CHAPTER 24 THE ORIGIN OF SPECIES

Different Species Of Japanese Ants!!!

What is a species ? How does speciation occur ?

Macroevolution:

--the origin of new species, genera,families, orders, classes, phyla, and kingdoms

Speciation—the origin of new species

Mutations + Sexual recombination + genetic drift +gene flow + natural selection! =

SPECIES “kind”-”appearance” – group of

populations whose members can interbreed and produce

fertile offspring;

Different Species Of HUMANS???

What is a species ? How does speciation occur ?

A biological species is the largest set of populations in which genetic exchange is possible and is genetically isolated from

other populations.

Distinctions between species are not always clear.Subspecies have small differences fromother subspecies and usually havegeographical variation. C. hutchinsii hutchinsii

C. canadensis canadensis

Concepts of species:

1. Biological species concept—reproductive isolation

2. Morphological species concept—measurable anatomical differences between species

3. Ecological species concept— based on the ‘niche’ – environment and organisms’ role in using it

4. Pluralistic species concept—cohesion of (2) and (3)

Situation:2 populations that are microevolving (different p,q)

-what will make them 2 species?-not having fertile offspring!

a) Prezygotic barriersb) Post zygotic barriers

Organisms of different species cannotinterbreed for a number of reasons.

Prezygotic barriers- hinder fertilization1)Habitat isolation—live in different

places ex: water vs. terrestrial in garter snakes

2) behavioral isolation—respond only to members of the same species; ex: firefly flashes

Prezygotic barriers hinder fertilization

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Ex. Firefly flashes, Bower Bird nest

Prezygotic barriers hinder fertilization

3) temporal isolation—different breeding times (ex. W. and E. skunks)

EASTERN- summer

WESTERN - winter

Prezygotic barriers hinder fertilization

4) mechanical isolation—anatomical incompatibility

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Ex. Damsel fly genitalia, flowers

Prezygotic barriers hinder fertilization

5) gametic isolation—gametes may not be recognized by other species for fertilization (molecular recognition missing between egg and sperm)

Postzygotic barriers - gametes can get together to make a zygote, BUT barriers prevent a zygote from developing properly

Postzygotic barriers prevent a zygote from developing properly.

1.Reduced hybrid viability—development is aborted at some embryonic stage. Ex. frogs

Postzygotic barriers prevent a zygote from developing properly.

2. Reduced hybrid fertility—hybrids are sterile—usually there is a failure of meiosis in these hybrids so they cannot produce viable (good) gametes

Postzygotic barriers prevent a zygote from developing properly.

3) hybrid breakdown—first-generation hybrids may be fertile, but second-generation offspring are not viable. Ex. cotton

SUMMARY

                                                                                        

                                     

                                                                                        

                                     

Anagenesis =one species changesinto another

Cladogenesis =branching of a newspecies from a species thatcontinues to exist

Recipe to make a New Species:

1) Need to create a barrier for gene flow within a population- that is a barrier for productive SEX

2) Need to maintain this barrier (prezygotic/postzygotic) so that the two groups can continue accumulating differences through mutation/sexual recombination (acted upon by natural selection - of course you knew that!)

3) And then PRESTO! You have a new species (give or take a million years!)

How do new species arise (barrier creation)• Allopatric speciation (“other homeland”)• Sympatric speciation (“together”)

Allopatric Speciation--occurs when geographical barriers

block gene flow*small populations are more likely tochange enough to become a new speciesRING

SPECIES

'I'IWI - Vestiaria coccinea Found in 'ohi'a lehua forests.  Feeds on the nectar of 'ohi'a lehua flowers high in the forest canopy and from tubular blossoms in the understory.

'AMAKIHI - Hemignathus virens Common in native forests above 2,000 feet.  Feeds more on insects and is less dependant on nectar.  Female is a darker, olive green color.

'AKOHEKOHE - Palmeria dolei  Crested honeycreeper - Endangered Found only in the rain forests of east Maui at elevations of 4,500 to 6,500 feet.

PALILA - Loxioides bailleui Endangered Found only in the dry forests on the slopes of Mauna Kea, Big Island, 6,000 to 9,000 feet.

HAWAIIN HONEYCREEPERS

Adaptive radiation—evolution of many different species froma common ancestor*common on islands*

Peripheral isolate = small population atthe fringe of a larger population’s range--good candidate for speciation

1. gene pool at the edge is probably different

(founder effect)

2. until the peripheral population becomes larger,

genetic drift will occur

3. natural selection may be different in the fringe

environment

Sympatric Speciation

--a new species can evolve without geographic isolation

--genetic changes can prevent membersof the same species from mating

ex. Apple maggot flies, polyploid plants

Sympatric Speciation--a new species can evolve without geographic isolation-- female lays egg where she grew up

                                                                                                                             

Apple Maggot Flies

Hawthorns (native to US)

Apples (introduced to US by immigrants)

One species=autopolyploidTetraploid plants can’tinterbreed with normalplantspostzygotic barrier2 different species form an allopolyploid hybridthese

usually propagate asexually (sympatric or allopatric?)

Wheat evolved from 2 meiotic errors.

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What type of speciation is this?

Speciation is at the boundary between microevolution (population allelle frequency change) and macroevolution (accumulation of change over millions of years).

Rate of Speciation -Gradualism vs. Punctuated Equilibrium

Gradualism—species diverge gradually over a long period of timePunctuated equilibrium—species diverge in spurts of relatively rapid change

--long periods of equilibrium punctuatedby short periods of speciation

Development genes are important inmacroevolution.

Allometric growth—differencein relative rates of growth ofvarious parts of the body

Paedomorphosis—adult retains featuresthat were juvenile structures in itsancestors. ex. some salamanders retain gills

•Heterochrony, an evolutionary change in the rate or timing of developmental events.

Temporal changes in development thatdiffer between species--heterochrony

Homeosis = alteration in basic body design controlled by small sets of gene in development—homeoticgenes (Hox complex)

Evolution is not goal-oriented--species selectionproduces an evolutionary trend