10, 11 Flashcards
what characterises eusocial insects?
division of labour, passing a no return point
what defines the level of social complexity in eusocial insects?
degree of caste differentiation
complex species - morphological castes
simple - behavioural castes.
in simple societies, what drives caste variation?
behavioural castes determined through interactions and dominance hierarchies, so vary with age.
all females remain totipotent, and caste can change over lifetime. temporal caste.
what drives morphological caste determination and in which societies?
individual size
eg Doley ants, size dictated duties of workers, 4 kinds of non rep worker of different sizes
castes at other biological levels
- cell specialisation in a multicellular body
- stem cell differentiation
- tissue specialisation in an embryo
common features of castes at any biological level
Specialised roles Mutually dependent Close proximity Committed roles Interacting Cooperating
phenotypic commitment is on a spectrum. describe it
SIMPLE SOCIETY
1. beh caste determination, high caste plasticity. all physiology the same.
2. morphological caste development. medium caste plasticity. workers functional ovaries, can mate
3. low caste placticity, workers functional ovaries but cant mate.
4. no caste plasticity, workers have vestigial ovaries, cant mate.
COMPLEX
examples of bee, wasp and ant species in 4 categories along the spectrum of phenotypic commitment
- SIMPLE:
wasp: stenogastrines, polistes
Bees: Halictidae, allodapini
Ants: some ponerines - Wasp: some Epiponines
Bees: some Allodapines
Ants: some Ponerines - Wasp: Vespine
Bee: most Apidae
Ants: most - Bees: some meliponinae
Ants: Some Ponerines.
life cycle of simple societies
- Foundress stage: nest building, rep, provisioning
- Pre-worker emergence:
Single egg laying queen establishes - Post worker emergence:
Young adults (callows) emerge, no provisioning or rep. - Callows become workers (provisioning). can either then start own colony, or stay and work at nest. - PLASTICITY
life cycle of complex societies
- foundress stage - nest building, rep, provisioning.
- Pre worker emergence:
single egg laying queen established. - Post worker emergence:
Young adults (callows) emerge, no provisioning or rep. - Callows become workers (provisioning). can either then start own colony, or
what are benefits of totipotency?
exp demonstrating this
plasticity allows workers castes exploit
direct fitness
opportunities and up-regulate their reproductive tract.
exp removed queen of polistes canadensis and workers were given opportunity to overtake nest. found larger eggs in workers rep tract from these colonies, huge upregulation after 5 days.
why do workers stay and help as workers even though they are totipotent?
- there are fitness payoffs to helping. if lone female dies, then zero fitness, esp as offspring have long dependency 40-60 days. however, if a helper dies, her fitness is preserved.
- exp removed helpers, and found part raised brood were brought to maturity by nest mates.
even though totipotency remains, why is there still conflict over castes in simple societies?
all females are potential replacement queens.
inheriting an established nest is v valuable, and gives potential for high conflict when queen dies.
when there is a cheat in the nest, fitness payoffs differ. if workers prefer siblings than own offspring, fight to keep queen, whereas if own offspring are preferred, then fight to BE queen.
2 mechanisms for avoiding conflict
hierarchy of hopeful reproductives in a ‘queue’
workers police adjacent ranks.
what determines task specialisation in complex societies?
age worker size nutritional environment genotype epigentics
if caste was determined by the individual, how?
- need low queen worker dimorphism
- developing females have control over own nutrition eg some bumblebees larvae feed communally in a pollen mass. Stingless bees, larvae can punch through to adjacent cell and steal food.
- simultaneous rearing of queens and workers.
Caste determination in honey bees
larvae cannot determine their own fate.
only 0.01% of brood become queens.
due to social coercion by workers, not voluntary altruism.
avoids costly overproduction of queens. if too many queens, royal larvae are removed and eaten by workers.
Caste determination in stingless bees
5-20% of brood become queens
Brood cells are the same size for all castes - self determination
Excess queens are murdered by sisters ripping them apart.
how do external factors affect the genome controlling caste fate?
external factors: Enviro, Maternal effects, Genetics, Age.
influence regulatory mechanisms, causing differential gene expression and protein synthesis, causing caste determination.
same goes for controlling tissue fate at a different biological level
how do identical genomes produce the extreme beh diversity seen in castes?
all membera of the colony have the same genome (same DNA in each cell), but extreme beh diversity. identical genomes produce this diversity by:
- queens express specific genes.
