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Sensory perception is the process by which an organism detects and interprets

information from the external world by means of the sensory receptors. This process

allows individuals to behave in a proper way in order to maintain their homeostasis, to

increase their chances of survival and to possibly bond with conspecifics. The return of

cetaceans to the aquatic environment implies strong adaptations, notably in terms of

behavior and anatomy. Delphinids are considered the most diverse and social family of

cetaceans. As each animal has a perceptually limited construct of its environment and

given the diversity of lifestyles in delphinids, we expect a strong variation in delphinids

sensory abilities. The goal of this report is to get together data about the sensory

abilities in the different modalities in delphinids and to assess their relative importance.

There is a general lack of information about delphinids perception. Delphinids have

mainly developed an exceptional auditory system that allows them to adapt to the

underwater transmission of sound. Nonetheless, the study of other sensory systems in

these animals has been relatively neglected. Vision perception in dolphins is mainly

adapted to rapid changes in light conditions, yet other aspects of the visual system

remains unclear, as the color vision or the laterality. Olfaction and taste seem to be very

closely related senses in delphinids. There is neuroanatomical evidence that connects

the rhinoncephalon with sensitive structures in the bottlenose dolphin tongue. Electric

perception in delphinids has only been studied in one species (Sotalia guianensis) and

has evidenced an electric sensitivity comparable to platypuses. Magnetic perception has

mostly been evidenced opportunistically due to strandings or field observations. There

are evidence that shows that dolphins integrate information received through vision and

echolocation. It would be suitable to explore other possible multimodal relationships

between the different modalities.

Key Words: Delphinids, multi-modal, visual perception, auditory perception,

olfactory perception, taste perception, tactile perception, electric perception, magnetic

perception

!

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21 &34567894:63!Sensory perception is the process by which an organism detects and interprets

information from the external world by means of sensory receptors (The Collins English

Dictionary, 2005). The reception of environmental information allows individuals to behave

in a proper way in order to maintain their homeostasis, to increase their chances of survival

and to possibly bond with conspecifics. Sensory perception is usually multimodal, but the

relative importance of each modality depends on the habitat quality as well as on the morpho-

anatomy and cognitive abilities of the studied species.

Cetaceans are molecularly and morphologically closely related to hippopotamus (Geisler

and Uhen, 2003, 2005), however, the phylogenetic evolution of these animals is very unique

as they re-entered into the aquatic environment at least seven times in the course of

evolutionary history (Uhen, 2007). The last return to the ocean occurred in the early Eocene,

approximately 50 my ago (Gingerich et al., 1983). Such a return to aquatic life implies strong

adaptations, notably in terms of behavior and anatomy. A review of aquatic mammals’

evolution made by Uhen (2007) explains that early cetaceans developed an elongated end of

the rostrum with external nares posterior to the tip of it, and with a high position of the eyes

on the lateral sides of the skull. The most representative adaptation of early cetaceans to

aquatic life was the enlargement and inflation of the ectotympanic lobe into a tympanic bulla,

a characteristic that seems to be an adaptation to aid in hearing sounds underwater rather than

in the air (Uhen, 2007). However, the main adaptation of odontocetes to aquatic life may be

the development of echolocation to assist locomotion in visually-limited habitats. This has

been highlighted in fossils by the development of facial structures involved in the production

of outgoing sound and the modifications of the inner ear for the perception of very high

frequencies (Uhen, 2007).

Currently, delphinids are considered the most diverse family of cetaceans with more than

36 species (Shirihai, 2006). They range in size and weight from 1.2 meters and 40 kilograms

(Cephalorhynchus heavisidii), up to 9 meters and 10 tons (Orcinus orca) and they present

equally many variations in color patterns between species (Perrin et al., 2002). Their social

lives are also very variable and includes some sedentary as well as migratory species that live

in varied aquatic habitats, going from rivers to deep artic waters (Connor et al., 1998). As

each animal has a perceptually limited construct of its environment (Uexküll, 1934) and

! 3!

given the above-mentioned diversity of lifestyles in delphinids, we also expect a strong

variation in the sensory abilities of delphinids.

