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Chapter 24, Speciation
Transcript of Chapter 24, Speciation
"The Origin of Species" has very little to do with the origin of actual species. "Biological species concept"
population whose members can interbreed & produce viable, fertile offspring
Not the only “species” definition:
Morphological: Based on appearance
Ecological: Based on niche
Paleological: Based on fossils
Phylogenetic: Based on molecular structure
Why are alternative definitions needed? Evolution Make Sure You Can An ongoing debate.
Does speciation happen gradually or rapidly? Gradualism Old thinking: Charles Darwin, Charles Lyell
Gradual divergence over long spans of time
Big changes occur as the accumulation of many small ones Punctuated equilibrium New Thinking: Stephen Jay Gould, Niles Eldredge
Rate of speciation is not constant
Rapid bursts of change, followed by long periods of little or no change
Species undergo rapid change when they first evolve from parent population Which one is correct? Stephen Jay Gould Niles Eldridge Speciation = Reproductive Isolation The flightless cormorant (Nannopterum harrisi), one of many new species that have originated on the isolated Galápagos Islands Allopatric Speciation Sympatric Speciation Allopatric = "other country"
Pop. isolated from other pop's due to physical, geographic barriers.
Given enough time/evolution, pop's will become reproductively isolated.
What sorts of barriers/events could contribute to allopatric speciation events? Sympatric = "same country"
Pop's remain in same physical area, but become reproductively isolated from other pop's due to other mechanisms.
What sorts of events could contribute to sympatric speciation events? Species Barriers Various mechanisms ("barriers") exist that prevent successful interspecies reproduction.
NOTE: "successful reproduction" = production of fertile offspring.
We can split these barriers into when they occur in relation to fertilization.
Prezygotic barriers: Barriers prior to fertilization
Postzygotic barriers: Barriers after fertilization Prezygotic Barriers Postzygotic Barriers Species breed during different times of day, different seasons, or different years Unique behavioral patterns & rituals isolate species. Identifies, attracts members of species (ex. calls, mating dances) Reproductive anatomy from one species does not fit with the anatomy from another species Proteins on the surface of gametes does not allow fusion of sperm and egg. Hybrid is weak Hybrid is sterile Offspring of hybrid loses hybrid genetic combinations over succeeding generations Effects of Isolation Isolation of a population does not always result in speciation.
There are several outcomes that can occur following isolation
Depending on the circumstances, hybrid populations can serve as genetic links between isolated populations.
This is typical of "ring species" like the larus genus of gulls in the Northern Hemisphere. Below are some examples of speciation studies. Two different species of antelope squirrel, one for each rim of the grand canyon The hybrid "Grolar Bear" offspring of a Polar bear and a Grizzly bear. Fruit flies raised on specific growth media show a preference for mating with flies raised on the same media Hybridization between 2 species of sunflowers has produced a new species in the wild. This hybridization has also been seen in the lab Allopatric populations of mice on the island of Madiera demonstrate different chromosomal fusion mutations Modern bread wheat is a hybrid species with genetic contributions from three wild wheat grass species The formation of the Isthmus of Panama has led to the creation of 15 pairs of sibling species in the snapping shrimp genus (2 pairs are shown) Any Questions? I've done enough! Let's leave it for the 1900's What sorts of processes can isolate a population? Only the loss of the "hybrid zone" leads to speciation ("Reinforcement") lives in the water lives on land skunk (c) mates in winter
skunk (d) mates in summer opposing whorls,
opposing genitals Happy Feet? Careful! I'm Frail! I'm Sterile! I'm Breaking Down! Microevolution: chnge allele (f) of pop.
Speciation: create new species
Macroevolution: lg.-scale chnge. Apply the biological species definition, and identify circumstances where it is not applicable.
Explain the circumstances that can lead to the production of a new species both allopatrically AND sympatrically.
Define all species barriers described in this presentation, and provide examples of these barriers.
Compare the common models of the pace of speciation, and cite evidence that supports both gradualism and punctuated equilibrium. Evolution