New Meredithiella species from mycangia of Corthylus ambrosia beetles suggest genus-level coadaptation but not species-level coevolution

ABSTRACT

Meredithiella norrisii (Microascales, Ceratocystidaceae) is an ambrosia fungus carried in mycangia of the North American ambrosia beetle, Corthylus punctatissimus. Reports on the identity of the fungal symbionts of other species of Corthylus have been inconsistent. This study tested the hypothesis that Meredithiella spp. are the primary symbionts of Corthylus spp. Cultures and/or internal transcribed spacer (ITS) rDNA barcode sequences of Meredithiella spp. were obtained consistently from beetles and galleries of nine Corthylus spp. The ITS sequences of three putative species of Meredithiella were associated with C. consimilis and C. flagellifer in Mexico and C. calamarius in Costa Rica. The symbiont of C. columbianus in the USA was identified as M. norrisii. Two new Meredithiella spp. are described: M. fracta from C. papulans in Florida and Honduras, and M. guianensis associated with C. crassus and two unidentified Corthylus spp. in French Guyana. The Meredithiella spp. propagate in the mycangia of adult females by thallic-arthric growth, and the ambrosia growth in larval cradles comprises bead-like hyphal swellings or conidiophores, with or without terminal aleurioconidia. Bayesian phylogenetic analysis of a combined 18S and 28S nuc rDNA and translation elongation factor 1-α (TEF1-α) data set demonstrated that Meredithiella is a distinct monophyletic clade within the Ceratocystidaceae, but its phylogenetic placement with regard to the other ambrosial genera in the family remains ambiguous. The mycangia of C. punctatissimus and C. papulans are also compared using light microscopy and micro-computed tomography (micro-CT) imaging, revealing that they differ in both size and shape, but these differences may not correlate with different lineages of Meredithiella.

KEYWORDS:

• Ambrosia symbiosis
• Microascales
• mutualism
• Scolytinae
• 2 new taxa

ACKNOWLEDGMENTS

The advice and assistance of Doug McNew (Iowa State University) is greatly appreciated. Salvador Ochoa-Ascencio (Universidad Michoacana de San Nicolás de Hidalgo), Sarah Smith (Michigan State University), and Caroline Storer (University of Florida) provided beetles preserved in ethanol, and Thomas Atkinson (University of Texas) supplied specimens of C. consimilis and helped identify other ambrosia beetle specimens. Edward Stanley and Gary Scheiffele of the Nanoscale Research Facility (University of Florida) helped to CT-scan and visualize Corthylus mycangia. The herbarium specimens provided by the University of Kansas Herbarium (KANU) with the help of collections manager Caleb Morse are greatly appreciated.

FUNDING

Chase Mayers was supported in part by fellowship funds from the Office of Biotechnology, Iowa State University. Craig Bateman and micro-CT scans were supported by the National Science Foundation, the United States Department of Agriculture Animal and Plant Health Inspection Service (USDA-APHIS), and the USDA U.S. Forest Service. Other financial support was provided by the U.S. Forest Service, Special Technology and Development Program.

Additional information

Funding

Chase Mayers was supported in part by fellowship funds from the Office of Biotechnology, Iowa State University. Craig Bateman and micro-CT scans were supported by the National Science Foundation, the United States Department of Agriculture Animal and Plant Health Inspection Service (USDA-APHIS), and the USDA U.S. Forest Service. Other financial support was provided by the U.S. Forest Service, Special Technology and Development Program.