Transcript Adaptive evolution

Speciation
What is a species anyway?
The idea of different species has been
around for thousands of years
- Groups of organisms share certain key
traits
The trick is figuring out how to split
species
“It is really laughable to see what different
ideas are prominent in various naturalists’
minds, when they speak of the ‘species’. It
all comes, I believe, from trying to define the
indefinable”
“I look at the term ‘species’ as one arbitrarily
given, for the sake of convenience, to a set
of individuals closely resembling each other”
What is a species?
Biological Species Concept
“actually or potentially interbreeding
populations which are reproductively
isolated from other such groups” –
Dobzhansy (1937), Mayr (1942)
….doesn’t work so well for asexuals (not to
mention hybrids)
Phylogenetic species concept
A monophyletic group composed of ‘the
smallest diagnosable cluster of individual
organisms within which there is a parental
pattern of ancestry and descent’
…look for unique traits that a group of
populations share, but are not found in other
closely related populations
What makes a good species?
1) Separation – morphological, behavioural,
genetic, etc.
2) Cohesion – actually or potentially
interbreed and occupy the same habitat
3) Monophyly – organisms and populations
must share a single most common
ancestor
4) Distinguishability – every organism has
those traits, no organism not in the
species has them
Good fences make good
neighbors
Reproductive Barriers
- Geography
- Time
- Anatomy
- Ecology
- Behaviour
- Post-zygotic
Can we detect the origin of new
species?
For most animals, the generation time is
simply too long
Experimental evolution with species like
houseflies can give us clues as to how it
happens
- 1000 flies in a chamber, traps at top and
bottom
- Plucked first 50 in top, bottom, allowed to
mate with others that flew same direction
- Repeated over generations
Result
1st round – 3-4 hours to capture 50 flies
16 gen – 10 minutes
Next:
-Mixed flies together to allow them to mate
-Almost all flies chose their own “breed”
Allopatric speciation
Classic cases of allopatric
speciation
• Galapagos finches
• Ground squirrels on Arizona sky islands
• Glaciation – salamanders (and many other
species)
Sympatric speciation
Lake Apoyo cichlids, Nicaragua
Lake Victoria Cichlids
Polyploid
speciation in
plants
Parapatric speciation
Speciation occurring in populations that live next to
each other, sharing a common border
•
•
•
•
Mexican deer mice
European house mice
Australian grasshoppers
Many bird and frog species
Ring species
Greenish
Warbler ring
species
Darren Irwin
(UBC)
Uncovering hidden species
Coevolution
Dr. Anne Gaskett
Cornell University
Types of interactions
++: mutualism
+-: parasite-host, pathogen-host, predatorprey
- -: competition
0+: commensalism
0-: one partner suffers and the other is not
impacted
Pathogen-host (+/-)
Red Queen interaction
Red Queen: coevolutionary dynamics in which the
participants struggle forever against each other with no longterm reduction in extinction probability
Sacculina parasite
Mutualism (+/+)
Competition (-/-)
Commensal (0/+)
(0/-)
How do we detect
coevolutionary speciation?
Mirror trees
Sharpshooters
Levels of coevolution
Coevolution can occur at all levels of the biological
hierarchy:
o Coevolution with elements within cells
o Ancient symbiosis
• Origin of mitochondria and chloroplasts
o
o
o
o
o
Cooperation between the sexes
Cooperation between parents and offspring
Coevolving species
Coevolving clades
Coevolution of genes and culture
Outcomes of coevolution
Butterfly mimics
o Batesian mimicry
o Mullerian mimicry
Aggressive mimicry
Plant - pollinator coevolution
Batesian mimicry:
Mocker swallowtails of Africa
Occurs when a
harmless species
imitates the warning
signals of a harmful
species directed at a
common predator
Müllerian mimicry: Parallel sets
of mimetic butterflies
Aggressive Mimicry
Cultural Coevolution