Territoriality and Aggression 2
Why do owners almost always win
territorial contests?
1. Have higher resource-holding potential
•
•
Larger & stronger
More energy reserves
e.g. Red-shouldered
widowbird
Body condition affects territoriality in
damselflies
• Research question: What determines whether a
male can defend a territory? (Contreras-Garduño,
Canales-Lazcano, & Córdoba-Aguilar 2006)
• Hypothesis: Territorial defense requires much
energy
• Prediction: Only individuals with high energy
reserves can defend territories
Body condition affects territoriality in
damselflies
• Methods:
– American rubyspot (Hetaerina americana)
– Identified and collected 30 territorial and 30
nonterritorial males of similar age
– Compared fat reserves of territorial males, and
nonterritorial males
War of attrition determined by fat
reserves in damselfly
• Results:
– Territorial males had higher
fat reserves than
nonterritorial males
• Conclusion:
– Territorial defense is
energetically expensive, so
only males with high energy
reserves can successfully
defend a territory
Why do owners almost always win
territorial contests?
2. Territory has more value
for the owner
•
•
•
Prior investment in
reproduction & nesting
Local knowledge of food &
shelter resources
Dear enemy phenomenon
Aggressive contest in
which costs are accrued
over the duration of
contest and the victor is
he/she who persists.
Territoriality
• In general, if forming territories is costly, then ‘dear enemy
phenomenon’ occurs
– Once neighbors establish boundaries, these boundaries
are generally respected
– Both parties conserve time & energy
– Territorial animals are less aggressive to neighbors than
they are to strangers
Among male fiddler crabs, contests with intruders begin at
higher intensities and escalate more rapidly than those
with neighbors
Quick Review
Why do territory owners typically win contests with intruders?
a. owners value the area more because they have learned
where food and shelter are located within it
b. owners value the area more because they have already
established territorial boundaries with their neighbors
c. territory owners are often inherently better competitors
than are intruders
d. territory owners typically have more energy reserves than
intruders
e. all of the above explain why territory owners usually win
contests
(Pratt & McLain 2006)
Quick Review
In general, the populations of sink habitats are replenished
by individuals who have dispersed from source habitats.
A. True
B. False
Sexual Selection
The Evolution of Reproductive
Behavior
•
•
•
What is sex?
Evolution of sex roles
Sexual Selection
Reproduction
Asexual
• Parthenogenesis
Sexual
•Internal fertilization
• Budding/Fission
•External fertilization
– Intrasexual
– Intersexual
Asexual reproduction by budding in corals
Asexual Reproduction
• Some whiptail lizards reproduce exclusively
through parthenogenesis
– Egg develops into new individual without fertilization
Intratentacular budding
Extratentacular budding
(Menezes et al. 2004)
Reproduction
Asexual
Fission/Budding
Benefits of Asexual Reproduction
Sexual
• Benefits?
External fertilization
100%
sea anemone
Benefits of Asexual Reproduction
• No need to find mates
• Maximize your genetic
contribution to the next
generation
• In stable environments,
can reproduce rapidly
– Offspring similar or
identical to parent
– Individuals maximize
reproductive potential
Asexual vs. Sexual Reproduction
Cost?
100%
50%
Shared parenthood in which 2
conspecifics combine their genes
to produce a novel genotype
Costs of Sexual Reproduction
Asexual vs. Sexual Reproduction
• Two-fold cost
• All else being equal,
an asexually
reproducing
population will grow
at twice the rate of a
sexually reproducing
population
50%
Costs of Sex?
Asexual vs. Sexual Reproduction
50%
Costs of Sex?
1. Cost of meiosis
2. Cost of producing males
3. Cost of courtship and mating
Gamete wastage:
Gamete wastage:
Asexual vs. Sexual Reproduction
50%
Costs of Sex?
1. Cost of meiosis
2. Cost of producing males
3. Cost of courtship and mating
Sexual reproduction takes time &
energy
Sexual reproduction involves risk
Benefits of Sexual Reproduction?
Female Mormon cricket has her mate for lunch
Benefits of Sexual Reproduction
1. Produce offspring that have different genotypes;
some capable of dealing with specific environmental
(abiotic) changes better than others
Raffle analogy
clone: 100 tickets with same number
sex: 100 tickets with different numbers
Benefit likely important in
unstable habitats
Benefits of Sexual Reproduction
2. Producing heterogeneous offspring also increases
the likelihood that some can deal with biotic
challenges
e.g. evolutionary arms races (predators, parasites & prey)
Red Queen Hypothesis
Benefit likely important in
stable habitats where biotic
interactions often more
intense
Through the Looking Glass
Benefits of Sexual Reproduction
Evolution of Sex Roles
3. Muller’s Ratchet
If deleterious mutation arises in asexual organism, it will be
passed on to each offspring.