- Workers express specific genes
AKA SOCIOGENOMICS
what methods are used in sociogenomics?
RNA sequencing eg of wasp brain tissues
gives a snapshot of gene expression at that exact time.
known as ‘next generation sequencing’
gene expression data can be used for quantitative measure of differences in the level of gene expression btw individuals
how is morphological caste determined by nutritional environment
Determined during larval development.
larvae fed different diets. Queens given royal jelly.
nutrition leads to differences in gene expression btw queens and workers.
Nurse and forager bees differ in gene expression, predicting beh based on expresison patterns
how can genotype influence caste?
eg Leaf cutter ants
1 queen mates with 15 males.
Father genotype influences Caste, type of worker. this is a predisposition, not determination.
how can epigentics influence caste?
Honeybee caste determination ‘switch point’ in larval development. could be induced by royal jelly, via DNA methylation.
~550 genes differentially methylated between castes.
experimentally knocked out DNMT3 - made queens from worker destined larvae.
having aswitch point earlier in dev would increase complexity, and having multiple switch points.
why are all workers female?
how does that impact sociality?
females forgo rep to raise siblings. as more related to sisters than own offspring.
only if there is a female biased SR, does relatedness asymmetry favour altruism, as average relatedness to both male and female siblings is 0.25, same as to offspring.
therefore workers can bias brood to have more females - adjust investment in response to changing payoffs.
what causes incentives for workers to bias sex ratio?
variation in social structure generates fitness incentives
experiment
Mueller 1991
Halictine bee
Brood 1 - Eusocial colonies, Mum and Daughter workers.
Brood 2 - Parasocial colonies, mum dies and daughter becomes queen. new queen mating changes relatedness of siblings.
sex ratio differs, in brood 1, female bias.
brood 2, equal SR, as a focal female is equally related to M and F offspring of new queen.
how does polygyny differ form monogamous haplodiploid systems?
multiple queens
reduces relatedness structure between workers and sexuals. Queens are usually sisters/half sisters.
creates a more equal SR.
focal females prefer own offspring to raising cousins.
Hammond et al - monogynous colony brood is more female biased, 68% than polygynous, 36%. workers can assess queen number and manipulate brood.
how does a polyandrous haplodiploid system affect sex ratio?
polyandrous societies are large and very complex.
queen mates multiply.
reduces sister-sister relatedness.
a focal female is raising half sisters, r=0.25, same as brothers.
so equal SR preferred, and own offspring favourable.
benefits of multiple mating
- caste diversity, predisposition.
2. parasite resistance
how does multiple mating increase diversity?
eg leaf cutter ants, highly polyandrous
15 male mates
genotyped and assigned brood to patrilines, found patrilines were predisposed to produce large or small workers, so increasing patrilines will increase the size variation.
how does multiple mating increase parasite resistance?
Hypothesis: genetic diversity among
offspring may offer protection from
parasitism.
exp variation in polyandry affects parasite loads in bumble bees. artificially inseminated queens with sperm of either high or low genetic diversity. then exposed to parasites under field conditions.high diversity protected them against certain parasite strains
costs of male production in single mating
conflict over male production
workers often have ovaries but cant mate, meaning they can still produce males.
conflict arises when r(workers with other worker male offspring) > r( queen male offspring).
costs of male production in polyandrous colony.
conflict between workers. each prefer their own sons.
worker relatedness to queens sons stays constant but worker relatedness to worker sons changes.
what is worker relatedness to:sons, other workers sons and queens sons, in singly and multiply mated queen colonies?
multiple - 0.5 to own sons, 0.125 to worker sons, 0,25 to queens sons.
Single - 0.5 to own son, 0.375 to worker sons, 0.25 to queens sons.
what has conflict between workers over reproduction caused to evolve?
Worker policing.
(Social coercion).
some workers lay male eggs, and are harrassed by other workers.
workers can discriminate between male eggs of other workers and queen laid eggs. Worker laid eggs are EATEN!
effective, as 1/1000 adult males in a queen right colony are worker produced.
queens chemically label their own eggs, stable system of signalling since both parties benefit.
is worker policing common?
widespread, in 4 species of wasps, and ants and 3 species of bees.
