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The evolution of caste polymorphism in social insects: genetic release followed by diversifying evolution

Gadagkar, Raghavendra (1997) The evolution of caste polymorphism in social insects: genetic release followed by diversifying evolution. In: Journal of Genetics, 76 (3). pp. 167-179.


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Caste polymorphism, defined as the presence within a colony of two or more morphologically differentiated individuals of the same sex,is an important character of highly eusocial insects both in the Hymenoptera (ants, bees and wasps) and in the Isoptera (termites),the only two groups in the animal kingdom where highly eusocials pecieso ccur. Frequently,caste polymorphism extends beyond mere variations in size (although the extent of variations in size can be in the extreme) and is accompanied by allometric variations in certain body parts. How such polymorphism has evolved and why, in its extreme form, it is essentially restricted to the social insects are questions of obvious interest but without satisfactory answers at the present time. I present a hypothesis entitled 'genetic release followed by diversifying evolution',that provides potential answers to these questions.I argue that genetic release followed by diversifying evolution is made possible under a number of circumstances. One of them I propose is when some individuals in a species begin to rely on the indirect component of inclusive fitness while others continue to rely largely on the direct component,as workers and queens in social insects are expected to do. Thus when queensb egint o rely on workers for most of the foraging, nest building and brood care,and workers begin to rely increasingly on queens to lay eggs-when queen traits and worker traits do not have to be expressedin the same individual-1 postulate the relaxation of stabilizing selection and new spurts of directional selection on both queen-trait genes and worker-trait genes (in contrasting directions) leading to caste polymorphism.

Item Type: Journal Article
Publication: Journal of Genetics
Publisher: Indian Academy of Sciences
Additional Information: Copyright of this article belongs to Indian Academy of Sciences.
Keywords: Sociale volution;Genetic release;Diversifying evolution; Eusociality;Social insects;Caste polymorphism
Department/Centre: Division of Biological Sciences > Centre for Ecological Sciences
Date Deposited: 28 Nov 2006
Last Modified: 19 Sep 2010 04:32
URI: http://eprints.iisc.ac.in/id/eprint/8740

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