Ageing and Death

Question 1

How can simple behaviour turn into complex behaviours

Answer 1

through the development of sensory and muscular systems leading to more complex responses

Question 2

Define semelparity

Answer 2

a single reproductive episode followed by death

e.g pacific salmon

Question 3

Define iteroparity

Answer 3

repeated reproductive episodes throughout life, before death

e.g atlantic salmon

Question 4

Define extrinsic mortality

Answer 4

Death due to external factors (predation, accidents, environmental extremes, starvation etc.) e.g the way the environment kills you

Question 5

Define intrinsic mortality

Answer 5

death due to internal factors (tissue deterioration, ineffective physiological maintenance, immuno-compromise, tumours etc.) e.g breaking down, disease creeping out from within

Question 6

Who was Ming

Answer 6

507 y/o icelandic marine clam

Question 7

What is the difference in ageing strategies between birds and mammals

Answer 7

Birds will usually live longer (3 times) than a mammal of the same size

Question 8

Why is it odd that birds live so much longer than mammals

Answer 8

2 - 2.5x higher metabolic rate
15x higher lifetime metabolic expenditure
3oC higher body temperatures
2 - 4x higher blood glucose levels
which are all thought to accelerate ageing and death

Question 9

Why are younger individuals more likely to to successfully proliferate a gene

Answer 9

Reproduction is additive and multiplicative through time e.g sooner you have kids, the sooner they can have ac child
Younger individuals have lower extrinsic probabilities of mortality e.g the longer you live, the more likely you will be killed
(Younger individuals have lower intrinsic probabilities of mortality)

Question 10

Why does senescence occue

Answer 10

Because the strength of selection for surviving in age-structure populations declines with age

Question 11

Define ageing

Answer 11

the progressive loss
of function accompanied by decreasing fertility and increasing mortality with
advancing age.

Question 12

What is negligible senescence

Answer 12

When an animals don’t lose their ability to reproduce over time and their death rates don’t necessarily increase with age

Question 13

Animals exhibiting negligible senescence

Answer 13

Galapagos tortoises and Lobsters

Question 14

What is the Hayflick Limit

Answer 14

The number of times a cell can divide (in humans around 50 divisions)

Question 15

What is the principle reason why animals have evolved different life spans

Answer 15

Evolution of longevity is predicted to be the
level of extrinsic mortality. If this level is high and life expectancy in the wild is short, the force of selection attenuates fast. Deleterious gene effects accumulate at earlier ages, and there
is little selection for a high level of somatic maintenance (intrinsic mortality) If there is a low level of extrinsic mortality, selection will postpone deleterious gene effects and direct greater
investment in building and maintaining a durable soma.

Question 16

In terms or reproduction, why isn’t there a drive to increase longevity

Answer 16

When you are young there is a high reproductive success but as you get older your probability of dying due to extrinsic factors increases, thus reducing reproductive fitness soooo a relaxation of selection on

1. investment to live longer/keep alive
2. invest in later-age reproduction

Question 17

What are the proximate reasons why we age

Answer 17

Reduced investment causes intrinsic ageing via
Free radical damage
Mitochondrial damage
Glycation 
DNA damage
Telomere shortening

Question 18

What are the 3 main specific senescence theories

Answer 18

1.Mutation accumulation
2a Antagonistic pleiotropy
2b. Disposable soma

Question 19

What is the relationship between high extrinsic mortality and reproduction

Answer 19

In environments of high extrinsic mortality e.g high predation, species will invest more into reproducing sooner

Question 20

Example of lifespan differences within a species

Answer 20

Mainland and island living Virginia opossums were studied. It was found that those living on the island lived significantly longer than those on the mainland as their mortality rate was significantly lower due to less predation

Question 21

Example of different levels of reproductive investment in the same species

Answer 21

Mainland Virginia opossums were younger when they had their first litter and that litter size is larger than opossums on the island

Question 22

Why is the maintenance of life inherently challenging (mutation accumulation)

Answer 22

Due to problems from
Errors in genetic mechanisms through germ-line/spontaneous deleterious mutations (e.g. cancer)
Errors in physiological maintenance (e.g. free radical cell damage: Parkinson’s, Alzheimers)
Deleterious alleles (e.g. Huntington disease)

Question 23

How does extrinsic mortality affect intrinsic mortality (mutation accumulation)

Answer 23

Due to extrinsic mortality there is a progressive weakening of the force of selection which avoids, repairs and evolves against mutations.
When one reaches an age where wild survivorship is really low, the selection which favours upkeeping the body is also really low

Question 24

Evidence for the mutation accumulation theory

Answer 24

Two populations or drosophila were maintained, one with high extrinsic mortality (killed after a few days) and low extrinsic mortality (killed after a few weeks). This was run for 5 years and then the adult intrinsic mortality was compared. HAM had a sig higher instricsic mortality than LAM

Question 25

In the drosophila experiment what was the HAM lines reproductive strategy

Answer 25

Faster time to adult ecolsion and higher early fecundity

Question 26

What is the theory of antagonistic pleiotropy

Answer 26

when one gene controls for more than one trait where at least one of these traits is beneficial to the organism’s fitness and at least one is detrimental to the organism’s fitness

Question 27

Example of antagonistic pleiotropy in humans

Answer 27

follicular depletion in human females causes both more regular cycles in early life and loss of fertility later in life through menopause, it can be selected for by having its early benefits outweigh its late costs Wood et al 2001

Question 28

What was Williams theory of why senescence evolved? (antagonistic pleiotropy

Answer 28

Genes coding for investing in early-life reproductive fitness antagonise with later-life survival maintenance
e.g heavy investment in offspring provisioning might reduce investment available to prevent against intrinsic ageing

Question 29

What is the disposable soma theory

Answer 29

It is an extreme form of antagonistic pleiotropy where somatic maintenance is shut off and resources diverted to reproduction to maximise fitness. Most applicable in semelparous taxa

Question 30

Example that supports the disosable soma

Answer 30

All Pacific salmon die after reproduction. An extreme increase in circulating levels of the stress hormone cortisol coincident with major primary investment in reproduction. Leads to multiple organ failure

Question 31

How can alleles with deleterious effects drift to fixation

Answer 31

If the allele shows its deleterious affect later in life, then the selection to remove it will be very weak