24. Mating systems: Monogamy

Quiz: Females can NOT influence male reproductive success after copulation.

A. True

B. False

B. False

Greek terms

• Terms ending with -____ refer to number of partners or characteristics of gametes

• Terms ending with -gyny refer to females

• Terms ending with -andry refer to males

• mono - “one” ; poly - “many”

gamy

Greek terms

• Terms ending with -gamy refer to number of partners or characteristics of gametes

• Terms ending with -____ refer to females

• Terms ending with -andry refer to males

• mono - “one” ; poly - “many”

gyny

Greek terms

• Terms ending with -gamy refer to number of partners or characteristics of gametes

• Terms ending with -gyny refer to females

• Terms ending with -____ refer to males

• mono - “one” ; poly - “many”

andry

Greek terms

• Terms ending with -gamy refer to number of partners or characteristics of gametes

• Terms ending with -gyny refer to females

• Terms ending with -andry refer to males

• mono - “____” ; poly - “many”

one

Greek terms

• Terms ending with -gamy refer to number of partners or characteristics of gametes

• Terms ending with -gyny refer to females

• Terms ending with -andry refer to males

• mono - “one” ; poly - “____”

many

Mating systems

__________ - 1 male, 1 female

mate guarding

mate assistance

female enforced

Monogamy

Mating systems

_______ - 1 male, >1 female

resource defense

female defense

scramble competition

explosive breeding assemblage

lek

Polygyny

Mating systems

______ - 1 female, >1 male

male defense

resource defense

Polyandry

Mating systems

Promiscuity or ____________

both sexes can mate w/multiple partners

Polygynandry

polygyny- means you are going to have some males with ___ mates, if 50/50 sex ratio is assumed, some have 0 mating success

no

strong polygyny = ___ male mating with all females and most males having no mates

one

strongest variance amongst males is strong polygyny

in moderate polygyny, some variance amonst male mating success

strength of sexual seleciton is greatest in strong polygyny

strong selection for either male male competioion or female choice

Social monogamy- differs by class

Mating with one partner for a breeding season or longer

monogamy where two individuals are interacting

genetic monagomy- did parantage anaylisis, only one father and one mother represented in a nest

social monogomy= two indiviudals are interacting with one another

could be either for one breeding season or longer than that

social monogamy is rare in mammals. Why? females can take care of young on their own, so males don’t need to express parental care, so then males are just going to use that time to try and find ____ females to mate with

more

Social monogamy- differs by class

Mating with one partner for a breeding season or longer

monogamy where two individuals are interacting

genetic monagomy- did parantage anaylisis, only one father and one mother represented in a nest

social monogomy= two indiviudals are interacting with one another

social monogamy is more common in birds= why? male birds can also incubate and feed young, no gender requirement, young often REQUIRE two parents to feed them, if males don’t help then babies ___.

die

Reptiles

social monogomy very rare in reptiles, unusual , one istance is the _________ lizards

Shingleback

SOCIAL Mating systems in birds:

Monogamy (pair bond between 2 individuals)

parental care shared

approx. ___% of all bird species

Polygyny (male mates with several females)

parental care usually by female

approx. _% of all birds

Polyandry (female associates with several males)

parental care typically by males

fewer than _% of all birds

Promiscuity (indiscriminant sexual relationships)

about _% of all birds

92, 2, 1, 6

Monogamy:

Pair bonds may last for a single breeding attempt, a breeding season, or many breeding seasons

Occurs when:

Male participation is _________ for successfully raising young

OR

Males cannot monopolize __________ necessary for supporting extra mates

essential, resources

Social versus Genetic monogamy

95% of superb fairy-wren nests contained extra-pair young.

________ means socially monogamous, but still 99% percent are from diff males, so not genitically monogamous

~100% of nestlings were produced by their

social parents in Florida scrub-jays.

Both are socially monogamous!

extra-pair

Why be monogamous?

