Lecture 5: Mating Systems.docx

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Ecology, Evolution and Natural Resources

Mating Systems 10/9/13 Saturday, November 2, 2013 3:38 PM I. Mating system : a social association and the number of sexual partners an individual has per breeding season I. Male I. Some species, a male's access is limited by access to females - male boosts R.S. by mating with more than one female. II. Female I. A female's success is limited by access to resources I. The female boosts reproductive success by getting male parental care, territory, food II. In birds: females invest more than 50% of body weight for a clutch of eggs III. A female can get all sperm she needs to fertilize all her eggs from one male III. Types of mating systems I. Monogamy I. 1 male and 1 female II. Male has sole access to 2 female in a breeding season III. Serial monogamy: 1 male and 1 female in a breeding season, but they choose different mates after that IV. Pair bond: 2 individuals living in close association with each other in a breeding season I. Long term relationship II. Biparental care V. Monogamy is extremely rare in mammals (including primates) I. Lifetime monogamy: rare II. Serial monogamy: more common III. Across animal kingdom I. Less than 3% of all mammal species are monogamous IV. Non-existent in large conspicuous diurnal species I. e.g. humans, gorillas, elephants II. Why? I. Easy to "cheat" : Extra Pair Copulation VI. Monogamy is much more common in small diurnal speces I. e.g. old field mouse (Permyseus polionotus) I. Live in underground burrows II. Dr. David Foltz (1980s) I. Excavated .500 burrows II. Tracked mating pairs III. Genetic analysis of all offspring IV. Behavioral studies V. Found that: I. 90% offspring in burrow belonged to adult male II. 13% burrows didn't have a male I. 1 female inside II. Why do males choose monogamy? Because fitness is related to male choice for females (although real situation is female mate choice) VI. EXPT 1: male is exposed to two females, so the first one becomes the "preferred" I. M1 x F1 produces 23 offspring, while M1 x F2 only produces 18 offspring II. Fitness is associated with mate choice VII. EXPT 2: another male is exposed to same F1/F2 I. During M2 x F2, 19 offspring, and M2 x F2 had 18 offspring II. Some hidden mate choice VII. Male cost-benefit of monogamy I. Cost: huge I. House wrens: I. 1 male x 2 females = 9 offspring, II. 1 male x 1 female <6 offspring II. Benefit I. California mouse: fathers participate completely in parental care I. Pups are born in coldest month of the year and cannot maintain body temperature for 1st 2 weeks II. Requires both parents in burrow for heat VIII. EXPT: (in cold temperature) I. One group given food, and all offspring survive II. Other group put on a wheel, and males had to run to obtain food, leading to lowered offspring survival IX. Biparental care correlates with monogamy X. In 2500 species, parental care is not important for driving monogamy XI. Distribution of females I. Clown shrimp I. Females widely scattered II. Receptive every three weeks III. Male waits: mate guarding, monogamy II. Dik-diks I. Monogamous for years, but the male doesn't contribute parental care II. Provide no protection against predators III. They have too much territory, so males can only guard one IV. When female Dik-diks is estrous, its pee smells different V. Male has to kick dirt over pee and defecate on it so that it won't attract others XII. Female-enforced monogamy I. Burying beetle I. Males and females find a carcass of a mouse/shrew II. They bury it, female lays eggs on carcass III. When the eggs hatch, offspring feed on carcass IV. Carcass can feed more than 1 female's worth of eggs V. Males climbing into lump, and releases his pheromones to attract another female VI. Female knocks down male VII. In the lab, a tethered female couldn't knock down male and releases pheromones XIII. SO: monogamy is rare, but several things will drive it: I. Scarce resources II. Widely spread females III. Parental care IV. Male want to ensure all offspring are his V. Male cost is a huge reduction in R.S. but female benefit is huge raise in R.S. II. Polygamy I. Males and females have multiple males in a breeding season I. Polygyny (1 male and 2 + females) I. Extreme intense competition to mate with as many
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