Fungal-Fungal Interactions in Leaf-Cutting Ant Agriculture

Table 1

A review of studies that correlate plant secondary metabolites with ant foraging preferences, with additional observations of whether these key families of compounds have antifungal properties, change as a result of plant-fungal interactions, or are known to be produced in in vitro endophyte cultures.

Plant secondary metabolites	Correlation with ant host plant preferences (− repellant, + attractant, 0 neutral)	Anti-fungal properties*	Fungal-induced changes in plants^§	Endophyte secondary metabolites
(1) Nonpolar compounds	− [12–15]			Aromatic compounds and nonanoic acid [16–19]
Terpenoids		Yes [20]	P infection triggers plant production of terpenoid phytoalexins^£ [21]
Monoterpenoids (e.g., trans-β-ocimene)	− [22]	Yes [23]	REs trigger increase of α-terpinene, but not other monoterpens [24]
Sesquiterpenoids (e.g., caryophyllene epoxy, caryophyllene, nerolidol, lasidiol, guaiacol, and spathulenol)	− [25–29]	Yes (cultivar) [25–27]	REs trigger increase of trans-β-caryophyllene but not other sesquiterpenoids [24] AM increase [30] or do not affect [31] emissions	Caryophyllene and derivates, bulnesene, valencene, cuparene, heptedilic acid, hydroheptelidic acid [16, 32–35]
Diterpenoids (e.g., kolavenol)	− [26, 27]	No (cultivar) [27]		Taxol, guanacastepene, and subglutinols [34, 36]
Triterpenoids (e.g., lupeol, 3a-hydroxyolean-12-en-27-oic acid derivates)	− [37, 38]		AM induce accumulation of triterpenoids in roots [39]
Cuticular waxes	− [15, 37, 38]	Yes [17]	P infection triggers production of alkene [23]
(2) Polar compounds (e.g., glycosides, and alkaloids, phenolics)	− [14]	Yes (e.g., lignants on cultivar) [40]	P infection triggers plant production of polar phytoalexins^£ (e.g., phenolics, alkaloids, and flavonoids) [21, 23, 41]	Phenolic acids, rugulosin, lignans, ergosterol, and steroid volatile alcohols [32, 34, 35, 42]
Alkaloids	0 [12, 13]	Yes [20, 43]		Cytochalasin compounds, ergot, loline alkaloids, lolitrems, and peramine [16, 34, 44]
Tannins		Yes [20]
Hydrolyzable	+ [12, 13], − [45–47]
Condensed	− [46, 48], + [45], 0 [12, 13, 47]
Glycosides (e.g., saponins and anthocyanins)	− [12, 49, 50]	Yes [20]	AM induce accumulation of glycosylated cyclohexenone derivatives [30]	Pestaloside and tricin [16, 34]

*General antibiotic effect against a common variety of tested fungi or, in particular, toward leaf-cutting ant cultivar (cultivar).
^§P: fungal pathogens, AM: arbuscular mycorrhizae, and RE: root endophytes.
^£Phytoalexins: low-molecular-weight antibiotic compounds produced de novo by plants in response to microbial stimulation [51].