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Transcript of Evolution: Speciation
“That mystery of mysteries…”
Species live in different areas
Rate of Speciation
Species are created by a series of evolutionary processes that result in the reproductive isolation of a population.
So…what is a species?
Darwin never actually tackled how new species arose…
"The Origin of Species" has very little to do with the origin of actual species.
Biological species concept
defined by Ernst Mayr
population whose members can interbreed & produce viable, fertile offspring
Not the only “species” Other definitions:
: Based on appearance
: Based on niche
: Based on fossils
Why are alternative definitions needed?
Make Sure You Can
An ongoing debate.
Does speciation happen gradually or rapidly?
Old thinking: Charles Darwin, Charles Lyell
Gradual divergence over long spans of time
Big changes occur as the accumulation of many small ones
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
Speciation = Reproductive Isolation
The flightless cormorant (Nannopterum harrisi), one of many new species that have originated on the isolated Galápagos Islands
= "other country"
A population is isolated from other populations due to physical, geographic barriers.
If given enough time, and enough evolution, the populations will become reproductively isolated.
What sorts of barriers/events could contribute to allopatric speciation events?
= "same country"
The populations remain in the same physical area, but become reproductively isolated from other populations due to other mechanisms.
What sorts of events could contribute to sympatric speciation events?
Various mechanisms ("
") 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.
: Barriers prior to fertilization
: Barriers after fertilization
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 "
" like the larus genus of gulls in the Northern Hemisphere.
Speciation has been observed in nature and in the laboratory in all major lineages of life
Below are some examples of speciation studies.
See if you can identify the species barrier(s) that are contributing to the speciation.
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.
Experiments with transgenic monkey flowers show different pollinator preference for species specific flower colors
Fruit flies raised on specific growth media show a preference for mating with flies raised on the same media
Observations in the field and in the lab show that color perception is important in maintaining cichlid species barriers
Hybridization between 2 species of sunflowers has produced a new species in the wild. This hybridization has also been seen in the lab
Sympatric populations of 2 flycatcher species are much less likely to interbreed than allopatric populations
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
Genetic analysis of the toad population of Europe shows that there is only a narrow zone where hybrids between the yellow-bellied and fire-bellied toads can be found
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)
Don't Let The Title Fool You!
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 "
" leads to speciation ("
lives in the water
lives on land
skunk (c) mates in winter
skunk (d) mates in summer
ladies love my booby dance
Sex in the sea
I'm Breaking Down!
What is a species?
How can evolutionary changes in a population lead to the production of new species?
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.
Polyploidy in Plants
The evolution of many diverse species from a common ancestor.
Importance of different barriers