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29 Cards in this Set
- Front
- Back
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Speciation |
The process by which one species splits into two or more species |
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Species |
A group that has the potential to interbreed and produce viable, fertile offspring -they do not breed well with other species |
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Biological Species Concept |
1. species has the potential to interbreed, and produces viable offspring 2. held together by gene flow |
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What holds a population together genetically? |
Gene flow |
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Reproductive isolation, 2 classifications |
Barriers that impeded members of diff species from interbreeding and producing viable, fertile offspring Classified according to whether they contribute to reproductive isolation before or after fertilization: 1. Prezygotic barriers 2. postzygotic barriers |
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Prezyogotic barriers |
before zygote: blocks fertilization from occuring Three ways: 1. impeeds mating 2. hinders fertilization |
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Types of prezyogtic barriers (5) |
1. habitat (same area, diff habitats) 2. temporal isolation (diff breeding seasons) 3. behavioural isolation (unique courtship rituals) 4. Mechanical Isolation (mating attempted but unsuccessful - two species of snails) 5. Gametic isolation (sperm of one, cannot fertilize egg of other - ex: sea urchins)
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Types of postzyogtic barriers (3) |
1. Reduced hybrid viability: genes interact an impair hybrid development and do not complete development 2. Reduced hybrid fertility : sterile 3. hybrid break down: firt-gen hybrids are viable and fertile but their offspring is feeble or sterile |
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Limitations of Biological Species Concept |
1. cannot be applied to fossils or asexual organisms (including prokaryotes) 2. emphasizes absence of gene flow BUT Gene flow can occur between two species: which can occur ex: grolar bears |
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Modes of Speciation |
Allopatric and Sympatric |
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Hybrid |
crosses between species |
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Advantages to biological species concept |
highlights a mechanism by which speciation occurs i.e the existence of barriers |
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Allopatric Speciation |
a population forms a new species while geographically isolated from its parent population -gene flow is interrupted or reduced -barrier depends on ability of population (i.e canyon is a barrier for rodent but not bird) -seperate pops may evolve independently through Nat sel, genetic drift, mutation |
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Sympatric Speciation |
a subset of a population forms a new species without geographic separation -gene flow is reduced without physical barriers just reproductive barrier |
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mosquito fish in different ponds evolved reproductive isolation under different predation what type of speciation is this? |
allopatric |
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Give an example of allopatric speciation occurring in nature |
30 species of snapping shrimp were separated by the Isthmus of Panama. 15 pairs of sister species. Originated 13-15 mill years ago.
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Do regions with more geographic barriers have an increase level or decreased level of species? |
Increased. |
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How can reproductive barriers form between sympatric populations while their members remain in contact with each other? |
1. Polyploidy 2. habitat differentiation (nat selection) 3. sexual selection |
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Polyploidy |
a species that originates from an accident duing cell division that results in extra sets of chromosomes Autopolyploid and Allopolyploid |
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Autopolyploid vs Allopolyploid |
Auto: an individual with more than two chromosome sets that are derived from a single species - one haploid set -fertile
Allo: has multiple sets of chromosome derived from two different species -sterile and must be propogated as clones |
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Habitat Differentiation |
a subpop exploits a habitat or resource not used by the parent population ex: apple maggot flies (developed both pre and post zyogtic barriers) |
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What are the three stages of speciation for cichlids in Lake Malawi? (HFC) |
1. Habitat differentiation and adaptation - to distinct rocky vs sandy habitats 2. Diversification of feeding apparatus: tropic morphologies as seen by their jaws 3. Diversification of colour pattern: of males with each linage Speciation probably occurred rapidly |
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Hybrid Zones |
A region in which different species mate and produce hybrids
Simple: toads Complex: plants (favourable patches so hybrid zones develop in disconnected patches) |
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Hybrids |
Are the result of incomplete reproductive isolation barriers |
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What happens when species with incomplete reproductive barriers come into contact with each other? |
Hybrid Zones |
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Give an example of a hybrid zone |
Yellow bellied and red bellied frogs. Frequency of allele goes from 100% to 50% in the centre of the hybrid zone. Does not create a new species because hybrids have poor survival and reproduction |
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What are the three changes in hybrid zones effected by time? |
1. Reinforcement: strengthening - hybrids are less fit, species continue to diverge until hybridization can no longer occur 2. Fusion: weakening - reproductive barriers weaken until two species become one 3. Stability: fit hybrids continue to be produced **These options depend on the cost of hybridization - assortative mating will be reinforced if hybrids have lower fitness |
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Punctuated Equilibria vs Gradual Equilibria |
Punctuated: periods of apparent stasis punctuated by sudden change
Gradual: changes over a long period of time |
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Give an example of a pre-zygotic reproductive isolating barrier that is effected by a small number of genes |
Minulus Lewisii and Mimulus Cardinalis M. Lewisii - pink, bumble bee M. Cardinalis - red, humming birds
Successful cross and transfer of alleles produced new colours. Increased visits from each of the associated pollinator |
