Evolution of Populations. AP Biology

Transcription

1 Evolution of Populations Doonesbury - Sunday February 8, 2004

2 Review of Darwin s Influence Geology Thomas Hutton Charles Lyll - Biology Jean Baptist Lamark - Tendency toward Perfection - Use and Disuse - Inheritance of Acquired Characteristics

3 Populations evolve Natural selection acts on individuals differential survival survival of the fittest differential reproductive success who bears more offspring Populations evolve genetic makeup of population changes over time favorable traits (greater fitness) become more common Presence of lactate dehydrogenase Mummichog

4 Individuals Individuals survive DON Tare evolve or selected don t survive Individuals Populations reproduce evolve or don t

5 Forces of evolutionary change Natural selection traits that improve survival or reproduction will accumulate in the population adaptive change (non-random) Genetic drift frequency of traits can change in a population due to chance events random change

6 Natural Selection Selection acts on any trait that affects survival or reproduction predation selection physiological selection sexual selection

7 Predation Selection Predation selection act on both predator & prey behaviors camouflage & mimicry speed defenses (physical & chemical)

8 Physiological Selection Acting on body functions disease resistance physiology efficiency (using oxygen, food, water) biochemical versatility protection from injury 5.5 mya The Antarctic Ocean freezes over

9 Sexual Selection Acting on reproductive success attractiveness to potential mate fertility of gametes successful rearing of offspring

10 Sexual selection

11 Sexual selection Acts in all sexually reproducing species the traits that get you mates sexual dimorphism influences both morphology & behavior can act in opposition to natural selection Jacanas

12 Types of Evolution 1) Divergent Evolution Isolated populations (from a common ancestor) evolve independently into many species.

13 Coevolution Two or more species reciprocally affect each other s evolution predator-prey disease & host competitive species mutualism pollinators & flowers

14 Convergent Evolution Different types of organisms evolve similar characteristics because they occupy similar niches.

15 Genetic Drift Chance events changing frequency of traits in a population not adaptation to environmental conditions not selection founder effect small group splinters off & starts a new colony bottleneck some factor (disaster) reduces population to small number & then population recovers & expands again but from a limited gene pool

16 Founder effect When a new population is started by only a small group of individuals just by chance some rare alleles may be at high frequency; others may be missing skew the gene pool of new population human populations that started from small group of colonists example: colonization of New World albino deer Seneca Army Depot

17 Bottleneck effect When large population is drastically reduced by a disaster famine, natural disaster, loss of habitat loss of variation by chance event alleles lost from gene pool not due to fitness narrows the gene pool

18 Cheetahs All cheetahs share a small number of alleles less than 1% diversity as if all cheetahs are identical twins 2 bottlenecks 10,000 years ago Ice Age last 100 years poaching & loss of habitat

19 Speciation

20 So what is a species? Biological species concept defined by Ernst Mayr population whose members can interbreed & produce viable, fertile offspring reproductively compatible Distinct species: songs & behaviors are different enough to prevent interbreeding Eastern Meadowlark Western Meadowlark

21 How and why do new species originate? Species are created by a series of evolutionary processes populations become isolated geographically isolated reproductively isolated isolated populations evolve independently Isolation allopatric geographic separation sympatric still live in same area

22 PRE-reproduction barriers Obstacle to mating or to fertilization if mating occurs geographic isolation ecological isolation temporal isolation behavioral isolation mechanical isolation gametic isolation

23 Ammospermophilus spp Geographic isolation Species occur in different areas physical barrier allopatric speciation other country Harris s antelope squirrel inhabits the canyon s south rim (L). Just a few miles away on the north rim (R) lives the closely related white-tailed antelope squirrel

24 QuickTime and a TIFF (Uncompressed) decompressor Ecological isolation Species occur in same region, but occupy different habitats so rarely encounter each other reproductively isolated 2 species of garter snake, Thamnophis, occur in same area, but one lives in water & other is terrestrial are needed to see this picture. QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. lions & tigers could hybridize, but they live in different habitats: lions in grasslands tigers in rainforest

25 Temporal isolation Species that breed during different times of day, different seasons, or different years cannot mix gametes reproductive isolation sympatric speciation same country Eastern spotted skunk (L) & western spotted skunk (R) overlap in range but eastern mates in late winter & western mates in late summer

26 Behavioral isolation Unique behavioral patterns & rituals isolate species identifies members of species attract mates of same species courtship rituals, mating calls reproductive isolation Blue footed boobies mate only after a courtship display unique to their species

27 Recognizing your own species courtship songs of sympatric species of lacewings courtship display of Gray-Crowned Cranes, Kenya firefly courtship displays

28 Mechanical isolation Morphological differences can prevent successful mating reproductive isolation Even in closely related species of plants, the flowers often have distinct appearances that attract different pollinators. These 2 species of monkey flower differ greatly in shape & color, therefore cross-pollination does not happen. sympatric speciation? Plants

29 Mechanical isolation For many insects, male & female sex organs of closely related species do not fit together, preventing sperm transfer lack of fit between sexual organs Animals

30 Gametic isolation Sperm of one species may not be able to fertilize eggs of another species mechanisms biochemical barrier so sperm cannot penetrate egg receptor recognition: lock & key between egg & sperm chemical incompatibility sperm cannot survive in female reproductive tract Sea urchins release sperm & eggs into surrounding waters where they fuse & form zygotes. Gametes of different species red & purple are unable to fuse. QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture.

31 POST-reproduction barriers Prevent hybrid offspring from developing into a viable, fertile adult reduced hybrid viability reduced hybrid fertility hybrid breakdown zebroid

32 Rate of Speciation Current debate: Does speciation happen gradually or rapidly Gradualism Charles Darwin Charles Lyell Punctuated equilibrium Stephen Jay Gould Niles Eldredge Niles Eldredge Curator American Museum of Natural History

33 Gradualism Gradual divergence over long spans of time assume that big changes occur as the accumulation of many small ones

34 Punctuated Equilibrium Rate of speciation is not constant rapid bursts of change long periods of little or no change species undergo rapid change when they 1 st bud from parent population Time

35 Evolution is not goal-oriented An evolutionary trend does not mean that evolution is goal-oriented. Surviving species do not represent the peak of perfection. There is compromise & random chance involved as well Remember that for humans as well!

36 Evidence for Evolution Unity of Pattern similarities (in structure and function) that show a common ancestry between organisms.

37 Fossil Record Darwin proposed that the Earth was millions of years old (Hutton and Lyell) By comparing fossils from older rock layers with younger rock layers, scientists conclude that life on Earth has changed over time

38 Evidence for Evolution Fossil Record Some fossils represent possible common ancestors, from which numerous species may have arisen. Archeopteryx Reptilian-traits teeth in jaw bony tail claws on forelimbs Avian-Traits asymmetrical feathers wings reversed hallux Common ancestor between reptiles and birds?

39 Tiktaalik fish with hands Discovered in 2004 Intermediate between fish and land-living animals Discovered in rocks from 375 million years ago Had scales, fins with fin webbing. Flat head and a neck. Bones of fin correspond to upper arm, and the wrist

40 Evidence of Evolution Similar, But Unrelated Species in different locations are the product of different lines of evolutionary descent Descent with modification Copyright Pearson

41 Evidence for Evolution Homologous Structures similar anatomical structures within different organisms arising from a common ancestor.

42 Evidence for Evolution Vestigial Organs Traces of organsno longer serve a useful function

43 Evidence for Evolution Similar Embryonic Development

44 Evidence for Evolution Shared Genetic Code The genetic code of every living organism is compromised of the same DNA units: C, G, A, T.