Evo Bio CH 5

• Natural selection is a mechanism, or cause, of evolution. 


  Adaptations are physical or behavioral traits that make an organism better suited to its environment.
• components of natural selection

  Variation

  Inheritance

  Differential reproductive success
• label the components of natural selection

  A) variation

  B) inheritance

  C) differential reproductive success

  
• Adaptation

  • Characteristic that enhances the survival or reproduction of organisms
  • Cause for adaptation = natural selection
  • example: Frog call signals females, and Bat uses frog call to find frog
• example of adaptation: Philodendron (a tropical American climbing plant)

  • Young growth toward dark = finds trunk
  • Trunk used for attachment
  • Later leaves are Large, Attracted to light
• Evolution of Complex Structures

  Complexity has suggested design– William Paley (Natural Theology)

  • Intricacy implies “watchmaker”, Cited example = human eye
  • However, adaptive processes can produce complex designs
  • Each step of evolution may have different functions
• • Evolutionary processes do not have a goal
  • All evolution is due to present conditions
  • Function of structures may change with changing conditions – Explains the improbability of “intermediate” forms that might be thought to have no function, thus, could not be caused by evolution”
• Natural Selection: Any consistent difference in fitness among phenotypically different classes of biological entities
• Lamarckism: all the physical changes occurring in an individual during its lifetime are inherited by its offspring
• Fitness (Reproductive Success): Average increase for given phenotype or genotype
• Sexual Selection: Variation in offspring as a consequence of competition for mates • Choosing a mate with certain characters
• Natural selection exists whenever there is variation in fitness
• Evolution can occur by genetic drift

  – This has nothing to do with natural selection

  However, characters that change by genetic drift could be acted upon by natural selection at a later date
• Pleitropy: a complication for selection

  • Pleitropy: one gene often affects more than one traits
  • Pleitrophic traits could have different selective value
  • fitness trade offs
• Experimental Studies of Natural Selection ... Yes , we can show experimentally that evolution occurs
• What about Tuberculosis?

  • Antibiotics supply selective pressures

  • This is why every doctor should understand evolution, but do they?
• Male Reproductive Success

  • Widowbird (Euplectes progne) males have long tail which practically inhibits flight

  • Experiment showed that long tail feathers of widowbirds were being selected, and Shortened tail feathers change reproductive success
• Four postulates of natural selection

  1. Individuals within populations are variable
  2. Some of that variation is heritable
  3. Some individuals are more successful at surviving and reproducing
  4. Survival and reproduction are tied to heritable variation 
• is ALL variation heritable ?

  no , environment has some effect
• Components of fitness

  1. Probability of survival to the various reproductive ages
  2. Average number of offspring produced via female function
  3. Average number of offspring produced via male function
• Levels of Selection

  • Selective pressures can work on groups as well as individuals

  • Altruistic trait

  – Reduces fitness of individual

  – Benefit to population

  – Cheater = selfish mutant

  • Example: females laying fewer eggs when food is scarce
• Group Selection favors Altruistic Genotype

  
• Selfish Genotype has a higher Individual Fitness

  
• Kin Selection

  • Viewed as selection at the level of the gene

  • Altruistic trait increases in population

  • Entire population benefits, thus benefiting individuals

  • Without population cooperation, all individuals are less fit and may vanish
• Species Selection

  • Differential proliferation of species

  • Some character changes give rise to speciation

  • Other character changes give rise to eventual extinction of derived species
• The Nature of Adaptations

  • Two definitions of an adaptation

  – Phenotypic variant that results in highest fitness in a given environment

  – A derived character that evolved in response to a specific selective agent
• The Nature of Adaptations

  • Preadaptation

  – Feature that fortuitously serves a new function

  – Can be co-opted to serve new functions

  Called an exaptation
• Exaptation: It is when a structure originally used for one purpose is modified for a new one. For example, penguin wings are exaptational in that they serve the (new) purpose of swimming and navigating underwater, but are still regarded as vestigial in that they've lost the function of flight.
• Adaptations

  • Not all characters are adaptations

  – Some are a byproduct of another adaptation

  • Red color produced by hemoglobin

  – Genetic drift

  – Character may have correlation to an adaptation character
• Recognizing Adaptations

  • Complexity

  – Complex structures are usually adaptive

  • Design

  – Something that fits in environment is usually adapted

  • Experiments

  – Alteration of characters can strongly suggest reason for the character
• Comparative Method

  • Means of inferring adaptive significance

  • Compare sets of species with function and structure of characters to test adaptations

  • Serves as natural evolutionary experiment
• What Not to expect from Natural Selection

  • Necessity of adaptation

  • Perfection

  • Progress

  • Harmony and the balance of nature

  • Morality and ethics