Evolution of Ageing Flashcards
1
Q
what is the inevitability theory about ageing?
A
this is the theory that ageing is inevitable; it didn’t evolve, it just happen.s The process of wear and tear would explain this
2
Q
how do we know that the inevitability argument is not true?
A
because some animals do not age: the urticina felina and hydras do not seem to age. one assume that this experiment might just show that they live for a long long time but when you bring in old ones they dont die there (this was for hydras)
3
Q
what 2 things dont seem to age?
A
urticina felina and hydras
4
Q
how were urticina felinas and hydras shown to not age?
A
they show no age specific mortality
5
Q
what is age specific mortality?
A
the proportion of individuals that enter a particular age class and die during it.
6
Q
what is the theory that ageingis a neutral trait
A
this is the argument that ageing is a neutral trait in that it is never seen in nature to be selected for or against because animals always die before it can happen.
7
Q
what is the argument against ageing being a neutral trait?
A
but ageing does occur in nature- studies mammals and tired and other groups have been found to survive following reproduction and that survival and fecundity declines later in life
8
Q
describe a study which demonstrates that animals do age in the wild?
A
hamadryas baboons: measurment was taken of the age related decline in different age groups in 3 populations (2 in wild and 1 in captivity) this showed that in all three populations death rates increased at an approximate exponential rate- doubling every 3.5 to 4.8 years and it occurs even when the hazard rate was different between the two wild populations
9
Q
what is the evolutionary paradox of ageing?
A
that it is detrimental to fitness. If animals did not age its lifetime reproductive success would be higher. SO ageing is not inevitable, it is subject to natural selection and it is deleterious to individuals. SO why does it exist?!
10
Q
what was the idea about ageing being disadvantageous to the individual but advantageous to the group?
A
this was the idea that ageing evolves to let individuals that have reproduced cease to consume resources and hence to increase the fitness of their successors- This can be seen in nature in some species of lizard for examples, where the mother is likely to stop breeding in the presence of the daughter but not when it leaves.
11
Q
what are the two theorists who tackle the argument that ageing exists to allow others in the group to thrive?
A
wallace and weismann
12
Q
what does wallace argue about ageing?
A
Wallace suggested that ageing evolves to let individuals that have reproduced cease to consume resources and hence to increase the fitness of their successors
13
Q
what does weismann argue about ageing?
A
suggested that ageing removes old and worn out individuals from the population to make way for the young. Problems with these suggestions include
14
Q
what is the problem with wallace and weismanns suggestions?
A
they both assume that ageing already exists
- wallace fails to address the point that deferring ageing benefits the individuals and individuals are replaced much more quickly than family groups- this idea would also apply only to animals that live in groups (not the case for a lot)
- Weismanns idea would mean that resources were made available to unrelated individuals that would not inherit the genes for ageing
15
Q
in addition to the qualms against wallace and weismanns ideas, what are other arguments against the kin selection idea of ageing?
A
- there has been revival in the idea that continuing parental care and resource transfer could mea that there is selection for continued survival, not ageing, beyond the age of personal reproduction.
16
Q
what animals seem to support the argument that there is selection for animals to live past their personal reproductive age?
A
- orca whales: older individuals are need for their memory and experience- the older females tend to lead pods especially when there is a shortage of food. They direct sons more than daughters but they offer ra great inclusive fitness benefit
- short finned pilot whale- post reproductive females also go through menopause but help their male members of the pod find food etc
- humans also go through menopause
17
Q
why is it bad for mothers and daughters to reprod at the same time?
A
when the mothers have a lower fertility rate and therefore should help the females daughters to reproduce- but this again assumes that ageing already exits- becoming less fertile
18
Q
what is the evidence that ageing is deleterious to fitness?
A
- in humans, orcas and short finned pilots whales, it is obviously deleterious because older animals can help the group and yet it has evolved
- in terms of animals that dont live in groups- it is also deleterious for obvious reasons- stops them from reproducing
19
Q
is ageing is deleterious but it exists, what does this mean?
A
that it must have evolved as a side effect of something else
20
Q
who was the first scientist to have a breakthrough about ageing? what were his theories?
A
medewar, he pointed out that the forces of selection on a genetic effect will decline with the age at which it affects the phenotype. this is because even in a potentially immortal species there will still be death from extrinsic hazard, for instance disease, predation and accident. so most individuals survive to be young to few live to be old.
21
Q
after medewar, who mad the next key discovery with ageing?
