Mating Systems & Social Behavior Lecture 7 Mating Systems & Social Behavior Sept. 22, 2010

Today’s topics 1. Parental care Investment Conflict 2. Mating systems (Monogamy, Polygyny, Polyandry) 3. Social behavior Cooperation Group living Selection theories Sept. 22, 2010

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/ Sept. 22, 2010

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. Sept. 22, 2010

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 Sept. 22, 2010

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. Sept. 22, 2010

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

Precocial vs. Altricial Males contribute less in precocial systems. Sept. 22, 2010

Common exceptions limited parental investment– Carnivora, Primates, Rodentia Sept. 22, 2010

Hardwiring? Changes in hormone levels in some males lead to parental care. Pregnant females urine enhances paternal behavior Sept. 22, 2010

“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. Sept. 22, 2010

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 Sept. 22, 2010

Offspring-Offspring conflict Born with fully erupt canines and incisors If litter mates are same sex, on is often killed by the other. Sept. 22, 2010

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. Sept. 22, 2010

Monogamy Relatively rare in mammals (<5% mammals) The bulk of instances is found in Primates, Carnivora, and Rodentia. Sept. 22, 2010

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 Sept. 22, 2010

Resource defense polygyny

Female Defense Polygyny

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

Polyandry Rare in mammals Although genetics is changing theories Multiple paternity? Sept. 22, 2010

Neuroendocrine control Higher levels of hormones implicate monogamy Oxytocin Vasopressin Sept. 22, 2010

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 Sept. 22, 2010

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 Sept. 22, 2010

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) Sept. 22, 2010

Huddling from cold specialists

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) Sept. 22, 2010

Social behavior theories The selfish herd Kin selection Reciprocal altruism Parent manipulation Sept. 22, 2010

The Selfish Herd theory 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? Sept. 22, 2010

Kin selection theory 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 Sept. 22, 2010

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

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

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?

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.