What is a species? Speciation?

1. 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

2. 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) Barriers that lead to speciation Stronglyocentrotus purpuratus Lytichinus pictus

3. 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

4. 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

5. 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 Postzygotic reproductive barriers

7. 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