A
haldane- he was studying huntingtin’s disease. he was wondering why selection hadn’t selected it out. it has a late onset. Haldane pointed out that for much of the evolutionary history of mankind the majority of people presumably did not live to be that old, and would have died before the presence of the mutation in carriers became apparent. This means that the selective pressure to remove the Huntington’s mutation from populations is relatively weak. Haldane then made a great conceptual leap… maybe that’s what ageing is - the effect of mutations that have late-onset bad effects.
22
Q
who developed the mutation accumulation theory?
A
Medewar
23
Q
what is the mutation accumulation theory?
A
recurrent, deleterious, germ line mutations occur (these are known from experimental evidence to enter natural populations at a steady low rate, from errors in DNA copying). Fewer bearers survive to express later-acting mutations because of the impact of extrinsic hazard, and the force of natural selection against them therefore declines with age. These late-acting mutations can therefore reach a higher frequency
under mutation-selection balance. Under this theory, ageing is evolving as a side-effect of mutation pressure
24
Q
what did Williams suggest about ageing at the same time around as medewar?
A
Suppose there are mutations are beneficial in youth, but at the price of a higher rate of ageing. More individuals will survive to express the early beneficial effect than will survive to suffer the later higher rate of ageing, because of the impact of extrinsic hazard. Mutations like this can therefore be incorporated by natural selection. This is the pleiotropy (means a single mutation with more than one phenotypic effect) or trade-off theory. Here ageing is evolving as a side-effect of natural selection in favour of mutations that cause a benefit during youth
25
what are the two kinds of processes given that could lead to a trade off between fitness and youth and the rate of ageing?
- there could be competition for nutrient between, for example, reproduction on the one hand and immune response or somatic repair on the other. This is the reproductive effort model, also known as the disposable soma theory. Increased investment in, for instance, reproduction, would necessarily withhold nutrients from somatic repair and maintenance, and hence lead to a higher rate of ageing.
- Second, traits that benefit the young, such as fat deposition for breeding, could cause somatic damage, in this case through cardiovascular disease and diabetes. In this case, activities related to reproduction cause accelerated ageing by inflicting damage
26
why are the disposable soma theory and the antagonistic pleiotropy not mutually exclusive theories?
. Both theories predict that the intrinsic rate of ageing is expected to evolve in accordance with the level of extrinsic hazard encountered. They both suggest that ageing is not a programmed process like development - no genes evolved to cause ageing; it is evolving entirely as a side-effect, of mutation pressure or of processes that were beneficial in youth. This may explain why ageing is such a variable process between different individuals.
27
what are the difference between the mutation accumulation theory and the trade off theory?
mutation accumulation would imply that we can slow down ageing without affecting events earlier in life, while the trade-off theory suggests that a lowered rate of ageing could be achieved only at the expense of fitness in youth.
28
what organism has been used to test the theories of ageing ? why?
fruit fly- it is useful because as a diploid outrider, like humans, its populations harbour high levels of genetic variation. It is easily clustered and has a reasonably short generation time. Being a model organism it also have useful genetic reagents, such as mutant stock and non recombining chromosomes.
29
what are the three predictions of the mutation accumulation theory? which were supported or not my experiments
1. Relatives should resemble each other for traits related to fitness (ie fertility and survival) more when they are old than when they are young. (age specific mutations will only show their effects once the age has been reached- for example huntingtins will only show themselves in relatives that are carrying the genes once the age that they are expressed is reached) In general the experiments with Drosophila do not support this prediction. 2. There must be mutations that specifically affect later age classes. Most new mutations are deleterious, and in Drosophila they affect a wide range of age-classes, and not specifically older age classes. Mutations like the HD mutation are therefore rare, although they could be common enough to play a role in ageing. 3. We would expect to see walls of death at post-reproductive ages, after selection for continued survival ceases
30
do individuals with relatedness resemble themselves more at later stages?
no- there are no specific late acting mutations in flies that are related
31
If you look at new mutations, do some of them specifically affect later age classes?
- you can test this by doing mutation accumulation theory by using a balancer to protect mutations from being selected out. If you do this most new mutations are harmful (lower survival or fertility or both). Generally they do this over more than one age class- very few mutations that only impair fitness later on- huntingtons is rare
32
do you see walls of death in animals, which theory is this linked to?
mutation accumulation theory- no in mammals there is mortality after birth and then mortality rates increases at a steady rate and then there is an exponential increase - no more than that- no walls of death
33
why would you see walls of death if the mutation accumulation theory is true?
- if you have animals that are wild but are kept in captivity, they would survive to a point that they would never reach normally- the force of natural selection falls to 0, so you would expect death rates to soar and fertility to plummet
34
how can you test the trade off theory?
