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

Protandry —> Protogyny —>

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 MalesNumber of Females __________________________________________________________________ Initial population Family A 4 0 Family C 2 2 Subsequent population (sum) C A = 4/106 = C C = 2/ /102 = (family C has a higher reproductive success) __________________________________________________________________ Note: The contribution of family x is designated C x.

Comparison of the Contribution to Future Generations of Various Families in Case a in Populations with Different Sex Ratios __________________________________________________________________ Case a Number of MalesNumber of Females __________________________________________________________________ Initial population Family E 0 4 Family C 2 2 Subsequent population (sum) C E = 4/106 = C C = 2/ /102 = (family C has a higher reproductive success) __________________________________________________________________ Note: The contribution of family x is designated C x.

Comparison of the Contribution to Future Generations of Various Families in Case a in Populations with Different Sex Ratios __________________________________________________________________ Case a Number of MalesNumber of Females __________________________________________________________________ Initial population Family A 4 0 Family C 2 2 Family E 0 4 Subsequent population (sum) C A = 4/106 = C C = 2/ /106 = All three families have equal success C E = 4/106 = __________________________________________________________________ Note: The contribution of family x is designated C x.

___________________________________________________________________________ Case bNumber of MalesNumber of Females ____________________________________________________________________________ Initial population Family A 2 0 Family B 1 2 Subsequent population (sum) C A = 2/103 = C B = 1/ /102 = (family B is more successful) Initial population Family B 1 2 Family C 0 4 Subsequent population (sum) C B = 1/ /106 = C C = 4/106 = (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 Family B 1 2 Family C 0 4 Subsequent population (sum) C B = 1/ /206 = C C = 4/206 = (family B now has the advantage) _____________________________________________________________________________ Note: The contribution of family x is designated C x.

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)