Ch.24 Flashcards
Speciation
-formation of new/distinct species in the course of evolution
Origin of new species are a focal point of revolutionary theory
-can occur rapidly/ slowly and can result in a few/many changes in genes
-can occur with/without geographic operation
Macroevolution
broad patterns in evolutionary change above species level
-larger changes over a longer period of time
-can result in speciation
Biological species concept
-emphasizes reproductive isolation
-characterizes a group as a pop. whose members have the potential to interbreed in nature and produce viable fertile offspring ( don’t successfully breed with other pop.)
Gene flow between pop.
holds phenotype of a pop. together
Reproductive isolation
-the existence of barriers that impede two species from producing fertile offspring
-prezygotic barriers
-postzygotic barriers
Prezygotic barriers (before)
-prevent members of different species from meeting to produce zygote in the first place
-habitat, temporal, behavioral, mechanical, and gametic barriers
Postzygotic barriers (after)
reduced hydra viability and fertility, and hybrid breakdown
Imitations of biological species concept
-Can’t be applied to fossils or asexual organisms
-emphasizes absence of gene flow
Morphological species concept
-Define species by structural features
-applies to sexual and asexual
-relies on subjective criteria
–difficult to determine the degree of difference required for separate species
Ecological species concept
-Use a species in terms of its ecological niche
-sexual/asexual
-emphasizes the role of disruptive selection
Phylogenetic species concept
-Defines a species of smallest group of individuals on phylogenic tree
-sexual/asexual
-difficult to determine the degree of difference required for separate species
Speciation can occur in 2 ways
-allopatric
-sympatric
behavioral isolation
Courtship rituals and other behaviors you need to species are effective barriers
allopatric speciation (AS)
-“other homeland”
-gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations
-driven by sexual selection
- in AS, Geographic isolation restrict gene flow between populations
Sympatric speciation
“together homeland”
-takes place in geographically overlapping populations
-can result from appearance of new ecological niches
-can result from polyploidy, natural selection, or sexual selection
Definition of a barrier depends on..
ability of a pop. to disperse
-ex: canyon may be a barrier for mice but not for birds
reproductive isolation
-May arise as a result of genetic divergence (evolution caused to be too different to breed), which won’t allow for fertile offspring
-increases as distance between populations increase
-may arise by natural selection, genetic drift, or sexual selection and isolated populations
polyploidy
Presents an extra set of chromosomes due to accidents during cell division
-more common in plants (crops, cotton, potatoes, tobacco, and wheat)
autopolyploid
Individual with more than two chrome zone sets derived from one species
allopolyploid
Species with multiple sets of chromosomes derived from different species sex
hybrid zone
Region in which members of different species meat and produce hybrids
-can occur in a single band where adjacent species meet
Hybrids
Results of the meeting between species with incomplete reproductive barriers
-often have reduced fitness
3 possible outcomes for hybrid zones
-reinforcement
-fusion
-stablilty
Reinforcement
-strengthening reproductive barriers
-hybrids less fit than parents
-overtime, rate of hybridization decreases
-reproductive barriers are stronger for sympatric than allopatric species
