In the early 1800’s, Charles Darwin was traveling the world, spending his time identifying and studying new exotic species. With his comprehensive analysis, accompanied by the work of less known world-renown naturists like Alfred Russel Wallace, the theory of evolution was conceived. Its conception shifted the modern world into new scientific paradigm opposed to the previous period dominated by religious theology. The cataloging and studying of Earth’s species allowed these driven fathers of evolution to see nature’s everchanging patterns through time. Now widely excepted as the backbone of modern biology, evolution was once heavily opposed by people outside of the scientific community. Although it may seem like there is an ongoing evolutionary debate when you log on to facebook today, I can ensure you there is not. If there is an ‘evolution debate’ it is based on feelingsand has no scientific merit. Again, the theory of evolution is supported by every biological discipline along with hundreds of thousands of peer reviewed articles. It really is common knowledge. We just have to accept that as long as humans are inhabiting Earth, so too will religious extremists. Some cling to a cross because they’re tired and lost, and we all just have to accept that.
This week’s Fungi Friday is featuring an organism first collected by Charles Darwin on the second voyage of the HMS Beagle. The ship anchored in Tierra del Fuego, which is a Chilean archipelago, the Southernmost chain of islands off the South American continent. The sample was later sent to the British mycological guru Miles Berkeley, where it was properly named Cyttaria darwinii. To this day, the original sample can be found within the herbarium at Kew Gardens in the United Kingdom. Now scientifically describing a species should not be confused with discovering a species. Darwin wrote in his journal that the native peoples of southern Chile would collect this golf ball sized fungus and eat it raw. In Spanish, the common name for this fungus is ‘Pan del Indio’ which translates to Indian bread. With its rich history, this small parasitic species has also been placed on my bucket list of species I will encounter before I die. I know if I find it, I will feel a direct connection to Charles Darwin. And that would be insanely cool.
This fungus has quite an interesting ecology that even Darwin was not aware of. Cyttaria darwinii infect trees within the plant family Nothofagaceae, also known as southern beech trees. Once inside its tree host, it affects the individuals sap ducts. Within the plant, the fungus most likely absorbs sugary plant solutions instead of the lignin rich woody materials. As a response to the growing fungus blocking phloem channels, the plant creates galls to bypass these fungal obstructions. Interestingly, Cyttaria species fruit from these tree cankers and galls, where they develop sexual spores to ultimately re-infect other suitable tree individuals. Though the species does reduce its host fitness, it is almost never a fatal interaction. For this reason, Cyttaria darwinii is called a weak parasite.
Another fascinating evolutionary insight this fittingly named species provides has to do with its biogeography. The species featured here today only occurs in the southern part of South America. That alone is not too interesting, but when we take a look at the distribution of the other species within its Cyttaria genus, an amazing evolutionary picture comes into focus. Cyttaria is composed of 12 species that grow within the tissues of with the other Nothofagus and Lophozonia trees in South America, Australia and New Zealand. These seem like distant places, but with a brief introduction of plate tectonics and an understanding of Earth’s geographical past, we realize that the ancient supercontinent called Gondwana connected these regions. It was here on this Gondwanan supercontinent that the ancestors of Cyttaria species evolved this parasitic strategy in which they began infecting these trees.
In fact, a few years after Cyttaria darwinii was described, Joseph Dalton Hooker found another Cyttaria species on Tasmania growing from a Nothofagus tree. This news was sent to Darwin and stirred up even more excitement as he realized that these fungi were growing from Nothofagus trees in these extremely distant places. It was this moment in which he realized the evolutionary trajectory of these two groups of species could be described by Earth’s biogeographical past. Nowadays, these biogeographical patterns that are already supported by the fossil record can be strengthened even further by sequencing mitochondrial DNA.
For instance, in 2010, Kristin R. Peterson, Donald H. Pfister and Charles D. Bell sequenced mitochondrial DNA and could adequately date separate divergences associated with the Cyttaria genus. These researchers concluded that the origin of these species occurred around 150 million years ago, just around the time of supercontinental breakup. Mirroring these geographical patterns, mitochondrial DNA in the Australian and New Zealand species diverge between 45-29 million years ago, just after Australian and New Zealand separated. Although it is widely accepted that these two regions started separating 80 million years ago, for nearly 40 million years these two land masses remained close enough for genes to flow from both Cyttaria and Nothofagus genera. Once genes stopped flowing from the mainland, new species endemic to just New Zealand evolved.
Darwin’s golf ball fungus is a unique species with an interesting parasitic ecology. When we look at the distribution of its closely related cousins, the theory of evolution as well as Earth’s long, magnificent ecological past just becomes strengthened. I hope learning about Cyttaria darwinii was as captivating to you as it was to Charles Darwin when he found the species while surveying Tierra del Fuego nearly 200 years ago. The evolutionary trajectory of today’s species can be accurately described by the fossil record as well as looking into extant genomes. Species of the forest floor have been here since the first plants made their way on terrestrial habitats and do not need religion to validate their existence.