polymorphism in insects

1. Polymorphism and
Polyphenism
Name : Muhammad Basit Ali
Roll NO : 17301510=108

2. Polymorphism
 Polymorphism is appearance of forms or "morphs" differing in colour and number
of attributes within a single species.
 It also includes the phenomenon of mimicry when mimetic morphs fly alongside
non-mimetic morphs in a population of a particular species.

3. Polymorphism in Lepidoptera
 In Lepidoptera, polymorphism can be seen in following
 sexual dimorphism
 geographical polymorphism
 seasonal polymorphism
 mimicry

4. Genetic polymorphism
 Genetic polymorphism occurs when the morphs are a result of genetic
determination only.
 The extreme case of genetic polymorphism is that of the papilionid great Mormon
(Papilio memnon), where four male forms and many as twenty-six female forms are
reported.

5. Sexual dimorphism
 Sexual dimorphism is the occurrence of differences between males and females in
a species. In Lepidoptera, sexual dimorphism is widespread and almost completely
determined by genetic determination
 Sexual dimorphism is present in all families of the Papilionoidoea and more
prominent in the Lycaenidae, Pieridae and certain taxa of the Nymphalidae
 Adult bagworm moths mating

6. Geographical polymorphism
 Geographical polymorphism is where geographical isolation causes a divergence of
a species into different morphs.
 A good example is the Indian white admiral (Limenitis procris)which has five forms
 interbreeding between populations of one species practically does not occur
 they form over 600 different morphs, with the size of spots on the wings of which
varies greatly.

7. Mimicry
 The phenomenon of mimicry when mimetic morphs fly alongside non-mimetic
morphs in a population of a particular species. Polymorphism occurs both at
specific level with heritable variation in the overall morphological design of
individuals as well as in certain specific morphological or physiological traits within
a species.
 Batesian and Müllerian mimicry complexes are commonly found in Lepidoptera.
 The Heliconius butterflies from the tropics of the Western Hemisphere are the
classical model for Müllerian mimicry.

8. Polyphenism
 A polyphenic trait is a trait for which multiple, discrete phenotypes can arise from
a single genotype as a result of differing environmental conditions.
 It is therefore a special case of phenotypic plasticity.
 Biston betularia caterpillars on birch (left) and willow (right), demonstrating a color
polyphenism.

9. Types
 Sex determination
 Insect castes
 Seasonal
 Predator-induced
 Resource
 Density-dependent
 Dauer diapause in nematodes

10. Conti….
 Sex determination
 Sex-determining polyphenisms allow a species to benefit from sexual
reproduction while permitting an unequal gender ratio. This can be beneficial to a
species because a large female-to-male ratio maximizes reproductive capacity
 Predator-induced
 Predator-induced polyphenisms allow the species to develop in a more
reproductively-successful way in a predator's absence, but to otherwise assume a
more defensible morphology.

11. Insect castes
 The caste system of insects enables eusociality, the division of labor between
non-breeding and breeding individuals.
 A series of polyphenisms determines whether larvae develop into queens,
workers, and, in some cases soldiers. In the case of the ant, P. morrisi, an embryo
must develop under certain temperature and photoperiod conditions in order to
become a reproductively-active queen.

12. Seasonal
 Polyphenic pigmentation is adaptive for insect species that undergo multiple
mating seasons each year.
 Birds and mammals are capable of continued physiological changes in
adulthood, and some display reversible seasonal polyphenisms, such as in
the Arctic fox, which becomes all white in winter as snow camouflage.

13. Cont….
 Resource
 Organisms with resource polyphenisms show alternative phenotypes that allow
differential use of food or other resources. One example is the western spadefoot
toad,
 Density-dependen
 Density-dependent polyphenism allows species to show a different phenotype
based on the population density in which it was reared. In Lepidoptera, African
armyworm larvae exhibit one of two appearances: the gregarious or solitary
phase.

14. Dauer diapause in nematodes
 Under conditions of stress such as crowding and high temperature, L2 larvae of
some free living nematodes such as Caenorhabditis elegans can switch
development to the so-called dauer larva state, instead of going the normal
molts into a reproductive adult
 Third stage dauer larva (resting stage) of Phasmarhabditis hermaphrodita

15. THANKS