Novelty stress and reproductive state alters responsiveness to sensory stimuli and 5-HT neuromodulation in crayfish

Testing the relationship between intraspecific competition and individual specialization across both behavior and diet

Individual specialization within populations is increasingly recognized as important in both ecology and evolution, but researchers working on intraspecific variation in behavior and diet infrequently interact. This may be because individual specialization on diet and behavior was historically difficult to investigate simultaneously on the same individuals. However, approaches like stable isotope analysis that allow hindcasting past field diets for laboratory organisms may provide opportunities to unite these areas of inquiry. Here, we tested the role of intraspecific competition on individual specialization through analysis of both behavior and diet simultaneously. We focused on intraspecific competition as a mechanism that might drive individual specialization of both diet and behavior. We conducted this study in Vilas County, Wisconsin, United States (US), using rusty crayfish Faxonius rusticus from six lakes across a relative abundance gradient. We conducted six assays to measure individual specialization of behavior and used stable isotope analysis to measure individual specialization of diet. We then related both measures of individual specialization to relative abundance of F. rusticus using linear and quadratic models. We found a unimodal relationship between intraspecific competition and individual specialization of diet for F. rusticus, likely because some preferred resources are unavailable to specialize on at the highest densities of this well-studied crayfish invader. Conversely, we found greater support for a linear relationship between individual specialization of behavior and intraspecific competition, perhaps because specialization by behavior is not inherently resource-limited. Our results show that dietary and behavioral specialization may exhibit different responses to increased intraspecific competition, and demonstrate a potential technique that can be used to investigate individual specialization of diet and behavior simultaneously for the same individuals and populations.

Physiological Changes as a Measure of Crustacean Welfare under Different Standardized Stunning Techniques: Cooling and Electroshock

Stunning of edible crustaceans to reduce sensory perception prior and during slaughter is an important topic in animal welfare. The purpose of this project was to determine how neural circuits were affected during stunning by examining the physiological function of neural circuits. The central nervous system circuit to a cardiac or skeletal muscle response was examined. Three commercially important crustacean species were utilized for stunning by immersion in an ice slurry below 4 °C and by electrocution; both practices are used in the seafood industry. The blue crab (Callinectes sapidus), the red swamp crayfish (Procambarus clarkii), and the whiteleg shrimp (Litopenaeus vannamei) responded differently to stunning by cold and electric shock. Immersion in ice slurry induced sedation within seconds in crayfish and shrimp but not crabs and cardiac function was reduced fastest in shrimp. However, crabs could retain a functional neural circuit over the same time when shrimp and crayfish were nonresponsive. An electroshock of 10 s paralyzed all three species and subsequently decreased heart rate within 1 min and then heart rate increased but resulted in irregularity over time. Further research is needed to study a state of responsiveness by these methods.

Effects of sertraline on behavioral indices of crayfish Orconectes virilis

Sertraline, a selective serotonin re-uptake inhibitor, is a widely prescribed antidepressant in North America. Though sertraline is continuously released from wastewater treatment plant discharge to surface water, effects of aqueous exposure of sertraline on behavioral responses of aquatic animals are largely unknown. Our study explored the effects of aqueous exposures of sertraline on antagonistic bouts and predator response behavior of virile crayfish (Orconectes virilis). Crayfish were either exposed or not exposed to waterborne sertraline and then size-matched for paired antagonistic bouts to determine if sertraline affects the aggression of each crayfish. We investigated the effect of sertraline on responses to visual predator cues and determined whether sertraline acts as an olfactory cue. Our results demonstrate that crayfish exposed to sertraline are more aggressive when paired with control crayfish but, when sertraline crayfish are paired, there is no change in aggression. Attraction response to sertraline in behavioral mazes was also observed, which may represent a maladaptive behavior, and in an ecological context may result in crayfish moving to areas with elevated levels of sertraline. However, aqueous exposure to sertraline had no effect on predator responses of crayfish. Future research is warranted to determine whether such medicine released in wastewater treatment plant effluents produces long-term ecologically important consequences for aquatic animals residing in urbanized aquatic ecosystems.

Serotonin modulation of caudal photoreceptor in crayfish

The sixth abdominal ganglion (6th AG) of the crayfish contains two photosensitive neurons. This caudal photoreceptor (CPR) displays spontaneous electrical activity and phasic-tonic responses to light pulses. In this paper, we analyzed the presence of serotonin in the 6th AG and its effects in the modulation of the activity of CPR. In the first part of our study, we identified serotonergic neurons in the 6th AG by immunostaining using an antibody against serotonin. Next, we quantified the serotonin contents in the 6th AG by using liquid chromatography. Finally, we searched for serotonergic modulation of the CPR electrical activity by using conventional extracellular recordings. We found 13 immunopositive neurons located in the ventral side of the 6th AG. The mean diameter of their somata was 23+/-9 microm. In addition, there was immunopositive staining in neuropilar fibers and varicosities. The contents of serotonin and its precursors in the 6th AG varied along the 24-h cycle. Its maximum value was reached by midday. Topic application of serotonin to ganglia kept in darkness increased the CPR spontaneous firing rate and reduced its light responsiveness. Both effects were dose-dependent within ED(50) approximately 1 microM and were blocked by the 5-HT antagonist methysergide. These observations support the role of serotonin as a neurotransmitter or neuromodulator in the CPR of the two species of crayfish Procambarus clarkii and Cherax quadricarinatus.

Involvement of norepinephrine in the hyperglycemic responses of the freshwater giant prawn, Macrobrachium rosenbergii, under cold shock

Hyperglycemic response of freshwater giant prawn, Macrobrachium rosenbergii, under acute cold shock was investigated, and the involvement and stimulatory pathways of norepinephrine (NE) on induced-glycemia were further examined. Remarkable elevations in hemolymph glucose at comparable magnitude were observed in both intact and eyestalkless prawn under cold treatments, suggesting that hyperglycemic response of this species is not solely mediated through the actions of crustacean hyperglycemic hormone released from X-organ sinus gland complex on the target tissues, but NE is involved. Positive and significant correlations were noted between the hemolymph glucose titers and NE contents in both thoracic ganglia and the hemolymph, suggesting that NE plays a significant role in the hyperglycemic responses of this species under cold. Depressive effects of various adrenoceptor antagonists monitored in vivo and in vitro further suggest that the action of NE is primarily mediated through both alpha1- and beta1-adrenoceptors.