Transcript Evolution of Mating Systems

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
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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?