- if you can experimentally reduce the rate of ageing, you can reduce the fitness earlier in life- do artificial selection for those that- allow females to mature and mate- the eggs are then collected from those after 18 days.
- in the older lines then selected animals from the F1 that have survived for 30 days and have still been fertile
you then repeat this for a while
- relative to the young lines there is a change in slope- the rate of death has been decreased- this shows that there is genetic variation which determines the rate of ageing which can be selected for
- in both the males and the females- there was a massive difference inf fertility- females less fewer eggs and they are less fertile. the males are less competitive with sperm competition
- to show this is causal not correlation- you can sterilise them so they have the same fertility and ask if the "young" and "old" flies then loose their differenc in age. This was gone by knocking out the OVOd gene which is expressed in the germline- this abolishes oogenesis. because you have to do a cross you need to do a control cross without the sterilising mutation. you see that when you cross the mutation- you lose the difference in mortality rate which is not the case in the control
35
give three examples of the difference in lifespan on mammals
- common shrews life for a few months
- humans live twice as long as chimps (50 years for chips)
- bowhead whales can life up to 200 years or more
36
how long can the bristle cone live?
around 5000 years
37
what animal can undergo negative ageing and what is this?
- fish- they can grow as adults and become more and more fecund and less likely to die as they get older
38
how can looking at nature be informative, perhaps more so than using lab techniques?
ageing is clearly genetic predominately and the variety in maximum life span is great naturally than what we see in mutants in the lab
39
The role of extrinsic hazard:
how can ageing evolve at all in theory; the intrinsic rate of ageing is expected to evolve in response to the level of extrinsic hazard that is encountered. . Does the impact of external hazard explain this biodiversity in rate of ageing that we see?
40
what is the idea about there being a link between ageing and body size?
We are used to the idea that big things - whales and oak trees - live a long time while smaller ones often do not. But why is this? Does large body size lead directly to longer lifespan, for instance by lowering metabolic intensity - is there some intrinsic reason why big things tend to have a slow rate of ageing, or is there some connection between large size and long life, such as co-selection in particular environments?
41
what is the general premise behind the role of extrinsic rate of hazard?
the idea is that a lifestyle that has low risk will have a low intrinsic rate of living
42
give three examples of type of organisms that would be expected to have a low extrinsic rate of hazard and therefore a low rate of ageing g
- flight or arboreality ( life up trees) are though tot have evolved at least in part as a mechanism of escape from predators and would therefor be expected to have low risk
- poisonous defences such as tough outer skins and shells and armour are also protected against predators
- in mammals and birds, being females is often associated with lower risk from intense competition for ames
43
what does comparison between arboreal and terrestrial mammals show about life span?
- arboreal species have longer lives
44
how does the mutation accumulation theory and the antagonistic pleiotorpic theory and the disposable soma theory supper the idea that less hazard= longer life?
- mutation accum: dont live as long so mutations can accumulate at a sooner point- as soon as reach this point you start to die
- anatgonistci pleit: processes that pose a short term advantage, say for a few months if I were to use a Shrew as an example, but become harmful after say 6 months, would not be selected out, but would be in animals that are more likely to live to 6 months
45
is the link between arboreality in mammals shared with other groups?
yes- it is seen in other groups of phylogeny with the exception of marsupials and primates
46
what is a specific example of a mammal that lives much longer than other mammals?
bats
47
when comparing body weight to longevity, which animals have a long life relative to their body sizes?
birds and bats
48
why is it surprising that birds live longer than would be expected relative to their body size? what does this suggest
Yet birds have a higher body temperature, higher circulating levels of blood glucose, a higher basal metabolic rate and their activity levels are higher. So if anything we would expect them to age faster on the basis of their physiology. this suggest that the differences are lily due to the decreased in extrinsic hazard
49
describe the state of study into the lifespans of poisonous of non poisonous forms?
There has been little in way of systematic study of the lifespans of poisonous and non-poisonous forms, but data are presented for Colubrids, non-venomous, and Viperids, venomous (two family of snakes) - not ideal measures - but there is an association with very large scatter. Again, no proper comparative analysis
50
what is general evidence for armour increasing lifespan?
Tortoises and terrapins, for instance, tend to be unusually long-lived, as are porcupines. This is anecdotal evidence, but it is a strong association and the effects are large. Porcupines are long-lived among their taxonomic group, and some bivalves are also extraordinarily long-lived – 100 even 400 years – more on this later.
51
what is an example of a striking difference in external hazard on the same genetic background, producing large differences in lifespan?
