APS 323 Social Insects: Lecture 3

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APS 323 Social Insects Lecture 3
Francis L. W. Ratnieks Laboratory of Apiculture
Social Insects
Department of Animal Plant Sciences University
of Sheffield
Lecture 3 The Individual
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Aims Objectives
Present roles specializations of individuals
with main emphasis on bees, wasps, ants
(Hymenoptera) Females Males Non-adults
(brood) Primary division of labour reproducing
v working queens (reproduction) workers
(work) Stages in the loss of worker reproductive
ability
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Big Picture
The individual is the building block of the
society A colony is a functional adaptive
unit (Although there may also be conflict among
the individuals) Like cells in a body there are
different types of individuals The types and
their roles vary among different taxa Unlike
cells in a multi-cellular organism they are
unfused (Unlike cells in a multi-cellular
organism , relatedness lt 1)
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Big Picture Reproductive Division of Labour
Reproductive division of labour The key defining
feature of eusociality Colonies have
reproductive individuals Female Queen Male
King in termites, sperm in Hymenoptera Often but
not always just one queen per colony Colonies
have non-reproductive individuals Workers But
workers sometimes reproduce queens sometimes
work
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Brood
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A. mellifera Comb With Brood Nectar
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A. mellifera Egg in Base of Cell
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A. mellifera Pupae in Wax-Capped Cells
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Brood
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Vespinae Wasp Brood
The brood of Vespinae and Polistinae wasps are
held in hexagonal cells. The larvae are fed
gradually (Progressive provisioning) and then
pupate. The larva spins a cocoon which seals the
cell. Photos Top row left eggs Bottom row
pupae Others larvae
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Wasp Larvae Help Colony Nutrition
Common Wasp Vespula vulgaris In Vespinae wasps,
the larvae have very large salivary glands. They
feed larvae insect prey. The larvae convert
protein into sugars. Adults consume a nutritious
saliva secreted by the larvae. In Japan, you can
buy a sports drink called VAAM (Vespa Amino Acid
Mixture) based on the saliva of hornets, Vespa.
The Japanese woman who won the marathon in the
Sydney Olympics was drinking it as she ran.
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Hornet Saliva Powers Sydney Marathon Gold
As it says above, the Japanese woman who won the
marathon at the Sydney Olympics was drinking
VAAM Vespa amino acid mixture.
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Oecophylla Weaver Ants Larval Silk
The two species of Oecophylla weaver ant are
found in Africa, Asia, and Australia. They have
massive colonies and nest in trees. The nest is
woven from live tree leaves held together with
larval silk. The larva is used like a living glue
gun by the workers. The workers also form living
chains to pull leaves together before gluing in
position.
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Camponotus senex, New Nest
Camponous senex colony building a new nest. Like
weaver ants they use larva as glue guns. Unlike
weaver ants they do not pull the leaves together
before gluing them. Photos Sao Paulo, Brazil.
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Role of Brood in Eusocial Hymenoptera
Hymenoptera are holometabolous with egg, larva,
pupa and adult stages. Queens and workers are
adults. The larvae are passive, lacking legs and
normally just immobile in a cell (most bees
wasps) or in a brood pile (ants). They are fed by
the workers. In most species they dont do
anything other than grow. In a few taxa they
perform some function for the colony. The use of
larval silk in nest building has evolved three
times in ants. In Vespidae wasps the larvae help
digest protein food, which they can convert into
sugars and feed back to the workers and queen in
their saliva. Larvae can also be cannibalized if
there is a food shortage.
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Termite Nymphs Soldier Worker
These individuals of the primitive termite,
Zootermopsis nevadensis from California,
including the soldier on the left, are nymphs and
can potentially metamorphose into reproductives.
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Role of Brood in Termites, Isoptera
Isoptera are hemimetabolous with egg, nymph and
adult stages. Queens and males are true adults,
usually with wings. The workers and soldiers are
nymphs. In termites, work is based on child
labour. In the higher termites (Termitidae, which
include the species that build huge nests in
Africa and cultivate fungus) the workers are a
terminal caste of sterile nymphs. That is, they
cannot metamorphose into another stage, such as
into a reproductive individual. In most termites
working individuals can metamorphose into
reproductive individuals.
