Mate choice and Life History

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Mate choice and Life History
Ch. 7.3-7.6, Bush
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Outline

• Mating systems and Mate choice
• Territoriality
• Sociality and altruism
• Life History and reproduction

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Outline

• Mating systems and Mate choice
• Territoriality
• Sociality and altruism
• Life History and reproduction

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Mating systems and mate choice

• Asymmetries in the game of sex begin with gametes
• Anisogamy
• not same-size gametes
• The sex with the big gamete is female - by
  definition

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Investment in offspring

• The sex with low investment per offspring
• selection for mating effort
• less choosy about mating
• Females begin with bigger investment per gamete.
• Often (esp. in mammals) females continue with
  greater parental investment per offspring.
• selection for parental effort
• choosy about mating

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Mating systems

• Polygyny
• Males mate with several females
• If sex ratio is 5050, some males never get to
  mate
• Common among mammals, 8 of bird species
• Polyandry
• Where a single female mates with a number of
  males
• Common among insects, some species of snakes, 2
  of bird species
• Monogamy
• Males and females mate only with one individual
• Most common mating system among birds (90)

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Mating systems and mate choice

• In polyandrous systems, general promiscuity
  reigns and very little mate choice occurs
• In polygynous systems, females are choosy with
  which males they mate
• In very few systems where male parental care
  occurs, males may be choosy

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Polygyny and Sexual selection

• Sexual selection
• depends on the success of certain individuals
  over others of the same sex, in relation to
  propagation of the species
• - Charles Darwin, 1871

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Mechanisms of sexual selection

• Intrasexual selection
• Male-male competition
• Intersexual selection
• Female mate choice

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Inciting male competition

• Squirrel mating chase
• Female leads group of males on marathon chase
• the winner among pack of males gets to mate
• Benefits of mate choice are generally clear
• Females mate with male that have superior genes
  which get passed onto offspring

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Female mate choice and Male ornaments
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Carotenoid pigmentation and mate choice

• Carotenoid pigmentation seen in many birds and
  fish come from diet
• Carotenoids increase resistance to parasites
  indicates that coloration may provide an honest
  signal of mate quality
• Frugivorous birds are more often sexually
  dimorphic than granivorous birds

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Polyandry and mate choice in insects

• Females have not evolved ornaments but are larger
• Some evidence that males choose bigger females
• No parental care

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Sperm storage in female insects and mate choice
Many female insects have the ability to store
sperm from many males, only choosing the best to
fertilize her eggs when the reproductive season
is over
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Male-male competition in Drosophila

• Drosophila flies have sperm cells that are up to
  6 centimetres long
• Their testes take up 11 of their body mass

Male Drosophila bifurca
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Deserting and mating systems

• In cases of external fertilization (like in the
  stickleback), the female deposits eggs first and
  can then flee the scene
• male is stuck with the responsibility of parental
  care

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Ornaments and parental care

• Pipefish
• male parental care
• polyandrous
• females are the more ornamented sex
• Seahorse
• monogamous
• Both males and females look similar

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Outline

• Mating systems and Mate choice
• Territoriality
• Sociality and altruism
• Life History and reproduction

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Territoriality

• Types of territories
• Territory, sexual dimorphism and mating systems
• Human mating systems

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Territoriality

• Territory
• An area that an individual defends and from which
  other members of the same species are excluded
• Home range an undefended area used by an
  individual

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Types of territories

• All-purpose
• are used for all the activities of the individual
  (mating, foraging, rearing young, etc.)
• Breeding
• are used for mating and rearing young, and
  foraging occurs elsewhere
• Lek a place where males display in groups and
  females choose a mate
• Foraging
• Used for foraging but breeding occurs elsewhere

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Territoriality is not always fixed

• Iwi bird of Hawaii is territorial only when food
  supply is low

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Territoriality and male size

• Keeping a territory takes energy
• Often territorial animals are ones where the
  males are rather large

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Size dimorphism and polygyny
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Sexual dimorphism

• Pinnipeds (e.g., sea lions, walruses) exhibit
  high levels of sexual dimorphism
• Male pinnipeds keep very large harems of females
• A few males get lots of mates whereas most males
  get none

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Patterns in Sexual dimorphism and mating system

• In species without polygyny, it is often the
  females that are larger
• E.g., the butterfly species, Eupterote harmani

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Territories, fitness, and polygyny
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Human mating system

• Average N. Amer. Female height is 162 cm, average
  male height 175 cm
• Does this mild sexual dimorphism translate into
  mild polygyny?

