Developmental adaptations Flashcards
How do insects avoid unfavourable conditions?
- where environments exhibit seasonal fluctuations, insect can either move to more favourable site or enter a dormant state during adverse periods
- insects that migrate often have dormant period upon arrival
- insect normally enter dormancy or begin migratory flights before unfavourable conditions - anticipate these conditions
diapause and quiescence - importance of photoperiod? how insects detect photoperiod?
- photoperiod significant as predicts future seasonal conditions
- insects detect photoperiod with accuracy through brain or photoreceptors (in eyes)
- hormones such as JH and ecdysone also have a role
Migration
- diapause allows break in development but migration provides an alternative by tracking resources in space
- aim = provide continuous suitable environment despite temporal fluctuations
- pre-migratory behaviours incl redirecting metabolism to energy storage, cessation of reproduction and in some cases production of wings
- principle cue = change in day length - linked to reproductive diapause
Mass insect ‘bioflows’
- recorded high-flying (>150 m) insects in southern UK
- ~3.5 trillion insects migrate above region annually
- insects >10 mg exploit seasonally beneficial tailwinds
- mechanisms for distribution of nutrients and energy
- may be most important movement in terrestrial ecology
diapause and quiescence - periods of dormancy
- periods of dormancy occur particularly in temperate areas when environmental conditions become unsuitable
- tropical climates, cues such as temp, moisture + changes in food quality dictate induction of diapause
- Dormancy may occur in summer = aestivation or winter = hibernation, and may involve diapause or quiescence
Quiescence
halted / slowed development as direct response to unfavourable conditions; development continuing with favourable conditions
Diapause
arrested development + adaptive physiological changes with development continuing w/ physiological stimuli rather than always w/ suitable conditions - linked to voltinism
Voltinism
- number of generations per year
- most take less than a year to develop:
- 1 generation/year - univoltine
- 2 generations/year - bivoltine
- more than 2 = multi/polyvoltine
- rarely some take > 1 year = semivoltine - associated with colder temperatures/nutritionally poor conditions - e.g. period cicadas, broad-bodied chaser dragonfly
Obligatory diapause
- insects that complete only one generation / yr frequently enter diapause at fixed developmental stage regardless of prevailing environmental cues
- diapause = genetically programmed = obligatory diapause
- requires no mechanism to measure daylength for start of diapause, but environmental cues important for timing of end and onset of development
- found in univoltine insects that elongate short life cycle to one full year
Facultative diapause
- optional diapause is faculative, e.g. to survive unfavourable conditions such as food shortage
- facultative diapause found in most insects and associated w/ bivoltine (2 generations per year) or multivoltine insects (more than two generations/year)
- diapause can last days to months, or rarely, years
diapause + quiescence - when does it occur? what can induce or terminate diapause?
- diapause - any life stage, egg and pupal diapause = most common
- reproductive diapause occur metabolism directed towards surviving environmental stress, e.g. migration, production of cryoproducts
- photoperiod, temp, food quality, moisture, pH + chemicals (urea, O2 + plant 2° compounds) can induce/terminate diapause
effects of climate change on diapause
- altering timing of diapause onset + termination critical for enabling insects to respond to climate change
- entering diapause or ending overwintering diapause too early or too late will be costly
- in warming environment photoperiod remains unchanged but temperatures elevated
- results in longer growing season + asynchrony between insect + host plants
Effects of environmental extremes on development
- temp + humidity = main extreme environmental factors influencing insects
- beh avoidance of extremes may be used, e.g. burrowing into soil, migration, diapause, in situ tolerance / survival w/ altered physiological condition
Environmental extremes - cold
many insects survive cold conditions - high elevations, snowfields
low temp produce physiological problems like desiccation - need to avoid freezing body fluids
possess range of cryoprotection allowing survival in cold extremes
Red flat bark beetle (Cucujus clavipes puniceus) larva = most cold-tolerant species recorded - survives -80°C
Methods of cryoprotection
- polyols + sugars - such as glycerol, trehalose + glucose, are cryoprotectants that decrease the insect’s supercooling point
- heat-shock proteins - bind to other proteins to protect them
- anti-freeze proteins - decrease insect’s supercooling point
- ice-nucleating agents - act as sites for controlled freezing - dehydrates cell contents to avoid freezing
- thermal hysteresis proteins - allow insect to build up antifreezes, + gain protection from freezing, w/o disruptive increases in osmotic pressure which accompany the accumulation of polyols or sugars
