of the wall, together with a brush border on the digestive cells, results in a large surface area for absorption. There is no grinding or filtering apparatus in the digestive tract. The behaviour of the phyllosoma, structure of the mouthparts, and ultrastructure of the digestive tract, suggest that the first-stage phyllosoma of J. edwardsii is adapted for removing soft tissue from gelatinous organisms and pumping it around the digestive tract.

Antennal receptors in puerulus and postpuerulus stages of the rock lobster Panulirus cygnus (Decapoda: Palinuridae) and their potential role in puerulus navigation

ABSTRACT This study describes the sensory structures on the antennae and antennules of the puerulus and postpuerulus stage juveniles of the western rock lobster Panulirus cygnus. Both stages have short and long spines, which probably function in protection and in contact-detection. Both also possess setae structurally similar to those shown to be near-field vibration receptors in other crustaceans. Both have aesthetasc setae on the antennules and petaloid setae on the antennae, with both types of setae appearing to be chemosensory. The puerulus stage has an almost continuous linear series of pinnate setae that overlie each other and also the segmental boundaries along the antenna in such a way that the series is well positioned to act as a detector for vibration of the whole antenna. This arrangement is unique to the puerulus stage, which is also noted for its 40-60-km directional swim from the offshore waters to the coast. We suggest that the complex receptor system formed by the antennae and the pinnate setal system plays a role in navigation by allowing the animal to orient to vibrational clues associated with the coast.

Embryonic Toxin Expression in the Cone Snail Conus victoriae: PRIMED TO KILL OR DIVERGENT FUNCTION?*

Predatory marine cone snails (genus Conus) utilize complex venoms mainly composed of small peptide toxins that target voltage- and ligand-gated ion channels in their prey. Although the venoms of a number of cone snail species have been intensively profiled and functionally characterized, nothing is known about the initiation of venom expression at an early developmental stage. Here, we report on the expression of venom mRNA in embryos of Conus victoriae and the identification of novel α- and O-conotoxin sequences. Embryonic toxin mRNA expression is initiated well before differentiation of the venom gland, the organ of venom biosynthesis. Structural and functional studies revealed that the embryonic α-conotoxins exhibit the same basic three-dimensional structure as the most abundant adult toxin but significantly differ in their neurological targets. Based on these findings, we postulate that the venom repertoire of cone snails undergoes ontogenetic changes most likely reflecting differences in the biotic interactions of these animals with their prey, predators, or competitors. To our knowledge, this is the first study to show toxin mRNA transcripts in embryos, a finding that extends our understanding of the early onset of venom expression in animals and may suggest alternative functions of peptide toxins during development.

Corners and bubble wrap: the structure and texture of surfaces influence crayfish exploratory behaviour

SUMMARY Touch is a principal sense in all animals. It is potentially important in species of freshwater crayfish that encounter murky waters or are nocturnal. Little is known about how tactile (touch) stimuli affect exploratory behaviour under these conditions. We placed animals in different tactile situations at the start of an exploration in a dark arena and tracked the position of the body and antennae to test whether subsequent search behaviour was affected. Individuals were exposed to differently textured walls, channelled out along a wall, or released in contact with no, one, or two walls. A corner arrangement of surfaces, where individuals started near two walls at right angles, produced behaviour that differed from that of other configurations; animals chose one wall and then maintained a close distance from the wall along which they were moving. The distance from a wall adopted by a crayfish walking parallel to it was affected by the texture of the wall. These results on the influence of tactile stimuli on crayfish exploratory behaviour may have implications for other taxa.

THE ABDOMINAL MOTOR SYSTEM OF THE CRAYFISH, CHERAX DESTRUCTOR. II. MORPHOLOGY AND PHYSIOLOGY OF THE DEEP EXTENSOR MOTOR NEURONS

Abstract Two opposing muscle systems underlie abdominal contractions during escape swimming in crayfish. In this study we used extracellular and intracellular stimulation, recording and dye-filling to systematically identify each of the five deep extensor excitors and single inhibitor of the crayfish, Cherax destructor. Functional associations of each neuron were characterised by recording its responses to sensory and abdominal cord inputs, its extensor muscle innervation pattern, and its relationships with other neurons. Each excitor receives excitatory input from the tonic abdominal stretch receptors and the largest neuron also receives input from the phasic stretch receptor. The two largest excitors innervate the muscle bundle containing the fastest fibres and may be electronically coupled. The smaller neurons may also be electronically coupled and innervate the remaining deep extensor fibres which display dynamic characteristics from fast to medium-fast. The inhibitor does not receive input from the stretch receptors, but is strongly excited by tactile afferents. The implications of these findings for the current models of the control of abdominal tailflips and swimming are discussed.