Animal Behavior Test

Which mating systems is used is influenced by?

Resources and the ability to monopolize them.

The greater the potential to monopolize mates/resources, leads to greater the chance has 1 sex mates several times

Monogamy

-Very rare

-The cost of mating multiply is too high

-Predicted when neither sex can monopolize access to mates or resources.

-Social vs genetic monogamy

Costs of Monogamy

-Time and energy lost, predation risk looking for new looking for new mates.

-Fitness cost from sexually transmitted diseases if multiple partners.

Relation with mates and wbcs

The more mates a female has related with, the higher Wbcs (indicates greater immune challenge)

Male assistance hypothesis

Resources are so critical to successful reproduction that both parents are necessary to rear young

For example: European starlings

Eggs kept warmer with both parents present

Warmer incubation temperatures correlated more hatching

Infanticide hypothesis

If infanticide risk is high, a partner can provide protection against infanticidal males.

Why is monogamy rare in mammals

internal gestation and lactase.

-If males provide some parental care, you could expect more monogamy.

Male presence and its effects.

Males with lower testosterone levels provided more care than those with high testosterone levels

-When males are present, there are more surviving offspring than when males are absent.

Examples: California mouse and Spotless Starling.

Polyandry

One female mates with multiple males

-Common in birds

Direct and indirect benefits of choosy females

-Good gene hypothesis

-Parental care

-Access to resources

-Safety from predators

-Reduced harassment from other males

Ex: Yellow-toothed Cavy. Females restricted to just one mate had fewer surviving offspring.

Why do some males not have their extra pair copulations?

-They might not have a choice to not be cuckolded

-Won’t/can’t give good parental care or show “good genes.” to get more mates

-Better perhaps to tolerate extra pair copulation and hope some of the fertilized eggs are his

Sex-Reversed species

Females possess spikes used to fight other females to secure territories

ex: Wattled jacuna

-Each territorial female gives multiple males their own egg clutch to fertilize (but maybe also by other males) and to raise by themselves

Ecological factors that play a role in sex-reversed species

-Lots of food to support several egg clutches

-Precocial young don’t need two-parent care.

Hypotheses for Polyandry female indirect benefits

Good gene hypothesis (sexy sons): offspring have higher genetic quality or viability

Genetic compatibility hypothesis: Increases the odds of receiving genetically complementary sperm.

Hypotheses for Polyandry female direct benefits

Additional resources hypothesis: Gain access to additional resources from their partner

Ex: Red-winged blackbirds, females who have extra-pair copulations are allowed to forage for food on neighboring males’ territories.

Additional Care hypothesis: Gain more caregivers to help rear young

Correlation with number of mates and offspring number

Females with more mates and more offspring bc more number of compatible sperm

Polygyny

-One male mating with multiple females

-Most common mating system

Hypothesis for Polygyny

Female Defense Polygyny Hypothesis: When resources are evenly distributed in space and females form groups to better access those resources or to help dilute the predation risk, males will follow and guard a group of females.

Resource defense polygyny hypothesis: When resources are clumped, attract females and are easily defensible, males will guard resources AND females by setting up a territory

Lek Polygyny Hypothesis: When resources are distributed heterogeneously, and females are widespread and do not form groups, males will wait for females to come to them

for ex: Grevy’s zebras females gather at scarce water sources, dominant males set up territories near water so they can mate with multiple females.

Harem Defense polygyny

Plain zebra males defend a harem of females after females group to reduce predation

-Males defend a harem of females since their grazing is less disturbed than with subordinate males.

Leks in satin bowerbirds

Serves no direct benefits for females; instead serves as a “lineup" for females to compare many males at once.

Why do males lek?

Multiple hypotheses, but no single hypothesis explains lekking for all species.

Polygynandry

-Both sexes mate multiple times

-Typically occurs in social groups

-Pair bonds form and parental care is require

Ex: Bonobos

Promiscuity

-Both sexes mate multiple times

-No social groups

-Often occurs with external fertilization

-Parental care is usually lacking( young are typically precoical)

- convenience polyandry

Polygynandry and Promiscuity

Population densities and resource availability can influence these mating systems.

Harsh reality

Parents don’t love all their kids the same

Reproductive value

Potential of individual to leave surviving descendants