Biology 2900 Principles of Evolution and Systematics

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Biology 2900Principles of Evolutionand
Systematics

• Dr. David Innes
• Jennifer Gosse
• Valerie Power

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Announcements

• Lab 3 handout ?print from course web page
• Midterm test Thursday Feb. 14
• (Based on material up to todays lecture)
• Example questions Online quiz 1
• Online quiz 2
  Friday Feb 8 Monday Feb 11

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Biology 2900Principles of Evolution and
Systematics

• Topics
• - the fact of evolution
• - natural selection
• - population genetics
• - natural selection and adaptation
• form and function reproduction
  life-history variation
• - speciation, systematics and
• phylogeny
• - the history of life

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Studies in Evolution

• Evolutionary Analysis
• Adaptation
• Sexual vs. Asexual
• Sex and Sexual Selection
• Life-history evolution

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• Sex
• Search for the adaptive significance of sex
  continues
• A diversity of theories exist for the
  predominance of sexual reproduction
• Much interest in the adaptive significance
  of variation in sexual reproduction

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Variation in Sexual Reproduction

• Separate sexes - dioecious (plants)
• - gonochoristic
  (animals)
• Co-sexual hermaphroditic
• (malefemale)

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Evolutionary Questions

• Hermaphrodites
• - selfing versus outcrossing
• - allocation to male versus female function
• - sequential hermaphrodites
• male ?female female?male

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Sequential Hermaphroditism

• Size advantage model
• protandrous (male ? female)
• more eggs when larger (shrimp)

Pandalus borealis
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Shrimp Size
DFO data Males 18 20 mm Females 23 26 mm
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Sequential of Hermaphroditism

• Size advantage model
• protogynous (female ? male)
• larger male gets more mates
• 
  

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Sequential of Hermaphroditism

• Size advantage model
• What factors determine the optimum
  size
• for sex reversal?
• 
  

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Evolutionary Questions

• Under what condition expect evolution of
• - hermaphroditism versus dioecy

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Hermaphroditism versus Dioecy
Single male produces N sperm Single female
produces n eggs Hermaphrodite produces
aN sperm male a 1, b 0
bn eggs female a 0, b
1 Fitness set described by a and b
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Hermaphroditism versus Dioecy
a b 1.0 a male function
b female function
concave
convex
1.0
1.0
b
b
a
a
1.0
1.0
Hermaphroditism favoured (a b gt 1.0)
Dioecy favoured (a b lt 1.0)
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Hermaphroditism versus Dioecy
Convex fitness set (hermaphroditism favoured)
- flowers attract pollinators and serve both
male and female function (saving of
resources) Concave fitness set (dioecy
favoured) - increased rate of return with
increasing investment (larger male gets more
mates)
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Evolution of Hermaphroditism

• Other models
• Low density model (mates hard to find)
• - selfing hermaphrodite (1)
• - outcrossing hermaphrodite (any 2)

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Summary

• Sex and evolution
• - active area of research
• - combination of theory and
• empirical observations to test
  theory

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Sexual Selection

• Chapter 14

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• Sexual Dimorphism
• Males and females often differ in size,
  appearance and behavior

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Whats he on about ?
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Male and female height dimorphism in 200 human
societies
In addition, Secondary sex characteristics
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• Adaptive significance of sexual dimorphism??
• Sexual dimorphism difficult to
• explain by natural selection
• Example long tail feathers
• How can the evolution of sexual dimorphism be
  explained?

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• Darwin and sexual dimorphism
• Challenges for passing on ones genes
• 1. Surviving
• 2. Reproducing
• And for sexual reproduction
• 3. Finding and mating with
  a
• member of the opposite
  sex

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• Sexual Selection
• Differences among individuals at getting mates
• i.e. Mating success

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• Sexual Selection
• Asymmetry
• - eggs are more expensive than ejaculates
• (eggs yolky sperm DNA propeller)
• - parental care by females, none by
• males (90 of mammal species)

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• Sexual Selection
• Asymmetry
• Females
  Males
• Limits to of eggs of
• reproductive produced matings
• success

Access to females a limiting resource for males
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• Batemans Experiment
• Test of asymmetric reproductive success
• D. melanogaster 3 virgin males
• 3 virgin females
• (each individual had 3 potential mates)
• Measured
• 1. number of actual mates
• 2. reproductive success ( of
  offspring)

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• Results

(a)
(b)
(c)
Variance in reproductive success males gt females
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• Results

Males reproductive success increases with
number of mates greater
variation in the number of mates
greater variation among males in reproductive
success Females no increase in reproductive
success with gt 1 mate less
variation in number of mates
little variation among females in reproductive
success
Other examples ??
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Rough-skinned newt
males
females

• Most males not mated
• All females mated
• Females number of mates doesnt increase of
  offspring
• Males increased of offspring with of mates

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• Consequences of asymmetry
• (Female parental care)
• Males should be competitive (intrasexual
  selection)
• Females should be choosy (intersexual
  selection)
• Because females commonly invest much more
  per offspring than males

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Sexual Selection

• Male-Male Competition
• 1. Combat
• 2. Sperm competition
• 3. Infanticide
• 4. Alternative mating strategies
• 5. Female Choice
• 6. Run away sexual selection

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• Male-Male competition
• (size matters)
• 1. Combat
• - favours larger body size
• - weaponry
• - armor

