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

Abstract

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.

Development of Multisensory Convergence in the Xenopus Optic Tectum

“…This theory is supported by studies showing that nonvisual mechanosensory modalities restructure immediately preceding stage 48/49. Specifically, some aspects of lateral line system, believed to be important for rheotaxis, become functional at stage 47 (Simmons et al 2004); although there is evidence that the lateral line system can function as early as stage 41 (Roberts et al 2009). The inner ear of Xenopus tadpoles contains specific compartments to detect auditory, vestibular, and acoustico-vestibular stimuli.…”

Movements ofRana catesbeianatadpoles in weak current flows resemble a directed random walk

“…Little is known about how these animals process biologically relevant sensory signals (Muntz, 1963;Shelton, 1971;Jaeger and Hailman, 1976;Stehouwer, 1988;Hoff et al, 1999;Simmons et al, 2004;Roberts et al, 2009). Because tadpoles are wholly aquatic but inhabit diverse ecological niches, examining their behavioral responses to local changes in water flow presents an excellent model for comparative studies of adaptive sensory processing over development.…”

“…Although tadpole neuromasts seem to resemble the superficial neuromasts of fish, there are only limited data on their detailed morphology (Jande, 1966;Lannoo, 1987;Roberts et al, 2009). Behavioral data on lateral line function in these animals are also sparse.…”

“…Behavioral data on lateral line function in these animals are also sparse. Larval Xenopus laevis, at developmental stages prior to hindlimb formation, exhibit positive rheotaxis to current flow (Shelton, 1971;Simmons et al, 2004;Roberts et al, 2009). Whether similar behavioral responses to flow are also characteristic of other species of tadpoles, with their different developmental trajectories, external morphologies and ecologies (Hoff et al, 1999;McDiarmid and Altig, 1999), is unknown.…”

Morphometric growth characteristics and body composition of bullfrog tadpoles in captivity

“…The bullfrogs (Lithobates catesbeianus) present a complex life cycle (SIMMONS; COSTA; GERSTEIN, 2004;ROBERTS et al, 2009). The first stage (tadpole stage) is essential for good functioning of the frog farm since the animals that emerge after metamorphosis will determine the conditions for frog culture.…”