In honeybees, the workers are all female and they are genetically identical to the queen - whether they become a worker or a queen depends only upon their early nutrition. Yet a queen may live for a decade or more whereas the lifespan of a worker is of the order of a few months. So exactly the same genome can produce this massive plasticity in lifespan.
52
describe the theory of eusociality and ageing in ants
- the evolutionary transition to eusociality haas happened independenty on 3 occasions and in all 3, it is associated with the evolution of great ly increased lifespan in the queens.
- lifespans are the longest in the species which have only one queen, which is in itself a response to low hazard enviornments: polygeny (multiple queens) evolves where the risk of queen loss is greatest
53
why is the lifespan of naked molre rats surprising?
- they can live longer than 27 years which is 9 times greater than predicted by their body size. Although mole rats have low metabolic rates, their prolonged longevity results in a lifetime energy expenditure more than 4 times that of mice.
- these animals are also eusocial
54
what is the structure of naked mole rat colony?
they live in colonies of single pairs of breeders and non breeding animals
55
in birds and mammals what is the difference in lifespan between the sexes?
females are thought to live longer
56
why are females thought to live longer than males in mammals and birds?
stronger competition between males for mates in polygynous mating systems, which are particularly common in mammals. This is generally associated with a shorter, more sharply peaked, reproductive rate in males, as illustrated by data from red deer, and higher mortality rates in males. In contrast, reproductive schedules and survival are much more similar between females and males in monogamous species, such as Bewick swans. In general, polygyny is associated with shorter lifespans and more rapid ageing in males.
57
what did Reckless do?
gathered info from both captive and wild populations of birds and mammals. The rate of increase in death rate with age against the initial mortality rate at young adult ages, a good measure of the impact of extrinsic hazard. They used a model of the way that death rates increase with age called the Weibull equation, which assumes that there is an initial low death rate to which ageing adds an amount, allowing the shape of the increase and its rate to vary. This W is the rate of increase in death rate with age from the Weibull, and for each species in the sample it is plotted against the initial mortality rate - the rate of mature, young adults. This initial rate is taken as an index of the level of impact of external hazard.
58
what were the results of the Ricklef's study show?
- low hazard correlates with slow ageing
- extrinsic hazard is lower in captivity
- quite generally slow ageing goes with low extrinsic hazard in nature. And things tend to live longer in captivity not because they age more slowly but because the level of extrinsic hazard is lower.
59
in mammals and birds, what is the relationship between body size and ageing?
In the bird and mammals data there is certainly a correlation. In both groups survival tends to be greater in longer-lived species
60
what is the general evidence for size and lifespan being correlative not causal?
- For a start, it only works WITHIN birds and mammals, not if we compare birds to mammals. And it does not work for bats either – they are much longer-lived than other mammals for their size.
- we have already seen that the tiny Hydra may not age at all
- there is no theory in physiology that suggests that small things should be incapable of living for a long time or that large things should automatically do so. There is no evidence that large body size is CAUSAL in producing a long lifespan. There is certainly a CORRELATION, but this could be because they are both correlated with something else.
- . Dog breeds with larger body size tend to be shorter lived. So where you artificially select for size, you change lifespan in the opposite direction. Interestingly, the variation in body size is strongly associated with genetic variation for Igf1, which is also implicated in ageing, as you will hear later in the course. And it is the same with natural genetic variation in mice - the genetically smaller mice tend to be the longer-lived.
61
why is body size and lifespan so correlated in nature?
One reasons is that large body size may be protective against some hazards – including predation. In addition, they may tend to evolve independently in low hazard environments. We have seen that slow ageing is expected to evolve with low hazard and that it does so in practice. Large body size probably also evolves in conditions of low hazard. It takes time to grow, and in a high-risk environment it is important to get breeding fast - or run the risk of failing to breed at all. So large size has evolved in low-risk environments. And it may be this common correlation with risk that explains the, rather low but significant, association between slow ageing and body size – co-adaptation.
-
62
why are mammals and birds used for reproductive studies?
Those species were chosen because there are good data on juvenile mortality, age of first breeding, and fecundity.
63
what did studies of the fecudnity and lifespan of mammals and birds give rise to?
- Annual offspring production in the two groups in relation to annual adult survival shows a tight, negative association in both groups, with very similar relationships for the two groups. All of the unexplained variation drops away to give a tight correlation. And within both groups, long-lived species start breeding late, and birds start later than mammals but, for a given age of first breeding, mammals and birds age at the same rate. So birds seem to pay for long life with a late start to offspring production. So again, over this much large set of evolutionary distances, it looks like a cost of reproduction story for the evolution of ageing.
