BIO220 Midterm Review
Lecture 1: Genes, Environment & behavior
Environmental effects on trait values can be described as “plasticity”, and these
responses can be adaptive
The influence of genes and environment can be visualized with plots of the “reaction
o Natural selection shapes the reaction norm
Bees and wasps behavior in the fall
o Drunken behavior due to an adaptation for locating ripen fruit, flowers attract
bees from nectar containing alcohol.
Genetic and environmental variation
o Phenotypes reflect both genetic and environmental effects
Z(phenotype) = G (genes) + E (environment)
Evolution by natural selection...
o Variation in a trait
o Variation in fitness for the trait
o Genetic basis for the trait
Experiment 1: Rover-Sitter polymorphism
Rover/sitter foraging polymorphism found in the fruit fly, Drosophila melanogaster
and discovered by Marla Sokolowski in the early 1980s. Under the presence patchy food,
Rovers eat less but move more than sitters during foraging and they are more likely to
explore new food patches than sitters.
o Rovers and sitters move for similar distance in the absence of food.
Genetic analysis these behavioural differences arise mainly from allelic variation in
foraging (for), which encodes a cGMP-dependent protein kinase (PKG). An enzyme
involved in cell signaling, (located in nervous system and the gut), Rovers are have the
o By inserting “rover” alleles in “sitter” larvae, able to change the behavior of sitter.
Under environment changes, food deprivationboth moves less, Rover slowly behaves
o Phenotypic plasticity,
Daphnia Morphological response to predators (grow helmets)
Tadpole under harsh environment, changes to cannibalism Reaction Norms
Describes the effect of some environmental variable on the phenotype of a single
Experiment 2: Daphnia Genetic variation and evolution of reaction norms
Daphnia tends to be attracted to lights (food is in the light, so are predators), Assayed
10 genotypes from each of 3 lakes with many, few to no predators. Tested with and
without fish smell.
o Daphnia population with a selective history of predation risks have evolved to
avoid habitats with high risks of predationevolution of a reaction norm shaped
by natural selection. Lecture 2: The Evolution of Sexual Differences (Dimorphisms)
Males and females shared a large portion of the autosomes (90%), but they are very
o Different in the expression of genomes, significant sexual difference at the
Sexual dimorphism: conspicuous ornaments
Big red pound in male frigate bird
Long tail variation in male widow birds
o No diversity in females. Huge diversity in mating males. Evolutionary biology
need to account for diversity.
o Males with big pouches doing dance with tail feathers.
Elephant seals, beetles fighting, stalk-eyed flies
o Why do males have huge tails? Terrible idea considers the survival of the fittest.
Bad for survival, but it will be good for increasing mating success.
Natural selection is about survival (everything about fitness); sexual
selection is just about mating success.
Depends on the advantage which certain individuals have over other individuals of the
same sex and species, in exclusive relation to reproduction (mating).
o Sexual selective traits enhance mating successcontribute to fitness
Subset of natural selection. Can be useful to consider them separately.
Natural selection increase survival, increase reproductive rate increase fitness.
o Sexual selectionincrease the number of matesincrease fitness
Fitness in males and females
FemalesFitness will be comprised of survival and reproductive rate.
Malefitness will be compered of survival, and access to eggs.
**sex roles can reverse in special cases.
Why do we have two sexes?
Fundamental difference is anisogamyunequal size gametes.
Femaleclass of individual produce large gametes
o Large resource rich eggloaded with energy, few of them
Male produce small gametes.
o No resource, inexpensive, can produce many of them (average ejaculate to
fertilize all America )
Consequence of interaction in sexes. Parental investment theory
Sexes are different in reproductive investment. There will be competition in those invest
little for access to fewer resource rich egg.
Members of the sex with low investments with compete among each other for high
investment eggs. The sex involve more in offspring, their gametes are limited resource.
o Males: tiny mobile games, fitness limited by access to eggs.
Male fitness depends on how many egg can he fertilize.
