No chapter (exam2) Flashcards
Causes of Similarities & Evolution of Adaptations
Causes of Similarities
o Homologous Similarity
o Homoplastic Similarities
Homologous Similarity:
Resemblance in structure or behavior due to inheritance from a common ancestor
Homoplastic Similarities:
Resemblance due to factors other than common ancestry, including
- -> Parallelism
- -> Convergence
- -> Analogy
- -> Chance Similarity
- -> Mimicry
Parallelism:
Similar characteristics develop separately in independent hereditary lines through each species’ response to similar ecological (environmental) conditions
(Diagram)
Convergence:
Similarities in independent hereditary lines through adaption to similar ecological stresses
1. Red Pandas: related to weasels, raccoons, skunks
2. Giant Pandas: a black and white bear
3. Both pandas belong to the order Carnivora, but are bamboo eating vegetarians. Their ancestors separated 43 million years ago, but both have a 6th digit on their for paws derived from the wrist bones that developed due to mutations of the same 2 genes
(Diagram)
Analogy:
Characteristics of independent lines that are similar in function, like wings in birds and insects
- Homologies: analogies developed from homologous structures
- Example: bat wings and bird wings
Chance Similarity:
Characteristics of independent lines from independent causes that happen to be similar
Mimicry:
Similarity in independent lines existing in similar environments
- Batesian Mimicry
- Mullerian Mimicry
- Automimicry
- Behavioral Mimicry
Batesian Mimicry:
Resemblance of a palatable (eatable) to an unpalatable species
- Example of viceroy butterfly whose pattern imitates monarch (that cannot be eaten)
Mullerian Mimicry:
Resemblance between 2 unpalatable species (even grater benefit for both (example of monarch and queen butterfly)
Automimicry
“Mimicry” of poisonous members of species by nonpoisonous
Behavioral Mimicry:
behavior enhances resemblance to surroundings (as opposed to appearance)
- Examples: insect looking like twig, rabbit looking like rock when it holds still, etc
Evolution of Adaptions
o Adaptationist Approach – Criticisms
Gould and Lewontin: Several reasons why existing traits may not be perfect
- The trait was once adaptive, but environmental change made it less so
- It may be the maladaptive byproduct of another adaptive trait
- Gene flow from populations subject to other selection pressures may prevent a local population from evolving a trait better for local conditions
- The trait cannot be perfect for one task because the underlying structures are involved in other necessary activities.
- The trait evolved based on previous structure, and you can’t start over from scratch
Evolution of Adaption
Adaptationist Approach – Benefits
- Hypotheses are necessary, and they all have assumptions. Assuming a trait is adaptive is better than assuming it is not adaptive, and thing of all possible reasons why
2. Traits are not necessarily perfect; but may contribute more to reproductive success than any alternative that has been available
3. Assuming adaptive value provides a testable hypothesis. If it is not correct, you often produce even more interesting hypotheses.
- Example of horse gait/speed