Pheromones (Definition, discovery, classification, pheromones in animals, functions) .docx

Detailed notes on Pheromones.
Subtopics included in these notes are:
*Definition of Pheromones
*Discovery of Pheromones
*Classification of Pheromones (Releaser pheromones, Primer Pheromones, Imprinting Pheromones)
*Pheromones in Animals:
**Pheromones in Insects (1. In Lepidoptera (Butterflies and moths) 2. In Hymenoptera (Bees and ants))
**Pheromones in Vertebrates (Fishes, Amphibians, Reptiles, Mammals)
*Functions of Pheromones

1. Pheromones
Definition of Pheromones:
Pheromone is a chemical/scent that is produced and released into the
environment by an animal which affects the behaviour of another animal of the
same species.
Pheromones are chemicals released by an organism into its environment
enabling it to communicate with other members of its own species.
The word pheromone, coined by Karlson and Butenend (1959), is derived from two
Greek words: pherein (to transport) and harman (to stimulate). The term was originally
applied to sex attractants of insects, but later it was broadened to include various kinds
of chemicals released into the environment and functioning differently in almost all
animals.
Pheromones are species-specific. They are generally hormones secreted by exocrine
glands. Pheromones (also called ectohormones) are released in minute quantity
bringing about major effect by functioning as chemical messengers and are used as
chemo-signals in intraspecific communication.
Discovery of Pheromones:
In the 18th century the discovery of pheromones took place by chance. A French
biologist, Bonnet, discovered the long trail of ants. Bonnet placed a colony of ants at one
end of a table and a small heap of sugar at the other end.
He observed that the ants coming out of the colony moved across the table to the pile,
picking up sugar and moving back to the colony with it. The ants moved to and fro along
a definite track, with none diverting from it.
Bonnet wanted to know why the ants followed such a definite trail and so he broke the
continuity of this path by rubbing his finger across the line of the ants. The ants stopped
and searched about at the rubbed area. They waved their antennae in the air and tapped
them on the ground. Gradually a crowd of ants accumulated on either side of the rubbed
area.

2. Subsequently, a few adventurous ants ran across the rubbed area. The ants of both the
sides then met, recognized each other and continued with their journey once again.
Bonnet thus inferred that the path of the ants was actually a trail of chemicals which the
ants could sense and follow.
Classification of Pheromones:
Pheromones can be broadly classified into three types:
A. Releaser pheromones:
Releaser pheromones induce immediate and reversible behavioral responses. It is used
mainly in recognition of species members, male and female sex attractant, sexual status,
aggression inducer and inhibitor, ejection of milk, trail and alarm substances etc.
A few example of releaser pheromones are:
1. Releaser pheromones in mammals are present in the urine and footpads. The
pheromones in footpads initiate aggressive behaviour in a mouse on encountering an
unfamiliar male. Urine of male mice, deer, dog, horses etc. contains releaser phero-
mones for attracting females or organizing aggressive activity.
2. The special flask-shaped cells of the skin of a fish produces alarm pheromones
whenever it encounters an intruder. The fish is frightened by the odour of the intruder.
Both marine and fresh-water fishes produce such alarm pheromones.
3. Alarm pheromones in the form of formic acid are produced by ants from the abdomen
to protect themselves from enemies.
4. Honey bees, while stinging an enemy, releases alarm pheromones along with poison.
Immediately after stinging she moves to other fellow members of the colony to show her
sting and flutter her wings to agitate the fellow members.

3. B. Primer Pheromones:
Primer pheromones trigger a change of developmental events (in which they differ from
all the other pheromones, which trigger a change in behavior).
These pheromones act at a physiological level triggering complex and long term
responses in the receiver and generating both developmental and behavioral changes.
Primer pheromones are most often used by social insects for the regulation of colony
activities.
In honey bee, the queen produces Queen mandibular pheromone (QMP)
from her mandibular glands to inhibit the ovarian development of workers and
maintains them as non-reproductive.
The size of the colony and the cast system in case of termites, are regulated by
pheromones, called social pheromones which is produced by a pair of
reproductive termite (king and queen).
C. Imprinting Pheromones:
Imprinting pheromones act at critical period of developmental age. It causes permanent
change in adult behaviour. This type of pheromones has been observed in some rodents
(mice, rat etc.).
Pheromones in Animals:
Pheromones in Insects:
In Lepidoptera (Butterflies and moths)
Female silk moth emits a sex pheromone called bombykol from a pair of sacs on
abdomen. Males of silkworm moth have long antennae and on each antennae
there are more than 1000 sensila. These sensila are like chemoreceptor and are
specialized to receive the smell of bombykol.
In queen butterfly, Danaus gilippus, pheromone is released by the male and
brushed on the female by a pair of brush-like structure called hair pencils. These
are present at the tip of the abdomen.

