S1. Coevolution or not?
Crossbills, Squirrels, and
Pinecones
Anne-Marie Hoskinson, Laura
Conner, Susan Hester, Mary Beth
Leigh, Andrew P. Martin, Tom Powers
1
What are the conditions for
coevolution?
think – pair – share
2
Necessary conditions
1) Two or more interacting species exist in the
same place and at the same time
3
Necessary conditions
1) Two or more interacting species exist in the
same place and at the same time
AND
2) Each species affects the other species’:
A. survival
B. reproduction (fitness) OR
C. some other allele that affects A or B
4
Coevolution requires…
BOTH
• Geographic overlap of populations
• Reciprocal effects on traits
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How is this coevolution?
http://www.arkive.org/cheetah/acinonyx-jubatus/video-08c.html
What happens to the gazelles when the cheetahs
get faster?
The Plot:
In the Rocky Mountains, red squirrels and crossbills both eat
lodgepole pine seeds. In some locations, squirrels are absent.
The species interact when they occur in the same place … but
do they have reciprocal effects on one another’s traits?
http://idtools.org/id/
dried_botanical/fac
tsheet.php?name=
Pinus+contorta+va
r.+latifolia
Red squirrels
Crossbill birds
Lodgepole pine cones
After http://evolution.berkeley.edu/evosite/evo101/IIIF1Casestudyofcoevo.shtml
Image credits (L to R): http://commons.wikimedia.org/wiki/File:Tamiasciurus_hudsonicus_CT.jpg
http://commons.wikimedia.org/wiki/File:Loxia_curvirostra_NRM2.jpg
http://idtools.org/id/dried_botanical/factsheet.php?name=Pinus+contorta+var.+latifolia
7
Lodgepole Pine
http://esrd.a
lberta.ca/lan
dsforests/trees
plants/trees/
images/GFXLodgepolePine-01.jpg
Figure 1, Benkman et al. 2001. Evolution 55:282-294
http://rockymountainbushcr
aft.blogspot.com/2012/12/ro
cky-mountain-treeidentification.html
Smaller, closed,
Larger, open, fewer
seeds
seedsadapted from Figure 2, Benkman etmore
al. 2003. Am. Nat. 162:182-194.
8
Crossbills
http://bootstrap-analysis.com/bootimages/crossbills_1.jpg
Complete overlap with
pine trees
shorter, right
crossover
longer, left crossover
Variation in crossover
direction and beak depth
(length)
Watch how crossbills manipulate seeds to feed:
http://www.youtube.com/watch?v=1NvU8WG9bg0
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Red squirrels
Pines +
crossbills, but
no squirrels
until 1950
Watch a red squirrel manipulate a
cone to feed:
http://commons.wikimedia.org/wiki/File:Tamiasciu
rus_hudsonicus_CT.jpg
http://www.arkive.org/american-redsquirrel/tamiasciurus-hudsonicus/video02a.html
10
What You Will Do
• Small groups of 4
• Each group gets one Exhibit (numbered 1 – 3)
• Work with:




Modeling Evolutionary Relationships
System Map
your team’s Exhibit
each other
in order to make a claim, backed by evidence
(your Exhibit) about what’s happening
• 10 minutes
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Exhibit 1.
From Benkman (2001) Evolution 55: 282-294.
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Exhibit 2.
Upper
CI*
Survival
Best fit
line
1 = survived
0 = died
Lower
CI*
Bill Depth (mm)
From Benkman (2003) Evolution 57: 1176-1181.
* CI = 95% confidence interval 14
Value
Exhibit 3.
9
8.8
8.6
8.4
8.2
8
7.8
7.6
7.4
7.2
7
Before crossbill
predation
After crossbill
predation
Cone Shape
(width/length*15)
Cone Mass (grams)
Pine Cone Trait
From Benkman (2003) American Naturalist 162: 182-194.
15
The three species
http://kurorisu.blogspot.com
/2010/03/america
n-redsquirrel.html
Squirrel photo
Lodgepole pine
cone photo
http://www.learner.org/jn
orth/images/graphics/ab/Beak-Crossbill.jpg
http://www.nps.gov/ro
mo/naturescience/image
s/lodgepole_pine.jpg
Crossbill bill photo
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Based on the data presented,
____________________ are in a
coevolutionary relationship.
A.
B.
C.
D.
E.
squirrels and pinecones
crossbills and pinecones
squirrels and crossbills
A and B
none of these species
What kind of additional evidence
would indicate a coevolutionary
relationship between squirrel traits
and pinecones?
Exhibit 4.
From Smith 1970. Ecological Monographs 40: 349-371
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…[Dependent variable] in
squirrels will change as a
result.
Sketching predictive graphs
When [independent variable] changes in
pine cones…
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