Title: Mate choice and Life History
1Mate choice and Life History
Ch. 7.3-7.6, Bush
2Outline
- Mating systems and Mate choice
- Territoriality
- Sociality and altruism
- Life History and reproduction
3Outline
- Mating systems and Mate choice
- Territoriality
- Sociality and altruism
- Life History and reproduction
4Mating 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
5Investment 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
6Mating 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)
7Mating 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
8Polygyny 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
9Mechanisms of sexual selection
- Intrasexual selection
- Male-male competition
- Intersexual selection
- Female mate choice
10Inciting 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
11Female mate choice and Male ornaments
12Carotenoid 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
13Polyandry and mate choice in insects
- Females have not evolved ornaments but are larger
- Some evidence that males choose bigger females
- No parental care
14Sperm 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
15Male-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
16Deserting 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
17Ornaments and parental care
- Pipefish
- male parental care
- polyandrous
- females are the more ornamented sex
- Seahorse
- monogamous
- Both males and females look similar
18Outline
- Mating systems and Mate choice
- Territoriality
- Sociality and altruism
- Life History and reproduction
19Territoriality
- Types of territories
- Territory, sexual dimorphism and mating systems
- Human mating systems
20Territoriality
- 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
21Types 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
22Territoriality is not always fixed
- Iwi bird of Hawaii is territorial only when food
supply is low
23Territoriality and male size
- Keeping a territory takes energy
- Often territorial animals are ones where the
males are rather large
24Size dimorphism and polygyny
25Sexual 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
26Patterns 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
27Territories, fitness, and polygyny
28Human mating system
- Average N. Amer. Female height is 162 cm, average
male height 175 cm - Does this mild sexual dimorphism translate into
mild polygyny?
29Size dimorphism and polygyny
30Territoriality in humans
- Because most humans do not live off the land,
we dont have typically territories - Analogous to territories, however, is wealth
31Human 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
32Extramarital 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
33Is 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
34Who 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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36Outline
- Mating systems and Mate choice
- Territoriality
- Sociality and altruism
- Life History and reproduction
37Social 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)
38Types of altruism
- There are two main types of altruistic behaviour
schemes - Eusociality
- Cooperative breeding
39Eusociality
- 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.
40Eusociality 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
41Co-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
42Altruistic behaviour
- Ground squirrels give warning calls when a
predator comes near - Protects others but increases risk to the caller
43Explaining altruism
- Kin Selection
- a process that favors evolution of traits that
enhance the reproductive success of related
individuals (genetically profitable altruism)
44Inclusive 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
45Evidence 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
46Reciprocal 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
47Explaining 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
48Outline
- Mating systems and Mate choice
- Territoriality
- Sociality and altruism
- Life History and reproduction
49What 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
50Resource allocation
- key activities
- survival-related activities (e.g. movement,
defense, baseline metabolism) - growth
- reproduction acquisition of mates, production of
gametes, parental care
51Principles 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
52Extreme 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
53Reproduction 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
54Opportunist 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)
55Semelparous 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.
56Iteroparous 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
57Semelparous 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
58Number 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)
59Number 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
60Selection 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
61Animals 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)
62Life 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
63Summary
- 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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