BI111 Lecture Notes - Lecture 3: Carl Linnaeus, Ring Species, Reproductive Isolation

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9 Feb 2017
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-Carl Linnaeus, AKA the "Father" of modern taxonomy and "Princeps botanicorum" binary
nomenclature: Genus and Species (a nested hierarchy)
The Nested Hierarchy of Life
So what is a Species?
A group of organisms that is biologically "distinct" from others and evolving along a lineage
o HOW is it distinct? WHY is it a group?, and WHAT makes and organisms an "other"?
o A long-standing question, many (>22) possible answers.. Depends on Species Concept
What is a species concept?
A set of conditions that are necessary and sufficient to identify a group of individuals as a species
Species concepts do not only define what a species is, but in doing so, they also define what
speciation is
Why do we need a species concept?
Important to many biologists working in the fields of:
o Taxonomy
o Evolutionary biology
o Ecological and Behavioural studies
o Conservation biology
Morphological Species Concept
Organisms are classified in the same species if they appear identical by morphological
(anatomical) criteria
Species delineations based on notable differences in phenotype
Pros:
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A practical approach that is widely understood by both scientists and non-scientists
Focuses on novelties that have arisen over time (diagnostic characters)
Useful for classifying the fossil record
Cons
Not useful in situations where "species" exhibit substantial phenotypic polymorphisms (or belong
to "rings")
Not useful in situations where there is no observable superficial difference between putative
species
Biological Species Concept
Species are groups of actually or potentially interbreeding individuals which are reproductively
isolated from other such groups
Species delineations based on ability to successfully interbreed and produce viable, fertile,
offspring
There is no gene flow, reproductive isolation is the key idea that keeps species distinct and gene
flow is the glue that holds the species together
Pros
Many 'sister' species are hard to distinguish
Uses species' own "perceptions" to set limits
Stresses idea that species as the key unit of evolutionary change, and that gene flow is the "glue"
that holds species together
Stepping stone for studying reasons (behavioural, ecological, physiological, morphological, etc..)
that underlie reproductive isolation
Cons
Can only be used in extant(not extinct) populations :no temporal dimension
Relies on reproductive isolation: not useful for species that are not sexually reproductive
Can you trust a species' own "perceptions"?
Gene flow can occur even between taxa that are otherwise genetically divergent (bacterial, ring
species)
Does not apply to organisms created by hybridization (a common phenomenon, especially in
plants and birds)
Reproductive Modes
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