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Males
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Eusocial Hymenopteran Males
The forgotten sex in eusocial Hymenoptera Most
attention is focused on females workers are
always female no king father present only as
sperm queen stores lifetime sperm supply from
nuptial flight Males are haploid arise from
unfertilized eggs eggs laid by workers are
generally male Diploid males can occur they are
a genetic dead end arise due to limitations in
the sex-determination process
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Eusocial Hymenopteran Males
One or two generations of males present in a
colony Parental Generation Sperm stored in the
queens spermatheca Disembodied
father Offspring Generation Males being reared
as reproductives Brood and adults Only part of
the year Can be queens sons and workers sons
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Eusocial Hymenopteran Males
Eusocial hymenopteran male is normally Winged Ma
tes away from the nest Does not work Does not
influence colony reproduction Never co-founds
nest with the queen However, males can show
specialisations that are a consequence of
eusociality.
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Drone Worker Honey Bees
Two drones and workers on a comb. The drone is
designed via sexual selection for male-male
competition, with large eyes and flight muscles,
to out-compete other males when chasing queens on
mating flights. Many males chase each queen
leading to strong scramble competition.
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Honey Bee Swarm
Small swarm of Apis mellifera, c. 5000 bees, in a
bush.
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Honey Bee Swarm, Close Up
Very few drones leave the parent colony with the
swarm
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Mating Common Wasps
Mating common wasps, Vespula vulgaris. Male is
above
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Male Bumble Bee
Male bumble bees and common wasps feed themselves
at flowers. They can be recognized by their long
antennae
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Mating Dinosaur Ants
Above. Mating dinosaur ants, Dinoponera
quadriceps. The male is winged and red in colour.
He is mating to a worker. In this species of ant
the morphological queen caste has been lost and
the colony is headed by a mated worker (sometime
called a gamergate) who is the functional
queen. This is unusual. Below. The male is
unwilling to disengage so the female severs his
genitalia.
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Honey Bee Mating Plug
Queen honey bee caught as she returns to her
hive. The white material in the tip of her
abdomen is the genitalia of the last male she
mated with. In the honey bee Apis mellifera the
male can only mate once. His genitalia cannot be
retracted and break off during mating, where they
function as a mating plug preventing the semen
leaking out of the queen. However, the mating
plug does not prevent other males from mating the
queen as they can easily remove it.
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Male Work
In some stingless bees males may secrete wax and
in bumble bees males may help incubate
brood. Why dont hymenopteran males work? The
reason is almost certainly not to do with
relatedness. Rather it is because in subsocial
Hymenoptera it is only the female who builds the
nest and provisions and looks after the young.
Thus, only the females were preadapted to
helping. Non-domesticated males originated in
subsocial Hymenoptera and carried over to
eusocial Hymenoptera.
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Male Reproductive Interests
Because males are not involved in brood rearing,
they can have little influence on colony
reproduction, for example causing the colony to
rear the ratio of queens and males (sex
allocation) that is optimal for their
interests. However, there are a few cases where
certain male reproductive interests can be
fulfilled. In the honey bee Apis mellifera, very
few males join the swarm. It is better for
everyone if they remain in the parental nest
where food is abundant. In Cardiocondyla ants
there are worker-like males without wings and
with large mandibles. In this species mating can
also occur in the nest. The worker-like males
mate in the nest with young sister queens. They
also fight with each other. They do not kill
winged males, who normally mate outside the nest,
as the winged males smell like females.
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Effects of Eusociality on Males
In some eusocial insects, the number of males
greatly outnumbers the number of females that
need to get mated because new colonies are formed
by colony fission. In the honey bee this is known
as swarming. Female reproduction is a swarm,
which is mostly workers with one queen. In
Dinoponera quadriceps ants colonies divide
without swarming and only one female needs to be
mated. In these species most males never mate.
Those that do put everything into the first
mating with their genitalia acting as a mating
plug. It is better to slightly increase paternity
from a single mating than to hold back and hope
for a second mating. These examples show that
eusociality can have effects on the reproductive
behaviour of males. In addition, males in many
species do not need to forage and can be designed
for a single purposemating. In the honey bee
intense male-male scramble competition has led to
large fast-flying males.
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Females
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Queens Workers Morphologically Distinct
Apis mellifera honey bee
Vespula vulgaris common wasp
Bombus terrestris bumble bee
Dorylus wilverthi driver or army ant
Lasius niger pavement ant
Atta cephalotes leafcutter ant
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Queen Honey Bee Laying Egg
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Honey Bee Female Reproductive Systems
queen
worker
ovaries
spermatheca
An Apis mellifera queen has massive ovaries with
hundreds of ovarioles, and can lay up to 2000
eggs per day. She has a large spherical
sperm-storage organ in which she can keep sperm
alive for years. The workers have smaller
ovaries, a vestigial spermatheca, and cannot
mate.
