Research on energy metabolism of seals in Antarctic research station

In April 2022, Professor Linnea E.
Pearson published online "Metabolic cost of thermoregulation decreases after the molt in developing Weddell seal pups after molt" in the International Journal of Experimental Biology pups" to understand how Weddell seal larvae stay warm on ice and in water, and whether older larvae with more fat use less energy to stay warm
.


Allocating energy to thermoregulation greatly increases the metabolic cost of endothermic animals, especially under extreme environmental conditions
.
Weddell seal larvae born in Antarctica must survive in ice and water, two environments with very different thermal conductivities
.
This difference may require the larvae to allocate additional energy to thermoregulation rather than the expansion of swimming capacity required for independent foraging
.
The experiment in this paper adopts the portable respiratory metabolism system shown in the figure above.
The internal volume of the mobile metabolism cabin is 204.
3 × 62.
1 × 99.
7 cm (length × width × height), and the external dimensions are 214.
5 × 72.
2 × 111.
3 cm.
6 Plexiglas animal behavior observation windows, and a custom-made animal carrying platform at the bottom, and record air temperature (TA _, °C), water temperature (Tw, °C) and the animal's core body temperature (Tc, °C)
.
In the experiment, the resting metabolic rate (RMR) and respiratory gas exchange ratio (RER) of Weddell seal larvae at different ages in air and water were measured.
C=Q/(T _C - T _E ), where Q is heat production (mlO2 kg ^{- 1}h ^-1 ), T _Cis the core body temperature, and TE _is the ambient temperature in the metabolic chamber
.
Some experimental results are as follows:

Fig.
2.
Resting metabolic rates in air and water of larvae seals at different ages and molting states
.
Light grey for air (MR _A ) and dark grey for water results (MR _W ), with data mean (white diamonds), median (hash), outliers (filled circles), and quartiles ( whiskers); different letters are considered significant differences, and the same letters are not significantly different
.
The mean metabolic rates in air at 1 and 5 weeks of age were 423 ± 112 ml O ₂  min ^-1 and 837 ± 157 ml O ₂  min ^{-1 , respectively, and dropped to 678 ± 148 ml O} ₂  min ^-1 at 7 weeks of age  (Fig.
2A )
.
Age has _a significant effect on MRA.
For example, 1-week-old is significantly lower than 3-, 5-, and 7-week- old _MRA values, but there is no significant difference between 3-, 5-, and 7-week-old MRA values; MR _{W value} is the change (3 weeks old: 908 ± 178ml O ₂  min ^-1 ; 7 weeks old: 832 ± 240ml O ₂  min ^-1 ) and there was no significant difference between the ages (Fig.
2A); MR in air and water at the same age point was compared 3 and 5 weeks old MR _WThe values ​​were significantly higher than the MRA values, and there was no significant difference between the MR _W and MRA values ​​at 7 weeks of age _{( Fig.
2A}
) .


      The MR _A value changed significantly with the molting state (Fig.
2B).
The MR _A value of the larvae before molting (456±110ml O ₂  min ^-1 ) was significantly lower than that in the molting (772±170ml O ₂  min ^-1 ; P<0.
001 ) and after molting (694±156ml O ₂  min ^-1 ; P=0.
0116), there was no significant difference between the latter two (Fig.
2B) .
The molting state had no significant effect
on the MR _W value (before molting: 945±945± 174 ml O ₂  min ^-1 ; 966±127 ml O 2 min -1 during molt _;  post ^molt : 809±254 ml O ₂  min ^-1 ; Fig.
2B)
.
In comparing the MR _{W of each molt stateWhen compared with MRA values, the MR W} before _and in the molt was significantly higher than its MRA _value , but there was no difference after the molt (Fig.
2B) .

 

 
 

     Table 2.
Changes in respiratory gas exchange ratio (RER), core body temperature, and heat transfer by treatment (air or water) and by group (age, weaning, and molting status)
.
RER varied from 0.
796 ± 0.
06 to 1.
040 ± 0.
09 (in air) and 0.
774 ± 0.
08 to 0.
844 ± 0.
16 (in water); no significant differences between treatments and age groups; within one treatment, no significant differences between molting groups; treatments Between groups, the RER of molting larvae in air was significantly higher than that in water (P=0.
0437; Table 2), and there was no significant difference in other RERs
.


    Total body heat transfer in air varied with age (range: 14.
3 ± 2.
7 to 19.
6 ± 6.
2 ml O ₂  kg ^{− 1}  h ^-1 ) and generally declined in water bodies (19.
5 ± 6.
2 ml O ₂  kg ^-1  h ^-1 at 3 weeks to 13.
4 ± 3.
7 ml O ₂  kg ^-1  h ^-1 at 7 weeks )
.
In water, premolt larvae (21.
8±5.
49 ml O ₂  kg ^-1  h ^-1 ) showed significantly higher than postmolt (13.
0±3.
89 ml O ₂  kg ^{-1 )} h ^-1 ; P=0.
005; Table 2) heat conduction
.
There were no significant differences in heat conduction between molting larvae and pre- or post-molting
.


    The findings suggest that the absolute metabolic rate (MR) in air follows the expected relationship of allometric growth to body weight
.
Absolute MR in water was not allometric with body weight, despite a 3-fold increase in body weight between 1 and 7 weeks of age
.
The developmental stage (or molting stage), not the calendar age, determines when the larvae are able to retain heat in the water
.
The RMR of postmolt larvae in air and water (6.
67 ± 1.
4 and 7.
90 ± 2.
38 ml O2 min ^-1  kg ^-1 , respectively ) was lower than that of premolt larvae (in air: 9.
37 ± 2.
42 ml O2 min ^-1  kg ^-1 , in water: 13.
40 ± 3.
46 ml O2 min ^-1  kg ^-1 ) and molting pups (in air: 8.
45 ± 2.
05 ml O2 min ^-1  kg ^-1 , in water: 10.
4 ± 1.
63 ml O2 min ^-1  kg ^-1 )
.
Despite the increased energy input, molting larvae spent three times as long in the water as other larvae
.
These results support the idea that seal larvae make energy tradeoffs during early development; larvae expend more energy to regulate body temperature in the water while gaining the experience needed for independence
.

     
Attached is the technical scheme of energy metabolism in aquatic mammals: FMS portable or modular respiratory metabolism measurement system + temperature, heart rate and activity recorder, which is used to measure the physiological adaptation mechanism of animals under extreme environmental conditions
.
The respiratory metabolism cabin can be selected for energy metabolism-related research under experimental conditions, or the suspension mask can be selected for energy metabolism monitoring of freely moving animals
.