some cases the leaves are redried and soaked in water before feeding them to the
organisms (Agatz et al. 2014; Blarer and Burkhardt-Holm 2016; Bundschuh et al.
2011b, 2013, 2017; Naylor et al. 1989), in order to prevent them from floating on the
surface. In this case, the drying process requires the use of an oven, but unsurprisingly the time and temperature used vary between research groups. Bear in mind that
the same food might be provided during the acclimation period and also during the
experiment itself, unless the feeding experiment aims to study the feeding variation
when a food source is either contaminated or compromised. In these studies, a
specific contaminant or mixture of contaminants are usually incorporated during
the conditioning process (Bundschuh et al. 2009; Hahn and Schulz 2007). When the
conditioned leaves are oven-dried, they need to be resoaked in water before being
provided to the organisms, in order to avoid floatation (e.g. Bundschuh et al. 2017;
Zubrod et al. 2010). The water used to soften the leaves varies between research
groups, and the water could act as a new source of contamination, especially if it
differs from the one used during the original conditioning process.
4 Exposure and Feeding Rate Calculation
After the conditioning process and the acclimation period, the next step in a feeding
study is the exposure itself. During this time, the Gammarids are exposed directly
(i.e. the contaminant is in the water with the Gammarus spp.) (Zubrod et al. 2010) or
indirectly (i.e. the contaminant is added during the conditioning process)
(Bundschuh et al. 2009) to a contaminant, and their feeding behaviour is studied
and estimated (see Table 3). These experiments might have different goals: they
might be undertaken to either measure the changes in Gammarid feeding activity,
Gammarid feeding preferences, or to study the effects on their growth. Consequently, the period of exposure could vary dramatically from a few hours
(Bundschuh et al. 2011a) to a week (Felten et al. 2008a) or even several weeks
(Weber et al. 2018), and sometimes fungal biomass analysis (estimated as ergosterol) and assimilation are incorporated, to strengthen the findings obtained from the
feeding rate (Bundschuh et al. 2009; Newton et al. 2018).
Occasionally in feeding studies, the organisms undergo a period of starvation
before the experiment is undertaken (De Castro-Català et al. 2017) (see Table 3). The
main purpose of this starvation phase is to ensure that the organisms are at the same
hunger state, but the duration of this phase varies in the literature. Once the
experiment starts, the Gammarids are commonly provided with a precise amount
of food, in other words the leaves provided have usually been dried, weighed and
conditioned. This latter step, as previously mentioned, could have been carried out
before the drying process or afterwards, so the final product could have different
characteristics depending on the study. In order to provide the organisms with the
same amount of food, the leaves are cut in small discs that range from a diameter of
0.7 to 4 cm depending on the research group (see Table 3). Before or after the
conditioning process, the leaf discs are oven-dried for a specific period of time,
24
G. Consolandi et al.
organisms (Agatz et al. 2014; Blarer and Burkhardt-Holm 2016; Bundschuh et al.
2011b, 2013, 2017; Naylor et al. 1989), in order to prevent them from floating on the
surface. In this case, the drying process requires the use of an oven, but unsurprisingly the time and temperature used vary between research groups. Bear in mind that
the same food might be provided during the acclimation period and also during the
experiment itself, unless the feeding experiment aims to study the feeding variation
when a food source is either contaminated or compromised. In these studies, a
specific contaminant or mixture of contaminants are usually incorporated during
the conditioning process (Bundschuh et al. 2009; Hahn and Schulz 2007). When the
conditioned leaves are oven-dried, they need to be resoaked in water before being
provided to the organisms, in order to avoid floatation (e.g. Bundschuh et al. 2017;
Zubrod et al. 2010). The water used to soften the leaves varies between research
groups, and the water could act as a new source of contamination, especially if it
differs from the one used during the original conditioning process.
4 Exposure and Feeding Rate Calculation
After the conditioning process and the acclimation period, the next step in a feeding
study is the exposure itself. During this time, the Gammarids are exposed directly
(i.e. the contaminant is in the water with the Gammarus spp.) (Zubrod et al. 2010) or
indirectly (i.e. the contaminant is added during the conditioning process)
(Bundschuh et al. 2009) to a contaminant, and their feeding behaviour is studied
and estimated (see Table 3). These experiments might have different goals: they
might be undertaken to either measure the changes in Gammarid feeding activity,
Gammarid feeding preferences, or to study the effects on their growth. Consequently, the period of exposure could vary dramatically from a few hours
(Bundschuh et al. 2011a) to a week (Felten et al. 2008a) or even several weeks
(Weber et al. 2018), and sometimes fungal biomass analysis (estimated as ergosterol) and assimilation are incorporated, to strengthen the findings obtained from the
feeding rate (Bundschuh et al. 2009; Newton et al. 2018).
Occasionally in feeding studies, the organisms undergo a period of starvation
before the experiment is undertaken (De Castro-Català et al. 2017) (see Table 3). The
main purpose of this starvation phase is to ensure that the organisms are at the same
hunger state, but the duration of this phase varies in the literature. Once the
experiment starts, the Gammarids are commonly provided with a precise amount
of food, in other words the leaves provided have usually been dried, weighed and
conditioned. This latter step, as previously mentioned, could have been carried out
before the drying process or afterwards, so the final product could have different
characteristics depending on the study. In order to provide the organisms with the
same amount of food, the leaves are cut in small discs that range from a diameter of
0.7 to 4 cm depending on the research group (see Table 3). Before or after the
conditioning process, the leaf discs are oven-dried for a specific period of time,
24
G. Consolandi et al.