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 Speciation

Speciation/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 Speciation

Speciation/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


Speciation/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