Variations within populations can be either genetic or non-genetic. Non-genetic variations include individual variations over time (age or seasonal variations), social variations, and ecological variations caused by different habitats or environmental conditions. Genetic variations are inherited and include sexual dimorphism where males and females differ, gynandromorphs which have both male and female characteristics in different parts of the body, and intersexes that have mosaic sex characteristics. Understanding these natural variations is important for taxonomists to accurately identify and classify species.

1. Population Variations
DR. MUHAMMAD RASOOL

2. Variations
 Variations within a population is known as intrapopulational variations.
Different individuals belonging the same species may be very different
like some species contains various phena. Often a phenon of one species
resemble a corresponding phenon of another species much more closely
that it does with any other phenon of the same species. This is called
intrapopulational variations or individual variations. For example, the
females of some species birds and insects more closely resemble the
females of other species than the males of its own species. These
individual varaints is a source of confusion for most of taxonomists. Thus
a thorough knowledge of individual variations is essential for taxonomist.

3. Types of Variations
1. Non Genetic
2. Genetic

4. Non Genetic Variations
Those variations in an individual that belong to same interbreeding
population and are non-inherited are called non genetic variations or
extrinsic variations. In preserved museum specimen it is impossible to
determine whether a given variant has a genetic basis or not. Nevertheless, it
is important for the taxonomist to understand that many types of variation
exist and it is usually possible to make valid conclusion about the status of a
given variant on the basis of field observation and available experimental
evidence.

5. Types of Non Genetic Variations
 Individual Variations in Time: individual variations in time may be either age variations or seasonal
variations.
 Age Variations: There are many larval stages in the life of some animals during which they are quietly
different, which cause confusion to taxonomist. In reptiles, birds and mammals there are no larval
stages but still their young ones differ from the adult stages. In fishes the young forms are so different
from the adult that they are often placed in different families. For example, young eel (Anguilla) and
caterpillars are quite different from their adults. The free living larvae of sessile coelenterates, the
larvae of molluscs, echinoderms and insects are quite different from their adults. The cercaria stage
larva of liver fluke does not resemble the adult, similarly in young deer there are less antlers than old
deer, all this cause confusion to taxonomists.
 Seasonal Variations in an individual: The animal appearance varies with the seasons during the year. Many birds
like ducks, shore birds, warblers and tangers have bright nuptial plumage during breeding season
which become dull after the breeding season. Aortic fox have grey colour in summer and white
appearance during winter. Similarly polar bear have grey appearance in summer and white in winter.

6. Types of Non Genetic Variations
 Individual Variations in Time:
 Seasonal Variations in consecutive generations: Many species of short lived invertebrates,
particularly, insects produce several generations in the course of year i.e. the
new forms of spring are quite different from the young ones produced in
summer. Similarly the individuals produced in the wet season differ from those
produced in the dry season. In some tropical butterflies this phenomenon of
dry and wet weather is more prominent.
 Cyclomorphosis: It is a special kind of seasonal variation where the population of a
species undergo regular morphological changes throughout the season due to
different kind of food, changes in temperature etc. This phenomenon is present
in fresh water organisms like Daphnia, Rotifers and Cladocerans.

7. Non Genetic Variations
 Social Variations: In social insects such as bees, wasps and termites
have different forms of individuals in their colonies (Queen, Worker,
Drone and soldier). These different forms are due to different food or
hormonal control.
 Ecological Variations: The different forms of a species produced due to
different environmental conditions. It may be of the following types.
 Habitat Variations (Ecophenotypic): Population of a single species that occur in
different habitats in the same region are often visibly different. In snails
and mussels there are different forms in different habitats and often they
are considered as different species.

8. Non Genetic Variations: Ecological
 Variations induced by temporary Climatic Conditions: Some animals like fish have
highly unusual phenotypic conditions throughout the year due to
unusual conditions like drought, cold and food supply.
 Host-Determined Variations: The same species of a parasite have different forms
in different hosts. As in different hosts, the conditions are different so
the parasite morphology is changed accordingly to adapt to the host
body conditions. Ebeling in 1938 studied variations in the scale insect
“Lecanum corni” grown on different hosts. Those of the apricot were
having large bodies and short appendages as compared to those from
Christmas berry which was having small bodies and long appendages.

9. Non Genetic Variations: Ecological
 Density Dependent Variations: The effect of crowding is some time reflected in
morphological variation. Uvarov (1921) has shown that gregarious
species of locusts exist in three unstable biological phases; solitary,
gregarious and transitional. These phases differ in anatomy, colour and
behaviour causing problems for the taxonomists.
 Allometric Variations: It is the disproportionate growth of a structure in
relation to the rest of the body. This phenomenon is well known in
insects which involves disproportionate growth of head in ants,
mandibles in stag beetle etc.

10. Non Genetic Variations: Ecological
 Neurogenic or Neurohormonal Variations: It refers to colour change in individuals in
response to environment. These changes are accomplished through the
concentration or dispersal of colour bearing bodies called
chromatophores. Such variations were first studied in chameleon. The
same phenomenon of colour change called metachrosis is also found in
crustaceans, cephalopods and cold-blooded vertebrates.

