Coevolution of plant-herbivores, Biology

There has been a perfect coevolution between plants and herbivorous animals. This has often developed into a mutually beneficial relationship. Whereas the plants have proved to be a good source of food for animals such as insects, birds and certain mammals, these animals in turn have been of great help to plants for dispersal of pollen and seeds. More specifically plants offer insects both nectar and pollen as food and insects in turn have developed olfactory, visual and structural adaptations for pollination as well as for seed dispersal. To attract pollinators, flowers have attractive colours and smell sweet as well. It is interesting to note that certain flies are attracted towards bad odours emanated by substances such as putrescin and cadaverine. The relationship developed between insect pollinators and entomophilous plants is an excellent example of coevolutionary process. Several instances involving insect pollinators and plants belonging to the families Malvaceae, Papilionacea and Labiatae could be cited. One study related to the gcnus Pedicularis (louse wort) and its pollinators, the bumble bee (Bombus) stands out. Certain species of louse wort such as P. canadensis and P. crenulata are pollinated nototribically, which means that bumble bees pick up the pollen grains from the plant on iheir notum (the dorsal 'sclerite of the insect). The insects get a generous brushing on their dorsal side from the stamens of the flowers as shown and on their visit to a next flower deposit the pollen on the stigma. Certain other species such as P. groenlandia pollinate sternotribically which means that the pollen is picked up by insects on their sternum (ventral selerites of insects) as depicted in Fig and then transferred to the stigma of the flower. What is to be appreciated in the coevolutionary process is the close correspondence between the structure of the flower and the structure and behaviour of insects involved.

Posted Date: 4/5/2013 6:15:02 AM | Location : United States







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