Marasmioid rhizomorphs in bird nests: Species diversity, functional specificity, and new species from the tropics

ABSTRACT

In tropical and subtropical rainforests, vegetative fungal rhizomorphs from the Marasmiineae are routinely used as construction material in bird nests. Because rhizomorphs seldom produce mushrooms within nests, the fungal species involved remain largely unknown. In turn, this limitation has prevented us from resolving broader questions such as whether specific fungal species are selected by birds for different functional roles (i.e., attachment, or parasite control). To fill some of these gaps, we collected 74 rhizomorph-containing bird nests from the Neo- and Afrotropics and used nuc rDNA internal transcribed spacer ITS1-5.8S-ITS2 (ITS) sequences to discriminate between rhizomorph-forming species. In total we recovered 25 Marasmiineae species used by birds in nest construction, none of which were shared between the Neotropics and the Afrotropics. We also collected Marasmiineae basidiomes in the vicinity of nests and used ITS sequences to match these sporulating morphs with nest rhizomorphs for nine species. Basidiomes from an additional five species were found fruiting from rhizomorphs incorporated within bird nests. Finally, an additional six species were putatively identified based on publicly available sequence data. Rhizomorphs of five species were found to be utilized almost exclusively as lining material in nests. Lining material comes in direct contact with nestlings and is hypothesized to play a role in parasite control. Rhizomorphs from 10 species were used to attach and anchor nests to substrates; we matched six of those to fruiting litter trap-forming species collected in the understory. Litter traps hold large quantities of fallen litter material, suggesting that birds may preferentially use rhizomorphs that are adapted to bearing heavy loads for nest attachment. Finally, we describe two species of Marasmius—M. neocrinis-equi, sp. nov., and M. nidus-avis, sp. nov.—that are commonly found associated with bird nests and show that rhizomorph production is common across the genus.

KEYWORDS:

• Avian nest architecture
• Crinipellis
• Gymnopus
• Guiana Shield
• Guineo-Congolian Basin
• Marasmiaceae
• Omphalotaceae
• symbiosis
• systematics
• 2 new taxa

ACKNOWLEDGMENTS

The authors wish to thank two anonymous reviewers for their helpful comments on this manuscript, Francino Edmund and Luciano Edmund for help collecting nests in Guyana, and Mule Jean, Djoakoho A. Medjo, Mamoho Narcise, Menele Massa, Adimpir Cyrille, and Aziem Jean Aimé for help collecting nests in Cameroon. In Cameroon, research permits were issued by the Ministry of Research and Scientific Innovation, and in Guyana research and collecting permits were issued by the Guyana Environmental Protection Agency and Iwokrama. Raquel Thomas-Cesar greatly facilitated research at Iwokrama. Bryce Westman and PUL are acknowledged for specimen accessions.

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Funding

Funding for this study was provided by a Mycological Society of America Forest Fungal Ecology Postdoctoral Award to R.A.K., a National Geographic Society Early Career Grant EC-59602R-19 to R.A.K., and a US National Science Foundation grant DEB-1556412 to M.C.A.