TO BUILD AN INVASIVE PREDATOR: INVESTIGATING THE MECHANICAL ROLE OF LIONFISH SPINES ON DEFENSE

The red lionfish, Pterois volitans, has arguably become the most successful marine invasive species to date. Yet, despite the invasion success of P. volitans, little is known about the morphology, physiology, and ecology of this species in their native and invaded habitats. The majority of recent studies have focused on the migration of P. volitans into new regions, digestion, and bacterial infections. Knowledge is lacking on the body plan of the invasive lionfish, specifically the numerous venomous spines that are protruding outward, making the body less streamlined. In this study we quantified the mechanical properties (bending and puncture) of the venomous spines of P. volitans, and related these properties to the cross-sectional morphology. We also documented variation in the cross-sectional morphology of spines from other lionfish species in their native regions. Lastly, we documented the dorsal spine joint morphology of the first three dorsal spines and the in situ range of motion as tissues were removed. We found that the long, numerous dorsal spines absorb more energy but are less stiff than the pelvic and anal spines. In addition, we found that the anal and pelvic spines are more effective at puncturing buccal skin from sharks and grouper. We found that the removal of connective tissue significantly changes lateral movement (abduction) for the first three dorsal spines. The removal of the fin sheath significantly alters forward movement (extension) for the first two dorsal spines. From morphology, mechanical property, and range of motion data for P. volitans, we propose that the numerous long dorsal spines are primarily used for intimidation, and are not as effective defense structures as the pelvic and anal spines. Having a substantial amount of intimidating, venomous spines may allow for the lionfish to conserve energy for other highly metabolically costly activities other than warding off predators, such as digestion and reproduction. Future studies could focus on the amount of venom in each spine, how long it takes for the venom to be made and replaced, how the venomous spines affect hydrodynamic flow, and in vivo range of motion during swimming and striking.