I. Introduction

A. There are 4 species of living sirenians and 1 historically documented extinct species

1. Amazonian manatee
2. West African
3. West Indian Manatee
4. Dugongs
5. Stellar Sea cow (extinct)

B. Manatees

1. Our study subject is the Florida Manatee Trichechus Manatus Latriorstris
2. Only living marine mammal herbivore
3. Live in fresh, brackish, or salty water (Stewart, 1999)
4. Feed under the surface and at the bottom
5. The bottom is a silty environment from sand and debris

C. What a face!

0. The unusual facial adaptations reflect their aquatic herbivory
1. Vibrissal-muscular complex (as described by Marshall, et al)

1. Short, muscular snout
2. Short sinus hairs and modified vibrissae
3. Bilobed lips

1. able to grasp food
2. manipulation of objects.

II. Objective

III. Methods

A. Total of 17 manatees studied

1. Homosassa Springs State Park
2. Lowry Park Zoological Gardens
3. Sea World of Florida

1. Crystal River Refuge
2. Homosassa River

0. Manatees were fed 6 different kinds of vegetation

1. 4 freshwater species
2. 2 seagrasses

IV. Results

1. Upper: U1 - U4

a. U1

i. play no active role in food gathering

ii. tactile exploration during feeding.

b. U2 used to ingest food

c. U3 and U4 work passively to aid in the movement of food into the oral cavity

2. Lower: L1-L2

a. L1

i. actively push vegetation further into the oral cavity

ii. used for scraping along the bottom

1. L2 passively aid in movement of food into the oral cavity

1. Submerged feeding is more common than surface feeding

1. in submerged feeding there were the usual cyclic grasping movements
2. U2 bristles were brought together in a prehensile manner in sweeping "side to side" motion (Marshall, et al.)

2. Other manipulative behavior

a. U2 bristle movements acted together or individually during surface feeding: flipper use was greatest here

b. When grasping anchored vegetation 1 or both U2 fields were used in non-prehensile manner.

1. overlapping the bristle fields allows for a firmer grasp on a desired object

C. Reversal

1. Ability to reverse the direction of U2 bristle field movement

a. expulsion of undesired vegetation either for taste or texture

b. accomplished by one U2 bristle field moving in opposition to the other

c. suggests that the manatees posses a high level of perioral tactile discrimination and dexterity (Marshall, et all)

D. Tactile Sense

1. Exploring involves

a. quick side to side movements of the snout in a quivering motion

b. sweeping the entire head side to side and up and down

2. The bristle-like hairs on oral disk are sensitive to touch, and will grasp for stimuli

1. Also used for object exploration

1. here they observed them exploring the introduced acrylic polygons (smooth and roughened) and several ropes of varying fiber types and diameters

3. In the wild

a. observations made of rope/anchor line manipulation/exploration

b. much time spent "chewing" on ropes and knots with U2 and L1 bristle fields.

c. some seen to move rope to corners of mouth using bristle fields and chewing on rope with teeth

V. Discussion

1. Eyes were often closed while feeding/exploring

1. Protects eyes when feeding in the silty environment

2. Shutting down one sensory system may enhance other sensory modes such as touch

1. Adults eat the equivalent of 10% of their body weight daily (Stewart, 1999)

2. Tooth morphology

a. teeth are disposable and rotate

b. not very hard; flat for grinding

3. Rostrum deflection

4. soft tissue structures

a. perioral bristles ands surrounding muscleclature

C. The vibrissal-muscular complex is best adapted to allow the manatee to their environment and to graze on a variety of aquatic vegetation

D. Social interactions

1. mouthing and nuzzling

a. primarily involves perioral bristles

b. mouthing primarily involved U2 and L2 bristle fields

c. nuzzling primarily involves the tactile bristle-like hairs on the oral disk

2. nudging

3. embracing

2. 4. pinching (to better position themselves to feed)

E. Debris detection/removal efficiency

1. It is unclear why manatee mortality arises form ingestion of debris when they have a mechanism to remove it.

a. they may not be able to detect certain kinds of debris if it is entangled in aquatic vegetation

b. they may not be able to remove debris once in the oral cavity

F. Where do they fit??

1. Comparison to other mammals

a. Pinnapeds -- posses "whisking" ability, but no prehensile behavior is observed

b. Walrus

i. Oralfacial anatomy most closely resembles that of a manatee

ii. not able to grasp food with vibrissae; use suction

c. Asian Elephant -- immobile vibrissae; rostral location only similarity

d. Giraffe -- uses tongue and prehensile lips to grasp foliage

e. Dugong

i. similar to manatees in structure and function of perioral bristles

ii. manner by which vegetation introduced into mouth varies

VI. Conclusion

A. Only mammals that use vibrissae in a prehensile manner.

B. Use tactile cues to detect vegetation.

C. Vibrissal-muscular complex has evolved to best fit its environment and feeding requirements.

VII. Where to from here?

A.The sensitivity of the bristles has not been widely studied. There have been some studies looking into innervation, but not many.

B. Explore relationship between behavior and anatomical adaptations as pertaining to foraging ecology.

C. Compare behavior/anatomy of other marine mammals possessing similar vibrissae

THE BIG PICTURE: A review of relevant studies

----- 1999. Does the thick skin of the Florida manatee provide ballast?. American Zoologist v39 i5 p114A.

Manatees are hind gut digesters, and because of their diet, they create a large amount of gas. To counter the effect of buoyant lungs and a voluminous intestinal tract, they have dense bones and a thick skin. This allows them to remain submerged while feeding.

Manatees evolved in the Cenozoic Era and have an important role in the ecology of seagrass beds. They are the biggest living consumers of marine vegetation.

Differing times for food-handling depending on type of aquatic vegetation consumed was determined as well as the effects of mean-feeding cycle length. Authors gave further indication that the modified vibrissae are used in a prehensile manner.

Whereas facial hair and bristles are involved in direct tactile discrimination and feeding, post cranial hairs function in sensing features of the underwater environment. They relay information regarding pressure gradients generated by other animals, as well as water currents.

Data shows that each tactile bristle and hair have associated clusters of neurons, which make them highly sensitive to their surroundings. This is advantageous for marine mammal herbivores living in turbid waters and lacking echolocation.

Manatees have no natural predators, nor do they prey upon others. As a result, the manatees have evolved into large bodied, relatively slow moving aquatic herbivores, lacking claws and sharp teeth.

For a feeding diagram, please see page 322 of our text book.

Link to the feeding video: http://www.vetmed.ufl.edu/ufmrg/manatee

[Course Homepage] [Syllabus] [Lecture Schedule] [Lab Schedule] [Student Presentations] [Marine Mammal Links]