Chapter 13: Evolutionary Biology

What are some examples of variation in reproductive strategies?

Mice mature early and reproduce quickly

Bears mature late and reproduce late

Some plants live and flower for one season, and some for centuries

Some bivalves produce millions of tiny eggs at once, and some produce fewer than 100 at a time

What is life history analysis?

A branch of evolutionary biology that tries to sort out reproductive strategies

What is the perfect organism strategy?

A perfect organism would mature at birth, produce many high quality offspring throughout life and live forever

Extreme life history strategies in Thrips egg mites

Thrips egg mites are born already inseminated by mating with their siblings inside of their mothers body, offspring eat their way out of their mother when she is four days old

Why is the perfect organism not attainable?

No organism can be perfect because there are tradeoffs in time, size of offspring, and parental investment

Extreme life history strategies in brown kiwi birds

They lay eggs 1/6 of their body weight and chicks are self reliant within a week but it takes one month for the female to produce each egg

How does organism size affect life history?

Organisms may grow to a large size to make large offspring or reproduce earlier at a smaller size to make smaller offspring, for organisms that wait chance of dying before reproducing is high

What is created by environmental variation?

Life history variation

How long do female Virginia Opossums nurse their young?

Three months

How long do female Virginia Opossums continue to grow after weaning?

Several months

How many offspring are typically in the first litter of a female Virginia Opossum?

8 offspring

How many offspring are typically in the second litter of a female Virginia Opossum?

7 offspring

At what age are female Virginia Opossums typically killed by predators?

20 months

What changes occur in energy allocation throughout the life of a female Virginia Opossum?

Energy allocation changes through life

How do differences in life history relate to differences in energy allocation? (possum example)

Other female opossums could mature earlier and reproduce earlier or devote less energy to reproduction and more to maintenance

What does natural selection maximize in life history?

Natural selection optimizes energy allocation in a way that maximizes total lifetime reproduction

What are the two types of winged female sand crickets?

Short winged and long winged

What do short winged female sand crickets devote more energy to?

Reproducing

What do short winged female sand crickets devote less energy to?

Flight

What is the trade-off in energy allocation for short winged female sand crickets?

More energy to reproduction and less to flight

What is senescence?

A late in life decline of fertility and the probability of survival, aging reduces an individual's fitness and should be opposed by natural selection

What causes senescence?

caused by accumulation of irreparable damage to cells and tissues, damage is caused by errors during replication, transcription, and translation, and by accumulation of poisonous metabolic by products

How does aging occur if it is selected against?

All organisms have been selected to resist and repair damage as much as physiologically possible, they age when they have reached the limit of possible repair

Why are populations not able to repair enough to stop aging?

Populations lack genetic variation needed to enable more effective repair mechanisms

What are the two predictions of the rate of living hypothesis?

- Because damage is partially caused my metabolic by products aging rate should be correlated to metabolic rate

- Because organisms have been selected to repair the maximum possible, species should not be able to evolve longer life spans

What is the rate of living hypothesis?

Senescence is unavoidable.It is caused by accumulation of irreparable damage to cells. Organisms have been selected to resist and repair cell and tissue damage to maximum extent possible.

Austad and Fischer tested first prediction (rate of living)

Calculated amount of energy expended per gram of tissue per lifetime for 194 mammal species, should expend the same amount regardless of length of life, instead found great variation in energy expenditure, bats expend three times the energy of other mammals their size

Luckinbill tested second prediction (rate of living)

Artificially selected for longevity in fruit flies, increased life span from 35 days to 60 days, these long lived fruit flies had lower metabolic rates during first 15 days of life

Conclusion of the rate of living hypothesis

Both of the prediction are not supported by experimentation, should examine energy expenditure on cells and chromosomes and not the whole organism

What is senescence in normal animal cells?

Senescence is the process where normal animal cells are capable of a finite number of divisions before death.

Which types of cells are not subject to senescence?

Cancer cells, germ cells, and stem cells are not subject to senescence.

What may result from chromosomal damage in normal animal cells?

Senescence may result from chromosomal damage in normal animal cells.

Why do organisms age and die?

