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
Why do females seek additional matings? Pro Con Assure fertility
Exposure to disease/parasite Good genes Risk of predation Genetic compatibility Energy expenditure
Resources More caregivers Male protection Reduced infanticide Many females show higher fitness with EPC!
Polygyny How do you find lots of females? Female-defense: find the females, guard them Resource-defense: defend territory with resources Lek: defend a display territory Scramble competition: try to find and guard a receptive female.
Lots of variation in male success 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? Why would this occur? 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 The evolution of Parental Care 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 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
Intensive, single parent care Selection for large size requires large eggs. 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. Do all adults recognize offspring? Ring-billed gulls adopt unrelated chicks Decreases the parents fitness so why? Cost-benefit analysis
Potential cost? 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? Can parents recognize parasites? Some species can. What is the risk?
Remove if risk of parasitism is low. What would cause egg acceptance? Small parents, can't throw out egg Few nesting sites, no options Late in the season, too late to start again 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 Invest more in the first larva so at least some will fully mature: burying beetles 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. Sibling Conflict Great Egret and sibling conflict. Why kill your sib?
Fitness cost to parent? Creates ParentOffspring 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?