Expect competition of males for access to femalesmale-male
o Female: resource rich gametes
Fitness limited by the resource they access to build gametes
Choosy among males to mate, choosing the best sperm/malefemale
o Special cases when male taking care of the gametes after fertilizationfemales
competing for males
o Relationship between mate and number of offspring.
Since males are limited by access to egg, by giving them eggs, they can
Females are limited by resource, but eggs are limiting their mating
rateweak relationship between mates and number of offspring.
Experiment 3: Bateman Curves
Set-up: a set of females mate one with male, twice with males, etc. And have males mate
once, twice with females etc.
o By recording the number of offspring, this provides the idea that females are
limited by resource; males are limited by access to eggs.
In many organisms, females are inseminated, and they store it. In flies, they mated once,
and they store the sperms. No matter how many times they mate, it will not increase the
number of offspring they produce since it is limited by egg numbers.
o Strong selection on male to mate more, no strong selection on females to mate
Data on max. number of offspring produce during lifetime.
o Elephant seal: male100, female8
o Red deer life-long monogamous, not significant difference.
o Man888 Women69 offspring in 27 pregnancies
Intra-sexual selectionmale competition
Competing among each other for eggs.
o Pre-copulatory (before mating happen, number of copulations)
o Post-copulatory (after mating happens, competition in sperms, given the number
of copulationsthe probability of fertilization)
Fighting behaviors (prevent others have access)
Territorialities (fight to setup territories) Social status
o Males walrus competing for status, females come and watch the males sing.
Most females will mate with the dominant male.
o Elephant sealsmales fight for beach, females want beach for pups.
Bigger beach gives more mates.
Males had no territories try to sneak in and mate.
Dominant males inseminated 50 females, lot of variation in mating
Strong selection, traits allow you to be dominant can allow you to
reproduce 50X, this selection cause such bazaar traits.
Sperm competition (post-copulation)
o Mate guarding
Females store sperm, males mate female, and it pays for them to guard
o Sperm removal & copulation duration
A female mated, another come in, wanted to remove the sperm of the
other male, increase copulation durationincrease number of sperm
o Sperm plug
Sperm plugs in lobsters male seals the pores of the female make it
difficult for others to mate.
o Traumatic insemination
Bed bugsmales inseminate females by stabbing in the stomach, and
sperms flow thru the blood stream to the reproductive organs
A butterfly put a scent on the female to tell others that this female is
o Male clasping the female's thorax (behind the head), prior grasping, males
transport sperm to the abdomen area. If the female want to be inseminated, she
brings the tip of abdomen to the male and gets the sperm. Then the male will
guard the females. Females store sperms in the abdomens; egg moves down the
tubes, squirts the stored sperms on the egg and lays the egg. In other case, male
continue to hold the female.
In the storage organ of sperm in male, they had another organ, inflated
with hocks, it will first pull out the stored sperm in female horns, whip
o In dragon fly, males lift the females up, and hit the water surface, every time she
hit the water surface, egg comes out.
Bluegill Sunfish (alternative reproductive strategies)
o Large males can guard eggs and provide territories for femalesfemale want
o Intermediate males pretend to be females.
o Smaller males comes out of the blue and shoot sperms. Experiment 4: Rock-Paper-Scissors Game in Nature (frequency dependent selection)
If everyone playing rock, the fitness of scissors loose, and ones that play paper will win
most of time.
Three strategies in side-blotched lizard (genetic basis)frequency changes overtime
Defend large territories
Extremely aggressive towards all males
Defend smaller territories (not going to have high quality female)
Detect and root-out yellow males
‘Sneaker’ male (on orange males)
Mimic throat colour and behaviour of receptive females.
If there are lot of orange, yellow will success. The fitness of each type depends on the
frequency of other.
o if blue is high, orange will increase
o If orange high, yellow will increase
o If yellow high, blue will increase
o Blue numerically dominant in 1991
o Orange begins increasing at the expense of blue in 1992
o Yellow begins reducing orange by 1994
o Blue returns to numerical dominance by 1995 Required Reading #1-2:
A successful male can potentially sire many offspring. If a male gains a disproportionate
share of reproduction, he will take away reproductive opportunities from other males,
leading to a high reproductive variance among males. A successful female, on the other
hand, will not take away reproductive opportunities from other females, leading to a
smaller variance in reproductive success.
o The higher the reproductive variance, the stronger the effects of sexual selection.
