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Mate choice and Life History

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Title: Mate choice and Life History


1
Mate choice and Life History
Ch. 7.3-7.6, Bush
2
Outline
  • Mating systems and Mate choice
  • Territoriality
  • Sociality and altruism
  • Life History and reproduction

3
Outline
  • Mating systems and Mate choice
  • Territoriality
  • Sociality and altruism
  • Life History and reproduction

4
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

5
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

6
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)

7
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

8
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

9
Mechanisms of sexual selection
  • Intrasexual selection
  • Male-male competition
  • Intersexual selection
  • Female mate choice

10
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

11
Female mate choice and Male ornaments
12
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

13
Polyandry and mate choice in insects
  • Females have not evolved ornaments but are larger
  • Some evidence that males choose bigger females
  • No parental care

14
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
15
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
16
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

17
Ornaments and parental care
  • Pipefish
  • male parental care
  • polyandrous
  • females are the more ornamented sex
  • Seahorse
  • monogamous
  • Both males and females look similar

18
Outline
  • Mating systems and Mate choice
  • Territoriality
  • Sociality and altruism
  • Life History and reproduction

19
Territoriality
  • Types of territories
  • Territory, sexual dimorphism and mating systems
  • Human mating systems

20
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

21
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

22
Territoriality is not always fixed
  • Iwi bird of Hawaii is territorial only when food
    supply is low

23
Territoriality and male size
  • Keeping a territory takes energy
  • Often territorial animals are ones where the
    males are rather large

24
Size dimorphism and polygyny
25
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

26
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

27
Territories, fitness, and polygyny
28
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?

29
Size dimorphism and polygyny
30
Territoriality in humans
  • Because most humans do not live off the land,
    we dont have typically territories
  • Analogous to territories, however, is wealth

31
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

32
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

33
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

34
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

35
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36
Outline
  • Mating systems and Mate choice
  • Territoriality
  • Sociality and altruism
  • Life History and reproduction

37
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)

38
Types of altruism
  • There are two main types of altruistic behaviour
    schemes
  • Eusociality
  • Cooperative breeding

39
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.

40
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

41
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

42
Altruistic behaviour
  • Ground squirrels give warning calls when a
    predator comes near
  • Protects others but increases risk to the caller

43
Explaining altruism
  • Kin Selection
  • a process that favors evolution of traits that
    enhance the reproductive success of related
    individuals (genetically profitable altruism)

44
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

45
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

46
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

47
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

48
Outline
  • Mating systems and Mate choice
  • Territoriality
  • Sociality and altruism
  • Life History and reproduction

49
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

50
Resource allocation
  • key activities
  • survival-related activities (e.g. movement,
    defense, baseline metabolism)
  • growth
  • reproduction acquisition of mates, production of
    gametes, parental care

51
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

52
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

53
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

54
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)

55
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.

56
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

57
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

58
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)

59
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

60
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

61
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)

62
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

63
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

64
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