Polymorphism and polyphenism

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 T he 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

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