Mammals Hydrodynamic reception

1 mammals

1.1 pinnipeds

1.1.1 seals
1.1.2 sea lions
1.1.3 species differences in vibrissae


1.2 manatees
1.3 platypuses
1.4 other mammals

mammals

detection of hydrodynamic stimuli in mammals typically occurs through use of hairs (vibrissae) or “push-rod” mechanoreceptors, in platypuses. when hairs used, in form of whiskers , contain follicle-sinus complex (f-sc), making them different hairs humans familiar.

pinnipeds

pinnipeds, including sea lions , seals, use mystacial vibrissae (whiskers) active touch, including size , shape discrimination, , texture discrimination in seals. when used touch, these vibrissae moved forward position , kept still while head moves, moving vibrissae on surface of object. in contrast rodents, move whiskers explore objects. more recently, research has been done see if pinnipeds can use these same whiskers detect hydrodynamic stimuli in addition tactile stimuli. while ability has been verified behaviorally, specific neural circuits involved have not yet been determined.

seals

research on ability of pinnipeds detect hydrodynamic stimuli first done on harbor seals (phoca vitulina). had been unclear how seals find food in dark waters. found harbor seal use whiskers sensory information (due being blindfolded , wearing headphones), respond weak hydrodynamic stimuli produced oscillating sphere within range of frequencies fish generate. active touch, whiskers not moved during sensing, projected forward , remain in position.

to find whether seals follow hydrodynamic stimuli using vibrissae rather detect them, blindfolded harbor seal headphones can released tank in toy submarine has left hydrodynamic trail. after protracting vibrissae forward position , making lateral head movements, seal can locate , follow trail of 40 meters when sharp turns trail added. when whisker movements prevented mask covering muzzle, seal cannot locate , follow trail, indicating use of information obtained whiskers.

trails produced live animals more complex produced toy submarine, ability of seals follow trails produced other seals can tested. seal capable of following center of trail, either following direct path of trail or using undulatory pattern involving crossing trail repeatedly. latter pattern might allow seal track fish swimming in zigzagging motion, or assist tracking weak trails comparing surrounding water prospective trail.

other studies have shown harbor seal can distinguish between hydrodynamic trails left paddles of different sizes , shapes, finding in agreement lateral line in goldfish capable of doing. discrimination between different fish species might have adaptive value if allows seals capture highest energy content. seals can detect hydrodynamic trail produced fin-like paddle 35 seconds old accuracy rate greater chance. accuracy diminishes trail becomes older.

sea lions

more recently, studies on hydrodynamic detection in california sea lion (zalophus californianus) have been done. despite structure of mystacial vibrissae, different of seals, these sea lions can detect , follow trail made small toy submarine. sea lions use undulatory pattern of tracking similar in seals, not perform increased delay before allowed swim , locate trail.

species differences in vibrissae

studies raise question of how detection of hydrodynamic stimuli in these animals possible given movement of vibrissae due water flow during swimming. whiskers vibrate frequency based on swim speed , properties of whisker. detection of water disturbance caused vibrissal movement should overshadow stimulus produced distant fish due proximity. seals, 1 proposal might sense changes in baseline frequency of vibration detect hydrodynamic stimuli produced source. however, more recent study shows morphology of seal s vibrissae prevents vortices produced whiskers creating excessive water disturbances.

in harbor seals, structure of vibrissal shaft undulated (wavy) , flattened. specialization found in true seals. in contrast, whiskers of california sea lion circular or elliptical in cross-section , smooth.

when seals swim vibrissae projected forward, flattened, undulated structure prevents vibrissae bending backward or vibrating produce water disturbances. thus, seal prevents noise whiskers unique whisker structure. however, sea lions appear monitor modulations of characteristic frequency of whiskers obtain information hydrodynamic stimuli. different mechanism might responsible sea lion s worse performance in tracking aging hydrodynamic trail. since whiskers of sea lion must recover characteristic frequency after frequency altered hydrodynamic stimulus, reduce whisker s temporal resolution.

manatees

similar vibrissae of seals , sea lions, florida manatees use hairs detecting tactile , hydrodynamic stimuli. however, manatees unique since these tactile hairs located on whole post-cranial body in addition face. these hairs have different densities @ different locations of body, higher density on dorsal side , density decreasing ventrally. effect of distribution in spatial resolution unknown. system, distributed on whole body, localize water movements analogous lateral line.

research being done test detection of hydrodynamic stimuli in manatees. while anatomy of follicle-sinus complexes of manatees have been studied, there learn neural circuits involved if such detection possible , way in hairs encode information strength , location of stimulus via timing differences in firing.

platypuses

in contrast sinus hairs other mammals use detect water movements, evidence indicates platypuses use specialized mechanoreceptors on bill called “push-rods”. these small domes on surface, ends of rods attached @ base can move freely otherwise.

using these push-rods in combination electroreceptors, on bill, allows platypus find prey eyes closed. while researchers believed push-rods function when in contact bill (implicating use tactile sense), believed can used @ distance detect hydrodynamic stimuli. information push-rods , electroreceptors combine in somatosensory cortex in structure stripes similar ocular dominance columns vision. in third layer of structure, sensory inputs push-rods , electroreceptors may combine platypus can use time difference between arrival of each type of signal @ bill (with hydrodynamic stimuli arriving after electrical signals) determine location of prey. is, different cortical neurons encode delay between detection of electrical , hydrodynamic stimuli. however, specific neural mechanism not yet known.

other mammals

the family talpidae includes moles, shrew moles, , desmans. members of family have eimer s organs, touch-sensitive structures on snout. desmans semi-aquatic , have small sensory hairs have been compared neuromasts of lateral line. these hairs termed “microvibrissae” due small size, ranging 100 200 micrometers. located eimer s organs on snout , might sense water movements.

soricidae, sister family of talpidae, contains american water shrew. animal can obtain prey during night despite darkness. discover how possible, study controlling use of electroreception, sonar, or echolocation showed water shrew capable of detecting water disturbances made potential prey. species uses vibrissae hydrodynamic (and tactile) sensing based on behavioral observations , large cortical representation.

while not studied, australian water rat (known “rakali”) may able detect water movements vibrissae these have large amount of innervation, though further behavioral studies needed confirm this.

while tying presence of whiskers hydrodynamic reception has allowed list of mammals special sense grow, more research still needs done on specific neural circuits involved.