Another Great Moment in Evolution

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Another Great Moment in Evolution
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• What is a species?
• Groups of interbreeding natural populations that
  are reproductively isolated from other such
  groups
• often species have a species-specific niche
• Monotypic Species
• Lack subspecies, e.g., the Catbird in U.S.
• Polytypic Species
• Most species consist of local populations that
  are more or less different from each other
• Taxonomists may find morphological differences
  among these local populations
• such local populations are called subspecies or
  varieties by botanists

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e.g.,
phasma decoloratus niveiventris
Subspecies of Beach Mice or Old Field
Mice Peromyscus polionotus
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• Sibling Species - sympatric populations that are
  morphologically similar or nearly identical and
  yet reproductively isolated
• e.g., Fruit flies Drosophila poseudoobscura and
• Drosophila persimilus were once thought to be one
  species
• crosses yield fertile and sterile

• salivary gland chromosomes were found to be
  different
• subtle differences in their anatomies were found
• sibling species are most common among species
  that
• use chemical communication, i.e., insects

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• Sympatric Species - closely related species that
  occupy the same geographic area at the same time
• if hybridization is rare (1/1000 or 1/10,000
  matings) separate species can be supported
• e.g., Florida oaks - Laurel oak and Water oak
• Allopatric Species - closely related species
  whose geographic ranges do not overlap
• cant determine if distinct biological species
  until opportunity to test reproductive isolation
• often these ranges are adjacent

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U.S. Distribution of Gopherus
G. polyphemus
G. agassizii
G. berlandieri
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• Variation within a Population
• Polymorphism - is a case where two or more
  discontinuous forms of a species found in the
  same locality in such proportions that the rarest
  of the forms cannot be maintained merely by
  recurrent mutation
• nearly all animals exhibit polymorphisms
• e.g., hair color, Rh factor, Blood type as other
  morphologic, physiologic, behavioral traits
• height in humans is not an example, it is
  continuous
• genetic control may be a single pair of alleles
  or linked genes
• in some cases heterozygosity is advantageous over
  homozygosity which ensures coexistence of alleles

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• Transient Polymorphism - case where a rare gene
  gains some advantage and spreads until its former
  normal allele is reduced to the status of a
  mutant
• This may occur if population invades a new
  environment or if the environment changes
• Best Example - Industrial Melanism of Biston
  betularia the peppered moth

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• B. betularia possess a melanic form carbonaria
• Studied in great detail in England
• 1st black specimen was caught in 1848 near
  Manchester during the midst of the industrial
  revolution
• By 1895 98 of the population was melanistic
• Evidence for environmental Change
• Tremendous pollution from burning coal destroyed
  the lichen cover on tree bark
• B. betularia was camouflaged on lichen-covered
  bark, but conspicuous on lichenless bark
• Vice versa for B. carbonaria

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B. betularia
B. carbonaria
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• Kettlewell released polymorphic moths to study
  their survival rates
• recaptured
• betularia carbonaria
• Dorset (unpolluted) 12.5 6.3
• Birmingham (polluted) 25.0 52.3
• Birds were the selective force, the non-cryptic
  forms made for easy pickens
• Worldwide over 200 species of moths have shown an
  increase in their melanic form
• Industrial Melanism has proved to be one of the
  most dramatic examples of evolution in action

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1960 1970
1980 1986