Polyandry has fitness costs. In primates, the number of mates accepted by females is correlated with the investment made in white blood cells, a component of an animal’s immune system. (The higher the measure of white blood cells, the stronger the immune system.) This result suggests that the more polyandrous the species, the greater the challenge to the female’s immune system. Each data point represents a different primate species.

why measure white blood cells, part of the _________ system, why related to mating system? if you have lots of sexual partners exposed to sexually transmitted diseases, so if exposed to a lot of STDs then you better have a good immune system

So this is a generic measure of immune function, the more sexual partners you have the more your going to invest in immune function

costly presumably, every white blood cell you make is some investment energy you could be spending elsewhere, so investment your making in immune function, due to having more sexual partners

correlation or causation?

Have to test by putting them in captive situation where no exposure to multiple males. response to having more mating opportunities or if evolutationary response

could test by giving more access to multiple mates, this is for a species, looing within a population, who would you expect to have strongest immune response here amongst the males? the one male that mates with all other females in Strong polygyny

so there are ways to test this idea

could just be a correlation because

why might you see this relationship but it’s not causative? what if polyangryous species have higher territories so interact with more envionrment and therefore exposed to more pathogens, possibly not related at all with number of sexual partners

immune

- Potential mates do not form groups but do roam widely,

making them costly to locate

Mate limitation hypothesis

Individuals have the ability to restrict mating behavior of

their partner.

Mate guarding hypothesis

Resources are so critical to successful reproduction that both

parents are necessary to raise young.

Mate assistance hypothesis

- The risk of infanticide is high and a partner can provide

protection against infanticidal males.

Infanticide hypothesis

Non-mutually exclusive hypotheses to explain WHY monogamous mating systems evolve

a. Mate limitation hypothesis

- Potential mates do not form groups and roam widely, making them costly to locate

Resource-based Mating Systems

Emlen and Oring (1977) - the ecology of an organism may not permit males to have more than one partner.

male follows around female to prevent her with mating with multiple ____

resources wildly distributed, he can’t prevent her from mating with multiple males

males

Non-mutually exclusive hypotheses to explain why monogamous mating systems evolve

b. Mate guarding hypothesis

- Individuals have the ability to restrict mating behavior of

their partner.

Mate guarding and mate assistance in the cricket Gryllus campestris. (A) A male that has acquired a mate remains with her in his territory. If the pair is attacked, the male permits the female to rush into the burrow first, at great cost to his personal safety. (B) Solitary territorial males are much more likely to survive an attack. A female that lives alone is less likely to survive than one paired with a self-sacrificing partner.

if paired, male gets eaten at a higher rate but female is not

in this case, not guarding from other males but from potential ________

predators

Non-mutually exclusive hypotheses to explain why monogamous mating systems evolve

c. Mate assistance hypothesis

- Resources are so critical to successful reproduction that both

parents are necessary to raise young. Paternal male European starlings help their mates. Males keep their clutches warmer by sharing in incubation duties. (A) Eggs that were incubated by both parents were kept at about 35°C most of the time, whereas eggs incubated by the female alone were often several degrees cooler. (B) Both male and female starlings incubate the eggs. In this nest, all the eggs hatched successfully.

why do you see diff in patterns? female leaves the nest - 35*, and when the male takes turn incubating the eggs, so eggs don’t change temperature

if female leaves and male doesn’t do anything then the egg temperature will drop

if maintaining a constant temperature is best for raising young, then __________ is going to be selected for

monogamy

Non-mutually exclusive hypotheses to explain why monogamous mating systems evolve

c. Mate assistance hypothesis

- Resources are so critical to successful reproduction that both parents are necessary to raise young.

Paternal care boosts reproductive success in spotless starlings. Males whose testosterone levels were reduced by the anti-androgen cyproterone acetate (CA) provided more food for their broods and had the highest fledging rates per brood. Males given extra testosterone (T) provided less food and had the lowest fledging rates. Untreated controls were intermediate with respect to both feeding and fledging rates.

