Allen Francis Mensinger - US grants

Understanding how animals navigate under water is not only fascinating in its own right, it also contributes to instrumentation designs of underwater vehicles, robots and surface vessels, impacts management of fisheries, and helps protect the marine environment. Sharks have been chosen to demonstrate how they navigate. While they can not detect a drop of blood a mile away, as often stated, sharks do have impressive prey tracking capabilities. Sharks are important in fisheries worldwide and have been severely depleted in recent decades, often taken as unwanted by-catch in other fisheries. Yet, they are essential top predators needed to maintaining a healthy ecosystem. This research project will show how sharks use all their senses in hunting behavior, starting with initial prey detection, through tracking and locating, and ending with striking their prey. For more complete understanding, we compare a few shark species that appear to use their senses differently mostly because they specialize in different prey in different habitats. A team of experts in sensory and shark biology, using unique testing facilities in Massachusetts and Florida, has been assembled including graduate students being trained in the many technical approaches needed for work on live sharks. The research directly involves undergraduate and high school students and provides extensive outreach to other students of all ages and to the public in general. The accumulated knowledge should lead to a model of shark navigation and predation that can be used for the conservation of sharks, protection of humans, and the engineering design of underwater steering algorithms. The inevitable presentation of this research in future television programs and video documentaries will disseminate new knowledge to the public at large, both of sharks and of rigorous science.

The main goal for this investigation is determine how vertebrate sensory systems are integrated to perform complex behavioral tasks. It will address how multimodal (auditory, vestibular and mechanosensory) sensory input is processed. The experiments will be performed in the oyster toadfish which possess the identical sensory cells (hair cells) and vestibular system found in mammals, assuring the results will have wide interest to vertebrate sensory physiologists. The investigator will use a neural telemetry transmitter tag, to record nerve impulses from free swimming fish which will transform the experiments from the bench top into the environment and allow the correlation of neural activity with normal behavior in a natural setting. The study will address two long standing questions in neuroethology: how fish localize sound underwater, and the effect of self generated movement on bimodal sensory (auditory and vestibular or mechanosensory) organs. The award will support training of undergraduate students from underrepresented groups at a research undergraduate institution and a middle school science teacher.

The experiments will delineate multi-modal sensory guidance of a complex behavioral sequence to further our knowledge of the neural mechanisms of sensory integration. Sound localization for fish plays important roles in prey detection, predator avoidance, and intraspecific communication. Although terrestrial animals use interaural time delays to localize sound, the faster speed of sound underwater, combined with very short interaural distances suggests that fish must utilize alternative mechanisms. The role of the mechanosensory lateral line in detecting water movement has been established, however, recent evidence suggest that it may serve an auditory role. The widely spaced neuromasts are distributed throughout the head and trunk in different orientations and could potentially assist in nearfield sound detection and localization. The researchers will investigate acoustic sensitivity in the lateral line in the toadfish to determine if it contributes to sound localization. Toadfish are reliable neuroethological models for bioacoustic studies as males will acoustically attract females to nesting sites. The broad head of the oyster toadfish contains widely spaced and easily accessible neuromasts and cranial nerves. The neural telemetry tag will allow examination of multimodal sensory integration by simultaneously recording from both the lateral line and otoliths during sound localization experiments in free swimming fish. Phonotaxis experiments will determine if superficial and/or canal neuromasts are necessary for sound localization. The study will provide clearer understanding of the neural mechanisms regulating behavior and provide training to underrepresented undergraduate students and K-12 teachers.