64
how can low extrinsic hazard be linked to longevity?
One has to be careful with comparative data, and particularly comparative data on life histories. For instance, these results could be at least in part explained by changes in population dynamics. If a species ages more slowly, then population numbers will increase and something has to give, because the population cannot expand in numbers indefinitely. What gives is reproduction, and in the same way in the two taxa.
So there is a general association with reproductive rate as well as with extrinsic hazard. With low extrinsic hazard, both birds and mammals pull back on reproduction - so the cost of reproduction seems to be very important in explaining diversity
65
what is semelparity?
The effect of reproductive rate is particularly obvious in cases where we see what looks very like suicidal reproduction. Some organisms undergo almost catastropic senescence
66
what are 3 examples of semelparity and what is an explanation?
Agaves are desert plants that grow a big rosette of fleshy leaves, over a period that can be a century or so. They then breed by sending up a huge flowering stalk by taking nutrients from other parts of the plant, and the plant then dies. It is not clear why they have adopted this strategy. One idea is that there is a shortage of pollinating insects in this environment, and to get pollinated requires this huge flower. So in a more general sense, if there is a very high capital cost to being able to breed at all, then it may pay to go for bust. That idea could apply to Pacific salmon as well - they have to migrate upstream to their breeding grounds. Both females and males stop feeding and start to use up their muscles and gut, the females turning them into eggs, the males using energy in fighting. At least at a qualitative level, these life histories where the organism lives for a long time as a pre-adult and then goes for bust are associated with high capital costs of breeding, but there has not been any rigorous comparative analysis of the trait.
- The more common situation with semelparity is that it is associated with being an annual – the organism overwinters as pre-adult - egg or juvenile, and then breed in the summer. This is very common in eg insects - the mayflies being a canonical case, they do not even feed as adults, they just emerge, breed and die in a few days. This habit is unusual in mammals but there is one quite famous case - this marsupial mouse. The males are annuals - they are born in spring, mate furiously over the summer and die, so that only pregnant females overwinter.
So these are cases where very rapid ageing and death are a clear and direct consequence of reproduction.
67
why are some organisms thought to decrease in age as it were as they get older?
a lot of organisms such as fish and reptile and many invertebrates. Theoretical analysis suggests that these are likely to occur in organisms that start to breed before they reach full size, and where fecundity goes up with body size, as it does in many types of organisms.
68
what is unusual about the naked mole rats
The naked mole rat is long-lived (~30 years) compared to other rodent species. The genome of this animal has been sequenced and, for instance, and shown. The animals are resistant to cancer. Interestingly they are resistant to certain types of pain, and recent work in mice has shown that mutation of pain perception increases lifespan. The also have increased fidelity of translation of their proteins, possibly as a result of a peculiarity of their ribosomes.
69
in what animals has reproductive decline long before the end of life been documented?
- humans, fish, birds and invertebrates
70
when are most post reproductive lifespans observed?
in captivity
71
what is the putative link between evolution and senescence
under natural conditions, organisms die from extrinsic hazards, since there re always fewer older individuals in a population than younger ones, the strength of selection on alleles with age specific fitness affected is expected to weaken with increasing agend alleles that confer advan- tages early in life, by increasing early-life fecundity, can spread to fixation even if they have deleterious effects later. the declining strength of selection with age sets the stage for thhe evolution of physiological mechanisms leading to both reprod and somatic sen
72
how are somatic and reprod sen inherently linked?
there is no point maintaining a viable germ line if somatic sen has progressed to the point that prevent successful reproduction
73
why is post-reproductive longevity that is seen in captivity likely an artefact?
because these animals are released from extrinsic drivers of mortality or are involved in breeding programmes with can accelerate reproducitve senescence
74
why is measuring post reproductive longevity troublesome?
- measuring the time between the end of fertility and the end of life is biaseed because it includes only individuals that survive for a certain time after the last reproductive event and does not capture the important of PRLS for the population/ species- an example of this is iif only 5% of the population that started live to a post-fertile age- this clearly shows that naturally, PRL is not important for this species. that is why it is important to note at what frequency and in what context post reprod females exist in nature
75
what is the antagonistic pleiotropy idea of PRL?
that early high reproductive success rates occur at the expense of fertility later in life
76
what is the insurance idea of PRLs?
that PRLSs have evolved as an insurance against the risk of dying by chance before the cessation of repro- ductive activity
77
what is the male related idea of PRL?
that it is due to the mating preference of older males by younger females or a section of longevity on males (older males are stronger or something)
78
how is the reason for PRL in females thought to differ between solitary and group animals?
