This document discusses the theory of co-evolution and the role of allelochemicals in host plant mediation. It defines co-evolution as reciprocal evolutionary change between interacting species. Examples of co-evolution discussed include predator-prey relationships, interactions between herbivores and plants, acacia ants and acacia trees, and flowering plants and pollinators. It also describes how plants have evolved physical and chemical defenses against herbivores, including thorns, spines, and compounds like phenolics and terpenoids. Finally, it explains that allelochemicals produced by plants can influence other organisms and protect the host plant by altering plant growth regulators and inhibiting pathogens.

1. THEORY OF CO-EVOLUTION
&
ROLE OF ALLELOCHEMICALS IN HOST
PLANT MEDIATION
PRESENTED BY:-
RAHUL KOIRI
B.SC 5TH SEMESTER
ZOOLOGY HONOURS
ROLL NO – 12
SESSION – 2022-2023

2. COEVOLUTION
Coevolution, the process of reciprocal evolutionary change that occurs between pairs
of species or among groups of species as they interact with one another.
Coevolution was first described in the context of insects and flowering plants, and
has since been applied to major evolutionary events, including sexual reproduction,
infectious disease, and ecological communities.
Coevolution Examples –
Predator-Prey Coevolution
Herbivores and plants
Acacia ants and Acacias
Flowering Plants and Pollinators

3. PREDATOR-PREY RELATIONSHIPS
 A relationship in which one organism kills another for food is called a predator-prey
relationship.
 The organism that does the hunting is the predator.
 The organism that is hunted is the prey.

4. HERBIVOROUS AND PLANTS
 Herbivores defences – Plants have evolved an impressive array of physical and
chemical defences to avoid herbivory.
 Herbivores need to eat plants in order to obtain energy and have therefore
coevolved mechanism to overcome these defences.
 Physical defences example – stings, thorns and spines.
 Chemical defences example – formed by chemical compounds stored, like phenolics,
terpenoids.

5. ACACIA ANTS AND ACACIAS
 The acacias trees produce specialized structures to shelter and feed the ant colony,
and the ants, in turn, defend the tree against herbivores.
 A mutual benefit to both plants and insect is that of acacia ants and acacia plants.

6. FLOWERING PLANTS AND POLLINATORS
 Birds, bats, butterflies, moths, flies, beetles, wasps, small mammals, and most
importantly, bees are pollinators. They visit flowers to drink nectar or feed off of
pollen and transport pollen grains as they move from spot to spot.
 In this respect, flowering plants and pollinators have developed co-adaptations that
allow flowers to attract pollinators, and insect and birds have developed specialized
adaptations for extracting nectar and pollen from the plants.

7. ALLELOCHEMICALS
 Allelochemicals are secondary metabolites produced by plants, algae, bacteria, and
fungi that influence the growth and development of other organism.
 It is defined as the interaction between plants and micro – organism by a variety of
compounds, usually refferred to as allelopathy, allelo chemicals, or allelopathic
compounds.
 The harmful chemicals released by allelopathic plants are known as
allelochemicals. Some allelo chemicals change the amount of chlorophyll production
in a plant and thus, they slow down on stop the photosynthesis process of that plant
which ultimately leads to the suppression or death of that plant.

8. ROLE OF ALLELOCHEMICALS IN HOST PLANTS
MEDIATION
 Allelochemicals like phenolics, steroids, saponins, terpenoids, alkaloids, and
flavonoids possessed by different tissues of several plants exhibit numerous
antioxidant production of antioxidant behaviors and ultimately protect the plants
from several deleterious pathogens.
 Allelochemicals can alter the contents of plant growth regulators or induce
imbalances in various phytohormones, which inhibits the growth and development
of plants.

9. THANK YOU