Lecture 8: Adaptive Explanation Non-perfect Adaptations Continued 6) Historical constraints Natural...
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![Page 1: Lecture 8: Adaptive Explanation Non-perfect Adaptations Continued 6) Historical constraints Natural selection acts at each gen’n must be advantageous.](https://reader035.fdocuments.net/reader035/viewer/2022072016/56649ef65503460f94c09d0b/html5/thumbnails/1.jpg)
Lecture 8: Adaptive ExplanationNon-perfect Adaptations Continued
6) Historical constraints• Natural selection acts at each gen’n must be advantageous in short term
• NS does not know the future – can’t plan
![Page 2: Lecture 8: Adaptive Explanation Non-perfect Adaptations Continued 6) Historical constraints Natural selection acts at each gen’n must be advantageous.](https://reader035.fdocuments.net/reader035/viewer/2022072016/56649ef65503460f94c09d0b/html5/thumbnails/2.jpg)
Historical Constraint
• May lead species in what will become the wrong direction & trap them there
local optimum
globaloptimum
selectionon character
selectionon character
fitne
ss
character state
time 1 time 2 time 3
![Page 3: Lecture 8: Adaptive Explanation Non-perfect Adaptations Continued 6) Historical constraints Natural selection acts at each gen’n must be advantageous.](https://reader035.fdocuments.net/reader035/viewer/2022072016/56649ef65503460f94c09d0b/html5/thumbnails/3.jpg)
Historical Constraint
Can (& does) lead to:
1) Imperfections
• b/c of “baby steps”
• Local optimum global optimum
b/c small s cannot overcome “fitness valley”
![Page 4: Lecture 8: Adaptive Explanation Non-perfect Adaptations Continued 6) Historical constraints Natural selection acts at each gen’n must be advantageous.](https://reader035.fdocuments.net/reader035/viewer/2022072016/56649ef65503460f94c09d0b/html5/thumbnails/4.jpg)
Pharyngeal Nerve
• First evolved in fish-like ancestors
• Direct route from gills to brain
• Mammals – from brain around dorsal aorta & back to larynx
• Long detour in giraffes (15+ feet!)
![Page 5: Lecture 8: Adaptive Explanation Non-perfect Adaptations Continued 6) Historical constraints Natural selection acts at each gen’n must be advantageous.](https://reader035.fdocuments.net/reader035/viewer/2022072016/56649ef65503460f94c09d0b/html5/thumbnails/5.jpg)
Historical Constraints
2) Nonadaptive differences:
• Many adaptive peaks at equal fitness
• Pop’n start out close to diff’t peaks
• Diff’t starting cond’ns not diff’t env’t adapt’ns
![Page 6: Lecture 8: Adaptive Explanation Non-perfect Adaptations Continued 6) Historical constraints Natural selection acts at each gen’n must be advantageous.](https://reader035.fdocuments.net/reader035/viewer/2022072016/56649ef65503460f94c09d0b/html5/thumbnails/6.jpg)
Non-adaptive Differences
time 1
time 2 time 3
Time 1: Character state with greatest fitness differs b/w pop’ns
Time 3: Either state equally fit but pop’ns constrained by historyfi
tnes
s
Character state (popn 1/popn2)
![Page 7: Lecture 8: Adaptive Explanation Non-perfect Adaptations Continued 6) Historical constraints Natural selection acts at each gen’n must be advantageous.](https://reader035.fdocuments.net/reader035/viewer/2022072016/56649ef65503460f94c09d0b/html5/thumbnails/7.jpg)
Cryptic colouration
Grouse chicks • Differ in colouration• Not diff’t env’tl cond’ns• Diff’t genetic
composition
![Page 8: Lecture 8: Adaptive Explanation Non-perfect Adaptations Continued 6) Historical constraints Natural selection acts at each gen’n must be advantageous.](https://reader035.fdocuments.net/reader035/viewer/2022072016/56649ef65503460f94c09d0b/html5/thumbnails/8.jpg)
8) Trade-offs
More than one function:
• can’t be optimal for both
• Behavioural trade-offs
• Life-history trade-offs
• Can’t look at adaptations in isolation
![Page 9: Lecture 8: Adaptive Explanation Non-perfect Adaptations Continued 6) Historical constraints Natural selection acts at each gen’n must be advantageous.](https://reader035.fdocuments.net/reader035/viewer/2022072016/56649ef65503460f94c09d0b/html5/thumbnails/9.jpg)
Example: Mouth
• Feeding vs. Breathing
• 2 palate in mammals
• Boas stop breathing
![Page 10: Lecture 8: Adaptive Explanation Non-perfect Adaptations Continued 6) Historical constraints Natural selection acts at each gen’n must be advantageous.](https://reader035.fdocuments.net/reader035/viewer/2022072016/56649ef65503460f94c09d0b/html5/thumbnails/10.jpg)
Summary
1. Adaptations do occur• They are characters appropriate to env’t
2. Adaptations only result from NS
3. Adaptations may not be recognized
4. Adaptations may be imperfect
![Page 11: Lecture 8: Adaptive Explanation Non-perfect Adaptations Continued 6) Historical constraints Natural selection acts at each gen’n must be advantageous.](https://reader035.fdocuments.net/reader035/viewer/2022072016/56649ef65503460f94c09d0b/html5/thumbnails/11.jpg)
How to tell if something is adaptative:
1. Adaptive prediction• Test observed against model• Beneficial, purposive
2. Measure selection• Usually experimental manipulation• Fitness of character variants • Problems: selection coefficients can be small,
hard to correlate with repro success, time-consuming, characters hard to measure
![Page 12: Lecture 8: Adaptive Explanation Non-perfect Adaptations Continued 6) Historical constraints Natural selection acts at each gen’n must be advantageous.](https://reader035.fdocuments.net/reader035/viewer/2022072016/56649ef65503460f94c09d0b/html5/thumbnails/12.jpg)
More…
3. Heritability• NS can only work on heritable traits• Low variability = low heritability
4. Cross-species comparisons• use comparative method• Adaptations should correlate to envtl diffns
Problem: Adaptation is hard to study!!