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?