11. Non Genetic Variations
 Traumatic (Injury or Disease) Variations: Traumatic variations occur with varying
frequency in different groups of animals. The abnormal nature of this type of
variation is usually obvious, but in some cases it is subtle and may misleading.
There are three types of this variation.
 Parasitic induced Variations: Apart from the familiar effects of parasitism as
swelling, distortion and mechanical injury, parasites also produce conspicuous
structural and morphological variations in the host due to parasitism. For example,
when stylop (bee parasite) enters the bee, the head size of the bee is reduced
abdomen enlarges and wing venation changes.

12. Non Genetic Variations
 Accidental/Terotological Variations: Accidental variations are usually extremely induced although
it may work internally through some developmental or hormonal system. Such variations are
extremely diverse and in most animals may be readily identified, because such individuals deviate
markedly from the type on those forms which undergo metamorphosis. Injuries to an earlier stage
may produce later abnormalities which are not easily recognized. For example, in beetles certain
types of pupal injury may produce symmetrical abnormalities in punctation, surface sculpturing or
segmentation of the appendages. In butterflies it may result in symmetrical modification of wing
pattern. In most cases even with such clearly notable differences the abnormal nature of the variation
may be detected by a specialist without much difficulty.
 Post-mortem changes: In many groups of animals, it is impossible to prevent post-mortem changes
of preserved specimens. For example, orange yellow bird of paradise fade to white in collections. The
Plumage of the chines jay white in life, but turns to blue in collection due to loss of volatile yellow
component in the pigment. Similarly yellow wasp when exposed to cyanide for preservation it gets
bright red.

13. Genetic Variations
 The variations in an individual that belong to the same interbreeding populations and
which are inherited are called Genetic, inherited or intrinsic variations. There are
three types of genetic variations.
Musca Spp

14. Genetic Variations: Types
 Sexual Dimorphism
 The difference between male and female is known as sexual dimorphism. In this case the
male and female are differentiated from one another. These are sex associated variations
which may be
 Primary Sex difference: The difference between male and female at the time of birth is
called primary sex difference like gonads and genitalia.
 Secondary Sex difference: The difference between male and female which occurs after
puberty is called secondary sex differences. For example, the king parrot, Electus roratus, of
the Paupan region in which the male is green with an orange bill and the female is red with
black bill. Both of these male and female were considered as different species for nearly 100
years which was later on proved by naturalist that they bonged to the same species.
Similarly the males of African ant Dorylus were so unlike than other ant species that they
were not considered as ant for a long time ant was put in different family. Similarly in some
wasps, the females have small wings and males have long and are so different that some
taxonomists used a different nomenclature for the two sexes.

15. Genetic Variations: Types
 Sexual Dimorphism
King Parrot: Male and Female

16. Genetic Variations: Types
 Gynandromorphs
The individuals that show male characters in
one part of the body and female characters in
other part of the body. Thus the two halves of
the body have different sexes. In these
organisms the sex characters are scattered in
mosaic form. They are produced by unequal
somatic distribution of chromosomes,
particularly sex chromosomes. For example,
Gynandromorphs of alfa alfa butterfly, (Papilis
dardanus) has the left wing of female and the
right wing of male.

17. Genetic Variations: Types
 Intersexes: Intersexes are
individuals with mosaic sex.
These are likely to exhibit a
blending of male and female
characters. It is due to either
hormonal imbalance or due
to male and female tendency
genes. Intersexes have been
studied in Lymantria (genus
of moth).

18. Genetic Variations: Types
 Reproductively Different
Generations
 In many insects one generation
alternates the other generation and
each generation differs from one
another, this is very confusing to
taxonomists. For example, in genus
Cynips (gall wasps) the agamic
generation is so different from the
bisexual one that it has given
different scientific names. Similarly
in the aphids (plant lice) the
parthenogenetic wingless females ae
very different from the winged
females of sexual generation.

19. Genetic Variations: Types
Ordinary Genetic Variations
 These variations do not involve sex
characters. It is of two types.

20. Genetic Variations: Types
 Ordinary Genetic Variation
These variations do not involve sex characters and is of Two types
Discontinuous Variations or Poly Morphism and Continuous Variations
Polymorphism:
The same individual with different shapes (appearance) are polymorphic individuals and the
phenomenon is called polymorphism. In many species of Hemiptera and Coleoptera, the same
population contain flying and flightless individuals. The spotting in lady beetles (Coccinellidae) is well
known example of genetic polymorphism, as industrial melanism in moths. Alfalfa butterfly, Colias
eurytheme, have different female forms, on is white and the other resembling the orange-coloured male.
The African Swallowtail butterflies of the genus Papilio have one male form and five female forms.
Alfa alfa Butterfly Melania Snail

21. Genetic Variations: Types
 Ordinary Genetic Variation
Continuous Variations
The commonest type of individual variations is due to slight genetic differences among individuals. No
two individuals (except monozygotic twins) in a population are exactly alike genetically or
morphologically. These differences are very slight and only detected by special techniques. A model
study of variability based on 2877 skins of the house sparrow (Passer domesticus) has been presented by
Selander and Johnston (1967). Among their skin colours each character showed different degree of
variability within a single population. The species of the snail genus Melania (fresh water and brackish
water) have been described largely on the basis of shell characters, so some have spines and spiral ribs
while absent in other members of the genus.
Alfa alfa Butterfly Melania Snail