The evolutionary importance of heritability
Measures of heritability
1. Parent-offspring regression analysis:
– Examines the similarity between parents and their
offspring in terms of the traits they possess
– If a trait has a genetic basis, then the trait values of
offspring should be similar to the trait values of their
parents: there should be a positive relationship
between offspring and parent trait values
2. Selection experiment method:
– Different groups of individuals are subjected to
differential selection on the trait in question
– If artificial selection acting on a trait results in changes
in that trait value in subsequent generations, then the
trait has a genetic basis
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Hirsch Maze
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Selection experiment
• Over four generations
of selection, found
strong changes in
exploratory behavior
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Parus major
http://en.wikipedia.org/wiki/Great_Tit
Variation within a population
Due to:
1. Differences in genetic composition
2. Differences in environmental conditions
3. Differences in learning
And
1. Variation in traits may not affect fitness
2. Frequency-dependent selection can maintain
different traits in a population
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Differences in learning
• Trial-and-error
learning results in
bees increasing rate
of food delivery
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Variation may not affect fitness
• Eastern screech owls
show great variation
in dispersal direction
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
2.2 Modes of natural selection describe
population changes
• Directional selection
– Individuals in a
population with an
extreme trait value at
one end of the
spectrum possess
the highest fitness
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Directional selection in juvenile ornate
tree lizards
• Methods:
– Ornate tree lizards (Urosaurus ornatus)
– Captured from wild
– Tested locomotor performance of individuals on 2
m raceway
– Measured body size and mass
– Uniquely marked individuals and released back
into wild
– Recorded survival for six months
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
2.2 Modes of natural selection describe
population changes
• Disruptive selection
– A situation in which
individuals in a
population with
extreme trait values
on both ends of the
spectrum have the
highest fitness
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Disruptive selection in spadefoot toad
tadpoles
• Methods:
– Spadefoot toad (Spea multiplicata)
• Detritivores consume detritus and
small invertebrates
• Carnivores consume invertebrates
• Intermediates are generalists
– Examined feeding efficiency
– Measured survivorship
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Disruptive selection in spadefoot toad
tadpoles
• Results:
– Feeding performance and growth rates of each
specialized morph were higher than those of
intermediate morphs
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Disruptive selection in
spadefoot toad tadpoles
• Results:
– Intermediate morphs
had lower survivorship
than either specialized
morph
• Conclusion:
– Individuals with
specialized morphology
have higher fitness
than individuals with
intermediate
morphology
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
2.2 Modes of natural selection describe
population changes
• Stabilizing selection
– A situation in which
individuals in a
population with
intermediate trait
values have the
highest fitness
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Figure 11-15
Featured Research
Sexual selection in house finches
• Methods:
– House finches (Carpodacus
mexicanus)
– Experiment 1
• Quantified male plumage color
intensity
• Allowed females to choose
among males
– Experiment 2
• Artificially dyed males
• Allowed females to choose
among males
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Sexual selection in house finches
• Results:
– Females spent the
most time with
males with the
most intense red
coloration
• Conclusion:
– Red is a sexually
selected trait
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Fitness and adaptation
• Adaptation
– A trait that enhances fitness
– An evolutionary process that results in a
population of individuals with traits best suited to
the current environment
• Fitness
– Survivorship and reproduction
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
“An adaptation is, thus, a feature of the organism, which
interacts operationally with some factor of its
environment so that the individual survives and
reproduces.” (Bock, 1979)
"The sutures in the skulls of young mammals have been
advanced as a beautiful adaptation for aiding parturition,
and no doubt they facilitate, or may be indispensable for
this act; but as sutures occur in the skulls of young birds
and reptiles, which have only to escape from a broken
egg, we may infer that this structure has arisen from the
laws of growth, and has been taken advantage of in the
parturition of the higher animals." (Darwin, 1859)
"The ground rule -- or perhaps doctrine would be a better term -- is that adaptation is a special and onerous
concept that should be used only where it is really necessary . . . A frequent practice is to recognize
adaptation in any recognizable benefit arising from the activities of an organism. I believe that this is an
insufficient basis for postulating adaptation and that is has led to some serious errors. A benefit can be the
result of chance instead of design. The decision as to the purpose of a mechanism must be based on an
examination of the machinery and an argument as to the appropriateness of the means to the end. It
cannot be based on value judgments of actual or probable consequences."
