Lec13 Mating Systems

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Mating Systems

Review of reproductive strategies from previous lecture

Mating Systems

Monogamy

Polyandry

polygamy

Mating System

You should be able to address the following questions:

What sexual strategies are used in different mating systems?

Mating System

You should be able to address the following questions:

Why is it questionable whether polyandry is adaptive? What factors would make it adaptive and what factors would not? Why are females polyandrous?

Mating System

You should be able to address the following questions:

Is monogamy adaptive? What theories and data indicate it is and is not? What factors may influence whether or not it is adaptive? Why are males ever monogamous?

Mating System

You should be able to address the following questions:

Why is there a high diversity of polygamous sytems?

Mating Systems:
What are we talking about?

Evolutionary point of view

What happens in a mating system related to natural selection?

Mating Systems:
What are we talking about?

Evolutionary point of view

What factors related to mating systems influence an individuals fitness?

Mating Systems

Mating systems primarily refers both to copulation events and offspring produced

Additional behaviors influence if offspring are produced/survive from copulation

Mating Systems

Several factors influence system

Amount of Parental care

Availability of other mates

Frequency of mating with same partner

Operational Sex Ratio

OSR operational sex ratio

Males ready to mate: females ready to mate

Ratio of males to females, given they have different energy investments in reproduction

Biased to sex with lowest reproductive investment in each offspring

Gives that sex greater potential to increase genetic fitness through polygamous mating

Reproductive Rate

What is a reproductive rate?

What factors influence a reproductive rate?

Potential reproductive rates

PRR potential reproductive rates

Sex with highest PRR has greatest capacity for polygamy

Temporal and spatial distribution of mates may alter the potential for polygamy and thus influence mating patterns

If females only encounter one mate ata a time then monogamous patterns may arise

Monogamy

Mate-assistance (male parental investment required)

Female-enforced monogamy

Mate-guarding (male mate-guarding is beneficial when females are receptive to males after mating and are rare, and females dont kill males)

Monogamy: Mate Assistance

Hypothesis: monogamy is advantageous to males because ecological factors when there are advantages to:

parental care of offspring

protection of offspring

Monogamy: Mate Assistance

Example

Seahorse (Hippocampus whitei)

Male seahorse broods offspring for 3 weeks

Pouch has room for one clutch of eggs

PRR of males and females is very similar

Females can't produce eggs faster than for one male

Synchrony of reproductive cycle with partner increases male fitness

Seahorse relative

Fitness price to break off relationship

Travel longer distance for new mate

Monogamy: Female Enforced

Female-enforced monogamy

Example birds

Female pokes holes in eggs of female

Razor bills

Rookeries attack females that demonstrate interest in mates

Burying beetle

Male and female find a carcass and bury it

Used to feed larvae

Male goes to top of mound to release pheremones for a second female

Female pushes male off perch

Monogamy: Mate Guarding

Prevent female from mating with other males

Advantageous for males if females

remain receptive after mating

are widely scattered

are difficult to locate

Beneficial if both have high value partner

e.g., cichlid fish

Removed male replaced with smaller male

Monogamy: Parental Care

Males that invest in parental care should be monogamous

Little support in mammals

Mating Systems

There is a wide range of behavior patterns within polyandry and polygamy

Polyandry

Female mates with multiple males

Polyandry

Examples

Honey bees

Queen honey bees mate with many drones (a dozen);

drones mate with one queen

Queens will produce offspring with up to 12 different paternities

Queen ants

Ability of ants to select sperm from different males (e.g., alternate generations different paternity, Sweden)

Polyandry: Female Choice

Female Choice

Females avoid extra-pair copulation

Female solicit extra-pair copulations

Selected sperm use by females

Sperm removal by females

e.g., birds

Ants control use of which sperm for offspring

Polyandry: Benefits

Benefits: Good genes hypothesis

Guppies

80% more offspring

Offspring hatched 9 days sooner

Mothers were more competent

Yellow-toothed cavy (wild guinea pig)

Reduced stillbirths and loss before weaning

How does sperm competition fit in here?

Female choice for males in good condition

Polyandry: Benefits

Benefits: Good genes hypothesis

Genetic compatibility

Number of offspring fertilized by one male was not consistent among females

Rooster sperm.

Female scorpions more likely to mate with stranger than a male she just mated with

Polyandry: Benefits

Benefits: Increase material benefit

Foraging territory

e.g., polyandrous red-winged black-birds can forage on male controlled territories while monogamous birds are chased away

Female Galapagos hawks control foraging territory

Turn over territory to Multiple males to patrol

Polyandry: Benefits

Spermatophore

Contains nutritional value for female in some species (e.g., butterflies)

Can be 15% of male's body weight

More males, more spermatophores, more offspring

Polyandry: Benefits

Parental assistance from more than one mate

Female dunnocks

Dominant and subordinate male

Both males will provide parental care if they have mated with female enough

Polyandry: Benefits

Protection against dangerous males

Primates

Reduce infanticide (Hanuman lemurs)

Males that have mated with a female will tend to leave her offspring alone

Polyandry: Benefits

Benefits: Fertility insurance hypothesis

Increased likelihood of

polyandrous red-winged blackbirds eggs to hatch

Pregnancies in Gunnison's prairie dogs

Rapid loss of sperm in bearded tit

Polyandry:Risks

Loss of partner (e.g., for parental care)

Polyandry:Risks

Venereal Disease

Relationship between degree of polyandry and white blood cell count

Polygamy

Does it make evolutionary sense?

See PRR theory

Polygamy

Diversity of Polygamy

Female defense

Resource Defense

Scramble competition

Lek

Polygamy

Female defense

Males fight with other males to monopolize females

e.g., elephant seal harems

Polygamy

Resource Defense

Males defend territories with resources that females need to reproduce

Polygamy

Scramble competition

Temporal competition for mates

e.g., butterflies

Avoid combat

Do not control territories

Polygamy

Lek

No food or resource benefits of a lek

Very few males mate with females

e.g., grouse

Similarly bower of bower bird contains few resources for female