BIOL 1030 Exam 1

Chapters 22-24, 26-28

evolution

“descent with modification”; both a pattern and a process.

The Darwinian Revolution

• challenged traditional views (young Earth with unchanging species)

• Darwin’s ideas had deep historical roots

• the study of fossils (remains/ traces of organisms) helped to lay the groundwork for Darwin’s ideas.

Superposition

Paleontology

Study of Fossils

George Cuvier (1769-1832)

• thought that older species were less similar to present species

• species could appear/disappear when moving to another layer (extinction common, against evolution)

• Catastrophism

Catastrophism

(disproven) speculating that each boundary between strata represents a catastrophe

Thomas Malthus (1766-1834)

• “an essay on the Principle of Population”

• Human populations will outpace food production

James Hutton (1726-1797) and Charles Lyell (1797-1875)

• perceived that changes in Earth’s surface can result from slow continous actions still operating today.

• Lyell’s principle of uniformitarianism states that the mechanisms of change are constant and slow

• this view strongly influenced Darwin’s thinking

Jean- Baptiste Lamarck (1744-1829)

• first hypothesis of evolution

• hypothesized “use and disuse of body parts” and the “inheritance of acquired characteristics”

• the mechanisms he proposed are unsupported by evidence

• acquired traits cannot be inherited (ex. Haircuts are not inherited)

Darwin’s Research

• during his travels on the Beagle, Darwin collected specimens of South American plants and animals

• He observed that fossils resembled living species from the same regions, and resembled other species of nearby regions.

• Darwin was influenced by Lyell’s “Principles of Geology” and thought that the earth was more than 6000 years old.

Adaptation

• inherited characteristics of organisms that enhance their survival and reproduction in specific environments

• ex: Galapagos finches (beaks adapted to food sources)

Evolution in Beta Development

• Darwin perceived adaptation to the environment and the origin of new species as closely related processes

• In 1844, Darwin wrote an essay on natural selection as the mechanism of descent with modification

  • he did not introduce his theory publicly

Natural Selection definition

a process in which individuals with favorable inheried traits are more liekly to survive and reproduce

Wallace’s Influence on Darwin

• 1858- Darwin receives a manuscript from Alfred Russel Wallace (1823-1913), who had developed a theory of natural selection similar to Darwin’s

• Quickly after, Darwin finished “Origin” and published it the next year

“On the Origin of Species”

• explained 3 broad observations

  • unity of life

  • the diversity of life

  • the match between organisms and their environments

• Darwin never used the word evolution in the first edition

• The “descent with modification” summarized Darwin’s perception of the unity of life

  • the phrase refers to the view that all organisms are related through descnet from ancestors that lived in the remote past.

Tree of Life

• in the Darwinian view, the history of life is like a tree with branches representing life’s diversity.

• Darwin’s theory meshed well with the hierarchy of Linnaeus

• Main Branches are Eukaryotes, Bacteria, and Archaea

Darwin’s Observations

1. members of a population often vary in inherited traits

2. reproductive potential exceeds environmental tolerances

Darwin’s Inferences

1. more “fit” individuals will leave more offspring than others

2. overtime, a pipulation will change to match its environment

Natural Selection

• populations evolve overtime, individuals DO NOT

• natural selection is NOT random

• natural selection can only increase or decrease heritable traits that vary in a population (doesn’t create new traits)

• Local environment determines which traits will be selected for or selected against

Artificial Selection

• humans have modified other species by selecting and breeding individuals with desired traits

Homology

similarity resulting from common ancestry

• anatomical

• molecular (DNA)

vestigial structures

remnants of features that served important functions in the organism’s ancestors

evolutionary trees

hypotheses about the relationship among different groups

divergent evolution (based on DNA)

the evolution of homologous characteristics into new forms/phenotypes in the same clade

• % homology

• orthologs

• paralogs

orthologs

divergent evolution across two species

paralogs

divergent evolution within a species

convergent evolution (no common ancestor)

• the evolution of similar or analogous features, in distantly related groups

• does not provide info about ancestry, but does demonstrate how similar traits can be adaptive in similar biomes

analogous traits

arise when groups independently adapt to similar environments similar ways

• ex: sugar glider and flying squirrel

fossil record

provides evidence of the extinction of species, the origin of new groups, and changes within groups over time

biogeography

the geographic distribution of species, and provides evidence of evolution

endemic species

• species that are no found anywhere else in the world

• islands have many of these that are often closely related to species on the nearest mainland or island

population

• the smallest unit of evolution (natural selection occurs on all levels: individuals, cells, genes, molecules. but evolution only occurs on this level)

