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Reproductive Strategies. vs. Three types of comparisons: across species within species/ within a sex (alternative mating strategies). Reproductive Strategies.

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slide2

vs.

  • Three types of comparisons:
  • across species
  • within species/
  • within a sex
  • (alternative mating strategies)

Reproductive Strategies

A set of behavioral and physical adaptations designed specifically to maximize an individual’s mating and reproductive success. (more definitions later)

specifically

  • Topics:
  • Why sex?
  • Male vs. female
  • Sexual selection
slide3

Why sex?

vs. asexual reproduction (cloning)

(sexual reproduction)

Whiptail lizards

some

examples

Aphids

Portuguese man-o-war

slide4

Why Not Sex?

Because Sex is Costly !

  • Gonads are expensive organs to produce and maintain
  • Mating is risky, costly, time-consuming, often involving elaborate structures and behaviors
  • Cost of meiosis – this is the most significant cost
slide5

Why Not Sex?

Sexual Reproduction:Cost of meiosis

Asexual cloning

Since each sexually-produced offspring only contains half the genetic material of each parent, there is a 50% reduction in fitness compared to asexual reproduction

slide6

Why sex?

Benefits of Sexual Reproduction

Natural selection is limited by fact that even as a species adapts to its biotic environment – its competitors, predators, parasites – that environment is also evolving. → “Arms Race”

Genetic variability among offspring permits response to changing biotic environment

Red Queen Hypothesis: whereas asexual reproduction is a ‘sitting duck’ target for competitors, pathogens, predators, sex and geneticrecombinationpresentamoving target

“It takes all the running you can do to keep in the same place!”

slide7

Male and Female

  • ♂♀
  • How define “male” and “female”?
  • Sex chromosomes not generally useful criterion:
      •  Mammals: M - XY, F - XX
      •  Birds: M – XX, F – XZ
      •  Hymenopterans: M – N, F – 2N
      •  Hermaphroditic species
      •  Turtles, alligators: Facultative
      • (incubation temp dependent)
slide8

Male and Female

Temperature-dependent Sex Determination

slide9

Male and Female

  • ♂♀
  • How define “male” and “female”?
  • Male and female defined by relative size of their gametes (sex cells):
  • Females produce relatively few but expensive (provisioned) sex cells.
  • Males produce many more but cheap sex cells.
slide10

Anisogamy = “Unequal gametes”

Eggs: few, large, energetically expensive

Sperm: many, small, cheap

Eggs and Sperm

Fig 10.6 Alcock

slide12

Natural Selection

Survival Parental

Care

slide13

Natural Selection

Survival Mating Success Parental

Care

slide14

Natural Selection

Survival Mating Success Parental

Care

Intrasexual Mate Choice

Competition (Epigamic)

Sexual Selection

slide15

Intrasexual Selection

Epigamic Selection

slide16

SEXUAL SELECTION

Occurs when (1) males compete among themselves for access to females (intrasexual selection) . . .

slide17

SEXUAL SELECTION

Occurs when (1) males compete among themselves for access to females (intrasexual selection) and/or (2) try

to attract females by flashy colors, behaviors etc (epigamic selection).

Greater Sage Grouse

1 23

slide20

Black Grouse

Norway

Black Grouse Lek in Norway

slide25

Intrasexual selection

→ weapons, fighting

National Geographic

Wild America

slide26

Alternative Strategies

come back to later

Bluegill Sunfish

slide27

Epigamic Selection

Flip side of epigamic selection:

Female choice

slide28

Reproductive Strategies

1. A set of behavioral and physical adaptations designed specifically to maximize an individual’s mating and reproductive success.

2. A set of behavioral and physical adaptations shaped by sexualselection.

slide29

Male-male competition (Intrasexual selection)

Female Choice (Epigamic selection)

Summing Up:

  • Sexual Selection tends to produce weapons and elaborate ornaments and displays
  • Sexual selection has two components:

What drives sexual selection?

