Download The Evolution of Flight Entognatha and the Paleoptera

The Evolution of Flight
Entognatha and the Paleoptera
D. L. A. Underwood
Biology 316 - General Entomology
A. Subphylum Hexapoda
1. Class Entognatha
a. Mouthparts pulled into the head
b. Two orders (Protura and Collembola)
c. Small (generally less than 5 mm in length) and wingless
d. Found in leaf litter, near water and moist areas
e. Some authors do not include the Entognatha with the insects. They interpret the
morphological data as best fitting the hypothesis of an independent evolution of sixleggedness.
2. Class Insecta
a. Mouthparts are not pulled into the head
b. Twenty-eight orders (depending upon authority)
B. Class Insecta
1. “Paleoptera”
a. Wings are "primitive."
i Wings cannot be flexed and laid down over the abdomen.
ii Wings must be extended laterally or held together above the thorax and abdomen
b. Two orders, the Ephemeroptera (mayflies) and Odonata (dragonflies and damselflies)
c. Nymphs are aquatic.
2. Neoptera
a. Wings have a wing-flexion mechanism or are descendants of insects that possessed
such a mechanism.
i Wings can be folded over the abdomen.
ii Twenty-four to 26 orders
C. Neoptera
1. Orthopteroids or Polyneoptera
a. "Generalized" mouthparts
b. Hindwings are typically larger than the forewings.
c. Cerci present
d. Nine orders - seven common orders you will probably encounter
i Phasmatodea - walking sticks
ii Orthoptera - grasshoppers, crickets, and katydids
iii Mantodea - mantids
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iv Blattodea - cockroaches
v Isoptera - termites
vi Dermaptera - earwigs
vii Plecoptera - stoneflies
2. Hemipteroids or Paraneoptera
a. Specialized mouthparts
b. Hindwings (if present) are not larger than forewings. Cerci are not present.
c. Five orders
i Psocoptera - psocids
ii Phthiraptera - lice
iii Hemiptera - true bugs, cicadas, hoppers, psyllids, whiteflies, aphids, and scale
insects
iv Thysanoptera - thrips
3. Holometabola or Endopterygota
a. Undergo complete metamorphosis
b. Nine orders - eight common orders
i Neuroptera - snakeflies, lacewings, antlions
ii Coleoptera - beetles
iii Mecoptera - scorpionflies
iv Siphonaptera - fleas
v Diptera - flies
vi Trichoptera - caddisflies
vii Lepidoptera - moths and butterflies
viii Hymenoptera - wasps, bees, ants,
D. Flight
1. Overview
a. The fastest insect is reported as being a large Australian dragonfly that flies at a speed
of 36 mph. Other large dragons have been clocked at speeds ranging from 16-19
mph. Humans can run a mile in 4 minutes (not this human, but some), a speed of
about 15 mph. Fastest human runs at about 25 mph, but only for a very short
distance. Here is a great web site that talks about other speed reports in science that
may not be quite accurate (www.abc.net.au/science/k2/moments/gmis9911.htm).
b. Flight is accomplished by both indirect and direct flight muscles.
c. The indirect muscles cause the up and down motion of the wings.
d. The direct muscles lead to the wing being angled or twisted during the flight stroke.
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e. The muscles may either contract once or many times per neuronal impulse.
f. Insects with relatively slow flight like Lepidoptera and Neuroptera have wings whose
muscles contract only once, limiting the number of wing beats to the rate the nervous
system can send impulses (about 50 beats per second). While this is considered slow,
it is very fast in comparison to vertebrate flight. The fastest wing beat of birds is
found in hummingbirds with a wing beat of 40 -80 beats per second.
g. In Diptera, Hymenoptera, and Coleoptera, the wing muscles contract asynchronously
with many contractions per impulse. A midge was clocked at a frequency of 2218
strokes per second! The 'lowly' mosquito beats its wings in excess of 1000 strokes
per second.
2. The evolution of flight
a. Flight is advantageous for numerous reasons.
i It promotes sexual outbreeding by allowing for dispersal.
ii Colonization of new habitats is made possible by flight.
iii Escaping predators is enhanced by the ability to fly.
iv Finding specific oviposition and feeding sites is more efficient by flying rather
than walking.
v It is perhaps no coincidence that the three most diverse orders, Lepidoptera,
Diptera, and Hymenoptera are primarily aerial in habit.
b. The mystery
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i
ii
iii
iv
v
Early insects lacked wings.
The first winged insects appeared in the fossil record with fully formed wings.
Wings are not modified walking appendages as they are in birds and bats.
From what structures did they arise?
What function did the early "wing" serve before it became a functional structure
used for flight?
3. Flight evolved independently in several animal groups.
a. Critics argue that natural selection is not adequate to explain the many transitional
steps required for the evolution of complex structures. What good is half an eye or a
nub of a wing?
b. Darwin countered that the function of a trait may change during evolution.
4. Team project - A takes notes, B speaks
a. Without referring to the lecture outline, come up with two possible functions of
protowings. A protowing is a small, wing-like structure.
