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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

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ecology lecture 11

Ecology Lecture 11

Life History Patterns 2

overview
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
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
Polygyny
  • Resource defense polygyny
    • Example: African cichlid fish, Lamprologus callipterus
      • Defended resource = shells in which females lay eggs
polygyny1
Polygyny
  • Female defense polygyny
    • Example: Elephant seals (females aggregate)

Photo: www.driftersister.com

polygyny2
Polygyny
  • Female defense polygyny
    • Example: Elephant seals (males compete for beachmaster status)

Photo: www.wetasschronicles.com

polygyny3
Polygyny
  • Lek polygyny
    • Males clump, but not due to another resource
      • Males become the clumped resource!
    • Example 1: satin bowerbirds
polygyny4
Polygyny
  • 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 costs
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
Monogamy
  • Common or rare?
  • In which group of animals is it most common?

www.magicmud.com

monogamy alternate hypotheses
Monogamy: alternate hypotheses
  • Mate assistance: it takes two parents to raise the offspring
    • Example: Adelie penguins
    • Both parents needed for chick survival
monogamy alternate hypotheses1
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 hypotheses2
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.

www.royalbertmuseum.ca

monogamy alternate hypotheses3
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

monogamy alternate hypotheses4
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
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
social monogamy and extra pair copulations1
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 copulations2
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
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
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 polyandry1
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 polyandry2
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 polyandry3
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
Patterns of reproductive effortVariations
  • 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
Patterns of reproductive effortVariations (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