Non-mutually exclusive hypotheses to explain why monogamous mating systems evolve

c. Mate assistance hypothesis

- Resources are so critical to successful reproduction that both parents are necessary to raise young.

Male care of offspring affects fitness in the California mouse. The number of offspring reared by female mice falls sharply in the absence of a helpful male partner.

if males are present, then go from mean number of young born 2 young, and if male is absent then it goes from 2 to less than 1, more babies are not emerging from the nest, why?

possibility is _________ showing up and no male there to guard young

predators

Non-mutually exclusive hypotheses to explain why monogamous mating systems evolve

c. Mate assistance hypothesis

- Resources are so critical to successful reproduction that both parents are necessary to raise young.

snow bunting

Remove male parental care and babies __.

if you don’t have the dad around then fewer nests fledged than if both parents are around

die

Monogamy: can be associated with promiscuity

• EPCs (extra-pair copulations)-promiscuity

• EPP (extra-pair paternity)

• EPFs (extra-pair fertilizations)

20%-50% of nestlings in songbird nests are from EPFs.

Advantage to males of promiscuity?

Advantage to females of promiscuity?

Extra-pair fertilizations

In many monogamous songbirds, the percentage of extra-pair young has been found to be about 10 - 25%. (as high as __%)

80

Who has EPC/F’s with whom?

mostly extra pair maturnity happens with neighbors

Benefits of EPC/P/F’s for males:

Increased fitness- more babies!

Possible future mate acquisition

Insurance against mate's _______

infertility

Possible costs for males:

Because not all individuals pursue EPCs

Sperm depletion & ejaculate production costs

Increased risk of cuckoldry - social female mate could also be finding other _____

Reduction in parental care

Increased likelihood of “divorce”

Sexually transmitted disease (STDs)!

mates

Benefits of EPC/P/F’s for females:

Fertility assurance (“better sperm” hypothesis)- higher hatch rate (redwing blackbirds), fewer stillborn babies (snakes).

Genetic compatibility hypothesis (no “duds” or “best” male per se, based on match of female and male genes (e.g., MHC) - could be “______ _____ for female

Increased genetic diversity of offspring might be favored by selection (particularly in a variable environment).

Improved genetic quality of young (good genes)

Access to resources (females can forage on territories of males they have mated with)

better match

Possible costs for females:

Because not all individuals pursue EPCs

Male retaliation

Risk of injury

___________ from extra-pair (or potential extra-pair) males

Sexually transmitted disease (STDs)!

Harassment

Hormones and mating systems

In polygynous species, males tend to have _____ testes and higher testosterone than in monogamous species.

larger

The Vole Story

Two similar species:

• Prairie Vole - Microtus ochrogaster

– Socially monogamous

• Montane Vole – Microtus montanus

– Highly polygynous

Hormone/neurotransmitter differences in reward centers in the brain that are associated with behavioral differences. Good system to study biology of mating systems!

Hormones and Pair Bonding

Oxytocin (OT)

Vasopressin (VP)

• Released from posterior pituitary into circulation.

• But also produced/used in brain as neurotransmitter/ neuromodulator.

• Very ancient family of peptides - all vertebrates have a form… highly conserved.

OT, VP and Behavior

Prairie Vole (monogamous species)

• Give OT to females- facilitates pair bonding.

• Give OT antagonist (blocker)- inhibits pair bonding.

• Give VP to males- facilitates pair bonding.

• Give VP antagonist (blocker)- inhibits pair bonding.

• VP and OT do not influence copulation, just ______.

bonding

Neuroanatomy

• Montane and Prairie Voles differ in both OT and VP receptor distribution

• Prairie Vole (monogamous)– OT receptors found in brains areas related to ______

• Montane Vole (polygynous)- OT receptors found in areas not associated with reward.

prairie vole gets positive experience with monogamous behavior, the montane vole gets a lot of receptors for oxytocin, not a reward center, does not make them feel good.

reward