Understanding Speciation: Cladogenetic, Reticulate, and Phyletic Processes, Slides of Geology

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How does a new species “emerge”?

• New species evolve from preexistent species

• Speciation processes

– Cladogenetic speciation

– Reticulate speciation

– Phyletic speciation

Time

Time

Time

Speciation Processes Cladogenetic speciation new species originate from a splitting event in which each branch is a species

Reticulate speciation new species results from interbreeding of two existing species

Phyletic speciation ancestral species transforms into a single descendant species

From White 2008Docsity.com

When can we say speciation happens?

• When two populations of one species become

sufficiently different so they are no longer the

same species (this will partly depend on the

species concept that you choose)

• The divergence of an ancestral

species into 2 or more daughter

species requires genetic change

among populations

Brief genetics review

• Diploid organisms have 2 homologous copies of each chromosome (2n)
• Allele – one of two or more alternative forms of a gene located at a single point (locus) on a chromosome

-Homozygote: alleles same -Heterozygote: alleles different

• Populations contain individuals with different alleles Docsity.com

Mutation

• Random changes in DNA
• Source of all new alleles
• If beneficial, allele frequency increases
• Negative & neutral mutations also occur

Genetic Drift

• Change in allele frequencies that occurs entirely from chance
• Largest effects in small,

isolated populations

Jaguars Docsity.com

Genetic drift

1. Genetic drift acts faster and has more drastic results in smaller populations
2. Can reduce genetic variation in populations
3. Genetic drift can contribute to speciation