Lateral line-mediated rheotactic behavior in tadpoles of the African clawed frog (<Emphasis Type="Italic">Xenopus laevis</Emphasis>)

Tadpoles (Xenopus laevis) have a lateral line system whose anatomical structure has been described, but whose functional significance has not been closely examined. These experiments tested the hypothesis that the lateral line system is involved in rheotaxis. Tadpoles in developmental stages 47–56 oriented toward the source of a water current. Orientation was less precise after treatment with cobalt chloride or streptomycin, but was similar to that of untreated animals after exposure to gentamicin. In no current conditions, tadpoles exhibited a characteristic head-down posture by which they held themselves in the water column at an angle around 45°. This body posture became significantly less tilted in the presence of water current. Treatment with cobalt chloride or streptomycin increased the angle of tilt close to that seen in no current conditions, while gentamicin treatment tended to decrease tilt angle. The data are consistent with anatomical and physiological findings that tadpole neuromasts are similar to superficial, but not canal, neuromasts in fishes, and they suggest that the lateral line system is involved in both directional current detection and current-related postural adjustments in Xenopus.     

流速对红鳍银鲫幼鱼游泳状态的影响

在28℃水温下,采用特制的鱼类游泳行为测定装置,研究体重(125.94±13.87)g的红鳍银鲫(Barbodes schwanenfeldi)幼鱼在0.0m/s(对照组)和0.1m/s、0.3m/s、0.5m/s3种流速下的游泳行为。结果表明,从0.0～0.3m/s,红鳍银鲫幼鱼平均趋流率和摆尾频率均随着流速的增加而增大,而0.5m/s组在90min内随时间延长而下降。红鳍银鲫游泳状态明显受到所处流速的影响,在静水对照组以"逆流前进"和"顺流而下"为主,两者共占总观察时间的98%以上;各流速组均以逆流静止为主,且随着流速的增大,逆流静止所占时间比例从45.8%增加至81.3%,而逆流前进所占时间比例由24.1%减至5%以下;逆流后退所占时间比例以0.1m/s组最大,为16.4%;顺流而下的比例随着流速增大先减小后增大,3个流速组依次为13.7%、2.1%和10.9%。红鳍银鲫幼鱼的游泳速度(V)和摆尾频率(TBF)在逆流前进及逆流静止两种游泳状态下呈线性正相关,而在逆流后退和顺流而下两种状态下两者没有显著相关。     

Function of the type 11 microtrich sensilla on the lotic amphipod,Gammarus pseudolimnaeus Bousfield

The type II microtrich sensilla on the lotic amphipod Gammarus pseudolimnaeus Bousfield enable it to control body orientation while swimming, as animals with their sensilla masked spent significantly more time swimming on their sides. These sensilla appear to be involved in the behavioural process that allows the animal to orient into the current (positive rheotaxis), as significantly fewer masked animals were able to turn into novel current flows compared with controls. The sensilla do not appear to play a role in detecting gravity. Results suggest that the sensilla transmit hydromechanical sensory information to the animal, and it is thought that the individual sensilla act in unison as a kinetic sensory organ. The sensilla are well adapted for such a hydromechanical role, as they would likely only be stimulated by currents hitting them broadside on. The sensilla are grouped, with each sensillum facing in a different direction, and the groups are located at appropriate positions for detecting current flows. The sensilla do not play a role in the detection of vibrations. Nor do they play a chemosensory role in the detection of food or predators; however, a role in conspecific chemodetection cannot be ruled out.     

