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AP Bio-Forbes-Evolution 5: Speciation

5 of 6 of my evolution unit. Image Credits: Biology (Campbell) 9th edition, copyright Pearson 2011, & The Internet. Provided under the terms of a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. By David Knuffke.
by

Shani Forbes

on 29 May 2013

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Transcript of AP Bio-Forbes-Evolution 5: Speciation

Speciation
Case Study “That mystery of mysteries…” Species live in different areas Rate of Speciation Speciation What How When 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:
Morphological: Based on appearance; similar morphological features
Ecological: Based on niche; share a single niche
Phylogenetic: Based on genetics; share ancestry
Paleological: Based on fossils Big Questions 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"
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? Sympatric = "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? 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 Examples of 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. 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. The formation of the Isthmus of Panama has led to the creation of 15 pairs of sibling species in the snapping shrimp genus Any Questions? 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? lives in the water lives on land skunk (c) mates in winter
skunk (d) mates in summer opposing whorls,
opposing genitals ladies love my booby dance Sex in the sea I'm Frail! I'm Sterile! 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. Speciation and the Maggot Fly Destroying the Misconceptions Speciation can only be observed over millions of years? T or F Species are going extinct, but no new species are forming on Earth? T or F Hawthorn trees are native to North America. The hawthorn fruit is eaten by the larvae of the hawthorn maggot fly, Rhagoletis pomonella. Rhagoletis Pomonella; The Maggot Fly female lays fertilized eggs

larvae emerge, feed on fruit, and molt

maggots drop from tree and pupate in soil


adults emerge from soil and mate on fruit But there are parasites! Parasitoid wasps try to lay
eggs in the maggot's body,
paralyzing and ultimately
killing the maggot. The Host Shift Hawthornes are native
North American shrubs
in the genus Crataegus. Hawthorn fruits range
between 5 mm and 20 mm
in diameter, with an
average of 12.6 mm. Domesticated apples were
introduced into North America
in the 1600s. They belong to
genus Malus. They are the most
widely grown fruit in North America. A typical commercial apple has
a diameter of 70mm. When apples were introduced into North America, Rhagoletis Pomonella larvae starting feeding on them. Apple vs Hawthorne:
The Maggots Viewpoint: The large apple fruit provides 220 times more food than hawthorn fruit.

But the nutritional quality of hawthorn fruit is superior:

52% of hawthorn maggots survive vs. 27% of apple maggots. Apple vs Hawthorne:
The Risk of Attack Larger fruits of apples are much deeper than hawthorn fruits.

Apple maggots can burrow to avoid parasitoid wasps.

Apple maggots carry fewer parasitoid wasp eggs than hawthorn maggots do. Today: There are Hawthorne
and Apple Maggot Flies Hawthorn and apple maggot flies are physically indistinguishable.

However, they are genetically distinct, with different genetic profiles.

There is no geographic isolation or physical separation between hawthorn and apple maggot flies. Maggot flies tend to mate with their own kind.

Hawthorn maggot flies strongly prefer to mate on and lay fertilized eggs in hawthorn fruit.
Apple maggot flies strongly prefer to mate on and lay fertilized eggs in apple fruit.

There is only a 4-6% hybridization rate between hawthorn and apple maggot flies. Rhagoletis Host Shift Hawthorne raised Apple raised Hybrids are viable and fertile There are six genetic differences in apple maggots that alter the timing and emergence of adult flies. This leads to adaptive change and synchronizes apple maggot fly with peak fruiting of apple trees. Adult flies emerge from pupae in the soil to reproduce before fruit mature. Apple fruits ripen approximately one month earlier than hawthorne fruits, but there is overlap between the end of the apple fruiting season and the beginning of the hawthorne fruiting season. Timing of Host Fruit Ripening Rhagoletis Speciation small fruit (13mm)

high nutritional quality

shallow burrows

more parasitoid wasps

fruit available later large fruit (70mm)

low nutritional quality

deep burrows

fewer wasps

fruit available early Based on the information provided, do you think hawthorne and apple maggot flies are separate species?
A. Yes
B. No According to the biological species concept, are hawthorne and apple maggot flies separate species?
A. Yes
B. No What evidence supports the biological species concept?
A. Hawthorne and apple maggot flies are physically indistinguishable.
B. There is a 4-6% hybridization rate between hawthorne and apple maggot flies.
C. Hawthorne and apple maggot flies are genetically distinguishable and have a distinct genetic profile.
D. Hawthorne and apple maggot flies strongly prefer to mate and lay fertilized eggs in hawthornes and apples respectively. Biological Species Concept Ecological Species Concept According to the ecological species concept, are hawthorne and apple maggot flies separate species?
A. Yes
B. No What evidence supports the ecological species concept?
A. Hawthorne and apple maggot flies are physically indistinguishable.
B. There is a 4-6% hybridization rate between hawthorne and apple maggot flies.
C. Hawthorne and apple maggot flies are genetically distinguishable and have a distinct genetic profile.
D. Hawthorne and apple maggot flies strongly prefer to mate and lay fertilized eggs in hawthornes and apples respectively. Morphological Species Concept According to the morphological species concept, are hawthorne and apple maggot flies separate species?
A. Yes
B. No What evidence supports the morphological species concept?
A. Hawthorne and apple maggot flies are physically indistinguishable.
B. There is a 4-6% hybridization rate between hawthorne and apple maggot flies.
C. Hawthorne and apple maggot flies are genetically distinguishable and have a distinct genetic profile.
D. Hawthorne and apple maggot flies strongly prefer to mate and lay fertilized eggs in hawthornes and apples respectively. Phylogenetic Species Concept According to the phylogenetic species concept, are hawthorne and apple maggot flies separate species?
A. Yes
B. No What evidence supports the phylogenetic species concept?
A. Hawthorne and apple maggot flies are physically indistinguishable.
B. There is a 4-6% hybridization rate between hawthorne and apple maggot flies.
C. Hawthorne and apple maggot flies are genetically distinguishable and have a distinct genetic profile.
D. Hawthorne and apple maggot flies strongly prefer to mate and lay fertilized eggs in hawthornes and apples respectively. Speciation in Rhagoletis is.... A. Allopatric
B. Sympatric What evidence supports your claim? Do hawthorne and apple maggot flies exhibit prezygotic or postzygotic barries? What reproductive barrier limits interbreeding between hawthorne and maggot flies?
A. mechanical isolation
B. habitat isolation
C. temporal isolation
D. hybrid breakdown Would you expect natural selection
to favor pre-zygotic or post-zygotic isolating mechanisms between
sympatric species?
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