Week 8 Flashcards
What are examples of cooperative breeding?
Slime mold - Dictyostelium discoideum
Ant colonies
Long-tailed tits
What is an overview of the cooperative breeding of Dictyostelium discoideum?
Single cell eukaryote
Lives in colonies
1 cell becomes spore which produces next generation and another sacrifices itself to become a stalk
What is the evolutionairy paradoc of cooperative breeding?
Individuals help other individuals to reproduce, at a cost to themselves
Contradicts the idea that individuals should maximise their own reproductive success
What are examples of species verterbrate cooperative breeding systems?
Cichilids
Acorn Woodpeckers
Meerkats
How frequent is veterbrate cooperative breeding?
> 200 spp of birds
120 spp of mammals
50 spp of fish
What is cooperative breeding?
Situation where adult individuals, in addition to the genetic parents, stay within a group and regularly aid in the rearing of young
What are examples of types of cooperative breeding?
Helpers at a nest (~80% of CBS)
Plural breeding
What is an overview of helpers at the nest cooperative breeding strategies?
Situation where adult individuals, in addition to the genetic parents, stay within a group and regularly aid in the rearing of young
Seen in scrub jays and jackals
What is an overview of plural breeding?
Several males and females share a nest and raise a communal brood
Seen in Gray-breasted jay Banded mongoose
What is the variation in cooperative breeding strategies?
A spectrum - ostrich is some where in the middle has a couple breeding pairs lay in a nest but also has helpers who arent breeding
What are examples of cooperative breeding systems not in nonmonogamous systems?
Polyandry - Naked mole rat
Polygyny - Moustached Tamarin
Polygynandry - dunnocks
Do helpers benefit dominants?
Increasing the reproductive success of the breeders
Increase breeder survival
What is an example of reproductive sucess of breeders increasing with help?
Jackals - Mooehlman 1979
As number of helpers increases the number of offspring survive
How have additional helpers increase breeder survival?
Scrub jays - annual breeder Mumme 1992
With helpers survival increase from 77% to 85%
Is there a cost to helping?
Individuals that helped most had worse body condition at the end of the season and lower future survival Colonial pied kingfishers (Reyer 1984) and Stripe backed wrens (Rabenold 1990)
What is an example of condition helping?
In Meerkats helping is condition dependent (Russell et al 2003 PNAS)
– Only help when above threshold weight
– Short term cost – lose weight
– Stop helping when drop below threshold
– No reduction in survival
Behavioural modification – reduce long term costs
What is kin selection?
An individual can increase the number of copies of its genes in future generations by helping to increase the reproductive success of close relatives (W.D Hamilton 1964)
What is hamilton’s rule?
A costly action should be performed if:
C < B x R
C = cost in fitness to the actor,
B = fitness benefit to the recipient
R = genetic relatedness between the actor and the recipient
Why do cooperative breeding systems evolve?
Eusocial insects/microrganisms
- consistently high levels of relatedness between sibs
- kin selected benefits do seem to explain altruistic behaviour
What can cause vertebrate cooperative breeding systems to evolve?
Ecological constraints
Benefits of philopatry (staying in a group)
What is the outcome of ecological constraints enforcing cooperative breeding systems?
Individuals join a group (or don’t leave their natal territory) because there are no good breeding opportunities available
What is an overview of the benefits of philopatry for cooperative breeding?
Increased survival
Increased chance to inherit territory
Ability to safely look for breeding opportunites
What is an example of ecological changes resulting in changes in cooperative breeding?
Superb fairy-wrens. Male helpers always leave when an opportunity to pair with an unmated female arises. (Pruett-Jones & Lewis 1990 Nature)
Why does helping evolve?
Indrect (kin selected benefits)
Direct benefits - increase an individuals own lifetime reproductive success
What is an overview of indirect (kin selected) benefits?
In many systems, young individuals delay dispersal and help parents raise subsequent offspring
So kin selection has been the favoured explanation
What are examples of direct benefits of cooperative breeding?
Pay to stay - kicked out if not helping - seen in Neolamprologus pulcher (cichlid)
Acquisition of a mate
Group augementation - whole group does better and you may be able to benefit if you take over group
Gain breeding experience
Direct breeding
What are the direct and indirect benefits of cooperative breeding?
Direct present - Increased survival
Direct future - Increased probability of breeding improved reproductive success as breeders
Indirect present - increased production of non-descendent kin
Indirect future - increased survival and production of kin + increased production of future helpers
What is an example of cooperative breeding?
Seychelles warbler which live on a small island in the Seychelles
What is an overview of cooperative breeding in the seychelles warbler?