- in solitary animals it is likely to occur as a byproduct of selection on other traits such as with males
- There is, however, mounting evidence that in humans, resident killer whales, and social aphids post-reproductive females increase the survival or reproductive success of their kin
79
what is the mother hypothesis of PRL? what is the grandmother hypothesis?
emales that terminate repro- duction in mid-life gain fitness advantages by investing in previously born children.By stopping reproduction, females escape the increased risk of mortality associated with late-life pregnancy.Simi- larly, Hawkes [5], suggests that post-reproductive females increase their inclusive fitness by supporting weaned grand-offspring that are dependent on provisioned food for some time following weaning.
80
what is empiriical evidence that the presence of a mother is important in killer whale survival?
resident killer whales mothers contribute to their offspring’s survival well into adulthood [27]; in the year after their mother’s death, mortality risk increases by 2.7 times in adult daughters and 8.3 times in adult sons (aged > 30 years)
81
why is PRL important in which type of fly?
Among invertebrates, some of the best evidence that post-reproductive mothers contribute to the survival of their adult offspring comes from work on the social aphid Q. yoshinomiyai, where wingless females switch from reproduction to colony defence
82
what is a theory explaining why females in groups would stop reproduction early
This model predicts that repro- ductive overlap between generations should involve substantial fitness costs, favouring early reproductive ces- sation and separation of reproductive generations. It appears that longevity alone does not necessary lead to a PRLS [14] and that the unusual patterns of kinship dynamics in humans and some cetaceans might have predisposed them to the evolution of a PRLS
83
generally, when would we expect PRL to evolve?
We should expect females to forgo late-life reproduction only where doing so boosts the fitness of their kin and where helping is more effective if females are no longer reproducing themselves
84
why would we generally expect PRL to be more prevelant among group species?
There is substantial evidence that mothers and grandmothers provide significant survival and reproduc- tive benefits to their children and grandchildren and that intergenerational reproductive conflict is detrimental in some societies.
85
what did medewar state that was very wrong?
that animals in the wild do not senesce
86
what evidence is there that medlar's mutation accumulation theory is wrong in that ageing does not suddenly occur?
in humans, signs of ageing can be seen from the age of 30 and gradually progress, humans even years ago would have lived to 30 years old- so it is not that most ageing traits are out of the realsm of selections
87
what is the disposable soma theory?
it hypothesizes that because critical resources such as energy are limited, natural selection will adjust the allocation of cellular and physiological resources between the fundamental pro- cesses of somatic maintenance and reproduction appropriately for an organism’s ecological context . Since natural selection is expected to weaken with age, selection will tend to favour investment in early reproduction over long-term somatic maintenance, and senescence will result
88
what is the antagonism of mutations to IGF and what theory does this support ?
prolongs lifespan but has depressive effects on early reproduction - antagonistic plea
89
give two studied examples of sen in wild animals?
Dall sheep in alaska can be aged form their horn rings and they show increased mortality with age,
- yellow eye penguins in new zealand showed a decline in reproductive traits with age
90
how many different animal species have shown sen in the wild?
175/340 studied
91
what can be said about the rare in ageing in females and males and the reason for this
Based on the idea that the strength of natural selection against senes- cence hinges on the rate of ‘extrinsic mortality’ experienced in nature, Williams (1957) predicted “where there is a sex differ- ence [in “extrinsic” mortality], the sex with the higher mortality rate and lesser rate of increase with fecundity should undergo the more rapid senescence.” Male-biased natural mortality rates are very widely observed in polygynous species, including many mammals and insects, where males tend to be larger and show mating behaviours and secondary sexual characteristics associated with substantial energy expenditure and mortality risk.Some support for the prediction has been obtained from a comparative study using data from long-term field studies of birds and mammals which found that male-bias in survival senescence rates increased with the degree of polygyny, and was largely absent in monogamous birds
92
what are the contrasting ideas about differences in sex age
- some claim that PRL in females may result from a a selection for older males
- but then males normally live for less time than females and this is thought to be due to more external hazards
93
what was a key study that suggested that males age faster than females due to differences in resource allocation?
The study took starting tooth size as an indicator of resource allo- cation to somatic maintenance and wear rate as a proxy of the need for repair and showed that, despite males being considerably larger and heavier than females and showing faster molar wear, sexual dimorphism in molar height in early life was minimal (Carranza et al., 2004). This supports life history theories, suggest- ing males allocate less in maintenance in accordance with theirshorter life expectancy
94
how does semelparous normally manifest itself?
