Chapter 24 The Origins Of Species Flashcards
The origin of new species, is at the focal point of evolutionary theory
Speciation
Consist of changes in allele frequency in a population over time
Microevolution
Refers to broad patterns of evolutionary change above the species level
Macroevolution
Group of populations whose members have the potential to interbreed in nature
Produce viable, fertile offspring
Do not breed successfully with other populations
Species
____________ between populations holds the phenotype of a population together
Gene flow
- The existence of biological factors (barriers) that impede two species from producing viable, fertile offspring
- can be classified by whether factors occur before or after fertilization
Reproductive isolation
What does reproductive limitation limit the formation of?
Hybrids
What are the reproductive barriers?
- habitat isolation
- temporal isolation
- behavioral isolation
- mechanical isolation
- gametic isolation
- reduce hybrid viability
- reduced hybrid fertility
- hybrid breakdown
Block fertilization from occurring by
- impeding different species from attempting to mate
- preventing the successful completion of mating
- hindering fertilization if mating is successful
Prezygotic barriers
Species that breed at different times of the day, different seasons or different years cannot mix their gametes
Temporel isolation
Two species encounter each other rarely, or not at all, because they occupy different habitats, even though not isolated by physical barriers
Habitat isolation
Courtship rituals and other behaviors unique to a species are effective barriers
Behavioral isolation
Morphological differences can prevent successful mating
Mechanical isolation
Sperm of one species may not be able to fertilize eggs of another species
Gametic isolation
Prevents the hybrid from developing into a viable, fertile adult:
- reduce hybrid viability
- reduced hybrid fertility
- hybrid breakdown
Postzygotic barriers
Genes of the different parent species may interact and impair the hybrids development
Reduced hybrid viability
Even if hybrids are Vigorous, they may be sterile
Reduced hybrid fertility
Some first generation hybrids are fertile, but when they mate with another species or with either parent species offspring of the next generation are feeble or sterile
Hybrid breakdown
Cannot be applied to fossils or asexual organisms (prokaryotes)
Emphasizes absence of Gene flow
Ex: growler bear?
Biological species concept
Can Gene flow occur between distinct species?
Yes
Applies to sexual and asexual species but relies on subjective criteria
Appearances
Morphological species concept
Applies to sexual and asexual species and emphasizes the role of disruptive selection. Where they live, food sources.
Ecological species concept
Defined as a species as the smallest Group of individuals on a phylogenetic tree
It applies to sexual and asexual species, but it can be difficult to determine the degree of difference required for separate species
Phylogenetic species concept
Can speciation take place with or without geographic separation?
Yes
Speciation can occur in what two ways ?
- allopatric speciation
- sympatric speciation
How do the numbers of geographic barriers affect the numbers of species in the area?
More variety of species
What can result as the distance between populations increase?
Reproductive isolation
Speciation takes place in graphically overlapping populations
More common In plants
Sympatric speciation
What are the three ways sympatric speciation can occur?
- polyploidy
- habitat differentiation
- sexual selection
The presence of extra sets of chromosomes due to accidents during cell division
Much more common in plants than in animals
Polyploidy
An individual with more than two chromosomes sets derived from one species
Autopolyploid
A species with multiple sets of chromosomes derived from different species
Sterile hybrid
Allopolyploid
- An individual with more than two chromosome sets
- derive from one species
Autoployploid
Can drive sympatric speciation
Sexual selection for mates
Ex: speciation in Cichlid fish in lake Victoria
Sexual selection
A reproductive barrier isolates a subset of a population without geographic separation from the Parent species
Can result from polyploidy, natural selection, or sexual selection
Sympatric speciation
Geographic isolation restricts gene flow between populations
reproductive isolation may then arise by natural selection, genetic drift, or sexual selection in the isolated populations
-even if contact is restored between populations, interbreeding is prevented
Allopatric speciation
the area where two species meet and mate to form hybrids
Hybrid zone
The result of mating between species with incomplete reproductive barriers
Hybrids
What is the level of fitness in hybrids compared with the parent species?
Lower
What are the three possible outcomes when closely related species meet in a hybrid zone?
- reinforcement
- Fusion
- stability
Occurs when hybrids are less fit than the parent species. This reinforces natural selection and barriers between them.
Reinforcement:
Strengthening reproductive barriers**
Does reinforcement strengthen or weaken reproductive barriers?
Strengthen
Are reproductive barriers stronger in allopatric or sympatric species?
Sympatric
Ex: birds that look the same in allopatric speciation
Birds that look completely different in sympatric speciation, no attempts to mate
Fusion (strengthens or weakens) reproductive barriers?
Weakens
In hybrids zones, Reproductive barriers weaken until the two species become one.
Ex: cichlids
Fusion
Hybrid survive or reproduce better than the parent species
Continues formation of hybrid individuals
Stability
*Not common
- each new species evolves continuously over long spans of time
- large phenotypic differences that produce new species are due to the accumulation of many small genetic changes
Gradualism
Species in equilibrium (stasis) for long periods and then short rapid burst of change
Punctuated Equilibrium
The _____________ in the fossil record and evidence from lab studies suggest that speciation can be rapid
Punctuated pattern
