Week 11, Class 2

1
How do we define species?
That’s a
cow!
Wiki part 1: How would YOU decide if two
animals/plants/etc. were the same species or
different species?
Plato - immutable forms underlie perceived reality
Evolution happens, people!
Evolution
presents different
(non-Platonic)
perspective on
species
Ancestral bunny
How do you define species?
Morphological Species Concept
Organisms are grouped together as species
when they share similar morphological /
anatomical traits.
Phylogenetic Species Concept
Organisms are grouped together as species when they
can be shown to represent a distinct clade
Biological Species Concept
Organisms are grouped by
populations that actually
or potentially interbreed
in nature
Zonkey/zebonkey/zebronkey/zebrinny/
zebrula/zebrass/zedonk/zebadonk
It is sterile, demonstrating that horses
and zebras are different species
Part 2-4 of wiki
Problems with
Morphological Species
concept
Cryptic morphology
Sexual dimorphism
Intraspecific variation
Problems with biological species
concept
• Asexual “species”
• “Can interbreed” vs.
“do interbreed”
• Hybrids
Problems with phylogenetic species concept
Incomplete lineage sorting & Introgression
Incomplete lineage sorting
Introgression
Problems with Phylogenetic species concept
Gene genealogies from the Y chromosome and mtDNA.
Example of introgression
Llopart A et al. Genetics 2005;171:197-210
Part III: “Patterns of Speciation”
Allopatric vs. Sympatric Speciation
Barriers to gene flow lead to speciation
Allopatric
B
A
Sympatric
B
A
Barriers to gene flow here are likely
non-geographic
Such as…?
Dispersal and Vicariance
• Dispersal: Organisms
move away from one
another and become
geographically
separated
• Vicariance: Organisms
become separated from
one another when
geographic barriers
emerge
• Two processes that can
lead to sympatric
speciation?
– Polyploidy
– Habitat selection
• How can polyploidy
result in speciation?
• What two conditions
are necessary for new
species to arise?
• Genetic variation
• Barrier to gene flow
• Have Fuchsia finished
speciating?
NO
Advanced Studies:
Mosquitoes and Cougars