AP Biology Mom, Dad… There’s something you need to know… I’m a MAMMAL! The Origin of Species

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

AP Biology 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

AP Biology  Obstacle to mating or to fertilization if mating occurs Pre-reproduction barriers behavioral isolation geographic isolation ecological isolation temporal isolation mechanical isolation gametic isolation

AP Biology 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 Ammospermophilus spp

AP Biology Ecological isolation  Species occur in same area, but occupy different habitats so rarely encounter each other 2 species of garter snake, Thamnophis, occur in same area, but one lives in water & other is terrestrial lions & tigers could hybridize, but they live in different habitats:  lions in grasslands  tigers in rainforest lions & tigers could hybridize, but they live in different habitats:  lions in grasslands  tigers in rainforest

AP Biology Temporal isolation  Species that breed during different times of day, different seasons, or different years cannot mix gametes  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

AP Biology Behavioral isolation  Unique behavioral patterns & rituals isolate species  identifies members of species  attract mates of same species  courtship rituals, mating calls Blue footed boobies mate only after a courtship display unique to their species sympatric speciation?

AP Biology Mechanical isolation  Morphological differences can prevent successful mating 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. Plants sympatric speciation?

AP Biology 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: hard to imagine for us… but a big issue for insects with different shaped genitals! Animals I can’t even imagine!

AP Biology 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. sympatric speciation?

AP Biology Post-reproduction barriers  Prevent hybrid offspring from developing into a viable, fertile adult  reduced hybrid viability  reduced hybrid fertility  hybrid breakdown zebroid

AP Biology Reduced hybrid viability  Genes of different parent species may interact & impair the hybrid’s development Species of salamander genus, Ensatina, may interbreed, but most hybrids do not complete development & those that do are frail. sympatric speciation?

AP Biology Mules are vigorous, but sterile Reduced hybrid fertility  Even if hybrids are vigorous they may be sterile  chromosomes of parents may differ in number or structure & meiosis in hybrids may fail to produce normal gametes Donkeys have 62 chromosomes (31 pairs) Horses have 64 chromosomes (32 pairs) Mules have 63 chromosomes!

AP Biology Hybrid breakdown  Hybrids may be fertile & viable in first generation, but when they mate offspring are feeble or sterile In strains of cultivated rice, hybrids are vigorous but plants in next generation are small & sterile. On path to separate species. In strains of cultivated rice, hybrids are vigorous but plants in next generation are small & sterile. On path to separate species. sympatric speciation?

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

AP Biology Gradualism  Gradual divergence over long spans of time  assume that big changes occur as the accumulation of many small ones

AP Biology 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

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AP Biology Fitness  Survival & Reproductive success  individuals with one phenotype leave more surviving offspring Body size & egg laying in water striders

AP Biology Variation & natural selection  Variation is the raw material for natural selection  there have to be differences within population  some individuals must be more fit than others

AP Biology Mean beak depth of parents (mm) Medium ground finch Dry year Wet year Beak depth Beak depth of offspring (mm) Where does Variation come from?  Mutation  random changes to DNA  errors in mitosis & meiosis  environmental damage  Sex  mixing of alleles  recombination of alleles  new arrangements in every offspring  new combinations = new phenotypes  spreads variation  offspring inherit traits from parent

AP Biology 5 Agents of evolutionary change MutationGene Flow Genetic DriftSelection Non-random mating

AP Biology 1. Mutation & Variation  Mutation creates variation  new mutations are constantly appearing  Mutation changes DNA sequence  changes amino acid sequence?  changes protein?  changes structure?  changes function?  changes in protein may change phenotype & therefore change fitness

AP Biology 2. Gene Flow  Movement of individuals & alleles in & out of populations  seed & pollen distribution by wind & insect  migration of animals  sub-populations may have different allele frequencies  causes genetic mixing across regions  reduce differences between populations

AP Biology 3. Non-random mating  Sexual selection

AP Biology Warbler finch Tree finches Ground finches 4. Genetic drift  Effect of chance events  founder effect  small group splinters off & starts a new colony  bottleneck  some factor (disaster) reduces population to small number & then population recovers & expands again

AP Biology Founder effect  When a new population is started by only a few individuals  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

AP Biology 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

AP Biology 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

AP Biology Conservation issues  Bottlenecking is an important concept in conservation biology of endangered species  loss of alleles from gene pool  reduces variation  reduces adaptability Breeding programs must consciously outcross Peregrine Falcon Golden Lion Tamarin

AP Biology 5. Natural selection  Differential survival & reproduction due to changing environmental conditions  climate change  food source availability  predators, parasites, diseases  toxins  combinations of alleles that provide “fitness” increase in the population  adaptive evolutionary change

AP Biology 5 Agents of evolutionary change MutationGene Flow Genetic DriftSelection Non-random mating

AP Biology

Hardy-Weinberg Theorem genetic structure of a non-evolving population remains constant + sexual recombination cannot alter the relative frequencies of alleles - Hardy-Weinberg equilibrium Hardy-Weinberg equation p 2 + 2pq + q 2 = 1 p 2 : frequency of AA genotype 2pq: frequency of Aa genotype q 2 : frequency of aa genotype - p: frequency of A allele - q: frequency of a allele

AP Biology Hardy-Weinberg  HW law states --> original of a genotypes alleles remains CONSTANT  HW Equilibrium... is defined algebraically any gene with 2 allelic forms... A and a  let frequency of one allele (A) = p & frequency of other allele (a) = q  then by definition, p + q = 1  HW equation... (p + q)2 = p2 + 2 pq + q2 = 1  AA Aa aa

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