systematics taxonomy
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SYSTEMATICS/ TAXONOMY. CHAPTER 13 BIOL 1120. SPECIES. MACROEVOLUTION—large, complex changes in life Changes accumulate in populations slowly over time TIME!!!!! Evolution—produced diversity of life Organisms grouped into species—distinct types of organisms

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systematics taxonomy



BIOL 1120

  • MACROEVOLUTION—large, complex changes in life
    • Changes accumulate in populations slowly over time
    • TIME!!!!!
    • Evolution—produced diversity of life
    • Organisms grouped into species—distinct types of organisms
    • The meaning of the term “species” has evolved over time
linnaeus 1707 1778
Linnaeus (1707-1778)
  • Species—all examples of creatures that were alike in minute detail of body structure
  • Two-word naming—binomial nomenclature
    • First name—genus
    • Second name—species
  • Hierarchical system for classification: grouped similar genera into orders, classes, kingdoms
  • His system did not consider evolutionary relationships (each species was created separately and could not change)---meaning species could not appear/disappear, not related to one another
darwin 1809 1882
Darwin (1809-1882)
  • Connected species diversity to evolution
  • As natural selection became accepted, scientists no longer viewed classification as a way to just organize life
  • Classification became thought of as hypotheses about the evolutionary history of life
ernest mayr 1940s
Ernest Mayr (1940s)
  • Amended Linneaus’s and Darwin’s work

by considering reproduction and genetics.

  • Biological species—a population, or group of populations, whose members can interbreed and produce fertile offspring
  • Speciation (formation new species) occurs when members of a population can no longer successful interbreed
  • Species—does not rely on physical appearance (less subjective than Linnaeus’s observations)
  • Linneaus-2 similar looking butterflies cannot belong to different species
  • Mayr—if two groups can produce fertile offspring, share a gene pool, same species
species conflicts
  • Mayr’s concept of species—cannot relate to asexual reproducers
  • Cannot apply to extinct organisms (fossil)
  • Some organisms can interbreed in captivity, but do not in nature
  • Reproductive isolation is not absolute—closely related plants can produce fertile offspring together
  • Species concept cannot always be used to decide if organisms are the same/different species
  • DNA analysis is helpful (if >97% identical, same species)
    • DNA drawback—cannot determine if organisms currently share a gene pool
    • ISOLATION is mot common criterion used to define species
reproductive barriers speciation
Reproductive Barriers/Speciation
  • Interruption in courtship, fertilization, embryo formation, or offspring development.
  • 2 broad groups: prezygotic and prostzygotic
    • Prezygotic occur before formation of zygote
    • Postzygotic: reduce the fitness of a hybrid offspring (offspring from two different species)
prezygotic barriers affect the ability of two species to combine gametes and form a zygote
Prezygotic BarriersAffect the ability of two species to combine gametes and form a zygote
  • Barriers include:
    • Ecological (habitat) isolation: difference in habitat preference in same geographic area
    • Temporal isolation: Mating will not occur if two species are active at different times of day or reach reproductive maturity at different times of year
    • Behavioral isolation: behavioral differences (distinct calls of different species of tree frogs to attract mates
    • Mechanical isolation: any change in the shape of gamete delivering or receiving structures can prevent interbreeding
    • Gametic isolation: sperm cannot fertilize egg; aquatic organisms release sperm, gametes have distinct surface molecules to recognize gametes
postzygotic barriers hybrid incompatibility
Postzygotic Barriers (hybrid incompatibility)
  • Barriers include:
    • Hybrid inviability: hybrid embryo dies before reaching reproductive maturity; genes of parents incompatible
    • Hybrid infertility (sterility): mule; infertile because horse egg has 1> chromosome than donkey, meiosis does not occur because chromosomes are not homologous
    • Hybrid breakdown: a hybrid that can reproduce, but their offspring may have abnormalities that reduce their fitness

Successful hybridization rare in animals; occurs frequently in plants

speciation spatial patterns
Allopatric SpeciationSpeciation/Spatial Patterns
  • allo-other; patric-fatherland
  • Geographic barrier
  • River, desert, glacier, changes in sea level, formation or destruction of mountains, bodies of water
  • No interaction=no gene flow
  • Microevol. act independently in each group
  • Most common mechanism; abundant evidence
speciation spatial patterns1
Sympatric SpeciationSpeciation/Spatial Patterns
  • Sym-together
  • Populations diverge genetically while living in the same area
  • Habitats-consist of microenvironments; species specialize in different zones
  • Plants: polyploidy, increases the # of sets of chromosomes
  • Occurs when gametes of 2 diff species fuse; also when meiosis fails
  • ½ flowering plants are polyploids; 95% ferns
  • Rare in animals (extra chromosomes are often fatal)
speciation spatial patterns2
ParapatricSpeciationSpeciation/Spatial Patterns
  • Para-alongside
  • Part of a population enters a new habitat bordering range of parent species
  • Gene flow can occur among individuals that venture into shared border zone
  • Can be a result of disruptive selection: ind. w/ intermediate forms have lower fitness than at either extreme; selection would counteract gene flow by eliminating ind. not well suited for either habitat
speciation gradualism

One species gradually transforms into another through a series of intermediate stages


speciation punctuated equilibrium
Gould and Eldredge

Brief bursts of rapid evolution interrupting long period of little change

(transitional forms don’t exist—explains lack in fossil record)

Fits w/allopatric speciation – geographic isolation

Speciation—Punctuated equilibrium
speciation and adaptive radiation
Speciation and Adaptive Radiation
  • Occurs in rapid bursts
  • Gives rise to multiple specialized forms in a short time
  • Heterogeneous environment (multiple food sources)
  • Death of an entire species
  • Factors:
    • Failure to adapt to environmental change
    • Lack of alleles in gene pool to produce fertile offspring
    • Habitat loss
    • Predators
    • Disease
    • Smaller populations likely to endure a major change
    • Low genetic diversity
    • Inbreeding (lethal recessive alleles, reduce reproduction/survivabilty)
    • HUMANS!!!!
  • Background extinction rate
    • Gradual loss of species as populations shrink when facing new challenges
  • Mass extinction
    • A great number of species disappear over short period of time (impact theory)
taxonomic hierarchy
Taxonomic Hierarchy
  • Taxonomists—classify based on similarities
    • 3 Domains (Archaea, Bacteria, Eukarya)
    • Kingdom King
    • Phylum Phillip
    • Class Called
    • Order On
    • Family Five
    • Genus Great
    • Species Soldiers
    • Taxa: a group at any rank
    • The more features two organisms share, the more taxonomic levels they share
  • Evolutionary tree (also called phylogeny)
    • Illustrate specie’s relationships based on decent from common ancestors
    • Evidence used to construct:
      • Anatomical features of fossils and existing organisms
      • Behaviors
      • Physiological adaptations
      • Molecular sequences
      • May be misleading
        • Cladistics solves this problem
  • Phylogenetic system
  • Groups by distinguishing between ancestral and derived characters
  • Ancestral character: inherited traits that resemble ancestors
  • Derived character: features that are different that the ancestor
  • Builds on concept of homology (homologous structures-common ancestor)
  • Shared, derived characters are used to define groups
  • A clade (monophyletic group) group of organisms consisting of a common ancestor and all its descendants
  • Treelike diagram depicting shared, derived characteristics (based on historical relationships/ not similarities)
  • Tips of branches = taxa (existing species)
  • node = indicates where two groups arose from a common ancestor
  • Branching pattern =

populations that diverge

genetically, split off, form

new species

Common ancestor

Common ancestor