Telomeres of chromosomes consist of tandem repeats added by telomerase ( overactive in cancer cells), during each replication pieces are lost and progressive loss is associated with senescence and death, cells die because chromosomes are too damaged to function

What are life spans of mammals correlated with?

Life spans of skin and blood tissue

p53 gene

A gene that causes cell senescence, deficiency in p53 causes cancer susceptibility, trade off between cancer risk and aging

What is the evolutionary hypothesis of aging?

aging is not caused by damage itself but the failure to repair the damage, damage is not repaired because of deleterious mutations or tradeoffs between repair and reproduction

What is the mutation accumulation hypothesis?

Natural selection is weak in late life: alleles expressed late in life(after reproduction has taken place) has little impact on fitness

How can mutations affect individuals late in life?

Deleterious mutations late in life can accumulate in populations and be the cause of aging they are strongly selected against and can accumulate randomly, causing senescence and death with few fitness consequences

What is the affect on fitness of cancers late in life?

cancers that usually occur late in life only slightly affect individuals fitness

Pleiotropic

a gene that influences many traits

Antagonistic pleiotropic effects

Trade off between early reproduction and survival later in life

Example of advantage of death

Species matures at 2 years and dies at 10, trade off between early reproduction and survival late in life reproductive success is only 2.66 so mutation for early death is beneficial

How can aging be slowed down?

Reproduce so early that early death is not selected against, mutation devote less to repair and more to reproduction

What is the function of heat shock protein hsp70?

Prevents damage due to denaturation.

How does hsp70 binding affect normal cell function?

It interferes with normal cell function.

When are heat shock genes expressed?

During environmental stress.

What effect does the expression of hsp70 have on Drosophila lifespan?

It causes a longer lifespan.

What is the effect of hsp70 on early reproduction in Drosophila?

It leads to lower reproduction early in life.

What trade-off is mediated by hsp70 in Drosophila?

The trade-off between early fecundity and late survival.

Do heat shock proteins mediate trade-offs in organisms other than Drosophila?

Yes, they may mediate this trade-off in many organisms.

What is a characteristic of collared flycatchers when they begin reproduction?

They are polymorphic.

How does the age at which collared flycatchers begin breeding affect their clutch size?

Birds that begin at age 1 have smaller clutch sizes throughout life.

What is the clutch size of collared flycatchers that begin breeding at age 2?

They have larger clutches throughout life.

Do first year breeders of collared flycatchers have higher or lower reproductive success?

Higher reproductive success.

Polymorphic

having various forms

What is the effect of high adult mortality rates on Virginia opossums?

High adult mortality rates should lead to earlier maturation.

Who compared Virginia opossums on the mainland and a barrier island?

Austad.

Where did Austad compare Virginia opossums?

On the mainland southeastern US and on a barrier island off of Georgia.

What ecological condition do mainland Virginia opossums face?

They have high ecological mortality rates.

What is the ecological condition of Virginia opossums on the barrier island?

They have no predators.

How do the two habitats of Virginia opossums compare?

The two habitats are otherwise similar.

When did the populations of Virginia island females separate from the mainland?

4000-5000 years ago

What evolutionary trait should Virginia island females have developed due to their separation?

Delayed senescence

In what aspects did island females show delayed senescence?

Reproductive performance, survival probability, and connective tissue physiology

What is currently our best explanation for life history variation?

The evolutionary hypothesis of senescence

What is David Lack's Hypothesis?

selection will favor the clutch size that produces the most surviving offspring. When researchers added eggs to nests, the survival of all chicks decreased. Number of surviving offspring reaches a maximum at intermediate clutch sizes.

Boyce and Perrins tested Lack's hypothesis

Study on great tit birds, mean clutch size was 8.53, greatest number of survivors came from clutches of 12, experimentally larger nests still had 12 survivors

Why was Lacks hypothesis wrong?

study was no consistent with lack's hypothesis many studies have shown that birds have smaller clutches than predicted, must be a violation of one of the underlying assumptions

What was Lacks first assumption?

No trade off between parents reproductive effort in one year and survival and reproduction in the future

How was lacks first assumption proven wrong?

Linden and Moller review 60 bird studies and found that 26 showed a trade off between current and future reproductive effort, 4 of 16 studies found tradeoff between current reproduction and future survival, optimal clutch size may be less than most productive clutch size

What is Lacks second assumption?