Pedal neuron 3 serves a significant role in effecting turning during crawling by the marine slug <Emphasis Type="Italic">Tritonia diomedea</Emphasis> (Bergh)

The marine nudibranch Tritonia diomedea crawls using its ciliated foot surface as the sole means of propulsion. Turning while crawling involves raising a small portion of the lateral foot margin on the side of the turn. The cilia in the lifted area no longer contribute to propulsion, and this asymmetry in thrust turns the animal towards the lifted side. Neurons located in the pedal ganglia of the brain contribute to these foot margin contractions. T. diomedea has a natural tendency to turn upstream (rheotaxis), and pedal flexion neuron Pedal 3 elicits foot margin lift and receives modulatory input from flow receptors. To assess the contribution of this single cell in turning behavior, two fine wires were glued to the surface of the brain over left and right Pedal 3. We determined that Pedal 3 activity is correlated with subsequent ipsilateral turns, preceding the lift of the foot margin and the change in orientation by a consistent interval. Both Pedal 3 cells show synchronous bursts of activity, and the firing frequency of the ipsilateral Pedal 3 increased before turns were observed to that side. Stimulation of the electrode over Pedal 3 proved sufficient to elicit an ipsilateral turn in Tritonia.     

Rhythmic swimming activity in Anguilla anguilla glass eels: Synchronisation to water current reversal under laboratory conditions

Synchronisation of swimming activity to water current reversal every 6.2 h was tested in the European glass eel (Anguilla anguilla L.). When presented with a change in water current direction, glass eels exhibited rhythmic patterns of activity with a period close to the tidal one. Glass eels began to swim with the current and then alternated between positive and negative rheotaxis after each change in the water current direction. Results are discussed in relation to the flood tidal transport theory. Following synchronisation to current reversal, glass eels subjected to constant conditions displayed a weak rhythmic activity suggesting that locomotor behaviour might, in the wild, synchronise to several environmental cues related to the tide. Results obtained with different densities also suggest that social cues might improve the synchronisation.     

不同流速下杂交鲟幼鱼游泳状态与活动代谢研究

为研究水流速度对杂交鲟幼鱼行为和代谢的影响,探讨游泳状态与活动代谢及相关游泳运动参数之间的关系,在26℃水温下,使用特制的鱼类游泳行为和活动代谢同步测定装置,测定了杂交鲟幼鱼在0.1、0.3、0.5 m/s三种流速和静水条件下的游泳状态、趋流率、摆尾频率和耗氧率。结果表明:随着流速的增大,杂交鲟幼鱼逆流前进和逆流静止游泳状态所占时间比例显著减少,而逆流后退所占时间比例显著增加,顺流而下时间比例有所上升。在0.0—0.3 m/s的流速范围内,杂交鲟幼鱼各个时段的平均趋流率、摆尾频率和耗氧率均随着流速的增加而增大,在0.3 m/s流速下分别达到100%﹑(2.53±0.34)Hz和(490.99±164.59)mg O2/(kg.h)。当流速增加至0.5 m/s时,在趋流率仍保持100%的情况下,其耗氧率相比0.3 m/s增加了21.86%,而摆尾频率却减小了6.70%。实验过程杂交鲟幼鱼趋流率与摆尾频率呈显著线性正相关,而摆尾频率与耗氧率在大部分时段却无相关性。随着时间的延长,各流速组杂交鲟幼鱼趋流率、摆尾频率和耗氧率呈现不同的变化趋势,其趋流率均相对稳定;但摆尾频率均随时间延长呈下降趋势,而耗氧率则在实验前9h随时间延长逐渐增加,随后趋于稳定。研究结果提示:杂交鲟幼鱼游泳状态的变化与流速有关,而反映运动强度大小的摆尾频率与活动代谢率的关系受到游泳状态的显著影响,同时也与运动代谢特征的时间变化有关。       

Swimming ability and burrowing time of two cirolanid isopods from different levels of exposed sandy beaches

