Download Size Surface Area and Volume

SCI 355B: Lecture 7
Size, Success, & Build-A-Bug
Size
• Small size of insects has both advantages &
disadvantages.
• The advantages are numerous, but there is
one major disadvantage = water loss
• Water loss (or prevention of..) is especially
critical in organisms with a high surface
area to volume ratio.
Surface Area and Volume
• Surface area (SA) = the “exposed” area of
the body expressed in squared2 units.
• Volume (V) = the three dimensional space
occupied expressed in mL or cm3
• The problems insects face can be traced
back to one relationship:
• The surface area/volume ratio (SA/V)
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SA/V Ratio
• Transpiration (water loss) increases as a
function of an increased SA/V ratio.
• The smaller the animal, the less its volume
and the greater the SA to V ratio
• In other words, small animals can maintain
little water reserves, yet the evaporative
surface is high.
EXAMPLE
• Consider two cubes: one is 2 cm and the
other is 4 cm
• SA=height x width x number of sides
• SA of the 2-cm cube = 2cm x 2cm = 4cm2 x 6
sides = 24cm2.
• SA of the 4-cm cube = 4cm x 4cm = 16cm2 x
6 sides = 96cm2
EXAMPLE
• Consider two cubes: one is 2 cm and the
other is 4 cm
• V = height x width x depth
• V of 2-cm cube = 2cm x 2cm x 2cm = 8cm3
• V of 4cm cube = 4cm x 4cm x 4cm = 64cm3
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EXAMPLE
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•
•
•
2-cm Cube
SA = 24cm2
V= 8cm3
SA/V= 24/8 = 3:1
•
•
•
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4-cm Cube
SA= 96cm2
V= 64cm3
SA/V= 1.5:1
Transpiration increases as a function of an increased
SA/V ratio. There is a much larger difference
between SA and V in smaller animals compared to
larger animals
Why are insects so successful?
• Small size (huh?) - can exploit a greater
number/variety of habitats and muscle strength is
proportional to cross-sectional area. Insect
muscles are very powerful since they are moving a
volume that is relatively small.
• Exoskeleton + jointed appendages
• Wings
• Reproductive capacity (numbers + speed)
• Anatomical diversity - (e.g., mouthparts)
Insect
Basic Body Plan
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Head
6 segments fused into a solid capsule
that houses the brain & mouthparts
Prognathous
Hypognathous
Cicada
Opisthognathous
Two antennae can be used for touch, smell,
taste and hearing
Scape and pedicel alone have intrinsic muscles
Filliform
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Setaceous & Aristate
Dragonfly
Horsefly
plumose
geniculate
capitate
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thrips
dragonfly
whirligig beetle
Mayfly
blow fly
March fly
Insects have 2 compound eyes composed of
many individual photoreceptors (ommatidia);
dragonflies have up to 30,000
Compound eyes can be present or absent
Most insects see in ultraviolet range
Each ommatidia can “see” a portion
of the field of view
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Compound Eyes
in UV range: greens + reds not detected
Human visual spectrum
“Bee purple” = yellow + UV
Nectar Guides
Ocelli - light and dark perception
Simple Eyes
Caterpillar
Stink bug
Cicada
Insect Mouthparts
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Back of Grasshopper head
Insects have modified mouthparts that
reflect their food sources
Chewing
Piercing-sucking
Sponging
Siphoning
Rasping-sucking
Cutting-sponging
Chewing-lapping
Vestigial
Beetles & caterpillars
Aphids, true bugs,
mosquitoes
Flies (some)
Moths & Butterflies
Thrips
Horse flies
Wasps
Some flies
Thorax - primary function is
locomotion via legs & wings
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Legs
1-5 ‘segments’
Tarsus (singular) Tarsi (plural)
Leg Modifications usually
occur in fore or hind legs
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Leg Modifications
Cursorial
Raptorial
Fossorial
Saltatorial
Natatorial
Water Boatman (Hemipteran)
Swimming/natatorial Legs
Raptorial Legs
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Special Leg Structures
Antennal comb
Wings
• Lateral outgrowths of the body walls
with no muscles attached inside them
How do insects move wings = IFM
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Halteres
Flight stabilizers – swing in out, vibrate in a plane at right angle to long axis of body;
changes in body attitude create torque at base of halteres
Abdomen
Houses digestive organs, excretory organs &
reproductive structures
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•
•
9-11 segments
Spiracles along the sides of each section
Cerci, sensory structures of crickets & cockroaches, etc
Ovipositor = egg laying device of females
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Ovipositor - used for defense in some insects
Central Nervous System
(Ocelli)
(CE’s)
(antenna)
(Labrum + SEG)
•Brain - proto-, deuto- & tritocerebrum (3 fused ganglia)
•Circumesophageal connectives - “around” esophagus
•Subesophageal ganglion - controls mouthparts
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Alimentary Canal
• The alimentary canal extends from the mouth to the anus
• Food is acquired & processed in the foregut, midgut & hindgut to
breakdown organic material into absorbable molecules and excrete
non-usable products of digestion
Salivary Glands
• in addition to digestive enzymes, salivary glands may secrete silk
(caterpillars & Hymenoptera) and anticoagulants (blood feeders)
Foregut (Stomodeum)
• The foregut extends from the mouth to the end of the proventriculus &
is lined with a layer of cuticle, the intima, which is shed with each molt
& serves as mechanical protection
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Foregut (Stomodeum)
•Food taken into the cibarium (preoral cavity), ground, pushed into the
mouth by maxillae, bathed & lubricated with saliva, & moves down the
esophagus via peristalsis, a series of muscular contractions, then may
be stored in a crop.
(cardiac)
Midgut
(Mesenteron)
• midgut - - main site of digestion & absorption of food, where gastric
caecae increase surface area for digestion.
Proctodeum (Hindgut)
•from pyloric valve to anus, resorption of H2 O, salts & amino acids
•lined with cuticle = little absorption
•Malpighian tubules, anterior intestine, and rectum
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•Open system consisting of:
•dorsal vessel – elongate tube
extending length of the body
•hemocoel – body cavity where the
hemolymph flows
• Dorsal Vessel
•Aorta – anterior
•Heart- posterior w/ segmented
chambers
•Ostia – pair of openings/segment
• No direct involvement in gas exchange
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