Gergs and Rothhaupt 2008; Graça et al. 1993a, b; Hahn and Schulz 2007; Lahive
et al. 2015; Taylor et al. 1993; Weber et al. 2018; Xuereb et al. 2009; Zubrod et al.
2017) (see Table 1).
As a rule, and not only in feeding studies, gravid females and organisms affected
by the acanthocephalan parasite are usually excluded from experiments (Agatz et al.
2014; Alonso et al. 2009; Blarer and Burkhardt-Holm 2016; Bundschuh et al. 2011b,
2013; Forrow and Maltby 2000; Zubrod et al. 2015, 2017) unless they are specifically chosen for the purpose of the study (Agatz and Brown 2014; Pascoe et al.
1995). Alonso et al. (2009) developed a feeding study using the Multispecies
Freshwater Biomonitor, and neither length nor sex influenced the feeding activity
of either sex of Gammarus pulex. However, it is debatable whether these results
might only be applicable to the type of contaminant used in the investigation, as
some contaminants might affect male and female Gammarid feeding behaviour in
different ways.
3 Food Preparation
The food source selected for an experiment using Gammarids is important, but
especially so for feeding studies, both in the acclimation period and in the experiment itself. Gammarids are shredder detritivores, and they usually feed on conditioned organic material, in other words material that has been colonised by
microorganisms, such as leaf litter. In the natural environment, freshly abscised
leaves are colonised by fungi and then by bacteria (Baldy et al. 1995), which
facilitate the decomposition process and transform the material, making it more
palatable and accessible to the organisms (Bärlocher and Kendrick 1975; Cummins
1974; Gessner et al. 1999).
Gammarus spp. have displayed selective behaviour towards leaf species and their
conditioning level (Agatz and Brown 2014; Graça et al. 1993a, b, 2001) and the type
of fungi (Arsuffi and Suberkropp 1989). Interestingly, Graça et al. (2001) compared
food preferences of shredders from temperate (Gammarus pulex and Sericostoma
vittatum) and tropical (Nectopsyche argentata and Phylloicus priapulus) streams.
When provided with conditioned and/or unconditioned leaves from either a temperate (Alnus glutinosa) or tropical (Hura crepitans) country, Gammarus pulex showed
a significant preference for the conditioned leaves compared to unconditioned leaves
of the same species. Leaves are characterised by different hardness, texture and more
importantly by dissimilar C:N ratios, which means the various leaf species provide
the organisms with differing energy supplies. A lower C:N ratio signifies a better
quality food, and conditioned material is usually characterised by a lower C:N ratio
compared to unconditioned material (Graça et al. 1993b). Some species such as alder
(Alnus spp.) are characterised by a lower C:N ratio and higher palatability compared
to others, such as horse chestnut (Aesculus spp.) (Agatz and Brown 2014), which
could lead to the organisms growing larger (Bärlocher and Kendrick 1973b).
Feeding Behavioural Studies with Freshwater Gammarus spp.: The. . .
11
et al. 2015; Taylor et al. 1993; Weber et al. 2018; Xuereb et al. 2009; Zubrod et al.
2017) (see Table 1).
As a rule, and not only in feeding studies, gravid females and organisms affected
by the acanthocephalan parasite are usually excluded from experiments (Agatz et al.
2014; Alonso et al. 2009; Blarer and Burkhardt-Holm 2016; Bundschuh et al. 2011b,
2013; Forrow and Maltby 2000; Zubrod et al. 2015, 2017) unless they are specifically chosen for the purpose of the study (Agatz and Brown 2014; Pascoe et al.
1995). Alonso et al. (2009) developed a feeding study using the Multispecies
Freshwater Biomonitor, and neither length nor sex influenced the feeding activity
of either sex of Gammarus pulex. However, it is debatable whether these results
might only be applicable to the type of contaminant used in the investigation, as
some contaminants might affect male and female Gammarid feeding behaviour in
different ways.
3 Food Preparation
The food source selected for an experiment using Gammarids is important, but
especially so for feeding studies, both in the acclimation period and in the experiment itself. Gammarids are shredder detritivores, and they usually feed on conditioned organic material, in other words material that has been colonised by
microorganisms, such as leaf litter. In the natural environment, freshly abscised
leaves are colonised by fungi and then by bacteria (Baldy et al. 1995), which
facilitate the decomposition process and transform the material, making it more
palatable and accessible to the organisms (Bärlocher and Kendrick 1975; Cummins
1974; Gessner et al. 1999).
Gammarus spp. have displayed selective behaviour towards leaf species and their
conditioning level (Agatz and Brown 2014; Graça et al. 1993a, b, 2001) and the type
of fungi (Arsuffi and Suberkropp 1989). Interestingly, Graça et al. (2001) compared
food preferences of shredders from temperate (Gammarus pulex and Sericostoma
vittatum) and tropical (Nectopsyche argentata and Phylloicus priapulus) streams.
When provided with conditioned and/or unconditioned leaves from either a temperate (Alnus glutinosa) or tropical (Hura crepitans) country, Gammarus pulex showed
a significant preference for the conditioned leaves compared to unconditioned leaves
of the same species. Leaves are characterised by different hardness, texture and more
importantly by dissimilar C:N ratios, which means the various leaf species provide
the organisms with differing energy supplies. A lower C:N ratio signifies a better
quality food, and conditioned material is usually characterised by a lower C:N ratio
compared to unconditioned material (Graça et al. 1993b). Some species such as alder
(Alnus spp.) are characterised by a lower C:N ratio and higher palatability compared
to others, such as horse chestnut (Aesculus spp.) (Agatz and Brown 2014), which
could lead to the organisms growing larger (Bärlocher and Kendrick 1973b).
Feeding Behavioural Studies with Freshwater Gammarus spp.: The. . .
11