BIOL 112 Lecture 9

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Chapter 24: The Origin of Species

species concepts, cont'd

Ecological Species Concept

Organisms with same niche in same environment are same species

Paleontological

morphologically similar fossils are the same species (morphological Species Concept applied to fossils)

Phylogenetic Species Concept

Shared morphological and genetic (molecular characteristics

i.e. they would be in same branch of phylogenetic tree

Speciation Models

How are species made? How does one species become one or more new species?

Allopatric Speciation

Allo- (other); patric (country)

Insertion of geographic barrier between two groups of a population (vicariances)

now-isolated populations undergo separate microevolutionary events to become new species

Sympatric Speciation

Sym- (same); patric (country)

No isolation between populations

Reproductive isolation: no gene flow between two "subpopulations"

1. change chromosome number (ploidy), so sets are incompatible; usually result of
   • failed cell division in meiosis (autopolyploidy)
   • hybridization between species (allopolyploidy)
2. Habitat differentiation between subpopulations and nonrandom mating within subpopulations
3. Sexpal selection: nonrandom mating wihin population
   • for example, subpopulation of females prefer males with certain characteristics

Chapter 25: History of Life on Earth

Adaptive Radiation

fairly dramatic emergence of numerous species from a common ancestor as a singe species adapts to multiple niches

1. colonization of a new landmass (Galapagos, Hawaiian islands)
2. mass extinction events (cretaceous: dinosaurs were dominant predators and went extinct; mammals exploded)

Evolution of Body Form

What genetic changes (genes or gene families) are responsible for new traits?

Hox Gene Family

Encodes transcription factors

Master regulators (Homeodomain TF) regulate many genes to mace proteins for a specific body structure