Slime moulds are organisms that use spores to reproduce. Slime moulds were previously classified as fungi, but are nowadays considered a polyphyletic group with several supergroups. None of the supergroups belong to the fungi. The interactions between slime moulds and beetles are very old: group Agathidium is the largest beetle group that mainly feeds on slime mould fruiting bodies. The round fungus beetle (Agathidium pulchellum) is one of the rarest and most poorly known European species in the genus. The species is very small, under four millimetres. The elytra, i.e. hardened forewings, are heart-shaped and black. Slime mould Trichia decipiens is the main host of the round fungus beetle and the beetle is classified as endangered (EN) in Finland.
Trichia decipiens is a common slime mould species worldwide. It depends on the dead wood of conifers and broadleaf trees. The round fungus beetle was recently discovered to prefer deadwood-dominated environments, especially old-growth forests dominated by spruce. The round fungus beetle was previously believed to associate with aspen, but more information is needed on the species preferences. The conservation and management of an endangered species is successful only once enough knowledge is available on their biology and habitat requirements.
A study conducted in Kuhmo, eastern Finland attempted to find all the slime mould species that the round fungus beetle associates with. In addition, the study wanted to discover which tree species T. decipiens grows on, and whether it is possible for the round fungus beetle to live in managed forests. Forests in Kuhmo are dominated by Scots pine (Pinus sylvestris) and intensive forestry is practiced in the region. Rapid loss of old-growth forests is occurring as a result of these practices. The study sites were restricted to spruce-dominated forests, with approximately half of the sites located in nature reserves and the other half in managed forests. In addition to slime mould and beetle surveys, the researchers determined the number of decaying logs and their decay stages, along with the density of each tree species.
In total, 26 slime mould species were found in the nature reserve sites and T. decipiens was the most common slime mould species found in early summer. Spruce was the main tree species for T. decipiens (65%), but it was also found on birches, aspen and pines and once from alder. T. decipiens preferred large-sized logs in middle decay stages (DC2-DC4). The round fungus beetle was only found on T. decipiens growing on spruce, birch and aspen. The beetle occurred mainly in nature reserves, although once in a managed forest site, but this site was not managed ordinarily. A preference for sites with log densities over 30 m3 per hectare was a limiting factor for the round fungus beetle occurrence. As predicted, the quantity of dead wood was higher in nature reserves than in managed forests.
Although three other common slime mould species (Hemitrichia clavata, Trichia persimilis and Trichia varia) were found in the Kuhmo region, the round fungus beetle was only found from T. decipiens. The average dead wood volume in Fennoscandian managed forests is two to ten cubic metres per hectare, and T. decipiens requires at least 10 cubic metres per hectare, so dead wood volume restricts the occurrence of T. decipiens in managed forests. T. decipiens is a spore-dispersed species, so the quantity of available substrate limits its occurrence. Managed forests do not have enough available substrates to disperse to.
T. decipiens is most likely the main host species of the round fungus beetle and it occurs in old-growth forests with high conservation value. Quite little is currently known about the habitat requirements of the round fungus beetle. The species occurs in only a few localities in Finland, but it may be more common than previously believed. T. decipiens, the host species of the round fungus beetle, is very hard to find, because its sporangia are very small and it lives under tree trunks and bark.
Close Encounters of the Natural Kind 