In the past decades a stronger focus has been put on auditory perception than on other

sensory modalities. There are several potential reasons for that. Focal and acoustic signals are

very often emitted by delphinids and they are known for their exceptional ability in vocal

learning and plasticity in acoustic production (compared to other nonhuman mammals). Also,

the auditory channel seems to be well adapted to aquatic life. Indeed, sound spreads five

times faster through water than in the atmosphere, and it allows for communication at long

distances, which is very important for this kind of animal, especially between mothers and

calves, where the anatomy and habitat does not allow the mother to hold on to its offspring or

to construct a den to leave the calves behind while foraging (Janick, 2009). Nevertheless,

neurobiology, physiology, anatomy, genetics, and behavioral studies have gathered data,

sometimes preliminary and controversial but still promising, on other modalities as well. For

example, due to dolphins’ lives in underwater conditions, their eyes are adapted to an

amphibious vision (Dral, 1977). Since these animals spend less than 13% of their lives at the

surface (Mate et al., 1995), the perception of in-air particles (olfaction) should be less

important than perception of dissolved particles in water (taste) (Wartzok and Ketten, 1999).

Because the offshore marine environment lacks spatial signals, animals can use magnetic

perception in order to navigate (Walker et al., 1992). Also, the physical conditions of

movement in water forced delphinids to develop a particular tactile perception in order to

control their navigation and breathing behavior (Wartzok and Ketten, 1999). The goal of this

report is to get together data about the sensory abilities in the different modalities of

delphinids and to assess their relative importance.

Another potential reason for the general lack of information about delphinids’ perception

comes from the difficulties of conducting any research on these animals. Dolphins are

difficult to observe in the wild since they spend most of their time underwater, making it

extremely risky to interpret their behavioral response to a particular stimulus. Also, dolphins

are very rare in captive facilities, with limited space for research and groups are most often

composed of very few animals. Even in captivity, where animals are observable in clear

water, other constraints occur. For example, dolphins can vocalize without opening their

mouths or showing any visible sign of producing a sound (Dormer, 1979), making it

impossible to attribute a recorded signal to a given individual. However, these species can be

easily trained to be manipulated by humans and to cooperate during neurological or

! 6!

physiological inspections. In sum, only a small number of delphinid species have been

investigated (Shirihai, 2006), and the available information usually neglects any possible

inter-individual variability. Nonetheless, I am going to present the state of knowledge

(notably regarding morpho-anatomy and behavior) of the different facets of delphinid

perception with the aim of identifying the remaining information gaps and thus contributing

to the orientation of new research projects.

;1 ,6837!<=59=<4:63!!!

!"#" $%&'()*%+(,()-.+/0/1)/)*&2(+Delphinids are considered the most social cetaceans, but the aquatic environment presents

particular constraints for social interactions, group spatial cohesion and orientation. These

conditions have been the evolutionary engine for adapting the acoustic system of dolphins to

an aquatic environment (Janik, 1999a). The auditory system of dolphins is adapted to the

aquatic environment. In order to reduce the hydrodynamic drag while swimming, there is a

lack of protruding parts associated with external ears. The middle and the inner ear are

encased in a bony structure (tympanic bulla) that is connected to the skull by cartilage,

connective tissue and fat, instead of bones. The absence of an external acoustic meatus is

compensated by the presence of a thin region on each side of the mandible that is in intimate

contact with the tissues that connect to the tympanic bulla. Trough this connection between

mandible and tympanic bulla, dolphins allows sound to enter into their auditory system while

keeping a low hydrodynamic drag. The physical isolation of the bullae from the skull allows

the dolphin to localize sounds received by bone conduction. Lastly, there are important

variations in the stiffness of the basilar membrane and a large number of ganglion cells that

suggests that dolphins have an excellent capacity for pitch discrimination and perception of

high frequency sounds (reviewed in Au, 1993). Finally, dolphin brains are specialized for

sound processing. For example, even if human and dolphin brains are about the same size

(Marino, 1998) the inferior colliculus, a major hearing center, is 40 times larger in the

bottlenose dolphin than it is in humans (Glezer et al., 2004, in Harley, 2008).

