short sweet male intraspecific competition
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Short & Sweet Male Intraspecific Competition

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Short & Sweet Male Intraspecific Competition. Male-Male Competition. Andersson, 1994 “Sexual Selection” 5 fundamental areas of male-male competition Scrambles Endurance Rivalry Contests Sperm competition Mate choice (Female choice). Contest Competition. Combat Contests

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male male competition
Male-Male Competition
  • Andersson, 1994 “Sexual Selection”
  • 5 fundamental areas of male-male competition
    • Scrambles
    • Endurance Rivalry
    • Contests
    • Sperm competition
    • Mate choice (Female choice)
contest competition
Contest Competition
  • Combat Contests
    • Traits that improve success in fights
      • Large size
      • Strength
      • Weaponry
      • Agility
  • Strength signals
    • Favors Threat signals
  • Alternate tactics
    • Alternate mating tactics of inferior competitors, avoiding contests with superior rivals
strength signal contests
Strength Signal Contests
  • Signals of strength or fighting ability used to assess each other to avoid direct combat
  • Adaptations
    • Visual
    • Auditory
    • Tactile
    • Chemical
tactile strength signal
Tactile Strength Signal
  • Rattlesnake
  • Ritualized wrestling to avoid deadly battles
auditory strength signal
Auditory Strength Signal
  • Red deer in rutting season
  • Avoid conflict by signaling strength with auditory signals
  • Frequent & long bellows
    • Night & day
    • Prevents from feeding
    • Lose stamina
  • Signal stamina, size & confidence
strength signal
Strength Signal
  • Elephants use visual, vocal, tactile & chemical strength signals to avoid conflict
  • Typical Male bull
    • Display with trunk
    • Lock tusks
    • “shove” match
  • Male bull in musth
    • Musth gland
    • Increased levels of testosterone
    • Temporal gland secretes
    • Urine dribbles
    • Posture- head high, chin tucked, long stride
      • Ear wave, tusk wave
elephant musth
Elephant Musth
strength signal9
Strength Signal
  • Gorilla
  • Male signals dominant status
    • Silverback
    • Musk
    • Posture
    • Display
strength signal10
Strength Signal
  • Manakin
  • Ritualized display to avoid conflict
alternative contests
Alternative Contests
  • When it pays to be a wimp
  • Poor competitors avoid direct contests by using alternative behaviors
  • Adaptations that promote
    • Sneaky behaviors
    • Hermaphrodites
    • Dwarfism
    • Coersion & forced copulations
    • Infanticide
  • Alternate strategy used by non dominant & immature males (small)
    • Short term & long term strategy
  • Strategies involve taking advantage of dominant males distraction
  • Selection favors small & inconspicuous males
  • Cost benefit analysis
    • Dominant aggressive lifestyle is risky & expensive
male sneakers
Male Sneakers

Smaller payoff, but it’s better than nothing!

yellow throated sneaker
Yellow Throated Sneaker
  • Mimic the throat color of receptive females
    • Also mimic female behavior
    • Female rejection bob, nips & chase
  • High reproductive success rate
  • When a dominant male is encountered the sneaker mimics a female
  • Behavior only effective on Orange males
blue throated monogomous
Blue Throated Monogomous
  • Mate guard a female
    • Ensure paternity
  • Moderate testosterone levels
  • Moderate life ~7
  • Aggressive with other blue males over territory
    • Display to maintain territory
    • Typically avoid battle
  • Recognize sneaker males
    • Drive out sneakers
    • Low sneaker success
orange throated dominant
Orange Throated Dominant
  • High levels of testosterone & aggression level
    • Short lived ~2yrs
  • Defends territory & multiple females
  • Invade blue male territory to gain paternity in blue clutches
    • Vulnerable to sneakers
rock paper scissors22
  • Multiple polymorphism exist in unison
  • Each polymorphism dominates in 6 yr cycle
  • Yellows can fool oranges
  • Blues attack yellows
  • Orange defeat challenging males, but fooled by yellows
bluegill sunfish
Bluegill Sunfish
  • Nest in dense colonies
  • Territorial males build nests
    • 15% of males have territories
  • Females arrive & lay eggs
  • Male tends eggs & nest
bluegill sunfish28
Bluegill Sunfish
  • 3 male reproductive tactics w/ 3 polymorphisms
  • Age independent
  • Parental Male
    • Reproductive maturity at 7 yrs
    • Large size
    • Build & defend nests
  • Satellite male
    • Sexual maturity 2-5 yrs ave 4 yrs
    • Die early (less than 7yrs), if persists remain as satellite
    • Intermediate size
    • Mimic females
  • Sneaker
    • Small & inconspicuous
    • Sexual maturity 2-3 yrs
parental male
Parental Male
  • Grows rapidly & steadily until reaches maturation
    • 7 yrs
  • Immature males stay away from mating colony & focus on growth
    • “Stayaways”
  • Immature males have relatively small testes per body size
satellite male
Satellite Male
  • Average male in colony ~4 yrs
    • Grow fast initially then slows growth rate
  • Large testes relative to body size
  • Hovers above colony
  • When female visits parental male nest satellite drops down into nest
  • Satellite mimics female sinks down slowly into nest while female is present & releases sperm
    • Confuses parental male
  • Achieves reproductive success without having to care for young
  • Will never mature into parental type
sneaker male
Sneaker Male
  • Small & inconspicuous male
    • Ave age in colony 2-3 yrs
    • Grow fast initially then slows growth rate
  • Large testes relative to body size
  • Darts rapidly into nest while parent male & female are mating
  • Releases sperm onto eggs
  • High risk of injury from attack
  • Sneaker male will mature into satellite male
game theory
Game Theory
  • Maynard Smith & George Price, 1973
    • “The Logic of Animal Conflict”
  • Genetic equilibrium between alternate strategies
    • One strategy can’t be completely invaded by an alternate strategy
  • Game Theory used to understand patterns of conflict
    • Which strategy provides highest fitness
    • Warrior vs. Wimp
    • Hawk & Dove
hawk dove
Hawk & Dove
  • Competing for a limited resource
  • Hawk
    • Initiates aggressive behavior
    • Aggression continues until injured or opponent is down
  • Dove
    • Retreats immediately if opponent initiates aggressive behavior
contest results
Contest Results
  • Dove-Dove
    • Resource shared equally
    • Neither injured
  • Hawk-Hawk
    • Both injured badly
  • Hawk-Dove
    • Dove immediately retreats
    • Hawk gains resource

