Trophic preference and preliminary indication of phylloplane fungal influence on the diet of the non-native <em>Gammarus roeselii</em> Gervais 1835 (<em>Amphipoda, Gammaridae</em>) in the sub-lacustrine Ticino river basin (Lombardy, Northern Italy)
10.6092/issn.2531-7342/6796
Gli anfipodi gammaridi, grazie alla loro plasticità in termini di dieta e al loro elevato tasso riproduttivo, possono facilmente colonizzare gli ecosistemi di acqua dolce. Uno di essi, Gammarus roeselii, ha recentemente colonizzato la parte meridionale del bacino sub lacuale del fiume Ticino (Nord Italia), andando ad occupare una nicchia ecologica parzialmente sovrapponibile con quella della specie nativa Echinogammarus stammeri. In questo lavoro sono state analizzate le preferenze trofiche della specie G. roeselii, tramite un esperimento di laboratorio in cui è stata testata l’appetibilità di differenti risorse: tre idrofite e tre tipologie diverse di detrito fogliare. Il detrito fogliare utilizzato durante l’esperimento, inoltre, è stato analizzato in termini di biomassa fungina. I risultati ottenuti hanno evidenziato come le idrofite siano meno appetibili rispetto al detrito fogliare, probabilmente perché ricche di metaboliti secondari (tannini) con minor valore nutritivo e contenenti molta acqua. È invece emerso come G. roeselii manifesti una netta preferenza per le foglie di quercia, risultate colonizzate da una più consistente biomassa fungina e, probabilmente, maggiormente appetibili.
application/pdf
2531-7342
6796
en
Anna Maria Picco
Italian Journal of Mycology
food source
Trophic preference and preliminary indication of phylloplane fungal influence on the diet of the non-native <em>Gammarus roeselii</em> Gervais 1835 (<em>Amphipoda, Gammaridae</em>) in the sub-lacustrine Ticino river basin (Lombardy, Northern Italy)
Text.Serial.Journal
https://italianmycology.unibo.it/
46
Articles
2017-03-30
2017-03-29
2017-01-24
2018-08-20
37-47
Ital J Mycol
Anna Maria Picco
2017/03/30
10.6092/issn.2531-7342/6796
37
University of Pavia
2531-7342
food source
en
47
Trophic preference and preliminary indication of phylloplane fungal influence on the diet of the non-native <em>Gammarus roeselii</em> Gervais 1835 (<em>Amphipoda, Gammaridae</em>) in the sub-lacustrine Ticino river basin (Lombardy, Northern Italy)
https://italianmycology.unibo.it/article/download/6796/6592
46
D. Paganelli, A. Gazzola, M. Rodolfi, R. Sconfietti, A. M.   Italian Journal of Mycology vol. 46 (2017) ISSN 2531-7342
Picco
DOI: https://doi.org/10.6092/issn.2531-7342/6796




  Trophic preference and preliminary indication of
  phylloplane fungal influence on the diet of the non-
  native Gammarus roeselii Gervais 1835
  (Amphipoda, Gammaridae) in the sub-lacustrine
  Ticino river basin (Lombardy, Northern Italy)
  ________________________________________________________________________________

                   Daniele Paganelli1, Andrea Gazzola2, Marinella Rodolfi3,

                                Renato Sconfietti1, Anna Maria Picco3
  1
    Laboratory of Ecology, Department of Earth and Environmental Sciences, University of Pavia, Via S.
  Epifanio 14, 27100 Pavia, Italy
  2
    Laboratory of Eco-ethology, Department of Earth and Environmental Sciences, University of Pavia, Via
  Ferrata 1, 27100 Pavia, Italy
  3
    Laboratory of Mycology, Department of Earth and Environmental Sciences, University of Pavia, Via S.
  Epifanio 14, 27100 Pavia, Italy

  Correspondig Author e-mail: daniele.paganelli@unipv.it

  Abstract

  Gammarids are one of the most successful invaders in freshwater ecosystems due to both their diet plasticity
  and high reproductive capacity. One such amphipod, Gammarus roeselii, has recently colonised the southern
  part of the sub-lacustrine Ticino River basin (Northern Italy), where its ecological niche overlaps with the
  native species Echinogammarus stammeri.
  In the present paper the food preferences of G. roeselii have been investigated, testing the palatability of
  different food sources: three macrophytes and three different leaf debris. Moreover, an explorative
  mycological analysis on the three different leaf debris used in the experiment has been performed. Results of
  the short-term experiment suggest that aquatic plants are less palatable than allocthonous detritus, probably
  because they can contain secondary metabolites (i.e. tannins) and they have lower nutrient tissues with very
  high water content. On the contrary, G. roeselii showed a clear preference for the oak leaves, resulted
  colonized by a more abundant fungal biomass and, therefore, more palatable too.

