The morphology and mechanical sensitivity of lateral line receptors in zebrafish larvae ( Danio rerio )

125

The characid fish species Astyanax mexicanus offers a classic comparative model for the evolution of sensory systems. Populations of this species evolved in caves and became blind while others remained in streams (i.e. surface fish) and retained a functional visual system. The flow-sensitive lateral line receptors, called superficial neuromasts, are more numerous in cavefish than in surface fish, but it is unclear whether individual neuromasts differ in sensitivity between these populations. The aims of this study were to determine whether the neuromasts in cavefish impart enhanced sensitivity relative to surface fish and to test whether this aids their ability to sense flow in the absence of visual input. Sensitivity was assessed by modeling the mechanics and hydrodynamics of a flow stimulus. This model required that we measure the dimensions of the transparent cupula of a neuromast, which was visualized with fluorescent microspheres. We found that neuromasts within the eye orbit and in the suborbital region were larger and consequently about twice as sensitive in small adult cavefish as in surface fish. Behavioral experiments found that these cavefish, but not surface fish, were attracted to a 35 Hz flow stimulus. These results support the hypothesis that the large superficial neuromasts of small cavefish aid in flow sensing. We conclude that the morphology of the lateral line could have evolved in cavefish to permit foraging in a cave environment.

Section: Cupula Visualizationmentioning

confidence: 99%

The sensitivity of lateral line receptors and their role in the behavior of Mexican blind cavefish (Astyanax mexicanus)

Yoshizawa

Jeffery

Netten

et al. 2013

125

“…The preparation and rationale of these two tests is illustrated in Fig. 8A,B which shows a diagram of a typical excised fish neuromast where the kinocilia are embedded in a jelly-like cupula (Van Trump and McHenry, 2008). In the first test, probe 1 is moved in towards the kinocilia and it should contact the cupula first.…”

Section: Observations On Living Hair Cellsmentioning

confidence: 99%

Responses of hatchlingXenopustadpoles to water currents: first function of lateral line receptors without cupulae

Roberts

Feetham

Pajak

et al. 2009

SUMMARYAt later stages in larval life and also as adults, Xenopus can respond to water currents detected by their lateral-line sensory system. We have investigated when responses to water currents first appear and whether the first lateral line neuromasts operate in the same way as the adult organs. Just before and after hatching from their egg membranes we show that Xenopus embryos and tadpoles can respond to water currents by swimming into them. Local stimulation in immobilised animals where motor activity was recorded electrically suggested that the receptors detecting water currents were located between the eyes and the gills and were innervated by cranial nerves. In behaving tadpoles, responses to water currents were reduced following skin abrasion caudal to the eyes or treatment with neomycin, which is known to block hair cell function. We therefore used scanning electron microscopy to establish that rows of lateral line neuromasts with hair cells and kinocilia are present just caudal to the eyes at these stages of development. However, careful observations and manipulations of the kinocilia of neuromasts in living tadpoles failed to find any evidence that kinocilia were embedded in a jelly-like cupula. We conclude that, when they first start to function, these early neuromasts detect water movements which directly move their freely exposed hair cell kinocilia projecting out from the skin surface. Possible behavioural roles for the tadpoles responses to water are discussed.

“…We addressed whether foraging is mediated primarily by the cranial lateral line by compromising only that region. Morphometrics of superficial neuromasts tested whether flow sensing is augmented by heightened sensitivity to flow Van Trump and McHenry, 2008). Finally, we raised fish that were naïve to the flow of Artemia to test the effects of associative learning.…”

Section: Methodsmentioning

confidence: 99%

“…The cupula is an extracellular component of a superficial neuromast that extends from the surface of the body. The dimensions of the cupula and number of hair cells are the major structural features that determine the sensitivity of a superficial neuromast Van Trump and McHenry, 2008;van Netten and McHenry, 2013). These measurements were performed for the supraorbital (SO1-SO4), infraorbital (IO1-IO3), and mandibular (MN1-MN3) neuromasts in fish of varying age (15, 25, and 30 dpf ).…”

Section: Lateral-line Morphometricsmentioning

confidence: 99%

“…The microspheres adhered to the surface and provided sufficient contrast to see the peripheral shape of the cupula (Van Trump and McHenry, 2008) under Nomarski optics using a compound microscope (Zeiss Axioskop 2 FS plus, Carl Zeiss). The cupula diameter was measured from photographs (AxioCam HRc, Carl Zeiss) taken with the microscope focused on the base of the cupula.…”

Section: Lateral-line Morphometricsmentioning

confidence: 99%

See 1 more Smart Citation

Zebrafish learn to forage in the dark

Carrillo

McHenry

2016

Self Cite

A large diversity of fishes struggle early in life to forage on zooplankton while under the threat of predation. Some species, such as zebrafish (Danio rerio), acquire an ability to forage in the dark during growth as larvae, but it is unclear how this is achieved. We investigated the functional basis of this foraging by video-recording larval and juvenile zebrafish as they preyed on zooplankton (Artemia sp.) under infrared illumination. We found that foraging improved with age, to the extent that 1-month-old juveniles exhibited a capture rate that was an order of magnitude greater than that of hatchlings. At all ages, the ability to forage in the dark was diminished when we used a chemical treatment to compromise the cranial superficial neuromasts, which facilitate flow sensing. However, a morphological analysis showed no developmental changes in these receptors that could enhance sensitivity. We tested whether the improvement in foraging with age could instead be a consequence of learning by raising fish that were naïve to the flow of prey. After 1 month of growth, both groups foraged with a capture rate that was significantly less than that of fish that had the opportunity to learn and indistinguishable from that of fish with no ability to sense flow. This suggests that larval fish learn to use water flow to forage in the dark. This ability could enhance resource acquisition under reduced competition and predation. Furthermore, our findings offer an example of learning in a model system that offers promise for understanding its neurophysiological basis.