Plant-Animal Mutualism: Acacia and Ant Interaction Review

This literature review examines the mutualistic relationship between acacia plants and ants, a classic example of plant-animal interaction. The paper delves into the benefits for both species, with the acacia providing shelter and food, and the ants offering protection against herbivores and pathogens. The review explores the plant defense mechanisms, including chemical defenses and the role of extrafloral nectaries in attracting ants while deterring pollinators. It discusses the evolutionary ecology of the acacia-ant relationship, focusing on the plasticity of food production in response to herbivory, the role of bacteria in nutritional ecology, and the co-evolution of this symbiosis. The methodology includes a literature search using databases like CINAHL, Google Scholar, and PubMed, with specific keywords and inclusion/exclusion criteria. The review highlights gaps in current research, particularly regarding the chemical defense mechanisms and the microbial contribution to the immune system. The paper also explores the cost and benefits of this symbiosis and the role of ants in host plant sterilization, providing a comprehensive overview of the current understanding of this fascinating ecological relationship.

Running head: ACACIA AND ANT INTERACTION
ACACIA AND ANT INTERACTION
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1ACACIA AND ANT INTERACTION
Abstract
The interaction between the plants and the animals can be referred to as any kinds of interactions
taking place between the various types of organisms present in nature. The most widely studied
plant and animal interaction that can be perceived is the plant - animal interaction. Among the
various kinds of interactions, the most widely studied interaction is the mutualism, where both
the partners involved in the relationship is benefitted. The mutualistic relationship that has been
discussed in this paper is the relationship between the Acacia plant and the ants. The Acacia
plants serves as an attractive option to live for the ants due to its hollow thorn like structures. The
fooding bodies and the extra floral substances secreted by the plant also makes it an attractive
living place for the ants. The main rationale behind his literature review is because of the
presence of very less research regarding the role of the ants in the chemical defense mechanism
of the plant against herbivory and other plant pathogens. The paper had also provided a wide
account of the microbial flora involved in this interaction, including information about the
evolution of the extra floral nectaries for especially attracting the ants and not the pollinators.
However, relevant literatures had been chosen by using the electronic data bases like CINAHL,
Google scholar and PubMed by using suitable keywords. However, although a large numbers of
papers are available on plant animal interaction, but more research work is required to validate
those works.

2ACACIA AND ANT INTERACTION
Table of Contents
Highlight:.........................................................................................................................................3
Introduction......................................................................................................................................3
Methodology....................................................................................................................................5
Inclusion and exclusion criteria...................................................................................................6
Literature review..............................................................................................................................7
Mutualistic relationship between Ants and Acacia.........................................................................9
Plant defense mechanism..........................................................................................................10
Recent issue in the evolutionary ecology of the Acacia-ant relationship..................................13
Plasticity in the food production in response to the herbivory..................................................14
Relationship between the ant and the bacteria in the nutritional ecology................................14
Cost and benefits of the Acacia and ant symbiosis....................................................................15
Co-evolution of the mutualism between the Acacia plant and the Ants....................................16
Conclusion.....................................................................................................................................18
References......................................................................................................................................20

3ACACIA AND ANT INTERACTION
Highlight:
Acacia plants and the ants show symbiotic relationship. The ants stays in the domatia of the plant
and feeds on extrafloral food. The ant on the other hand protects the plants.
Introduction
Plant –animal interaction can be defined as any kind of interaction taking place between
the organisms in the kingdoms Animalia and Plantae. The plant-animal interaction can be
considered as one of the common feature of ecology including the freshwater, marine and the
terrestrial biomass (Traveset and Richardson, 2014). The functioning of the biosphere is
dependent on the evolutionary principles of the plant-animal interaction. The preeminent
biologist had described about the plant animal interaction (PAI) in his famous book “The origin
of species by Natural selection”. Today, plant animal interaction still remains the center piece of
man of the ecological theories. Plant animal interaction might be general or can be highly
specific and might involve a detailed evolutionary adaptations. An example of a general plant
animal interaction is that it provides shelter for the animals like a tree providing a critical habitat
for the nesting bird. Again some of the animals are specific in their choices of plants, in contrast,
some of the insects might be highly specialized who live or lay eggs on only one plant species.
For categorizing describing the plethora of the plant-animal interaction, the biologists have
further categorized plant animal interaction as- Commensal interactions, antagonistic interactions
and mutualism (Orona‐Tamayo & Heil, 2013).

