Biology 4250 Evolutionary Genetics

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Biology 4250 Evolutionary Genetics

• Dr. David Innes
• Dr. Dawn Marshall
• W 2008

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Monday Feb 4

• Computer Lab 2
• - Computer Lab.CS-1009
• - Discussion based on
• Why Sex?
• http//www.mun.ca/biology/dinnes/B4250/PalandLync
  h2006.pdf

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Outline of
topics 1. Introduction/History of Interest in
Genetic Variation 2. Types of Molecular
Markers 3. Molecular Evolution 4.
Individuality and Relatedness 5. Population
Demography, Structure Phylogeography 6.
Phylogenetic Methods Species Level
Phylogenies 7. Speciation, Hybridization and
Introgression 8. Human Evolutionary
Genetics 9. Conservation Genetics
Background
Applications
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Individuality and Parentage

• Sexual reproduction genetic variation large
• amount of genotypic variation
• - every individual in a population
  genetically
• unique

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Individuality and Parentage

• Ramets and Genets
• (sexual and asexual) (Lab
  2)
• Genetic parentage

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Genetic Parentage

• Sexual reproduction ? Mendelian genetics
• Genetic parentage
• combining genetic markers with
  rules of Mendelian
• inheritance (segregation
  independent assortment)

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Genetic Parentage

• Question addressed
• Are the adults associated with particular
• young the true biological parents?
• Genetic exclusion
• - one parent known problem becomes
• determining paternity or maternity
• - both parents sometimes can be specified

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Genetic Parentage - Situations

• 1. Maternity and paternity uncertain
• 2. Maternity certain paternity among candidate
  males
• - mating systems monogamy
• polyandry
• polygyny
• polygynandry
• 3. Hermaphroditic selfing
• outcrossing
• 4. Selfing vs. parthenogenesis

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Genetic Parentage - Situations
Intensity of sexual selection
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Mating Systems

• Genetic and evolutionary consequences of
  different mating systems
• Evolution of mating systems

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Parentage

• Behavioural and evolutionary context of
  parentage
• - realized reproductive success
• - genetic mating system vs. social
• mating systems (ie. monogamous)

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Parentage

• Empirical examples
• Humans
• maternity certain paternity can be
  less
• certain

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Are -U Dad ? (273 8323)
Is-He-Dad (474 3323)
299 399 499 599
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Other Primates

• Social structure dominance hierarchies
• Do males of higher social rank exhibit higher
  fitness?

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Examples

• Rhesus Macaques
• Offspring fathered by alpha male 24
• Offspring fathered by lower ranks 76
• Behaviour-based methods of fitness estimation
  inadequate

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Examples

• Orangutan
• Dominant male
• secondary sex characters (SSC)
• Subordinate males
• suppression of SSC
• Microsats ? subordinate male sired 50
• alternative mating strategy
• (Also found in Salmon small sneaker males)

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Parentage in Birds

• Parental Care significant investment
• Parental fitness
• - mate and produce offspring
• - ensure parental care of own
  offspring
• Males and females pair to mate and rear offspring

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Genetic markers and bird parentage

• Socially monogamous species
• high frequency of EPO
• EPC extra-pair copulation
• EPF extra-pair fertilization
• EPO extra-pair offspring
• Examples
• Range Monogamous to extreme EPO
• (1 34 )
• Superb fairy-wren ? gt 70 EPO

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Evolutionary Significance

• - no correlation between EPF rate and nesting
  density or
• coloniality
• - females actively seek EPC
• Selective advantage
• - generate high genetic diversity among
  offspring
• - increased chance of obtaining good
  genes
• - high genetic compatibility with male
• - fertilization insurance

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Evolutionary Significance

• EPO benefit females and cuckolding males
• Disadvantage for cuckolded males (where males
  helps raise
• offspring that are not his own)
• Selection for cuckoldry avoidance
• Reed Bunting - high rate of extra-pair
  paternity
• - males can assess
  likelihood of paternity and
• can adjust nestling
  provisioning rates

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Evolutionary Significance

• Correlates of High rates of EPF
• - species that have males with bright plumage
• - relatively large testes
• - males provide little or no offspring care
• - high molecular variation (therefore EPO can
  increase
• genetic diversity of offspring)

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Extra-pair paternity sexual dimorphism
Male
Female
Moller and Birkhead (1994)
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Parentage in Fishes

• Often very large clutches
• Diverse reproductive behaviour
• - group spawning
• - cooperative breeding
• - social monogamy

salmon
Eretmodus cyanostictus is a monogamous
mouthbrooding cichlid in which the clutch is
successively incubated first by the female and
then by the male.
African cichlids
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Parentage in Fishes

• Variation in Parental Care
• - nonexistent
• - one gender only (usually male)
• - biparental
• - communal

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Parentage in Fishes

• sexually monomorphic in appearance and socially
• monogamous.
• microsatellite markers in order to test whether
  social
• monogamy predicts genetic monogamy
• 23/26 nests full sibs
• The first genetic documentation of near-monogamy
  and biparental care in a vertebrate with external
  fertilization.

