1. Function vs effect
Otte, D Effects and functions in the evolution of signalling systems
Annual Review of Ecology and Systematics 5: 385-
Library ann.
Red of the deepwater sponge, red of the male cardinal, red of maple leaves in the fall: only the cardinal’s red is a structure associated with adaptive consequence.
Re communication systems: we need to “distinguish between evolved functions and incidentaI effects” (Otte 1974)
Function defined here as: “the special action of any part of a living organism that evolved because such action fostered survival or reproduction”
Effect: a by-product of a characteristic.
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Structural adaptation, another defn: structural features with a history of genetic selection to a specified end of increased fitness.
Structural effect would then be one with no history of selection to a specified fitness goal*.
*teleology

2. Fall Colours an adaptation?
Anthocyanins can give flowers red and purple colour, a structural adaptation for attracting pollinators (e.g., hummingbirds). As a plausible hypothesis, red (anthocyanin) coverings of fruits could be selected to attract animals whose feeding on this food gift leads to dispersal of plant seeds.
In photosynthetic tissues (such as leaves and sometimes stems), anthocyanins have been shown to act as a "sunscreen", protecting cells from high-light damage by absorbing blue-green and ultraviolet light, thereby protecting the tissues from photoinhibition, or high-light stress. (Wikki). The anthocyanins of sugar maple leaves are a structural adaptation: they have a history of selection to promote fitness of trees by protecting from too much light.
Fall Colours an adaptation?
This red colour of maples in the fall has probably not been selected as a signal or cue (e.g., conveying information to leaf-feeding insects) The redness is a beautiful effect, a by-product of having anthocyanins revealed by the dying away of green chlorophyll.
G.K. Morris

3. What are the boundaries of a structural adaptation? What are its limits? Think about evolutionary timelines: generation after generation comprising a history of adaptation. Adaptations group together into a historical theme: e.g., flight.
Multiple structural adaptations of the historical theme of flight: structural features with a history of genetic selection toward the specified end of increased flight fitness: from bones, to feathers, to an aerofoil wing shape, a nontidal respiratory system, air sacs: multiple structural adaptations contributing toether to better flight fitness.
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What were once adaptations become vestigial, like the human tailbone, or occur as a partial reading out of genes during development that has no cost but never comes to function and is not subject to selection in males: e.g., breasts (nipples) of male humans.

4. Arthropods waltz about in chitin, cuticular exoskeleton
Arthropods waltz about in chitin, cuticular exoskeleton. Like a human wearing a suit of armor, the surface needs be segmented and jointed – and presumably parts moving against parts – rather noisy. One part comes near another and makes contact – one wing bangs into another as they are flexed and put away after landing. To start with this sound of wings being put away is incidental. At first the sound produced has no history of selection and so by these definitions would be properly regarded as an effect – an incidental effect.
The singing of a cricket to attract a mate comes about via an evolutionary process the ethologists called ritualization. Sound effects (intentional pun) of putting the wings away could be selected for because they helped bring the attention of a female nearby in the dark. Sound became an adaptation enhanced by special wing structures furthering the sound-maker’s fitness. Stridulation (the production of sound through frictional contact by exoskeleton) is another historical theme of selection.
Alexander, R.D Sound production and associated behavior in insects. Ohio Journal of Science 57: 101- “The number and variety of insects which produce sounds with specialized apparatus undoubtedly exceed those of all other living organisms combined…”

5. Tettigonia viridissima (a katydid): the arrows indicate the level of the tentorium within the head, just above the articulations, anterior and posterior, of the mandibles. During development tentorial arms like other apodemes, arise as inflections of ectoderm; the inflected embryo tissue acts to produce chitin, fusing internally into the body of the tentorium. One has a paradox of exoskeleton that functions internally.
Orthoptera all have a tentorium: the Order includes katydids, crickets, grasshoppers.

6. Locust tentorium from below: a truss anchoring the
Ventral corners of the head for mandible support
Condyle for mandible
Anterior arm
Posterior arm
Sara Jane Gutierrez
dissection

7. Locust tentorium from above
posterior
Region into which the abductor and adductor apodemes project
anterior

8. A diagram of forces: the tentorium is what an engineer would call a truss.

9. Function of the tentorium: a truss that keeps the head stable as a
The insect head can be modelled as a six-sided box, one with no bottom and no rear. Lacking two sides leaves the two rear corners movable under stress. The mandibles, mounted beneath the cheeks and rotated together toward the midline to crush vegetation, needs a firm base. Crushing in the absence of the tentorium would let the two ‘free’ box corners move apart and so reduce the squeezing force.
Function of the tentorium: a truss
that keeps the head stable as a
base for mandible rotation. .
Variation in tentorium structure among taxa

10. Evolution of the beetle gular sclerite
Prognathous – forward directed – mouthparts are typical of the Order Coleoptera and so is the sclerite called a gula (a sclerite is a region of the insect’s exoskeletal surface, set off by membrane, sutures or sulci). Early ancestors of beetles, had hypognathous mouthparts, but evolved this prognathous orientation, accessing food (or prey) in front rather than at its feet. The region where the posterior arms meet the cranium was involved in this head angle change and internally drew the posterior arms (red) out into a very lengthened structure helping to offset forward-originating forces..