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Honey Bee Queen Rearing
Apis mellifera queens are reared in special queen
cells on special food known as royal jelly. The
special cell triggers the feeding of royal jelly
by workers, and the royal jelly triggers the
larva to develop as a queen.
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Honey Bee Queen Rearing
Type of Cell
Queen lays
Workers feed larvae with
Duration from egg to adult
Unfertilized egg
Normal brood food
24 days
Drone cell 20 of comb area
Fertilized egg
Normal brood food
21 days
Worker cell 80 of comb area
Fertilized egg
Royal jelly
16 days
Queen cell 10-30 in swarming season
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Honey Bee Queen Rearing
queen
Female larva
Female egg
worker
In the honey bee, and in most eusocial
Hymenoptera with morphologically-distinct queen
and worker castes, any female can develop into
either a queen or a worker. In most species the
developmental programs diverge in the larval
stage.
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Honey Bee Queen Rearing
Royal jelly is rich in mandibular gland
secretions of workers. The quality of food in the
first 3 days determines caste fate. Larvae lt3
days old are totipotent. After this they have
chosen one pathway or the other. Commercial
queen rearing involves transferring one-day-old
larvae from worker cells into queen cells.
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Commercial Queen Rearing
Capped queen cells reared from plastic cells
bases.
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Commercial Queen Rearing
Capped queen cells reared from plastic cells
bases. A one-day old female larva is transferred
into a queen cup and placed into a hive without a
queen. The larvae is fed royal jelly and the cell
is extended. The queens have emerged from the
two cells in the centre.
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Queen Rearing
In almost all species of eusocial Hymenoptera
with morphologically-distinct queen and worker
castes, a female can become either. In a few
ants, such as Pheidole, this is determined in the
egg stage by the contents of the egg provided by
the queen. In most cases caste fate is determined
in the larval stage by the quantity and quality
of food given to the larva. Because queens are
generally larger than workers, this gives the
workers the ability to control the caste of the
larvae, and to avoid too many developing as
queens. In Melipona stingless bees queens and
workers are the same size and reared in the same
cells. This gives the larvae the ability to
choose their own caste fate. This leads to more
larvae developing as queens than is needed by the
colony. The excess are executed soon after
emerging from their cells.
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Queen Not Larger than Worker
Melipona beecheii Queen Worker
Queen and worker are the same size although
different morphologically. Note smaller head and
lack of pollen basket in queen.
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Melipona beecheii Brood Comb
A brood comb in which the cell cappings have been
removed to show queen (circled) and worker pupae
being reared in the same cells.
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Stages in the Loss of Worker Reproductive
Potential
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Stages in Loss Worker Reproductive Potential
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Stage 1. Paper wasps, Polistes
Female castes (queen, worker) not morphologically
distinct. Ancestral situation. Found in some bees
and wasps.
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Stage 2. Dinoponera ants
Female castes (queen, worker) not morphologically
distinct, all can pot-entially be queen, but
individual females cannot found nest on their own.
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Stage 3. Many Species
Vespula vulgaris common wasp
Bombus terrestris bumble bee
Lasius niger pavement ant
Female castes (queen, worker) morphologically
distinct. Workers retain ovaries but cannot mate
so can only lay male eggs. This is by far the
most common stage and also includes bumble bees,
most stingless bees, Vespinae wasps, and most
ants.
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Stage 4. Atta Leafcutter Ants
queen
workers
Female castes (queen, worker) morphologically
distinct. Workers have vestigial or
non-functional ovaries and so cannot lay eggs.
Found in a few genera of ants including Atta
leafcutter ants and Pharaohs ant Monomorium
pharaonis and stingless bees. Also in higher
termites.
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Some Other Points
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Apis mellifera Worker-Laid Eggs
Workers lay many eggs in queenless colonies. In
the honey bee less than 0.1 of the workers in a
colony with a queen have active ovaries, versus
up to 50 in queenless colonies.
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Specialized Queens
Eciton army ant queen. Army ants have queens
specialized for walking and great fecundity. They
are wingless as a new colony is founded not by a
dispersing queen but by colony fission. Aftican
army ant queens, Dorylus, can lay as many as
20,000 eggs per day.
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Queens Fighting
Honey bee queens are famous for fighting, trying
to kill each other with their sting. During
swarming several new queens are reared but only
one can inherit the colony. A queen cannot found
a nest on her own. As a result they fight.
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Worker Morphological Castes
In some species of ants and termites, the workers
can vary greatly in size. We will discuss this in
the lecture on division of labour