Download presentation
Presentation is loading. Please wait.
Published byLouisa Chambers Modified over 9 years ago
2
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
3
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)
4
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)
5
Mom, Dad… There’s something you need to know… I’m a MAMMAL! The Origin of Species
6
“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.
7
So…what is a species? Biological species concept population whose members can interbreed & produce viable, fertile offspring reproductively compatible Western MeadowlarkEastern Meadowlark Distinct species: songs & behaviors are different enough to prevent interbreeding
8
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
9
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
10
Begin class by working on speciation vocabulary assignment for 10 minutes Please do so QUIETLY
11
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=p 2 +2pq + q 2 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?
12
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 Crossing Over (meiosis) In your notes, fill in the t-chart above with the terms listed to the right
13
Isolation Leads to Speciation
14
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
15
PRE-reproduction barriers Obstacle to mating or to fertilization if mating occurs behavioral isolation geographic isolation ecological isolation temporal isolation mechanical isolation gametic isolation
16
Geographic isolation Species occur in different areas physical barrier 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 Ammospermophilus spp
17
Geographical Isolation
18
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
19
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.
20
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
21
Temporal Isolation
22
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
23
firefly courtship displays courtship display of Gray-Crowned Cranes, Kenya courtship songs of sympatric species of lacewings Recognizing your own species
24
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
25
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! Damsel fly penises Animals
26
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.
27
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
28
POST-reproduction barriers Prevent hybrid offspring from developing into a viable, fertile adult reduced hybrid viability reduced hybrid fertility hybrid breakdown zebroid
29
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.
30
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!
32
Reduced Hybrid Fertility
33
The Liger -massive, but sterile
34
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. In some strains of cultivated rice, hybrids are vigorous but plants in next generation are small & sterile. On path to separate species.
35
Isolation Can Lead to Speciation
36
One Gene Pool
37
Isolation
38
Independent Adaptation
39
Many Generations
40
Removal of Barrier
41
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?
42
Trends in Evolution Adaptive Radiation Divergent Evolution Convergent Evolution Gradualism Punctuated Equilibrium Polyploidy Transient Polymorphism Balanced Polymorphism
43
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
44
Adaptive Radiation Rapid and repeated divergence Often occurs when a multiple varying niches are available
46
Convergent Evolution Organisms sometimes adapt similar solutions to physiological problems presented by similar selective pressures Unrelated species show striking similarities
47
Convergent Evolution of Marsupial and Placental Mammals
48
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
50
Gradualism Gradual divergence over long spans of time assume that big changes occur as the accumulation of many small ones
51
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
52
Visualizing Evolution
53
The Cambrian Explosion: Evidence of Punctuated Equilibrium
54
The Tale of Two Snails
55
Environment Changes
56
Snails in new environment adapt
57
Two different population
58
Environment keeps changing
59
Survival of the Fittest
60
Everything’s back to normal (kind of)
61
The Fossil Record
62
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
64
Speciation via polyploidy A diploid cell undergoes failed meiosis, producing diploid gametes, which self-fertilize to produce a tetraploid zygote.
65
Polymorphisms: Traits with multiple, distinct phenotypes (morphs)
66
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.
67
Pepper Moths
68
Balanced Polymorphism The various morphs are maintained with a population throughout multiple generations Sickle Cell Anemia is the most thoroughly researched example of this.
69
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?
Similar presentations
© 2025 SlidePlayer.com. Inc.
All rights reserved.