Fungi woven into birds鈥� nests may not only help keep nests flexible and intact, but also control nestling-attacking parasites by releasing antibiotics and volatile chemicals.
Baby birds, especially when naked and newly hatched, should be vulnerable to skin infections and parasites. Yet even in the stuffy confines of a nest in a steamy tropical rainforest, nestlings generally manage to remain fester-free. Why this is has long puzzled scientists, but at Purdue University in Indiana and her colleagues wondered if they may derive protection from the long strands of fungal material many tropical birds weave into their nests.
Called rhizomorphs, these long, pliable and highly decay-resistant structures protect the feeding parts of a fungus, the hyphae, inside a sheath so they can grow from one聽 hospitable place to another. But their length and flexibility also make them ideal as the basic scaffolding for nests under construction. As a result, they are common components of nests throughout the tropics.
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Rhizomorphs are also known to be potent producers of defensive chemicals, designed to keep insects, slugs and even other fungi at bay while the rope-like extensions seek out new spots of decomposable succulence.
Previous studies in forests that were tropical, but seasonally dry, had found rhizomorphs in nests were dried out and dead, and so made a purely physical contribution to any they were woven into. But Aime and her team thought things might be different in the perpetual sogginess of a rainforest.
To find out, they collected rhizomorphs from just-vacated nests built by 22 bird species in Iwokrama rainforest, Guyana, cleaned the fungal strands and then placed then on agar, a fungal growing medium. They found that, far from being dead, the cord-like strands were active and capable of producing chemical substances.
鈥淩ainforests are challenging places, so rhizomorphs produce a huge variety of protective chemicals,鈥� says team member , also at Purdue University.
Many of these chemicals are volatile, meaning they easily evaporate and travel through the air, so they could protect nestlings in the close confines of a nest, says Aime.
The team considers it highly likely that birds actively choose rhizomorphs as strong supports but also for keeping their nestlings free of the skin-infesting parasites so abundant in the humidity of a tropical rainforest.
鈥淭his is an interesting study,鈥� says at the University of Georgia. 鈥淚 hope their next step is to measure volatile production for rhizomorphs in nests, and test whether the chemicals produced directly reduce nestling fungal skin infections.鈥�
Symbiosis
