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