No single best strategy, each strategy is the best answer to the other

  • An organism with both male & female reproductive organs
  • Common in invertebrates & fishes
  • 2 hermaphroditic strategies
    • Individual persists as hermaphrodite throughout lifetime
    • Sequential hermaphrodites
      • Individual transitions from one sex to another within lifetime
hermaphrodite as a lifestyle
Hermaphrodite as a lifestyle

sequential hermaphrodites have sex change
Sequential Hermaphrodites have Sex Change
  • Change sex in response to size, age, environment
  • Size advantage hypothesis
    • Reproductive success increases with body size differently in males & females
    • By altering sex over lifespan can maximize reproductive success
  • 2 modes
    • Protandry
    • Protogynous
protandry sex change
Protandry Sex Change
  • Adults change from male to female as grow
  • Sex change favored when female reproduction capacity increases faster with body size than does the number of eggs produced by the male
  • Large females produce lots of eggs
  • Small males produce lots of sperm
  • Start out as male, then as reach large size switch to female
  • Found in species that have no direct male-male competition
  • Examples mollusks, crustaceans, fish & some plants
protandry sex change45
Protandry Sex Change
  • Example Amphiprion Anemone fishes
  • Live in or near sea anemones w/o being injured
  • Protected by anemone stinging cell in a symbiotic relationship
    • Males don’t have to fight to maintain territory
  • Group contains 1 monogomous pair & juveniles
  • Females larger produce more eggs
    • Smaller individual of pair is male
  • Increased reproductive fitness for both
protogynous sex change
Protogynous Sex Change
  • Adults change from female to male as grow
  • Opposite pattern of sex change favored when males protect spawning site or territory
  • Large males have increased fertility as they are able to monopolize multiple females
  • Start out as females & change sex into males as grow large enough to defend a territory
  • Examples some fish
protogynous sex change49
Protogynous Sex Change
  • Dascyllus damselfish
  • Social groups of several males & females
  • Male-male competition is high
    • Selection favors large males
  • Individuals start as female & become male as become large enough to compete for females
cleaner wrasse lambroides dimidiatus52
Cleaner WrasseLambroides dimidiatus
  • Social group of one male & multiple females
  • Male competition is high to maintain access to females
  • Selection favors large male
  • If males removed the largest female will transform into a male
    • Exhibits male behavior w/in few hrs
    • w/in 10 days can produce sperm
dwarf males
Dwarf Males
  • Males that exhibit an extreme sexual dimorphism, with dwarf male being many times smaller than the female
  • Observed in marine invertebrates, algae, some vertebrates (fish)
  • Selection favors dwarfism when
    • Low population density (hard to find a date) & low motility (even harder to find a date)
    • Long lived females, short lived males
dwarf males54
Dwarf Males
  • Ability to find a mate is very strong selection pressure
  • The probability of mating with multiple females very low
    • Pick one & stick to her
  • Some species the male physically attaches to the female
    • Males exists as parasite to the female
    • Female provides nourishment in exchange for sperm
      • Ex. Marine invertebrates, Ceratioid anglerfish
low density
Low Density
  • Deep Sea Angler fish
  • 2000-3000m, dark!
  • Low population density
  • Very difficult to find a mate
  • Male uses olfaction to find females
    • Largest nasal organ relative to body size
    • Large eyes
    • Streamlined shape
  • Female body designed for maximizing foraging
low motility
Low Motility
  • Some barnacles
  • Males in low motile parasites exhibit dwarfism
  • Male has to find host AND a host with female
  • Strong selection for dwarfed male size