A characterization of tardigrade energetics from oxygen microgradients in relation to temperature, salinity and the termination of cryptobiosis.

Bjarke Haldrup Pedersen

Studenteropgave: Speciale

Abstrakt

The aim of this project was to determine the metabolic rate of tardigrades and how it depends on
conditions such as temperature and salinity, as well as how it changes during termination of the putatively
ametabolic state of cryptobiosis and from this to discover novel insights into how tardigrade metabolism
and the extraordinary abilities it facilitates may function. To this end, tardigrades were collected in Öland
and a method was developed for measuring their metabolic rate (nmol O2 · mg-1 · hour-1) using oxygen
microsensors and microgradients. The metabolic rate of active Richtersius coronifers at 22 °C and a salinity
of 0 ppt was 10.8 ± 1.84 (n = 28) and for dead specimens, it was 0.21 ± 0.03 (n = 4). For the Macrobiotus
macrocalix species, it was 13.4 ± 2.19 (n = 17). The metabolic rate of both species was found to be
unaffected by scaling within the inherent size variation of the populations. The following metabolic rates
(nmol O2 · mg-1 · hour-1) were also determined for R. coronifer at different temperatures and a salinity of
0 ppt. 2 °C: 2.28 ± 0.48 (n = 8); 11 °C: 3.56 ± 0.59 (n = 6); 16 °C: 8.42 ± 0.82 (n = 6) and 33 °C: 19.5 ± 1.19 (n
= 6). Q10-values were calculated to be ~ 1.5 in all temperature ranges – except from 11 – 16 °C where it
was ~ 5.5. This was concluded to be a range of relative temperature dependence (RRTD). The activation
energy of the rate-limiting step in the metabolic pathway was calculated to be 50.8 kJ/mole O2. At 22 °C,
the metabolic rate increased with salinity from 0 – 4 ppt and decreased from 14 – 32 ppt. Survival rate was
100 % at 0 – 4 ppt, 50 % at 14.4 ppt perchlorates and 0 % at 16 – 32 ppt NaCl. Plotting the metabolic rate
over time revealed a spike to 286 % of the previous metabolic rate over 18 minutes for one tardigrade and
180 % over 8 minutes for another during exposure to 14.4 ppt perchlorates. Both spikes occurred after 60
minutes of exposure, where metabolic rate had been declining exponentially. The metabolic rate during
termination of anhydrobiosis was determined for two R. coronifer tuns that successfully regained activity
and 8 tuns that did not survive the process. For all 10 tuns, the metabolic rate was found to go through
three distinct zones: heightened metabolic rate (~ 20 – 25 for successful tuns) with one or more local peaks
for less than one hour, followed by an exponential decrease as the tardigrades hydrated over the next
several hours and finally a period of low metabolic rate (~ 5 for successful tuns) that continued for more
than 24 hours after rehydration. The method allows precise determination of the oxygen consumption for
individual tardigrades and can be repurposed for a wide range of experimental set-ups – opening up a rich
field of inquiry into the metabolism and energetics of tardigrade biology.

UddannelserMolekylærbiologi, (Bachelor/kandidatuddannelse) KandidatMedicinalbiologi, (Bachelor/kandidatuddannelse) Kandidat
SprogEngelsk
Udgivelsesdato17 aug. 2018
Antal sider117
VejledereHans Ramløv & Kai Finster

Emneord

  • Cryptobiosis
  • Energetics
  • Metabolism
  • Microgradients
  • Tardigrades