Dolphins have developed two different uses of acoustic signals, for locomotion via

echolocation (ultrasonic clicks), and for social interaction (audible frequency-modulated

calls) (Janik, 2009). Delphinids use echolocation by projecting pulses of sound and by

listening to the echoes returning from any object that is present at distances up to a few

! 8!

hundred meters (Au, 1993). For short- as well as long-distance social interactions (up to

20km away), delphinids rely on whistles and a variety of burst-pulsed sounds (Janik, 2009).

Dolphins may process these two types of signals differently using two functionally

independent auditory subsystems (“calls”: passive hearing, and “clicks”: active hearing -

(Dubrovsky, 1990). Nonetheless, there are several species of dolphins that use clicks for

environmental exploration as well as for social communication (e.g. Peale’s dolphin

(Lagenorhynchus australis)- Schevill and Watkins, 1971; Hector’s dolphin

(Cephalorhynchus hectori)- Dawson, 1991).

!"!" 3/((*4-+5-/6*27+The hearing range of delphinids is 50 Hz to 150kHz, with some variation between

species (reviewed in Richardson et al., 1995). This wide range allows the perception of

several harmonics as well as large frequency modulations for communication with tonal

acoustic signals. Hence, the call repertoire of delphinids is usually composed of a large

number of whistle types, some being specific to a given individual and others being shared by

group members (Kremers et al., 2012). Behavioral experiments have shown that bottlenose

dolphins can spontaneously distinguish different whistle types even if they come from other

dolphin species (Caldwell et al. 1973a in Janik, 2009). Furthermore, the frequency

discrimination abilities of delphinids are exceptional as they can discriminate tonal sounds

that differ by only 0.2–0.8% of the base frequency of the tone (Thomson and Herman, 1975,

in Janik, 2009). Harmonic shapes can also be discriminated by dolphins and may carry

additional information (Lammerset al., 2003; Yuen et al., 2007). However, further studies are

needed to determine which information might be encoded in harmonics and which acoustic

parameters are most important to dolphins for whistle categorization (Janik, 2009).

!"8" $%)*4-+5-/6*27+Dolphins typically echolocate with click repetition rates of 5 pulses per second (pps) for a

target range of 120m, 25 pps for a target range of 10m, and 50pps for a target range of 1m.

(Reviewed in Au, 1993). Several experiments have been done in order to set the dolphins’

echolocation limits. Using a 2.54 cm-diameter solid steel sphere and a 7.62cm-diameter

stainless steel water-filled sphere (this is a bibliographic report, do you really need that

precise a measurement or can you just say solid and water-filled spheres?), Au and Snyder

(1980) measured the maximum detection range of the bio sonar in two bottlenose delphinind

individuals. Results showed that dolphins could reach a 50% correct answer threshold at 75m

! 9!

with the 2.54 cm-diameter sphere and at 113m with the 7.62cm-diameter sphere. Same

results were registered by Thomas and Turl(1990) with a false killer whale individual

(Pseudorca crassidens). Dolphins can also detect objects under very noisy conditions. In fact,

bottlenose dolphins present a generally unbiased detection of a target sphere of 7.62cm-diam.

at levels of noise of 77dB or lower (Au et al., 1982). Delphinids have, as a result of being

able to recognize differences in the order of 1dB in the amplitude of echoes, and an ability to

perceive subtle differences in targets with their sonar. This ability allows them to

discriminate for example between a 6cm cube and a 6cm cylinder with a performance of 96%

accuracy (reviewed in Au, 1993).

>1 ?:@8AB!<=59=<4:631!Visual perception in aquatic animals can be divided according to two main functional

categories: visual detection and visual acuity. Visual detection concerns all the adaptations

that maximize the opportunity of animals to detect predators or prey in an environment that

filters and reduce the passage of light. Visual acuity is defined as a measure of how well an

animal can deal with the properties of its visual environment after the detection of an object

(Wartzok & Ketten, 1999). In order to have good performance in both functional categories,

several morphological and neuroanatomical adaptations are needed.

