Download Evolution, Natural Selection, and Adaptation

Evolution, Natural
Selection, and Adaptation
“Nothing in biology makes sense except
in the light of evolution.”
(Theodosius Dobzhansky)
Charles Darwin (1809-1882)
• Voyage of HMS Beagle
(1831-1836)
• Thinking about natural
selection & collecting
supporting evidence
(1837-1858)
• Origin of Species (1859)
(HMS Beagle)
Alfred Russel Wallace (1823-1913)
• Natural history collecting
trips to Brazil and SE Asia
• Author of The Malay
Archipelagio
• Wrote a letter to Darwin
explaining his idea of
natural selection - 1858
Evolution via Natural Selection
• Process whereby heritable traits that confer the
highest relative reproductive success increase in
frequency over evolutionary time
“…as many more individuals of a species are
born than can possibly survive and, as there is
a frequently recurring struggle for existence, it
follows that any being, if it vary however
slightly in any manner profitable to itself, under
the complex and sometimes varying conditions
of life, will have a better chance of surviving,
and thus be naturally selected. From the strong
principle of inheritance, any selected variety
will tend to propagate its new modified form.”
(Origin of Species, 1859)
Definitions
• Natural selection: Differential reproduction and
survivorship among individuals within a
Artificial Selection
• Process whereby humans selectively breed some
varieties over others, causing one or more varieties to
increase in frequency
population
• Fitness: relative lifetime reproductive success
• Survival & Reproduction
• Adaptation: trait that increases the fitness of
an individual, relative to its competitors, in a
population.
(Dugatkin, 2004)
Time to go fishing!
Time to go fishing!
• Start with 5 of each color in your pond
• Mix them up well
• Use only chopsticks in one hand to fish
• Keep caught “fish” in pile
• At the end of each round, count the number of each color
fish that you caught
• Each surviving fish replicates at the end of each round
• Keep track of how many of each color you add to the
pond
Fishing for M & M’s
• Why wouldn’t populations evolve to have only one
color, for example, only red M&M’s?
• Are we stuck with only five colors of M&M’s forever?
What if the environment changed to a new color, such
as black? What would happen?
• Why is variation useful?
Natural selection occurs
when…
1. Trait is variable within a population
2. Variation contributes to differences in
reproductive success
3. Variation is heritable
Variation within a population
Due to:
1. Differences in genetic composition
2. Differences in environmental conditions
3. Differences in learning
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Figure 2.4. Honeybee food delivery.
Variation within a population
Due to:
1. Differences in genetic composition
2. Differences in environmental conditions
3. Differences in learning
Variation may not affect fitness
Eastern screech owls show
great variation in dispersal
direction
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
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Frequency-dependant Selection
Frequency-dependant Selection
Positive frequencydependent selection:
the fitness of a trait
increases as it becomes
more common
Negative frequencydependent selection:
the fitness of a trait
decreases as it becomes
more common
Frequency-dependant Selection
Origin of new traits
New traits originate by:
random changes in genetic material
(mutation, sexual recombination)
survive or disappear due to
selection by environmental factors
(thus affecting the composition of
the population as a whole).
Lamarckism
• ‘Inheritance of
acquired characters’
• Useful characters are
acquired during the
lifetime of an organism and
passed on to offspring.
Characters that are not
useful are diminished.
• Continuous, gradual
change
(Jean-Baptiste Lamarck, 1809, Philosophie Zoologique)
Genetics
• Gene: segment of protein-encoding DNA
• Allele: variant of a gene
• Gene pool: sum of all alleles in the population
• Evolution: change in the allelic frequency of a
population
• Heritable: A genetically-based trait that can
be passed from parents to their offspring
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
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
Adaptation and
Tinbergen’s 4 Levels
Adaptationist Approach to Study of Behavior
Adaptation
• What methods are employed to determine if and how
a trait that increases the fitness of an individual,
relative to others in its population
behaviors are adaptive?
Aren’t all traits adaptive?
Constraints on Adaptive Perfection
1. Failure of appropriate mutations to occur
•
Not all traits are adaptive, AND those that are
adaptive are not perfect.
Selection can’t keep up with environmental change