Trivers: Key to sexual selection is parental investment (PI) = effort put into helping your offspring reach reproductive age.

slide30

Trivers: Differential Parental Investment drives Sexual Selection

Female PI

Sexual Selection

♂ - ♂

slide31

PARENTAL INVESTMENT (PI)

  • Initial PI
  • female's provisioning of egg cell
  • Specialized PI (mammary glands, incubation patches, etc) – usually supplied by one sex only, and that
  • is almost always the female
  • female’s nourishing of the embryo
  • female’s producing yolk-filled egg (reptiles and birds)
  • incubation (reptiles and birds)
  • female lactation
  • Generalized PI – usually behavioral and can be supplied by either sex
  • guarding the offspring
  • feeding the offspring
  • defending a territory/nest used for feeding and protecting young
slide41

Male Randall’s Jawfish

Mouth-Broods Eggs

slide47

PARENTAL INVESTMENT (PI)

1. initial PI: females produce large egg cells, males produce small sperm

2. specialized adaptations directly related to reproduction (e.g., gestation, nursing): usually the female

3. behavioral adaptations (and costs): egg-guarding, protecting and feeding young: females or males (more commonly the female)

Generally, female PI is much greater than male PI

slide48

SEXUAL SELECTION

  • Trivers: Key to sexual selection is parental investment (PI).
  • Trivers: Sexual selection =
  • Sex investing less will compete for sex investing more (intrasexual selection)
  • 2. Sex investing more will be discriminating in choosing mates (epigamic selection)
  • Typically: Female PI > Male PI
  • so usually its males competing among themselves for females and females choosing among males.
  • First: consider some consequences…
slide49

General Sex Differences in Behavior

Male: ardent, indiscriminant

Female: reluctant, discriminating

  • FEMALES – “Don’t you Dare.”
  • MALES – “Laissez Faire.”
slide52

SEXUAL SELECTION

  • Trivers: Key to sexual selection is parental investment (PI).
  • Trivers: Sexual selection =
  • Sex investing less will compete for sex investing more (intrasexual selection)
  • 2. Sex investing more will be discriminating in choosing mates (epigamic selection)
  • Typically: Female PI > Male PI
  • so usually its males competing among themselves for females and females choosing among males.
  •  How do we test this hypothesis?
slide53

Reproductive Variance (RV) = variance in reproductive success

female bowerbirds

Alcock

Fig 10.5

male bowerbirds

Just from the point of view of RS, which would you rather be:

A male or female bowerbird?

slide54

Reproductive Variance (RV) = variance in reproductive success

1

1

1

1

1

1

1

1

monogamy

male RV  female RV

slide55

Reproductive Variance (RV) = variance in reproductive success

1

1

1

1

4

0

0

0

polygyny: male RV > female RV

slide56

Reproductive Variance (RV) = variance in reproductive success

4

0

0

0

1

1

1

1

polyandry: female RV > male RV

slide57

An extreme case: elephant seals

  • Polygyny
  • Female parental care
  • Male RV >> Female RV
slide58

Trivers: Differential Parental Investment drives Sexual Selection

Female PI

Sexual Selection

♂ - ♂

slide59

Testing Trivers’ Hypothesis

Female PI > Male PI → Male RV > Female RV

Female PI  Male PI → Female RV  Male RV

males compete, females choose

competition more equal, less intense

Male PI > Female PI → Female RV > Male RV

females compete, males choose

PI: Parental Investment

RV: Reproductive Variance

Sex role reversals

Seahorses & pipefish –

male ‘gestation’ &lactation

Mormon crickets – spermatophores

Polyandrous species (e.g., Jacana)

slide60

Fig 11.2 Alcock

A pregnant male Seahorse

slide62

Spermatophores

Mormon cricket

slide64

Sex role reversals

Seahorses & Pipefish – specialized PI

Mormon crickets – spermatophores

Jacanas – Polyandry, ♂ parental care

In all* these cases, males are the more choosey sex and/or females compete among themselves for males.

  • Trivers: Sexual selection =
  • Sex investing less will compete for sex investing more (intrasexual selection)
  • Sex investing more will be discriminating in choosing mates (epigamic selection)
slide65

Sex role reversals

Seahorses & Pipefish – specialized PI

Mormon crickets – spermatophores

Jacanas – Polyandry, ♂ parental care

In all *these cases, males are the more choosey sex and/or females compete among themselves for males.

But why is male PI > female PI in these

sex-role reversed species in the first place?

  • Trivers: Sexual selection =
  • Sex investing less will compete for sex investing more (intrasexual selection)
  • Sex investing more will be discriminating in choosing mates (epigamic selection)
slide66

♂ usually ♀

Competition for mates

Selection among mates

Biased operational sex ratio

High potential

reproductive rate

Low potential

reproductive rate

lower PI higher PI

initial differences in parental investment

Alcock Fig 10.8