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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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Short sweet male intraspecific competition l.jpg

Short & SweetMale Intraspecific Competition

Male male competition l.jpg
Male-Male Competition

  • Andersson, 1994 “Sexual Selection”

  • 5 fundamental areas of male-male competition

    • Scrambles

    • Endurance Rivalry

    • Contests

    • Sperm competition

    • Mate choice (Female choice)

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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

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Strength Signal Contests

  • Signals of strength or fighting ability used to assess each other to avoid direct combat

  • Adaptations

    • Visual

    • Auditory

    • Tactile

    • Chemical

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Tactile Strength Signal

  • Rattlesnake

  • Ritualized wrestling to avoid deadly battles



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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


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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

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Elephant Musth


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Strength Signal

  • Gorilla

  • Male signals dominant status

    • Silverback

    • Musk

    • Posture

    • Display


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Strength Signal

  • Manakin

  • Ritualized display to avoid conflict


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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

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  • 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

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Male Sneakers


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Smaller payoff, but it’s better than nothing!

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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


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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


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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


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  • 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

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Bluegill Sunfish

  • Nest in dense colonies

  • Territorial males build nests

    • 15% of males have territories

  • Females arrive & lay eggs

  • Male tends eggs & nest

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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

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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

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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

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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

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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

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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

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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

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  • 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

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Hermaphrodite as a lifestyle

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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

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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

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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

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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

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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

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Dascyllus Damselfish

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Cleaner WrasseLambroides dimidiatus

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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

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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

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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

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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

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Low Motility

  • Some barnacles

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  • Males in low motile parasites exhibit dwarfism

  • Male has to find host AND a host with female

  • Strong selection for dwarfed male size