FROM ORGANISMS TO ECOSYSTEMS: IMPACTS OF LIMB LOSS AND REGENERATION ON CRAYFISH BEHAVIOR

The ability of some organisms to regenerate tissues and organs has fascinated naturalists since antiquity, dating back to the earliest accounts of scientific inquiry with Aristotle in Ancient Greece. Then, Darwin’s theory invigorated some scientists’ dream of stimulating (or reactivating) regenerative capacities in human beings by showing that we are related to highly regenerative organisms. More recently, a renewed interest in discovering the molecular and genetic basis for organ and tissue regeneration has led biologists to focus more specifically on a restrictive set of model organisms. Although the process of limb regeneration is different between invertebrate and vertebrate organisms, it follows the same general principles and steps. The presence or absence of regenerative ability appears to broadly correlate with the incidence of autotomy (reflex severance of a limb). Autotomy allows individuals to reduce costs associated with damaged structures, often limbs, by severing the appendage at a predetermined breakage plane, thus limiting wounding and helping the regeneration process. Individuals capable of rebuilding damaged structures during their lifespan may have higher fitness than individuals without this. This may help to explain how selective pressures for regenerative capacities could be maintained or acquired. The regenerative process, induced by autotomy, may also have high physiological costs and this comes with its own set of challenges in turn affecting how regenerating individuals interact with and change their environment. Organisms capable of regeneration can also have impacts on their environment through their behavior. Therefore, regeneration of structures important for behavioral effects on the environment can mediate organisms’ environmental impacts. Recently, these reciprocal impacts have been the focus of new theory conceptualizing the ecological implications of organismal habitat, namely, ecosystem engineering (defined as the process by which organisms modify their physical environment from one physical state to another). Furthermore, regeneration creates periods of time during which regenerating organisms face newfound challenges mediated by the way those organisms interact with their environments. Once again, regenerating crayfish might not be able to dig a burrow when needed (during drought, reproduction, etc.). Thus, they could find themselves competing for existing burrows or facing a now necessary migration to find water all of which non-regenerating crayfish may not experience. Therefore, ecosystem engineers capable of regeneration represent a powerful system allowing us to develop a clearer understanding of how regeneration might evolve as well as persist through its effects on organismal fitness