The role of wild boars in spore dispersal of hypogeous fungi

A.: The role of wild boars in spore dispersal of hypogeous fungi . Acta Mycol. 47 (2): 145–153, 2012. Wild boars ( Sus scrofa L.) are well-known for soil disturbance in natural and cultivated truffières but their role in spore dispersal is poorly investigated. In the present work we studied the occurrence of hypogeous fungal spores in faecal contents of 14 wild boars randomly hunted in “Parco dei Gessi e Calanchi dell’Abbadessa” Regional Park (North of Italy) where truffle production has been previously investigated for three years. Six methods for spore analysis in faeces were compared and the suspension of faeces in ZnSO 4 (70%) solution resulted to be the most reliable. Hypogeous fungal spores, including Tuber magnatum and Tuber aestivum spores , were detected in 9 animals. This result suggests that the detection of fungal spores in faeces of wild boars may provide information on the presence of hypogeous fungi in an area. However, the poor abundance of spores suggests that the wild boar can be considered an opportunistic mycophagist, ingesting truffles only occasionally, as a seasonal source of food. Considering the magnitude of wild boar movements during seasonal migrations, it is possible to speculate that they play a key role in truffle long distance dispersal.


INTRODUCTION
Hypogeous fungi comprise species belonging to several genera of Ascomycota (true truffles), Basidiomycota and Muromycotina (false truffles) (Trappe et al. 2009;Bonito et al. 2013).The hypogeous lifestyle comported several morphological changes, as the loss of the ability to discard spores actively (Trappe, Claridge 2005).This led to develop several survival strategies, as the development of a strong aroma, even typical of any truffle species (Gioacchini et al. 2005).This aroma is useful to the fungus to be found and eaten by wild animals, mainly rodents and mammals, ensuring spore dispersal into the environment by animal faeces (Cazares et al. 1999;Trappe, Claridge 2005).
Among mammals, wild boars (Sus scrofa L.) are sadly known to damage truffle production in natural and cultivated truffières (Ricci 2008;Moreno-Arroyo et al. 2005).The negative impact of wild boars on truffles is attributed to soil disturbance and ascoma consumption, as we demonstrated for Tuber aestivum in natural truffières in Central Italy (Salerni et al. 2011).
However, less is known on the possible ecological role of wild boars in truffle spore dispersal (Genard et al. 1986;Steiner, Fielitz 2009).As far as we know, only the former Authors reported specifically about T. aestivum consumption by wild boars, but the paper lacks in technical information about spore isolation methods.
Thus, in the present work we investigated the occurrence of hypogeous fungal spores in faecal contents of wild boars hunted in "Parco dei Gessi e Calanchi dell'Abbadessa" Regional Park, an area known for truffle production.

Study area.
The study was carried out in "Parco dei Gessi Bolognesi e Calanchi dell'Abbadessa" (Ente di gestione per i Parchi e la Biodiversità -Emilia Orientale, 2013) which is located in the South Eastern hilly area of Bologna (Central Italy) in the Municipalities of Bologna, Ozzano dell'Emilia, Pianoro and San Lazzaro di Savena (surface area 4.815,87 ha).
In this area, the forests are mainly represented by Ostrya carpinifolia Scop.and Quercus pubescens Willd.(all.Orno Osrtryon Auct.Ital.and all.Ostryo-Carpinion orientalis, Horvat 1954) (Corbetta 1994).The park is characterized by a temperate Mediterranean climate (Köppen-Geiger classification), where the highest and lowest temperatures occur in July-August and December-January, respectively, and the annual average precipitation is 750 mm (Pieri et al. 2011).Truffles, in particular T. aestivum and T. magnatum, are principally found in Q. pubescens mixed forests, in calcareous soils derived from marnous arenaceous rocks, within the Municipalities of Ozzano dell'Emilia, Pianoro and San Lazzaro di Savena.
Hypogeous sporoma collection.Fruiting bodies of truffles were collected in Q. pubescens forests of the Park, using trained dogs, between September and January 2004-2007.
Animals.Between October 3 rd and December 4 th 2011, the faeces of 14 wild boars hunted in the Park area, in compliance with the permitted hunter-kill ratio actions established by Bologna Province, were examined.Animals, randomly chosen regardless sex, age and weight, were dissected by the "Azienda Agricola S. Uberto" accredited slaughtering house (Monterenzio, Bologna) (Provincia di Bologna 2007).
For the first 5 methods, the faecal precipitate (10 g) was 5-fold diluted with the corresponding solution and centrifuged (1500 rpm, 3min).After centrifugation, new solution was added to the very top of the tube and a cover slip was placed on it for 10-15 min for recovering the floating fungal spores.Cover slips were mounted on a slide and immediately examined under a light microscope.Each sample was treated in triplicate.
Among the six methods tested, the ZnSO 4 (70%) solution resulted to be the most reliable to isolate spores and thus it was used for analyzing all faecal samples.Morphological identification.Fresh samples of fruiting bodies were preliminary identified on the basis of their macroscopic (colour, surface, smell, etc.), and microscopic characteristics (morphological and biometric characteristics of spores and peridium cells) numbered, dried and stored in the herbarium of the Dipartimento di Scienze Agrarie (CMI-Unibo), University of Bologna (Italy).The spores found in the faeces were identified basing on their external characteristics (shape, dimensions and type of ornamentation).TuberKey (Zambonelli et al. 2000) was used as reference for Tuber spp.identification whereas Montecchi and Sarasini (2000) monography was used as reference for the species of hypoeous fungi belonging to different genera of ascomycetes and basidiomycetes.

