Developmental flexibility and polyphenism Flashcards
sources of intraspecific diversity
genetic polymorphisms:
differences in genotype giving rise to different phenotype by driving development differently
polyphenism/phenotypic plasticity:
same genotype
because of different conditions during development
certain environmental cues modify their development - cause different body form/phenotype
two morphs in locust (cricket, planthopper…?)
dispersal:
developed wings/ flight muscles
reduced ovaries
reproductive:
-reduced wings - less active
-developed ovaries - large full of eggs
main environmental cue for morph is crowding levels
mechanism for deciding which morph(planthopper)
setting up different levels of hormone
2 hormones
Ecdysone
Juvenile hormone
in different stages of larva
insect - ecdysozoan so molts allowing animal to expand before new cuticle hardens
pulses of ecdysone drives this moulting process (peak just before molt)
JH relatively level throughout most larva stages
nothing changes - goes into another larval
during last larval stage - sensitive period to JH levels
JH drops to none
triggers transition into adult stage next moult
(where JH comes back with different function)
JH levels in future cricket morphs
JH levels change due to crowding
low crowding - High JH (in many pints of instar larva) - future reproductive form (R)
evidence for JH level being causative of R vs F form
took future long winged F forms
injected with JH analog
increase their low levels
converts large proportion (80%) of future F (flight) forms into R forms
with reduced wings - developed ovaries
injected future R forms with JH antagonist
reduced higher levels of JH
FUture R forms converted into F forms (longer wings)
degree of crowding influences level of JH
which affects F or R form
downstream of JH control is insulin activity
manipulating insulin also can determine R or F form
resident vs migrant butterflies phenotypes
monarch populations in north USA and south CA
local pops of monarch - several gens a year (short lived)
larvae feed on milkweed plants (v restrcited all they eat)
resident pops in summer that stay in same location
in autumn - larvae in autumn form adults which are slightly different from summer resident generations
physiology and behaviour difference:
-eats and build up lipid stores
-reproductively inactive
-then migrates to winter roost in mexico, spends 4-5 mo in high altitude cool but constant temp
-spend most of time inactive with dropped metabolic rate
-are in reproductive diapause (sex organs not develped and they are inactive)
warming temps break diapause
eggs develop
mate
warm rests migration direction - back to where they came from
lay eggs on milkweed (dies in winter but comes back in spring) - back in time to reach most southern earliest milkweed
die
new larvae emerge in milkweed’adult form then move gradually more north as more milkweed sprouts
until theyre back to regular north habitat
cool to warm monarch transition
breaks reproductive diapause
reverses migration direction
study this
capture monarch
restrict them with tether in enclosure
residents captured in summer that will never migrate - no direction specific??
then do for migrant forms that hatch in autumn and will migrate
will fly in correct direct (S or SW)
how do migrant forms know direction to migrate?
use sun as cue
internal 24hr clock adjusts for time of day/position of sun
so will fly in different orientation to sun at different time of day to stay in same direction
keeping them in light dark cycles that desync them from normal daytime
will fly in wrong direction
as knowledge of time of day messed with so fly in incorrect orientation to sun
returning migrants after cool to warm transtition do same thing but direction is reversed
resident form doesnt show any of this
environmental cue for resident vs migrant forms
cue - day length experienced as larva
reared in long days - develop into summer residents - reproductive active, dont migrate, shorter lived
reared in short days - develop into migrant form - repro diapause (underdevelop gonads), lipid storing, migration
decreasing day length day by day makes it more likely migration form
also - cold nights, old food plants
hormone level differences in migrant vs resident
high JH in summer res
low JH in autumn migrants
JH inhection into captured migrant form
-shortened its lifespan
-Triggered ovary development
JH inhibition into residents reared in long days - -resident form - legnthened lifespan
-ovaries stayed immature
shows correlation between JH levels in adult and characteristics of migrant and resident forms by manipulating JH levels
(though didnt check if displayed appropriate migration)
day length and monarch butterfly larva JH levels
shorter day length experienced by larva
changes (lowers) JH levels in pupa (probably) affecting development
then in adult JH producing gland in brain too - affects lifespan - migration –lipid storage
dung beetle polyphenism
large males - have horns
small males - no horns/ rudimentary horns
these particular polyphenisms can be tied to JH levels (injecting/inhibiting in larva to investigate)
(many insect polyphenisms come from JH levels
polyphenism down to feeding
amount of dung ingested (as larva?)
body size in some way determines juvenile hormone levels
JH levels then determine horns/no horns in pupa
can take small larva just before sheds late larval coat to become pupa
add JH analog
get small with horns
experiment prone to artifacts:
analog injection in one big spike
-uses analog - not 100% the same to begin
-changing level of one hormone can change others - could be indirect
blowfly development?
dipteran - so holometabolous
larve, larva, larva, progress through different pupal stage instead of straight to adult, adult
absence of JH in last stage larva
triggers small ecdysone release
causes mature larva to then leave food and burrow into soil becoming pre-pupa
transforms when next big peak of ecdysone arrives - accompanied by JH reappearance
triggers transfer into pupal stage
Blowfly development polyphenism
diapause in pre pupa
can stand colder temperature much better than non-d
change in physiology enables diapause stage to overwinter
warming comditions triggers diapause break and resumption of rest of development
Blowfly diapause polyphenism cue?
