Ecology Lecture 11Ecology Lecture 11

Life History Patterns 2

OverviewOverview

A mating system includes how members of a particular species (or

population) choose and bond with mates how many mates per individual how parental care (if it occurs) takes place.

Types of mating systems Monogamy: One male mates with one female Polygyny: One male mates with several females Polyandry: One female mates with several

males

“Social” vs. “genetic” monogamy

Key principlesKey principles

The system that evolves depends upon the individual interests of each gender

Male and female interests are often in conflict. Why?

Differences in gamete investment and/or total parental investment

Male “default” = ____________. Why? Is there a female default?

Interests/behavior of one gender serve to constrain options available to the other gender.

PolygynyPolygyny

Resource defense polygyny Example: African cichlid fish,

Lamprologus callipterus Defended resource = shells in which females

lay eggs

PolygynyPolygyny

Female defense polygyny Example: Elephant seals (females

aggregate)

Photo: www.driftersister.com

PolygynyPolygyny

Female defense polygyny Example: Elephant seals (males compete for

beachmaster status)

Photo: www.wetasschronicles.com

Male-male competition and sexual Male-male competition and sexual dimorphism (seals)dimorphism (seals)

NOTE: Each point represents a NOTE: Each point represents a speciesspecies

PolygynyPolygyny

Lek polygyny Males clump, but not due to another resource

Males become the clumped resource! Example 1: satin bowerbirds

Satin Bowerbirds: multiple signals Satin Bowerbirds: multiple signals of health and fitness (and good of health and fitness (and good

genes?)genes?)

PolygynyPolygyny

Lek polygyny Example 2: bullfrogs

Females choose males with longest, loudest and deepest calls

But don’t forget the sneaky f--kers

www.tc.umn.edu

Polygyny: benefits/costsPolygyny: benefits/costs

Male number of offspring likely to correlate

with number of mates (+) Female:

gets a high-quality male (+) gets less of the male’s time and

attention for raising young being defended against predators

MonogamyMonogamy

Common or rare?

In which group of animals is it most common?

www.magicmud.com

Monogamy: alternate Monogamy: alternate hypotheseshypotheses

Mate assistance: it takes two parents to raise the offspring

Example: Adelie penguins

Both parents needed for chick survival

Monogamy: alternate Monogamy: alternate hypotheseshypotheses

Mate guarding: guarding assures paternity; not guarding jeopardizes it

Especially critical if females are rare or receptive for a limited time

Example: many crab species (see sexual selection lecture)

Monogamy: alternate Monogamy: alternate hypotheseshypotheses

Female-enforced monogamy

Similar to mate-guarding, but done by female.

Example: Burying beetles

A female would lose resources, and possibly her offspring if she allows her male to mate again.

www.royalbertmuseum.ca

Monogamy: alternate Monogamy: alternate hypotheseshypotheses

Danger “theory” Leaving

increases chance of dying if predation rates are high.

Example: The mantis shrimp Lysiosquilla sulcata

Lysiosquilla sp. Opencage.info

Mantis shrimp (another Mantis shrimp (another type)type)

Monogamy: alternate Monogamy: alternate hypotheseshypotheses

Pop ‘em out “theory”

Highly fertile mate Not worth

time/energy to seek another.

Example: Djungarian hamsters

bbs.petsky.com.cn

Social Monogamy and Social Monogamy and extra-pair copulationsextra-pair copulations

Extra-pair copulations can increase fitness of participants

Males: More mates more offspring possible.

Females: Historical (not current) ideas: no advantage

for females Observational/experimental evidence: clear

fitness benefits documented for some species Example: Yellow-toothed cavy

Yellow-toothed cavy: Offspring survival Yellow-toothed cavy: Offspring survival as a function of multiple mates for as a function of multiple mates for

femalesfemales

Social Monogamy and Social Monogamy and extra-pair copulationsextra-pair copulations

Direct fitness benefits: genetically based

Good genes What does this mean?

Genetic compatibility What does this mean?

Genetic variability among offspring Why important?

Social Monogamy and Social Monogamy and extra-pair copulationsextra-pair copulations

Other benefits that may improve fitness for females

More resources hypothesis Example: Orange-rumped honeyguides

swap food for sex.

Better protection/care hypothesis Example: Dunnocks (European song

bird) Mate with two males both care for young

Infanticide reduction hypothesis Example: chimpanzees (who’s dad?)

Polyandry (w/o polygyny)Polyandry (w/o polygyny)

Spotted sandpipers: near-complete sex-role reversal

Females arrive on breeding grounds; compete with other females for territories.

Initial male arrives, mates, cares for her first clutch.

Second male arrives later, mates, and cares for her second clutch.

What circumstances What circumstances promote polyandry?promote polyandry?

Female: only lays 4 eggs at once Add eggs (experimentally) decrease

the total young successfully raised Related to incubation effort and protection

Female can reproductive success by laying a second brood Needs second mate

Reproductive success limited by mates rather than gametes in this case

What circumstances What circumstances promote polyandry?promote polyandry?

Why would males “comply?” Operational sex ratio biased toward males

(related to absolute ratio for this species) She abandons

He stays offspring survive He leaves offspring die

Male 1: Certain of paternity for clutch 1; possibility of paternity for clutch 2 How is this possible?

Male 2: Later arrivals less dominant, but still have a chance of paternity if they stay.

What circumstances What circumstances promote polyandry?promote polyandry?

Food fluctuation hypothesis In food-poor years, females put all

energy into eggs and have no energy left for care of eggs/young. Mate assistance (by male) essential

monogamy

In food-rich years (i.e. many mayflies), the female “recovers” her body mass and can lay another batch Monogamy Polyandry

What circumstances What circumstances promote polyandry?promote polyandry?

Heavy predation pressure on nests

Multiple nests assure that at least some young will survive. Male is needed to prevent predation Young will all be lost if he doesn’t stay.

Patterns of reproductive Patterns of reproductive efforteffort

VariationsVariations Numbers of young produced at

a time More young = less parental

investment/individual high mortality among young

Care of eggs/larvae Variability in parental investment

Type of young produced Precocial vs. altricial offspring (What is

the difference?)

Patterns of reproductive Patterns of reproductive efforteffort

Variations (cont.)Variations (cont.) Number of reproductive events in a

lifetime Semelparous: one big reproductive event

in lifetime/many offspring Many are relatively short-lived (squid, annual

plants) But some are long-lived (periodical cicadas)

Itoparous: many reproductive events in lifetime/ fewer offspring per event.

Common especially birds and mammals Timing is an issue:

begin early materials/energy into reproduction,

Begin later materials/energy into survival and growth

““r”-strategistsr”-strategists ““K”-strategistsK”-strategists

Semelparous Itoparous

Many offspring Few offspring

Little/no parental investment per individual offspring

High levels of investment per individual offspring

Relatively short lifespan Relatively long lifespan

Begin to reproduce relatively early in life

Begin to reproduce relatively later in life

Good colonizers of newly available habitat, but often not effective competitors

Not usually colonizers, but arrive later in succession, compete successfully

““r” vs. “K” strategistsr” vs. “K” strategists