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Parentage in Fishes

• Paternity studies of nest-guarding male
• Compare genotype of suspected father with
  offspring
• Examples
• 1 male gt 1 female (multiple maternity?half
  sibs)
• 1 male 1 female (monogamy rare)
• 3. Some offspring not sired by resident male
  (cuckoldry)

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Stickleback
Jones et al 1998 A microsatellite assessment of
sneaked fertilizations and egg thievery in the
fifteenspine stickleback Microsatellites 6 loci
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Exclusion Probability
Combined exclusion probability 0.9998
Expected proportion of unrelated males excluded
as the father
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Sneaked 5/28 nests Egg Thievery 4/24 nests
Benefits of sneaking ? obvious Benefits of egg
thievery? - prime the nest - predation
dilution
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Plant Mating Systems
In a word Diverse
Silene acaulis Gynodioecious (hermaphrodites
females)
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Plant Mating Systems

• Individual Flowers
• Hermaphrodite -- bisexual flower with both
  stamens and pistil
• Unisexual -- flower is either staminate
  (male), or pistillate (or carpellate) (female)
• Individual Plants
• Hermaphrodite -- the plant has only
  hermaphrodite flowers
• Monoecious -- unisexual male and female
  flowers are on the same plant
• Dioecious -- unisexual male and female
  flowers are on different plants
• Gynoecious -- has only female flowers
• Androecious -- has only male flowers
• Plant Populations
• Hermaphrodite -- only hermaphrodite plants
• Monoecious -- only monoecious plants
• Dioecious -- only dioecious plants
• Gynodioecious -- has both female and
  hermaphrodite plants
• Androdioecious -- has both male and
  hermaphrodite plants

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Parentage in Plant

• Paternal fitness
• ? spread of pollen (wind or insect)
• Mother known (seeds)
• - paternity to be determined

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Parentage in Plant

• Many plant species hermaphroditic
• Prevention of selfing (several mechanism)
• - M F mature at different times
• - anther stigma separation
• - genetic self-incompatibility
• - sex expression

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Parentage in Plant

• 1. Relative proportion of selfing vs. outcrossing
• Mother known ? paternity assessed using genetic
  markers
• non-maternal alleles outcrossing
• Statistical models mixed mating model
• s selfing rate
• t outcrossing rate
• s t 1.0

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Out-crossing Rates

• Distribution of outcrossing rates Bimodal
• most species either predominantly
  outcrossing or selfing
• - Outcrossing selected when inbreeding
  depression high
• - Selfing selected in species that have purged
  recessive deleterious alleles
• Large variation among populations in outcrossing
  rate

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Outcrossing Rates
Pollination Wind animal
Variation among hermaphroditic species
Variation among populations
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Paternity in Plants

• 2. Outcrossing established determination
  Paternity
• - compare seeds (progeny) genotype with
  mother
• - deduce haploid genotype of fertilizing
  pollen
• - candidate fathers screened ? paternity
  exclusion
• - direct estimate of gene flow
• Example wild radish (Raphanus sativus)

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Paternity in Wild Radish

• - Self-incompatible, insect pollinated
• - Six highly polymorphic allozyme loci
• - Multiple paternity found for all maternal
  plants (85 of all fruits
• - Minimum of 2.3 paternal donors per maternal
  plant
• - Most multiply-sired fruits due to a single
  insect visit
• (pollen carryover)
• 44 of paternity from gt 100 m (gene flow between
  1 generation)

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Paternity in Moss

• Female (n) sporophyte (2n) ? deduce male (n)
  genotype
• Results
• - only 2/137 matings involved a single male
  not previously sampled in the area
• - at sites where both M F occurred, 93 of
  94 matings involved M F at the same site
• - Conclusion sperm dispersal limited

SS SF SM 2n S F M female S
S S male
known
inferred
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Other Topics in Parentage

• Sperm storage females can store sperm
  after a
• single copulation?
• - mammals few days
• - birds, insects weeks
• - salamander months
• - snakes, turtles several years

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Other Topics in Parentage

• Sperm and pollen competition
• - sperm from two or more males in direct
  competition
• for fertilization of eggs of a single
  female
• - many mechanisms for a male to ensure his
  sperm
• fertilizes a females eggs (paternity
  assurance)
• - plugs scoop out previous
  males sperm
• prolonged copulation multiple
  copulation
• with same female mate guarding
• Females may encourage sperm competition

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Other Topics in Parentage

• Sperm and pollen competition
• - multiply inseminated females? markers used
  to
• determine the success of each male
• first male, last male, no mating order
  effect
• Insects often last male has greatest
  fertilization success
• Plants pollination by multiple pollen donors
• competition ? rate of pollen tube
  growth
• usually advantage for first
  pollinating male

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Paternity Software

• http//www.bio.ulaval.ca/louisbernatchez/downloads
  .htm
• Others CERVUS, PAPA, KINSHIP, PROBMAX