      Keywords: Gammarus roeselii; trophic behaviour; microfungi; food source


  Riassunto

      Gli anfipodi gammaridi, grazie alla loro plasticità in termini di dieta e al loro elevato tasso riproduttivo,
      possono facilmente colonizzare gli ecosistemi di acqua dolce. Uno di essi, Gammarus roeselii, ha recentemente

                                                                                                                37
D. Paganelli, A. Gazzola, M. Rodolfi, R. Sconfietti, A.            Italian Journal of Mycology vol. 46 (2017) ISSN 2531-7342
M. Picco
DOI: https://doi.org/10.6092/issn.2531-7342/6796




       colonizzato la parte meridionale del bacino sub lacuale del fiume Ticino (Nord Italia), andando ad occupare una
       nicchia ecologica parzialmente sovrapponibile con quella della specie nativa Echinogammarus stammeri.
       In questo lavoro sono state analizzate le preferenze trofiche della specie G. roeselii, tramite un esperimento di
       laboratorio in cui è stata testata l’appetibilità di differenti risorse: tre idrofite e tre tipologie diverse di detrito
       fogliare. Il detrito fogliare utilizzato durante l’esperimento, inoltre, è stato analizzato in termini di biomassa
       fungina. I risultati ottenuti hanno evidenziato come le idrofite siano meno appetibili rispetto al detrito fogliare,
       probabilmente perché ricche di metaboliti secondari (tannini) con minor valore nutritivo e contenenti molta
       acqua. È invece emerso come G. roeselii manifesti una netta preferenza per le foglie di quercia, risultate
       colonizzate da una più consistente biomassa fungina e, probabilmente, maggiormente appetibili.

       Parole chiave: Gammarus roeselii; comportamento trofico; microfunghi; nutrimento

  Introduction

  Gammarids are one of the most successful invaders in freshwater ecosystems, mainly due to their diet
  plasticity: they are shredders of allochtonhous detritus (Cummins and Klug, 1979), herbivores that use
  freshwater macrophytes as a food source (Thiébaut et al., 2008), and predators of other macroinvertebrates
  (Kelly et al., 2002).
  Feeding habits are related to food source availability and quality, and to intra- and interspecific competition
  (Kelly et al., 2002; van Riel et al., 2007). Omnivory is widespread in freshwater gammarids and differences
  in preferred food sources seem likely (Maier et al., 2011).
  Some species, such as the “killer shrimp” Dikerogammarus villosus (Sowinsky 1984), have modified
  mouthparts that are suitable for predator activity, whereas other species, such as Gammarus roeselii Gervais
  1835, are well-suited for grinding plant material and well-adapted for scraping off fungi and other adherent
  biofilm layers from the substratum or decaying plant material (Mayer et al., 2009).
  In small streams, leaf decomposition is an important process carried out by invertebrates and microorganisms
  such as Hyphomycetes (Hieber and Gessner, 2002; Pascoal and Cássio, 2004). As Suberkropp (1992) stated,
  freshwater macroinvertebrates have a preference for foliar tissue associated to a rich mycobiota: for example,
  Gammarus pseudolimnaeus grows better on leaf litter colonised by fungi than on uncolonised leaves and it
  showsa well-defined preference for several fungal assemblages. In particular, the presence of fungi on the
  surface or inner part of leaves can increase their palatability for shredding invertebrates (Graça, 2001).
  Recently, one such successful gammarid invader, Gammarus roeselii (Fig. 1), has colonised the southern
  part of the sub-lacustrine Ticino River basin, from Vigevano (45°20'29.0"N 8°53'03.6"E) to the mouth of the
  Ticino River (45°20'29.0"N 8°53'03.6"E) (Po river floodplain, Northern Italy), where its ecological niche
  overlaps with the native species Echinogammarus stammeri (Karaman 1931). In this area of 150 km2, these
  two species survive in sympatry with dense populations, and their possible competitive interactions (e.g.
  food competition) are still unknown (Paganelli et al., 2015).
  In the present paper, we investigate the food preferences of G. roeselii testing the palatability of different
  food sources and considering the possible role of phylloplane fungi, the mycota growing inside and on the
  surfaces of leaves (Langvad, 1980), as a food source or as a modifier of plant resources.




  38
D. Paganelli, A. Gazzola, M. Rodolfi, R. Sconfietti, A. M.        Italian Journal of Mycology vol. 46 (2017) ISSN 2531-7342
Picco
DOI: https://doi.org/10.6092/issn.2531-7342/6796




                                                                               1.5 mm

  Fig. 1. Specimen of G. roeselii used for the laboratory experiments.
  Fig. 1. Un esemplare di G. roeselii utilizzato per gli esperimenti di laboratorio.

  Materials and methods

  Laboratory experimental design
  In October 2014, specimens of Gammarus roeselii were collected in the Gaviola Stream, one of the small
  right-bank tributaries of the Ticino River (Fig. 2), where we found the highest density of G. roeselii
  compared to other small streams in the sub-lacustrine Ticino River basin (unpublished data).




  Fig. 2. Sample site of G. roeselii specimens. The Gaviola Stream (grey rectangle; 1:75000), one of the right-bank
  tributaries of the Ticino River (45°11′27.4″N 09°04′03.7″E, WGS84).
  Fig. 2. Sito di campionamento degli esemplari di G. roeselii. La roggia Gaviola (rettangolo grigio; 1:75000), uno degli
  immissari di sponda destra del Fiume Ticino (45°11′27.4″N 09°04′03.7″E, WGS84).

