Transcript Speciation
Review All populations of species have within them genetic variation that results in qualitative and quantitative differences in phenotype Environments cycle through periods of stasis and flux Organisms best suited to compete for available resources produce the most viable offspring What are the sources of variation? Mutations in genes Recombination of alleles during meiosis (crossing over) Orientation of homologous chromosomes during metaphase I Fertilization (one sperm and egg out of many variations) What causes the change of variation (allele frequency) within a population? Mutations Gene flow (immigration) Nonrandom mating Genetic drift (founder and bottleneck effects) Selection (artificial and natural) The Origin of Species Mom, Dad… There’s something you need to know… I’m a MAMMAL! “That mystery of mysteries…” Darwin never actually tackled how new species arose… Both in space and time, we seem to be brought somewhat near to that great fact —that mystery of mysteries— the first appearance of new beings on this Earth. So…what is a species? Biological species concept 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 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 Speciation The process by which a new species is formed from a related preexisting species The development of a new branch on the tree of life The formation of a new and isolated gene pool Begin class by working on speciation vocabulary assignment for 10 minutes Please do so QUIETLY Hardy-Weinberg Equilibrium Assume a population of monkeys living on an island is in Hardy-Weinberg equilibrium No mutations, large population size, no gene flow, no genetic drift, no natural selection. This means that the allele frequencies of the gene pool does not change from one generation to the next. 1=p2 +2pq + q2 If 25% of the monkeys exhibit the dominant trait of black fur, and there are 200 monkeys in the population, how many of have a heterozygous genotype? Factors the affect variation within a population (Changes allele frequency in a gene pool) Reduces Variation Increases Variation Mutations Immigration Independent Assortment Bottleneck Effect Natural Selection Random Fertilization Emmigration Non-random Mating In your notes, fill in the t-chart above with the terms listed to the right Crossing Over (meiosis) Isolation Leads to Speciation Types of Isolating Mechanisms Pre-zygotic Isolating Mechanisms Ecological Geographical Mechanical Temporal Behavioral Gametic Post-zygotic Isolating Mechanisms Reduced Hybrid Viability Reduced Hybrid Fertility Hybrid Breakdown PRE-reproduction barriers Obstacle to mating or to fertilization if mating occurs geographic isolation behavioral isolation ecological isolation temporal isolation mechanical isolation gametic isolation Geographic isolation Species occur in different areas physical barrier Ammospermophilus spp Ex. canyon, river, forest, desert, ocean, mountain, etc. 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 Geographical Isolation Ecological isolation Species occur in same region, but utilize habitats differently so they rarely encounter each other Sympatric speciation (same country) 2 species of garter snake, Thamnophis, occur in same area, but one lives in water & other is terrestrial Ecological Isolation The Anopheles genus consists of six mosquito species The species are virtually indistinguishable morphologically, but are isolated reproductively They breed in different habitats. Some breed in brackish water, others in running fresh water, and still others in stagnant fresh water. Temporal isolation Species that breed during different times of day, different seasons, or different years cannot mix gametes reproductive isolation sympatric speciation Eastern spotted skunk (L) & western spotted skunk (R) overlap in range but eastern mates in late winter & western mates in late summer Temporal Isolation Behavioral isolation Unique behavioral patterns & rituals isolate species identifies members of species attract mates of same species • courtship rituals, mating calls, etc. Blue footed boobies mate only after a courtship display unique to their species Recognizing your own species courtship songs of sympatric species of lacewings courtship display of Gray-Crowned Cranes, Kenya firefly courtship displays Mechanical isolation Morphological differences can prevent successful mating Plants 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. Mechanical isolation Animals 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! Damsel fly penises Mechanical isolation Bush babies, a group of small arboreal primates, are divided into several species based on mechanical isolation. Each species has distinctly shaped genitalia that, like locks and keys, only fit with the genitalia of its own species. 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 POST-reproduction barriers Prevent hybrid offspring from developing into a viable, fertile adult reduced hybrid viability reduced hybrid fertility hybrid breakdown zebroid 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. 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 Mules are vigorous, but sterile Horses have 64 chromosomes (32 pairs) Donkeys have 62 chromosomes Mules have 63 chromosomes! (31 pairs) Reduced Hybrid Fertility The Liger -massive, but sterile Hybrid breakdown Hybrids may be fertile & viable in first generation, but when they mate offspring are feeble or sterile In some strains of cultivated rice, hybrids are vigorous but plants in next generation are small & sterile. On path to separate species. Isolation Can Lead to Speciation One Gene Pool Isolation Independent Adaptation Many Generations Removal of Barrier Design an Experiment! Work with a partner, record your ideas on a separate sheet of paper that will be turned in. Choose a laboratory organism… Fruit fly, convict cichlid, pea plant Develop an experiment that you think could result in the formation of two distinct species from the original. Describe your procedure in as much detail as you can, as if you were going to perform this experiment. Hint: How will you know when two species have formed? Trends in Evolution Adaptive Radiation Divergent Evolution Convergent Evolution Gradualism Punctuated Equilibrium Polyploidy Transient Polymorphism Balanced Polymorphism Divergent Evolution Speciation often happens repeatedly, to form a group of species from one ancestral lineage. Often these species evolve in different ways due to random genetic variation and varying selective pressures This is known as divergence Adaptive Radiation Rapid and repeated divergence Often occurs when a multiple varying niches are available Convergent Evolution Organisms sometimes adapt similar solutions to physiological problems presented by similar selective pressures Unrelated species show striking similarities Convergent Evolution of Marsupial and Placental Mammals 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 Gradualism Gradual divergence over long spans of time assume that big changes occur as the accumulation of many small ones 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 1st bud from parent population Visualizing Evolution The Cambrian Explosion: Evidence of Punctuated Equilibrium The Tale of Two Snails Environment Changes Snails in new environment adapt Two different population Environment keeps changing Survival of the Fittest Everything’s back to normal (kind of) The Fossil Record Polyploidy Errors during meiotic cell division result in extra sets of chromosomes, a condition called polyploidy 30-70% of flowering plants thought to be polyploid Polyploid types are labeled according to the number of chromosome sets in the nucleus: triploid (three sets; 3x), for example the phylum Tardigrada tetraploid (four sets; 4x), for example Salmonidae fish Pentaploid (five sets; 5x) hexaploid (six sets; 6x), for example wheat, kiwifruit octaploid (eight sets; 8x), for example Acipenser (genus of sturgeon fish) decaploid (ten sets; 10x), for example certain strawberries dodecaploid (twelve sets; 12x), for example the plant Celosia argentea and the amphibian Xenopus ruwenzoriensis Speciation via polyploidy A diploid cell undergoes failed meiosis, producing diploid gametes, which self-fertilize to produce a tetraploid zygote. Polymorphisms: Traits with multiple, distinct phenotypes (morphs) Transient Polymorphisms One morph or allele with gradually replace the other as generations pass because it confers a reproductive advantage Pepper Moth is the classic example of this. Pepper Moths Balanced Polymorphism The various morphs are maintained with a population throughout multiple generations Sickle Cell Anemia is the most thoroughly researched example of this. 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 Is this also true for humans as well?