Announcements
Exam 1, ♥♥♥ 14-Feb. ♥♥♥
If you last name begins with A – L: 116 RAL (right here)
If you last name begins with M – Z: 151 EVRT
Coevolution = The occurrence of genetically determined traits
in two or more species selected by the mutual interactions
controlled by these traits. -Ricklefs
Species Interactions:
- Mating (usually -,-)
- Competition (-,-)
- Predator-prey (+,-)
- Mutualism (+,+)
Character Displacement
Fig. 20.12; Ricklefs “Economy of Nature”
Displacement of beak size and diet
Fig. 20.13; Ricklefs “Economy of Nature”
What kinds of interactions can lead to
character displacement?
“Reproductive Character Displacement”
Hybridization between species
(mate recognition)
“Ecological Character Displacement”
Competition – for resources
Optimal Threshold Model
signals you want to
accept
signals you want
to reject
acceptance errors
rejection errors
adapted from Reeve 1989, Starks 2003
Species A
Allopatry
Accept
T
Reject
Frequency
Reject
Frequency
Accept
T
???
Species B
Allopatry
Dissimilarity between
template and cues
Dissimilarity between
template and cues
To avoid costly mistakes (i.e., mating with the wrong species):
Signal
Perception
Cue
Receiver
Signaler
Reject
Frequency
Accept
T
Dissimilarity between
template and cues
Green Tree Frog
Hyla cinerea
Barking Tree Frog
Hyla gratiosa
Sympatry
Allopatry
Male Hyla cinerea songs differ
In allopatry and sympatry
(with H. gratiosa)
Sympatry
Allopatry
Female Hyla cinerea preference
differs in allopatry and sympatry
Hybrid calls are unattractive!
Höbel and Gerhardt 2003, Evolution
Greenish Warbler,
Phylloscopus trochiloides
Irwin et al. 2000, Nature
A
B
C
Birds from A and C respond to each other’s mating calls.
Birds of both species at B don’t respond to each other.
“Ring” Species
Response to songs is a function of distance:
2 co-occurring species in the Caribbean
One morphologically specialized to trunk life
The other specialized for life in the branches
Hurricane
1. A and B live in sympatry
A on trunk
B on branches
3. Species A reintroduced (allopatry with B)
2. No species
4. Species A on trunk
and branches
Evidence for developmental flexibility
Anolis lizards: morphology of hind legs changes
when raised on large trunks or small branches.
Losos et al. 2002 Evolution
Anole
• Rapid evolution of species A?
• Character displacement when in sympatry?
If yes, then what
character?
Answer: phenotypic plasticity (environment)
Species A
Long leg and
Short leg
Species A – long leg
Species B – short leg
Species B
Long leg and
Short leg
Brief Recap
• Green Frogs: displacement of both male
call and female preference in sympatry
• Greenish Warbler: ring species; female
call preference in sympatry
• Sticklebacks: displacement of male
preference in sympatry (differentiating
from the role of the environment); ultimate
and proximate explanations
• Anoles: competition repressing plasticity
Predation/Parasitism
• Having your life threatened by another
organism is a heavy selection pressure.
• Getting enough to eat, especially when
you are very specialized, is a heavy
selection pressure.
Evolutionary Arms Races
BOOM!
The Red Queen Hypothesis
Red Queen said to Alice:
“…it takes all the running you
can do, to keep in the same place.”
Lewis Carroll, “Through the looking glass”
Predation/Parasitism
Coyotes discover rabbits are food
Rabbits that don’t avoid coyotes are eaten
Some rabbits are able to hide from coyotes
Coyotes can’t catch as many rabbits
Some coyotes are able to smell rabbit pheromone
Rabbits using the pheromone are eaten
Only rabbits that have altered the pheromone live
Predator-Prey, Host-Parasite
Coevolution
• Bat predators are specifically tuned to the
songs of their frog prey.
Social parasites mimic recognition
properties of their hosts.
photograph © Alex Wild 2004
Mutualisms
• Mutualism = a relationship between two species
that benefits both. – Ricklefs
• Mututalists have complimentary functions
– Obligate: they cannot survive without each other
– Facultative: they each do better when both are
present
• Obligate mutualisms have been pivotal in major
evolutionary advances.
Types of Mutualisms
• Trophic – partners provide nutrients that can’t be
obtained individually.
– Digestive bacteria, Lichens
• Defensive – one partner defends the other in
exchange for food, shelter, or etc.
– Ants and plants, humans and chickens (?)
• Dispersive – one partner transports something
for the other in exchange for food, or etc.
– Pollination