- often a sudden loss of function after reproduction- adult mayflies and pacific salmon
95
what does iteroparous mean?
- reproduce more than once
96
what is evidence that ageing doesn't simply occur from external stresses?
- captivity in which animals are exposed to the same stresses, animals have different lifespans
97
why are eusocial species protected from extrinsic rate of risk?
they live in colonies that are defended against predators- queens that express late life mutations will not be selected for very strongly because will not produce many offspring- the late acting mutations will be exposed
98
in old mammalian populations, what are the rates of old males?
very low
99
describe an extreme sex difference in mammals?
marsupial mouse, the male shows accelerated ageing after the end of the mating season while females can live more than one season
100
what is t he general premise for the reduced age of males? what would be predicted if this were true
A probable explanation for the evolution of earlier senescence in males than females is that intense intrasex- ual competition for breeding opportunities between males in polygynous societies, combined with the costs of traits or strategies that enhance competitive success, shorten the period for which adult males are able to attract or defend females against their competitors, so that selection pressures favouring longevity are weaker than in females- fewer sex differences between polygamous and monogamous species
101
what did a study looking at the sex differences in lifepsan find in polygamous and monogamous animals? what was an issue with this study and studies of this kind in general
in long-lived polygynous vertebrates, adult males commonly show higher rates of annual mortality and an earlier onset of age-related increases in mortality as the end of the lifespan approaches in adult females. Together, these effects generate sub- stantial differences in adult life expectancy between the sexes. In contrast, sex differences in mortality and adult life expectancy are smaller and less consistent in monogamous species
- there are few monogamous mammals and few polygamous birds
102
what did three studies find about monogamous mammals?
males did not significantly lower... hmmm..
103
who first suggested that metaolic rate was linked to longevity and what was his theory and what theory di this link with
Rubner,He thus concluded that the increase in longevity accompanying increasing body size among mammalian species was likely causally associated with the concomitant decrease in expenditure of energy at the tissue level, suggesting life span itself was limited by energy expenditure. This was linked with the free radical theory because metabolic rate is linked with i increased ROS production and CR may be decreasing metabolic rate and increasing age
104
what evidence in birds vs mammals showed that the metabolic rate theory was not true?
birds, with higher basal metabolic rates than mammals, would be predicted by the rate-of-living hypothesis to be shorter-lived than similar-sized mammals, yet the opposite is true. Birds live on average about three times as long as similar-sized mammals
105
why is looking at ageing across phylogeny (comparative biology of ageing) so important?
Studies of single species yield information about single species. It is only by comparing multiple, phylogenetically diverse species that broad hypotheses can be supported or rejected. In this sense, the most striking evidence that insulin-like signaling broadly and causally modulates longevity is the observation that mutations reducing insulin-like signaling in Caenorhabditis elegans, Drosophila melanogaster, and house mice (Mus musculus)—three laboratory species separated by a billion years of evolutionary history—all significantly extend life
106
why is reduced ribosomal biogenesis thought to expand life span?
at reduced ribosomal biogenesis may have its effect by reducing protein synthesis, which may in turn diverts more cellular energy to maintenance activities such as DNA repair or the degradation of damaged or misfolded proteins or leads to the synthesis of fewer damaged or misfolded proteins
107
what cross species evidence is there that the integrity of the proteosome is important in ageing
protein oxidation and stability was compared between naked mole-rats (Heterocephalus glaber) which can live nearly 30 years (Buffenstein 2008) and same-sized house mice which live no more than 4 years (Turturro et al. 1999). Livers of naked mole-rats accumulated fewer damaged proteins with age than did mouse livers and general protein stability, in the face of induced unfolding stress, was substantially greater in naked mole-rats than in mice
108
even though body size is corrrelated with longevity in the wild but the opposite is found in animals such as dogs and horses, why is this not maybe very important?
It may be worth noting that this within-species pattern of an inverse relation between size and longevity has been reported only in species subjected to strong artificial selection during the course of domestication. Thus, it could represent the disruption of evolved physiological systems and feedback mechanisms by selection for extreme traits and may not be more generally relevant.
109
how long can bivalve molluscs live for?
500 years
110
give two reasons why studying short lived animals is importune ?
- they can be used to study the genetics of changing lifespan
- they can be used as a comparison to longer lived animas- mouse vs naked mole rat
111
how long does the killifish live for?
9 weeks
112
is it better to compare closely related spices or distant species and why?
hylogenetic affinity is an important concern, because the more closely related species are, the fewer are the likely functional and genetic differences among them that are unrelated to differences in longevity. Thus, it would likely be more informative to contrast long-lived and short-lived bats rather than long-lived bats with short-lived rodents.
