Social Relations

1. Social Relations Chapter 7

2. Introduction • Behavioral Ecology: Interactions between organisms and the environment mediated by behavior. • Sociobiology: Branch of biology concerned with study of social relations; intraspecific behavioral interactions. • Fitness: Number of offspring (genes) contributed by an individual to future generations. • Sexual reproduction. • Survival of young.

3. Introduction • Fundamental Question: • What is male and female ? • Females produce fewer, larger, more energetically costly gametes. • Males produce more, smaller, less energetically costly gametes.

4. Gamete Dimorphism is Huge

5. Introduction • Female reproduction success is thought to be limited by resource access. • Male reproduction success is limited by mate access.

6. Introduction • Hermaphrodites • Exhibit both male and female function. • Simultaneous • Sequential • Charnov et.al. identified (3) conditions favoring hermaphroditic populations: • Low mobility limiting male:male competition. • Low overlap in resource demands by male and female structures. • Sharing of costs for male and female function.

7. Simultaneous Protogyny =♀→♂ Protandry =♂→♀ Protogyny =♀→♂ Protogyny =♀→♂ Hermaphroditic Reef Fish

8. Mate Choice • Sexual Selection • Differences in reproductive rates among individuals as a result of differences in mating success. • Intrasexual Selection: Individuals of one sex compete among themselves for mates. • Intersexual Selection: Individuals of one sex consistently choose mates among members of opposite sex based on a particular trait.

9. Intrasexual selection Intersexual selection

10. Mate Choice and Sexual Selection in Guppies • Given a choice, female guppies will mate with brightly colored males. • Brightly colored males attract predators. • Color characteristics that have been shown to confer mating advantage: • Brightness • Number of spots • Total pigmented area

11. Mate Choice Among Scorpionflies • Adult scorpionflies (genus Panorpa) feed on dead arthropods in the forest understory. • Dead arthropod supplies are often limited. • Thornhill found that male Panorpa will take possession of, and guard, dead arthropods as nuptial offering to female. • Larger males are more successful. • Small males offer spit.

12. Nonrandom Mating Among Wild Radish • Wild radish flowers have both male (stamens) and female (pistils) parts, but cannot self-pollinate (self-incompatible) • Marshall found non-random mating in wild radish populations. • Interference Competition - Aggressive or inhibitory interaction between individuals. • Some characteristic of the pollen from certain individuals increases pollination success seed plants.

13. Sociality • Evolution of sociality is generally accompanied by: • Cooperative feeding (or other assistance) • Defense of the social group. • Restricted reproductive opportunities. • Cooperation generally involves exchanges of resources or other forms of assistance.

14. Cooperative Breeders • Species living in groups often cooperate in rearing offspring. • What benefit do helpers gain ? • Inclusive fitness: Improve survival and reproductive rates of family members. • Inherited territory: May increase helper’s probability of future reproduction and recruiting helpers. • Kin Selection

15. Packer and Pusey studied cooperationamong African lions in the Serengeti.

16. Acorn Woodpeckers (Melanerpes formicivorus) • Live in groups of up to 16 individuals. • Cooperative defense of acorn stores and raising of young.

17. Sociality • Eusociality • More complex level of sociality. • Three major characteristics: • Individuals of more than one generation living together. • Cooperative care of young. • Division of individuals into non-reproductive and reproductive castes.