" Consider a fox on its way to the hen house for the first time after a heavy snowfall. It will probably
encounter considerable difficulty in forcing its way through the obstructing material. One subsequent trips,
however, it may follow the same path and have a much easier time of it, because of the furrow it made the
first time. This formation of a path through the snow may result in a considerable saving of time and food
energy for the fox, and such savings may be crucial for survival. Should we therefore regard the paws of a
fox as a mechanism for constructing paths through the snow? Clearly we should not. It is better, because it
avoids the onerous biological principles of adaptation and natural selection, to regard the trail-blazing as an
incidental effect of the locomotor machinery, no matter how beneficial it may be. An examination of the
legs and feet of the fox forces the conclusion that they are designed for running and walking, not for the
packing or removal of snow. At any rate, the concept of design for snow removal would not explain
anything in the fox's appendages that is not as well or better explained by design for locomotion.
Although the construction of a path through the snow should not be considered a function of the activities
that have this effect, the fox does adaptively exploit the effect by seeking the same path on successive trips
to the hen house. The sensory mechanisms by which it perceives the most familiar and leas obstructed
routes and the motivation to follow the path of least effort are clearly adaptations." (Williams, 1966)
“We wish to question a deeply engrained habit of thinking among students of evolution. We call
it the adaptationist program, or the Panglossian paradigm. It is rooted in a notion popularized
by A.R. Wallace and A. Weismann, (but not, as we shall see, by Darwin) toward the end of the
nineteenth century: the near omnipotence of natural selection in forging organic design and
fashioning the best among possible worlds. (Gould and Lewontin, 1978)
"Master Pangloss taught the metaphysico-theologo-cosmolonigology. He could prove to
admiration that there is no effect without a cause; and, that in this best of all possible worlds,
the Baron's castle was the most magnificent of all castles, and My Lady the best of all possible
baronesses.
"It is demonstrable," said he, "that things cannot be otherwise than as they are; for as all things
have been created for some end, they must necessarily be created for the best end. Observe, for
instance, the nose is formed for spectacles, therefore we wear spectacles. The legs are visibly
designed for stockings, accordingly we wear stockings. Stones were made to be hewn and to
construct castles, therefore My Lord has a magnificent castle; for the greatest baron in the
province ought to be the best lodged. Swine were intended to be eaten, therefore we eat pork
all the year round: and they, who assert that everything is right, do not express themselves
correctly; they should say that everything is best." (Voltaire’s Candide)
“The study of adaptation is the study of adaptedness in an historical
context. Adaptedness is a statement about the relationship between
fitness and the phenotype . . . In a community context, studying the
adaptedness of a particular species to its environment then requires
that one (1) identify the interactions affecting fitness (i.e., survival
and reproduction), (2) distinguish the phenotypic characters
influencing performance in these interactions, and (3) demonstrate
that altering the phenotype would lead to a decrease in fitness.
These studies of adaptedness should then be place in an historical
context to show that changes in the phenotype have occurred when
the selective environment has changed. (McPeek, Schrot and Brown,
1996).
Enallagma (Odonata: Coenagrionidae)
https://www.youtube.com/watch?v=ymvb4C6
1VKs
Brown, McPeek and May. 2000.
Syst. Biol. 49:697-712.
https://www.youtube.com/watch?v=ymvb4C61VKs
McPeek, Schrot and Brown 1996
Ecology
McPeek, Schrot and Brown 1996
Ecology
McPeek and Brown. 2000.
Ecology 81:904-920.