Coevolution Among Lake Organisms

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Coevolution Among Lake Organisms

• Sean Hurley

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Coevolution

• Classic Example
• -Prey evolves to run faster to avoid predators.
  Predator also evolves to run faster or become
  smarter to catch prey. Prey gets faster,etc.,etc.
• -Long-term relative fitness of both species
  stays constant

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Red Queen Hypothesis

• It takes all the running you can do to keep in
  the same place
• For evolution - Continuing development is need
  in order to maintain fitness relative to the
  systems coevolving with it

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Coevolution

• Can occur in any interspecies interactions
• Predator-Prey
• Host-parasite
• Mutualism
• Interspecific competition
• Abiotic vs. biotic
• Physical environmental factors do not respond
• to evolving species. Coevolution involves biotic
  relationships.

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Definition

• Coevolution
• a change in the genetic composition of one
  species (or group) in response to a genetic
  change in another
• Reciprocal evolutionary change in interacting
  species.

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Co-evolution
Species A evolves an adaptation in response to
species B
Species B evolves in response to the adaptation
of species A
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Importance of history

• Many cases in nature show strong evidence for
  co-evolution but another process could be
  responsible or by pure chance.
• Evolutionary history is key to supporting
  evidence of co-evolution.
• Often tough to find!

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• Coevolution first used or invented by Paul
  Ehrlich and Peter Raven in 1964 article
  Butterflies and Plants a Study of Coevolution
• The diversity of plants and their "poisonous"
  secondary compounds contributed to the generation
  of diversity of butterfly species.

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Risky Prey Behaviour Evolves in Risky
HabitatsMark C. Urban
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Predator-Prey Interaction

• Prey is Spotted Salamander larvae.
• Predator is Marbled Salamander larvae
• Interesting adaptation of Spotted Salamander.
• Increased foraging rates with increased predation
  - Risky behaviour
• Why?

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• -Expected behaviour is for prey to decrease
  foraging rates under increased predation.
• Why deviate?
• - Predator is gape-limited. Size of mouth.
• - Prey increases foraging to reach size refuge
  quicker

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• Increased Predation
• Increased Foraging
• Increased Mortality
• Increased long-term survival
• Size refuge alters the balance of costs and
  benefits.
• Short-term risk for long-term benefit

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What About predator?

• Does Marbled Salamandar larvae co-evolve?
• Breeds in fall and larvae grow in winter months
  to be able to feed on Spotted Salamandar which
  breed in the spring.
• Is this co-evolution?

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Relationship must be reciprocal
Species A evolves an adaptation in response to
species B
Species B evolves in response to the adaptation
of species A
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Large African Lakes as Natural Laboratories for
Evolution Examples From the Endemic Gastropod
Fauna of Lake Tanganyika(A.E. Michel, A.S.
Cohen, K. West, M.R. Johnston, and P.W. Kat, 1992)

• Lake Tanganyika known for its complex ecosystem
  and evolutionary history.
• 6 Million years old and relatively isolated.
• More endemic species than non-endemic species

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Endemic gastropods and predators

• Endemic gastropods heavily calcified and ornately
  sculptured shells - unusual for lake species,
  more like marine species
• Predators - many endemic fish and crabs well
  equipped with for eating armoured prey. Crushing
  teeth and calcified claws.

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Selection for larger, stronger-shelled Gastropods
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What about predators?

• Larger crabs with larger claws more successful
• Ability to crush smaller gastropods and spire
  larger ones.

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Co-evolution?

• There is highly suggestive evidence for a
  co-evolution.
• Heavily armoured prey more successful and
  predators with larger claws more successful.
• Unusual for aquatic systems.

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Coevolution?

• Evolutionary history?

Species A evolves an adaptation in response to
species B
Species B evolves in response to the adaptation
of species A
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One needs to know the evolutionary history before
we can make firm statements about coevolution.

• However, difficult to find long-term empirical
  evidence.
• Current data does not reveal temporal dynamics of
  co-evolution.

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Host Parasite Red Queen Dynamics Archived in Pond
Sediment Decaestecker, Sabrina Gaba, Joost A. M.
Raeymaekers, Robby Stoks, Liesbeth Van
Kerckhoven, Dieter Ebert Luc De Meester
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• Long-term empirical evidence of host-parasite
  co-evolution
• Dormant stage of Daphnia and parasite in pond
  sediment.
• Deeper the sediment, the older the evolutionary
  time.
• Similar studies for athropogenic effects and
  predation effects on Daphnia

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Infectivity vs.Host Resistance

• Eight layers of sediment tested. 2 cm each
  representing 2-4 years and 10-20 Daphnia
  generations.
• Each layer of Daphnia exposed to parasite from
  same layer (contemporary), the layer below
  (past), and the layer above (future)
• Number of infected Daphnia counted after 26 days.

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Parasite infectivity vs. Host Resistance

• Contemporary parasite the best adapted to the
  host
• Past parasite less infectious. Shows how host has
  adapted
• Loses adaptation in future. Now better adapted to
  future host

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Parasite Infectivity Over Time

• 5 Graphs showing same response.
• Different intervals.
• 1,5,11,15, 21 generations
• Graph C same as last slide
• Host infectivity highest in 3 Daphnia generations
  in the future
• Infectivity remains constant over time

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• Parasites are constantly evolving into new forms
  to avoid host resistance
• Hosts are constantly under selective pressure to
  evolve new resistance genes
• Result is a coevolutionary arms race in which
  both parasite and host must constantly evolve
  just to stay in place

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Long-term empirical evidence

• This type of experiment is very effective at
  supporting suggestive evidence for coevolution.
• Appears there is a distinct reciprocal
  coevolutionary relationship between the two
  species.

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Coevolution?

• Evolutionary history?

Species A evolves an adaptation in response to
species B
Species B evolves in response to the adaptation
of species A
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What about parasite virulence?

• Infectivity stays the same
• Virulence increases
• Spore production increases
• Daphnia fecundity decreases
• Will we see coevolution of Daphnia?

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Evolution of sexual reproduction

• Red-Queen theory suggests that the antagonist
  relationship between host-parasite is responsible
  for the evolution of host sexual reproduction.
• Parasites have short generations and evolve
  quickly.
• Sexual reproduction an advantage - more variation
  in offspring - species evolve faster.

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Summary of Coevolution

• Occurs in biotic interactions only
• Predator-Prey, Host-Parasite, Competition,
  Mutualism
• The evolutionary responses must be reciprocal.
• Long-term fitness of both species stays the same.
• Need to be careful when making assumptions about
  co-evolution. Need evolutionary history to
  support suggestive evidence.
• Sexual reproduction advantageous in host-parasite
  interaction.