Species and Speciation. Biological Species Concept A group of organisms that can interbreed and produce viable, fertile offspring. - презентация

1 Species and Speciation

2 Biological Species Concept A group of organisms that can interbreed and produce viable, fertile offspring

3 Biological Species Concept Assumes –Common characteristics –Genetically compatible –Interbreed under natural conditions –Sexual Reproduction Iguana iguana

4 Drawbacks of Biological Species Concept Cannot be used with exclusively asexual organisms –Prokaryotes –Amoeba & some other protists –Some animals, plants & fungi Amoeba proteus

5 Drawbacks: Isolated Populations How do you test for interbreeding under natural conditions? Can a deer in Florida interbreed with one in Wisconsin?

6 Drawbacks Can a Great Dane interbreed with a Chihuahua?

7 Drawbacks Some species look and behave differently Can interbreed and have viable, fertile offspring Example: coyotes, wolves, dogs

8 Drawbacks: Horizontal Gene Transfer Vertical gene transfer Parents offspring Horizontal gene transfer Individual individual Not parent-offspring

9 Horizontal Gene Transfer Can occur between organisms: –Different species –Different kingdoms –Different domains

10 Horizontal Gene Transfer in Bacteria (1) Transformation

11 Horizontal Gene Transfer in Bacteria (2) Transduction

12 Horizontal Gene Transfer in Bacteria (3) Conjugation

13 Horizontal Gene Transfer E. coli 0157:H7 has picked up Shiga toxin gene from Shigella Up to 25% genetic difference among E. coli strains

14 Horizontal Gene Transfer Normally, 25% genetic diversity different species Human and chimp genomes differ by only 1.2%

15 Drawbacks: Fossil Species Cannot tell if fossil organisms were capable of interbreeding

16 Fossils Normally cant compare genes of different fossil species

17 Morphological Species Concept Group of individuals that share common characteristics Used for: Fossils Exclusively asexual Traditional method for sexual organisms

18 Biological Species Concept: Reproductive Isolation Barriers between species Prevent viable fertile offspring (Lesser Bird of Paradise)

19 Reproductive Isolating Mechanisms Prezygotic mechanisms –Before fertilization Postzygotic mechanisms –After fertilization

20 Prezygotic Mechanisms Prevents: –Prevent mating from occurring –Prevents gametes from forming a zygote

21 Prezygotic Mechanisms: Temporal Isolation Isolated by time May breed: –Different times of day –Different seasons –Different years

22 Temporal Isolation Late WinterLate Summer

23 Prezygotic Mechanisms: Habitat Isolation Same geographic area Different habitats

24 Prezygotic Mechanisms: Behavioral Isolation Different courtship rituals Blue-Footed Booby

25 Behavioral Isolation Eastern and Western Meadowlarks Isolated by Songs

26 Prezygotic Mechanisms: Mechanical Isolation Structural differences prevent mating Example: Genital openings (arrows) not aligned No Mating

27 Prezygotic Mechanisms: Gametic Isolation Sperm cannot fertilize eggs Very important in aquatic species (broadcast spawners) Example: Sea Urchins

28 Postzygotic Mechanisms Prevents hybrid zygotes from developing into viable, fertile adults

29 Postzygotic Mechanism: Reduced Hybrid Viability If Sheep and goats mate Hybrid zygotes Die before birth.

30 Postzygotic Mechanism: Reduced Hybrid Fertility Male donkey x Female horse Mule Mules: –Healthy (viable) –Sterile.

31 Postzygotic Mechanism: Hybrid Breakdown First generation hybrids are viable and fertile. Offspring of hybrids are feeble or sterile.

32 Speciation Process of species formation Two main mechanisms: –Allopatric speciation –Sympatric speciation

33 Allopatric Speciation Geographic separation Genetic exchange Populations become genetically different Reproductive isolation

34 Sympatric Speciation Populations not geographically separated Can be due to rapid genetic changes: –Alter morphology –Alter behavior –Alter habitat preferences

35 Example: Sympatric Speciation Euhadra snails Mutation in one gene Shell spirals in opposite direction Instant mechanical isolation Two species

36 Adaptive Radiation A common ancestor Many new species Relatively rapid Common in island chains –Isolated –Numerous habitats & resources

37 Galápagos Finches Ancestral finch from South America Several finch species –Different diets –Different beak shapes –Different beak sizes

38 Galápagos Finches

39 Hawaiian Silverswords Tarweed arrived from North America ~ 5 mya Common ancestor Silverswords

40 Hawaiian Silverswords