2.2 Temperature
During the acclimation period, organisms need to be kept at a constant temperature
and with a precise light/dark cycle. Gammarids from temperate countries are usually
maintained at a temperature between 10 and 22
C (see Table 1). The temperature
adopted in an experimental design is often selected to reproduce seasonal conditions,
but unfortunately the literature does not always specify the selection criteria. Temperature can have a significant impact on Gammarids and on amphipods in general
(Labaude et al. 2017). Foucreau et al. (2014) discovered that temperatures higher
than 15
C altered various physiological parameters in Gammarus pulex populations
in North France. Southern specimens consumed more oxygen at higher temperatures
and had a higher glycogen content, which means they have a higher energy supply.
Cold-acclimated organisms consumed more energy and oxygen when they are
exposed to higher temperatures, and they presented a lower heat tolerance
(Semsar-kazerouni and Verberk 2018). Interestingly, Alonso et al. (2009) acclimated
their organisms at 15
C for 4 days, after which time the organisms were transferred
to a 20
C room to acclimate for a further 4 days. Moving organisms from a low to a
high temperature could have potentially affected the experimental results (Alonso
et al. 2009). Furthermore, temperature plays an important role in the immune system
of crustaceans (Le Moullac and Haffner 2000). Therefore, it is difficult to compare
studies where the test animals have been acclimated at different temperatures, as this
could have influenced their energy stores or their immune systems, for example.
These differences could also be reflected in the organisms’ behavioural reactions,
which could be incorrectly interpreted as a result of exposure to specific contaminants. In fact, both Nilsson (1974) and Coulaud et al. (2011) reported an increased
feeding rate with an increased temperature. The extent of the feeding rate increase
was also dependent on leaf species (i.e. Alnus glutinosa or Fagus sylvatica) (Nilsson
1974). Acclimation temperature plays an even greater role in in situ experiments
where the chosen temperature should be as close as possible to real-life environmental conditions. Interestingly, Coulaud et al. (2011) linked temperature and
feeding rate through a linear regression, in order to better understand the impact of
temperature on the Gammarids feeding. It was found that a small increase in mean
temperature (from 12 to 13
C) could enhance the feeding rate by 7.3%.
2.3 Light and Dark Cycles
The same principle could be applied to the different light/dark cycles used during the
acclimation period. The most commonly adopted light/dark cycle is 12:12 h (see
Table 1) that reflects typical equinox conditions. However, some studies acclimate
their organisms in total darkness, and in other studies, the adopted cycle is not
specified (see Table 1). Sometimes a seasonal cycle is selected, in order to replicate
the time of year when the organisms are collected from the wild, such as summer
8
G. Consolandi et al.
During the acclimation period, organisms need to be kept at a constant temperature
and with a precise light/dark cycle. Gammarids from temperate countries are usually
maintained at a temperature between 10 and 22
C (see Table 1). The temperature
adopted in an experimental design is often selected to reproduce seasonal conditions,
but unfortunately the literature does not always specify the selection criteria. Temperature can have a significant impact on Gammarids and on amphipods in general
(Labaude et al. 2017). Foucreau et al. (2014) discovered that temperatures higher
than 15
C altered various physiological parameters in Gammarus pulex populations
in North France. Southern specimens consumed more oxygen at higher temperatures
and had a higher glycogen content, which means they have a higher energy supply.
Cold-acclimated organisms consumed more energy and oxygen when they are
exposed to higher temperatures, and they presented a lower heat tolerance
(Semsar-kazerouni and Verberk 2018). Interestingly, Alonso et al. (2009) acclimated
their organisms at 15
C for 4 days, after which time the organisms were transferred
to a 20
C room to acclimate for a further 4 days. Moving organisms from a low to a
high temperature could have potentially affected the experimental results (Alonso
et al. 2009). Furthermore, temperature plays an important role in the immune system
of crustaceans (Le Moullac and Haffner 2000). Therefore, it is difficult to compare
studies where the test animals have been acclimated at different temperatures, as this
could have influenced their energy stores or their immune systems, for example.
These differences could also be reflected in the organisms’ behavioural reactions,
which could be incorrectly interpreted as a result of exposure to specific contaminants. In fact, both Nilsson (1974) and Coulaud et al. (2011) reported an increased
feeding rate with an increased temperature. The extent of the feeding rate increase
was also dependent on leaf species (i.e. Alnus glutinosa or Fagus sylvatica) (Nilsson
1974). Acclimation temperature plays an even greater role in in situ experiments
where the chosen temperature should be as close as possible to real-life environmental conditions. Interestingly, Coulaud et al. (2011) linked temperature and
feeding rate through a linear regression, in order to better understand the impact of
temperature on the Gammarids feeding. It was found that a small increase in mean
temperature (from 12 to 13
C) could enhance the feeding rate by 7.3%.
2.3 Light and Dark Cycles
The same principle could be applied to the different light/dark cycles used during the
acclimation period. The most commonly adopted light/dark cycle is 12:12 h (see
Table 1) that reflects typical equinox conditions. However, some studies acclimate
their organisms in total darkness, and in other studies, the adopted cycle is not
specified (see Table 1). Sometimes a seasonal cycle is selected, in order to replicate
the time of year when the organisms are collected from the wild, such as summer
8
G. Consolandi et al.