  Moreover, based on their availability and abundance in the stream during the survey, we collected six
  different food sources: three macrophytes [Myriophyllum spicatum L., Elodea nuttallii (Planch.) H. St. John,
                                                                                                                      39
D. Paganelli, A. Gazzola, M. Rodolfi, R. Sconfietti, A.     Italian Journal of Mycology vol. 46 (2017) ISSN 2531-7342
M. Picco
DOI: https://doi.org/10.6092/issn.2531-7342/6796



  Veronica anagallis-aquatica L.] and well-preserved tree leaf debris from three different species (oak -
  Quercus robur L., maple - Acer pseudoplatanus L., black locust - Robinia pseudoacacia L.).
  Once in the laboratory, the gammarids were acclimatised in dechlorinated tap water and were not fed for 48
  hours, while leaf debris and macrophytes were gently cleaned in order to remove the biofilm layer that
  usually covers aquatic plants and increases their palatability.
  This gentle cleaning of the food sources removed and de-activated both superficial inorganic contaminants
  and fungal propagules that may stick to the leaves. However, it does not influence the fungal communities
  associated to the leaf debris as they live inside the foliar tissue. Hyphae, mycelia and spores that are systemic
  in tissues maintain their morphological characteristics (e.g. texture, pigmentation, nutritional value) and their
  palatability.
  For the experiment, we set up a controlled environmental setting with a constant temperature of 18°C and a
  photoperiod of 10 hours of light and 14 hours of dark per day for a seven-day period.
  Each experimental unit (glass Petri dishes: 12 cm diameter, 2 cm high) was filled with 125 ml of
  dechlorinated tap water, as suggested by Maier et al. (2011). According to Boiché et al. (2010), the use of
  dechlorinated tap water, instead of water collected in-situ, can prevent possible alterations of the water due to
  bacteria and nitrogen compounds.
  The experimental design included a control with no available food sources and six treatments with M.
  spicatum, E. nuttallii, V. anagallis-aquatica, Q. robur, A. pseudoplatanus and R. pseudoacacia leaf debris
  (three replicates for each treatment, overall 21 experimental units). A total of 126 specimens, divided into
  groups of six adult gammarids of either sex (body length: 10-12mm), were placed in each experimental unit
  and were fed ad libitum with only one food source.
  During some preliminary tests, we tried to weigh the food sources at the beginning and at the end of the
  experiment, but it did not give reliable results because the photosynthesis activity of the hydrophytes
  produced a biomass increase interfering with the biomass consumed by grazing; for gammarids, the necessity
  to have the initial weight of the living specimens prevented us from using the dry weight as an accurate
  parameter to measure small weight increases, therefore in accordance with Pӧckl et al. (2003), we used the
  gammarids’ wet weight as an indication of the feeding rate. To avoid significant errors when measuring
  single individuals, and considering the similar size of the specimens, we fresh-weighted the whole group of
  six gammarids at the beginning of the experiment and the whole group of gammarids that had survived at the
  end for each replicate, using a laboratory precision balance (KERN ALJ 220_4; 0,000 g), in order to
  calculate the mean individual percentage of growth (G): the mean individual initial weight of the six
  gammarids was subtracted from the mean individual final weight of the surviving gammarids after the 7 day-
  experiment and then this result was divided by the mean individual initial weight of the six gammarids.
  Throughout the experiment, units were checked and dead specimens were removed twice daily, in order to
  reduce the effect of potential necrophagy, observed occasionally during our preliminary tests.
  Investigation of phylloplane fungi
  In order to investigate the potential role of fungi in the gammarids’ diet, an explorative mycological analysis
  was performed on the three different types of leaf debris collected in the Gaviola Stream: oak, maple and
  black locust. Five leaves from each species were gently washed with tap water and then immersed in sterile
  water (Dickinson, 1971). Subsequently, they were separately (i.e. one leaf in one dish) placed onto 90 mm
  Petri dishes containing Tap-Water Agar (TWA) to provide the necessary humidity and favour the growth of
  microfungi living in association with foliar tissue (Waller, 2002). Samples were maintained at room
  temperature (19±2°C) in natural day/night conditions for 30 days and constantly observed at low
  magnification (stereomicroscope 10-50x). All resulting fungal colonies were identified on the basis of their
  40
D. Paganelli, A. Gazzola, M. Rodolfi, R. Sconfietti, A. M.     Italian Journal of Mycology vol. 46 (2017) ISSN 2531-7342
Picco
DOI: https://doi.org/10.6092/issn.2531-7342/6796



  micro-morphology by means of specific taxonomical keys (Domsch et al., 1980; Ellis and Ellis, 1985;
  Leslie and Summerell, 2006), and the fungal biomass that had developed was expressed in terms of
  abundance of mycelia with or without fructifications.
  Although the aim of this analysis was to investigate fungal colonisation, observations of Actinomycetes and
  any other unidentified bacteria were also recorded.
  Statistical analyses
  All the statistical analyses were performed using MINITAB 16 software package. Food preferences were
  investigated through a General Linear Model, an ANOVA procedure in which the calculations are performed
  using a least squares regression approach to describe the statistical relationship between one or more
  predictors and a continuous response variable.
  Anderson-Darling and Bartlett tests were used prior to GLM to check the normality of data and the
  homogeneity of variance. Finally, pairwise Tukey post hoc tests were performed in order to determine which
  set of data mainly contribute to the differences found by GLM.