If females provide more parental care than males, the variance in male reproductive
success can be expected to be large, since females providing offspring care will not be
immediately available for further reproduction and competition for available females
will increase among males.
Females can directly increase their reproductive success by mating with certain, select
males and acquiring direct benefits.
o “Good genes”differences among males provide females with information about
the genetic qualities of the different males that can be inherited by the offspring
o Fisherian Arbitrary Choice female preference can evolve for arbitrary traits
that do not provide information about the male's quality, and that therefore do
no reinforce the effects of natural selection.
Females gain the indirect benefits of producing offspring that will be
more sexually attractive to females that carry the preference, result in a
positive feedback loop, whereby the trait becomes more exaggerated as
selection on the preference increases.
Although both sexes are seeking to optimize their reproductive success, their genetic
interests are not aligned, resulting in sexual conflict
o Some trains of male will increase his mating success at the expense of female,
this can spread across the population
Evolutionary arms raceharm traits induce counter-traits in other sex.
Harem: A group of females associated with a single male. Typically the male in the
harem defends his group of females.
Lek: A mating system which consists of an aggregation of males where each is seeking
to attract a mate. Leks are not associated with resources; however it is thought that leks
attract more females than a single male would attract.
Resource defense polygyny: A mating systems in which males establish a territory
around resources needed for mating success. In this system multiple females will join
the male in his territory.
Polyandry: A mating system where one female pairs with many males.
Polygyny: A mating system where one male is associated with many females.
Promiscuity: A mating system where there are no pair bonds. In this case is seems that
males and females mate randomly.
Serial monogamy: A mating system in animals where they pair with a mate for one
mating season but change mates over the course of a lifetime.
Social monogamy: The behavioral pairing of a single female with a single male. Lecture 3: Sexual Selection and Female Choice
Satin Bowerbird: Males set-up bowers and decorates them with colorful objects
(especially blue and yellow). Females would then inspect the bowers and go in the
backdoor to mate.
o Strong selection, large variationdraws bazaar differences among males
Any female traits (behaviors, morphology) that biases the mating success of males
toward the preferred type
o Satin bower bird
o Widow birds
o Tungara frogs
o Sierra dome spider play the web
o Mouse (pheromone)
Experiment 5: Tail manipulation experiment
Set up: manipulate tail length of widow birds to ask are long tails preferred by females.
o Nnatural tail length
o Rreduced tail length
o Lelongated tail length
o Ssham surgery (see if cutting and gluing will affect mating success, first cut
and then glue back. )
Hypothesis: L > N> R and N=S.
Result: Prior to treatment, relatively same mating success, after the treatment, natural
and sham are almost the same. The reduced tail reduces in mating success. And
elongated increase in matting success, this suggest that tail length itself lead directly to
Experiment 6: Female preference of eyespots in peacock tails
After treatment of removing eyespots, it significantly decreased mating success in
Experiment 7: Female preference of complex calls in Tungara frog
Tungara have 2 part in mating calls whining & chucks.
o Whining first attracts females. The more Chucks the betterFemales go for
more complex chuck.
Reasons why not all males have chucks?
o Predators like bats are can also be attracted to complex calls.
Therefore, 2 forces pushing the trait. Sexual selection driving it up and
predator driving it down. Hypothesis for female choices
Direct benefitsdirect natural selection on the female
o Female preferences are side effects of other forces (those traits are indicator of
parental investment )
Selection of resources rather than male attributes
Male traits act as an indicator of parental investment (PI)
Ornamentsprotection for female
Colorful furhealthier, free parasites
o Female preference for males with resources
Spermatophore in katydid or Mormon cricket: protein-rich capsule
produced by male that can weigh up to 25% of his weight. Containing
spermatozoa and transferred in entirety to the female's ovipore during
copulation. Female consume the protein mass, by mating, female receive
a huge resource. Female prefers larger male for bigger
Hanging fly: Females attracted by pheromone, and checks the food male
has. While mating occurring, she is consuming the food. In some species,
they get things are not food and trick the female. Longer the female eats,
the longer the male can mate.