The eyes of delphinids have evolved to satisfy the ecological needs of their aquatic

environment. While morphologically the muscles coordinating the eyes’ movement are the

same as other mammals, their functionality appears to be modified. Dolphins’ eyes do not

have torsional motion and eye rotations up-down and left-right are limited. The sclera is

unusually thick and the intraocular pressure (relative to the environment) is high compared to

that of terrestrial mammals. In addition, delphinids’ eyes have an operculum that is able to

achieve a wide brightness control range that is adapted to wide and rapid changes in

brightness when the animal dives from the well lit water surface into depths where the light

level is very low (reviewed in Mass and Supin, 2007).

Besides these morphological adaptations, delphinids may have differences in the use of

each cerebral hemisphere to solve tasks of the visual system. A functional laterality has been

also evidenced for visual detection and processing. A behavioral study with a single

bottlenose dolphin had reported right eye superiority in visual discrimination tasks, indicating

a left hemisphere dominance for visual object processing (Von Fersen et al., 2000). The same

results were observed by Killian et al. (2000) and Yaman et al. (2003), suggesting that this

! :!

condition could be a general population asymmetry. However, controversial results were

obtained more recently by Thieltges et al., (2012). The authors reported general left eye

superiority in a captive group of bottlenose dolphins when looking at humans either familiar

or unfamiliar. The same group also showed a preferential use of the left eye to observe very

familiar objects while the right eye was used to observe unfamiliar objects (Blois-Heulin, et

al., 2012).

A study of underwater visual acuity in one adult female Pacific white-sided dolphin

(Lagenorhynchus obliquidens) evaluated the ability of the female to discriminate between

one and two vertical lines presented simultaneously (Spong and White, 1971). Results

suggest that dolphins’ underwater vision is probably sufficiently well developed to be a

behaviorally significant modality, but that it should only play a reduced role in guiding the

underwater behavior of these animals. When analyzing in-air visual acuity of bottlenose

dolphins, it appeared that dolphins’ visual acuity was poorer than that of pinnipeds, but

comparable to those of antelopes, elephants and clawless otters (Pepper et al., 1973).

Color vision in these animals is still a mystery. Immunocytochemical, physiological, and

molecular genetic studies of the cone visual pigments in a large sample of species show that

cetaceans generally lack the blue cones, which means that they may not be able to see

variations of blue colors. They would have only green cone monochromats and should be

able to perceive light only in green. However, behavioral data indicate that they easily

discriminate objects (e.g. toys) presenting different colors. Hence, there should be to some

extent an underlying mechanism for color vision in cetaceans (reviewed in Griebel and

Schmid, 2002; Griebel and Peichl, 2003).

C1 -BDA9465E!<=59=<4:631!Olfactory perception is the ability to perceive chemicals in their gaseous state

(Kuznetzov, 1990). This kind of perception seems to be an adaptation to terrestrial life.

Consistently with this idea, we observe that other marine vertebrates that have returned to

aquatic life after an adaptation to terrestrial environments (pinnipeds and sea turtles) still

conserve their olfactory reception genes, which reflects the importance that the terrestrial

environment still has for these animals (Kishida et al., 2007).

Anatomically, the olfactory system of cetaceans is less developed than those of terrestrial

mammals. Both baleen whales (mysticetes) and toothed whales (odontocetes) have lost some

! ;!

of their olfactory receptor genes. However, this reduction in the olfactory system is bigger in

mysticetes than in odontocetes.

Mysticetes still have an olfactory bulb that makes up approximately 0.13% of brain

weight; and they can therefore smell in air (Thewissen et al., 2011). This capacity could be

explained by the filter-feeder hypothesis, which remarks the fact that clouds of plankton,

especially krill, give off a peculiar odor on the surface of the sea, making in-air olfaction

important for filter-feeders to locate their prey (Thewissen et al., 2011). On the contrary, in

adult odontocetes this structure is absent (Morgane and Jacobs, 1972 in Watkins and

Wartzok, 1985).

