We study the structural and functional development and evolution of fish sensory systems. Our work is focused on the mechanosensory lateral line system, a primitive vertebrate sensory system found in all 30,000+ fishes (and larval and aquatic adult amphibians) – and thus in more than half of the vertebrate species on earth. The lateral line system detects water flows facilitating prey detection, predator avoidance, communication, and navigation (including rheotaxis). Furthermore, unlike the nose, eyes and ears, which are found on the head of all vertebrates, the lateral line system is composed of many small sense organs (neuromasts) found on the skin and in pored canals, which in bony fishes are found within a conserved subset of skull bones on the head and in the trunk canal contained within the lateral line scales on the body.
Thus, the lateral line system has a dual identity – it is an essential sensory system that mediates critical behaviors, and it is a major component of the skull (of bony fishes). The role of the lateral line system in behavior will shed light on how fishes may overcome challenges presented by global change, such as reduced water clarity, which likely requires increased dependence on non-visual sensory systems for prey detection, predator avoidance, navigation, and communication. The study of the lateral line system contributes to our understanding of vertebrate sensory biology, evolutionary developmental biology, and development and evolution of the vertebrate skull.
We have studied the lateral line system in a wide range of taxa including: flounders, greenlings, zebrafish, skates, coral reef butterflyfishes, and gobies, Lake Malawi cichlids, and deep-sea (stomiiform) fishes. Each group has interesting or unique attributes that have allowed us to ask fundamental questions about lateral line evolution, development, functional morphology, and the sensory basis for behavior.We have used multiple methods including histology, SEM, CT/µCT, vital fluorescent imaging, and fate mapping to gain a comprehensive understanding of patterns of lateral line morphology and development. We have also used DPIV (for analysis of hydrodynamic stimuli), video analysis, and classical fish training (conditioned responses to artificial hydrodynamic stimuli) to study the sensory basis for feeding behavior under different environmental conditions.
Our work has been funded by the National Science Foundation, a NSF Graduate Research Fellowship, the Lerner Gray Fund of the American Museum of Natural History, the Marine Biological Laboratory (Woods Hole), RI NSF EPSCoR, and the University of Rhode Island.
Sensory Biology of Coral Reef Fishes – Coral reef fishes live in well-lit waters and are generally considered to be visually-oriented. However, our appreciation of sensory integration in fishes demands that we consider the non-visual senses and their roles in diverse behaviors.
- The Role of Larval Orientation Behavior in Determining Population Connectivity – Sensory Ontogeny in a Coral Reef Goby (ongoing) – Most coral reef fishes (and most marine fishes) have a complex life history that includes the dispersal of planktonic eggs and pelagic larvae, with remarkable swimming abilities. Late stage larvae of coral reef fishes are known to respond to olfactory, auditory, and visual cues to change their behavior and navigate to their settlement sites on reefs, but the morphology and the pattern and timing of development of the sensory systems that underlie these behaviors are not well known. In this collaborative project with colleagues at Boston University and University of Miami, we are using a goby (Elacatinus lori) for the first integrated analysis of the ontogeny of multiple sensory systems (olfaction, taste, lateral line, hearing, vision) and larval orientation behavior in a coral reef fish. The ultimate goal is to understand how the different sensory systems mediate navigation behavior of pelagic larvae, and the role of this behavior in determining settlement patterns and population connectivity in coral reef fishes. Funded by NSF grant 1459546 (Ocean Sciences). See: Goby Sensory Ontogeny page.
- The Laterophysic Connection in Butterflyfishes (completed) – A diversity of teleost fishes have convergently evolved associations of the swim bladder with the inner ear (otophysic connections) that enhance the reception of sound. We have described the comparative anatomy, development, and systematic significance of a unique swim bladder-lateral line linkage in butterflyfishes in the genus Chaetodon, the laterophysic connection, which has been shown to enhance sensitivity to acoustic stimuli in the context of critical behaviors, including territoriality and monogamous social systems. Tricas and Webb (2016) have reviewed their work on the morphology of the laterophysic connection, and behavioral and physiological work on sound production and sound reception in these fishes. Funded by NSF grants IBN 9603896 and IBN 0132607 to JFW. See: Butterflyfish Project page.