4ACACIA AND ANT INTERACTION
This paper would especially focus on mutualism, where both the members involved in the
symbiosis is benefitted. Plants and animals often develop mutualistic relationship with other
plants or animals or a wide range of microorganisms. Mutualistic relationship occurs when there
are shortage of resources in The Bull’s horn Acacia trees grows numerous structures that provide
shelter to the acacia ants. The tree and the ant have developed a mutualistic interdependency
(Ward & Branstetter, 2017).
Gaps in literature
Although this mutualistic relationship is quite common, only few literary sources are
there that discusses about the plant defense mechanism in details related to plant animal
interaction. Although the plant herbivory is quite obvious, but a debate is still on regarding the
chemical defense mechanism in plants. How the volatile components from the flowers of the
Acacia plants filters the advent of the pollinators and the ants is interesting and requires a lot of
researches. Furthermore, Palmer & Brody, (2013) have investigated about the microbial activity
associated with Acacia and ant interaction but how they contribute to the immune system is still
a vague concept. Again more researches are required in for analyzing the cost and the benefits
associated to Ant and Acacia interaction. Based on the secondary researches, this paper has
pointed out that the production of the food bodes in the Acacia plant modifies in response to
herbivory , but very less researches has been conducted in this field. The coevolution of the
mutualistic relationship between the Acacia plant and the ants is a very interesting side of
research, yet the theories cannot be validated due to lack of proper researches. Studying about
evolution of the mutualistic relationship would also help to provide an in-depth analysis of the
different ant-plant species that might have codiversified with time adapting with the
environmental change.

5ACACIA AND ANT INTERACTION
Based on this identified gaps, this paper had focused on the topics like plant defense
mechanism in plants, how the chemical defense mechanism in the Acacia plant attracts the
pollinators, but at the same time keeps away the ants. The paper would also research on how the
ants helps in the reducing some of the potential plant pathogens. Recently, some of the research
works have demonstrated the recent issues in the evolutionary ecology of the Acacia-ant
relationship, where discussion will be made in the nutritional ecology, the plasticity of the food
production in response to herbivory. The paper would also discuss about the relationship
between the ant and the bacteria in the nutritional ecology. Some of the other important concepts
related to the ant -acacia interaction, that would be focused upon are the cost and the benefits of
the plant Acacia and ant symbiosis. This report would further throw light on the role of the ants
in the host plant sterilization. While discussing about a mutual relationship it is necessary to
explore the evolutionary roots of this kind of relationship. Hence this paper would focus on how
the flowering plants have evolved in line with various types of ant species that have evolved or
had become extinct with time.
The main aim of this review is to present the recent findings on defense mechanisms and
evolutionary ecology of the interaction between Acacia and ants.
Methodology
A literature search has been conducted for choosing the relevant papers over some of the
electronic databases. The search strategy entails several databases, keywords, the inclusion and
the exclusion criteria (Aromatari & Riitano, 2014). Whether a search strategy is accurate or not
would depend upon the development of the research question. Before the conduction of the
literary search, it is necessary to search whether the reviews has already been published online.

6ACACIA AND ANT INTERACTION
However the databases that has been used for this review are CINAHL, Google Scholar,
Cochrane and PubMed. Articles between the years 2012- 2018 has been chosen for the literary
search.
Some of the main keywords that has been used in searching the literatures are “Plant”
AND “animal interaction. “Plant-ant AND Ant-plants”, Acacia AND Ants, “Plant defense”AND
Herbivory. While using the CINAHL database, the Boolean operators that has been used are
“Multualism”AND “plants” AND “ants”. “Acacia” AND “ants.
Keywords
Keywords Thesaurus terms Subject Headings
Plant-animal interaction Acacia-ant interaction Plant animal interaction
Mutualism Symbiosis Symbiotic relationship
Plant defence system Chemical defence Chemical defence
Inclusion and exclusion criteria
Using the inclusion and the exclusion criteria helps in saving the time for filtering the
information that are irrelevant. The boundaries in any sorts of literature review help in narrowing
down the resources that are available online. Some of the limiters that has been used for the
literary search are the published date and full text pdfs and English language. The papers were
chosen between the year 2012- 2019 owing to the fact that they were based on the recent
researches to reduce the biasness and increase the credibility. While searching for the papers, the
references of each of the papers had been searched manually , such that none of the important
papers related to the topic gets missed.