E. Fossil insects
1. Aquatic or terrestrial origins?
F. Four hypotheses on the evolution of insect flight
1. Courtship Display or Defensive Display
a. Sexual selection could lead to ever increasing size of the winglets.
b. Secondarily flightless insects, some crickets and longhorn grasshoppers, the
hindwings are reduced or absent, but the forewings are retained as stridulatory elytra
to produce sounds to attract females. Males of at least one species of cricket cannot
stridulate, but they still use the elytra in visual signaling during courtship.
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c. Alternatively (or in conjunction?), movable structures on the dorsal surface of the
insect may be more effective at advertising distasteful-ness than non-movable
structures.
d. Wings would have to have evolved in a terrestrial environment.
2. Aquatic Ventilation and Respiration
a. Nymphs of present day Ephemeroptera are aquatic and possess tracheal gills and gill
plates that act as paddles to provide ventilation (water movement) over the tracheal
exchange surfaces.
b. Many authors consider the gill plates on the abdominal segments serial homologs to
thoracic wings.
c. Physiological studies show that increasing the frequency of gill-plate beating can
raise rates of oxygen uptake, allowing effective gas exchange in water with a low
oxygen content.
d. The effectiveness of stationary (nonflapping) gill plates as exchange surfaces should
increase continuously with increasing plate length only while protowings are
relatively short.
e. The effectiveness of winglets as exchange surfaces and as paddles providing
ventilation has not been experimentally tested as functions of winglet size, body size,
and flapping speed.
3. Thermoregulation
a. Winglets initially functioned as thermoregulatory structures to increase body
temperature by absorbing radiation, thereby allowing more vigorous or longer periods
of locomotory activity.
b. Studies of models asked how do changes in wing and body size affect the
contribution of wings to body temperature.
c. Selection for increased body temperature could favor insects with short winglets over
those with none and could act to increase thoracic wing size in insects with short
wings.
d. Many extant species of insects use their wings for behavioral thermoregulation.
e. Requires the evolution of wings in terrestrial environment.
4. Aerodynamics
a. Three postulated early uses: parachuting, gliding, and attitude control
b. Gliding and parachuting could provide:
i energetically inexpensive horizontal travel
ii relatively fast, energetically inexpensive vertical descent from vegetation
iii pursuit of aerial prey
iv escape from predators
v protection from injury during vertical descent
c. Attitude control may enhance gliding or parachuting performance, enable falling
organism to land right side up so it can run from predators, and enable an organism to
steer as it falls.
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5.
6.
7.
8.
d. Mathematical models of falling cylinders or physical models of cylinders bearing
thoracic winglets of various sizes have been used to test the effects of body sizes and
air speeds, body morphologies and appendages, and performance criteria.
Summary of data
a. At smaller body sizes and lower movement speeds, short thoracic protowings have
little effect on aerodynamic performance.
b. Above some critical wing length, further increases in wing length alter performance
and hence might be subject to natural selection.
c. For all the functions considered except parachuting, the relative wing length at which
thoracic protowings improve aerodynamic performance decreased as body size
increased. Thus at larger sizes and higher movement speeds, even rather short
protowings could improve performance.
d. The presence of both thoracic and abdominal winglets reduces the protowing length
at which protowings can improve aerodynamic performance, at least for larger sizes
and/or faster speeds.
Things to consider
a. Confidence or uncertainty intervals allow us to potentially reject relevant null
hypotheses (e.g. that winglets have no effect) and also provide information on the
degree of support for the null hypothesis.
b. The entire approach is based on the notion that performance is directly related to
fitness, yet the quantitative relationship between performance and fitness (and hence
strength of selection) undoubtedly varies among functions and among performance
criteria.
c. Because we are considering multiple, nonexclusive hypotheses in many instances, a
more productive discussion would focus on the relative magnitude of effects on
variation in size and morphology rather than the presence or absence of such effects.
Potential costs of Protowings
a. Insect may be swept away by wind or current.
b. Terrestrial locomotion may be impeded.
Summary and Synthesis
a. Which proposed selective factors in the initial and early evolution of wings are likely
or plausible? It depends upon our assumptions about habits, size and morphology of
ancestral insects.
b. Evidence in favor of one hypothesis does not constitute evidence against another.
c. Perhaps a more productive approach is to focus on the range of possibilities. How
does functional performance vary with size and shape (the morphospace) and with
environmental conditions (the performance curve)?
d. In the multidimensional space representing functional performance, size, and shape
(e.g. body size, wing size, wing shape, wing number, body shape) and environmental
conditions (e.g. terrestrial vs. aquatic habits, flow velocity, thermal conditions), the
change in performance with change in wing length at any given point affords a
measure of the relative selection favoring changes in wing length.
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G. The Entognatha
1. Comprise two orders, the Protura and the Collembola
a. All live in very moist conditions, generally in leaf litter or loose soil.
b. They share a number of characters that unite them including
i mouthparts that are pulled within the head
ii absence or weak development of
compound eyes
iii thin and pale cuticle
iv generally very small
c. However some workers believe that these
characters arose independently and
represent convergent evolution as an
outcome of living in leaf litter and soil.