11. “Levers are practical applications of ...moments” Vogel
Force moment
When “a force has a line of action lying to one side of an axis of rotation... we call the shortest, or perpendicular, distance between the force’s line of action and the axis, the ‘moment arm’ or the ‘lever arm’ of the force” (Vogel 2nd). A moment of force is the product of the force magnitude and this lever-arm distance to the line of action.

12. Vogel 2nd edition, See Appendix 2 Motion and Direction, p. 547
Moments involve rotation.
“The effectiveness of a force is the product of the magnitude of the force and the perpendicular distance from the line of action of the force to the axis of rotation.” This is its moment. Making d large increases the moment of force that the mandible can apply.
Compromise is necessary.
Axis of rotation of the mandible is an imaginary line joining the two articulation points situated on the lower margin of the cranium.
The mandible turning about this axis, completes an arc of a circle, which can, e.g., crush a seed against the opposing mandible.
Vogel 2nd edition, See Appendix 2 Motion and Direction, p. 547
Imagine it as it isn’t: imagine the adductor apodeme insertion at any other locus around the base of the mandible -- the moment of force exerted would be smaller.
The mandible, suspended beneath the insect’s head, is anchored at two articulations ; joining these articulations with an imaginary straight line gives an axis of rotation or fulcrum. The mandible rotates about this axis, completing the arc of a circle. Forces at the mandible faces have magnitude and direction: vectors.

13. Skeletons both exoskeletons and endoskeletons, move forces about
Skeletons both exoskeletons and endoskeletons, move forces about. They translocate them, they leverage them.
Three classes of lever are named on the basis of sequencing* effort, load, fulcrum.
FIRST EFFORT FULCRUM LOAD
SECOND FULCRUM LOAD EFFORT
THIRD FULCRUM EFFORT LOAD
For more background on levers see Vogel 2nd ed. Chapter 24, p. 473.
*sequencing horizontally

14. Class 1 lever: insect wing

15. Scallop adductor works with a 2nd class lever
The load of the shell is taken as acting through the centroid of the bivalve, this being closer to the hinge than the muscle; the effort of the adductor muscle ‘lifts’ this load.
Centre of gravity taken as place where load is applied
Abductin at the hinge is not a muscle but a rubbery material, antagonist of the adductor muscle; it acts elastically, storing energy in its distortion when the adductor contracts, to return it at a later time.
Abductin as inner and outer ligament: one acts as a 2nd class other as 1st .

16. [Force can be represented as a vector,
showing magnitude and direction.]
Leverage involves a force causing body-part rotation: the force from shortening adductor muscles pulls on the adductor apodeme inserted on the mandible base; this rotates the whole structure through a short arc toward the midline (fat blue arrow)..
To decide where the load should be considered to act, you need the point of balance, i.e., the centroid or centre of gravity.

17. “Levers are practical applications of ...moments” Vogel
Force moment
When “a force has a line of action lying to one side of an axis of rotation... we call the shortest, or perpendicular, distance between the force’s line of action and the axis, the ‘moment arm’ or the ‘lever arm’ of the force” (Vogel 2nd). A moment of force is the product of the force magnitude and this lever-arm distance to the line of action.

18. Force-advantage levers vs distance- (or) speed-advantage levers
Vogel advocates using the term force advantage instead of mechanical advantage, because mechanical advantage can be misleading: a muscle often actually works at a leverage ‘disadvantage’.
Force advantage is the ratio by which the applied force is multiplied (amplified) by the lever.
Where force is more important than speed in the life of an animal evolution will want a force-advantage lever, one where the effort arm is longer than the load arm, so maximizing the moment of the effort – the force-in or effort moment.
Distance advantage is force advantage’s reciprocal: the ratio of the distance the load moves to the distance moved by the effort. [“Distance advantage must correspond to ‘speed advantage’ – if an action takes a given time, then going farther means going faster”.]
When speed and distance are more important than force you will want a longer load arm than effort arm giving a relatively greater moment to the load.

19. Redrawn Fig of Vogel
Force advantage: ratio by which
the effort is multiplied by the lever; moment arm of effort divided by moment arm of the load.
Distance advantage: ratio of the
distance moved by the load relative to
that moved by the effort.
Speed advantage: ratio of the speed at which the load moves relative to that of the effort.
Force and distance/speed advantage are inversely related: good force advantage goes with a relatively poor distance/speed advantage; good distance/speed advantage with a relatively poor force advantage.

20. Both up and down insect-wing movements are a (first class) distance-increasing lever – a lever with good speed advantage, and a relatively poor force advantage; there is a very short force arm, the moment arm of the effort is divided by the much larger moment arm of the load – the centre of gravity of the wing being much farther from the fulcrum.
“A muscle... is relatively
good at producing force
and relatively bad at getting
shorter. ...any engine that gets only 20 % shorter will have to operate with a substantial distance advantage to move a long limb [wing] through an angle that may approach 180 degrees. For that good distance advantage it will necessarily suffer a poor force advantage because the product of the two must be unity...” (Vogel 2nd , p. 475)