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The Origin of Species - Principles of Biology - Lecture Slides | BIO 101, Study notes of Biology

Suffolk County Community CollegeBiology
Prof. Marianne Mcnamara

Material Type: Notes; Professor: McNamara; Class: Principles of Biology; Subject: Biology; University: Suffolk County Community College; Term: Fall 2009;

Typology: Study notes

Pre 2010

Uploaded on 12/12/2009

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The Origin of Species
•If microevolution (the genetic changes within
a population over generations) were all that
ever happened, the Earth would only be
inhabited by a highly adapted version of the
first form of life
•Fortunately for us, however, the world is full
of biological diversity – many different
varieties of life forms, consisting of many
millions of distinct biological species
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Download The Origin of Species - Principles of Biology - Lecture Slides | BIO 101 and more Study notes Biology in PDF only on Docsity!

The Origin of Species

  • (^) If microevolution (the genetic changes within a population over generations) were all that ever happened, the Earth would only be inhabited by a highly adapted version of the first form of life
  • (^) Fortunately for us, however, the world is full of biological diversity – many different varieties of life forms, consisting of many millions of distinct biological species

Got biodiversity?

  • (^) Speciation (the emergence of a new species) is the bridge between microevolution and macroevolution (the broader pattern of evolutionary change over long periods of time) http://www.botany.uwc.ac.za/pssa/newsletter/images/sea-plants%20poster-A4.jpg

What defines a species?

  • (^) Biological species concept :
    • (^) A species consists of a population whose members have the potential to interbreed with one another in nature to produce viable, fertile offspring, but who cannot interbreed with other such groups
    • (^) Species are based on their ability to interbreed; not on physical similarities!

Origin of New Species

  • (^) Example: Eastern and Western Meadowlarks; 2 different species with similar shape and coloration, but differences in song help prevent interbreeding
  • (^) Barriers to breeding can be behavioral Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Speciation happens

  • (^) It takes a reproductive barrier to keep individuals of closely-related species from interbreeding
  • (^) Reproductive barriers may be behavioral, geographical, anatomical, or temporal

Allopatric Speciation

  • (^) How do reproductive barriers arise?
  • (^) One of the clearest forms of species is allopatric speciation caused by a geographic barrier
  • (^) When a geographic barrier occurs, the isolated populations each become adapted to their own environment, such that over time, they may no longer interbreed ( speciation)

Speciation

Prezygotic vs. Postzygotic Barriers

  • (^) Prezygotic – mechanisms preventing formation of a zygote; these can be ecological, behavioral, temporal, or mechanical
  • (^) Postzygotic – mechanisms preventing organisms (zygotes and beyond) from developing into a reproducing adult; these can be

Postzygotic examples

  • (^) Reduced hybrid viability - most hybrid offspring of different species do not survive; example – many species of salamanders are able to mate, but the offspring do not survive to reproduce themselves
  • (^) Reduced hybrid fertility – hybrid offspring reach maturity, but are sterile

Postzygotic example

  • (^) Mules are the reproductive product of a horse and a donkey mating
  • (^) Mules are viable (one got me nicely around Bryce Canyon, Utah without plunging me to my death…), but they are sterile
  • (^) Therefore, a horse and a donkey must be considered distinct species

Sympatric Speciation

  • (^) New species formed by having extra sets of chromosomes are considered to be polyploid
  • (^) Polyploid organisms have more than 2 complete sets of chromosomes
  • (^) For example, a polyploid containing 4 sets of chromosomes will produce diploid (2n) gametes! This species would be unable to mate with normal diploid species (which produce haploid gametes)

Parent species Diploid Polyploid (“tetraploid”) 1 Diploid gametes 2 Viable, fertile tetraploid species Self- fertilization 3 Error in cell division Polyploid cells undergo meiosis

Polyploid speciation

  • (^) Remember, polyploidy is a type of sympatric speciation
  • (^) As many as 80% of all living plants today are believed to have arisen by polyploidy!
  • (^) A polyploid contains twice (or sometimes more) the genetic diversity as its diploid predecessors, which provides an adaptive advantage!

Polyploid speciation

  • (^) Many of the plants grown for food are polyploids - (^) Oats and Barley - (^) Potatoes - (^) Bananas - (^) Peanuts - (^) Plums and Apples - (^) Wheat - (^) Coffee!