What is a species? Speciation?

• Macroevolution: origin of new species; increases diversity

• Species? Population (or group of populations) whose members can interbreed and produce fertile offspring

• Identified species are named = Taxonomy– binomial scientific name:

• Homo sapiens – Homo = Genus– sapiens = species

Barriers that lead to speciation• Reproductive barriers can prevent interbreeding of

closely related populations

• Temporal isolation: different seasons– E.g. western skunks in

fall; eastern skunks in late winter

– Purple sea urchins (late fall to early spring) vs. white sea urchins (late spring to early fall)

Stronglyocentrotus purpuratus Lytichinus pictus

• Habitat isolation– Living in different

places w/in general region

– e.g. herbivorous insects feeding on two different host plants

• Behavioral isolation– Different unique

mating rituals to attract mates of same spp.

– e.g. many birds have courtship rituals before mating can commence

• Mechanical isolation– Incompatible female and

male sex organs• Square peg into a round

hole problem

– e.g. flower parts of one species differs from another; pollinator only passes to one

• Gametic isolation– Fertilization success

depends on molecular recognition

– e.g. open spawning of aquatic species, windblown pollen of plants

Postzygotic reproductive barriers

• Hybrid zygotes = fertilization of two spp.– Hybrid inviability:

death in early devpmnt– Hybrid sterility: mature

individuals, but sterile– Hybrid breakdown:

F2 generation (or first- generation of hybrids) sterile

Geographic Barriers

• Allopatric speciation (allos = other, patra = fatherland)

– Mountain range emerged– Large lake subsides and splinters

into many smaller bodies of water– Baja peninsula and Isthmus of

Panama separates marine life on each side

– Grand canyon separated by Col. River