113
what evidence within species is there that a larger body size is negatively correlated with longevity? what does this suggest about the body mass theory?
- a human study found that the large body size (not just percent fat) was associated with reduced life span! this suggests that the theory that larger body size is linked to longer life is not true within species
114
how were phylogeny studies used to disprove the body size to lifetime link
Also, importantly, a phylogenetically-sensitive comparative analysis noted that once the impact of phylogeny was removed, there was no longer any relationship between basal metabolic rate and longvity
115
what is the disposable soma theory and how does it link pleitiopy and mutation accumulation?
The disposable soma theory, which was proposed by Kirkwood and Holliday [35], predicts that aging occurs due to the accumulation of damage during life and that failures of defensive or repair mecha- nisms contribute to aging [12, 35, 36]. It postulated a spe- cial class of gene mutations with antagonistic pleiotropic effects in which hypothetical mutations save energy for reproduction (positive effect) by partially disabling mo- lecular proofreading and other accuracy promoting de- vices in somatic cells (negative effect). In other words, given finite resources, the more an animal expends on bodily maintenance, the less it can expend on reproduc- tion, and vice versa. The distinction between somatic and reproductive tissues is therefore important because the reproductive cell lineage, or germ line, must be main- tained at a level that preserves viability across the genera- tions, whereas the soma needs only to support the sur- vival of a single generation. Thus, the key feature of the disposable soma theory is its emphasis on the optimal balance between somatic maintenance and repair versus reproduction. The theory also suggests that multiple kinds of damage will accumulate in parallel within cells, as the same logic limits the investment in each of wide range of maintenance and repair functions. To conclude, the disposable soma theory closes the gap between mech- anistic and evolutionary theories of aging by suggesting that aging results from progressive accumulation of mo- lecular and cellular damage, as a direct consequence of evolved limitations in the genetic settings of maintenance and repair functions
116
give two natural pieces of evidence that support the disposable soma theory
Support for the idea that the predation rate on a given population affects that population’s life-history strategy, including the evolution of altered life span, comes from studies of wild guppies. Such evolution in early life-history stategy occurs very quickly in response to mortality rate changes (Reznick, Buckwalter, et al.). Guppy populations that suffer high predation rates are smaller, grow faster, produce young at an earlier age, and allocate more resources to reproduction than those found in low-predation environments (Reznick, Buckwalter, et al.; Reznick, Butler, et al.). In has also been suggested that one reason why birds and bats live longer than ground-dwelling animals of similar size is that, through flight, they have been released from much of the predation pressure experienced by ground animals. (Austad and Fischer; Ricklefs). One study that tested some of the ideas behind the disposable soma theory was carried out on two distinct U.S. populations of Virginia opossums (Austad). One population was found on Sapelo Island, Georgia, and had no mammalian predators; the other population, found on the Georgia mainland, was predated by pumas, foxes, and bobcats. When life-history parameters were measured for both groups, it was found that the island population produced fewer pups per litter than the mainland group and generally survived to a second reproductive season, when they bred again. The island group had, on average, a 25 percent greater average life span and a 50 percent longer maximum life span than the mainland group.
117
what is the disposable soma theory
It proposes that individuals should invest in the maintenance and repair of their soma in relation to their expected life history objectives. However, an individual’s expectation of future survival prospects, and the likelihood of reproduction, are not constant. Distinct species, and sometimes distinct individuals within a species, therefore need to sustain their somas for different lengths of time. The disposable soma theory of aging predicts that species and cohorts in a population expecting, on average, to have high survival and low reproductive rates should invest more heavily in protecting their somas than species and populations that expect a short lifespan and to reproduce rapidly. When animals are released from natural selection, differences in somatic repair and maintenance manifest themselves in interspecific and interpopulation differences in aging rate and lifespan.
( so basically mutations that favour making lots of offspring early will be favoured because those that focus on slow lives but consistent reprod and the maintenance that goes with itwill never be selected for because the animal dies. so when nutrients is finite, more will be put in reproduction that maintainance )
118
what re some of the reasons given for why males live less than females naturally?
- For example, in many ungulates, males expend most of their fat reserves in the autumn rut, and their condition at the onset of winter is inferior to that of females, making them more susceptible to adverse weather or to density-dependent resource shortages
- The effects of testoster- one on immune responses may also affect the parasite loads of males, with downstream effects on their energy
- Secondary sexual characters (including weaponry and increased body size) of males may also have energetic costs to males and render them more susceptible to adverse environmental conditions.