  Results

  Food preferences
  During the 7-day period, a total of 25% of the specimens died (Tab. 1); however, the results of the
  experiment indicated that a weight increase was obtained when gammarids were fed with Q. robur (40.38%),
  A. pseudoplatanus (15.44%), V. anagallis-aquatica (11.69%) and E. nuttallii (2.05%), but not when they
  were fed with R. pseudoacacia (-5.85%) or M. spicatum (-6.34%) (Tab. 1 and Fig. 3).
  A GLM analysis indicated a statistical increase in G. roeselii’s weight when they were fed with leaf debris
  (DF = 3; F = 5.15; p: 0.028) compared to aquatic plants (DF = 3; F = 0.93; p: 0.468). Tukey tests highlighted
  that only specimens that had been fed with Q. robur had a significant weight (Tab. 3).

  Tab. 1. Mean initial, final weight and weight percentage growth (±standard deviation) recorded at the beginning and at
  the end of the seven-day experiment. Ni: initial number of specimens; Nf: final number of specimens; CTRL: control
  groups; E: E. nuttallii; M: M. spicatum; V: V. Anagallis-aquatica; Q: Q. robur; A: A. pseudoplatanus; R: R.:
  pseudoacacia.
  Tab. 1. Peso medio iniziale, finale e percentuale di crescita (± deviazione standard) registrati all’inizio e alla fine
  dell’esperimento durato 7 giorni. Ni: numero iniziale di individui; Nf: numero finale di individui; CTRL: gruppo di
  controllo; E: E. nuttallii; M: M. spicatum; V: V. Anagallis-aquatica; Q: Q. robur; A: A. pseudoplatanus; R: R.
  pseudoacacia.

                                     Mean individual                             Mean individual     Mean individual
               Total Mean initial                            Total Mean final
         Ni                           initial weight Nf                           final weight      weight growth ± sd
               weight ± sd (mg)                                weight (mg)
                                           (mg)                                       (mg)                 (%)
  CTRL   18   200.13±27.22          11.12              10   103.10±42.07         10.31             -6.30±11.58
  E      18   205.67±63.19          11.43              14   157.93±43.93         11.28             2.05±21.44
  M      18   196.43±44.42          10.91              14   142.80±48.45         10.20             -6.34±15.97
  V      18   201.27±75.97          11.18              15   183.47±56.17         12.23             11.69±9.77
  Q      18   207.53±53.19          11.53              12   190.13±60.79         15.84             40.38±27.67
  A      18   181.60±37.47          10.09              14   157.37±38.39         11.24             15.44±0.65
  R      18   270.07±56.37          15.00              16   223.47±51.02         13.97             -5.85±15.43



                                                                                                                      41
D. Paganelli, A. Gazzola, M. Rodolfi, R. Sconfietti, A.        Italian Journal of Mycology vol. 46 (2017) ISSN 2531-7342
M. Picco
DOI: https://doi.org/10.6092/issn.2531-7342/6796




  Fig. 3. Weight percentage growth (G) of Gammarus roeselii registered at the end of the experiment (7days). Letters
  indicate type of food: E: E. nuttallii; M: M. spicatum; V: V. Anagallis-aquatica; Q: Q. robur; A: A. pseudoplatanus; R:
  R: pseudoacacia; CTRL: control groups.
  Fig. 3. Percentuale di incremento di peso (G) di Gammarus roeselii registrato alla fine dell’esperimento (7giorni). Le
  lettere indicano la tipologia di cibo: E: E. nuttallii; M: M. spicatum; V: V. Anagallis-aquatica; Q: Q. robur; A: A.
  pseudoplatanus; R: R: pseudoacacia; CTRL: gruppi di controllo.


  Tab. 2. Results of pairwise Tukey post hoc tests (T) and relative p-values (NS: not significant; *: p < 0.05) of the
  gammarids’ weight increase when fed with different food sources compared to the control groups. CTRL: control
  groups; E: E. nuttallii; M: M. spicatum; V: V. Anagallis-aquatica; Q: Q. robur; A: A. pseudoplatanus; R: R.
  pseudoacacia.
  Tab. 2. Risultati del Tukey post hoc test (T) e relativa significatività statistica (NS: non significativo; *: p < 0.05)
  dell’incremento di peso dei gammaridi alimentati con le diverse fonti di cibo comparati con i gruppi di controllo.
  CTRL: gruppi di controllo; E: E. nuttallii; M: M. spicatum; V: V. Anagallis-aquatica; Q: Q. robur; A: A.
  pseudoplatanus; R: R. pseudoacacia.