Associated with this olfactory loss function, the region of the upper respiratory tract has

transformed in favor of the production of sound signals used to communicate and echolocate

(Cranford et al., 1996; Huggenberger, 2004). It seems that during odontocete evolution, the

mechanical impact of pneumatic sonar signal generation may have led to the elimination of

the nasal chemoreceptor system (Huggenberger and Schliemann, 2009). However, this is not

the case for all the odontocetes. In phocoenids, there is a study that found chemoreceptors in

the frontal and vestibular sac of harbor porpoises (Phocoena phoecoena) (Behrmann, 1989).

Nevertheless, there is still no evidence of chemoreceptors in delphinids.

F1 "A@4=!<=59=<4:631!Taste perception is the ability to perceive substances in liquids. In the aquatic

environment the diffusion of substances is slower than in the air due to the higher density of

the solvent. This way odorous traces stay in water for a longer time than in air (Kuznetzov,

1990). Neuroanatomy and tongue morphology indicate that odontocetes have the ability to

taste. Also, it seems that the well-developed olfactory lobes in the rhinencephalon of

bottlenose dolphins might be innervated by the trigeminal nerve (Oelschläger, 2008;

Oelschläger & Oelschläger, 2009) in place of the missing olfactory nerve, and thus might be

sensitive to substances stimulating receptors on the tongue (Wartzok & Ketten, 1999).

This idea of the neuro-anatomic replacement of the sense of smell by the sense of taste is

consistent with early behavioral observations that demonstrated the taste perception in

delphinids. Kuznetzov (1990), found that bottlenose dolphins are not sensitive to sweet tastes

but are sensitive to bitter, sour and salty ones. Conversely, Friedl et al. (1990), found that

bottlenose dolphins can detect the four primary tastes (sour, salty, bitter and sweet).

! ?!

Kuznetzov (1990) also argued that, while the main function of gustation could be the

homeostatic one, because it is crucial for acceptance or rejection of different food items, the

main function of olfaction could be communication and it could be mainly used during

reproductive, territorial and social interactions. The author used as an argument that male

toothed whales have perianal gland openings and that they also display a high frequency of

urination. He suggested that, using their taste perception, dolphins probably can lead some of

their social behavior. That is why he referred to dolphin’s chemical perception as a “quasi-

olfaction” sense (Kuznetzov, 1990).

However, when examining the presence of receptor-like structures in the tongue the

picture is not that simple. While Sokolov and Volkova (1971) (cited in Kuznetov, 1990)

found no taste buds in the striped dolphin (Stenella coeruleoalba), bottlenose dolphin, and

common dolphin (Delphinus delphis); Sukhovskaya (1972) (reviewed in Kuznetov, 1990)

reported the presence of taste buds for bottlenose dolphin and common dolphin. This

contradiction persisted for these same species for several years until Yamasaki et al., 1978

(reviewed in Kuznetov, 1990) investigated striped dolphin tongues at different ages. They

found that taste buds were completely atrophied in adults but present in young dolphins and

they suggested that taste buds are probably absent in adult toothed whales. Nonetheless,

recent studies have shown so-called receptor-like structures in three delphinid species

(Stenella coeruleoalba, Tursiops truncatus, Grampus griseus) (Ferrando et al., 2010) as well

as in other odontocetes: the franciscana (Pontoporia blainvillei) of the pontoporidae family

(Guimarães et al., 2012) and the common porpoise (Phocoena phocoena) of the phocoenidae

family.

G1 "A94:B=!<=59=<4:631!Delphinids present high swimming speeds that can go up to 16m/s for bottlenose dolphins

(reviewed in Rohr et al., 1998). Most of the studies of tactile perception are focused on the

understanding of how these animals maintain laminar flow over major portions of the body at

high-speed swimming. In order to do so, they have tried to appraise the tactile sensitivity of

these animals (reviewed in Wartzok and Ketten, 1999). Galvanic skin response tests showed

that some areas of the body of common dolphins are more sensitive than others (Kolchin and

Bel’kovich, 1973, in Wartzok and Ketten, 1999). They found the most sensitive areas within

2.5cm of the blowhole and within a 5cm-diameter circle around the eyes. Another area of

high sensitivity was the snout, the lower jaw and the melon. In contrast, the dorsal area

! "@!

