Cycle 8 - Lecture notes 16-17 PDF

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Professor Vera Tai Lecture...

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BIOLOGY 1001A Cycle 8 — Speciation Microevolution —> Macroevolution 

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Changes in allele frequencies in a population over time o New traits may evolve —> speciation o Process of species formation Differences evolving between populations may restrict gene flow Differences continue to accumulate separately from one population to another to the point they are considered two different species

What is a Species? "No one definition (of species) has as yet satisfied all naturalists; yet every naturalist knows vaguely what he means when he speaks of a species." – Charles Darwin, Origin of Species —> 160 years after Origin of Species, still no universal species concept o One accept does not apply to all life o Over 50 species concepts have been proposed Many ways (concepts) to identify and define a species:    

Populations that have distinctly different traits Populations that successfully mate with each other, but not with other populations Populations that do not exchange genetic material with other populations Populations that have distinct evolutionary histories

1. Ecological Species Concept 

Species = a group of organisms that are adapted to a particular set of resources (niche) in the environment

2. Morphological Species Concept — similar physical characteristics    

Species = a distinct cluster of individuals in phenotypic space. No intermediates or overlap with other clusters. Used when differences in measurable traits distinguishes species. Delineate species based on measurable, observable traits Can compare traits with fossils

BIOLOGY 1001A

PROBLEMS with the morphological Species Concept   

Phenotypic variability is not consistent for different species Difficult to distinguish species that look very similar Can identify differences, but no information on how these differences evolved

—> populations that cannot interbreed are different species (reproductive barrier) 3. Biological Species Concept  

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Species = group of interbreeding populations that are reproductively isolated from other groups Matches criteria that are typically used to define a species o A species compromises all individuals that can successfully mate and produce viable, fertile offspring Collection of alleles can potentially be shared with anyone in the species, but not outside the species Gene flow within species, cohesive, share traits o Not with other species.

—> is testable — put individuals from different populations together  Do they successfully mate? —> provides a means to explain how species have evolved  Investigate heritable traits, behaviour, physiology that lead to reproductive isolation.

PROBLEMS with Biological Species Concept   

For asexually reproducing organisms, species boundaries cannot be defined under BSC May not be possible to test whether individuals can successfully reproduce sexually Reproductive behaviour cannot be determined for extinct organisms.

4. Phylogenetic Species Concept

BIOLOGY 1001A

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Species = group of populations with a recent evolutionary history o Smallest group of populations that are all more closely related to each other than to anything else Construction of an evolutionary tree o Can use morphological information o Use genetic information = molecular phylogenetics  DNA sequences  Amino acid sequences

Ideally groups are monophyletic = all descendants from a common ancestor Must decide how much evolutionary change defines a group or species

Advantages of Phylogenetic Species Concept   

Can be applied to any/all organisms (if data can be collected) Molecular data not possible from fossils Molecular data is possible from preserved extinct animals o Ex. Mammoths frozen in permafrost, possibly amber

—> species compromise individuals/populations that share a recent evolutionary history = recent common ancestry of morphological traits.  DNA sequences, etc.  Must decide how much evolutionary change defines a species  For sexually reproducing organisms, implies reproductive isolation, but does not prove it —> can determine how traits have evolved to give rise to new species

BIOLOGY 1001A What Information to Compare Between Individuals  

Need to use info that matches the true evolution of the organisms o Shared traits reflect common ancestry ex. Traits are homologous Sometimes info is evolutionarily misleading o Homoplasies = evolved due to convergent evolution and NOT common ancestry

—> Homoplasies are evolutionarily misleading  Do not share the same ancestry or common ancestor  Similar trait, but evolved independently o Convergent evolution

Superficial Similarity: birds and bats both have wings     

Look more closely, the structure of the wings and bones is different Feathers. Vs skin supported by finger bones Birds have hollow bones Wings do not share a recent common ancestry Two different paths of evolution that resulted in wings

Misleading tree: 

Birds and bats shown to share ancestry because they share wings

Better Tree:  

Using more evolutionarily reliable information o Ex. DNA of a conserved gene Wings in birds and bats evolved independently

BIOLOGY 1001A

Comparing Species Concepts

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Different Concepts for delineating species can give you different answers o Not clear cut Male frogs have distinctive calls to attract males o Ex. Biological Species Concept DNA sequences were obtained from frogs of each population, and a phylogenetic tree was constructed: easier to decide with multiple sources of information

SUMMARY  

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Ideally, species are defined with multiple lines of evidence o Ex. Including morphology, behaviour, ecology, physiology, genetics, trees But there is not a universal definition of a species that equally applies to all life o Multiple species concepts o We have different "rules" for different groups of organisms By understanding speciation: o How do traits evolve? o How does diversity evolve? o How will a species evolve or adapt?...