Evolution of Mating Systems Chapter 8
Mating Systems-Chapter 8 1 Monogamy 2 Polyandry 3 Polygyny And the many combinations within!
Why should a male be monogamous? 1 extension of guarding, little chance of another mating 2 mate-assistance, big increase to fitness, gryllus crickets 3 male needed to have any success, seahorse 4 female-enforced, burying beetles Not common in mammals
More common in birds Having both parents increases nestling survival in many birds But 90% of bird species studied show EPC. So He might be raising babies who aren't his! Explain microsatellite analysis.
Polyandry High, male-biased sex ratio, females with territories are rare and can attract multiple males. Spotted Sandpipers Female can lay more eggs Ratio favors males Locally rich food supply No fitness benefit of 2 parents
Pro Why do females seek additional Assure fertility Good genes Genetic compatibility Resources More caregivers Male protection Reduced infanticide matings? Con Exposure to disease/parasite Risk of predation Energy expenditure Many females show higher fitness with EPC!
Polygyny How do you find lots of females? Scramble competition: try to find a receptive female. Female-defense: find the females, guard them Resource-defense: defend territory with resources Lek: defend a display territory Lots of variation in male success
Scramble Competition Can t defend females. Frogs and explosive breeding.
Female Defense Polygyny Females form groups for protection Males try to control access to these groups Oropendola
Resource-defense Polygyny Cichlid fish, male creates middens of shells Small, localized resource allows males to monopolize
Lek Males gather, display and few get most of the matings. Why do females come?https://www.youtube.com/watch?v=1kdo vnsdxws
Lek Females are drawn to the location, not defensible= hotspot hypothesis Males are drawn to successful males to cash in = hotshot hypothesis Females gather to compare males = female preference hypothesis Hard to distinguish among these.
The evolution of Parental Care What to do after mating? Chapter 9
Why provide parental care? Increased fitness! Cost-benefit analysis What are the costs? Consider lifelong reproduction and predation risk
Who gives parental care? If only one, typically females. Why? Males and paternity, less benefit, greater cost
So why do males ever care for young? Cost-benefit analysis (again) Males can care for multiple broods Greater benefit Females grow slower which impacts fertility Greater cost Therefore, males tend to guard eggs in sticklebacks.
Sexual Selection and parenting Females prefer male harvestman with eggs
Water bugs and parental care Selection for large size, requires large eggs (need oxygen)which led to evolution of parental care. Cost-benefit analysis favors males.
If parental care is costly, how do you recognize young? Smell and calls enable recognition Predict that species at risk of caring for non-related offspring are more likely to make distinct signals.
If parental care is costly, how do you recognize young? Compare species to breed colonially vs. individually: cliff swallows and barn swallows. Which has more variable calls? More accurate recognition?
Do all adults recognize offspring? Ring-billed gulls adopt unrelated chicks What are the costs and benefits?
Brood Parasite Behavior How did this behavior evolve? 1 Gradually, first parasitize your own species. 2 Suddenly, direct interspecific parasitism Support for the first from intraspecific brood parasites, such as wood ducks
Sneaky Egg Dumping Further intraspecific parasitism Adding eggs to the nests of other females even if she has her own nest
Recent vs. ancient brood parasites Cuckoos are 60 mya. Brown-headed cowbirds only 3 or 4 mya Predict who they will parasitize, closely related species or distant?
Parasitism of unrelated species Usually the parasite is much larger, chick or egg Sensory exploitation Could support sudden evolution of parasitism Unresolved!
So, you've got a parasite. Now what? Can parents recognize parasites? Some species can. What is the risk? Remove if risk of parasitism is low.
What would cause egg acceptance? 1. Small parents, can't throw out egg 2. Few nesting sites, no options 3. Late in the season, too late to start again 4. Mafia parents-cuckoos and brown-headed cowbirds
The Evolutionary Arms Race There is a conflict between host and parasite. Cuckoo and Fairy-wrens Parasite tries to closely imitate egg.
Unequal investment in offspring Red Mason Bees and sexual determination Provisioning controls sex
Unequal investment in offspring By age: Invest more in the first larva so at least some will fully mature: burying beetles By sex: Females with abundant foods more likely to produce males: humans, red deer. Why? Trivers-Willard hypothesis: parent should favor one sex of offspring over another if parental condition varies or fitness of offspring will vary with provisioning.
Parenting issues: sibling conflict Great Egret and sibling conflict. Why kill your sib? Fitness cost to parent? Creates Parent- Offspring Conflict. First born is larger with more androgens!
In Mammals Hyenas can have twins Siblicide happens more with long female travel time Siblicide twins get less milk than non-siblicides The surviving twin gets all the milk, no reduction Moms can stop the fighting and favor the smaller cub. What's happening?