(anterior and posterior to the dorsal fin) had a very low sensitivity. These results are

consistent with the anatomical findings in bottlenose dolphins and false killer whales of

Bryden and Moluneux (1986) (reviewed in Wartzok and Ketten, 1999). They found large

numbers of encapsulated nerve endings around the blowhole in both species, especially in the

anterior lip of this. The authors suggested that because the anterior lip is the first part of the

blowhole exposed when the animal surfaces, these mechanoreceptors were involved in

detection of pressure changes associated with the blowhole breaking the water surface.

Ridgway and Carder (1997) made electroencephalograms to map areas of tactile sensitivity

on bottlenose dolphins and confirmed those results. According to Wartzok and Ketten (1999),

the minimum detectable pressure values of 10 mg/mm!, obtained by Kolchin and Bel'kovich

(1973) using a static, weighted 0.3-mm wire, are similar to those obtained for humans in their

most sensitive areas such as the fingertips and lips.

Life in the aquatic environment means the skin is permanently subjected to the pressure

changes caused by the passage of water when the animal moves at different speeds and

depths. For this reason, the relationship between the information coming from body skin and

the vestibular system should be important for dolphin navigation. Nevertheless, the evidence

of this relationship still remains unclear (Oelschläger, 2008). Despite this lack of evidence,

there are some studies that suggest the importance of tactile perception in delphinids.

An experiment made with three captive subadult females bottlenose dolphins revealed

the discrimination of different types of oils by tactile perception. Dolphins were placed in a

pool with 3 different surface divisions: clear mineral oil, dark-tinted mineral oil or refined

motor oil. They avoided oil surface either in day or night. During the day–condition,

dolphins relied predominantly on vision. During the night-condition the dolphins’ tactile

perception played the main role in the avoidance of oil (St. Aubin et al., 1996). Social

behavior can indirectly demonstrate the importance of tactile perception in delphinids.

Dudzinzki (1998) analyzed different vocal and contact behaviors of a population of Atlantic

spotted dolphins (Stenella frontalis) in the Bahamas and described 16 types of contacts with

affiliative or aggressive functions. This has also been reported for spinner dolphins (Stenella

longirostris; Norris and Würsig, 1994) and for other small cetaceans (Pryor, 1990; cited by

Dudzinski, 1998).

! ""!

H1 $B=945:9!<=59=<4:631!Electroreception has been recently evidenced for the first time in one of the smallest

delphinids. The hairless vibrissal crypts on the rostrum of Guiana dolphins (Sotalia

guianensis) serve as electroreceptors (Czech-Damal et al., 2012). This was demonstrated by

the mean of histological investigations that revealed that the vibrissal crypts possess a well-

innervated ampullary structure reminiscent of ampullary electroreceptors in other species.

The same study also found behavioral evidence for electroperception. A male Guiana dolphin

was trained to respond to electrical stimuli in the order of magnitude of those generated by

small to medium-sized fish. The test used was a “go/no-go paradigm”. The dolphin was

trained to place its head in a hoop and to touch a target with the tip of its rostrum. He should

leave the hoop when a stimulus was presented (go response), and should remain in the hoop

for at least 12s when no stimulus was presented (no-go response). This experiment

determined a sensory detection threshold for weak electric fields of 4.6 µV cm!, which is

comparable to the sensitivity of electroreceptors in platypuses. As nearly all mammals

possess a mechanosensory organ that originates the electroreceptors, authors suggested the

possibility of finding such capability in other delphinids species (Czech-Damal et al., 2012)

I1 JAK3=4:9!<=59=<4:631!Relation between live stranding positions of cetaceans and the residual geomagnetic field

along the U.S. Atlantic continental margin seem to highlight the existence of a magnetic

sense (Kirschvink et al., 1985). Indeed, significant tendencies to strand at locations with low

magnetic intensity were found in several cetaceans, including delphinids species:

Globicephala machrorhynchus, G.melas, Tursiops truncatus, Stenella coeruloalba,

S.plagidon, Grampus griseus, Delphinus delphis, Orcinus orca, and Lagenorhynchus acutus

(Kirschvink et al., 1985). Although there is a general lack of information about magnetic

perception in delphinids, a few anatomical, functional, and behavioral clues have been found.