7ACACIA AND ANT INTERACTION
Inclusion and Exclusion Criteria
Inclusion Exclusion
Primary research, secondary research,
Systematic reviews
-guidelines or inappropriate study design
Language: English Other languages
Publication year: 2012 to 2018 Older than 2012
Systematic reviews and peer reviewed
articles related to plant-animal interaction
ecology, mutualistic relationship between the
Acacia plant and ants, the plant defence
mechanism and the chemical defences, floral
volatile substances and attraction of the
pollinators deterring the ants, the
evolutionary facts on the mutualistic
relationship between the plants and the
animals.
Literature review
The interaction between the plant and the animals are of special interest in the study of
ecology. Even though extensive researches has been carried out in the last few decades, many
theories has been culminated and the additional studies are require for the validation of the

8ACACIA AND ANT INTERACTION
findings. In particular the hypothesis related to the plant animal interaction and the defense
mechanism remain still a topic of debate.
In order to facilitate the research on plant and animal interaction, the interaction has been
classified in to- Commensal interactions, the antagonistic interactions, and mutualistic
relationship (Traveset and Richardson, 2014). Interactions has also been classified whether an
individual partner has more or less or equal number of off-springs due to the interactions.
Although the ultimate value is the reproductive success of the interacting plant and the animal,
some of the other metrics of the pant animal relationship is photosynthetic carbon gain, the
growth rate, longevity and the survival of the species (Borges, 2015).
The commensal interaction between the plants and the plants can be straightforward in
the theory but are difficult to demonstrate. In this type of interaction, one of the partner gets the
benefits and the other partner is not affected (Orona‐Tamayo & Heil, 2013). But, the questions
arise whether an interaction has neutral effect on any one of the species involved. Considering
the previous example of a bird residing in a tree, it clearly benefits the bird but might or might
not influence the tree. The presence of the nest will not have any effect on the growth of the tree
and in this case the relationship is truly a commensal relationship. Again, the presence of a nest
might block the sunlight or weigh down the branches away from sunlight, thus providing a
negative effect.
Another most important type of relationship is the antagonistic relationship between the
plants and the animals. It involves the direct consumption of plants as food (Traveset and
Richardson, 2014). This is a general PAI transferring the energy of the sun to the animal
biomass in the ecosystem. Sap sucking insects have specialized mouthparts for the piercing and

9ACACIA AND ANT INTERACTION
the sucking of fluids from the vascular system of the plants (xylem and phloem). Again some of
the insects have mouthparts in order to chew and tear away the plant parts.
Another type of relationship that can be seen in the ecology is mutualism, where both the
plants and the animals are benefitted by the relation. One of the ubiquitous example is the
pollination, where the insect extracts the nectar from the flowers and helps in pollination of the
plants (Orona‐Tamayo & Heil, 2013). Another type of mutualistic relationship can be due to the
seed dispersal. Animals are benefitted by the consumption of the fruits of that plant who are
having their sees dispersed by the dispersal agent (Borges, 2015).
Mutualistic relationship between Ants and Acacia
One of the best known mutualistic relationship can be seen among the Ants and the
Acacias. In the Central America and the Mexican region several ant species of the genus
Pseudomyrmex stay in obligate mutualism. Both the partners are highly adapted in this mutual
relationship. In the savanna grasslands and the tropical forests, the trees belonging to the Acacia
species Acacia Hindsii produces swollen and hollow structures on their branches and the twigs
called “domatia” that gives shelter to the stinging ants, Pseudomyrmex ferrugineus and
Pseudomyrmex gracilis (Campbell et al., 2013). The acacia plants produce domatia irrespective
of the presence of the anta but the ants residing in the plants might enlarge their nesting space by
the excavation of the pith tissue present in the stems and the branches. The plant provide food in
the form of extra floral nectar (EFN) and the protein and the lipid rich bodies as he food for the
developing larvae of the ants. Some glands are located at the base of the leaves that is
responsible for the secretion of the carbohydrate rich nectar on which the ants feed. There are
certain structures called “Beltian bodies” found on the tips of some of the species of Acacia that

