Ecology Lecture 11 Life History Patterns 2

Overview  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 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.

Polygyny  Resource defense polygyny  Example: African cichlid fish, Lamprologus callipterus  Defended resource = shells in which females lay eggs

Polygyny  Female defense polygyny  Example: Elephant seals (females aggregate) Photo:

Polygyny  Female defense polygyny  Example: Elephant seals (males compete for beachmaster status) Photo:

Male-male competition and sexual dimorphism (seals) NOTE: Each point represents a species

Polygyny  Lek polygyny  Males clump, but not due to another resource  Males become the clumped resource!  Example 1: satin bowerbirds

Satin Bowerbirds: multiple signals of health and fitness (and good genes?)

Polygyny  Lek polygyny  Example 2: bullfrogs  Females choose males with longest, loudest and deepest calls  But don’t forget the sneaky f--kers

Polygyny: 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

Monogamy  Common or rare?  In which group of animals is it most common?

Monogamy: alternate hypotheses  Mate assistance: it takes two parents to raise the offspring  Example: Adelie penguins  Both parents needed for chick survival

Monogamy: alternate hypotheses  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 hypotheses  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.

Monogamy: alternate hypotheses  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 type)

Monogamy: alternate hypotheses  Pop ‘em out “theory”  Highly fertile mate  Not worth time/energy to seek another.  Example: Djungarian hamsters bbs.petsky.com.cn

Social Monogamy and extra- 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 as a function of multiple mates for females

Social Monogamy and extra- 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 extra- 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)  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 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 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 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 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 effort Variations  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 effort 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”-strategists“K”-strategists SemelparousItoparous Many offspringFew offspring Little/no parental investment per individual offspring High levels of investment per individual offspring Relatively short lifespanRelatively 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” strategists