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