                                        T-test           p value    Statistical significance
                              CTRL vs E T=0.66           p: 0.90    NS
                              CTRL vs M T=-0.003         p: 1.00    NS
                              CTRL vs V T=1.43           p: 0.51    NS
                              CTRL vs Q T=3.38           p: 0.03    *
                              CTRL vs A T=-1.57          p: 0.44    NS
                              CTRL vs R T=0.032          p: 1.00    NS



  Phylloplane fungi
  A total of 9 fungal taxa were isolated from the leaf samples (Tab. 3).
  Two species grew on all tree samples: Alternaria alternata (Fr.) Keissl (Fig. 4a), a common saprophyte of
  plant material, and Cladosporium cladosporioides (Fresen.) G. A. de Vries, a ubiquitous fungus and
  secondary invader of damaged plants. The former species had abundant and fructifying mycelium, and the
  latter had a low presence of single conidiophores.
  In addition to these two phylloplane fungal species that grew on all samples, Q. robur was also colonised by
  another four taxa: the highly abundant Fusarium verticillioides (Sacc.) Nirenberg, which is able to establish a
  42
D. Paganelli, A. Gazzola, M. Rodolfi, R. Sconfietti, A. M.    Italian Journal of Mycology vol. 46 (2017) ISSN 2531-7342
Picco
DOI: https://doi.org/10.6092/issn.2531-7342/6796


  Tab. 3. Microfungi and microorganism colonisers of leaves grazed by gammarids. Five leaves from each species were
  investigated. The quantity of mycelia and/or fructification that had developed were expressed in terms of
  abundance:+: single or few fungal structures; ++: abundant fungal structures emerging from the leaves; +++:
  very abundant fungal structures, almost totally covering the surface of leaves.
  Tab. 3. Microfunghi e microorganismi colonizzatori delle foglie consumate dai gammaridi. Sono state
  analizzate 5 foglie per ciascuna specie. La quantità di micelio sviluppatasi è stata espressa in termini di
  abbondanza: +: poco abbondante; ++: abbondante; +++: molto abbondante, ricoprente la quasi intera superficie
  fogliare.

                                                     Quercus                 Acer                   Robinia
  Fungal taxa and microorganisms
                                                     robur              pseudoplatanus           pseudoacacia
  Alternaria alternata (Fr.) Keissl.                     +++                 +++                      ++
  Botrytis cinerea Pers.                                   -                 +++                       -
  Chaetomium globosum Kunze                                -                  -                        +
  Cladosporium cladosporioides (Fresen.) G.A.
                                                              +                 +                       +
  de Vries
  Epicoccum nigrum Link                                        +                -                       +
  Fusarium verticillioides (Sacc.) Nirenberg                 +++                -                       -
  Periconia byssoides Pers.                                    -                -                       +
  Phoma eupyrena Sacc.                                        ++                -                       +
  Trichoderma atroviride P. Karst.                             +                -                       +
  Actinomycetes                                                -                -                      +++
  Bacteria                                                     -                -                       +

  wide range of interactions with plants, from parasitic to devastating; the moderately abundant Phoma
  eupyrena Sacc., a potentially phytopathogenic fungus; the scarce Epicoccum nigrum Link, an early
  secondary invader of plants; Trichoderma atroviride P. Karst, a cosmopolitan fungus primarily living in soil.
  Robinia pseudoacacia shared five of its seven taxa with Q. robur, but all fungi showed a low presence
  except for A. alternata. Among these fungi, Periconia byssoides Pers., often isolated from blackened areas of
  leaf and stems, and Chaetomium globosum Kunze (Fig. 4b), a cellulolytic fungus of soil and decaying plants,
  were only observed on R. pseudoacacia, which also hosted Actinomycetes and Bacteria.
  Finally, Botrytis cinerea Pers. (Fig. 4c), a cosmopolitan pectinolytic fungus which damages leaves and other
  parts of various plants, developed with high fertile biomass exclusively on A. pseudoplatanus.




  Fig. 4. a. Conidia of Alternaria alternata (40x); b. Ascomata of Chaetomium globosum (5x); c. Conidiophore of
  Botrytis cinerea (25x).
  Fig. 4. a. Conidi di Alternaria alternata (40x); b. Ascomi di Chaetomium globosum (5x); c. Conidioforo di Botrytis
  cinerea (25x).

                                                                                                                 43
D. Paganelli, A. Gazzola, M. Rodolfi, R. Sconfietti, A.   Italian Journal of Mycology vol. 46 (2017) ISSN 2531-7342
M. Picco
DOI: https://doi.org/10.6092/issn.2531-7342/6796



