Vertebrate Flight • True flight is found in 3 vertebrate groups. • Reptiles (Pterosaurs etc) • Aves • Mammalia • Many vertebrate glider groups, including mammals, frogs, geckos, lizards, snakes, and fish.
Questions to Ponder: • What selective pressures led to the evolution of flight in bats? • How did bats take to the air? • Top down hypothesis • Bottom up hypothesis • Where there intermediate forms? • Why are bats nocturnal & birds diurnal?
Some Weirdness. • Bats do a number of interesting morphological things. • Musculature differences. • Forearm specialization. • Modification of the shoulder. • Hind limb rotation. • Tricks w/ echolocation.
Another Question: • Why is there but 1 group of bats (maybe 2), but 4 marsupial glider groups, 3-4 rodent glider groups, 1 dermopteran group, 1 amphibian glider group, and numerous reptilian glider groups?
Basic Physical Requirements of Vertebrate Flight • Need for a lifting surface • each group evolved wings. • Means of propulsion • again, wings provide thrust. • Control of stability • wt. Concentrated near center of mass for metabolic efficiency • decreased wt. of appendages • increased appendage manageability • Physiological and CNS changes.
Modes of Flight • Reptiles: little flapping & primarily gliding. • Aves (all w/ varying degrees of maneuverability) • rapid gliding • slow gliding • rapid flapping • slow flapping
Modes of Flight • Bats • low speed w/ extreme maneuverability. • NOTE: bats forage and eat on the wing, whereas flycatches land to eat. Also, bats echolocate whereas birds require “log-distance” vision. Bats use “short-distance” hearing.
Mechanics of Flight • Based on Bernoulli principle: • Air moving over top of wing moves faster than air on bottom. • This creates negative pressure on top of wing. • Leading edge is raised above Plane of Motion. • Air is directed against ventral surface of wing. • = angle of attack.
Mechanics of Flight. • Camber is anteroposterior curvature. • The greater the camber & angle of attack, the more lift is produced • If camber & angle of attack is too great, turbulence results and you reach a stalling point. • Drag is opposite to direction of movement. • Depends on speed, surface area, and shape. • Drag increases in proportion to wing surface area, as square of speed, with angle of attack and camber.
Bat Wings. • High camber • High lift at low speeds. • Excessive drag at high speeds. • Camber & angle of attack • Held constant during wing beat cycle. • Controlled by propatagium and plagiopatagium. • Humerus and radius + occipito-pollicalis control leading edge.
Bat Wings. • Camber & angle of attack cont. • Trailing edge controlled by hind foot and tensor plagiopatagii. • Camber vie humerus and digit 5. • Can be modified for extreme lift at low speed. • Thrust • Thrust during cycle because of give of trailing edge of chiropatium while leading edge is rigid.
Bat Wings. • Aspect ratio. • Length / width or • (wing span)2 / wing area. • Low aspect ratio wings are good for low speed and maneuverability. • High aspect ratio wings are good for rapid flight and endurance.
Bat Wings. • Wing loading (wt / wing area). • Reduced wing loading results in greater ability to fly at low speed. • High wing loading is associated with ability to achieve high speed.
Some Examples • Family / species Food WL AR • Phylostomatidae • Macrotus waterhousii Insects / fruit .112 6.8 • Artibous jamaicansis Fruit .219 5.6 • Choeronycteris mexicana Nectar 6.9 • Vespertilionidae • Myotis yumanensis Insects .084 6.7 • M. evotis Insects .077 6.5 • M.lucifugus Insects .099 6.5 • Plecotus townsendii Insects .090 6.0
Some Examples • Family / species Food WL AR • Molosidae • Tadaridae brasiliensis Insects .165 8.6 • T. molosa Insects .159 9.7 • Eumops parotis Insects .266 10.0 • Brown Creeper .112 4.6 • Yellow Warbler .137 4.9 • Brown Headed Cowbird .283 5.7 • Chimney Swift .215 8.6 • Cliff Swallow .181 7.5
Echolocation • True echolocation occurs only in the microchiroptera. • Sound is produced in the larynx. • Sound is emitted through the nose or the open mouth.
Echolocation • Sound quality. • Some bats produce high intensity pulses. • Used primarily by insectivores and piscivores. • Molossids • Noctilionids • Vespertilionids • Some HIP bats emit the pulses through the nose. • Rhinolophids.
Echolocation • Some bats produce Low Intensity Pulses. • These bats are called whispering bats. They feed primarily on fruits, nectar, and some small vertebrates. • Why use high frequency sounds? • High frequency sounds attenuate rapidly in air. • Higher frequencies are associated with shorter wavelengths.
Echolocation • Why use high frequency sounds? • Shorter wavelengths are more efficient at detecting small insect sized prey. • High frequency sound may be distrinct from background noise.
Echolocation • Sound Force. • A dyne is defined as the force required to accelerate a 1g mass to 1 cm/s/s. • Humans have a lower force threshold of about .0002 dynes. • Bats are capable of producing sound with forces ranging from 1 dyne to 200 dynes (equivalent to a top fuel dragster).
Echolocation • Morphological specialization • Tensor tympani and stapedius are extremely well developed. Also, these muscles receive action potentials shortly after (3 milliseconds) sound action potentials are produced. • Changes in neural pathways. • Ability to “beam” sound through nose leafs and lips.
Echolocation • Tragus and antitragus used to detect sounds. • Bones housing the inner ear and middle ear are insulated from the rest of the skull by fat and blood filled sinuses.
Echolocation • Echolocation signals. • FM signals • These signals have a short duration, but sweep a broad frequency range. • FM signals are ideally suited to determining size, shape, surface qualities, and range of a target.
Echolocation • CF signals • CF signals are constant frequency (or nearly so) but have a significant time duration. • CF signals are good for detecting presence, and through dopler shift, whether prey is approaching or departing.
Bat Diversity • Earliest bat fossils are from the early Eocene of North America: • Icaronycteris index • There are no intermediate forms - earliest bats are good bats. • Underived characters include 38 teeth (compared to 44 for underived eutherian number).
Bat Diversity • Icaronycteris was capable of flight and echolocation, but lacked a keeled sternum. • Icaronyceris had only partial fusion of the radius and ulna, and dorsal position of the scapula. • Earliest megachiroptera are from the early Oligocene of Europe and Africa • Archaeopteropus and Propotto.
Bat Diversity • As is often the case in biology, there has been a rather ugly controversy concerning the evolutionary history of the megachiroptera and microchiroptera. Are they diphyletic or monophyletic?
Megachiroptera • Pteropodidae • 36 genera and 154 species of tropical and subtropical Old World fruit and nectar feeding bats. Predominantly nocturnal, with body sizes ranging from 15g to 1.6Kg. • They do not echolocate like micro-chiroptera, they are specialized for feeding on fruit and nectar (note teeth and palates: they do not consume pulp), and they have odd eye structures.
Teeth & Diet • Contrast the teeth of an insectivorous vespertilionid (A & B), a nectivorous phyllostomatid (C & D), and a frugivorous phyllostomatid (E & F).
Pteropus, Myotis, and Molossus. • Anterior and posterios views of the proximal end of humerus. • Note the extensive change inposition of the head.
Flight engine • Think about the forces involved in the wing-beat cycle, and why the humeri of megachiroptera and microchiroptera might differ. • Molossid shoulder is shown on next slide.