More foodlonger copulation durationmore sperm transferred
Indirect benefitsfemales prefer male traits indicate high genetic qualityher
offspring will have a higher fitness.
o Goof genesnumber of eyespot in peacock as an indicator of good genes
Larger display sizes tend to give genes to female that increase the
survival of offspring, choosing those male increases the fitness of her
Parental Investment (PI) Theory
Members of the sex that invest little in offspring will compete among themselves to
mate with members of the sex that invest more in offspring
o Difference in sex of the reproductive investments
When male have to invest more in parental care, then sexual role reversal
o Giant water bug, pipefishHigh male PI
Water bugfemale lay eggs on the back of the male, so the male transfer
oxygen to the eggsMale back is the limited resources. Pipefish sex role and mating system
During copulation, females dump eggs into the brood pouch in male, eggs get fertilized.
Pouch is sealed until the babies are born.
o Male’s reproductive success is limited by size of their brood pouch
o Females’ reproductive success is limited by access to male
Female compete for access to male
Sexual selection on female size and ornamentation.
Small, weed-looking male
Large, ornamented femaleindicate good eggs.
Experiment 8: Experiment evidence of sex role reversal
Question: do males exercise mate choice?
Result: males prefer larger highly fecund females in pipefish population.
o Longer length, larger fold size.
Experiment 9: Relative PI and flexible sex role in Katydids
When food is abundant, males call for female, but females does not want to mate with
male because they have food in the nature. At this time, male tend to mate with any
When food is in decline, males don't often call female. But females need food from male.
Therefore, male choice of females and female-female competition happens.
Mate choice in Mice and Humans
Human tend to favor symmetrical faces
Major Histocompatibility Complex (MHC)codes for antigen recognition for
immunity response, more genetic variation at MHC the better.
o HLA in human
Mice choose mates based on MHCto avoid inbreeding, to increase genetic variation at
MHC loci for their offspring.
Females can detect MHC; they tend to mate with males with different MHC. Females
and males are choosing mate due to their difference, human chose among MHC for the
o Experiments in human have males wear the same T-shirt for 2days, and bags are
choices from female. (Female prefers the ones with difference MHC-type).
However, Females tends to prefer the same MHC when they are on birth control
pill. Lecture 4: Social Behavior (good for individuals to good for genes)
o Ground squirrels and Meerkats stands up and guard for others
Individual gives alarm call making itself seen by predator, increase the
probability being eaten, decrease the probability of others being eating,
This behavior can only be explained on a genetic level.
o In population of meerkats , Some individuals are producing offspring, others are
helping to breed offspringaltruistic
decrease their own fitness, increase fitness of the group
unbreeding individual lactate to help feed the offspring in the
o Multiple generations with different reproductive role in a group.
Wasp, ant mount
Definitions in social behaviors
Social behaviors: The interaction with and responses to other individuals of the same
Altruistic behaviors: the behavior increases another individual’s reproductive success at
a cost to one’s own reproductive success
Cooperative: Behaviour that, if adopted by two (or more) individuals, benefits both.
o Understand why there are no cheaters?
Cooperation and natural selection
Hard to understand altruistic behavior with natural selection, if genes are selfish
(replicate at the cost of alternate alleles), how can we explain cooperation?
Developed in the cold war. Post-secondary world understand how to interact each other,
favor themselves but does not involve destroy the world.
o Imagining hawk-like behavior and dove-like behavior in the same species, having
them interact each other over food. Ask when two individuals come for the food,
what do they do. Act hawk or dove?
When two doves come, they work out, split the
resource. The payoff is R/2.
If dove against hawk, the dove have nothing.
If a hawk plays against dove, the hawk gets
If hawk play against hawk, the resource be divided,
and cost them the energy for fighting. The question
is what should you play? o
Evolutionary explanation of cooperative behavior
o If you know the other will cooperate, and then you would want to cooperate, if
you don't know, you might not cooperate.
o Imagine a game two individual are communicating, compete strategies to
explain this, the best strategy is “Tit for Tat”
Cooperate on the first encounter. Copy your opponents’ last move
thereafter. Being nice first, and if the other did not being cooperative, you
do the same.