A dominant pair with suboridinates that are typically female
What are the constraints placed in the seychelles warbler?
Limited breeding territories available
When translocated – independent breeding – until the new island was saturated
What are the benefits shown for cooperative breeding on Seychelle warbler?
Direct benefits - Acquisition of parental experience
(Komdeur 1996)
Indirect kin benefits - Subordinates appear to improve the reproductive output of the territory (Komdeur 1994)
What does previous work on cooperative breeding in Seychelle Warbler suggest?
Suggested that indirect (kin) benefits = main benefit but assumed relatedness!
What is a rough status of the Seychelle warbler on Cousin Island in 1997?
> 96% of birds individually colour ringed and blood sampled
All territories mapped and monitored
Breeding attempts followed
Status of adults in cooperatively breeding territories (30%) was determined
All chicks blood sampled (1 or 2 chicks/nest)
How did they determine parentage in the Seychelle Warbler?
30 microsatellite loci used for genotyping
Parentage – Assigned using CERVUS; Marshall 1998
Relatedness – Based on genotype similarity
What was the overview of cooperative breeding in Seychelle warbler?
30% of territories were cooperatively breeding
44% of subordinate females layed an egg = 11% of nestlings
15% of subordinate males fathered an egg = ~1% of nestlings
Female subs more likely to gain parentage than males
What was the extra pair paternity of inthe Seychelles warbler?
40% Extra-pair paternity
What does the high levels of extra pair paternity mean for cooperative breeding?
High levels of extra pair paternity may explain why there is high levels of sneaking eggs in. As there is a high chance that chick will be a half sibling which has a lower genetic relatedness than offspring
What is the relatedness between subordinates and nestlings in the seychelle warblers?
Previously expected R = 0.5
Female subordinate-nestlings = 0.13
Male subordinate-nestlings = 0.07
How many offspring are produced by dominant and subordiante seychelle warblers?
Dominant breeders only produce ca. 1.00 per year
Female subordinates 0.46 ± 0.63
Male subordinates 0.14 ± 0.35
What are the benefits of cooperative breeding in seychelle warbler?
Benefits = Increase in offspring produced by dominants as a result of helping (b) x relatedness between helper and helped offspring (r)
What is the quantifiable genetic benefit of cooperative breeding in Seychelle warbler?
Extra offspring produced due to the presence of a subordinate, excluding
subordinate parentage = 0.18 ± 0.50 x Subordinate-nestling relatedness
What is the offspring equivalents/sub in Seychelle warbler (Indirect kin benefits)?
Female subordinates = 0.07 ± 0.26
Male subordinates = 0.04 ± 0.17
What is an overview of indirect and direct benefits for the seychelle warbler?
High direct benefits
Low indirect benefits
Females gain more benefit than males
What is an overview of cooperative breeding in the Seychelles warbler?
High levels of subordinate breeding and extra-group paternity
Reduced subordinate-nestling relatedness
More direct than indirect benefits to cooperative breeding
What is an overview of the monogamy hypthesis?
Independent breeding (R x B) or Cooperative breeding (R x B)
R = 0.5 to offspring , B = own offspring produced
R = ? , B = extra dominant’s offspring
Given equal effort by sub - number of own offspring or of extra dominants’ offspring = the same
(B is equal)
So the equation depends on R
How is R impacted by the monogamy hypothesis?
R depends on levels of dominant female promiscuity
If promiscuity occurs then R between potential helper and dominants’ offspring is reduced
If total monogamy, then R is the same (always full sibs = 0.5)
Therefore both strategies are equal with total monogamy
What can cause for the selection of cooperative breeding?
Additional benefits to cooperative breeding (i.e. direct benefits)
Reduced benefits to independent breeding (i.e. ecological constraints, or inexperience)
Monogamy and kin benefits should therefore favour the transition to CB
But the extra benefits that cause the transition could be direct benefits
What is the evolutionary history of cooperative breeding on birds with relation to monogamy?
Comparative phylogenetic study in birds indicates CB
more likely to evolve where the ancestors are
monogamous. Cornwallis et al. 2010.
Why does cooperative breeding not disappear in the promiscuous Seychelles warbler?
Massive ecological space meaning it is hard for breeding pairs to go off and start new nests
What is semelparity?
A single reproductive episode followed by death eg Pacific/ Sockeye salmon
What is iteroparity?
Repeated reproductive episodes throughout life, before death eg Atlantic salmon
What is extrinsic mortality?
Death due to external factors (predation, accidents, environmental extremes, starvation etc.)
What is intrinsic mortality?
