Waterborne chemical communication: Stimulus dispersal dynamics and orientation strategies in crustaceans

Abstract

Many animals obtain information about conspecifics or heterospecifics that is transmitted in waterborne chemical plumes or trails. The ability to use chemicals for distance communication minimally requires that the receiver of a chemical signal be able to detect and identify the chemical constituents. Since animals often use plumes or trails to find conspecifics, they frequently must also be able to extract directional and distance information from odor plumes and trails. As odor plumes are strongly affected by flow dynamics, whether animals can even detect chemical signals, or use them to navigate towards a source, are strongly contingent on the fluid physical environment. Here I review basic information on how to quantify the relevant fluid physical aspects of the environment, and discuss major findings concerning the relationship between odor-guided navigation, odor plume structure, and the fluid dynamic environment. A major result is that greater flow or more properly, fluid mixing, diminishes the ability of crustaceans to extract the information required for efficient navigation. Despite this straightforward conclusion, the consequences of turbulent mixing for chemical communication are not as easy to predict for several reasons. First, animal size and mobility are an important factor in how animals respond to changes in odor plume structure. Thus, the consequences of increased turbulence depend on the interaction between animal size and scale, and scales of spatial and temporal variation in odor signal structure; not all animals will be affected equally by turbulent mixing. Second, increased flow or mixing will cause plumes to be dispersed more widely, potentially increasing the active space of the signal if concentrations remain high enough to be detected. Finally, chemical signaling often may involve reciprocal information transfer, where a given animal acts as both a sender and a receiver. Differences in the perceptive abilities of animals may make it difficult to predict how fluid mixing affects this process. Given that much of what we know about the mechanisms and ecological consequences of waterborne chemical communication has been derived from examining predator-prey interactions, there is considerable potential for similar investigations in systems where social communication is mediated by the transmission of chemicals via flow.