Thursday, 6 July 2017

Plotting fungi distribution against host distribution

Tom May
Royal Botanic Gardens Victoria

Many larger fungi such as mushrooms are associated with particular plant hosts. Some form mutualistic partnerships with trees (mycorrhizas), others are decomposers of wood or litter.

Fungimap records provide interesting comparisons of the distribution of host plant and fungus. We can use the spatial portal of the Atlas of Living Australia to map individual species, and to map several species at once, a very useful feature. Here, we use the co-mapping ability of the ALA Spatial Portal to investigate the distribution of two Fungimap target species, Cortinarius metallicus and Craterellus cornucopioides.

Mapping Cortinarius metallicus

Cortinarius metallicus growing under Nothofagus
(note the characteristic leaves of the tree on the mushroom's pileus).
Image: Geoff Lay CC BY-NC-SA.
Cortinarius metallicus is a distinctive mycorrhizal fungus that is always reported in close association with Myrtle Beech Nothofagus cunninghamii. Sporophores of the fungus are found under the canopy or very near Myrtle Beech trees, where the mycelia (growing portion) of the fungus in the soil wraps around the fine roots of the tree, providing an interface for a reciprocal exchange of nutrient between tree and fungus.

In the Spatial Portal of the ALA we can see that the overall distribution of the fungus spans Victoria and Tasmania (map not shown here).

Map of records of Cortinarius metallicus in Victoria
 in the Atlas of Living Australia (June 2017).
In Victoria, two dots seem more isolated from the main distribution (which is in the Central Highlands to the east of Melbourne), one dot is to the west and one is to the east. Perhaps these outlying occurrences are incorrect records or maybe there have been mistakes in assigning the geographic coordinates. Outliers that are several 100s or 1000s of kilometres away from the main distribution would be suspect. However, in this case, from the map alone, it is difficult to be sure if any dots are in the wrong place as none sit more than about 100 km away from the main distribution in the Central Highlands.

In the ALA spatial portal, mapping Cortinarius metallicus over Nothofagus cunninghamii provides an interesting perspective. Co-mapping shows that both host and fungus are found widely in Tasmania and in certain areas within Victoria. The scattered isolated green dots for Myrtle Beech outside of the main areas of distribution, especially seen in Victoria, are usually records of cultivated trees in parks and gardens.

Distribution in Tasmania of Cortinarius metallicus (red dots)
mapped over Nothofagus cunninghamii (pale green dots),
using the spatial portal of the Atlas of Living Australia (June 2017)

Closer inspection of the fungus records (red dots) in Tasmania shows that some of the dots are well outside of the areas where Myrtle Beech is found (pale green dots). For example, there is an isolated red dot in the lower east coast of Tasmania. Inspection of the record data shows that the original record is in fact from the Tarkine region of northern Tasmania, and there has been a mistake in assigning the geographic coordinates. In addition, the two records in the sea off the west coast obviously have mistakes in their geographic coordinates.

Distribution in Victoria of Cortinarius metallicus (red dots)
mapped over Nothofagus cunninghamii (pale green dots),
produced in the spatial portal of the Atlas of Living Australia (June 2017)

In Victoria, there is an isolated record from north-east of Melbourne, in an area where there is no Myrtle Beech. This record was checked against the original locality data and is not an incorrect geographic coordinate. In a case like this, we inspect any images associated with the record; but for this record, there is no image. Given that all other records of the species are in very close association with Myrtle Beech, the record must be regarded as dubious, and will therefore be marked as such in the Fungimap database. When Fungimap data are next uploaded to the ALA dubious records such as this will not be included. The second somewhat isolated record in Victoria, from the Baw Baw plateau, to the east of the main distribution in the Central Highlands, is associated with Myrtle Beech, and there is no reason to doubt the record (and a further record with an image was recently received from that area, as reported in A virtual foray in Cool Temperate Rainforest).

Mapping Craterellus cornucopioides

Craterellus cornucopioides
Photo: Richard Hartland. CC BY
A Fungimap target species that has been suggested as having a strong association with Myrtle Beech is Horn of Plenty Craterellus cornucopioides. This name is from the Northern Hemisphere. It would not be at all surprising if the local fungus turns out to differ from the Northern Hemisphere species. For the moment we refer to it as Craterellus cornucopioides. The fungus occurs from Tasmania to Queensland. FunGuild (a database on the trophic status of fungi, i.e. whether particular fungi are decomposers, mycorrhiza-formers, parasites etc.) lists the genus Craterellus as highly likely to be ectomycorrhizal.

Distribution in south-eastern Australia of
Craterellus cornucopioides (red dots) mapped over
Nothofagus cunninghamii (pale green dots),
produced in the spatial portal of
 the Atlas of Living Australia (June 2017)

Plotting Craterellus cornucopioides (red dots) against Nothofagus cunninghamii (pale green dots) as a potential host (in Victoria and New South Wales) shows that at a broad scale, where Myrtle Beech is present, most records of the fungus seem to be within the distribution of Myrtle Beech. However, the fungus also occurs in areas very distant from Myrtle Beech, in the east of Victoria and in coastal New South Wales, as well as Queensland.

Another species of Nothofagus, Nothofagus moorei, occurs in New South Wales and southern Queensland. In New South Wales this Nothofagus is restricted to the Barrington Tops and areas to the north. The northernmost record of C. cornucopioides in New South Wales is in fact from the Barrington Tops, although there is no mention of the presence of Nothofagus. However, all other reports of C. cornucopioides from New South Wales are to the south of the distribution of Nothofagus moorei.

Distribution in Victoria of Craterellus cornucopioides (red dots)
 mapped over Nothofagus cunninghamii (pale green dots),
produced in the spatial portal of  the Atlas of Living Australia (June 2017)
Closer inspection of the Victorian occurrences of Craterellus cornucopioides shows that some dots that fall over the Mrytle Beech distribution, when mapped at a wide scale, are in fact are close to, but not co-incident with the distribution of Myrtle Beech, when mapped at a finer scale. There are also occurrences of the fungus to the east, far from the current distribution of Myrtle Beech, and so the fungus is able to grow in a much wider overall range compared to the tree. If Craterellus is indeed mycorrhizal, it remains to be seen which trees in particular it is associating with. Observations of exactly which types of trees the sporophores occur under will be useful in determining this. Co-mapping certainly shows that it is not a strict associate of Nothofagus.

The uses of co-mapping

Co-mapping of host and fungus is a useful tool for understanding the strength of association between particular fungi and plants, and also for detecting erroneous records, either due to misidentification or to incorrect geographic coordinates. Co-mapping also suggests areas to explore where the plant is present but the fungus has not yet been reported. For example, Cortinarius metallicus has not yet been reported from three areas in Victoria where Myrtle Beech is present: The Otways, the Strzelecki Ranges and Wilsons Promontory - so look out for this distinctive fungus in these areas.

Tom May
Fungimap / Royal Botanic Gardens Melbourne

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