What makes for differences between individuals?
Polyphenic genes • environment Insects genotype X environment = phenotype
POLYPHENISM
poly – many (more than one anyway) genetic polymorphism phen - form vs polyphenism insects that are polyphenic have the natural potential to have more than one form at one or more stages of their lives
Polymorphism the peppered moth
insects that are polymorphic have the natural potential to be only one form but more than one form occurs in the population genotypes for dark or light moth Genetic vs environmental control
light is favored on a light background Genetic control - cannot adjust form in 1 dark is favored on a dark background generation Environmental control - can adjust form to current environment Selection for genetic vs environmental control can shift over evolutionary time Sometimes doesn’t take a large genetic shift (not many genes) to make the difference
Polyphenism in insects Environmental Signals
Typically controlled by genes Larval size responsive to environmental variables Season (food type, day length) that include nutrition and season Food quality, crowding In social insects, a large part of the Other species (competitors, predators) environment is other individuals in Sloppy developmental practices their colonies Food quality Social cues
a spectacular case of Polyphenism in insects can occur polyphenism within individuals within a single individual over its life time (sequential) in successive generations (such as larva seasonally) pupa in individuals in the same generation adult as in social insects, parasitic wasp larvae decision mediated by hormones what kind of individual will I become (size, nutrition, growth…) at the next molt
L, P L L, P L L, P, or A P P, or A A
IMPORTANT CONCEPT: CRITICAL/SENSITIVE PERIOD
polyphenism in oak catkin caterpillar alternate forms for same (Geometridae) life stage spring - leaves are different generations - seasonal young, catkins in polyphenisms bloom same generation - social insects fall - leaves are tough, no catkins
oak catkin caterpillar buckeye butterfly (Nymphalidae) (Geometridae)
linea form in the diet induces the right summer form, regardless of light rosa form in fall how? controlled by photoperiod aphids linea - long day ecdysone the student of titer rosa - aphids should be short day cautioned never to generalize long day minus brain
24 48 72 hours after pupation
aphid forms aphid forms
wings/wingless = alate/apterous parthenogenetic FFF F sexual + F,M M
aphid forms aphid forms
eggs/live bearer soldier forms Aphis fabae Aphis fabae
ANNUAL forms CYCLE controlled by food, daylength, crowding
Short days causes aphids to develop as Short days causes aphids to develop as winged autumn gynopara winged autumn gynopara
long days Short days + extra JH = virginopara short days
JH in second instar short days prevents transition (mimics effect of long days)
JH
JH in 4th instar mother determines whether embryo will become embryonic ovipara or another future egg remember... autumn migrant producer two forms responding to day length are determined by JH controlled by crowding one sensitive period in larval stage JH and another during embryogenesis daylength have no effect
Copidosoma Copidosoma
egg-larval parasitoid lays its egg in egg of Lepidoptera produces two types of larvae FROM THE SAME EGG one is a soldier that doesn’t complete development one is a normal larva that completes wasp development parasitoid of Lepidoptera
defender egg divides without differentiating typical each daughter cell is capable of developing as an embryo polyembryony morula (blackberry) what controls which type of larva develops? Copidisoma’s sometime problem
competition from other parasitoids, like Microplitis = other wasps that lay eggs in either eggs or larvae of host same environment does the presence of larval wasp of other species effect development of same genome Copidosoma defenders? no effect of extra hormones
EXPERIMENT EXPERIMENT
Copidosoma allowed to lay eggs in host egg Yes, a larger percent of larvae become Microplitis allowed to lay defenders when the host is parasitized by eggs in larvae of the second host, especially early different instars But that doesn’t get to the basic question Does this affect the number of either defender or typical larvae per host?
Expression of “reproductive” vs. soldier vas gene
Soldiers don’t reproduce Indicator of germ cells and don’t have By 4 cell stage, restricted reproductive organs to small blastomere Do they lose them? Cells with expression are daughters, gdaughters, etc of blastomere 4 Soldiers Possible soldiers Secondary morulae
Reproductive Soldier larva larva
what controls which type of larva develops?
Not the usual hormones Random? loss of germ cell blastomere results in soldiers % becoming soldiers increased by presence of competitors Macrotermes
Termites termite castes winged imagos (kings all are social and queens) replacement hemimetabolous reproductives - not so larvae serve as workers sclerotized, wingless both sexes involved in social organization of colony termite castes imagos start colony soldiers older larvae serve as workers (pseudergate) winged replacement in some higher termites, imagos larvae, special worker castes soldiers reproductives
king and/or queen die
how are the developmental Social Hymenoptera switches regulated?
strong inhibition by adult termites - ants, some bees, sexuals and soldiers some wasps loss of sexuals or soldiers allows new societies only ones to develop females: queens JH provokes soldier determination - and workers the first discovery of the role of JH honey bees one of in caste determination in social best studied insects!
Many morphological differences between bee queens and worker QUEEN WORKER less sensilla on antenna more sensilla smaller eyes larger eyes small mushroom bodies larger mushroom bodies vestigial food glands large food glands smooth curved sting barbed sting no pollen collectors on pollen collectors on legs legs major difference in ovary, short tongue longer tongue spermatheca development In bees, queens receive a more nutritious diet than Royal jelly workers Worker jelly This difference is followed by higher levels of juvenile hormone in developing queens Days of larval development Q
W
Diet determines caste, effect mimicked by JH The hormonal difference is followed by major differences in gene expression
3.5
How does nutrition get translated into 3 Insulin
hormonal difference? 2.5 2 Insulin 1.5 Nutritionsignaling Juvenile hormone 1 0.5 pathway? % relative expression 0 16h 40h 64h 88h -0.5
• Expression levels shifts to match those appropriate for food type.
1.25 Insulin Summary: ILPs and IR 1 receptor
0.75 Insulin pattern is consistent with response to improved diet quality in 0.5 queen larvae
% relative expression 0.25 Insulin receptor expression shows a maximum difference between castes 0 on day 2 16h 40h 64h 88h So the insulin signaling system is • In queen larvae, insulin receptor expression probably the link between diet and JH is at levels far above those of workers at levels 40h. Why are there horns?
Species of Onthophagus have a variety of horn types for males.
Three species
M
males vary in size large males are horned small males are not F
M
Different sizes, different horn size Why (proximal)? What is the cause of variation in size?
dung quality varies with species supply of dung can vary with time larva gets only the amount of food in the dung ball (no refills) complete development with Onthophagus taurus the resources available compare body size to horn size not many intermediates
larval food determines horn
What signals that the larva has enough food/size to develop horns?
Juvenile hormone Who wins fights?
large males do
are small males losers?
Who runs best in burrows? Horns vs. genitalia
small males do
Evidence for an allocation trade-off between weapons (horns) and testes in the beetle genus Trade off Onthophagus (Coleoptera: Scarabaeidae)
Simmons L W, Emlen D J PNAS 2006;103:16346-16351
©2006 by National Academy of Sciences Other tissue tradeoffs Mating strategies
testes wings antennae mouthparts
males compete (fight) for Without competition, both types females, then guard them of male guard
Small males have an alternative male mating alternative to fighting strategies
larger size males with horns guards burrow that contains dung ball and female ‘sneaking’ male mating alternative reproductive tactics strategies
smaller males are hornless, move better in burrows and dig new burrow to sneak to female
Small males can have same success as large, horned ones by switching to the sneaking strategy when forced into direction competition