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Male Combat
(Marine Iguana)
Variation in mating success
observer
territories
Largest male
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Male combat (Marine Iguana)
Santa Fe Island N
Length (mm) Males that copulated 253
401 All males that tried to
343 390 Genovesa Island Males
that copulated 25
243 All males that tried to 147
227
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• Male-Male competition
• 2. Sperm competition
• Male mating success not determined by
  copulation but, whether his sperm fertilizes eggs

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• Sperm Competition
• Internal fertilization
• If female mates
• with 2 or more males,
• sperm race to the eggs

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Sperm Competition
M F offspring potential fathers

• external fertilization
• Internal fertilization
• - polyandrous species
• - socially monogamous
• species (extra-pair
• copulation)

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• Sperm Competition
• Adaptations to increase chances of winning the
  sperm race
• Large ejaculates with many sperm
• prolong copulation
• mate guarding
• copulatory plug

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• Sperm Competition
• Med. Fruit fly males
• sperm
• ejaculated
• 1. Private mating 1,379
• 2. With a potential 3,520
• competitor

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Mate Guarding
Root Weevil
natural
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Mate Guarding
Male barn swallows
Eggs laid
Female fertile period
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• Sperm Competition
• Other Adaptations
• Damsel flies

Removes sperm from previous mating
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Sperm Storage

• Birds, insects, mammals
• Control of sperm use by female
• - Last male sperm precedence
• - First male sperm precedence
• - Mixing of sperm

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Sperm Mixing(wood louse)

• Female Progeny Genotype
• 2/2 2/3 2/4 2/5
  2/6
• 2/2 2 10 7 21
  1
• Paternal alleles 2, 3, 4, 5, 6
• Possible male genotypes 2/3, 4/5, x/6
• (sperm from at least 3 males)
• 20 females gt 80 multiple
  paternity

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Testes Size in bats- increased testes size with
increased group sizeadaptation to increased
sperm competition(correlation corrected for
shared phylogeny)
Testes size (corrected for body size)
Group size
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An Evolutionary History of Sperm Competition T.
R. Birkhead (2000)
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Sperm Competition
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• Male-Male competition
• 3. Infanticide
• Pride basic social group of lions
• Newly mature males move to another pride
• New male kills nursing cubs
• - not his offspring
• - causes females to return to breeding
  earlier

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• Male-Male competition
• 4. Alternative mating strategy

Female
Sneaky males
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• 5. Female Choice
• Males unable to monopolize females
• Males advertise for mates
• Females inspect and choose
• sexual selection leads to elaborate
  courtship displays by males

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• Female Choice
• Example
• Barn Swallows
• Males have longer tail feathers
• Used in courtship display

males
females
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• Experiment
• (Anders MØller)
• Groups (males)
• 1. Shortened tail feathers
• 2. Control I (mock alteration)
• 3. Control II (unaltered)
• 4. Elongated tail feathers

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• Results

Premating period second clutches
of fledglings
Demonstrates females prefer males with longer
tails long-tailed males have high RS
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Extra-pair copulation

• Shortened Control
  Control Lengthened
• tails I
  II tails
• By their
• female 0.036 0.014
  0.017 0.00
• pair-mates
• Females with the least desirable mate, had the
  highest rate of
• extra-pair copulations

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Extra-pair copulation

• Paternity Analysis
• DNA fingerprinting
• Socially monogamous species (red-winged black
  birds) show extra-pair copulations
• 50 64 of nests

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• Female Choice

• Why should females be choosy ?
• Male display an indicator of good genes
• Male free of parasites
• Acquisition of resources from males (gifts)
• Preexisting sensory biases
• Runaway sexual selection

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• 6. Runaway Sexual Selection

• Example Stalk-eyed flies
• Females preferred males
• with long eyestalks
• 2. Males with long eyestalks left
• more offspring

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• Runaway Sexual Selection

3. Sons inherit long eyestalks, daughters a
preference for long eyestalks (assortative
mating) 4. Each generation males have longer
eyestalks and females prefer longer
eyestalks 5. Positive feedback loop
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Sexual Selection in Plants
Dimorphic
male
female
Wurmbea dioica
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Sexual Selection in Plants

• Female invests more (seeds)
• Access to pollinators limits mating success in
  males more than females
• Increased flower size in males increases
  pollinator visits

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Sexual Selection in Plants

• Male-Male competition
• - pollen tube growth
• (sperm competition)
• Female Choice
• - manipulate pollen tube growth
• - selective seed abortion

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Sexual Selection in Humans

• Cognitive processes underlying human mate choice
  The relationship between self-perception and mate
  preference in Western society
• Peter M. Buston and Stephen T. Emlen (2003) PNAS
  1000, p. 8805
• We conclude that, in Western society, humans use
  neither an opposites-attract nor a
  reproductive-potentials-attract decision rule
  in their choice of long-term partners but rather
  a likes-attract rule based on a preference
  for partners who are similar to themselves across
  a number of characteristics.
• 10 Characteristics indicative of
• - wealth and status
• - family commitment
• - physical appearance
• - sexual fidelity
• 
  (1000 Cornell University undergraduates)

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• Sexual Selection

Summary 1. Differences among individuals at
getting mates 2. Asymmetry in limits to
reproductive success - females
of eggs - males of
matings 3. Male competition, female choice
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• Sexual Selection

Summary 4. Reversed when males invest more than
females ( male parental care pipe
fish) 5. Principles of sexual selection in
animals can be applied to flowering plants
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• Sexual Selection

Dr. Ian Jones (Biology) Sexual selection in
Auklets
Aethia pygmaea I. Jones