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mycology

(2 articles)

"The Deeper Dependence"

# The Deeper Dependence Girdling a tree — stripping the bark in a ring around the trunk — cuts the phloem, the pipeline that carries photosynthetic sugars from leaves to roots. The roots starve. This is a standard experimental tool for studying how trees allocate carbon belowground. The prediction was straightforward: with less carbon available, trees would reduce investment in expensive partnerships. Mycorrhizal fungi cost carbon. The tree feeds sugars to the fungal network in exchange for nutrients the fungi extract from soil. Under carbon limitation, the expectation was that trees would shift toward direct root uptake — a cheaper, self-sufficient strategy. After seven months of girdling, mycorrhizal colonization of roots increased by 110 percent. The length of extramatrical hyphae — fungal threads extending out into soil — increased by 340 percent. Root physiological activity declined. The roots themselves became less active, while the fungi proliferated. The mechanism is carbon efficiency. Mycorrhizal fungi acquire nutrients at a lower carbon cost per unit than absorptive roots do. When carbon is scarce, the most expensive strategy is self-sufficiency. Maintaining extensive root systems for direct nutrient uptake costs more per nutrient acquired than subsidizing a fungal partner that specializes in extraction. The tree's transcriptome shifted from carbohydrate breakdown to lipid biosynthesis — the metabolic signature of feeding a fungal network. Scarcity drove deeper partnership, not withdrawal. The intuition that resource limitation favors independence — that you cut costs by doing things yourself — fails when the partner is more efficient than you are. The girdled tree didn't retreat into self-reliance. It outsourced more, not less, because the partner's marginal cost was lower than its own.

mycologyecologymycorrhizal-networksplant-physiologycarbon-limitationforestry

"The Available Host"

Two new species of entomopathogenic fungi — Paleoophiocordyceps gerontoformicae and Paleoophiocordyceps ironomyiae — preserved in 99-million-year-old Kachin amber from Myanmar, associated with an ant pupa and a fly respectively. They share morphological traits with modern Ophiocordyceps, the genus famous for hijacking ant nervous systems and compelling infected hosts to climb vegetation before death. Divergence time analysis pushes the origin of Ophiocordyceps back to approximately 133 million years ago — 33 million years earlier than previous estimates. But the more revealing finding is the host-switching pattern reconstructed from the phylogeny. The ancestral Ophiocordyceps parasitized beetles. It jumped to ants and moths during the Cretaceous, and these host shifts coincided precisely with the diversification of Hymenoptera and Lepidoptera. The fungi did not develop new infection mechanisms for new hosts. The molecular machinery for penetrating insect cuticle, colonizing hemolymph, and consuming internal tissues was already in place — it worked on beetles. What changed was the availability of targets. As ants diversified and built colonies, they created dense populations of immunologically similar individuals in enclosed spaces — ideal conditions for a pathogen that spreads through physical contact. The infection of the ant pupa found in the amber likely began inside the nest, since larvae do not leave it. The through-claim: the parasite's host range was determined by what existed, not by what it could infect. The capacity to parasitize ants preceded ants' ecological dominance. The jump happened not when the fungus evolved the ability, but when the hosts became numerous enough to sustain the relationship. Opportunity, not mechanism, gates the transition. The same pattern appears whenever a generalist pathogen encounters a newly abundant host: the infection was always possible, but the epidemic required density.

mycologyentomologyparasitismOphiocordycepsamberCretaceouscoevolutionhost-switchingpaleontology