Speciation How new species form What exactly is

Speciation… How new species form!

What exactly is a species? • A species is a population that can breed with each other to create viable offspring, but cannot create viable offspring with members of other species (Biological Species Concept)

How does Speciation Occur? • Two populations become reproductively isolated from each other • The populations can no longer make viable offspring together • Natural selection acts on the two populations independently

How does Speciation Occur? • Pre-zygotic (before zygote) Isolating Mechanisms: 1. Behavioral Isolation: mating rituals differ 2. Geographic Isolation: rivers, mountains, etc. separate two groups 3. Temporal Isolation: reproduce at different times of day or year

More Pre-Zygotic Barriers 4. Mechanical Isolation: Structural differences in genitalia prevent successful mating 5. Gametic Isolation: Mating occurs, but gametes fail to fertilize each other correctly

Post-Zygotic Barriers • If the two new species do try to mate, they will not make offspring because of: 1. Reduced hybrid viability: hybrid zygotes do not develop or reach sexual maturity 2. Reduced hybrid fertility: hybrids cannot reproduce 3. Hybrid breakdown: hybrids have unviable or infertile offspring

Results of Post-Zygotic Barriers Male Ligers are infertile Many ligers die young from neurological disorders Mules are infertile