Outcomes of Natural Selection
• Changes in a population in response to
fluctuating environment
• Formation of new species
What is a Species?
Species is Latin for “kind” or
“appearance” - therefore, we are
referring to something that is
similar in some way
Why are Species Important?
• Species fit into the hierarchy of life
beginning with the population level
• Types of species present over geological
time important in understanding gains
and losses of diversity
Okay, So What is a Species?
• Biological Species Concept (Mayr 1942)
• A group of actually or potentially
interbreeding individuals that are
capable of producing viable offspring and
are reproductively isolated from other
individuals
Biological Species Concept
• Actually or potentially interbreeding?
• Viable offspring?
• Reproductively isolated?
Limitations of the
Biological Species Concept
• Does not fit all situations
• Depends on sexual reproduction
– Some species reproduce asexually or without
a mate
• How to deal with subspecies?
– Subspecies may represent the middle stages
of speciation (formation of new species)
See Table 25.1
of your text
and related
material in the
text
Reproductive Isolation
• Prezygotic Isolation - mechanisms
develop that prevent interbreeding
• Postzygotic Isolation - Interbreeding
takes place but either the embryo does
not develop or sterility of offspring
prevents further interbreeding
Fig. 25.2-1
Fig. 25.3
Temporal Isolation – Reproductively active at different
times of the year
Fig. 25.4
Behavioral Isolation – Mating behaviors become
different over time.
Fig. 25.2-2
Fig. 25.2-3
Speciation
• Speciation requires that some members
of a population become reproductively
isolated in some way
• Therefore, any process or action that
leads to part of a population to stop
interbreeding with the rest of the
population (if over long enough period of
time) can lead to speciation
See Feature Investigation as an
example of reproductive isolating
mechanism directly linked to the
character on which selective force
is acting (p. 515 – 517)
Note – book addresses allopatric
speciation differently from the way
I (and a number of people) do
Allopatric Speciation
Distribution of a Species
Geographic Barrier Splits Distribution
No longer interbreeding; therefore, no exchange
of genes and could be undergoing different selection
pressures
Over time, the gene pool of each group
can become quit different
If two groups are brought back together and
do not interbreed, they are now two separate species
figure 22-03.jpg
Parapatric Speciation
• Members of a population move into a
new habitat
• No longer interbreed with individuals
from the original range
Parapatric Speciation
Distribution of a Species
Individuals move into a new habitat
If no interbreeding occurs between individuals
in new habitat and those in the old, reproductive
isolating mechanisms can develop.
figure 22-05-1.jpg
22.5 – Part 1
Figure 22.5 – Part 1
figure 22-04.jpg
22.4
Sympatric Speciation
• Occurs in same habitat (adaptation to
local environments)
• Abrupt genetic change
• Common in plants
• Polyploidy (see Fig. 25.11)
• Can occur with balancing selection
Sympatric Speciation
Isolating mechanism develops within the existing
distribution of a species
Sympatric Speciation
Isolating mechanism develops within the existing
distribution of a species
Speciation
• Speciation involves individuals of an
existing species to branch off to form new
species
• For this to happen, the new species must
become reproductively isolated from the
original group
• If they are not reproductively isolated,
they continue to interbreed and are not
different species
Evolutionary Developmental Biology
• Comparison of development of organisms
to understand evolutionary relationship
and ancestral linkages
– Theory of Recapitulation
– Principle of Continuity
– Signature Principle
Figure 25-14
• Webbed vs unwebbed
feet
• Two genes
– BMP4 = gene for foot
development
– Gremlin = gene inhibits
BMP4
• Natural selection takes
over
• Can introduce gremlin
gene and produce webfeet in chickens
Hox Genes – Fig. 25-15
• Controller genes
• Regulate activation of other genes
• Critical in the development of “body
plans”
• The more Hox genes, the greater the
complexity
Genomes and Proteomes
• Evolution of eye
• Visual eye has
evolved
independently in a
number of animal
groups
Fig. 25.18