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Size dimorphism and polygyny
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Territoriality in humans

• Because most humans do not live off the land,
  we dont have typically territories
• Analogous to territories, however, is wealth

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Human polygyny

• Wealthiest 5 of males in the U.S. have more
  extramarital offspring than do other men
• Sex is what is called a zero-sum game, caused by
  the fact that every child has one father and one
  mother
• if some males are having more offspring, then
  other males are having fewer

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Extramarital matings by females

• Based on A, B, O blood types, an estimated 10 of
  children born in North American hospitals could
  not possibly be the genetic offspring of the
  putative fathers
• Cuckolded males waste valuable resources and get
  no evolutionary fitness
• Females may seek extramarital copulations as a
  way to gain good genes for their offspring

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Is monogamy a myth?

• Socially monogamous birds are often not sexually
  monogamous
• The Dunnock has an extremely varied mating system
  with polygyny, polyandry, and monogamy
• In polyandrous trios, the dominant male tries to
  prevent the subordinate male from mating with the
  female, while the female tries to copulate with
  him so that he contributes parental care to
  offspring

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Who wins the war between the sexes?

• From a fitness point of view, nobody
• Because every product of a sexual union has one
  mother and one father, each sex has the same
  fitness
• If ever one sex is at a serious disadvantage,
  their offspring suffer and selection will act
  upon the system to increase the other sexes
  investment in offspring

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Outline

• Mating systems and Mate choice
• Territoriality
• Sociality and altruism
• Life History and reproduction

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Social Mating Systems

• Mating systems are ultimately determined by the
  fitness realized by individual males and females
  under different behavioural schemes
• Some mating systems are puzzling in that
  individuals appear to sacrifice their own fitness
  for the good of others (altruism)

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Types of altruism

• There are two main types of altruistic behaviour
  schemes
• Eusociality
• Cooperative breeding

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Eusociality

• Eusociality occurs mostly in 3 orders
  Hymenoptera (all ants, some bees, wasps),
  Isoptera (termites) and Homoptera (aphids)
• Eusocial insects are characterized by 3 traits
• (1) cooperative care of young by more individuals
  than just the mother
• (2) sterile castes
• (3) overlap of generations so that older sterile
  offspring aid their mother in raising younger
  siblings.

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Eusociality in mammals

• The naked mole rate represents the only known
  case of eusociality in mammals
• One queen mates with 1-3 males in the colony
• Non-breeding workers number between 70-295

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Co-operative breeding in higher vertebrates

• additional adults play a role in raising young
  Female lionesses often suckle one anothers young
• Exists among rodents, mammalian carnivores,
  more than 300 species of birds
• E.g., female lionesses often suckle one anothers
  young
• Occurs mostly in species where a lot of parental
  care is required to rear young

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Altruistic behaviour

• Ground squirrels give warning calls when a
  predator comes near
• Protects others but increases risk to the caller

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Explaining altruism

• Kin Selection
• a process that favors evolution of traits that
  enhance the reproductive success of related
  individuals (genetically profitable altruism)

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Inclusive fitness

• a measure of an individuals total genetic
  contribution to subsequent generations
• directly through production of viable offspring
• indirectly through effects on the ability of
  relatives to produce viable offspring

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Evidence for kin selection

• Ground squirrels are much more likely to give
  warning calls when they are in the presence of
  kin members than when they are not

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Reciprocal altruism

• exchange of altruistic acts between two or more
  individuals
• acts can be separated considerably in time
• only found in social mammals and birds
• E.g, vampire bats in Costa Rica

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Explaining altruistic behaviour between non-kin

• Reciprocal altruism is a strategy than wins over
  all other strategies
• Analogy is the Prisoners Dilemma
• Separate two criminals and interrogate each alone
• If either one incriminates the other, one is
  imprisoned. If they both incriminate the other
  then both are imprisoned
• If neither turns the other one in, both go free
• When both prisoners do not rat their buddy out,
  the pair has a higher fitness overall even if
  individuals that cheat might win in the short
  term

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Outline

• Mating systems and Mate choice
• Territoriality
• Sociality and altruism
• Life History and reproduction

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What is meant by Life History?

