No abstract

Signal transmission is influenced by the physics of an environment. Consequently, a physical effect on sensory signals can influence how animals send or sample sensory information. Habitat-specific physics may constrain or enhance signal transmission (e.g. sound transmission in a flowing river versus a still pond) and provide a mechanism for the evolution of sensory biases. This study investigated how the transmission of chemically mediated social signals in crayfish is influenced by two different aquatic environments. Agonistic bouts between crayfish were performed under lotic (flowing water) and lentic (nonflowing, still water) conditions. When crayfish (Orconectes rusticus) collected from a lotic system (river) interacted under lotic conditions, we noted that dominant O. rusticus spent more time upstream than subordinate O. rusticus. Orconectes rusticus positioned themselves randomly and spent equal amounts of time with respect to upstream and downstream in the nonflowing environment. We tested another species, Orconectes virilis, collected from a nonflowing environment (lake) and they showed no positional preference when tested in flow. Additionally, both O. rusticus and O. virilis took longer to reach high fight intensities under flow conditions. It was possible to visualize O. rusticus urine release, and they released urine more often when upstream of an opponent in a flow environment during these agonistic bouts. These results suggest that O. rusticus collected from lotic environments release urine to maximize the transmission of chemical cues to a fight opponent. It appears that crayfish may adapt their signalling processes based upon their long-term ambient environments.

Conspecific distribution across differing microhabitats may arise due to individual differences in resource requirements, vulnerability to predation, environmental tolerances, and as a direct result of social interaction. The aim of this study was to examine crayfish distributions across habitats with varying resource availability and to examine whether such distributions are correlated with dominance relationships among individuals. Agonistic interactions, habitat use, and shelter use were observed in mixed-sex populations of eight crayfish, Orconectes virilis. Populations were placed in a semi-natural, 4 × 4 m arena for 20 h that was split into shelter-poor (low), shelter-rich (high) and shelter-free (free) areas. The presence of shelter was associated with a significant increase in crayfish habitat use. Overall agonism also increased in habitats where shelter was present. Status specific differences in shelter and habitat use were observed and were dependent upon environmental context (e.g., day versus night). Lower ranking crayfish were found to occupy and defend shelter less frequently than dominant crayfish and low ranking crayfish were also found more often in shelter-poor habitat. These status-specific differences in behavior were only observed during the day when shelter-related behaviors were increased overall. Distinct shelter use strategies were also apparent between top-ranked (alpha) and bottom-ranked (omega) crayfish. Taken together, these results suggest that shelter use and habitat use are, in part, mediated by social status. Additionally, these results indicate that habitat selection may arise as a consequence of status-specific differences in resource use.