Polyphenism in Insects

Question 1

Example of a seasonal polyphenism

Answer 1

Squinting bush brown Butterfly (Bicyclus anynana)

• during the wet season butterflies have large eye spots while in the dry season the eye spots are decreased and the are brown in colour.
• Behaviour also changes with the dry season morph being less active
• temperature dependent

Question 2

Example of a diet induced morph

Answer 2

Nemoria arizonaria (moth)

• mimic host of plant (oak)
• 2 generations per year spring and summer
• spring generation feed upon and mimic oak flowers (catkins)
• summer feed upon leaves and mimic twigs
• entirely diet dependent

Question 3

Example of a density dependent phase polyphenism

Answer 3

Locusts

• grasshopper morph solitary and cryptic
• locust morph swarm forming and gregarious
• differences in colour, shape, metabolic and hormonal physiology, brain structure, immune function and reproductive life history
• change induced by contact with other locusts

Question 4

Example of beetle horn polyphenism

Answer 4

Onthagophagus nigriventus (dung beetle)

• horned and non-horned male morphs
• horn size is dependent on a critical size being met in the larval stage
• horn influences mating strategy (horned guarding, non-horn sneak)
• size and quality of the dung ball influences phenotype

Question 5

Example of wing polyphenism

Answer 5

Aphids

• wings polymorphic in males, polyphenic in females
• numerous cues influence phenotypes; population density, host plant quality, temperature, photoperiod, alarm pheromone, interactions with predators, parasites, mutualists, endo-symbionts and pathogens

Question 6

Example of reproductive vs caste worker determination

Answer 6

Honey bees (Apis mellifera)

• royal jelly the determining factor
• low amounts in larval stage leads to worker morph
• high levels of royal jelly lead to queen morph

Question 7

Example and description of sequential polyphenism

Answer 7

Drosophila melanogatser
SP is the differentiation of growth stages in insects
holometabolous insects - larvae, pupae, adult

Question 8

How is polyphenism expressed and where is the definition from?

Answer 8

Expression begins when one or more signals are transduced into physiological or cellular responses that result in a developmental switch. Differential gene expression leads to different characteristics in organisms (Evans and Wheeler 2001)

Question 9

Additional reading - wing polyphenisms

Answer 9

Hardie 1981
Aphis fabae (aphid) - winged forms can be induced by both decreasing day length (autumn form) and crowding (summer form). Increased juvenile hormones responsible for autumn form and neurohormones responsible for summer form

Question 10

Additional Reading - genetic and polyphenic mix

Answer 10

Dingle 1997
Soapberry bug (Jadera haematoloma)
- has 4 distinct morphs, short winged and 3 long winged morphs (differentiated by degrees of muscle histolysis)
- wing length can be either genetically controlled or a response to food availability
- all morphs are a result of different levels of juvenile hormone

Question 11

Additional Reading - crowding and immunisation

Answer 11

Wilson and Reeson 1998

Gregara forms melanisation is linked to immunity increase due to overcrowding and increased likelihood of disease spread

Question 12

Additional Reading - locusts and immunity

Answer 12

Wilson et al., 2002
Schistocera gregaria
- gregarious phase is less susceptible to entomopathogenic fungi than is the solitaria phase

Question 13

Additional Reading - moths and immunity

Answer 13

Reeson et al., 1998
African armyworm (Spodoptera exempta)
- melanistic forms were less susceptible to infections than were the paler morphs

Question 14

Additional Reading - insects that have gregaria phase and why they get darker

Answer 14

Cotter et al., 2004

• Many locust, phasmid and lepidoptera spp. have a crowd induced gregaria phase
• Key enzyme in synthesis of melanin pigment that darkens the cuticle is Phenoloxidase (PO)
• This enzyme has been linked to the resistance of numerous pathogens
• likely increases in response to crowding and as a secondary effect causes melanisation

Question 15

Additional Reading - Bicyclus anynana

Answer 15

Hartfelder and Emlen, 2005

• Temperature dependent dry season (20 degrees) vs wet season (27 degrees)
• Dry season - Low temp -> threshold for endysteroid hormones not met
• wet season opposite results in eye spots
• wet season morphs are more active and hence the eye spots are protective