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Ant-Herbivore-Plant Mutualisms

Lecture for Tritrophic Interactions

Rob Morrison

on 4 December 2012

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Transcript of Ant-Herbivore-Plant Mutualisms

Ant-Herbivore-Plant Mutualisms Importance of ants About 13,000 species Present in every ecosystem Biomass about equal to humans on planet Characterized by highly social societies Often form mutualisms with other species +/+ interaction These can have positive or negative
consequences for plants, depending on who the mutualism is between + + Plant Herbivore Ant-Plant Mutualisms Case Study: Ant/Plant Mutualism Two sister species of myrmecophytes
Subspecies of Leonardoxa africana Lenardoxa africana Plant provides domatia Acts as housing Plant emits volatiles when damaged (Vittecoq et al., 2011) Petalomyrmex phylax Aphomomyrmex afer Ants come pouring out to defend against herbivore Who benefits? Ants
Plant Who loses? Herbivore Plant Rewards Domatia Extrafloral Nectaries Ant Services Plant Defense Mutualisitic Interaction Obligate Mutualism Facultative Mutualism (opportunistic) (no choice) Who gains? + Plant
- Herbivore - Plant
+ Herbivore Mutualism between: Required for survival Strong co-evolution (1:1) Increases fitness when present Weak co-evolution (not 1:1) Plants Ants Plants Ants Reproductive division of labor

Overlapping generations

Haplodiploidy system of inheritance + ant/+mutualist Herbivore Rewards Honeydew /Deceit Chemical Mimicry Caterpillar Ant Ant Services Predator Defense Housing/Refuge Seed dispersal Pollination Food Bodies Food What about when the mutualism is between ant & herbivore? It depends... + ? Specifically... The cost of sap removal
& virus transmission ≤ The benefit of suppression of other
herbivorous arthropods by ants ...in order for the mutualism between
the ant and aphid/herbivore to be beneficial
to the plant Case Study - Ant/Herbivore Mutualism Holm Oak Native Invasive Lachnus roboris Lasius neglectus Lasius grandis (Paris et al., 2011) * * * * Volatile Emissions
ug/g*h Volatile emissions of a plant are indirectly affected based on which ant species is tending the aphid
Over 400% increase in VOC when native species tends aphid
Has potential to affect natural enemy recruitment to aphids Who benefits? Aphid
Ant Who loses? The tending ant changes the physiology of the acorn by prompting the plant to change its fatty acid allocation in the reproductive structure.
Linolenic acid is a precursor to jasmonic acid, so may be evidence of local response to a species that the oak did not coevolve with.
Change in fatty acid does not affect development of acorns. It is uncertain... The plant did not experience a decrease
in fitness, so it is not directly suffering.
But, decreased VOC emission in the invasive case could lead to other repercussions, such as decreased natural enemy abundance. Costs < Other benefits of ants (?) However... there are some cases where the ant-aphid mutualism is deleterious to plants... decreased seed set
decreased plant growth
decreased # flowers/fruits
decreased seed viability (Renault et al., 2005) A +/+/+ relationship for plant, herbivore, ant? Likely so! 73% of 30 reviewed studies showed a positive effect on the plant when there was a mutualism between a herbivore and ant. (Styrsky and Eubanks, 2007) Positive! Positive! Positive! Positive! Positive! Positive! Why is there this trend? Damage from more
severe pests by ants = Net benefit from aphid/
ant mutualism for plant Plant
fitness 1) when ants indirectly benefit the herbivore population, which results in: ...and these outweight the benefits of ants, or 2) when ants directly eliminate other predators, and these are otherwise more efficient/abundant than ants (Banks & Macaulay, 1967) (Sipura, 2002) (Rico-Gray and Thien, 1989) (Renault et al., 2005) Overall Interactions for Ant/Herbivore Mutualisms Cost<Benefit Cost>Benefit Case Study: Ant-Herbivore Mutualism, + for Plant Trees attacked by LC % Leaves attacked by LC # Trees w/ dead Coccids # Trees w/ dead stem scales # Trees w/ predators Citrus in Trinidad The ANTagonist Herbivore Community Azteca sp. Soft green scale Stem scale Atta cephalotes (Jutsum et al., 1981) (Jutsum et al., 1981) # Trees w/ Azteca Trees w/ Trees w/ Leaf
damage Trees w/ Trees w/ Trees w/ Azteca decreased defoliation of citrus by 32% in 1976 and 49% in 1977.
Increased biological control of more severe herbivores benefits the plant Who benefits? Ants (Azteca sp.)
Plant Who loses? Other herbivores (leafcutters) Case Study: Ant-Herbivore Mutualism, - for Plant Field beans in the UK The ANTagonist Herbivore Community Lasius niger Aphis fabae * * * Significant decrease in fitness for the beans when aphids are tended by ants
Translates to yield loss Who benefits? Who loses? Ant
Aphids The plant But, the plant is not necessarily always on the losing side... Video Pick of the Week Today, we meet:

Brian Fisher
Ant Systematist
Chairperson, Department of Entomology
CA Academy of Sciences Take-Home Messages Ants are cool!
Ants provide services such as protection to herbivores and plants, while herbivores and plants provide food and/or housing.
These relationships range from mutualism to parasitism in some cases.
Some of the mutualisms have negative outcomes for the plant, but most are positive
Depends on cost to benefit ratio ENT890: Tritrophic Interactions
Guest Lecture: Rob Morrison What happens if you remove the ant from the plant? Decreased fitness! Increased herbivory! Decreased symbiont! Decreased fitness! Increased herbivory! Regardless of region! (Rosumek et al., 2009) Mighty ants!
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