• localized group of individuals capable of interbreeding and producing fertile offspring

microevolution

• a change in allele frequencies in a population over generations

• driven by natural selection, genetic drift, and gene flow

• only natural selection consistently causes adaptive evolution

genetic drift

chance events that alter allele frequencies

gene flow

• the transfer of alleles between populations

• alleles can be transferred through the movement of fertile individuals or gametes (ex: pollen)

• tend to reduce variation among populations overtime

• can increase the fitness of a population

genetic variation

• describes how allele frequencies fluctuate unpredictably from one generation to the next

• caused by differences in DNA

• tends to reduce genetic variation through losses of alleles

• phenotype is the product of inherited genotype and environmental influences with a genetic component

• natural selection can only act on variation with genetic component

discrete characters

can be classified on an either-or basis

• ex: bloodtype

quantitative characters

vary along a continuum within a population

• ex: height

sources of genetic variation

new genes and alleles can arise by mutation or gene duplication

• only mutations in cells that produce gametes can be passed to offspring

point mutation

change in one base in a gene

• silent- no change in amino acid

• missense- change in amino acid

• nonsence- change in STOP codon

effects of point mutations

• mutations in noncoding regions of DNA are often harmless

• mutations in a gene can be neutral because of redundancy in the genetic code

• mutations that result in a change to the protein are often harmful but can sometimes be beneficial

altering gene number or position

• chromosomal mutations that delete, disrupt, or rearrange many loci are typically harmful

• duplication of small pieces of DNA increases genome size and is usually less harmful

  • duplicated genes can take on new function by further mutation

  • an ancestral odorant receptor gene has been duplicated many times (ex: humans have ~380 receptors and mice have ~1200 receptors)

sexual reproduction

• can shuffle existing alleles into new combinations

• in organisms that reproduce sexually, recombination of alleles is more important than mutation in producing the genetic differences that make adaptation possible.

fixed locus

all individuals in a population are homozygous for the same allele

frequency of an allele in a population can be calculated

• diploid organisms: the total number of alleles at a locus is the total number of individuals times 2

• the total number of dominant alleles at a locus is 2 alleles for each homozygous dominant individual plus 1 allele for each heterozygous individual

allelic frequency

• will add up to 1 (100%)

• dominant (A) and recessive allele (a)

  • frequency of A is represented as p

  • frequency of a is represented as q

  • p + q = 1

genotypic frequency

• frequency of all genotypes in a population will also add up to 1

• dominant (A) and recessive allele (a)

  • frequency of A is represented as p

  • frequency of a is represented as q

  • (p+q) x (p+q) = p² +2pq + q² = 1

• p² represents frequency of AA

• q² represents frequency of aa

• 2pq represents frequency of Aa

Hardy-Weinberg Principle

• states that frequencies of alleles and genotypes in a population remain constant from generation to generation

• describes a population that is NOT evolving

• if a population does not meet the criteria of the Hardy-Weinberg principle, it can be concluded that the population is evolving

• NULL model for the case where evolution is NOT occurring

Conditions for Hardy-Weinberg Equiibirum

The five conditions for nonevolving populations are rarely met in nature

1. No mutations

2. random mating

3. no natural selection

4. extremely large population size

5. no gene flow (Immigration or emigration)

Three major factors that alter allele frequencies

1. natural selection

2. genetic drift

3. gene flow

founder effect

occurs when a few individuals becoe isolated from a larger population

bottleneck effect

• a sudden reduction in population size due to a change in the environment

• the resulting gene pool may no longer be reflective of the original population’s gene pool

• if the population remains small, it may be further affected by genetic drift

sexual selection

• it can result in sexual dimorphism, marked differences between the sexes in secondary sexual characteristics

• can drive sympatric speciation

intra-sexual selection

competition among individuals of one sex (often males) for mates of the opposite sex

inter-sexual selection

(mate choice), occurs when individuals of one sex (usually females) are choosy in selecting their mates.

neutral variation

genetic variation that does not confer a selective advantage or disadvantage

diploidy

maintains genetic variation in the form of hidden recessive alleles (heterozygotes can carry recessive alleles that are hidden from the effects of selection)

balancing selection

occurs when natural selection maintains stable frequencies of two or more phenotypic forms in a population (heterozygote advantage and frequency - dependent selection)

heterozygote advantage

occurs when heterozygotes have a higher fitness than do both homozygotes

frequency dependent selection

the fitness of a phenotype declines if it becomes too common in the population

Why Natural Selection Cannot Fashion Perfect Organisms

1. selection can act only on existing variations

2. evolution is limited by historical constraints

3. Adaptations are often compromises

4. Chance, natural selection, and the environment interact

speciation

the origin of new species, is at the focal point of evolutionary theory

evolutionary theory

must explain how new species orginate and how populations evolve

macroevolution

broad patterns of evolutionary change above the species level

biological species concept

• states that a species is a group of populations whose members have the potential to interbreed in nature and produce VIABLE, FERTILE OFFSPRING; they do no breed successfully with other populations.