These workers conclude that the
Entognatha are a polyphyletic group and
they elevate each order to the rank of class.
2. Alternative points of view regarding the sister taxon to the Insecta
a. The Diplura share with the Insecta caudal filaments and a very unusual microtubule
arrangement in the axoneme of sperm. Most animals have a 9+2 arrangement while
the Diplura and the Insecta have a 9+9+2 arrangement.
Protura
Protura
Collembola
Collembola
Diplura
Diplura
Insecta
Insecta
3. The Insecta (Ectognatha) is an uncontested monophyletic group.
a. They consist of both winged and wingless forms and are united by sharing many
characteristics including
i mouthparts not pulled into the head
ii simple and compound eyes
iii well-developed ovipositors
b. They are sometimes divided into two groups, the Apterygota and the Pterygota.
However, this produces a paraphyletic grouping.
c. The Pterygota or winged insects form a monophyletic group and it is divided into two
groups, the Paleoptera and the Neoptera. It is equivalent to your text's usage of the
'Insecta.'
i While the Neoptera are a monophyletic group, the Paleoptera are not.
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ii It is still unresolved as to which Paleopterous order is the sister group to the
Neoptera.
4. Team Project – C takes notes, D speaks
a. We discussed why placing animals into monophyletic groups is one goal of
systematics. Review this idea and come up with three reasons for this goal.
H. Order Collembola (springtails)
1. Natural history
a. Seven families in North America, 6500 species worldwide are found from the Arctic
to the tropics.
b. Fossils of collembolans date back to early Devonian (400 million years ago). They
comprise the oldest living insect order. The other major insect orders first appeared
in strata dating to the late Carboniferous (approx. 300 mya).
c. Many have a specialized abdominal structure (furcula or furca) that allows them to
jump great distances. A springtail of about 5 mm in length can jump up to 100 mm!
Not all springtails have a furcula, however. The furcula bends forward and 'hooks'
onto the retinaculum. When the furcula is released, it catapults the springtail forward.
d. Species can be herbivorous, carnivorous, or fluid feeders; many feed on fungal
hyphae and pollen.
e. They occur in a variety of habitats including leaf litter, decaying logs, soil, under
bark, on the surfaces of freshwater pools (like my dog's water dish!) or along
seashores, in vegetation, termite nests, on snow, and in caves.
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f. Some species are pests on mushrooms, greenhouse, agricultural, and garden plants,
and in households.
I. Order Thysanura (silverfish and firebrats)
1. Natural history
a. Three families in North America, 320 species worldwide.
b. Most species live in soil, leaf litter, rotting wood, nests of ants, termites, or mammals,
and other damp habitats.
c. A few species are domesticated and live with humans. These species feed on starchy
substances like the bindings of books, labels, starched clothing and other fabrics, and
the starch paste in wallpaper.
d. In some species, individuals may live as long as five years with up to 60 molts.
e. They exhibit a cool seminal transfer system.
J. Order Ephemeroptera (mayflies)
1. Natural history
a. 17 families in North America, 2000 species worldwide.
b. Nymphs are entirely aquatic and feed primarily on algae and detritus.
c. It may take up to two years for a nymph to mature into an adult.
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d.
e.
f.
g.
The adults do not feed and rarely live for more than a day or two.
Adults often emerge synchronously and engage in mating flights.
Mating occurs on the wing and females oviposit immediately afterwards.
As they emerged in great numbers, so they die in great numbers and there are records
of piles of mayfly adults as deep as 1.2 meters in Illinois.
h. However, recently their numbers have declined due to pollution levels in lakes.
i. Mayflies are often used as indicator species for measuring habitat health (more on
this later in the semester).
j. Mayflies are important source of food for many species of fish.
K. Order Odonata (damselflies and dragonflies)
1. Natural history
a. Eleven families in NA, 4870 species worldwide.
b. Nymphs are entirely aquatic, predaceous, and
can live for several years before maturing into an
adult. The have elaborate labial masks used in
prey capture. Dragonfly nymphs lack external
'gills' instead drawing water into the rectum
where gas exchange occurs. They can also
forcibly expel this water and use the force
generated for locomotion (jet propulsion).
c. Adults are active predators of flying insects and
live at most two or three months.
d. Odonates are peculiar in their method of mating.
Males must move their sperm from the gonopore
(located at the end of the abdomen) to sternite #3
where it is stored until mating. He clasps the
female either on the prothorax (damsels) or on
the head (dragons). The female, if receptive,
curls her abdomen under and initiates copulation.
If the female has mated previously, the male first
removes the spermataphore of the previous male
before injecting his own.
e. Adult male dragons typically
defend territories.
f. Dragonflies in the fossil record
are famous for their amazing size.
One fossil measured over 71 cm
(that's 28 inches for the nonmetrically inclined)! Great
debates rage over why our present
day dragons are so small.
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