Download - Lec13 Mating Systems
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