What makes for differences between individuals?

Polyphenic „ genes • environment Insects X environment =

POLYPHENISM

„ poly – many (more than one anyway) genetic „ 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

„ insects that are polymorphic have the natural potential to be only one form but more than one form occurs in the population 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 „ seasonally) „ „ in individuals in the same generation „ adult as in social insects, parasitic wasp larvae decision mediated by 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 (Nymphalidae) (Geometridae)

„ linea form in the „ diet induces the right summer form, regardless of light „ rosa form in fall „ how? „ controlled by photoperiod 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

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 „ 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 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 , 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 - „ , 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 workers Worker jelly This difference is followed by higher levels of juvenile 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 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

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