Speciation

Species: A group of organisms capable of interbreeding = they are isolated reproductively from other species 1)Live together but cannot interbreed 2)Live a distance apart

Isolating Mechanisms Prezygotic isolating mechanisms: Barriers that are in place before fertilization can occur. Eg. A mountain range between two populations Eg 2) Red clawed crab

Isolating Mechanisms Prezygotic isolating mechanisms: Barriers that are in place before fertilization can occur. Eg. A mountain range between two populations Postzygotic isolating mechanism: Barriers that are in place after fertilization which prevent the production of fertile offspring Eg. 1) Sperm and egg come together but the sperm is not able to enter the egg Eg. 2) Offspring are produced but are infertile (mules)

Reproductive Isolating Mechanisms Prezygotic Isolations DefinitionExample Habitat Isolation Two species that live in the same location but in different habitats One species may live in the trees one on the forest floor

Reproductive Isolating Mechanisms Prezygotic Isolations DefinitionExample Habitat Isolation Two species that live in the same location but in different habitats One species may live in the trees one on the forest floor Temporal Isolation Two species have different breeding seasons. Individuals become fertile at different times. One flower may produce reproductive structures in May another in August

Reproductive Isolating Mechanisms Prezygotic Isolations DefinitionExample Habitat Isolation Two species that live in the same location but in different habitats One species may live in the trees one on the forest floor Temporal Isolation Two species have different breeding seasons. Individuals become fertile at different times. One flower may produce reproductive structures in May another in August Behavioral Isolation Animals have specific mating dances, calls and pheromones A female peacock will only breed with a male who can put on a good display

Reproductive Isolating Mechanisms Prezygotic Isolations DefinitionExample Habitat Isolation Two species that live in the same location but in different habitats One species may live in the trees one on the forest floor Temporal Isolation Two species have different breeding seasons. Individuals become fertile at different times. One flower may produce reproductive structures in May another in August Behavioral Isolation Animals have specific mating dances, calls and pheromones A female peacock will only breed with a male who can put on a good display Mechanical Isolation Two species are not capable of mating Genitalia does not match up

Reproductive Isolating Mechanism PostzygoticDefinitionExample Gamete Isolation Sperm can’t get to the eggSperm is designed for a shorter reproductive tract and cannot make it

Reproductive Isolating Mechanism PostzygoticDefinitionExample Gamete Isolation Sperm can’t get to the eggSperm is designed for a shorter reproductive tract and cannot make it Zygote Isolation Fertilization occurs but zygote cannot survive Fetus does not develop properly and dies

Reproductive Isolating Mechanism PostzygoticDefinitionExample Gamete Isolation Sperm can’t get to the eggSperm is designed for a shorter reproductive tract and cannot make it Zygote Isolation Fertilization occurs but zygote cannot survive Fetus does not develop properly and dies Hybrid SterilityHybrid survives but cannot produce its own offspring Two species mate to produce an offspring that is sterile such as a mule

Reproductive Isolating Mechanism PostzygoticDefinitionExample Gamete Isolation Sperm can’t get to the eggSperm is designed for a shorter reproductive tract and cannot make it Zygote Isolation Fertilization occurs but zygote cannot survive Fetus does not develop properly and dies Hybrid SterilityHybrid survives but cannot produce its own offspring Two species mate to produce an offspring that is sterile such as a mule F 2 FitnessHybrid can reproduce but their offspring cannot The offspring of 2 species is able to reproduce but their offspring can’t

The Process of Speciation Speciation: When one species divided into two different species. Usually by mutation. Allopatric Speciation: Geographic barriers such as rivers or mountain ranges divide a population. This prevents gene flow between the populations. Overtime the two populations develop into different species.

Allopatric Speciation

Sympatric Speciation Sympatric Speciation: A new species is created within a population without the presence of geographical barriers. Eg.

Sympatric Speciation Sympatric Speciation: A new species is created within a population without the presence of geographical barriers. Eg. One organism in a population of plants loses a chromosome. Because the chromosomes do not line up with its own species it can only reproduce with itself. Eventually it creates its own population of interbreeding plants.

Pace of Speciation 2 Hypothesis that address the pace of speciation 1)Phyletic Gradualism Model: Slow and steady change from one species to another.

Pace of Speciation 2) Punctuated Equilibrium: Long periods of no change are followed by short periods of rapid change

Fossil Records How do Both Models Explain the lack of Transition Fossils in the Fossil Record? Phyletic Gradualism: The change from one species to another is the result of reproductive isolation (RI). RI cannot be seen in the fossil record so we can’t tell if two similar organisms are able to reproduce. Therefore we cannot tell if they are different species? Punctuated Equilibrium: Because the new species forms suddenly there are few individuals that show the transition from the old species to the new species

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