Individuals and Populations

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Individuals and Populations
Reproductive Behaviour
Why?
To get genes into the next generation
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Reproductive Behaviour
Males and females have different reproductive
interests
What does each sex have to provide to produce
offspring?
Females
Males

• Manufacture eggs
• (expensive)

• Manufacture sperm
• (cheap)

2. Incubate eggs or fetus (expensive)
3. Post partum care (expensive)
Males invest less in any offspring
4. Loss of mating opportunity when
pregnant (expensive)
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Reproductive Behaviour
Operational vs Numerical Sex ratio
Numerical Sex Ratio The ratio of the number of
males to the number of females in the population
Operational Sex Ratio The ratio of the number of
males to the number of females in the population
who are available for reproduction
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Reproductive Behaviour
Operational vs Numerical Sex ratio
Numerical Sex Ratio (close to 11)
Males
Females
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Reproductive Behaviour
Operational Sex Ratio
Males
Females
Remove females for
Remove males for
1. Pre-puberty
2. Sterile
( Post-menopause)
3. Age
4. Pregnant
5. Lactating
Operational sex ratio
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Reproductive Behaviour
Operational vs Numerical Sex ratio
Numerical Sex Ratio (close to 11)
Males
Females
Operational Sex Ratio (very different from 11)
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Reproductive Behaviour
Lets look at the reproductive bank balance

• Females
• Expend lots of time and metabolic energy in
  reproduction
• Greatly decreased numbers of females available
  for mating

• Males
• Expend little time and metablolic energy in
  reproduction
• Lesser decrease in numbers of males available for
  mating

Large investment in each mating
Small investment in each mating
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Reproductive Behaviour
Females should be very choosy in mate choice
Large investment in each mating
Conflicting Strategies
Small investment in each mating
Males should mate with as many females as possible
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Reproductive Behaviour
Large investment in each mating
means that females
- are a limited resource
- control reproductive investment by males
Small investment in each mating
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Reproductive Behaviour
How do females control reproductive investment by
males?
Imagine a male that does something extra to
enhance the survival of eggs he fertilized
If the something extra reduces the investment
by the female, more offspring should be able to
be produced
More offspring (male) are produced that carry the
trait for providing something extra and the
trait spreads in the population
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Reproductive Behaviour
What does the something extra mean??
Males can demonstrate their willingness to ease
the reproductive burden of females in two ways
1. Offer evidence of genetic quality
2. Offer some resource
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Reproductive Behaviour
Evidence of Genetic Quality
How does a male demonstrate this?
1. Courtship
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Reproductive Behaviour
Evidence of Genetic Quality

• How does courtship indicate genetic quality?
• Male needs to be healthy
• Male has survived costs associated with courting
• - competition from other males
• - increased predator pressure

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Reproductive Behaviour
Evidence of Genetic Quality
Does it work?
Sage grouse
Mating territories
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Reproductive Behaviour
Evidence of Genetic Quality
Does it work?
Sage grouse
Mating territories
75 of all matings
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Reproductive Behaviour
Evidence of Genetic Quality
Do females respond to structures used in
courtship?
Widow bird -uses tail to display during courtship
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Reproductive Behaviour
Do females respond to structures used in
courtship?
short
normal
long
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Reproductive Behaviour
Do females respond to structures used in
courtship?
Percent response
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Reproductive Behaviour
Evidence of Genetic Quality
2. Compete with other males
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Reproductive Behaviour
Evidence of Genetic Quality
2. Compete with other males
Why?
Strongest (and presumably most fit) males win
such fights
The reward??
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Reproductive Behaviour
Evidence of Genetic Quality
2. Compete with other males
How else do males compete?
Bluegill sunfish
Males set up territories where females lay eggs
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Reproductive Behaviour
Bluegill sunfish Three kinds of males 1.
Parental - larger, aggressive territory
holders 2. Sneaker - smaller 3. Satellite -
look like females
spawning
Male digs nest
Female lays eggs
Male fertilizes eggs
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Reproductive Behaviour
Male digs nest
Female lays eggs
Male fertilizes eggs
Parental male
Parental - larger, aggressive territory holders
Female
Sneaker - smaller - rush in before parental male
and fertilize eggs
Satellite
Satellite - look like females - spawn with pair
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Reproductive Behaviour
Offer resources
1. Territory

• males establish and defend territories that have
  resources females need
• food, nesting sites

Costs to male -time -energy -predation
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Reproductive Behaviour
Offer resources
2. Food

• Often in the context of courtship

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Reproductive Behaviour
Offer resources
4. Care for offspring
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Reproductive Behaviour
Offer resources
4. Care for offspring - extreme cases - role
reversal
Female
Phalarope
Male
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Summary
Females invest a lot in reproduction
Males invest little in reproduction
Females should be choosy in mates
Males should be promiscuous
Females are a limited resource and can exert
selective pressure on males to provide more
Males respond with courtship, resource provision
and/or parental care
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Human Mating Strategies
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Central Question
1. Can humans be shown to mate in a manner
consistent with the hypotheses surrounding mate
choice by either perception of genetic quality or
of ability to provide resources?
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Most primates
Males ? concentration on mating effort
Females ? concentration on parental effort
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Dominance in a Social Group
Underlying principle Higher status males ?
more copulations more offspring
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Dominance in a Social Group
Kipsigis
wives
Acres owned
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Human mating systems
Sperm competition
How monogamous is monogamy?
Indigo bunting
Within pair
Extra-pair
0
12
Days before egglaying
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Human mating systems
Sperm competition
When does it occur?
1. Adolescent courtship
Triobrand Islands
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Human mating systems
Sperm competition
When does it occur?
2. Facultative polyandry
polyandry
Polyandry
monogamy
polygyny
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Human mating systems
Sperm competition
When does it occur?
2. Facultative polyandry
polyandry
Polyandry
monogamy
polygyny
Facultative Polyandry
universal
moderate
occasional
uncommon
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Human mating systems
Sperm competition
Why should females be polyandrous?
1. Good genes
2. Genetic Diversity
3. Fertility Backup
- 25 of couples - sterility (35 -male)
4. Material Resources

• females mate extramaritally more often with men
  of
• higher socioeconomic status

• females mate extramaritally more often with men
  older than their primary mate

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Human mating systems
Sperm competition
What attributes of humans may have evolved in
context of sperm competition?
Males
1. Mating patterns
- most common -monogamy (with extramarital
mating?)
-only if cost of any extramarital tactic is free
or lt cost of supporting second mate
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Human mating systems
Sperm competition
What attributes of humans may have evolved in
context of sperm competition?
Males
2. Sexual Jealousy and Paternity Assurance
Spousal homocide related to sexual jealousy
USA - 33 Africa (several studies) - 45
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Human mating systems
Sperm competition
What attributes of humans may have evolved in
context of sperm competition?
Females
1. Cryptic ovulation and continuous sexual
receptivity
Most primates
Humans
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Human mating systems
Sperm competition
What attributes of humans may have evolved in
context of sperm competition?
Females
2. Perennially obvious breasts
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Human mating systems
Sperm competition
What attributes of humans may have evolved in
context of sperm competition?
Females
3. Female Orgasm
- may help draw sperm through the cervix
400 mm
0
-260 mm