Nicestart by cooperation
Retaliatorystop if partner stops
Forgivingif partner has cheated in past but changed, then
Experiment 10: Predator Inspection in Guppies
o In population of guppies, few individuals inspect for predators for group of fishes
The two approach of fish are cooperating and can be viewed as an
iterated prisoner’s dilemma
o Question: Do guppies play Tit-for-Tat during predator inspection?
Examine predator inspection behaviour with “cooperating” and with
“defecting”partner Kin selection
o Results: If there is a cooperating mirror, overtime, it gets closer. With defecting
mirror, it stays the same distance away. Group selection
o Reduce the frequency of male in the population, every male fertilize many eggs,
females producing fewer eggs. Imagine there is an alleles produces more male,
those male will be successful, because they can then fertilize a lot of females
Group selection does not work because is invasible by cheaters.
o Special case when group selection works
Crows have alarm calls, and have dialogue. How can we account for such
In a population, two genotype, calling genotype and non-calling
genotype. Callers appear altruistic. When selection happens, reduction in
a caller. This removed the frequency of caller gene.
Add social groups into this case. They gather on tress interacting with
each other, imagine groups have no caller, many caller, and intermediate
caller. They interact, and mixed up in breeding season, they redistribute
again randomly again.
Instead of having one group, we will have three groups with different
number of callers.
In the absent of caller, high mortality, they get eaten,
In a group that all are caller, low mortality.
In intermediate, the increase frequency in non-caller.
Non-caller decrease in frequency after breeding season, within
group, caller is always worse than non-caller, but a group with all
no caller is the worst.
Experiment 11: Evidence for group selection (Impatiens Capensis )
Large plants out-compete small plant, but small plants are still common
Question: how are small plants still around? Why don’t large plants take over the
Hypothesis: Groups with many large “selfish” plants do worse than groups with many
small “cooperative” plants
o Large individuals in well-spaced groups tended to have high fitness.
o Groups consisting of many small individuals tended to have high fitness.
o These two effects tend to cancel one another out. Reasons why small still exist. o 2 force of selection: group effect push the size down, and individual effect push it
o Selection applies to the family.
o Under normal circumstance, presence of altruistic alleles. And it gives benefit to
everyone, and it pays a cost every time. All recipients get that benefit. Non-
altruists do best and we will eventually lose the altruist alleles.
o In altruism among related individuals, the cost and benefit only felt by altruist,
this might work when the benefit is higher than cost.
c = Cost of altruism to the actor
b = Benefit of altruism to the recipient
R = Genetic coefficient of relatedness (Probability that the recipient
carries the altruist gene)
Altruism can evolve, if the benefit of recipient multiplied by the genetic coefficient and it’s
larger than the cost of altruism.
Experiment 12: Alarm Calling In Ground Squirrels
Question: Do squirrels with close relatives nearby give more calls than those without?
Result: compare group relatedness, if there are no close relatives, low proportion of time
calling. Alleles for calling are directed to other individuals having these alleles. The
benefits is felt by caller themselves
Evolution by natural selection
Natural selection cannot favor sacrificial genes, in contrasts, natural selection favor
individuals that self-sacrifice.
Trade one sacrificial allele to three more sacrificial alleles
o Although the individuals’ action is altruistic. Overall picture, the allele increase
Favoured genes ALWAYS increase in frequency each generation Required Reading #3:
Animals living in groups, however, beneﬁt from many more pairs of eyes to provide
vigilance or help forage. But living in groups may also confer costs to members.
Although choosing not to help is typically the best choice for an individual’s ﬁ tness in
the short-term, it could mean that the individual will not receive reciprocal help from
others when it is needed in the future. This provides incentive for altruistic behavior in
situations where individuals interact repeatedly, which typically occurs when animals
live in stable groups.