  Discussion and conclusion

  The Gaviola Stream, with its highly abundant aquatic vegetation, provides a suitable habitat for both
  gammarids that are present, i.e. the native E. stammeri and the alien G. roeselii, as demonstrated by their
  dense populations found during our surveys.
  Although Dehedin et al. (2013) discovered that G. roeselii and another two crustacean species (Asellus
  aquaticus and Gammarus pulex) prefer the submerged leaves of aquatic plants to other food sources, our
  results reveal a substantial rejection for M. spicatum and E. nuttallii. Myriophyllum spicatum is known to be
  a tannin-rich aquatic plant and a low quality food source (Li et al., 2004; Orav-Kotta et al., 2009; Wong et
  al., 2010). It contains a high level of phenolic, which can reduce the growth rate and feeding rate of
  herbivores (Choi et al., 2002; Boland et al., 2008; Qiu and Kwong, 2009). Aquatic plants can also contain
  secondary metabolites (i.e. tannins) and they have lower nutrient tissues with higher water content than other
  plants. Tannins are a deterrent for macroinvertebrates and they can also interfere with the growth and
  development of some herbivorous insects (Smolders, 2000; Choi et al., 2002; Elger and Willby, 2003; Parker
  and Hay, 2005).
  Furthermore, other studies have demonstrated that Elodea nuttallii, despite its high nitrogen content, can
  produce chemical defences (i.e. flavonoids) against herbivorous freshwater macroinvertebrates (Erhard et al.,
  2007) and has an intense allelopathic activity against epiphytes (Erhard and Gross, 2006). All these traits
  might explain the low palatability of these aquatic plants.
  A small weight increase was observed for V. anagallis-aquatica, notwithstanding the lack of statistical
  relevance.
  The generalised preference for allogenous detritus vs aquatic plants that emerges from our investigations is
  mainly supported by the marked palatability shown for oak leaves, because the growth of the gammarids’
  weight waslow and not statistically significant for maple leaves, and negative for locust leaves. This food
  preference disagrees with the observations by Macneil et al. (1997), who stated that another gammarid
  species, i.e. Gammarus pulex, had a very low shredding capacity for oak leavesbecause they are hard and
  rich in tannins and thus not very palatable.
  Macroinvertebrates generally consume hard leaves less than soft leaves (Li and Dudgeon, 2008; Ratnarajah
  and Barmuta, 2009). Moreover, according to Abelho (2008) and Foucreau et al. (2013), soft leaves are
  readily available to macroinvertebrates, whereas hard leaves may be used as a reserve of organic matter for
  the rest of the year.
  In our study, the oak leaves hosted a very abundant phylloplane fungal biomass; fungi are notorious for
  being an important component of the food supply to many animals (Shaw, 1992; Graça et al., 1993; Graça,
  2001; Sterner and Elser, 2002; Cross et al., 2005), due to their high levels of proteins and vitamins. As
  reported by Reddy and Das (1983) and Aßmann et al. (2011), fungi improve the nutritional quality of leaf
  debris for shredders, and different fungi may have different nutritional values, with some species being more
  beneficial and others detrimental to population growth. Furthermore, the presence of fungi on the surface and
  inner part of leaf debris makes it more palatable or energy-rich, increasing the level of N and P (Aßmann et
  al., 2011).
  The nutritional value of phylloplane fungi cannot be neglected: they are an important source of
  carbohydrates, proteins, minerals, nucleoproteins and glycoprotein structural components of the whole
  fungal body (Bowman and Free, 2006).
  Considering the gammarids’ clear preference for oak detritus and the high abundance of the phylloplane
  fungi within these leaves, we hypothesise that fungi play a role in this selective choice.


  44
D. Paganelli, A. Gazzola, M. Rodolfi, R. Sconfietti, A. M.   Italian Journal of Mycology vol. 46 (2017) ISSN 2531-7342
Picco
DOI: https://doi.org/10.6092/issn.2531-7342/6796



  Another two characteristics that can favour grazing on allogenous leaves are: (i) leaf debris is much more
  digestible than aquatic plants because bacteria have already started decomposing the organic matter (Abelho,
  2001; Albelho, 2008); (ii) long exposure to stream water may reduce the effect of the toughness and tannins
  of leaf debris (Foucreau et al., 2013; Cornut et al., 2015).
  The preference for leaf debris over macrophytes is probably due to the different food sources we chose to use
  in our experiment and may also be related to local conditions which can make the former food source more
  palatable than the latter.
  In conclusion, this study can be considered as a preliminary assessment of the trophic behaviour of G.
  roeselii to be followed by future experiments that will compare the competition for food between the non-
  native species G. roeselii and the native E. stammeri. Furthermore, the mycological investigation we carried
  out could become the basis for future inoculation tests to delineate the fungal potentiality as a rich food
  source and/or as a useful modifier of plant resources, in order to provide a better understanding of the largely
  unknown influence of fungi on animal communities.

  Acknowledgements

  We express our thanks to Dr. Nicola M.G. Ardenghi for the identification of the freshwater plants and to
  Charlotte Buckmaster for the linguistic revision of the English text.