4. In Hymenoptera (Bees and ants)
Queen honeybee attracts males by a pheromone produced in the mandibular
glands, stimulating drone’s olfactory receptors.
Egg marking pheromone released by the queen bee allows worker bees to
distinguish between queen-laid eggs, which are attractive, and worker-laid
eggs.
When an ant is disturbed, it releases a pheromone that can be detected by
other ants several centimeters away. They are attracted by low concentrations
of the pheromone and begin to move toward the region of increasing
concentration. As they get nearer to their disturbed nest mate, their response
changes to one of alarm.
Certain ants, as they return to the nest with food, lay down a trail pheromone.
This trail attracts and guides other ants to the food.
Pheromones in Vertebrates:
In Fishes:
Fresh water and marine fishes produce alarm pheromones by flask shaped cells present
in the skin, whenever an intruder approaches a school of fish.
In Amphibians:
Alarm pheromones are also produced in the skin cells of a toad tadpole. Whenever the
tadpole in injured, all other tadpoles in the medium moves either to the location or run
away from the site of occurrence.
In Reptiles:
Chemical trails are left behind by female garter snake which the male follows. The
female snake, while moving, pushes against one side of certain objects and leaves
behind scent in her direction of travel. The male snake tests each side of these objects
with its forked tongue and recognizes which side the female has pushed against.
In Mammals:
(a) Markings with urine and faeces:

5. Many mammals communicate through pheromones present in urine and/or faeces.
These are used to scent mark home range or territory, pathways, resting grounds,
feeding grounds and sleeping sites.
Male tigers produce tigeramine through urine for sex attraction.
Male rabbits excite the female rabbit, spraying a stream of urine on her. This
makes the female rabbit receptive to the male for mating.
Adult males of pronghorn and sambar mark their areas during their mating
season with their droppings and urine.
(b) Scent marking by special glands:
Some animals have special types of glands located on different regions of their body that
produce pheromones.
The ring-tailed lemur has scent glands in their forearms and anus. Both the males
and females rub their glands to mark their territory. Males have additional scent
glands under the chin and on the penis which secrete pheromones to attract
females.
A female rat deposits saliva on its nipples by licking them and leaving scent
marks so that its blind pups can reach them.
Bulls of elephants have temporal glands which produce a scent to indicate that
they are ready to mate and are looking for a cow elephant in the breeding season.
Dominant male reindeer have scent glands between their hind toes, which help to
leave scent trails for the remaining members of the herd.
Functions of Pheromones:
1. Sex attractants:
Pheromones are used by various animals to attract the other sex for mating.
2. Communication in social insects:
Pheromones are used for communication purposes in various social insects, e.g. Alarm
pheromones warn the other members of a potential danger. Trail pheromones left by an
ant will mark the pathway to the food source.

6. 3. Marking the territories:
The territory is first acquired by fighting and then the males mark their territories with
scent (by urinating) and ward off the rivals (Example: deer, antelope etc.).
4. Maintenance of social structure:
Pheromones are helpful in maintaining the social structure of a colony. The queen bee
produces pheromones which help in controlling the social structure of her colony.
Similarly, the queens of certain wasps, who live in smaller colonies, produce
pheromones that maintain the stability of the colony.
5. Trapping prey:
Some insects use pheromones to trap the prey. For example, bolas spider tricks the male
moths that are searching for mates. To attract the moths, the bolas spider secretes a
scent that is similar to the scent secreted by the female moth. The male moth comes
near to the scent and is eaten up by the spider.
6. Marking fellow animals:
Male sometimes mark their mates with scent. For example, male rabbit marks his
mates with his chin gland secretions.
A mother sniffs her newborn calf to form a permanent olfactory bond with her
offspring. The calf also sniffs the odour of her mother.
7. Controlling insect pests:
With the help of pheromones insect pest can be controlled in an eco-friendly way. By
using artificially synthesized sex-attractant pheromones, harmful insects like
mosquitoes, flies, cockroaches etc. can be eliminated.