Coevolution among Lake Organisms

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Coevolution among Lake Organisms

• BIOL 402
• 24 November 2009

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Coevolution
The process of reciprocal evolutionary change
that occurs between pairs of species or among
groups of species as they interact with one
another. The activity of each species that
participates in the interaction applies selection
pressure to the others. Encyclopaedia Britannica
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Common Coevolution Questions

• How quickly do species coevolve?
• What types of ecological relationships spur
  strong coevolutionary development?
• What genetic (phenotypic and gene pool)
  conditions are necessary?
• What traits are subject to coevolution selection
  pressure?

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Examples from the literature...

• The response of morphology and behaviour to
  coevolution of crabs and gastropods in Lake
  Tanganyika
• Coevolution of resource partitioning in Lake
  Michigan fish communities
• Coevolution in the timing of emergence between
  damselflies and their water mite ectoparasites

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Host-parasite Red Queen dynamics archived in
pond sediment

• Decaestecker et al. 2007. Nature.

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The Red Queen Hypothesis
Alice (of Carrolls Through the Looking Glass) is
led up a hill by the Red Queen. Once they reach
the top, the Red Queen begins to run, faster and
faster. Alice runs after her but when they stop,
they are both in exactly the same place. And so
it may be with coevolution. Evolutionary change
may be necessary to remain in the same place.
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The experiment conducted by Decaestecker et al.
investigated the theory that host-parasite
interaction imposes frequency-dependent selection
that leads to Red Queen dynamics.
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Complication
It is difficult to study evolutionary dynamics
in nature because a time series of many
generations is necessary
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Solution
Laminated lake sediments Organisms that
produce dormant stages Reconstruction of
evolutionary dynamics
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Host Daphnia magna
Parasite Pasteuria ramosa (a bacterial
endoparasite)
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Methods

• Two sediment cores were taken from a pond where
  D. magna coexisted with P. ramosa
• Cores divided into layers measuring 2cm
  (analogous to 2-4 years)
• Daphnia clones were obtained by hatching dormant
  eggs from each depth
• Parasite isolates were obtained by exposing
  random daphnids to to sediments from each depth

Oldest layer 29-39 years
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Each depth represents a snapshot in the arms
race of these antagonists, corresponding with a
historical time fragment of the parasite and the
Daphnia population.
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The Treatment
Daphnia clones were exposed to parasite isolates
from three different sediment layers same
below above These layers corresponded to
contemporary past future parasites
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Results
Infectivity was highest when Daphnia were exposed
to contemporary parasites

• Contemporary 0.65
• Past 0.55
• Future 0.57

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Conclusion
Our study reveals fast evolutionary changes,
with parasites adapting to infect contemporary
host genotypes.
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Model Results

• Most infective parasites from near future
• Least infective parasites from recent past
• Cyclic pattern of infectivity

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• More alleles peaks further apart
• Decrease virulence flatter peaks
• Increase mutation rate faster adaptation

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The cyclic pattern dampens when infectivity
values are averaged over several
generations. This averaging is analogous to
analyzing several Daphnia generations in one
sediment layer. It explains why the
experimental results found contemporary parasites
to be the most infective.
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Fine resolution of generations
PRESENT
NEAR FUTURE
DISTANT FUTURE
NEAR PAST
DISTANT PAST
PAST
FUTURE
FUTURE
PRESENT
PAST
Coarse resolution of generations
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Interestingly...
Despite rapid evolutionary changes, the data did
not show a net change in parasite infectivity
with time.
Running to stand still.
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The concentration of parasite spores did increase
with time. This increase was associated with a
decline in Daphnia fecundity and may reflect an
adaptation of the parasite to the
host. Different genes with different
evolutionary dynamics?
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Risky prey behaviour evolves in risky habitats

• Mark C. Urban. 2007. PNAS.

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History
Well-established ecological theory
Prey should lower foraging activity to reduce
predation risk Growth-predation risk tradeoff
Reduce foraging during high-risk periods
Time-variable predation risk
Increase foraging during low-risk periods to
compensate for lost opportunities
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Debunk
Prey can reduce the duration of predation risk
through foraging and growth into a large body
size Size refuge from gape-restricted predators
Alters growth-predation risk tradeoff despite an
increase in short-term mortality
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General Prediction
The evolution of divergent feeding strategies
(i.e. foraging activity) can be predicted based
on variation in predator size-selectivity (i.e.
gape-limitation) and the preys capacity for
rapid growth
But only if gene flow between populations is
limited by physical barriers.
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Supplies genetic variation
A happy amount...
Gene flow
Too much...
Swamps existing variation with less fit alleles
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Amystoma maculatum The spotted salamander
PREDATOR
PREY
Ambystoma opacum The marbled salamander
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Breed in the fall and larvae hatch in winter
A. opacum
Feed on hatching prey
GAPE-LIMITED
Breed the following spring
A. maculatum
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Hypotheses
Higher prey foraging
Intense gape-limited predation risk
Rapid growth rates
In the absence of strong gape-limited predation
risks, slow growth rates are expected to evolve
as a trade-off between gain in fecundity and
mortality from gape-unconstrained predation
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Methods

• foraging
• growth
• survival

measure...
Common garden experiments
subjects...
salamander larvae originating from 10 natural
population that varied in gape-limited predation
risk
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Common Garden Results
Higher mortality
A. maculatum larvae originating from ponds with a
high A. opacum predation risk
Higher foraging rates
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A refinement...
A. maculatum has a plastic response to predation
risk
Preference for low-risk microhabitats and
reduced foraging
Prey from high gape-limited risk environments
decease foraging in the presence of predators,
but the decrease is less than the decrease in
populations exposed only to gape-unconstrained
predators.
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N.B. The foraging rates of all A. maculatum
individuals converged in the fifth week. This
corresponds with the time necessary for larvae to
reach a size refuge.
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Field Patterns

• Higher growth rates observed in ponds with
  greater A. opacum predation risk during the first
  2 weeks of A. maculatum development
• Growth rate correlated with survival - rapid
  growth into a size refuge associated with higher
  survival despite initial declines in survivorship
• Loss of significance between populations after 4
  weeks

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Spatial Patterns
A. opacum predation risk
High in the southwest
Low in the northeast
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NE
SW
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Predation risk and A. maculatum foraging rates
were positively spatially correlated. Population
size was not spatially correlated therefore...
higher rates of foraging, growth and mortality
could not be attributed to genetic drift in small
populations.
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In conclusion...
Intense gape-limited predation risk is
associated with the local evolution of risky prey
foraging strategies.
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To sum up...
Decaestecker et al. dug through sediment cores
and reconstructed the evolutionary dynamics
between Daphnia and the endoparasite P. ramosa.
Parasites underwent rapid evolutionary changes to
adapt to contemporary hosts.
In the lab and out and about, Urban studied the
effect of gape-limited predation on the foraging
behaviour of larval salamander prey.
Prey evolved risky foraging behaviour when
subjected to gape-limited predation.
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Tie em together...
Host-parasite
Coevolution
Predator-prey
Sexual selection
???
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Guppies Sexual Selection
Predator intensity varies between populations
Females prefer more conspicuous males
Polymorphic colour pattern in males a trade-off
between sexual selection and predation risk
Increase predation risk
Decrease colour intensity
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Literature Cited
Decaestecker, E. et al. 2007. Host-parasite Red
Queen dynamics archived in pond sediment. Nature
450870-874. Endler, John A. 1995.
Multiple-trait coevolution and environmental
gradients in guppies. TREE 10(1)22-29. Urban,
M. 2007. Risky prey behavior evolves in risky
habitats. PNAS 104(36)14377-14382.