- The Lateral Line System of Damselfishes, Wrasses, and Parrotfishes – We have examined the diversity and evolution of trunk canal phenotypes with respect to body shape and lateral line scale morphology (see Webb PhD Dissertation and Webb, 1990, in Copeia).
Flow Sensing in the Deep Sea: The Lateral Line System of Stomiiform Fishes – The deep sea is a hydrodynamically quiet environment characterized by low light levels or complete darkness. Specializations of the visual system are well known among mesopelagic fishes, in particular. Several groups of mesopelagic and bathypelagic fishes are known to have specializations of the lateral line system, but little had been known about the most speciose group of deep-sea fishes – the hatchetfishes, bristlemouths, and barbelled dragonfishes of the Order Stomiiformes. The lateral line system in stomatiiform fishes was investigated for the first time using a range of morphological methods including histology, SEM, and µCT imaging. This work revealed a dramatic enhancement of the lateral line system (proliferation of superficial neuromasts) that had gone unnoticed until now (submitted). This discovery demands that the flow sensing capabilities of these fishes be considered in the context of their sensory ecology to understand their roles in the deep sea. Funded by an NSF Graduate Research Fellowship, Lerner-Gray Fund for Marine Research Grant (ANMH, NY), and University of Rhode Island (A. Marranzino, MS Thesis 2016). See Deep Sea Lateral Line project page.
Cichlid Fishes: Development and Evolution of the Mechanosensory Lateral Line System – Representatives of two genera of Lake Malawi (Africa) cichlid fishes (Aulonocara [widened canals] and Tramitichromis [narrow canals]) are being used for comparative anatomical, developmental, and behavioral studies that address fundamental issues in post-embryonic lateral line development, diversification of lateral line phenotypes, and functional evolution of the lateral line system (MAB Schwalbe PhD Dissertation, EA Becker, MS Thesis; L Carter, MS Thesis). Funded by NSF grant IOS 0843307. See: Cichlid Project page for details and publications.
We are also using cichlid fishes to understand how developmental processes and their underlying mechanisms contribute to patterns of lateral line canal morphogenesis, growth, and evolution of the cranial lateral line canal phenotypes in bony fishes. We seek to determine: a) how lateral line canals become integrated into the dermatocranial bones in bony fishes, and b) how patterns of bone remodeling defines lateral line canal phenotypes (JW Johnstone, ongoing MS thesis). Funded by University of Rhode Island.
Lateral Line Development in Elasmobranch Fishes
We have studied the development of the lateral line canal system in the little skate, Leucoraja erinacea. In contrast to the bony fishes, the cranial lateral line canals in elasmobranch fishes are not associated bone, but are contained in the soft tissue of the dermis surrounding the elements that compose the cartilaginous skull of these fishes. Furthermore, the pattern of development of the lateral line system in elasmobranchs contrasts with that in bony fishes in fundamental ways. The study of this contrast will shed light on how lateral line development evolved with the divergence of the cartilaginous (elasmobranch) and bony fishes hundreds of millions of years ago. This work has been carried out at the Marine Biological Laboratory (Woods Hole) in collaboration with Dr. Andrew Gillis (Cambridge University, UK). Funded by a Laura and Arthur Colwin Endowed Summer Research Fellowship at the MBL and the University of Rhode Island. See: Skate Project page.
Imaging of the Cranial Lateral Line Canal System with µCT – We are continuing to develop methods for visualizing and quantifying the morphology of the cranial lateral line canals of teleost fishes in both 2D and 3D. See: µCT Imaging Page.
Photo credit: Dr. Margot Schwalbe