• emphasizes reproductive isolation

reproductive isolation

• the existence of biological factors (barriers) that impede two species from producing viable, fertile offspring

• can be classified by whether factors act before fertilization (pre-zygotic) or after fertilization (post-zygotic)

hybrids

offspring of crosses between different species

pre-zygotic barriers

• block fertilization from occury by impeding different species from attempting to mate, preventing the successful completion of mating, and hindering fertilization if mating is successful

1. Habitat isolation

2. temporal isolation

3. behavioral isolation

4. mechanical isolation

5. gametic isolation

habitat isolation

two species encounter each other rarely, or not at all, because they occur different habitats, even though not isolated by physical barriers

• apple magots and blueberry magot fly

temporal isolation

species that breed at different times of the day, different seasons, or different years cannot mix their gametes

• western spotted skunk mates in late summer and eastern spotted skunks mate in late winter

behavioral isolation

courtship rituals and other behaviors unique to a species are effective barriers

• blue footes boobies (high step)

mechanical isolation

morphological differences can prevent successful mating (if their shells are opposite directions, their genital openings will not align)

gametic isolation

sperm of one species may not be able to fertilize eggs of another species

• red and purple seas urchin gametes cannot fuse b/c their extracellular proteins bind poorly)

post-zygotic barriers

• prevent the hybrid zygote from developing into a viable, fertile adult

1. reduced hybrid viability

2. reduced hybrid fertility

3. hybrid breakdown

reduced hybrid viability

genes of the different parent species may interact and impair the hybrids development

• most Ensatina hybrids do not complete development

reduced hybrid fertility

even if hybrids are vigorous, they may be sterile

• mules (female horse x male donkey) are usually infertile

hybrid breakdown

some first-generation hybrids are fertile, but when they mate with another species or either parent species, offspring of the next generation are feeble or sterile

limitations of the biological species concept

• it cannot be applied to fossils or asecual organisms (including all prokaryotes)

• it emphasizes absence of gene flow, however, gene flow can occur between distinct species

  • grizzly bear and polar bear can produce “grolar bears”

morphological species concept

defines a species by structural features

• applies to sexual and asexual species but relies on subjective criteria

ecological species concept

views a species in terms of its ecological niche

• it applies to sexual and asexual species and emphasizes the role of disruptive selection

phylogenetic species concept

defines a species as the smallest group of individuals on a phylogenetic tree

• it applies to sexual & asexual species, but it can be difficult to determine the degree of difference required for separate species

allopatric speciation

• a population forms a new species while geographically isolated from its parent population

• "other country”

• ex: the grand canyon

• evidence: 15 pairs of sibling species of shapping shrimp (Alpheus) are separated by the Ithmus of Panama

sympatric speciation

• a subset of a population forms a new species without geographic separation (geographically overlapping populations)

• cases are rare

• caused by gene flow reduction: polyploidy, habitat differentiation, and sexual selection

polyploidy

• the presence of extra sets of chromosomes due to accident during cell division

• much more common in plants than in animals

• oats, cotton, potatoes, tobacco, and wheat are polyploids

autopolyploid

an individual with more than two chromosomes sets, derived from ONE SPECIES (Not hybrids)

allopolyploid

a species with multiple sets of chromosomes derived from DIFFERENT SPECIES (hybrids)

habitat differentiation

sympatric speciation can also results from the appearance of new ecological niches

hybrid zone

• a region in which members of different species mate and produce hybrids

• hybrids are the result of mating between species with incomplete reproductive barriers

Hybrid Zone - Reinforcement

strengthening reproductive barriers

Hybrid Zone- Fusion

weakening reporductive barriers

Hybrid Zone- Stability

continued formation of hybrid individuals (increased fitness)

Niles Eldredge & Stephen Jay Gould

coined the term punctuated equilibria to describe periods of stasis by sudden change

Biodiversity

number of species, genera, etc

taxonomy (taxa, taxon)

the naming of groups of organisms

classification

assigning organisms to hierarchical groups

systematics

study of diversification and relationships

phylogeny

evolutionary history

Carolus Linnaeus (1707-1778)

• discovered the science of naming and classifying organisms (taxonomy)

• many of his classifications were inaccurate but much of his system persists today

• binomial nomenclature

Linnaean Classification

1. Domain

2. Kingdom

3. Phylum

4. Class

5. Order

6. Family

7. Genus

8. Species

(Dear King Phillip Comes Over For Good Soup)

clades

a lineage of organisms that is derived from a single common ancestor and contains ALL descendants

• e.g. Mammals