When I think of invasive species, I immediately think of species that have originated from a foreign place, that have impacted the ecosystems I know and love in a negative way. Living right by the Great Lakes, I became aware of invasive species from a very early age. I remember vividly my mother driving my two siblings and I 40 minutes to Sunset beach in Lakeshore NY, to soak up some summertime rays and take a dip in Lake Erie. I would find aquatic plants that washed up on the shore that were riddled with little tiny clam-like organisms. I soon learned that those tiny clam-like organisms were called zebra mussels, and that they were not native to the Great Lakes. Originating from Europe and brought to the Great Lakes via ballast tanks from cargo ships, the zebra mussel now has a new home. I think more about invasive species through this perspective, not really recognizing that there are native species from my own backyard that have infiltrated ecosystems in Europe. Take Aureoboletus projectellus for example.
Three color variations of the Great Lake invader, the zebra mussel.
This bolete is native to a wide range in North America. You can readily find this species in many ecosystems where pines dominate since it forms mycorrhizal relationships with these trees. These reddish-brown boletes can grow to be rather robust, with some caps measuring 20 centimeters across. Its 1-2cm wide, slightly tapered stipe has intricate ridges that also aid in proper identification. This mushroom has a cap margin that slightly projects outward past the spore bearing surface. This easily identifiable feature is the reason why this species is called Aureoboletus projectellus. Flip the cap over, and fresh specimens will reveal a yellow pore surface, that turns olive brown with age. The pore surface soon turns olive brown because that is the exact color of the spores this fungus produces. Interestingly, these species produce the largest spores of any bolete in North America. I wonder if that spore morphology has anything to do with this species success…
Picture of this species giant spores. From Michael Kuo.
Aureoboletus projectellus and its projecting cap margin. Photo by Geoff Balme.
In the year 2007, this species was identified from a location Near the Baltic Sea. Ever since then, its range has been ever expanding and can now be found fruiting from the forest floor throughout many Baltic states. Like the zebra mussel mentioned above, this North American bolete was most likely vectored by us humans shipping lumber, or live pines colonized by this fungus. Łukasz Banasiak along with his team of six other biologists studied this species in hopes of better understanding the spread of invasive fungi. By using state of the art computer modeling techniques, these researchers concluded that Aureoboletus projectellus colonization of Europe is basically unstoppable.
Aureoboletus projectellus living amongst pines with a rare cap mutation. Photo by Murrill Halling.
By using models, researchers can predict novel invasions by focusing on certain ecosystems before dispersal has occurred, and look more in-depth at the ongoing invasion process. The goal of the above researcher’s project was to successfully predict the potential distribution of this North American invader. The present-day occurrence of these fungi along with climatic data and the distribution of compatible pine trees reveals that Aureoboletus projectellus will continue to spread around the Baltic sea. Already being well-established in Poland this species is bound to spread throughout Europe where suitable abiotic and biotic niches exist.
A.) White circles depict Aureoboletus projectellus occurrence. Darker regions show higher probability of invasion. B.) Dark region shows pine distribution. Banasiak et al. 2019.
The term invasive species is reserved for non-native organisms that cause ecological damage. Although Aureoboletus projectellus is not native to Europe, its place within these ecosystems has not yet been assessed. In other words, we don’t know if this species has a negative impact in non-native European ecosystems. Many invasive parasitic and pathogenic fungi are extreme threats to biodiversity. So, this invader is unique, given that it forms symbiotic relationships with trees. We know the mutualistic nature of mycorrhiza but clearly competition with other mycorrhizal fungi is involved with this species European encroachment. For example, Suillus flavidus and Tricholoma apium fruit from the same forests Aureoboletus projectellus is being found in. Both native European species are found on the IUCN list, and Tricholoma apium is actually categorized as vulnerable. Although mutualistic, this North American invader can possibly outcompete these native fungi, and overtime, replace them completely. Clearly, this is something no mycologist wants to see.
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