The only effect of clutch size on offspring determining whether offspring survive

How was Lacks second hypothesis proven wrong?

Schluter and Gustafsson added or removed eggs from collared flycatcher nests, and when those offspring had their own clutches, the ones from clutches that had been augmented produced smaller clutches and vice versa, effects of clutch size extend further into future than thought

What is Lacks third assumption?

Clutch size is fixed by a particular genotype

How was Lacks third assumption proven wrong?

Phenotypic plasticity of clutch size has been shown in many bird species, if birds predict good or bad environmental conditions, they can adjust their clutch size to the optimum value for that season

Why is Lacks hypothesis valuable?

Although his hypothesis is proven incorrect and too simple to accurately predict clutch size it serves as a valuable null model

What are parasitoid wasps?

Wasp that inject their eggs into a host insect, the larvae eat the host, pupate, and emerge. Host insect is analogous to a nest

What was Lacks hypothesis applied for parasitoid wasps?

Wasp deposits eggs in many different host species, Charnov and Skinner calculated optimal clutch sizes for three insect hosts, females shift behavior in response to different hosts and lay smaller clutches than predicted by Lacks hypothesis

Why are some wasp clutches smaller than optimal?

Larger clutches may reduce female fitness in unknown ways, there may be a tradeoff in current and future reproduction and survival, parasitoids may lay two clutches in succession, fitness may be related to all clutches and not just one

How do female wasps gain fitness?

While female is searching for a host her fitness is zero, fitness is gained by the number of eggs laid in one host before leaving, she may lay smaller clutches than Lack predicted because it may be optimal to begin the search for a new host

What is the principle of allocation?

States that if organism use energy for one function the amount of energy available for other functions is reduced, leads to trade offs between functions such as number and size of offspring, can either have many small young or few large young

What were the two assumptions of Smith and Fretwells analysis?

- Tradeoff between size and number of offspring

- Individual offspring survival correlated to size

Smith and Fretwells analysis

Optimal offspring size for parents is often smaller than optimal size for offspring, offspring always want to be bigger to survive better, parents want to ration out resources to all offspring current and future, high polymorphism in offspring size in population is needed to test this analysis

What is phenotypic plasticity in the context of beetle egg size?

It refers to the ability of seed beetles to change egg size based on the host plant.

What do seed beetles do with their eggs?

They lay eggs on various seeds, and the larvae burrow inside to feed and pupate.

Who studied seed beetles and on which seeds?

Fox studied seed beetles grown on acacia and palo verde seeds.

Which host plant is a good host for seed beetle larvae?

Acacia is a good host and most larvae survive.

Which host plant is a poor host for seed beetle larvae?

Palo verde is a poor host and less than half of larvae survive.

Do female seed beetles lay larger eggs on acacia or palo verde?

Females lay larger eggs on palo verde than on acacia.

Why do female seed beetles have to change egg size?

Poor environment or poor host seeds forces females to expend more energy on a larger clutch size, phenotypic plasticity is selected for in this generalist species

Why is there conflict between mammal mothers and fathers?

Mother is equally related to all of her offspring and unless their is pure monogamy the male is only related to some of her offspring, he wants more resources expended on his genetic offspring

What is genomic imprinting?

Occurs during gamete production in ovaries and testes, imprinting affects transcription in embryo

What is the IGF-II gene?

Insulin-like growth factor 2 gene.

Which copy of the IGF-II gene is transcribed?

Only the paternal copy.

What should natural selection favor regarding alleles?

Both alleles contributing equally to phenotype.

What is the function of the IGF-II hormone?

It stimulates cell division.

To which receptor does IGF-II bind?

The IGF-II receptor.

What effect does the IGF-II allele have on placental resources?

It causes more placental resources to be devoted to the embryo.

What does the maternal allele do in IGF-II?

Codes for an alternative IGF-II binding site to the CI-MPR receptor, its job is to bind excess IGF0II and equalize the flow of resources to each embryo

What is CI-MPR?

A receptor that does not bind IGF-II in amphibians and birds.

How are the embryos of amphibians and birds provisioned?

Their embryos are provisioned before fertilization.