These groups are called eusocial (i.e., truly social) because they share three key criteria:
1. cooperative care of young; 2. Overlapping generations (i.e., parents and offspring
cohabitating); and 3. a reproductive division of labor, often culminating in caste
Hamilton's rule details the conditions under which altruistic behavior should evolve. It
weighs the beneﬁts and costs (in terms of reproductive beneﬁts, or offspring produced)
of a donor performing an altruistic behavior towards a recipient. According to
Hamilton's rule, the donor receives a direct cost C (in terms of lost direct ﬁtness) for
cooperating, whereas the recipient receives an additional beneﬁt B (in terms of increased
direct ﬁtness). However, the donor also receives a portion of the beneﬁt B that is
discounted by the genetic relatedness r (i.e., degree of shared genes) between the two
individuals. This discounted portion of the beneﬁt is equivalent to the donor's indirect
Cooperation and sociality are widespread in animals. Seemingly altruistic behaviors, like
raising the offspring of others instead of trying to reproduce, can largely be explained
by the shared genetic heritage between interacting individuals.
The cooperative and often complex collective action that arises from such family groups
is a product of the interaction of individuals seeking to maximize their own evolutionary
ﬁtness. Lecture 5: Parent-Offspring Conflict
Trade-off between parents and offspring
o Provision of food increase fitness of the offspring, decrease the number of future
o Offspring want food, parent provide food
In offspringthe cost provided
now will not be provide for future
offspring, need to discount by a
half due to sibs. B minus C is the
optimal provision rate.
by a half and the cost is
discounted by a half,
The optimal provision rate in
offspring is higher than parent.
Expect to have conflict.
Optimal provision rate in Conflict, this conflict can be resolved in many ways
1) Parent wins
2) Offspring wins
Parents are equally related to their offspring, who should provide care?
Why don't all parents desert their offspring immediately? Experiment 13: Kentish Plover experiment
Question: can we account for the pattern of predominately male care in terms of cost
Part 1(benefits of deserting)Catch both parents, remove the nest, remove either the
mother or father, and test how long it is to re-mate.
o Fast re-mate time means the benefit of desertion is high.
o Females can mate very fast the benefit of desertion is high in female
This suggests a bias in sex ratio. Hard for male to pair with female. Easy
Part 2(Cost of deserting)In some nests, you take male away, in others take female.
Measure brood survival.
o When female is taken away, the survival rate is high, suggest the male is
providing the resource. Survivorship decrease when male removed.
Male provide better care, bi-parental care had no different as male care.
The cost in female exerting is no cost, but high cost in male.
Overall, since there are high benefits but low cost to desert offspring, females does not provide
care for offspring. Lecture 6: Evolutionary Medicine and an Introduction to Aging
Evolutionary medicine application of evolutionary principle to the health problems
Asks why (ultimate) rather than how (proximate)
o Why do we age?
o When do we expect resistance to evolve?
Reasons why we are vulnerable to disease
Trade-off: structures and systems must balance conflicting demands
o We are accumulating mutation, the cost to repairing them is expensive, it may
decrease reproductive rate.
o Change that exceed the rate of our evolution, if it slow done, see matching
phenotypes. If the environment fast, mismatch with the environment.
Pathogen evolution: they evolve faster than we do, their generation time is rapid, with
each generation, and evolution happens faster, we are constantly behind.
Historical contingency (意外事故)
Definition of aging or senescence
Progressive decline in somatic function reflected in reductions in fertility as well as
Proximate cause: Progressive degeneration of the soma
Manifestation of aging
General degeneration of the soma
o Impaired function (speed, strength, sight, etc.)
o Increased disease (cancer, organ failure)
Mortality rate increases with age
For 45-55, the rate of death is increasing. An individual of 65 have a high probability suffering
from cancer than a 30 years old. As we age, the probability of mortality increases. And age
specific fitness declining
Free Radicals and Vitamins
Molecules containing at least one unpaired electrons
Attack and modify macromolecules
o “Oxidation” of DNA, proteins, lipids
We have our own defenses (various amino acids that act as antioxidants)
Vitamins E and C act as antioxidants
Why not enough repair?
