Speciation Section 8.2

Speciation Learning Goal: To explore the factors leading to the evolution of a new species. Success Criteria: I know I am succeeding when I can… define the concept of speciation identify the modes of speciation explain how human activities affect the evolution of other species Not all evolutionary changes are result of NS Sometimes changes in genetic makeup of pop. not influenced by traits of individuals These changes tend to reduce genetic diversity within pop

Speciation recall… a species includes all the members of a population that can interbreed under natural conditions microevolution: changes in gene (allele) frequencies and phenotypic traits within a population and species speciation: the formation of new species Individuals of different species cannot interbreed under natural conditions and are described as being reproductively isolated from one another. Populations of different species do not exchange genetic information—they have different gene pools.

Reproductive Isolating Mechanisms for a new species to form, individuals from the original species must evolve to become reproductively isolated from the remainder of the population and establish a new interbreeding population  reproductive isolating mechanism: any biological factor that prevents the two populations from interbreeding when living in the same region Prezygotic: prevents fertilization and zygote formation Postzygotic: prevents a fertilized egg from growing into a viable and reproducing adult Individuals of different species cannot interbreed under natural conditions and are described as being reproductively isolated from one another. Populations of different species do not exchange genetic information—they have different gene pools.

Prezygotic Reproductive Isolating Mechanisms Cont’d… behavioral isolation: different species use different courtship and other mating clues to find and attract a mate ex. male frogs of different species have unique calls that attract only females of their own species

Prezygotic Reproductive Isolating Mechanisms Cont’d… temporal isolation: different species breed at different times of the year ex. pussy willows produce flowers in the early spring, other plant species flower at different times of the year

Prezygotic Reproductive Isolating Mechanisms Cont’d… ecological isolation: very similar species may occupy different habitats within a region the mountain bluebird lives at high elevations, while the eastern bluebird prefers lower elevations and does not encounter the mountain species

Prezygotic Reproductive Isolating Mechanisms Cont’d… mechanical isolation: differences in morphological features may make two species incompatible ex. the male and female genitalia of each species of damselflies are uniquely shaped and are physically incompatible with other species Picture of damselfly penises.

Prezygotic Reproductive Isolating Mechanisms Cont’d… gametic isolation: male gametes may not be able to recognize and fertilize an egg of a different species Ex. Many marine animals including corals, clams, and sea cucumbers release their sperm and eggs into open water. The sperm recognize eggs of their own species through chemical markers on the surface of the eggs. Picture of sea cucumber.

Postzygotic Reproductive Isolating Mechanisms zygotic mortality: mating and fertilization are possible, but genetic differences result in a zygote that is unable to develop properly ex. some species of sheep and goat are able to mate, but the zygote is not viable

Postzygotic Reproductive Isolating Mechanisms Cont’d… hybrid inviability: a hybrid individual develops but either dies before birth or, if born alive, cannot survive to maturity ex. when tigers and leopards are crossed, the zygote begins to develop but the pregnancy ends in a miscarriage or stillborn offspring

Postzygotic Reproductive Isolating Mechanisms Cont’d… hybrid infertility: hybrid offspring remain healthy and viable but are sterile ex. mules are the sterile hybrid offspring of a horse–donkey cross

Modes of Speciation What causes these reproductive isolating barriers to form? Two modes of speciation: Allopatric Speciation Sympatric Speciation

Allopatric Speciation allopatric speciation is when new species forms after a single species is geographically separated into two isolated populations ex. Anole Lizards

Allopatric Speciation Cont’d… geographic splitting of a species into two populations can occur by mountain ranges, continental drift, isolation on remote islands etc. The scene: a population of wild fruit flies minding its own business on several bunches of rotting bananas, cheerfully laying their eggs in the mushy fruit... Disaster strikes: A hurricane washes the bananas and the immature fruit flies they contain out to sea. The banana bunch eventually washes up on an island off the coast of the mainland. The fruit flies mature and emerge from their slimy nursery onto the lonely island. The two portions of the population, mainland and island, are now too far apart for gene flow to unite them. At this point, speciation has not occurred — any fruit flies that got back to the mainland could mate and produce healthy offspring with the mainland flies.

Allopatric Speciation Cont’d… any mutation that arises in one population is not shared with the other population differences in the environments of the two populations will lead to different forms of natural selection over many generations the populations will gradually become less and less alike The populations diverge: Ecological conditions are slightly different on the island, and the island population evolves under different selective pressures and experiences different random events than the mainland population does. Morphology, food preferences, and courtship displays change over the course of many generations of natural selection.

Allopatric Speciation Cont’d… once enough time has passed, there is a good chance that the two populations will have evolved some sort of reproductive isolating mechanism Perhaps their courtship rituals will have changed, the time of year they breed or produce pollen will have shifted, or they may no longer be physically compatible. So we meet again: When another storm reintroduces the island flies to the mainland, they will not readily mate with the mainland flies since they've evolved different courtship behaviors. The few that do mate with the mainland flies, produce inviable eggs because of other genetic differences between the two populations. The lineage has split now that genes cannot flow between the populations.

Sympatric Speciation sympatric speciation is when a new species evolves from within a large population occurs when individuals within a population become genetically isolated from the larger population

Sympatric Speciation Cont’d… a mutation may occur within an individual or individuals of a species that prevents breeding gene flow is reduced and over time genetic differences accumulate between the species A mutation occurred and now some flies can feed on mango fruit. Flies find mates by hanging out on preferred foods, the flies that eat the mango will not end up mating with the flies that eat the bananas. Gene flow would be greatly reduced; and once gene flow between the two species is stopped or reduced, larger genetic differences between the species can accumulate.

Human Influence on Speciation human activities, such as agricultural expansion and the construction of roads, are causing once large habitats to be fragmented into smaller areas that isolate populations reduces gene flow and biodiversity amongst a species making them at greater risk of disease and changing environmental conditions A recent study of timber rattlesnake populations in the state of New York revealed that roadways are a significant barrier to gene flow and that genetic diversity within each isolated population was low. Similar research in China has shown that the survival of giant pandas, a critically endangered species, is threatened by their separation into small isolated populations in patches of bamboo forest.

Human Influence on Speciation gene flow can be maintained and enhanced if the connectivity between habitats is ensured (ex. fragmented habitats can be joined by wildlife corridors)

Speciation Learning Goal: To explore the factors leading to the evolution of a new species. Success Criteria: I know I am succeeding when I can… define the concept of speciation identify the modes of speciation explain how human activities affect the evolution of other species Not all evolutionary changes are result of NS Sometimes changes in genetic makeup of pop. not influenced by traits of individuals These changes tend to reduce genetic diversity within pop

Activity: Monster Speciation explore how mutations and natural selection lead to new species over time A recent study of timber rattlesnake populations in the state of New York revealed that roadways are a significant barrier to gene flow and that genetic diversity within each isolated population was low. Similar research in China has shown that the survival of giant pandas, a critically endangered species, is threatened by their separation into small isolated populations in patches of bamboo forest.

Homework Answer 8.2 questions #2-6 on page 340