Speciation

Microevolution Small (hence “micro”) shifts in allele frequencies in populations and species Causes changes in phenotypes in populations and species Genetic drift, directional, disruptive, stabilizing, sexual selection Evolution at the species level

Species A group of organisms that can interbreed and produce fertile offspring Some species can interbreed; e.g., bacteria, dogs, wolves, coyotes, plants (tangelo= tangerine+pomelo) Sometimes it is necessary to rely on DNA evidence to distinguish between species, different ecological niches of the organism

Tangelo

Speciation Formation of a new species

Reproductive Isolating Mechanisms Any behavioural, structural, or biochemical traits that prevent individuals of different species from reproducing successfully

Prezygotic Mechanisms Prevent mating, fertilization and zygote formation Ecological isolation – occupy different habitats Temporal isolation – breed at different times of year Behavioural isolation – different mating rituals and signals All methods that prevent mating Behavioural: Male frogs of different species have unique calls that attract only females of their own species

Prezygotic Mechanisms 4. Mechanical Isolation: Difference in physical features that make mating impossible. Different/Incompatible genitalia 5. Gametic isolation – gametes not able to recognise each other Methods that prevent fertilization The genitalia of male and female Damselflies of different species differ

Postzygotic Mechanisms Mechanisms that prevent fertilized egg from growing into a fertile adult

Postzygotic Mechanisms Zygotic mortality – zygote dies Hybrid inviability – the hybrid does not live long, either as an embryo or new born Hybrid infertility – the hybrid is unable to produce offspring

Modes of Speciation Isolated populations that undergo mutations, followed by selection, will eventually not be able to share their alleles with other populations that were once related Results from geographical isolation, commonly

Allopatric Speciation Evolution of populations into separate species because of geographical isolation; e.g., canyon, mountains

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. 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. 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 Evolution of populations within larger populations in the same geographical area Occupy different niches and become quite distinct over time due to selection

Sympatric Speciation Polyploidy – more than the regular 2 copies of each chromosome Humans are diploid as are many other species Polyploidy can result from a mutation. Many plants (30% to 70%) and some frogs and fish are polyploid Polyploid gametes are 2n  homologous pairs  diploid hybrid Polyploids can produce fertile offspring when mated with other polyploids Hybrid is new species that will not produce fertile offspring if crossed with the parent species.

Human Influence Destruction of habitat Separation of habitats – dams, roads, etc.

Your Task Read pp. 336-340 #1-5