Lecture 7

1. Lecture 7 Mating Systems & Social Behavior

2. Today’s topics • 1. Parental care • Investment • Conflict • 2. Mating systems (Monogamy, Polygyny, Polyandry) • 3. Social behavior • Cooperation • Group living • Selection theories

3. Parental Investment • Any behavior that increases the offspring’s chances of survival at the cost of the parent’s ability to rear future offspring. • A tradeoff to maximize fitness • http://www.alaskaphotographyblog.com/2010/06/wolf-pack-kills-moose-calf/

4. Uniqueness of Mammals • While most animals provide no care for their offspring, one or both parents provide at least some care in ALL Mammalia species.

5. Sexual differences • Females often invest more in each individual offspring (gestation, lactation) • Because of limitations in number of offspring, females are more “choosy” in mates (quality over quantity) • Males often invest little. Many males only contribute sperm. • Investment not as trivial as you many think • Limits to ejaculation rate • Remember sperm competition • In most cases, quantity over quality

7. Internal fertilization • Males of species that internally fertilize can not confirm that their sperm actually fertilized the egg. • The female knows the offspring is hers. • Trivers (1972) hypothesis of why males may be less willing to invest.

8. 63% of litters multiple paternity with 4 males siring offspring from 1 litter

9. Precocial vs. Altricial • Males contribute less in precocial systems.

10. Common exceptions limited parental investment– Carnivora, Primates, Rodentia

11. Hardwiring? • Changes in hormone levels in some males lead to parental care. • Pregnant females urine enhances paternal behavior

12. “K” vs. “R” selection • K = stable environmental conditions, larger body size, develop more slowly, longer lifespan, lower mortality rates. • “K” is a reference to carrying capacity. • R = fluctuating environments, high reproductive rates, rapid development, small body size, little parental care • “r” is reference to reproductive rate.

14. Parent-Offspring Conflict • Why do offspring resist the weaning process? • Natural selection may operate differently on the 2 generations (Trivers 1974). • Mother wants to invest to a point, then move on to the next offspring • Offspring wants the mother to continue to invest twice the benefit

15. Born with fully erupt canines and incisors If litter mates are same sex, on is often killed by the other. Offspring-Offspring conflict

16. Mating systems • Polygyny – Males mate with multiple females • Polyandry – Females mate with multiple males • Monogamy – One male and one female • Promiscuity – Absence of prolonged association and multiple mating by at least one sex.

17. Monogamy • Relatively rare in mammals (<5% mammals) • The bulk of instances is found in Primates, Carnivora, and Rodentia.

18. Polygyny • Most common in mammals • Resource defense polgyny – males defend good habitat important to females • Female defense polygyny – females herd for protection from predators and males exclude other males from their harem • Male dominance polygyny – males congregate and advertise their fitness using courtship signals

19. Resource defense polygyny

20. Female Defense Polygyny

21. Male Dominance Polygyny • Male display sites • Leks – more common in birds • http://www.youtube.com/watch?v=aTr0KimaN70&p=49CD6F80A4148072&playnext=1&index=6

22. Polyandry • Rare in mammals • Although genetics is changing theories • Multiple paternity?

23. Neuroendocrine control • Higher levels of hormones implicate monogamy • Oxytocin • Vasopressin

24. Social behavior • Society – a group of individuals of the same species that is organized in a cooperative manner. • Complex social behavior has evolved in almost all orders, but especially among carnivores, cetaceans, and primates

25. Cooperative rearing (although not common) • Individuals other than the young’s mother provide care • Lionesses share nursing • Subordinate wolves regurgitate food • Meerkats young may be raised by up to 30 helpers

26. Why do some mammals live in groups? • Benefits • Protection from physical factors (huddling from cold) • Protection against predators • Finding and obtaining food • Group defense of resources • Assembling members to locate mates • Division of labor among specialists (rare in mammals – mole rats) • Richer learning environment (dolphins and primates)

27. Huddling from cold specialists

28. Why do some mammals live in groups? • Costs • Increased intraspecific competition (more strain on local resources) • Increase chance of spread of disease and parasites (lice, CWD) • Interference with reproduction (new male takes over, infants are killed – common in lion prides)

29. The selfish herd Kin selection Reciprocal altruism Parent manipulation Social behavior theories

30. Aggregating reduces an individual’s chance of being caught by a predator An individually “selfishly” moves to the center of the group to avoid being picked off. Musk ox? The Selfish Herd theory

31. An altruistic gene’s success depends not on how the individual benefits, but on the gene’s benefit to itself. Hamilton’s rule (b/c > 1/r) b = benefit to recipient c = cost to altruist r = coefficient of relationship Kin selection theory

32. Inclusive fitness • Reproductive success of an individuals own offspring + reproductive success of relatives.

33. For kin selection to work, individuals need to be able to determine relatedness • 1. Familiarity • 2. Phenotypic matching • 3. Recognition of genes • Example = MHC

34. Reciprocal Altruism • Individuals may cooperate and behave altruistically if there is a chance that they will be recipients of such acts later • “you scratch my back, I’ll scratch yours.” • Carma?

35. Parent Manipulation • Parents manipulate the offspring the the parents advantage • Giving parental care so offspring have equal chance of surviving and reproducing • Restricting parental care when resources are scarce • Killing some offspring • Temporary or permanently sterilizing offspring and enslaving them as helpers.