Most of the macroinfauna from sandy beaches is highly mobile, emerging out of the sediment when the tide rises, and using the swash to migrate up and down the beach face or feed (searching for prey or carrion). After swash excursions, they usually burrow back into the sediment, maintaining zonation at low tide. Therefore, the different species abilities to emerge, move around and burrow under different swash climates and sediment conditions are expected to influence observed distribution patterns. Nonetheless, few attempts have been made to understand behavioral mechanisms of these organisms in moving fluids.In this study, we used a flume tunnel to investigate the orientation, swimming ability and burrowing time of two similar species of cirolanid isopods, Excirolana armata Dana and Excirolana braziliensis Richardson, under current velocities ranging from 5 to 30 cm·s⁻¹. E. armata inhabits middle levels of dissipative to intermediate beaches, while E. braziliensis is found towards the upper level of a wider range of beach states. Both species oriented countercurrent above a threshold velocity, which turned out to be significantly lower for E. armata than for E. braziliensis. E. armata proved to be a stronger swimmer as shown by the higher velocities surmounted, and the less drags experienced at the highest current velocity. E. armata also burrowed faster than E. braziliensis. Burrowing time was affected by sediment grain size and water content, but not by water flow. Once organisms managed to begin burrowing under different flow conditions, they were not affected by current velocity. Nonsaturated sand precluded burial, while coarse sand retarded it. Differences in the observed patterns of across-beach distribution may thus be the result of species-specific behavioral responses to swash climate, manifested in swimming ability, burying and orientation in directional flows.     

The sensory basis of rheotaxis in the blind Mexican cave fish, Astyanax fasciatus

The sensory basis of rheotaxis (orientation to currents) was investigated in the blind Mexican cave fish, Astyanax fasciatus. An unconditioned rheotactic response to uniform velocity flows was exhibited, with a threshold of less than 3 cm s⁻¹. Disabling the entire lateral line or the superficial neuromast receptor class increased the rheotactic threshold to greater than 9 cm s⁻¹. A pharmacological block of the lateral line canal system alone had no effect. These results demonstrate that the superficial lateral line system controls rheotaxis at low current velocities. The effect of pairing an odor stimulant with the water current dropped the rheotactic threshold to less than 0.4 cm s⁻¹. This study provides a clear behavioral role for the superficial neuromasts where none previously existed, and also establishes a link between the mechanosensory lateral line and olfactory systems in the olfactory search behavior of the cave fish. Accepted: 9 January 1999     

Mechanosensory based orienting behaviors in fluvial and lacustrine populations of mottled sculpin (Cottus bairdi)

We compared prey-orienting and rheotactic behaviors in a fluvial (Coweeta Creek) and lacustrine (Lake Michigan) population of mottled sculpin. Blinded sculpin from both populations exhibited unconditioned, mechanosensory based rheotaxis to low velocity flows. Whereas Lake Michigan sculpin generally showed increasing levels of positive rheotaxis to increasing velocities, Coweeta Creek sculpin show varying levels of positive rheotaxis at low to intermediate velocities and often reduced positive rheotaxis or even negative rheotaxis at the highest velocities (12 cm s^-1). Blinded Lake Michigan, but not Coweeta Creek mottled sculpin exhibited an orienting response to a small (3 mm diameter) artificial prey (50 Hz vibrating sphere). In conclusion, the two populations differed in the strength and polarity of the rheotactic response at higher velocities and in their responsiveness to mechanosensory cues from epibenthic prey sources. These behavioral differences have most likely arisen from different learning experiences in different habitats and from the greater importance of visual cues to the Coweeta Creek mottled sculpin and mechanosensory cues to Lake Michigan mottled sculpin in the sensory guidance of orienting behaviors.     

Water-flow sensitive pedal neurons in Tritonia: role in rheotaxis

Summary We have identified 13 pairs of neurons in the pedal ganglia of the marine nudibranch slug Tritonia diomedea that responded tonically and/or phasically to water-flow directed at the rhinophore sheaths and oral veil tips. Most of the neurons responded equally to inputs from either side of the body, but 6 pairs responded with greater intensity to ipsilateral water-flow stimuli. When stimulated intracellularly in a semi-intact, whole-animal preparation, 4 of these 6 pairs of neurons caused ipsilateral movements that may turn the animal towards that side. These observations suggest a role for these current-sensitive neurons in the previously described orientation to water-currents in Tritonia diomedea.