Death due to internal factors (tissue deterioration, ineffective physiological maintenance, immuno-compromise, tumours etc.)
What are examples of contrasting ageing profiles in different species?
Icelandic marine clam ‘Ming’ - 507 years
Marine gastrotrich - ~ 3 days
What are examples of contrasting ageing profiles in closely related species?
Cicada – 17 years
Aphid – 28 days
What are examples of contrasting aging profiles in within the same species?
Honey bees:
Queens: 3-8 years
Workers: 320 days
Drones: 59 days
What are examples of contrasting aging profiles in different fish species with similar body sizes?
Red rockfish - ~100 years
Sockeye salmon - ~5 years
What are examples of contrasting aging profiles in different insects species with similar body sizes?
Fruitfly - <1 month
Flour beetle – 1 to 2 years
What are examples of contrasting aging profiles in different bird and mammal species with similar body sizes?
Razorbill – 42 years
Rabbit – 5 years
Turnstone – 20 years
Rat – 3 years
What is the difference between mammals and birds in terms of aging?
Compared with equivalent-sized mammals, birds are on average 3x longer-lived
What is the difference between bird metabolic processes compared to mammals?
Birds 2 - 2.5x higher metabolic rate than mammals
Birds 15x higher lifetime metabolic expenditure than mammals
Birds 3oC higher body temperatures mammals
Birds 2 - 4x higher blood glucose levels mammals
What is believed to the reason birds live longer than mammals?
Flight - Once flight accomplished, relatively lower extrinsic mortality than terrestrial mammals
What is an example of the difference in lifespan between flight and terrestrial mammals?
Light brown bat – 34 years
Mouse – 4 years
What can cause changes in ageing?
Wide variation in ageing patterns independent of body size and phylogenetic affinity
What is the logic of senescence?
Investment is partitioned between survival and reproduction
What is a hypothetical example of the logic of senescence?
The probability of that gene being reproduced and proliferated is dependent upon the age of the individual carrying it, (once reproduction has begun)
Older individuals are less likely to successfully proliferate the gene because:
1 - Reproduction is additive and multiplicative through time
2 - Fewer individuals survive to old age
What happens in a model with only extrinsic mortaility?
Fitness relationships in a non-senescing model subject only to extrinsic mortality risks
Strength of selection to survive therefore declines with age
What happens with selection strength over time?
Selection on investment to survive is greatest when young and decreases once reproduction has begun
What is a real-life example that proves the selection strength decreases with age?
Survival curves for female and male elephant seals on Macquarie Island and South Georgia shows selection strength decreases over time
What is an overview of type 1 ageing profile?
Low mortality (both extrinsic and intrinsic) when young slowly increases over time until reaches a point where mortality rapidly increases e.g. humans
What is an overview of type 2 ageing profile?
Fairly consistent mortality rate over time seen in birds
What is an overview of type 3 ageing profile?
High mortality (both extrinsic and intrinsic) when young slowly decreases over time until reaches a point where mortality rapidly decreases e.g. oak tree (few acorns make it to oak tree but oak trees can live a long time_
Why does senescence occur?
Senescence occurs because the strength of selection for surviving in age-structured populations declines with age
Why does selection not select long living organisms?
As you get older, your probability of dying due to extrinsic factors increases, reducing your reproductive fitness
A relaxation of selection on:
1) investment to live longer/keep alive
2) invest in later-age reproduction
What is an ultimate driver for ageing?
Decreasing selection on investment to remain alive as an individual ages through reproduction (Hamilton 1966)
What is a proximate driver for ageing?
What makes us age? reduced investment causes intrinsic ageing
What biological factors can cause intrinsic aging?
Free radical damage (unbonded single orbiting atoms: damage to nucleic acids, proteins, lipids)
Mitochondrial damage (mtDNA has no protective histone proteins, free radical damage to metabolic ability)
DNA replicative damage (high threat from oxidation, hydrolysis, alkylation, radiation, or toxic chemicals)
Telomere shortening (disposable buffers blocking the ends of chromosomes consumed during cell division)
Is it possible to artificially extent a lifespan?
Yes as seen in Drosophila where a large number of known mutations which can extend the lifespan
What is an example of a single gene effect on senescence?
Caenorhabditis elegans, age-1 (hx546) mutant
What is an overview of the C.elegans age-1 (hx546) mutant?
65% increase in average lifespan
110% increase in maximum lifespan
Genetic regulation of a range of stress responses
Resistance to pathological effects of H2O2, paraquat, UV light, free radical damage to mitochondrial genome, heat shock resistance
Increased production of antioxidant enzymes (dismutase and catalase)
What is an consequence of the C.elegans age-1 (hx546) mutant?
