Transcript 10-Sociality-Sex

Social Behavior
Hermits must have lower fitness than social individuals
Clumped, random, or dispersed (variance/mean ratio)
mobility = motility = vagility (sedentary sessile organisms)
Social Behavior
Use of Space
Philopatry
Fluid versus Viscous Populations
Coarse-grained versus fine-grained utilization
Individual Distance, Daily Movements
Home Range
Territoriality (economic defendability)
Resource in short supply
Feeding Territories
Nesting Territories
Mating Territories
Net
Benefit
^
Sexual Reproduction
Monoecious versus Diecious
Evolution of Sex —> Anisogamy
Diploidy as a “fail-safe” mechanism
Costs of Sexual Reproduction (halves heritability!)
Facultative Sexuality (Ursula LeGuin -- Left Hand of Darkness)
Protandry -- Protogyny (Social control)
Parthenogenesis (unisexual species)
Possible advantages of sexual reproduction include:
two parents can raise twice as many progeny
mix genes with desirable genes (enhances fitness)
reduced sibling competition
heterozygosity
biparental origin of many unisexual species
Sexual Reproduction
Protandry—>
Monoecious versus Diecious
Protogyny—>
Evolution of Sex —> Anisogamy
Diploidy as a “fail-safe” mechanism
Costs of Sexual Reproduction (halves heritability!)
Facultative Sexuality (Ursula LeGuin -- Left Hand of Darkness)
Protandry -- Protogyny (Social control)
Parthenogenesis (unisexual species)
Possible advantages of sexual reproduction include:
two parents can raise twice as many progeny
mix genes with desirable genes (enhances fitness)
reduced sibling competition
heterozygosity
biparental origin of many unisexual species
Why have males?
“The biological advantage of a sex ratio that is
unbalanced in favor of females is readily apparent in
a species with a promiscuous mating system. Since
one male could fertilize several females under such a
system, survival of a number of males equal to the
number of females would be wasteful of food, home
sites, and other requirements for existence. The contribution
of some of the surplus males to feeding the predators on the
population would be economically advantageous. In other
words, the eating of the less valuable (to the
population) males by predators would tend to
reduce the predator pressure on the more valuable
females.” — Blair (1960) The Rusty Lizard
W. Frank Blair
Sex Ratio
Proportion of Males
Primary, Secondary, Tertiary, Quaternary
Equilibrium sex ratio
Fisher’s theory: equal investment in the two sexes
Ronald Fisher
Comparison of the Contribution to Future Generations of Various
Families in Case a in Populations with Different Sex Ratios
__________________________________________________________________
Case a
Number of Males
Number of Females
__________________________________________________________________
Initial population
Family A
Family C
Subsequent population (sum)
100
4
2
106
100
0
2
102
CA = 4/106 = 0.03773
CC = 2/106 + 2/102 = 0.03846 (family C has a higher reproductive success)
__________________________________________________________________
Note: The contribution of family x is designated Cx.
Comparison of the Contribution to Future Generations of Various
Families in Case a in Populations with Different Sex Ratios
__________________________________________________________________
Case a
Number of Males
Number of Females
__________________________________________________________________
Initial population
Family E
Family C
Subsequent population (sum)
100
0
2
102
100
4
2
106
CE = 4/106 = 0.03773
CC = 2/106 + 2/102 = 0.03846 (family C has a higher reproductive success)
__________________________________________________________________
Note: The contribution of family x is designated Cx.
Comparison of the Contribution to Future Generations of Various
Families in Case a in Populations with Different Sex Ratios
__________________________________________________________________
Case a
Number of Males
Number of Females
__________________________________________________________________
Initial population
Family A
Family C
Family E
Subsequent population (sum)
100
4
2
0
106
100
0
2
4
106
CA = 4/106 = 0.03773
CC = 2/106 + 2/106 = 0.03773 All three families have equal success
CE = 4/106 = 0.03773
__________________________________________________________________
Note: The contribution of family x is designated Cx.
___________________________________________________________________________
Case b
Number of Males
Number of Females
____________________________________________________________________________
Initial population
100
100
Family A
2
0
Family B
1
2
Subsequent population (sum)
103
102
CA = 2/103 = 0.01942
CB = 1/103 + 2/102 = 0.02932 (family B is more successful)
Initial population
100
100
Family B
1
2
Family C
0
4
Subsequent population (sum)
101
106
CB = 1/101 + 2/106 = 0.02877
CC = 4/106 = 0.03773 (family C is more successful than family B)
Natural selection will favor families with an excess of females until the population
reaches its equilibrium sex ratio (below).
Initial population
100
200
Family B
1
2
Family C
0
4
Subsequent population (sum)
101
206
CB = 1/101 + 2/206 = 0.001971
CC = 4/206 = 0.01942 (family B now has the advantage)
_____________________________________________________________________________
Note: The contribution of family x is designated Cx.
Differential Mortality of the sexes during the
period of parental care.
Differential Mortality of the sexes during the
period of parental care.
Evolution of Sex : Isogamy —> Anisogamy
Sexual reproduction halves heritability, offsetting factors
Diploidy as a backup system
Simultaneous vs. sequential hermaphroditism
Monecious vs Diecious, Protandry, Protogyny
Why have males?
Fisher’s theory of sex ratio, equal parental investment
Heterozygosity
Biparental origin of many unisexual species
Sexual Selection
Mating Preferences
Sex that invests the most is the most choosy about mates
Competition for the best mates of the opposite sex
Jealousy, Desertion, Cuckoldry
Certainty of Maternity, Uncertainty of Paternity
Epigamic selection (intersexual, between the sexes)
“Battle of the sexes”
Natural selection produces a correlation between
male genetic quality and female preference
“Sexy son” phenomenon (females cannot afford to mate
with males that are not attractive to other females)