• life history ('strategies')
• history of the life of an individual
• species-specific pattern of development,
  reproduction, and mortality
• life-history characteristics
• size, longevity/survival
• age of first reproduction, number of reproductive
  events in a lifetime
• degree of investment per offspring
• dispersal abilities, competitive abilities,
  responses to disturbance

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Resource allocation

• key activities
• survival-related activities (e.g. movement,
  defense, baseline metabolism)
• growth
• reproduction acquisition of mates, production of
  gametes, parental care

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Principles of allocation

• allocation of resources to one kind of
  tissue/activity leads to reduced allocation to
  other activities
• finite supply of resources
• all activities require resources and have costs
• trade-offs between reproduction and all other
  activities

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Extreme Energy allocation

• Divert all energy to reproduction and as little
  as possible to growth
• Opportunist Species
• Divert all energy to growth and little per year
  to reproduction
• Competitor Species

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Reproduction and survival

• Fitness Reproductive output X Probability of
  Survival until next year
• If you have a chance to reproduce again, then the
  benefit of saving your offspring is not as great
  as the benefit of saving yourself
• E.g, when food becomes scarce, the Galapagos
  penguin will abandon its chicks and try again
  next year

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Opportunist versus competitor species

• Opportunist species are often very small and
  devote all their resources to reproduction in one
  year (Semelparous)
• Competitive species are often larger and often
  survive for a number of years and can reproduce
  each year (Iteroparous)

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Semelparous and opportunist

• After hatching and feeding for a few weeks, the
  mayfly becomes a sexually mature adult
• Shortly thereafter both sexes flies over the
  water and mate.
• Then, the female lays her eggs on the surface of
  the water both sexes then die.

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Iteroparous and competitive

• Provide a lot of resources for their cubs and
  defend them
• Bears have 2 cubs 10 times in their lifetime of
  20 years

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Semelparous and competitive

• A bamboo plant reproduces asexually for 100
  years. Along with other individuals, it forms
  dense stands of plants
• Then in one season, all the individuals in the
  population flower simultaneously, reproduce
  sexually and die
• One hundred years later the process is repeated

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Number vs. survivorship of offspring

• Type I species are those such as humans with
  highest mortality among elderly
• Type II experience steady mortality throughout
  life (some birds and invertebrates)
• Type III experience mortality peak at young ages
  (salmon)

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Number of offspring and parental care

• Human babies need to be taken care of for up to
  20 years
• Hence, we do not have too many babies during our
  lifetime
• As plants give minimum parental care, they often
  have very large number of offspring

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Selection on clutch size

• Experiments have shown that increasing the number
  of young a bird must raise in one season has
  resulted in a decrease in the fitness of all the
  young
• This has resulted in some organisms being
  genetically programmed to have the same number of
  offspring every reproductive season

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Animals with pre-programmed clutch size

• Galapagos penguin has 2 eggs every season
• Humans (and a large number of other mammals)
  usually only have one young at a time (there is a
  higher mortality of twins)

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Life history and applied ecology

• invasive threatened species do not possess a
  random collection of life history characteristics
• invasive/non-native species
• rapid growth rates
• well-developed dispersal abilities
• disturbed environments
• opportunists
• endangered species
• large size, low density/low population size
• poor dispersers
• stable environments
• competitive

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Summary

• The sex that is most choosy in picking mates is
  the sex that has the most investment per
  offspring
• Mating systems are constantly in flux as the war
  rages between the sexes, with different points of
  balance between investment per offspring and
  number of offspring
• Opportunist, competitor, iteroparous and
  semelparous species are all extreme strategies in
  a continuum of strategies for optimum fitness

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