Final Exam Flashcards
(32 cards)
Allopatric Speciation
- Speciation that occurs when populations are geographically separated
- The mechanism would be physical barriers like mountains and rivers that prevent gene flow
Parapatric Speciation
- Speciation that occurs when populations are adjacent to each other but occupy different habitats, leading to limited gene flow
- Divergence occurs because of environmental gradients. Strong selection pressures favor divergence
Sympatric Speciation
- Speciation that occurs within the same geographic area, without physical barriers to gene flow. Overlapping
- Reproductive isolation arises due to factors like ecological specialization. Ecological/behavioral factors.
Two ways to disrupt gene flow
- Reproductive isolation (intrinsic)
- Geographic isolation (extrinsic)
3 step process to disrupt gene flow
1- Isolation of populations (reduce gene flow)
2 - Divergence of populations (selection/drift)
3- Evolution of reproductive barriers
Divergence
- Divergence that has no effect on ability to interbreed, and divergence that does
- Divergence is typically a slow process of accumulating differences
Evolution of reproductive barriers
Some divergence in characters affecting the ability to interbreed can occur due to drift or selection while populations are isolated
Prezygotic “Premating”
- Temporal/habitat isolation - Mates do not meet when reproductive
- Behavioral/sexual isolation - Mates meet but do not choose to mate
- Mechanical isolation - Mating occurs, but gametes are not transferred
- Gametic Incompatibility - Chemical differences between species preventing fertilization
Postzygotic “Postmating”
- Zygote mortality
- Hybrid inviability (F1 has reduced survival)
- Hybrid sterility (F1 viable but reduced fertility)
- Hybrid breakdown (reduced viability or fertility in F2 or backcross)
Reinforcement
The process by which selection acts to reduce interbreeding by assortative mating so as to decrease the formation of hybrids
Prezygotic isolating mechanisms evolve much faster in
sympatric species than allopatric species
“Instantaneous” isolating mechanisms
- Chromosomal rearrangements disrupts pairing during meiosis can be instantaneous with some translocations or inversions or gradual after several fusions/fissions
What is phylogenetic history ?
- As a species diversifies, all of its descendants collectively form a clade
Where do we find evidence for phylogenetic relationship ?
- If a new character state evolves in a species, that state will be passed down to all descendants species
Homoplasy
Incongruence among characters due to convergence between lineages or reversal to ancestral state
Clades
The same if they contain exactly the same members, no more, no less
Parsimony
Least amount of state changes
- Occam’s razor - Given more than one equally good explanation, the simplest should be preferred.
Character polarity
Determines the direction of changes in character states
Support for nodes
Consensus trees and Congruence test
Consensus trees
Summarize agreement among different phylogenies
Congruence Test
A phylogenetic hypothesis makes predictions about the distribution of other characters.
Bootstrapping (Data resampling)
Bootstrapping resamples a data set repeatedly to estimate confidence
Outgroup method
“Pulling” down the root on the branch between ingroup and outgroup
Allometry
Change in the relative growth of morphological structures
