Joseph A. Sisneros - US grants

This proposed study will investigate the functional organization of the central auditory system in the brainstem of a vocal fish, the plainfin midshipman (Porichthys notatus). Vocalizing species, including humans, are faced with the fundamental problem of segregating concurrent vocal signals during social communication. Recent studies in the midshipman have revealed insights into the neural mechanisms that underlie vocal signal segregation. Specific aims are to: (1) use neuroanatomical methods to determine the central projections to the medulla of physiologically identified afferents from inner ear otolithic endorgans that may serve an acoustic function, (2) characterize the response properties of medullary auditory neurons to individual and concurrent social acoustic signals that mimic natural vocalizations using standard extracellular recording techniques, and (3) use neuroanatomical methods coupled with neurobiotin injections and extra-and intracellular recording techniques to identify the central projections of physiologically-characterized medullary auditory neurons to the midbrain and other brainstem auditory nuclei. This proposed study will determine how the midshipman auditory brainstem processes biologically meaningful stimuli and may provide novel information of how individual and concurrent signals, such as vowels in human speech, are coded and segregated within the vertebrate auditory system.

This research will investigate sound source localization by fishes to ascertain how fish integrate the various sound cues available to them to behave appropriately in complex acoustic environments. Evidence suggests that the capacity for sound source localization is common to mammals, amphibians, birds and reptiles, but surprisingly it is not known whether fishes locate sound sources in the same manner. Therefore, sound source localization by fishes remains an important topic in biology and in the hearing sciences. This study will test the major assumptions of several related theories, including the leading theory of sound source localization by fishes. The plainfin midshipman fish (Porichthys notatus), in which females locate males by sounds that the males produce, will be used as a general model to investigate how fishes localize underwater sound sources. Two hypotheses will be tested: 1) fish orient to the direction of acoustic particle motion to localize sound sources (a major assumption of several, related theories including the leading theory of sound source localization), and 2) both particle motion and sound pressure detection (via the swimbladder) are necessary for sound source localization, but neither alone is sufficient. As an integral part of this research program, both graduate and undergraduate students will receive training and mentoring. In addition, annual public lectures regarding this research will be presented at the University of California Bodega Marine Laboratory.

The ability to locate the source of sounds enables animals to detect prey, avoid predators and communicate with others and is thus basic to survival in many species. While decades of behavioral, physiological and neuroanatomical research have revealed the physical cues and neural mechanisms that terrestrial animals use to localize sound, the mechanisms used by fish, the oldest living vertebrate group, remain a mystery. Collectively, these experiments will investigate the mechanisms of sound localization utilized by fish that likely formed the evolutionary foundation for more recent modes of vertebrate hearing and sound localization. Throughout the project, Drs. Sisneros and Forlano will train and mentor both graduate and undergraduate students and give annual public lectures regarding the supported research at the Friday Harbor Labs (FHL). As an integral part of this research program, Drs. Sisneros and Forlano will host GK-12 teachers every summer at FHL where they will participate in field and laboratory experiments. The researchers will also develop lesson plans, student projects and an educational website with the teachers at their home institutions.

The investigation will take an integrated behavioral, anatomical, and brain activational approach to determine whether fish are fundamentally similar to other studied vertebrates, and use binaural information (information from both ears) to localize sound, or are fundamentally different, and achieve robust localization on the basis of monaural (single-ear) information alone. The central hypothesis to be tested is that binaural integration is essential for sound source localization in midshipman. To test this hypothesis, the investigators will 1) determine which inner ear endorgans are required for sound localization behavior by testing animals in an established sound playback paradigm before and after systematic unilateral or bilateral removal of each endorgan's otolith (saccule, lagena, utricle), 2) characterize the ipsilateral and contralateral projections of inner ear afferents from all three endorgans to known auditory processing regions in the hindbrain by bulk labeling each endorgan separately or in double or triple combination with different fluorescent-labeled dextran amine tracers, and 3) characterize the brain activation patterns resulting from controlled auditory directional stimulation in intact animals and in those that have undergone systematic endorgan removal, using c-Fos as a marker for neural activation. Duplicate digital files of all raw, processed and consolidated data will be stored locally and in the cloud by both researchers and will be made publically available within two years following publication.

This award provides partial support for the sixth International Conference on "The Effects of Noise on Aquatic Life" in Berlin, Germany, July 10-15, 2022. This meeting follows the very successful meetings on the same general topic held in Nyborg, Denmark (2007), Cork, Ireland (2010), Budapest, Hungary (2013), Dublin, Ireland (2016), and Den Haag, Netherlands in 2019 The major goal of this conference would be to define the current state of knowledge on the impact of underwater noise and explore the progress made in this field in the three years since the previous conference. The extension of renewable energy and petroleum projects to offshore waters, the prospect of industrial development of previously pristine waters (e.g., polar regions), and recent proposals to open new areas for petroleum lease (e.g., US Atlantic coast) has resulted in greater interest in the effects of underwater noise on aquatic life on the part of regulators, industry, and scientists.

The meeting should help shape future research and understanding of effects of noise on aquatic life. Based on experience from the earlier meetings, the interactions and networking that took place has resulted in new collaborations between investigators, a broader understanding of the science that can be used in their work by regulators, a better understanding of regulatory issues by scientists and industry, and substantial cross-fertilization of experimental design and approaches by investigators.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.