MacroevolutionMacroevolution•A change of one species into an entirely new species!

**Macroevolution encompasses the grandest trends and transformations in evolution, such as the origin of mammals

SpeciationSpeciationFormation of new species

What Is a Species?What Is a Species?• How can you determine whether a group

of plants or animals belong to the same species?

• Appearance isn’t sufficient.

Let’s take a look…

What Is a Species?What Is a Species?

These happy face spiders look different, but since they can interbreed, they are considered the same species:

Theridion grallator.

What Is a Species?What Is a Species?BIOLOGICAL SPECIES CONCEPT

• a group of organisms that can reproduce in nature and produce fertile offspring (meaning the offspring are also capable of mating and producing offspring)

• members of one species cannot successfully interbreed with members of other species.

How New Species FormHow New Species Form

GEOGRAPHIC ISOLATION• Separation of population as a result of

geological change or dispersal to a remote location.

• Example – harris’ antelope squirrel and the white tailed squirrel – opposite rims of the Grand Canyon (Ammospermophilus)

• Causes: Emergence of mountain range, slow moving glacier, colonization of an island

This is a simplified model of speciation by geographic isolation

• 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 unviable eggs because of other genetic differences between the two populations. The lineage has split now that genes cannot flow between the populations.

How New Species How New Species FormForm

REPRODUCTIVE ISOLATION

• The inability of two different species to successfully interbreed in nature.

How New Species FormHow New Species FormCAUSES OF REPRODUCTIVE

ISOLATION

• Timing - two similar species may have different breeding seasons

• Ex: Great Plains – western spotted skunks breed in fall, eastern spotted skunks breed in late winter (coexist on great plains)

How New Species FormHow New Species Form

CAUSES OF REPRODUCTIVE ISOLATION • Behavior - two similar species may have

different courtship or mating behaviors.• Ex. Eastern vs. western meadowlarks –

identical in shape, coloring, habitat – ranges in US overlap – but have different songs to attract mates

How New Species FormHow New Species FormCAUSES OF REPRODUCTIVE ISOLATION

• Habitat (niche) - Some species remain reproductively isolated because they are adapted to different habitats in the same general location.

• Ex. lakes in Canada, contain two different species of three-spine stickleback fish. One species is adapted to living along the lake bottom, feeding on small snails.

• Fish of the other species spend most of their lives in the open water, filtering plankton (small floating organisms). The two species' preferences for different habitats help maintain their isolation.

How New Species FormHow New Species Form

CAUSES OF REPRODUCTIVE ISOLATION

Incompatibility - two seemingly similar species may be unable to mate because their reproductive structures are physically incompatible.

Ex. Not showing you this one!

How New Species FormHow New Species FormCAUSES OF REPRODUCTIVE ISOLATION Death of hybrid - the offspring of two

different species may die or may mature into infertile adults. (Remember that the definition of a species requires that its members be able to produce fertile offspring.)

Ex: Horses and donkeys remain separate species because their hybrid offspring (mules) are infertile

Rate of SpeciationRate of SpeciationGRADUALISM = long term gradual change

in species – slow, progressive change of one species into another

Rate of SpeciationRate of SpeciationPUNCTUATED EQUILIBRIUM – some species

remained unchanged for millions of years and then underwent periods of very rapid, major change

Major environmental changes in predation pressure, food supply, climate, long droughts, major volcanic eruptions, beginning and end of ice ages

Mutations in regulator genes can provide radically new variations in the organization of the body