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 25.1of your textand relatedmaterial 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

Distribution of a Species

Allopatric Speciation

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

Distribution of a Species

Parapatric Speciation

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.

22.5 – Part 1

Figure 22.5 – Part 1

figure 22-05-1.jpg

22.4

figure 22-04.jpg

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

Isolating mechanism develops within the existing

distribution of a species

Sympatric Speciation

Isolating mechanism develops within the existing

distribution of a species

Sympatric Speciation

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 web-feet 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