  References

  Abelho M. (2001). From litter fall to breakdown in streams: a review. The Scientific World Journal 1, 656-
      680.
  Abelho M. (2008). Effects of leaf litter species on macroinvertebrate colonization during decomposition in a
      Portuguese stream. International Review of Hydrobiology, 93, 358-371.
  Aßmann C., Rinke K., Nechwatal J., von Elert E. (2011). Consequences of the colonisation of leaves by
     fungi and oomycetes for leaf consumption by a gammarid shredder. Freshwater Biology, 56, 839-852.
  Boiché A., Gierlinski P., Thiébaut G. (2010). Contrasting seasonal patterns in the acceptability of a
      naturalised and an introduced macrophytes for a generalist shredder. Fundamental and Applied
      Limnology, 177 (2), 133-141.
  Boland B.B., Meerhoff M., Fosalba C., Mazzeo N., Barnes M.A., Burks R.L. (2008). Juvenile snails, adult
      appetites: contrasting resource consumption between two species of apple snails (pomacea). Journal of
      Molluscan Studies, 74, 47-54.
  Bowman S.M., Free S.J. (2006). The structure and synthesis of the fungal cell wall. Bioessays, 28, 8, 799-
     808.
  Choi C., Bareiss C., Walenciak O., Gross E.M. (2002). Impact of polyphenols on growth of the aquatic
      herbivore Acentria ephemerella. Journal of Chemical Ecology, 28, 2245-2256.
  Cornut J., Ferreira V., Goncalves A.L., Chauvet E., Canhoto C. (2015). Fungal alteration of the elemental
      composition of leaf litter affects shredder feeding activity. Freshwater Biology, 60, 9, 1755-1771.
  Cross W.F., Benstead J.P., Frost P.C., Thomas S.A. (2005). Ecological stoichiometry in freshwater benthic
      systems: recent progress and perspectives. Freshwater Biology, 50, 1895-1912.
  Cummins K.W., Klug M.J. (1979). Feeding ecology of stream invertebrates. Annual Review of Ecology,
     Evolution and Systematics, 10, 147-172.
  Dehedin A., Maazouzi C., Puijalon S., Marmonier P., Piscart C. (2013). The combined effects of water level
      reduction and increase in ammonia concentration on organic matter processing by key freshwater
      shredders in alluvial wetlands. Global Change Biology, 19, 763-774.
  Dickinson C.H. (1971). Cultural studies of leaf saprophytes. In: T.F. Preece and C.H. Dickinson, Ecology of
      leaf surface microorganisms. Academic Press, London, UK, 129-137.

                                                                                                               45
D. Paganelli, A. Gazzola, M. Rodolfi, R. Sconfietti, A.   Italian Journal of Mycology vol. 46 (2017) ISSN 2531-7342
M. Picco
DOI: https://doi.org/10.6092/issn.2531-7342/6796


  Domsch K.H., Gams W., Anderson T.H. (1980). Compendium of soil fungi. Academic Press, London, UK,
     865 pp.
  Elger A., Willby N.J. (2003). Leaf dry matter content as an integrative expression of plant palatability: the
       case of freshwater macrophytes. Functional Ecology, 17, 58-65.
  Ellis M.B., Ellis J.P. (1985). Microfungi on land plants. An identification handbook. The Richmond
       publishing co. Ltd., Slough, UK, 868 pp.
  Erhard D., Gross E.M. (2006). Allelopathic activity of Elodea canadensis and Elodea nuttallii against
       epiphytes and phytoplankton. Aquatic Botany, 85, 203-211.
  Erhard D., Pohnert G., Gross E.M. (2007). Chemical defence in Elodea nuttallii reduces feeding and growth
       of aquatic herbivorous lepidoptera. Journal of Chemical Ecology, 33, 1646-1661.
  Foucreau N., Puijalon S., Hervant F., Piscart C. (2013). Effect of leaf litter characteristics on leaf
      conditioning and on consumption by Gammarus pulex. Freshwater Biology, 58, 1672-1681.
  Gessner M.O., Suberkropp K., Chauvet E. (1997). Decomposition of plant litter by fungi in marine and
      freshwater ecosystems. In: D.T. Wicklow and B. Soderstrom, The mycota IV: Environmental and
      microbial relationship. Springer-Verlag, Berlin, 303-322.
  Graça M.A.S. (2001). The role of invertebrates on leaf litter decomposition in streams: a review.
      International Review of Hydrobiology, 86, 383-393.
  Graça M.A.S., Maltby L., Calow P. (1993). Importance of fungi in the diet of Gammarus pulex and Asellus
      aquaticus. Effects on growth, reproduction and physiology. Oecologia, 96, 304-309.
  Hieber M., Gessner M.O. (2002). Contribution of stream detritivores, fungi, and bacteria to leaf breakdown
      based on biomass estimates. Ecology, 83, 1026-1038.
  Kelly D.W., Dick T.A., Montgomery W.I. (2002). The functional role of Gammarus (Crustacea,
       Amphipoda): shredders, predator, or both? Hydrobiologia, 485, 199-203.
  Langvad F. (1980). A simple and rapid method for qualitative and quantitative study of the fungal flora of
      leaves. Canadian Journal of Botany, 26, 666-670.
  Leslie J.F., Summerell B.A. (2006). The Fusarium laboratory manual. Blackwell publishing, Oxford, UK,
       388 pp.
  Li Y., Yun D., Yan X. (2004). Are polyphenolics valuable in anti-herbivory strategies of submersed
      freshwater macrophytes? Archiv für Hydrobiologie, 161-8,3, 391-402.
  Li A.O.Y., Dudgeon D. (2008). The effects of leaf litter characteristics on feeding and fitness of a tropical
      stream shredder, Anisocentropus maculatus (Trichoptera: Calamoceratidae). Marine and Freshwater
      Research, 59, 897-901.
  Macneil C., Dick J.T.A., Elwood R.W. (1997). The trophic ecology of freshwater Gammarus spp.
      (Crustacea: Amphipoda): problems and perspectives concerning the functional feeding group concept.
      Biological Reviews, 72, 349-364.
  Maier G., Kley A., Schank Y., Maier M., Mayer G., Waloszek D. (2011). Density and temperature
      dependent feeding rates in an established and alien freshwater gammarid fed on chironomid larvae.
      Journal of Limnology, 70,1, 123-128.
  Mayer G., Maier A., Maas A., Waloszek D. (2009). Mouth-part morphology of Gammarus roeselii
      compared to a successful invader, Dikerogammarus villosus (Amphipoda). Journal of Crustacean
      Biology, 29, 161-174.
  Orav-Kotta H., Kotta J., Herkül K., Kotta I., Paalme T. (2009). Seasonal variability in the grazing potential
      of the invasive amphipod Gammarus tigrinus and the native amphipod Gammarus salinus in the
      Northern Baltic Sea. Biological Invasions, 11, 597-608.
  Paganelli D., Gazzola A., Marchini A., Sconfietti R. (2015). The increasing distribution of Gammarus
      roeselii Gervais, 1835: first record of the non-indigenous freshwater amphipod in the sub-lacustrine
      Ticino River basin (Lombardy, Italy). Bioinvasion Record, 4,1, 37-41.
  Parker J.D., Hay M.E. (2005). Biotic resistance to plants invasions? Native herbivores prefer non-native
       plants. Ecological Letters, 8, 959-967.


