Can selection act on characters that respond to different environments

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Can selection act on characters that respond to
different environments?
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Two individuals of a single clone of the Asian
and African water flea, Daphnia lumholtzi. The
individual on the left was exposed to chemical
cues from predaceous fish (induced) the
individual on the right was not (control).
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Sundew green red morphs
H1 Morphs have different genotypes. H2 Morphs
have same genotype but developed in different
environments. If H2, why should the plant have
the capability of producing different forms?
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What are the questions?

• Can flexibility be an adaptation?
• What is phenotypic plasticity?
• How does p.-p. contrast with canalization?
• What aspects of phenotypic plasticity are
  heritable?
• How can we test the hypothesis of adaptive
  plasticity?

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Phenotypic plasticity defined

• environment-dependent phenotypic expression
• identical genotypes are exposed to different
  environments
• traits of interest measured

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Antonym canalization

• a developmental process that produces the same
  phenotype in spite of environmental variability
  ( homeostasis)
• reduces the effect of environmental noise
• variability in a trait in a population represents
  a balance between plasticity and canalization

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Measuring phenotypic plasticity

• Norm of Reaction
• Different phenotypes produced by the same
  genotype in different environments
• X- axis represents range of environmental
  conditions
• Y-axis represents the resulting phenotype

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Forms of Norms of Reaction
Red lines indicate optimal reactions
Arrows indicate optimal phenotypes for each
environment
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Norm of Reaction curves for biomass allocation
in Polygonum
From Sultan, S. E. 2003. Phenotypic plasticity in
plants a case study in ecological development.
Evolution Development 525-33.
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Norms of reaction for leaf area (morphological
plasticity)
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Norms of reaction for reproductive plasticity
(lifetime output)
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Is phenotypic plasticity an adaptation?

• It depends
• Are patterns heritable?
• Do plastic genotypes have more success than
  canalized genotypes?
• Nijhout, H. F. 2003. Development and evolution of
  adaptive polyphenisms. Evolution Development 5
  9-18.

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What is a polyphenism?

• Two or more discrete alternative phenotypes,
  without intermediate forms

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Why, in nature, are there just 2 forms?
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Hormonal developmental programs influence
polyphenism a heritable mechanism
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Correlated characters in beetles size mating
tactics (variation in success)
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Other examples of polyphenism

• castes of social insects (Nature 26 Oct 2006)
• alternative seasonal form of insects
• alternative leaf forms in plants
• predator-induced polymorphism in cladocerans
  polymorphism in migratory behavior of locusts
• sedentary vs. dispersal morphs of aphids other
  animals

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Is Polyphenism adaptive? - tadpoles

• Relyea, R. A. 2005. The heritability of inducible
  defenses in tadpoles. J. Evol. Biol. 18 856-866.

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Tadpole norms of reaction
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Heritability of Plasticity
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What is different about phenotypic plasticity as
an adaptation?

• Compared to selection on a continuous trait
  influenced by additive genetic effects?
• Consider rate of response
• in context of rate of environmental change
• in context of shifting gene frequencies
• As a response to spatial heterogeneity?

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Spea hammondii
Scaphiopus couchii
Pelobates syriacus
Pelodytes punctatus