5. insect musculature, locomotion, and limb diversity

for bugs, is the SA:V ratio high or low? why?

very high

• enables cuticle to support far more RELATIVE weight

• light weight means surface tension of air and water is higher for insects

5 universal segments of legs + 2

• coxa

• trochanter

• femur

• tibia

• tarsus

• pretarsus and claws

gait

coordination of limb mvmts to adjust for speed and stability

tripod gait characteristics

• ipsilateral fore- and hindlegs step w contralateral middle leg

• center of mass remains in triangle, so more stable

metachronal wave gait characteristics

• limbs lift in a wave (hind legs first)

• enables higher speeds, but less stable

• most visually obv for millipedes

ambulatory/cursorial legs (what kind of mvmt, shape, example insects)

• walking and running (fast mvmt on ground)

• slender, relatively unmodified

• ex: cockroaches, ground beetles, ants

saltatorial legs (kind of mvmt, 2 leg traits, example insects)

• jumping

• enlarged hind femur w powerful muscles

• long lever-like tibia for jumping

• ex: grasshoppers, crickets, locusts

what do hoppers use for rapid, precise jumps?

gears

raptorial legs (2 leg traits, example insects)

• forelegs modified into spines/claws for seizing prey

• often folded like a trap for grasping

• ex: mantids, mantisflies, some aquatic bugs

fossorial legs (kind of mvmt, 2 leg traits, insect examples)

• digging

• broad, shovel-like forelegs

• strong spines and flattened shape

• ex: mole crickets, cicada nymphs

natatorial legs (1 leg trait, example bug)

• flattened w fringe of hairs increasing SA for propulsion

• ex: water striders (they have many microscopic hairs to trap bubbles)

label + identify what kind of legs they are

raptorial

label + identify what kinds of legs they are

limb coordination for swimming/skating

swimming/skating use gaits that BILATERALLY synchronize limbs

scansorial legs (2 traits, example)

• clinging legs adapted for climbing and holding onto hair or feathers

• hook extension from tibia and strong claw on tarsus tip

• ex: biting and sucking lice

describe legs for pollen collecting

metathoracic legs of bees flattened, wide tibia and femurs w fringe of hairs (basket)

describe legs for adhesion

tarsomeres w pads (“pulvilli” or “arolium”) for smooth surface or grasping, often w hooks (“ungue”)

prolegs

• hydrostatic legs used by caterpillars + sawfly larvae

• not articulated like thoracic legs

5 benefits wings provide

• expansion of access to resources

• means of escape or crypsis

• increased access to genetic diversity

• means of communication

• physical protection

general structure of wings

• composed of 2 membranes

• hardened on the costal (front) edge

• hinges alter angle to maximize lift on downstroke, shearing on upstroke

• wings are wind and chemical sensors

2 hypotheses on the origin of wigns

• Gill-Exite hypothesis

• Paranotal hypothesis

Gill-Exite hypothesis

wings arose from a leg outgrowth

Paranotal hypothesis

wings are a novel body wall structure

vertebrate vs. insect winsg

• vertebrate wings are limbs → muscles inside the wing allow flapping

• insect wings are not limbs → muscles connect to base of wing

halteres

highly reduced wings that sense initial forces rather than generate lift`

elytra and hemielytra

hardened FWs protect against mechanical damage and dehydration

what are the only wings beetles beat?

beetles only beat HWs, though its elytra generates lift

how many times did insect evolve wings?

once — then it lost it many times

2 reasons why insects lost wings

• to prevent catching while crawling

• crypsis

examples of insects that lost their wings

• subterranean: termites, ants, snow flies

• parasitic: batflies, keds, fleas, bedbugs, aphids (sometimes)

• specifically for crypsis: walking sticks

how do muscles move limbs?

by connecting cuticle w apodemes

synchronous insect muscles (function, # contractions, used by which insects)

• function: precise control, for strong direct force output

• one motor neuron AP = one muscle contraction

  • max freq of contraction limited by refractory period of the motor neurons (<100 Hz)

• used by walking and jumping legs, mouthparts, wings of “slow-flying” insects (e.g., dragonflies, butterlifes

asynchronous insect muscles (function, AP mechanism, kinds of insects)

• function: high frequency (up to 1000 Hz), energy efficient but less precision

• AP initiates contraction, but stretch continues to trigger (myogenic/mechanical)

  • 1 AP = ~20 contractions

• used by wings of “fast-flying” insects (e.g., flies, bees)

direct flight muscles + order

• attach directly to wings to provide power

• Paleoptera

indirect flight muscles + order

• attach to thorax, not wings

• deforms thorax to provide power in wing strokes

• direct flight muscles are reduced, provide flight control

• most Neoptera