temperate latitude
so day length differs through year
short days in critical stage - MOTHER that will eventually lay eggs triggers onset of diapause in offsprings late larva pre pupa stage
not understood how short days affect mother’s oocytes to impact her offspring
HOWEVER very clear
blowfly diapause adaptations?
abilty to switch between diapause and continuous development
expect that this mechanism can evolve/adapt
day length threshold needs to be correct
ones that do it wrong will be selected against
threshold for day length in mother for late larva diapause has diverged in different populations
below 14.5hrs in UK pop
below 16hrs in finnish pop
-appropriate day length for winter conditions - finland - later day length as need to diapause earlier in year as harsher conditions start earlier
seasonal polyphenism in Pontia (western white bttrfly)
found in temperate NW US with harsh winters
2 seasonal morphs
-larvae developing in spring/early summer (L days) - develop straight into adults which have pale wings (summer morph)
-larvae developing later on in year (S day length) - form pupa in sheltered environemnt - overwinter like this – warms up in spring - complete development - complete development and emerge as SPRING MORPH - melanated wings
mechanism for morph switch or cue that cause it both unknown
Pontia morph reasons?
wing melanation important in THERMOREGULATION
in cool but sunny condiitons - spring morphs bask under sun allowing them to be more motile in cooler conditions
summer morph cannot do this in same condiitons (pale wings)
give spring morph advantage in cooler spring conditions
however in high temps spring morph will overheat
giving pale summer morph advantage then
aspect of selection (survival aspect) reversed
summer morph advantage test (Pontia)
take summer morphs
mark them with yellow sharpie (control)
then others with black sharpie to darken them
darkened males less survival in winter (though no difference in females possubly die to behavioural differences that make males more sensitive)
seasonal polyphenism in wing colour - Bicyclus butterflies
in tropical forest edge environment
wet and dry seasons
forest lush vs dry conditions
butterflies in DRY season are DRAB
long lived
inactive
are in reproductive diapause - nof full developed gonads - hang around and wait for rains
resembles background
rain comes
eggs layed
larvae feed
form wet season adult
ventral wing surfaces (shown in flight and perching) bright colour with eyespot patterns
very active
flying
breeding
laying eggs
does not resemble bg
cues for bicyclus polyphenism change
not day length (tropical)
temperature
dry cooler
wet hotter
wandering larva stage critical sensitive stage
stage where it moves around and hangs up to pupate
figured out by keeping different stages cool (17C) then spiking temp by 10C in different stages and cooling back down before next
burst of high temp had effect on wings when in W larva
shifted it from the dry season form (cold larva) to wet season form (hot larva)
(works other way around - 27C larvae, drop 10C - shift from cool to dry)
developmental hormones in bicyclus morphs
difference in ecdysone levels in each morph
ecdysone peaks at wandering stage in both
peaks much higher in wet season larva when they experience wet season hot conditions
future eyespot regions produce lots of ecdysone receptor - v sensitive to ecdysone in wandering stage
so higher ecdysone in W larva of future wet season morph = more brightly patterned wings
(proven with hormone level manips in cold and hot larvae)
bicyclus eyespot response to ecdysone
higher ecdysone in W stage
=more cell division in focus of eyespot
focus ends up bigger
focus signals to nearby cells to create eyespot pattern with morphogen gradient
different morphogen conc experienced = different TF expressed
=different pigment
higher ecdysone = bigger focus = bigger signalling radius = bigger eyespot
smaller ficus other way
ecdysone wing patterning polyphenism response in species close to bicyclus
2 other related species to bicyclus
DO NOT show eye spot polyphenism between warm and cool
difference in background colour of wing but EYESPOT does not change
however looking at ecdysone levels in W stage in different environmental conditions - same pattern as bicyclus - higher in wet season form
HOWEVER their focuses dont respond to it so no change in eyespots
same ecdysone mechanism - just isn’t plugged into eyespot size
another related species - other way round eyespot size to bicyclus - dry season cold one has larger eyespots
ecdysone levels same where higher in wet morph but eyespots dont respond the same
function of bicyclus seasonal polyphenism
catch release of different morphs in dry season
much longer survival time for dry morph
advantage in dry season
painting eyespots on dry season morphs also reduced survival in dry season
shows camouflage is main reason over behavioural differences
same thing done in wet season
no significant survival difference found
so did experiments where introduced different morphs with range of predators
still no significant difference with vertebrate predators
however
when done with invertebrate predator (mantids)
adult mantids predominant in wet season (diapause in dry)
-mantid attacks to wards wet morphs - happened much quicker but were oriented towards ends of wings where eyespots are
higher first attack survival and overall survival
-matid attacks towards dry morphs - happened slower - but were mainly towards the main body - much lower first attack and overall survival rate
-dry morph with wet edges put on its wings also reaped the benefits against matid
so butterfly polyphenism can swithc throughout year to help it survive conditions in that time of year
