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). The lateral line system detects water flows, which facilitates critical prey detection, predator avoidance, communication, rheotaxis, and navigation . Furthermore, unlike the nose, eyes and ears, which are bilateral sense organs found on the head, the lateral line system is composed of many small sense organs (neuromasts) located in arrays on the skin and in tubular canals on the head, trunk and tail. In bony fishes, canal neuromasts are found within a conserved subset of skull bones on the head and in the trunk canal in the lateral line scales on the body. Thus, the lateral line system has a dual identity – as an essential sensory system that mediates critical behaviors, and a major component of the skull of bony fishes. An understanding of the role of the lateral line system in behavior will shed light on how fishes may overcome challenges presented by global change, including reduced water clarity.
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 taxon has interesting or unique morphological or behavioral attributes that have allowed us to ask fundamental questions about lateral line evolution, development, functional morphology, and the sensory basis for behavior. We use 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.
We were the first to use CT imaging for the study of the comparative morphology of the swim bladder and ear in live, anesthetized fishes (Webb et al., 2006; 2010). See: Butterflyfish Project page). We are continuing to develop µCT visualization methods for the study of the development and comparative morphology of the cranial lateral line canals of teleost fishes (e.g., Alberg et al., 2010 [poster]; Webb et al., 2014), and for modeling of lateral line canal function. See: µCT Imaging Page.
We recently completed a histological investigation of the 3-D configuration of the lateral line canal within the lateral line scales of teleost fishes (Webb and Ramsay, 2017). It showed that the iconic figures found in textbooks, and reproduced throughout the literature, are not accurate. The diagram here is the consensus configuration of the lateral line canals based on several species of pomacentrids, embiotocids, and pleuronectiforms, which have unspecialized lateral line scales. Abbreviations: llc – lateral line canal, p – pore, plln – posterior lateral line nerve, m – muscle, n-neuromast, s – scale. Figure – Copyright 2017 American Society of Ichthyologists and Herpetologists
Our work has been funded by several National Science Foundation grants (1997-Pres.), 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, the George and Barbara Young Chair in Biology, 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, the diversity of sensory systems possessed by fishes and our appreciation of sensory integration in fishes demands that we ask fundamental questions about the roles of non-visual senses in diverse behaviors.
- The Role of Larval Orientation Behavior in 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 developmental anatomy 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 contribute to the navigation behavior of pelagic larvae, and the role of navigation behavior in determining settlement patterns and population connectivity in coral reef fishes. Funded by NSF grant 1459546 (Ocean Sciences) and the George and Barbara Young Chair in Biology. 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 in the field. Tricas and Webb (2016) reviewed their work on the morphology of the laterophysic connection, and on sound production and sound reception in butterflyfishes. 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).
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. This work has established the role of the lateral line system in the detection of benthic prey in Aulonocara, and distinct differences in the sensory basis for prey detection in Aulonocara and Tramitichromis, which both feed on benthic invertebrates in nature (MAB Schwalbe PhD Dissertation). We continue to use cichlids as a model system to understand the development and evolution of lateral line phenotype in bony fishes (EA Becker, MS Thesis; L Carter, MS Thesis; JW Johnstone, MS Thesis). Funded by NSF grant IOS 0843307 and the University of Rhode Island. See: Cichlid Project page for details and publications.
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 (Marranzino and Webb, Zool. J. Linn. Soc., 2017). 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), the George and Barbara Young Chair in Biology, and University of Rhode Island (A. Marranzino, MS Thesis 2016). See Deep Sea Lateral Line project page for details and publications.
Lateral Line Development in Elasmobranch Fishes – We are studying 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 for details.
Photo credit: Dr. Margot Schwalbe