Hypogeous sporoma collection.
During the surveys, only a few ascomata of T. aestivum and T. magnatum were found because the area is regularly visited by other truffle hunters, although truffle harvesting within the Park is forbidden.Other hypogeous Ascomycetes were common in the park, such as T. excavatum, T. rufum, T. macrosporum T. borchii, T. dryophilum, T. brumale, Balsamia vulgaris, Stephensia bomycina, Genea spp.Basidiomycetes were only represented by the species of the Hymenogaster genus and by Melanogaster ambiguus (Tab.1).
Detection and identification of faecal spores.The data of the 14 wild boars examined and the characteristics of the truffle spores detected in the corresponding faecal samples are shown in Table 2.No fungal spores were detected in 5 animals whereas in 9 ones spores of hypogeous fungi, including T. magnatum and T. aestivum, were identified (Fig. 1).
Other unidentified fungal spores were present in most faecal contents, including several spores of Alternaria spp.(data not shown).Truffle spores were found in both sexes and in the animals from all the Municipalities within the Park.

DISCUSSION
In this study a simple method to detect truffle spores in wild boars' faeces was perfected.This method can be used for ecological studies involving the role of wild animals in hypogeous fungal spore dispersal.
Examining the faeces of just 14 animals hunted in two months, we were able to detect seven hypogeous fungal species including T. aestivum and T. magnatum, which are the most widespread and economically important species growing in the studied area.These results suggest that the detection of fungal spores in the faeces of wild boars may provide a first rough indication of the presence of hypogeous fungi in an unknown area, when trained dogs are not available.This methodology may also be useful in countries were truffle harvesting is forbidden even for scientific purposes.For example, in the Czech Republic and in Slovakia truffles are considered endangered species and they are, thus, protected by the law (Grynder et al. 2011).
The spores of hypogeous fungi were found in most of the animals analyzed (9/14) regardless of weight, age or sex.In the past, truffles were harvested with female pigs as it was thought that truffle scent resembled that of the male pig's pheromone (To Tuscany 2012).In fact, the steroid 5α-androst-16-en-3α-ol, which is a major component of the boar pheromone (Claus et al. 1981) has been detected in the black truffle (Tuber melanosporum).In the studied area, the lack of preference by female boars for truffles could be explained by the presence of truffle species different from T. melanosporum, which probably do not contain this specific pheromone.
Although most animals revealed the presence of hypogeous fungal spores in the faeces, the abundance of spores was poor, limited to just one or few spores in the amount of sample analyzed.This suggests that the wild boar may occasionally eat truffles and that the main damages in natural and cultivated truffières are mainly due to soil disturbance caused by excavation with the snout (Moreno-Arroyo et al. 2005;Salerni et al. 2011;Ricci 2008).On the opposite, other small mammals, like the northern flying squirrels or some marsupials, just eat truffles or simply prefer to eat truffles, whose spores accumulate in faecal pellets (Lehmkuhl et al. 2004;Claridge, Trappe 2005).According to the Claridge and Trappe (2005) classification of mycophagous animals in obligate, preferential, casual, opportunistic or accidental mycophagists, the wild board can be considered an opportunistic mycophagist, ingesting truffles only occasionally, as a seasonal source of food.
In mycophagous animals, there is an evidence of spore germination stimulation by the passage through the digestive system, although the effect on spore metabolic activities may differ among animals and among hypogeous fungal genera (Trappe, Claridge 2005).In fact, most studies on hypogeus asco-and basidiomycetes report a positive effect on spore germination (Colgan, Claridge 2002;Claridge, Trappe 2005).In contrast Miller (1985) reported that the germination of spores of Tuber spp. was not stimulated by digestive process in rodents.However, all the studies were carried out only on small hydnophagous mammals or marsupials and never considered large mammals like wild boars (Claridge, Trappe 2005).
Wild boars have larger movements than small sized animals, ranging between 2 and 15 km in one night and up to 300 km for males and 100 km for females during seasonal migrations (Andrzejewski, Jezierski 1978;Singer et al. 1981;Defra 2005).Thus, their role in truffle long distance dispersal may be extremely important if the vitality and infectivity of truffle spores after the passage through the digestive tract, are not negatively affected.In this way, it is possible to speculate that wild boars may have played a key role in postglacial recolonization of truffles from Southern refugia (Murat et al. 2004).
Studies are in progress to verify the effects on vitality and infectivity of truffle spores ingested by a pig, as an animal model, to support these conclusions.

Table 2
Wild boar data and characteristics of the spores detected in the faecal material