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6 - Sociobiology - Altruism - Coggle Diagram
6 - Sociobiology - Altruism
Origins
evolutionary biology, ethology and ecology
driven by natural selection theory
Dawkins - the selfish gene (1976)
hypothesis testing in field experiments
Wilson - Sociobiology: the new synthesis (1975)
concerned with contribution of social behaviour to fitness
mid 1970's
Advantages of sociality (Alcock, 2009)
foraging and cooperative hunting (info and prey size)
Manipulation of environment (burrows, hives(
Protection against predators (group defence)
division of labour (specialisation)
mating and care of young (contact and kin availability)
cultural transmission (vicarious learning)
Altruism
major challenge to sociobiology
evolutionary theory doesn't support altruism in animals as personal risk implies reduced fitness
altruism is common in the animal kingdom so what's the explanation?
definition = putting oneself at risk to help another
Wynne-Edwards
Animal dispersion and its relation to social behaviour (evidence)
social subordinates (lower rank) do not reproduce
breeding delayed beyond reasonable age
can produce more offspring than they do
long intervals between breeding
animals avoid exploitation of their habitats by regulating birth rates
parents sometimes consume their offspring
Explanation: group selection theory
local overpopulation is avoided by altruistic restraint on reproduction to benefit the whole group
info on population density provided by epideictic displays
communal displays
roosting aggregations
Epideictic displays = animals advertise their presence to allow others to assess population density
Group vocalisation
info on population density used to regulate reproductive effort (via hormones) - Problems
self - sacrifice is not an evolutionary stable strategy (always open to selfish variants)
epideictic displays can be explained more easily
how does a gene that reduces the amount of offspring survive in a gene pool?
lots of contradictory empirical findings
optimum effort
Perrins (1964) found English Swift birds normally lay 2 eggs but some do lay more. the ones who lay more see less of their eggs surviving.
field observations show that reproduction is done to ensure for the maximum surviving offspring
explanations of altruism
Parental manipulation theory (Alexander 1974)
Multi-level selection (Nowak 2010)
selection can operate at levels ranging from the gene to the population (depending on many factors)
new theory
Reciprocity theory (Trivers 1971)
social contract between the altruist and the recipient
you scratch my back, ill scratch yours
only works in a species that recognises animals as individuals
Kin selection theory (Hamilton 1964)
animals behave altruistically towards relatives
care for offspring is only important if they share genes
major explanatory effect since published in 1960s
Group selection theory (already talked about)
Theory - simple formula
K = ratio of recipient benefit (b) to altruistic cost (c)
r = coefficient of relatedness
altruistic behaviour will be selected if K > 1/r*
close relatives = 1/r small and K doesn't need to be large
distant relatives = 1/r large and K must be very large
altruism more probable between close relatives
Hamiltons rule = K > 1/r; r >c/b; rb > c
Evidence
1 - Alarm calling (Beldings ground squirrels - Paul Sherman)
kin selection theory predicts that alarm calling will be more common in females due to high levels of genetic relatedness
kin recognition is based on phenotype matching which isn't apparent until 30 days of age
Males - leave to join other groups
females - stay in natal groups and do most of the alarm calling. High level of genetic relatedness
2 - Helping behaviour
most common in birds but also in diverse species (foxes, meercats)
young birds stay with parents to help rear future offspring
to evolve, benefits must outweigh costs
evolution of helping
for selection to favour helping (H x rH > S x rS)
H = number of helped siblings brought to maturity beyond parents capacity
S = number of offspring raised without help
rH = coefficient of relatedness between helper and helped
rS = coeffiecient of relatedness between parent and offspring
because rH = rS equation simplifies to H > S
Tests
1 - Florida scrub jay
H = 1.3 - 0.5 = 0.8
H is greater than S meaning helping behaviour is common
parents with help = 1.3 young/nest
parents no help (S) = 0.5 young/nest
2 - Superb blue wren
H = 2.83 -1.5 = 1.33
H is less than S helping should not occur
Parents with help = 2.83 young/nest
females don't help but some males do
Parents no help (S) = 1.5 young/nest
males only have 70% mating chance due to unequal sex ratio so we need to devalue S strategy for males by 70% (1.05 from 1.50). Use this value in calculation (H = 2.83 - 1.05 = 1.78) which is greater than 1.5 favouring males helping behaviour
Helping in birds studies
Reyer
kingfishers - primary helpers = older siblings provide food for parents
secondary helpers = unrelated older male birds who provide much less food to the young but gain parental experience and meet young females to mate with
Brown and Mumme
removed helpers from nest caused more than 50% reduction in surviving offspring
Komdeur
Seychelles warbler bird
removing birds from nest created nesting and breeding success fell
young birds living with step parents gave less assistance to half siblings and none to unrelated birds
helping experience has major influence on future parental success of helpers
birds that inherit territory do better than those who locate own territory
they will breed if possible, help if not possible
Alarm calling
altruistic as it warns others while drawing attention to caller
done to warn genetic relatives
detect danger, animal use alarm call
beldings ground squirrel
Inclusive fitness (Hamilton, 1964)
involves direct fitness (yourself) and indirect fitness (your relatives)
evolution is concerned with genes, not fate of individuals
inclusive fitness = net gene representation in succeeding generations including all relatives
most significant development of Darwins NS theory
Eusocial insects
example of phenotypic altruism
Darwin recognised that their existence posed a threat to theory of NS
sterile females dont reproduce and instead work for the reproductive success of their mother = the queen
bees, ants, termites
Trivers and Hare 1976
their fitness is better served by helping to rear more sisters than starting own family
workers provide 3x more food for sisters than brothers
average relatedness of workers = 75%
explains kamikaze bees = they die to protect their sisters when they sting
female workers are 100% related on paternal side and 50% on maternal side
Doubts about gene selfishness
because new male has little to gain by raising another males offspring
because while the mother is lactating, she cannot be fertilised
infanticide by intruder males seen in >50 species of mammals and birds and spiders
sex determination
haplodiploidy = peculiar system
males = haploid (develop from unfertilised eggs. Half no chromosomes)
Females = diploid (develop from fertilised eggs. Normal no chromosomes)
in many species, queen mates with one male and all daughters receive identical set of parental chromosomes