Forensic Mycology: Taking Hebeloma to Court

A few years ago, I must have been 2009, I was part of the Netherlands Forensic Institute, in particular of the Line Department Microtraces (Non Human Biological Traces). This experience has had great impact on my evolution as a scientist. Likewise, I’ve become more than moderately interested in forensics – the study of evidence discovered at a crime scene and used in a court of law. Forensic science is a multidisciplinary field, considering the full range of botanical, zoological, and inorganic evidence [1]. The next couple of articles deal with some aspects of forensic mycology, a very specific sub-discipline of forensics, starting with the genus Hebeloma and its possible applications.  

Introduction   

Hebeloma (Fr.) Kumm. is a genus of ectomycorrhizal fungi in the Cortinariaceae (Basidiomycota: Agaricales) consisting of, mostly, pioneer species – they occur as the firsts during sequential successive steps – while a few other species decompose animal wastes. Species delineation is traditionally based upon morphological characters. The different species in Hebeloma, however, are neither distinctive nor colorful [2]. David Arora, in his Mushrooms demystified [2], refers to Hebeloma as “[…] yet another faceless and featureless collection of brownish mushrooms.” Species identification, even for specialist in the field, is difficult and the different species concepts and infrageneric classifications are controversial. And pretty confusing, too. Depending on the author, sections, subsections, or even stirps exist to “solve” the genus [3]. Attempts have been made to clarify phylogenetic relationships within the genus, although these approaches were restricted to specific sections [4] or contained many unresolved or unsupported branches [3]. Yet, species are still being described and the interest for Hebeloma remains, as to providing unbiased scientific evidence for use in the court of law, and in criminal investigation and trial.

First Findings on Animal Remains

Hebeloma vinosophyllum Hongo was described as an agaric species without any specific ecological requirements, but, indeed, it does have a preference for dead (mammalian) carcasses. In 1968, a bunch of fruiting bodies of H. vinosophyllum was found in Kyoto [5]. Close examination of the soil showed that the remains of a dog constituted the source of nitrogen. In 1975, again, a single fruiting body of the same species was found near the Kyoto University campus, upon soil in which cat bones were found in the top 20 cm layer [5]. The year after, at the same spot, more fruiting bodies appeared.

Maybe the forest tree type was more influential than the animal remains? Well, no. The first collection of H. vinosophyllum was found in a stand of angiosperm Castanopsis cuspidata (clade rosids, family Fagaceae); the second in an area dominated by gymnosperm Pinus densiflora.

Also in 1998 fruiting bodies of H. vinosophyllum were observed in close association with a skull and bones, this time originating from a jungle crow (Corvus macrorhynchos) in Urawa (Saitama City, Japan) [6] – the first and so far only case with birds.

So far it is unclear whether or not the closely related Hebeloma sarcophyllum Peck, occurring in Europe, North Africa, and North America, has the same ecological tendencies.

Also other Hebeloma species, like the eastern North American and European H. syrjense, Japanese and European H. radicosum, and Australian H. animophilum have been reported to grow in association with (rotting = decomposing) animal remains [7]. Hebeloma syrjense is often referred to as the “corpse finder”, yet may turn out to be synonymous with H. radicosum [8].

Thus?

Is there a forensic potential for Hebeloma species? Sure. Then can we start using it in crime investigation? Not exactly. We don’t know how trustworthy the findings are as to forensic cases. Different authors have stated that more research is needed to develop fungi into suitable forensic tools [7,8].

For example, it is important to understand that fungi do not grow upon buried cadavers, but rather on the subsequent release of nitrogen during the cadaver’s decomposition (in the microclimatic patch, which is called the cadaver decomposition island, CDI) [7,9]. How this relates to carcass decomposition is unclear, though. How much nitrogen is released? Under what form is nitrogen released (simple organic nitrogen, ammonium, nitrate)? These approximations are needed in order to make accurate estimations of the post-burial interval (PBI).

Also, experimental settings should be taken into account – temperature, humidity, oxygen availability, and soil characteristics – as these can influence the rate of decomposition. Also the carcass species (body composition, fat ration, muscle mass) and size will have effects on decomposition rate as well as carcass-associated species composition and succession.

Cited References

[1] Mildenhall DC, Wiltshire PEJ & VM Bryant 2006. Forensic Science International 163: 163-172. [2] Arora D 1986. Ten Speed Press Berkeley (CA). [3] Aanen DK, Kuyper TW, Boekhout T & RF Hoekstra 2000. Mycologia 92 (2): 269-281. [4] Eberhardt U, Beker HJ, Vesterholt J, Dukik K, Walther G, Vila J & SF Brime 2013. Fungal Diversity 58: 103-126. [5] Sagara N 1976. Nature 262 (5571): 816. [6] Fukiharu T, Yokoyama G & T Oba 2000. Mycoscience 41: 401-402. [7] Carter DO & M Tibbett 2003. Journal of Forensic Sciences 48 (1): 168-171. [8] Bunyard BA 2004. Journal of Forensic Sciences 49 (5): 1134. [9] Carter DO, Yellowlees D & M Tibbett 2007. Naturwissenschaften 84: 12-14.