Transcript Diversity of Life Chapter 24

Diversity of Life
Chapter 24
The Origin of Species
Speciation
• Happens when microevolution causes
reproductive isolation
• What is a species?
• What mechanisms are at work as populations
diverge?
• How does this lead to macroevolution?
Evolutionary change can
lead to:
-Anagenisis; heritable changes
within a species
-Cladogenesis; heritable
changes that lead to branching
(speciation) events
Biological species concept
• A species is a population whose members can
interbreed and produce viable offspring
Biological Species Concept
• A species is a population whose members can
interbreed and produce viable offspring
• Reproductive isolation
– Prezygotic barriers
– Postzygotic barriers
Speciation details
• Biological species concept and asexual
organisms:
– Need new definition of species
• Life classification schemes can be based on :
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Morphological species concept (subjective)
Paleontological (fossil record only)
Ecological (similar niche)
Phylogenetic (unique genetic history)
Speciation and Geographic Separation
• Allopatric speciation – geographic barrier
separates a population
• Sympatric speciation – speciation within a
population
– Chromosomal changes
– Non-random mating
– Exploiting different food sources
Adaptive Radiation
• Movement of a few individuals to new
environment (founder effect)
– Eg Hawaii
• or extinction event opens new niches (dinosaurs
and mammals)
Speciation tempo:
Punctuated equilibrium:
change may occur in
relatively short time
Macroevolution and speciation
• Evolution of complex structures
– Small speciation events + geological time = incredible
diversity now and in fossil record
– Even a partial structure can provide an advantage
– If a change is heritable then selection can act on it
– Eg. eyes
Evolution and development (evo-devo)
• Development and growth from embryo to adult
based on genes that control rate, timing, and
spatial events
• Allometric growth – how body proportions alter
during development
Evolution and development (evo-devo)
• Development and growth from embryo to adult is
based on genes that control rate, timing, and
spatial events
• Allometric growth – how body proportions alter
during development
• Heterochrony – change in rate or timing of
development
Homeotic genes
• Control placement and spatial organization of
body parts
• Eg. Hox gene expression and development of
limbs
– location of expressed genes and timing play critical
role in final morphology
So, how does evolution work anyway?
• Does each change lead in one direction?
• NO! Change environmental conditions and
trends can change or end.
So, how does evolution work anyway?
• Evolution may seem random but it is dependent
on changing conditions