Only way to get rid of deleterious alleles would be reverse
mutation.
In sexual reproduction, deleterious mutations can be edited
out via recombination.
Each turn of the ratchet
tightens the asexual
organism’s demise
Critique of Sexual Selection
Some animals are hermaphrodites
Dr. Joan Roughgarden - Stanford University
Evolution’s Rainbow
•
Hundreds of vertebrate species engage in same sex sexual behavior
•
Many species are hermaphroditic
• Hermaphrodite:
• an individual producing
both eggs and sperm
• Can perform the role of
either male or female
during sexual
reproduction
• Sponges
• Many worms, snails, &
slugs
• Some crustaceans
• Some fishes
Hermaphrodites
• Simultaneous hermaphrodites
• Always capable of producing both eggs &
sperm
• Sequential hermaphrodites
• Undergo a sex change once or more per
lifetime
Most hermaphrodites refrain from fertilizing themselves
Evolution of Sex Roles
Isogamy
both gametes are the same size
(microorganisms, algae, fungi)
What are sexes
Anisogamy: gametes are different sizes
• Anisogamy
• Females produce eggs
•Large
Small
•Immobile
Mobile
•Food-rich
Food Poor
•Expensive to produce
Cheap to produce
•Few produced
Many Produced
Why two sexes?
• How did anisogamy evolve from isogamy?
• Geoff Parker and colleagues developed a model to answer this
question (Parker, Baker, & Smith1972; Bulmer & Parker 2002)
• Assumptions
1. In the ancestral marine environment, individuals in a population produce
different-sized gametes
2. Each parent has a fixed amount of energy to allocate to gamete production,
resulting in a size-number trade-off: as the number of gametes produced
increases, their size will decrease
3. Zygote viability is related to its size. Larger zygotes have higher viability
because they contain more resources for survival
• Males produce sperm
Why two sexes?
• Results:
– Large (female) gametes have high survivorship while small (male) gametes
have a numerical advantage; both have high fitness. Intermediate size
gametes have low fitness
Why two sexes?
• Results:
– Large (female) gametes have high survivorship while small (male) gametes
have a numerical advantage; both have high fitness. Intermediate size
gametes have low fitness
What type of selection does
this illustrate?
A. Directional selection
B. Stabilizing selection
C. Disruptive selection
D. There is no name for this
Evolution of Sex Roles
• Basic asymmetry in gamete size between sexes
means that there are A LOT more male than female
gametes.
Male kiwi can have >
8, 000, 000, 000
sperm in his testes at
any one time
Female, 1 egg
~25% body mass
• Consequently, males and females tend to have…
– Different reproductive strategies
– Differential variability in reproductive success
Bateman’s hypothesis and parental
investment
• Bateman’s hypothesis:
– Female reproductive
success is most strongly
limited by the number and
success of eggs that she
can produce, whereas
male reproductive success
is limited by the number
of mates
Male Reproductive Success
• Dependent upon number of mates obtained
• Strong correlation between number of mates a male obtains
and the number of progeny he produces
• As some males are better at obtaining mates
than others, there can be tremendous variability
in male reproductive success within a population
mates
individual males in population
Female Reproductive Success
• Seldom a shortage of potential mating partners
• Limiting factor is egg production
• Very costly to waste eggs on poor quality males
Events promoting sexual dimorphism in
parental investment
True/False: Females usually perform close to their
reproductive capacity, but males usually don’t.
A. True
B. False
The more females invest in offspring, the
less they are available for mating
• Operational sex ratio
– # sexually receptive males / # sexually receptive females
• Greater the OSR, the more males must compete for
access to available females
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•
•
•
Internal fertilization
Gestation
Placentation (mammals only)
Lactation (mammals only)
What is the operational sex ratio of the following
spotted hyena population?
- 25 adult females, 3 of whom are sexually receptive
- 15 adult males, 15 of whom are sexually receptive
a. 0.2
b. 0.6
c. 1.67
d. 5.0
e. 6.67
Can the OSR go below one?
• There are species in which males, due to parental
or material investment, become the limiting sex
• When this occurs, females compete for access to
choosy males
pipefish
OSR can fluctuate with resource
availability
• When food supplies are low,
male spermatophores are rare &
valuable
– Females compete for choosy males
• When food is abundant, egg
production is the limiting factor
– Males compete for choosy females
Australian katydid