What is a species? Speciation?
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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
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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
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• 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
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• 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
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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
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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