Macroevolution And Speciation Flashcards
No gene flow
Recipe for speciation
Macro revolution
Origin and extinction of species
- it can happen gradually (gradualism: microevolution) or in chests (punctuated equilibrium)
- understanding of speciation began in 100 years after Darwin
Speciation
Origin of new species. With extinction, it is one of two keystone processes of macroevoltion
- Darwin wrong about origin of species
- evolution of new species results from barriers to allele flow amount populations
- when barriers occurs via genetic or behavioral mechanism they do not allow two populations interbreeding. They become reproductively isolated
Reproductive isolation
Without isolation mechanisms, closely related species would hybridize: allele flow and recombine would eventually transform them into a single (polymorphic) species
Two categories of isolation mechanisms
Pre
Post
Prezygotic isolation: prevents mating. Gametes of sympatric species never form hybrid zygotes
Postzygotic: acts after a mating has occurred. Prevents fertilization
Pre-zygotic (no mating)
Habitat isolation:
Temporal isolation:
Behavioral:
Mechanical:
Gamete mortality:
Habitat isolation: occurs because sympatric species prefer different habitats and seldom or never meet
- sympatric spadefoot tods prefer diff soil types
- many species of closely related parasites live/mate on different hosts
Temporal isolation: occurs because species mate at diff times
Behavioral isolation: diff in courtship behavior, diff in chemical signals or vocalizations that allow individuals to recognize their own species
-keep closely related sympatric animals from interbreeding
Mechanical isolation: occurs because sexual organs of closely-related sympatric species are incompatible: they do not fit together (ex: Arthropods)
Gametes mortality: special male gametes can only perform well in reproductive tract of female of same species
Postzygotic
Hybrid fertility
Hybrid sterility
Low hybrid fitness
Hybrid inviability: species that do not ordinarily interbreed occasionally do so. Progeny die at some point during development
Hybrid sterility: when hybrid of an interspecifc mating is unable to reproduce
Low hybrid fitness: if interspecifc hybrids survive, they have low fitness.
Allopathic speciation
Sympatric speciation
Involves a geographic barrier
Does not involve a geographical barrier
Allopathic speciation
A population forms a new species while geographically isolated from its parent population
-once isolated, allopathic populations accumulate genetic differences due to natural selection, sex sel, genetic drift and new mutations
Vicariance (allopathic speciation)
Formerly widespread population becomes fragmented
Peripatric speciation
Speciation in a peripheral isolate
-due to rare dispersal or colonization events… founder effect
If geographical barrier is removed, two populations
Meld together by allele flow and recombine to form a single species
- remain repro isolated
- formation of new, incipient species, depends upon wether isolation mechanisms (pre or post mating) have evolved during isolation
Sympatric speciation
Autopolyploidy
-Results from intrinsic factors, such as chromosomal changes and nonrandom mating
-become genetically isolated even though their ranges overlap
Ex: chromosome doubling to new tetrapods species
Autopolyploidy: chromosome # doubles instantly producing a new species
Allopolyploidy
Gametes of 2 diff species meet and form a hybrid (usually sterile). Chromosomes can not pair during meiosis, but may reproduce asexually
- hybridization between animal species occurs in nature though products are not considered to be species because they are not often sterile
- some cases: interspecific hybrids in animals produce asexual repro offspring
Parapatry
Speciation not always clear cut. Some populations being reproductively isolated, while others are able to interbreed
Phylogeny
Family tree. Describing how species are related. Branching pattern of diff groups of org caused by repeated claogenesis
Taxonomy
Process of describing and naming org. Our modern process is based on phylogeny that
Two major categories of evolutionary change
- evolutionary change within lineages over time (anagenesis)
- Splitting of lineages over time (cladogenesis)
