ECR feature: Jeff Stallman on mushrooms and the theory of island biogeography

Jeff Stallman is a PhD candidate at the Purdue University. He is particularly interested in the taxonomy, systematics, and biogeography of macro-fungi, with an emphasis on the Hawaiian Islands. Here, Jeff shares his recent work on mushrooms endemic to oceanic islands and how they fit in with the theory of island biogeography.

On a collecting trip with his lab at Purdue University, Jeff was happy to find a large Amanita species in southern Indiana.

Personal links. Twitter.

Institute. Purdue University, Indiana, USA.

Academic life stage. PhD candidate.

Major research themes. Fungal taxonomy, biogeography, and conservation.

Current study system. For my PhD, I study Leotiomycetes. This class of fungi in the Ascomycota contains fungi that cause powdery mildew in plants and white-nose syndrome in bats, among many other lifestyles. I focus on small cup-shaped fungi in the order Helotiales, particularly from tropical locations where little sampling has been done. I use DNA sequence data from these collections to improve our systematic understanding of the order. Currently, the number of described species is far below the estimated diversity (as is true for most fungal taxa) and there are an estimated 90–151 incertae sedis genera in the order.

Recent JBI paper. Stallman, J. K., Robinson, K., & Knope, M. L. (2022). Do endemic mushrooms on oceanic islands and archipelagos support the theory of island biogeography? Journal of Biogeography, 00, 1–11.

Motivation behind this paper. I worked as a field technician in various conservation jobs in the Hawaiian Islands. During these jobs, and while pursuing my MS degree at the University of Hawaiʻi Hilo, I became quite obsessed with Hawaiian plants. I loved seeing them in the wild and learning about their unique evolutionary and biogeographic histories. For several reasons, data with the same level of detail on plants was not available for Hawaiian mushrooms (Agaricomycetes). So, we set about gathering these data to see if Hawaiian mushrooms followed similar biogeographic patterns as plants.

Key methodologies. We use a traditional checklist-based method in this paper. We updated a checklist of Hawaiian mushrooms, then used checklists of angiosperms, ferns, lichens, bryophytes, and mushrooms from Hawaiʻi, Canary Islands, Azores, Cabo Verde, Galápagos, Madeira, and Christmas Island to compare endemic species in different organism groups among and between different islands and archipelagos.

Photographing fungi in MacKenzie State Recreation Area in the Puna District of Hawaiʻi Island. Mushrooms are often abundant in the litter of the introduced Casuarina trees.

Unexpected challenges. I didn’t know what to expect, so everything was unexpected! The main challenges were dealing with limitations in the data that are inherent to checklists and studies of biogeography. Our knowledge of species diversity and distributions is incomplete, particularly in cryptic groups such as mushrooms, and DNA sequence data is lacking in most fungi from these locations on these checklists. In the end, many species could not be assigned to a known category (non-native, native, native and endemic), so they needed to be excluded from the analysis. These and other limitations are discussed in a (long) limitations section in the paper!

Major results. We provide baseline evidence that mushrooms follow similar island biogeographical principles to plants. For example, percent endemism in mushrooms is positively correlated with island size and distance to mainland. But we did not find evidence that maximum elevation or a closer proximity to the equator was correlated with increased endemism percentage. There has been recent interest in this topic in general, and we hope our research can be built upon and used as an argument to gather more data in the future. This adds to evidence accumulating over the last 30 years that in many cases microbes are dispersal-limited, in contrast to the ideas of the Baas-Becking hypothesis that “everything is everywhere, but the environment selects.”

A container of colorful collections from a walk in Cusuco National Park, Honduras.

Next steps for this research. Continuing with the same methodology, checklists from the seven islands and archipelagos can be updated, and checklists from more islands/archipelagos can be added to improve sample size. More DNA sequence data on fungi from these islands and archipelagos would also help with quick comparisons via global databases. Particularly, incorporating DNA data to explore anagenesis (evolution of a single endemic species from its ancestral continental counterpart) versus cladogenesis (diversification into multiple, endemic species after establishment on an island or archipelago) would improve this aspect of the analysis. Public databases such as Globalfungi and the Global Soil Mycobiome consortium have exciting potential in addressing these questions.

If you could study any organism on Earth, what would it be? Tough question! The putative Hawaiian endemic Hygrocybe noelokelani is a beautiful mushroom and there seems to be a pattern of endemic Hygrophoraceae on oceanic islands, so I would pick that species, or the family on islands/archipelagos more broadly.

Published by jbiogeography

Contributing to the growth and societal relevance of the discipline of biogeography through dissemination of biogeographical research.

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