Reproductive output is reduced under competition for resources
How can you test the ageing theories?
General measures of relationships between ageing - reproduction - extrinsic mortality
What are specific ageing theories?
Mutation accumulation
Antagonistic pleiotropy
Disposable soma
What is cross-species relationships between extrinsic mortality and age-at-first reproduction?
Higher the adult mortality rates the younger the age of first reproduction
What is an example of the differences between extrinsic mortality and age at first reproduction?
Polygonia c-album – matings through out the 22 days recorded lives for around 30 days
Inachis io – matings stop around day 11 life span is around 15 days
Both butterflies
What is an example of inducing different life-history strategies depending on extrinsic mortality risk?
Guppies
Group 1 – natural population split into high and low predation
Group 2 – population isolated for 7 days then split into high and low predation
Group 3 – population isolated for 18 days then split into high and low predation
Low predation group for both males and females had older age of first birth (fe) or age at full maturity (male)
What is an overview of mutation accumulation theory of aging?
Maintenance of life carries inherent challenges because of:
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, Alzheimer’s)
Deleterious alleles (e.g. Huntington’s disease)
Why does mutation accumulation occur?
As a result of extrinsic mortality, there is a progressive weakening in the force of selection with increasing age against: 1. avoiding / 2. repairing / 3. evolving against - these challenges
How does mutation accumulation lead to ageing?
By an age when wild survivorship probability has declined to low levels, the force of selection to 1. avoid / 2. repair / 3. evolve is too weak
What happens with ageing over time even when extrinsic mortality doesn’t change over time?
Maintaining the soma is difficult and the odds of an error occurring become increasingly likely with time
Any genes which have negative effects later in life, will take effect AFTER reproduction and AFTER many individuals have died anyway
What is an example of experimental evolution under increased extrinsic adult mortality rate??
Drosophila replicate lines
High Adult Mortality (HAM): adults killed within a few days of emergence
Low Adult Mortality (LAM): adults killed after a few weeks of emergence
Run selection lines for 5 years in this way
Then check life-history traits including adult intrinsic ageing
What were the results of results of experimental evolution under increased extrinsic adult mortality?
After 5 years HAM lines evolved higher intrinsic mortality rate after emergence
HAM lines evolved a faster development time to adult eclosion
Higher early reproductive output
What is an example of a deleterious gene that would hard for selection to remove?
Huntington’s disease
Human brain disorder caused by single gene
Gene for the disease is dominant!
Hundreds of thousands suffer & disorder is fatal
Why has selection not removed the gene for huntington’s disease?
Because it disables fitness above age 45 when selection to remove it is very weak
What is antagonistic pleiotropy?
Genes coding for investing in early-life reproductive fitness antagonise with later-life survival maintenance
What does antagonistic pleiotropy make worse?
Exaggeration of the mutation accumulation model due to trading investment away from maintenance and towards reproductive investment
What is a hypothetical example antagonistic pleiotropy?
E.g. heavy investment in offspring provisioning –
Reduces opportunity for building up hibernation fat reserves???
Increases demand to invest in extra foraging, increasing predation vulnerability???
Reduces investment available to prevent against intrinsic ageing
What is an example of an experiment that delayed death from reproduction in Drosophila?
‘YOUNG’ and ‘OLD’ selected lines created from eggs laid on day 7 and day 25
Artificially diverge extrinsic mortality to diverge intrinsic mortality
Then controlled for reproductive effort using pupal irradiation (which stops oogenesis)
What were the results from an experiment that delayed death from reproduction in Drosophila?
‘Young’ selected lines had higher adult intrinsic mortality than ‘old’ selected lines
But when reproduction stopped (A), the intrinsic mortality difference between ‘old’ and ‘young’ lines disappeared
What is disposable soma?
Somatic (non-gametic) maintenance is shut-off, and resources diverted to reproduction to maximise fitness
More specific and extreme form of antagonistic pleiotropy
Most applicable in semelparous taxa
What is an example of disposable soma?
Pacific salmon
What happens during disposable soma with Pacific salmon?
All individuals die after reproduction
Not the case in other anadromous salmonids
= TERMINAL INVESTMENT
Extreme increase in circulating levels of cortisol coincident with major primary investment in reproduction
Degeneration (NOT of gonads) and death through multiple organ failure
What is the benefit of disposable soma in Pacific salmon?
Lay eggs in nutrient low environments
Death releases nutrients to water and attracts macroinvertebrates which their offspring will prey on