As you increase DNA repair, decrease fecundity, if DNA repair is resource-expensive,
you are not using these resource for reproduction, your fitness will depend on
reproductive rate and longevity, there will be a balance point that balance both factors. Constraints
Cannot have free repair mechanism, taking in the forms of trade-offs.
o Balance of conflicting forces.
Trade-off affects the evolution of all traits
Display size (morphological traits)
o Tail length in peacock
Foraging rate (behavioral traits)
o The best habitat with more food will have more predators
Longevity (life history traits)
Cost of reproduction
Higher reproductive rates accelerate senescence and thereby shorten lifespan.
o More offspring you have at a higher rate, the more reduction in longevity.
o Investment in reproduction increase reproductive rate, if you do that , you
decrease longevityrelated to why we age
Experiment 14: Reproductive costs in water striders
Male spend time little eating, and mating
Female avoid male, and collect the food, turn it into egg.
o If there is reproductive cost, if we induce female to reproduce at a high rate, we
should see them die faster.
Hypothesis: High reproductive rates accelerate senescence and thereby shorten life span.
Set-up: manipulated reproductive rate of females by
changing food ration
o Female reproductive rate is limited by food
supplies. Decrease food supply, decrease egg
produce. Collect data of reproductive rate and
the side effect of that on longevity.
o Those reproducing at a low rate live for a
long time. Those who get a lot of food, and
reproduce at a high rate will live shorter, die
It appears there are costs of
reproduction, females that reproduce
faster die fast.
Over the course of days, egg develops. And burst with baby strider, early eggs go
through regular reproduction; later egg by older female has problems in the egg, in
really old female, they produce egg that produces poorly, or part of the embryo develops.
o Egg quality can be a measure of the quality of her soma, because her whole life is
used to develop egg. Poor eggspoor soma
Graph: when the 30 day old, 100% alive, and they start dying,
before they die, they stop reproducing.
Prior to stop producing, their egg develops abnormally.
This suggest the soma is decline before they actually die, just
like in human The time female start to produce bad egg is early if they reproduce at a high rate. Later in life if
they reproduce at low rate. Hence higher reproductive rate increase the decline of the soma.
Different ways to modify test method, showing same result (high reproductive rate, low
Crustaceans Diet restriction
Insects Egg addition
Fish Removal of oviposition sites (sites to put eggs)
Birds Delay of reproduction
There is a cost of reproduction, and it is wide spread, increase reproduction decrease longevity,
implication is that traded-off are involved in the evolution of senescence.
Experiment 15: A Study of Reproductive Costs in British Aristocracy
Record goes back 200 years in the royal family.
o In that data set, do we see a correlation between longevity and number of
Look at probability of death across ages.
Mothers born before 1700, 2.8 offspring each,
probability of death increase, the old it is, the higher
chance she die, high fetal mortality
Mother born between 1700-1875, similar shapes,
but below the other one. Relate to the fact that they
are producing less offspring; problem with
correlation maybe due to the advancement in
Within the period, mother produce one children live longer than mother produce two
Sex differences in aging and cost of reproduction
In high birth rate population, females live similar age as male
In low birth rate, females outlives male.
This suggest reproductive cost
Theorized of senescence
Mutation accumulation: Deleterious mutations with age-specific effects accumulate at
o If a gene is expressed late in life, selection does not remove it, stays in the
population. You expressed deleterious genes as you age, that is why it harms
soma. Antagonistic pleiotropy: Genes with beneficial effects early in life will be favoured in
spite of negative effects late in life
o A gene early in life will be negative in later life. Pleitropy suggest a gene with 2
The strength of selection decline with age
Age specific survivorship
Accumulation of probability this suggest few individuals will live a long age, this is
independent from aging. It’s just the longer you live, the higher change you will be
Mutation accumulation Theory
Imagine a deleterious gene, if the gene is expressed early in life, then more people will
die, and that the gene might not accumulate. However, if the gene express later in life,
then the individual carry this gene may already reproduced, passed on the genes.
o Strength of selection decline with age.
Old age is a dust bin of late acting deleterious mutation