Chapter 24

• Microevolution: change in allele frequencies in a population over time

• Macroevolution: broad pattern of evolution above the species level

Animation: Macroevolution Right-click slide / select “Play”

• Speciation, the origin of new species, is at the focal point of evolutionary theory

The biological species concept emphasizes reproductive isolation

• Species is a Latin word meaning “kind” or “appearance”

• Biologists compare morphology, physiology, biochemistry, and DNA sequences when grouping organisms

The Biological Species Concept

• The biological species concept: a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; they do not breed successfully with other populations

• Gene flow between populations holds the phenotype of a population together

Biological Species

a) are members of different populations

b) cannot mate and produce viable, fertile offspring

c) are geographically isolated

d) live in different habitats

e) Look different

Two animals are considered members of different species if they _____.

https://www.polleverywhere.com/multiple_choice_polls/NPQORV3Fk6ffpEZ

Biological Species

a) are members of different populations

b) cannot mate and produce viable, fertile offspring

c) are geographically isolated

d) live in different habitats

e) Look different

Two animals are considered members of different species if they _____.

https://www.polleverywhere.com/multiple_choice_polls/NPQORV3Fk6ffpEZ

Figure 24.2a

(a) Similarity between different species

Figure 24.2b

(b) Diversity within a species

Reproductive Isolation

• Reproductive isolation is the existence of biological factors (barriers) that impede two species from producing viable, fertile offspring

• Hybrids are the offspring of crosses between different species

• Reproductive isolation can be classified by whether factors act before or after fertilization

Homework

• 1) Page 491

• List each type of reproductive barrier, explain it, and give an example. Due tomorrow

• 2) Read pp 488-492

• 3) essay #1 due this Thursday• Typo!!!! Recheck the updated version!!!!!

Exit ticket

• What is one thing that you like about class so far, and one thing that you don’t like?

• What do you think would make this class better for you?

Figure 24.3_b

Prezygotic barriers

HabitatIsolation

TemporalIsolation

BehavioralIsolation

MechanicalIsolation

GameticIsolation

Individuals of

differentspecies

MATINGATTEMPT FERTILIZATION

(a) (c) (e) (f)

(b)

(g)

(d)

Reduced HybridViability

Reduced HybridFertility

HybridBreakdown

FERTILIZATIONVIABLE,FERTILE

OFFSPRING

Postzygotic barriers

(k)

(h) (i)

(j)

(l)

Figure 24.3_c

Limitations of the Biological Species Concept

• The biological species concept cannot be applied to fossils or asexual organisms (including all prokaryotes)

• The biological species concept emphasizes absence of gene flow

• However, gene flow can occur between distinct species

• For example, grizzly bears and polar bears can mate to produce “grolar bears”

Figure 24.4 Grizzly bear (U. arctos)

Polar bear (U. maritimus)

Hybrid “grolar bear”

Other Definitions of Species

• Other species concepts emphasize the unity within a species rather than the separateness of different species

• The morphological species concept defines a species by structural features

• It applies to sexual and asexual species but relies on subjective criteria

• The ecological species concept views a species in terms of its ecological niche

• It applies to sexual and asexual species and emphasizes the role of disruptive selection

• The phylogenetic species concept defines a species as the smallest group of individuals on a phylogenetic tree

• It applies to sexual and asexual species, but it can be difficult to determine the degree of difference required for separate species

Biological Species

a) See whether the two populations are morphologically different from each other: coloring, bone structure, and so on.

b) Determine whether captured individuals from the two different populations will mate and produce offspring in a laboratory fish tank.

c) Determine whether individuals from one population will interbreed with individuals from the other population when introduced into each other’s native habitats.

Cynotilapia afra, introduced at West Thumbi Island in Lake Malawi in the 1960s, has split into two genetically distinct populations, located at the north and south ends of the island. How can scientists determine whether these populations are now different species, according to the biological species concept?

https://www.polleverywhere.com/multiple_choice_polls/ZP4LYZENF6kKH0V

Biological Species

a) See whether the two populations are morphologically different from each other: coloring, bone structure, and so on.

b) Determine whether captured individuals from the two different populations will mate and produce offspring in a laboratory fish tank.

c) Determine whether individuals from one population will interbreed with individuals from the other population when introduced into each other’s native habitats.

Cynotilapia afra, introduced at West Thumbi Island in Lake Malawi in the 1960s, has split into two genetically distinct populations, located at the north and south ends of the island. How can scientists determine whether these populations are now different species, according to the biological species concept?