Filamentous algal endophytes in macrophytic Antarctic algae: prevalence in hosts and palatability to mesoherbivores

Abstract

Amsler C.D., Amsler M.O., McClintock J.B. and Baker B.J. 2009. Filamentous algal endophytes in macrophytic Antarctic algae: prevalence in hosts and palatability to mesoherbivores. Phycologia 48: 324–334. DOI: 10.2216/08-79.1.

Five individuals, each from 13 common species of large macroalgae (‘macrophytes’) from the western Antarctic Peninsula, were surveyed for the presence of filamentous algal endophytes both macroscopically and microscopically using dissecting and compound microscopes. Of the 13 species surveyed, endophytes were either rare or absent in five. The remaining species all supported endophytes in most or usually all individuals with maximum endophyte densities per species ranging from 3% to 75% of the thallus area. Thallus fragments from all individuals with endophytes were placed into culture, and 99 unialgal, filamentous brown algal strains were isolated. The ITS1 gene was sequenced in each strain to sort these into distinct genotypes. Brown algal endophytes grew well in culture, and 10 distinct filamentous genotypes were present. The green endophytes did not grow well in culture, and only two green algal species present in the thallus fragments were isolated. No-choice feeding rate bioassays were performed with thallus fragments of all 13 macrophyte species and with cultures of seven filamentous brown endophytes and both green endophytes. Feeding rates on the endophytes were 2–3 orders of magnitude higher than rates on 12 of the macrophyte species and 2- to 6-fold higher than on the only truly palatable macrophyte, Palmaria decipiens. These data support the hypothesis that Antarctic macrophytes are commonly endophytized and that the endophytes benefit from the association by being protected, at least in part, from amphipod herbivory.

Key Words::

• Amphipods
• Antarctica
• Endophytes
• Epiphytes
• Macroalgae
• Mesoherbivory

ACKNOWLEDGMENTS

We are grateful to Drs J. Lopez-Bautista and A. Peters for assistance with the techniques of molecular systematics and to Dr Peters as well as Dr S. Dudgeon and an anonymous reviewer for constructive comments on earlier versions of the manuscript. We also thank Dr R. Angus for advice on statistics, Dr R. Moe for advice on taxonomy, Mr P. Bucolo for assistance with feeding bioassay methodology, and Ms K. Nelson for laboratory assistance. This project would not have been possible without the hard work of the other members of our 2007 and 2008 Antarctic field teams or without outstanding logistical support in Antarctica from the employees and subcontractors of Raytheon Polar Services Company. Supported by National Science Foundation awards OPP-0442769 (CDA, JBM) and OPP-0442857 (BJB).