evolution of mating systems chapter 8. mating systems-chapter 8 1 monogamy 2 polyandry 3 polygyny...
TRANSCRIPT
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 birdsHaving 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 eggsRatio favors malesLocally rich food supplyNo 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 higherfitness 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 benefitFemales grow slower which impacts fertility
Greater costTherefore, 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 careSelection 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 fornon-related offspring are more likely to makedistinct signals.
Do all adults recognize offspring?
Ring-billed gulls adopt unrelated chicksDecreases 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 broodparasites, such as wood ducks
Sneaky Egg Dumping
Further intraspecific parasitismAdding eggs to the nests of other females
even if she has her own nest
Recent vs. ancient brood parasitesCuckoos are 60 mya.Brown-headed cowbirds only 3 or 4 mya
Predict who they will parasitize, closely related species or distant?
Parasitism of unrelated speciesUsually the parasite is much larger, chick or egg
Sensory exploitation
Could support suddenevolution 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 RaceThere is a conflict between host and parasite.
Cuckoo and Fairy-wrens
Parasite tries to closely imitate egg.
Unequal investment in offspringRed Mason Bees and sexual determinationProvisioning controls sex
Unequal investment in offspringInvest 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 ConflictGreat Egret and sibling conflict. Why kill your sib?
Fitness cost to parent? Creates Parent-Offspring Conflict.
First born is larger with more androgens!
In MammalsHyenas can have twinsSiblicide happens more with long female travel timeSiblicide twins get less milk than non-siblicidesThe surviving twin gets all the milk, no reductionMoms can stop the fighting and favor the smaller cub.What's happening?