Parasitic Fungi and Carpenter Ants: The adaptive extended phenotype of

OphiocordycepsAlex McColl

An Adaptive extended Phenotype

Cam Goater; Lecture 1Google images

Definition- The genotype of one organism affecting the phenotype of another organism Ex) Morphology, behaviour...ect

In Context- “ The expression of parasite genes in host tissue for the purpose of increasing parasite fitness” Anderson

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The Players

O. unilateralis• Parasitic Fungus• Entomopathogenic

Camponotus leonardi• Arboreal Carpenter Ant

Anderson et al

The Death Grip

The parasitic fungus takes over the ant’s brain causing it to bite hard ontovegetation right before it dies

Andersen et al

Andersen et al

Life Cycle

<48 Hours post mortem

9 days

A few weeks post mortem

*P= Perthecial plate contains asci

Spore dispersal creates an infectious killing field

Andersen et al

Andersen et al

Andersen et al

Step 1

Step 2

Step 3

Video

• http://www.youtube.com/watch?v=vgkL8PulPdE&feature=related

Parameters

A)Dead host location on the leafB)Ant lengthC)Height leaf bearing the dead host above the

groundD)The total height of the plantE) The leafs compass orientationF) Host use after death

Methods (sample collection)• Took quadrates (samples of 2m2) from ant graveyards

and looked at parameters A-E

• Controls • Height- relocated infected (24 post-infection) and

uninfected ants to canopy and ground level.• Where infection occurred - Used secondary minor

parasite of Camponotus leonardi (Polyrhachis)

• Abiotic Factors (Humidity and temperature)- took measurements at 30cm & 5, 10, 15, & 25 m

Results A (Location of death grip)

Biting ants all on the underside of the leaf-98% were found on a leaf vein. Controls showed less specificity

B (infected Ant length)

C (Height above Ground)

D height of Plant (forest)

E (Orientation) Significantly biased towards the North- Northwest side of the leaf

Mean= 5.63 mm

All Camponotus leonardi were found at a mean height of 25.2 cm in low temperature, high humidity ; little variation. Infection outside this range resulted in abnormal fungal growth

Canopy <30m; Ant graves- understory; healthy ants – near the canopy

Adaptive Significance• Location of death grip -Securing shelter & nutrients-Shade• Height Above ground -Optimal location for spore dispersal and fungal

growth- Infectious kill zone• North/Northwest bias- ?

Host Use after infection (f)Measured fungal growth at 2 weeks, 48hr,9

days, & 9 days w/ Perthecial Plate-Scalpel sectioning of infected ants (Left)- Treatment and staining of infected ant heads

at various infection times (middle)-C:N analysis (right)

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Results• Fungi inside infected ants (within niche area) had

a complex structure

• The cuticle of the ant was not colonized by the fungus per se, rather it was remodelled

• Muscles remained preserved for many weeks post infection

• C:N showed that the orange fungal structure has higher C:N ratio

Why?

Cuticle Remodelling- Protection- reduces contact with other competitors

Muscle Preservation- Important for the biology of the fungus

C:N ratio- Speculate: storage function

• O. Unilateralis has evolved many traits to manipulate host behaviour, and host bodies

• O. Unlateralis changes host behaviour by manipulating hosts into dyeing in a location optimal for fungal growth

• O. Unilateralis uses host tissues in a specific way to achieve energy allocation, protection, and reproduction

• Collectively these traits represent a complex extended phenotype

References

Andersen, S. B., Gerritsma, S., Yusah, K. M., Mayntz, D., Hywel-Jones, N. L., Billen, J., & ... Hughes, D. P. (2009). Natural History Note: The Life of a Dead Ant: The Expression of an Adaptive Extended Phenotype. American Naturalist, 174(3), 424-433.

http://classes.uleth.ca/201101/biol4800a/papers%20for%20review/3.hostinds/Anderson.pdf

Questions?