During a necropsy on the brain tissues of four stranded common dolphins, all individuals

showed magnetite in their supraoccipital region (Zoeger et al., 1981). The authors suggested

that because this kind of tissue was found to be associated with some nerve fibers, the

magnetite is not simply a metabolic by-product but should have a sensory function and may

notably play a navigational role. However, in 1983, Bauel et al. were unable to demonstrate

magnetic conditioning in Tursiops spp. (reviewed in Watkins and Wartzok, 1985).

! ",!

Functional responses of dolphins to changes in magnetic fields were registered by

Kunestov (1999). Comparing electrocardiograms, cutaneogalvanic reactions, and respiration

during different states of motion and acoustic activity of the animals, he observed functional

responses to permanent magnetic fields of 32, 108, and 168 micro teslas.

Finally, behavioral observations have suggested the presence of a magnetic sense in

dolphins. Eight captive bottlenose dolphins where observed during rest in the Southern

hemisphere and they spent the majority of the time (85%) engaged in swimming behaviors

that can be considered clockwise (Stafne & Manger, 2004). The authors suggested two

potential explanations. The first one is the existence of a magnetic sense in dolphins. The

second one is the preference for a swimming direction by the action of the coriolis force.

L1 +639B8@:63!The umwelt theory proposes that each animal has a perceptually limited construct of its

environment (Uexküll, 1934). According to this, it is suitable consider that delphinids'

perception still holds several mysteries. More behavioral studies are needed to understand to

which extent animals use the different anatomical structures available. Moreover, most of the

studies have been done with captive Atlantic bottlenose dolphins and there is a general lack

of evidence of the different facets of sensory perception in the majority of delphinid species.

Delphinids have mainly developed an exceptional auditory system that allows them to

adapt to the underwater transmission of sound. Nonetheless, the study of other sensory

systems in these animals has been relatively neglected. Visual perception in dolphins is

mainly adapted to rapid changes in light conditions, yet other aspects of the visual system

remains unclear, as the color vision or the laterality. There is a potential interference between

these two sensory modalities. For instance, dolphins integrate information received through

vision and echolocation (Harley et al., 1996). In a discrimination experience with an adult

female bottlenose dolphin, the performance accuracy using both vision and echolocation was

of 95%, while the performance was of 70% and 77% respectively, using vision or

echolocation alone.

Also, olfaction and taste seem to be very closely related senses in delphinids. There is

neuroanatomical evidence that connects the rhinoncephalon with sensitive structures in the

bottlenose dolphin tongue. This adaptation may have influenced the partial absence of taste

buds in the tongue of delphinids. Since taste perception may have a mainly homeostatic

function, and olfactory perception a mainly communicative and social function (Kuznetzov,

! "3!

1990), it would be interesting to clarify the influence of the close relation between taste and

olfaction on dolphin behavior.

Electric perception in delphinids has only been studied in one species (Sotalia

guianensis)! ACzech-Damal et al., 2012), and has demonstrated an electric sensitivity

comparable to platypuses. Similar behavioral experiments could be done with bottlenose

dolphins in order to highlight the existence of this sense in another delphinid. In the same

context, magnetic perception has mostly been demonstrated opportunistically due to

strandings or field observations. No behavioral responses to magnetic stimuli have yet been

demonstrated by controlled experiments.

It would be suitable to explore other possible multimodal relationships between the

different modalities, however this relationship has been only demonstrated between the most

well known sensory systems in delphinids: audition and vision. The study of the information

gaps of the remaining modalities is necessary to test the existence of other interferences

between different senses and to better understand the adaptations of delphinids to the aquatic

environment.

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