Concerted effects of plant compounds and endophytic fungi on food quality of giant bamboo to bamboo lemurs

Background/Question/Methods Giant bamboo (Poaceae: Cathariostachys madagascariensis) is the main food plant of endangered bamboo lemurs in Madagascar. In particular, the Greater Bamboo Lemur (Prolemur simus) is highly specialized on this plants species, which makes up 98% of its diet. Giant bamboo is characterized by strong cyanogenesis, that is, the release of toxic hydrogen cyanide in response to tissue disruption. We predict that this lemur, due to its extreme specialization, is significantly affected by variation of chemical features of its food plant. In addition to quantitative variability of toxic and nutritive plant compounds, plant-associated organisms, such as endophytic fungi might affect overall food plant quality by production of secondary compounds. In this study we analyze the interplay between these three factors and their potential effects on the bamboo’s food quality for the lemur. Endophytes are a diverse and ubiquitous group of fungi, known to benefit cultivated temperate grasses (Poaceae) by conferring herbivore resistance through synthesis of toxic alkaloids. To which extent giant bamboo-also member of the Poaceae-is colonized by fungal endophytes, whether these fungi synthesize bioactive compounds, and which ecological role the bamboo’s endophytes play in nature is currently unknown. We analyzed the variability of chemical plant features of giant bamboo and the colonization by endophytes at natural sites in southeastern Madagascar (Ranomafana National Park).

Results/Conclusions

Plant traits showed distinct quantitative variation depending on study site, plant individual, plant organ, and ontogenetic stage of organs.
Cyanide content in shoots ranged from 139 to 217 mmol cyanide per gram dry weight. Leaf soluble protein concentration varied between 37 in young and 95 mg protein per gram dry weight in fully developed leaves. Besides variability of the plants’ chemical features, we found diverse communities of fungal endophytes in bamboo. More than 200 fungal isolates were obtained from plant tissues. According to sequence data (ITS, nuLSU, nuSSU) and subsequent comparison to existing sequences from GeneBank endophytes mainly belonged to the Phyllacorales and Xylariales. Remarkably, a range of endophytes was repeatedly detected in various plant samples indicating a putative systemic occurrence in giant bamboo. Under laboratory conditions, fungal isolates produced a variety of chemical compounds including substance classes with potentially high biological activity. We propose that food quality of giant bamboo to lemurs is not only determined directly by plant traits, but also by endophytic fungi communities via the production of mycotoxins.