Fun Fact! Imagine this… • A human chain formed by joining your left hand to your mother's right hand, & your mother links her left hand to her mother's right hand, & so on through your maternal ancestors in a straight line… • Achimpanzee faces you & does the same thing with his or her mother, grandmother, & ancestors in a line paralleling your ancestral line, forming a chimpanzee chain…
Fun Fact! • The 2 lines will form a common line after about 280 miles! That’s about the distance from here to Baton Rouge, Louisiana! This represents humans & chimps forming separate species from a common ancestor.
The most recent common ancestor of humans & chimps… Humans & chimps evolved as separate species 4-6 mya!
Wolf & dog… same species? What about great dane & chihuahua?
First of all, what is a species? • The Biological Species Concept states: “Species are groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other groups.” Ernst Mayr articulated the Biological Species Concept in 1942. There is still much debate over what makes a species a species.
What causes new species to arise? • Speciation: they must be separated & no longer be able to produce fertile offspring (reproductive isolation) in order to officially become separate species A donkey & horse can mate & produce offspring (a mule), but mules are infertile. So, donkeys & horses are separate species!
Speciation • There are several different mechanisms that can occur that will reproductively separate populations. • These will separate the populations into different species! • These are called Reproductive Isolating Mechanisms (RIMs). • Prezygotic: prevent mating or fertilization • Postzygotic: reduced viability of offspring
Prezygotic Isolation • Geographical Isolation: different habitats or rarely encounter each other These squirrel populations are separated from each other by the Grand Canyon!
Prezygotic Isolation • Temporal Isolation: breed/flower at different times of the year or day The American Toad & the Fowler’s Toad have bred in the lab, but they never do in nature! The American Toad mates in early summer, while the Fowler’s Toad mates in the late summer.
Prezygotic Isolation • Behavioral Isolation: differences in mating/courting; usually a result of sexual selection The Eastern Meadowlark (left) and Western Meadowlark (right) do not interbreed, because they have different mating songs.
Prezygotic Isolation • Mechanical Isolation: anatomically incompatible sex organs on plants or animals Mating between a great dane & a chihuahua is unlikely due to a size difference.
Postzygotic Isolation • Hybrid Inviability: hybrids do not develop or are less likely to survive • Fertilization occurs, but the embryo dies (miscarriage). Mating between water buffalo & cattle will result in a failed embryo.
Postzygotic Isolation • Hybrid Sterility: hybrids develop, but are infertile The mule is a hybrid (donkey + horse), but mules are sterile.
Postzygotic Isolation • Hybrid Breakdown: F1 hybrids are viable, but F2s are not Some species of cotton plants can produce fertile offspring, but the offspring of those are sterile.
Speciation in the Galapagos Islands • Because the Galapagos are a group of islands, there are separate ecosystems on each. • Founder populations arrived on an island from the mainland (South America).
Speciation in the Galapagos Islands • Reproductive isolation occurred (geographic). • Frequencies of different traits changed in populations over time due to natural selection (based on food source, soil types, predators, etc.).
Speciation in the Galapagos Islands • Eventually, over a long period of time, the original population & the founder population on the 2nd island are very different & are considered separate species.
Are your toes normal or webbed? • On your tables, there is a cup of beads. Some are red & some are white. • White allele = webbed toes, red allele= normal. Red is dominant. • WITHOUT LOOKING, draw 2 beads. • Raise your hand if you have 2 white alleles. • Raise your hand if you have 2 red alleles. • Raise your hand if you are a heterozygote.
Answer the following question on a sheet of paper (share!): • If an earthquake separated the population (in the spot that I showed you), what would happen over time? Describe how the 2 populations would differ.