BIOL 100 Chapter Notes - Chapter 14: Coccinellidae, Species Problem, Carl Linnaeus
Chapter 14: Speciation and Extinction
14.1 The Definition of Species Has Evolved over Time
•Macroevolution: large, complex changes in life’s panorama
•Species: distinct types of organisms
A. Linnaeus Devised the Binomial Naming System
•Swedish botanist Carolus Linnaeus gave every species a two-word name
•Each name combines the broader classification genus with the word that designates the species
•humans: homo sapiens
•Devised a hierarchical system for classifying species
B. Ernst Mayr Developed the Biological Species Concept
•Harvard biologist Ernst Mayr defined a biological species as a population, or group of populations,
whose members can interbreed and produce fertile offspring
•Speciation: formation of new species, occurs when members of a population can no longer interbreed
•Mayr’s species definition raises difficulties:
•can’t apply to asexually reproducing organisms
•impossible to apply the biological species definition to extinct organisms known only from fossils
•some types of organisms have the potential to interbreed in captivity, but don’t always do so
•reproductive isolation isn’t always absolute
14.2 Reproductive Barriers Cause Species to Diverge
•Biologists divide mechanisms of reproductive isolation into two groups: prezygotic and postzygotic
A. Prezygotic Barriers Prevent Fertilization
•occur before the formation of the zygote, or fertilized egg
•mechanisms of prezygotic reproductive isolation affect ability of two species to combine gametes and
form a zygote
•includes the following:
•Ecological (habitat) isolation: A difference in habitat preference can separate two populations in the
same geographic area
•ex) one species of ladybird beetle eats one type of plant, while a closely related species eats a
different plant. The two species never occur on the same host plant, although they interbreed in the
lab. The different habitat preferences are the reproductive barrier that keeps the gene pools separate
•Temporal isolation: Two species that share a habitat will not mate if they are active at different times
of day or reach reproductive maturity at different times of the year
•ex) Among field cricks in Virginia, one species takes longer to develop than another, os the adults of
the two species may not meet until late in the season if at all
•Behavioral isolation: behavioral differences may prevent two closely related species from mating
•ex) males of tree frogs use distinct calls to attract mates, females choose based on unique calls
•Mechanical isolation: any shape in of the gamete-delivering or receiving structures may prevent
groups from interbreeding
•ex) although two species of sage plant in California can interbreed, they rarely do because they use
different pollinators
•Gametic isolation: if a sperm can’t fertilize an egg cell, then no reproduction will occur
•ex) Sea urchins release sperm and egg cells into the water; displays surface molecules that enable
an egg to recognize sperm of the same species
B. Post zygotic Barriers Prevent Viable or Fertile Offspring
•postzygotic reproductive isolation may keep species separate by selecting against the hybrid offspring,
preventing genetic exchange between the populations
•includes the following:
•Hybrid inviability: a hybrid embryo may die before reaching reproductive maturity because the genes
of its parents are incompatible
•ex) hybrid seeds fail to germinate or seedlings die soon after sprouting
•Hybrid infertility (sterility): some hybrid offspring are unable to reproduce
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