Intraspecific Variation

1
Intraspecific Variation

• Chapter 6

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Preconditions

• Environments vary
• Organisms vary
• Genetic variation in the population
• Genetic variation determines possible adaptive
  responses
• Genetics and ecology of an organism strongly
  related. Does genetics of an organism determine
  its ecology, or vice versa

3
Genetic Mechanisms of Variation

• Central dogma of Molecular Bio DNA?RNA?Protein
  (aka genotype?phenotype)
• Mutations affect protein structure or gene
  regulation
• Chromosomal rearrangements
• Crossing over

4
Persistence of alleles

• Seems advantageous phenotype should lead to
  eradication of alleles
• Mechanisms maintain diversity
• Dominance protects recessive alleles
• Heterozygote advantage
• Genetic drift leads to loss or fixation of
  alleles
• Effective population size (Ne) of individuals
  that actually breed

5
Persistence of alleles

• Inbreeding (coefficient F) affects variation by
  increasing homozygosity of alleles that are
  identical by descent (from the same copy of an
  allele in past generation)

6
Measuring Genetic Variation

• Morphological variation, Chromosomal variation,
  Allozymes, DNA fingerprinting, Mitochondrial DNA

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Morphological variation

• Phenotypic variation
• Occurs with geographic variation
• Can occur within a small patch, or over a
  continent
• Sufficient morphological variation leads to
  subspecies or races
• Care must be taken to distinguish between genetic
  basis and response to the environment

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Chromosomal variation

• Karyotype the number and morphology of an
  individuals chromosomes
• Staining techniques and microscopy can allow us
  to view chromosomes and their differences
• Chromosomal variation changes with geographical
  variation
• Different races based on chromosomal variation

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Allozymes

• Variants of protein coded for by different
  alleles at a locus
• Variants can be identified by gel electrophoresis
• Allozymes can be used to determine genetic
  similarity and genetic distance between
  individuals

10
DNA Fingerprinting

• Relies on minisatellites, non-coding regions of
  proteins containing repeated segments of DNA
• Variability in repetition can be detected, and
  used to compare individuals and populations
• RFLP banding pattern in DNA fingerprinting

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Mitochondrial DNA

• Mitochondria contain their own set of DNA
• Inherited exclusively through the mother
• Mitochondrial DNA mutates over time
• Can be used to measure branching events within
  populations

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A measure of genetic differentiation

• F-statistic greater F value means greater
  variation

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The Interaction of Genetic and Ecological
Processes
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Interactions that affect variation

• Selection
• Dispersal
• Population size

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Selection

• Environment applies selective force on population
• Different local habitats yield different
  selective forces, which yields different genetic
  populations (different ecotypes)
• Different ecotypes can occur on very small
  geographic scale
• E.g. snails, wild oats

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Dispersal

• Dispersal creates gene flow, which homogenizes
  subpopulations (reduces variation)
• Barriers to dispersal increase variation
• Barriers can be small (e.g. power lines and
  white-footed mouse)
• E.g. monarch butterfly, pocket gopher

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Population size

• Allele frequency changes occur more rapidly in
  small populations
• Small populations feel the effects of drift or
  inbreeding much more strongly than larger
  populations

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Effects of genetic variation

• Reduced variation means reduction in polymorphic
  loci
• Loss of variation leads to
• Reduction in adaptive capability
• Inbreeding depression
• Fixation of deleterious alleles
• Important implications for conservation biology

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When the ecology affects variation

• Coyotes and gray wolves in North America
• Coyotes have low F values, whereas wolves have
  high F values
• Coyotes have expanded their range and size as a
  result of habitat alteration, increasing gene
  flow
• Wolves have experienced a decline in size and
  fragmented habitat, reducing gene flow

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