BIO325H5 Study Guide - Winter 2019, Comprehensive Midterm Notes - Muscle, Insect, Exoskeleton

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Lecture 1: Imagine As It Isnt
January 7, 2019
Important Concepts
D’Arcy Thompson
Dynamic optimization
BIO325 is about the form of organisms
Form of a body speaks to its evolutionary history
As an adaptation:
o Evolved because it enhanced fitness
o Was subject to selection for survival & reproduction
Body parts also achieve their form within the limits and ‘laws’ of Newtonian mechanics
Ennos defines “Biomechanics” as how the adaptations of animals & plants are constrained to
their mechanical environment
o The study of forces, stresses in solids, pressures in fluids, acting, via elasticity, viscosity,
etc. to achieve movement
o Structures also allow you to infer their capacities to transduce force
“Analysis of biological form must emphasize the concept of adaptation- the fitness of a structure to
perform functions beneficial to an organism” (Stephen Jay Gould 1971)
Function in physiology is how a structure- organ, tissue, cell, or molecule- works to the benefit of
an organism
The gut functions in digestion, a lophophore functions in respiration, a leg functions in jumping
Know How to Place Animals (& Plants) in Their Largest Groupings
Phylum, Class, Order, Family, Genus, Common Names ** important to know which phylum **
Learn diagnostic structural features of major phyla (especially Chordata, Arthropoda)
Plant groups- Vascular Plants: angiosperms (flowering) & gymnosperms (conifers)
Understanding of the concepts of natural & sexual selection
Increase vocabulary of morphological descriptive terms
o Sagittal & transverse; Dorsal & ventral
o Distal & proximal; Promote & remote
o Flex & extend; Anterior & posterior
Draw structures as a means of learning
Three Main Lines of Living Arthropods
Chelicerates (spiders)
Crustaceans (crabs)
Terrestrial mandibulates (insects & myriapods)
o Commonly encountered myriapod is Scutigera coleopteran aka house centipede
Grasshopper’s common name is Marsh meadow grasshopper (Order Orthoptera, Phylum Arthropoda)
Hind legs are disproportionately large, with a (blackened) dicondylic femorotibial joint
Within femur, muscle fibres are attached pinnately to a tendon (apodeme)
Row of pegs on the inner face of each hind femur & two pairs of wings
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Lecture 1: Imagine As It Isnt
January 7, 2019
Theme: aim is to change the way organisms are regarded
Get into the habit of questioning the form of the body parts of organisms & to search structures for
possible adaptiveness, as the products of a history of selection evolved within physical constraints
House centipedes emphasize running, while grasshoppers emphasize climbing
Grasshoppers jump & climb between the substrates that may present different angles to gravity
o Makes a two-tyne mobile (ungue) grappling hook really useful
Jumping millipedes are unheard of, but they need to run down their prey (other smaller arthropods)
o Almost vestigial tarsal claws
Bodies & Body Parts Behave
Samaras move in the wind, pollen grains move on a bee
Organisms move by growth
o Sunflower turns to track the sun, one side of the stem growing faster than the other
o Strangler fig vine climbs on a tree
One part of an organism may move relative to another, as an atrium squeezes blood into a ventricle
or segments of a limb extend in a jump
An animal may pick up & move from one spot to another
o Crawling, burrowing, jumping, running, jetting, swimming, flying
Behaviour involves movement or its purposeful absence eg. holdfasts, playing possum
To understand a form, its shape, size, colour, strength, smoothness, opacity, stiffness, resilience
o You are greatly helped by knowing its behaviour
Scutigera coleopteran
15 pairs of tapered-tip walking legs, differing in length along the body- get longer rearward
Arthropodia end in a multijointed segment & animal moves with a side
Cursorial adaptation- legs moving in waves metachronally
Adaptations build on a foundation of other adaptations & a form may serve multiple functions
These ‘little’ machines never stop running (ie. evolution is always working on a living organism)
Adaptations arise from parts that were selected for historically in other contexts
- Here are leg segments from a millipede & a
- They contact the substrate very differently
- Tarsal parts of the millipede are many & relatively
tiny, tapering away to a vestigial claw (ungue)
- The grasshopper end in a robust two-clawed
grappling hook
- Comparison between taxa is important to generate
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Lecture 1: Imagine As It Isnt
January 7, 2019
Imagine (It) As It Isn’t
When inferring the function of a structure from its form, it can be useful to fancifully redesign it,
perhaps as it occurs in some other animal
Suppose we change the number of scutigerid legs from 15 pairs to 30? Would there be an increase
or decrease in top running speed? What if we make the legs all the same length or put the longer
ones at the front instead of the back? What would be the result of reducing the large number of
tiny joints in tarsus 2
These kinds of redesigns get you thinking about just what might have been the selective basis for
15 pairs as optimal- why are the legs of Scutigera not all the same length? Why do they get longer
along the body axis? Has this something to do with the metachronal movement & phase or do the
anterior legs play a different role in steering around obstacles, which of course by definition are
encountered first at the front end?
T2 with its many subsegments seems adapted to conform closely to uneven ground, i.e. no matter
where it is placed, there is necessary friction to apply stepping forces
Not everything is an adaptation- some things are effects
A bear’s shadow in the woods is an effect not an adaptation
Hypothesis: tube sponge on a coral reef is an effect- not an adaptation
Red wavelengths of light are reflected by this sponge in a flash picture- but under the conditions of
its evolution, at depth in the sea, there are no reds
The sponge is red only from the diver’s camera flash
o This feature of the sponge’s morphology is an effect- pigmentation of its integument has
not been selected because of its red-wavelength reflecting properties
The material of the sponge’s body that happens to reflect red isn’t adaptive in some other respect
o Red pigment could also exist because of pleiotropy (genes may have multiple phenotypic
effects) so the presence of this colour might be the result of selection acting on one of the
other phenotypic effects
D’Arcy Thompson
Believed that organic forms arose not just from selection, but also from the direct effects of forces
He called them ‘direct adaptation’
“There may well be a mathematical law of growth which is common to…the spiral form in
Nautilus… in the ram’s horn and in the inflorescence of the sunflower”
Spiral horns of the mountain sheep are a sheath of keratin formed around a bony core- they are not
shed like antlers “a zone of active growth at the base of the horn… trihedral prism… keeps adding
to this sheath, ring b ring…” year by year
Each part of the zone grows at a different rate bringing about the spiral
- On the inner face of the metathoracic legs, are a row of pegs
that engage a vein of the forewing- stridulatory mechanism, a
frictional way in which the exoskeletal cuticle, can make a sound
- Pegs pluck the forewing (tegmen) & this causes regions of the
wing to oscillate & radiate sound waves into the surrounding air
- Sound made by a male attracts a conspecific (of his species)
- Functions of this leg are 2: leaping & stridulating
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