  46
D. Paganelli, A. Gazzola, M. Rodolfi, R. Sconfietti, A. M.   Italian Journal of Mycology vol. 46 (2017) ISSN 2531-7342
Picco
DOI: https://doi.org/10.6092/issn.2531-7342/6796


  Pascoal C., Cássio F. (2004). Contribution of fungi and bacteria to leaf litter decomposition in a polluted
      river. Applied and Environmental Microbiology, 70, 5266-5273.
  Pӧckl M., Webb B.W., Sutcliffe D.W. (2003). Life history and reproductive capacity of Gammarus fossarum
      and G. roeselii (Crustacea, Amphipoda) under naturally fluctuating water temperatures: a simulation
      study. Freshwater Biology, 48, 53-66.
  Qiu J.W., Kwong K.L. (2009). Effects of macrophytes on feeding and life-history traits of the invasive apple
       snail Pomacea canaliculata. Freshwater Biology, 54, 1720-1730.
  Ratnarajah L., Barmuta L.A. (2009). The effects of leaf toughness on feeding preference by two Tasmanian
      shredders. Hydrobiologia, 636, 173-178.
  Reddy M.V., Das P.K. (1983). Microfungal food preference of soil microarthropods in a pine plantation
      ecosystem. Journal of Soil Biology and Ecology, 3, 1-6.
  Shaw P.J.A. (1992). Fungi, fungivores, and fungal food webs. In: G.C. Carrol and D.T. Wicklow, The fungal
      community: its organization and role in the ecosystem. Marcel Dekker, New York, 295-310.
  Smolders A.J.P., Vergeer L.H.T., Van der Velde G., Roelofs J.G.M. (2000). Phenolic contents of submerged,
      emergent and floating leaves of aquatic and semi-aquatic macrophytes species: why do they differ?
      Oikos, 91, 307-310.
  Sterner R.W., Elser J.J. (2002). Ecological stoichiometry: the biology of elements from molecules to the
       biosphere. Paperback, Princeton University Press, New Jersey, USA, 464 pp.
  Suberkropp K. (1992). Interaction with invertebrates. In: F. Barlocher, The ecology of aquatic
      Hyphomycetes. Springer, Berlin/Heidelberg, 118-134.
  Thiébaut G., Gierlinski P. (2008). Gammarid (Crustacea: Amphipoda) herbivory on native and alien
      freshwater macrophytes. In: B. Tokarska-guzik, J.H. Brock, G. Brundu, L. Child, P. Pys̆ ek, Plant
      invasions: human perception, ecological impacts and management. Backhuys Publishers, Leiden, 333-
      340.
  Van Riel M.C., Healy E.P., Van der Velde G., Bij de Vaate A. (2007). Interference competition among
      native and invader amphipods. Acta Oecologica, 31, 282-289.
  Waller J.M. (2002). Detection and isolation of fungal and bacterial pathogens. In: J.M. Waller, J.M. Lenné,
      S.J. Waller, Plant Pathologist’s Pocketbook. CABI Bioscience, Egham, Surrey, UK, 208-215.
  Wong P.K.., Liang Y., Liu N.Y., Qiu J.W. (2010). Palatability of macrophytes to the invasive freshwater
     snail Pomacea caniculata: differential effects of multiple plant traits. Freshwater Biology, 55, 2023-
     2031.




                                                                                                              47