10ACACIA AND ANT INTERACTION
are rich in lipids, proteins and sugars. They are the sources of food for the ants. The mutualistic
Pseudomyrmex ferrugineus fully depends on the acacia plant for the nesting and the fooding. As
per the integrative analysis of the genetic microsatellite data, the cuticular hydrocarbon and the
behavioral assay has shown that an acacia plant might be inhabited by the workers of the P.
gracilis queens , whereas the ants belonging to the species Pseudomyrmex ferrugineus, they
inhabit one or more host trees (Kautz et al., 2012). Despite of the differences, none of the spices
exhibited aggressive behavior amongst the co-specific workers sharing the same tree. Thus the
ants are benefitted by receiving a place for the colonization as well as the source of an energy
rich food. According to some of the recent studies, the ant mutualists in the acacia-
Pseudomyrmex have a reduced digestive capability and hence have to depend entirely on the host
plant. The ant association of the myrmecophytes has been studied well. In spite of an extensive
research, the neither genetic factors nor the chemical factors that are behavior mediated of the ant
partners have been thoroughly researched.
Plant defense mechanism
The relationship can be considered as mutualistic as the trees are benefitted in return, the
ants attack the insect herbivores and the leaf eating mammals. It has been found that these plants
plays an important role in the protection of the acacias from the African elephants, the largest
terrestrial herbivore on the earth (Pringle, Dirzo & Gordon, 2012). The plants can be exploited
by the parasitic non-defending ants that makes use of the pant derived food and also make use of
the nesting facility but necessarily does not provide any benefit to the plants (Pringle, Dirzo &
Gordon, 2012).
Chemical defense mechanism

11ACACIA AND ANT INTERACTION
One of the interesting thing associated to this is that the ants generally does not attack the
pollinators like the bees that pollinate the acacia flowers due to the secretion of the chemicals
released from the plants that prevents the ants from approaching the plant at the time of
pollination. According to the researches there are several species of plants that are able to attract
the insects for the defense against the herbivores. However De Vega, Herrera and Dötterl, (2014)
have identified ants might be unwelcome as the flower visitors due to many reasons- firstly they
have very little potential as pollinators as they are small in size, making them physically
incompatible for the sexual parts of most of the flowers, their smooth and the hairless cuticles are
not suitable for the adhesion of the pollens and their restricted mobility due to the absence of
wings Pringle, Dirzo & Gordon, 2012). Again most of the stinging ants have the metapleural
glands that secrets antimicrobial agents typically for the nest hygiene are detrimental for the
longevity and the fertility of the pollens (De Vega Herrera & Dötterl, 2014). Again the ants
might impede with the potential pollinators. The hostile ants might deter the pollinators from
coming in contact with the plants, including the legitimate pollinators. Again Cembrowski et al.,
(2013) have stated invasive ants cam significantly reduce the diversity of the flower visitors.
Again the ants might act as the “nectar thieves”, thereby decreasing the appeal of the flowers to
the pollinators by the removal of the nectar rewards that might reduce duration of the pollinators
visit. Mithöfer and Boland (2012), have stated that the volatile substance derived from the pollen
can deter the ants at the time of dehiscence, the impacts being stronger in the ant-guarded
species. They are more active on the resident ants both in the Neotropical and the African
species. The repellence involves some volatile that are considered as the known components of
the ant alarm pheromones, but are not repellant to the beneficial bee visitors. Surprisingly, it has
been found that some of the acacia plants attract the pollinators and deter the protective