variability on maximal swimming speed in helmeted water toad tadpoles. We obtained ... gives partial evidence to support the âfaster-slowerâ and âgeneralist-specialist trade offsâ ... We used programmable thermostatic heaters and air ... Locomotion is a relevant trait because determines if an organism is able to escape from.
Thermal variability reduces maximal swimming performance in a threatened tadpole José L.
1 Bartheld ,
Paulina
2 Artacho
& Leonardo
1 Bacigalupe
1 Instituto de Ciencias Ambientales y Evolutivas, Universidad Austral de Chile, Valdivia, Chile. 2 Instituto Tecnológico del Salmón, Salmón Chile. Puerto Montt, Chile.
Abstract
Results
Daily temperature variability has been recognized as an important factor that can affect physiological processes and fitness related traits. We evaluated the effects of diel thermal variability on maximal swimming speed in helmeted water toad tadpoles. We obtained estimates of maximal swimming speed from 23 individuals assigned to a fluctuating temperature treatment (20 °C 1.5 SD) and 19 assigned to a constant temperature treatment (20 °C 0.1 SD). This work showed that thermal fluctuating conditions reduced maximal swimming speed of tadpoles (especially near the Topt) and triggered a flatter curve. This finding gives partial evidence to support the “faster-slower” and “generalist-specialist trade offs“ hypothesis. Alternatively, the observed reduction of maximal performance can be explained by Jensen’s inequality, a mathematical property of non-linear functions.
Diel thermal fluctuations tended to reduce performance at intermediate body temperatures, especially near the thermal optimum. Both TPCs had the same Topt, but there were significant differences in their curvatures and slopes (table 1, figure 3). Thermal acclimation resulted in lower maximal swimming performance (AT:Bt effect) and a flatter curve (AT:Bt2 effect) in the fluctuating thermal treatment. The model that best described the individual differences in TPCs (figure 3) was the model that accounted for individual differences in both, the linear slope and curvature of the TPCs (table 2, model 4).
Helmeted water toad tadpole Calyptocephalella gayi
10 cm
Introduction In the current global warming scenario, an increasing in the mean environmental temperatures altogether with a higher frequency of extremely high temperatures and greater temporal variability has been predicted to occur. A practical approach to studying the physiological capabilities of ectotherms given environmental temperature is by estimating thermal performance curves (TPCs). Most of studies have focused on the effects of changes in averages environmental temperatures, however, temperature variability has been recognized as an factor that can affect several physiological processes and fitness related traits. Here, we investigated the effects of acclimation to thermal variability using a simple experimental protocol to separate the effects of mean and diel temperature variation on maximal swimming speed in Calyptocephalella gayi tadpoles. Fluctuating Constant
Material and Methods 48 helmeted water toad tadpoles (gosner 25-27) were randomly selected and acclimated for two weeks in a constant temperature treatment (20°C ± 0.1 SD) or in a fluctuating temperature treatment (20°C ± 1.5 SD). We used programmable thermostatic heaters and air pumps. P 12L:12D and tadpoles were fed ad libitum. Water temperature was recorded using data loggers (Figure 1).
Temperature (°C)
23
Figure 3. Maximal swimming performance curves (Quadratic functions) of tadpoles acclimated to constant (20 ºC ± 0.1 SD) and fluctuating (20 ºC ± 1.5 SD) treatments. Gray area indicates 95% CIs. Table 1. Significance tests of the most simple random effect model (model 1). β
s.e.
d.f.
2000
4000
6000
8000
10000
Minutes
Figure 1. An example of the first week of temperature in the two acclimation treatments.
Maximal swimming speed was measured for each individual at 6 temperatures (5, 12, 20, 25, 30, and 35 °C). Measurements were made using a thermal bath provided with a swimming track. Individuals were randomly assigned to sequence of temperatures. The fastest speed of 3 trials estimated over a 25 cm interval was considered the maximal swimming speed (Body lengths per seconds).
< 0.001***
1
(1 | ID)
21.33 < 0.001***
2
(Bt | ID)
3
0.660 0.003**
Bt
0.48
0.02
205
Bt 2
- 0.01
0.00
205 -21.27
AT
0.13
0.29
232
- 0.09
0.03
204 - 3.02
0.00
0.00
204
AT : Bt
*P < 0.05; **P < 0.01; ***P < 0.001
18
Random terms
233 - 4.11
21
19
Model
0.22
AT : Bt 2
1
p-value
(intercept) - 0.89
22
20
t
Discussion
Table 2. Comparisons of random effect models used
0.44
< 0.001***
3.52 < 0.001***
ref M
χ2
d.f.
-221.92
1.22
1
0.269
462.11
-220.06
4.95
3
0.175
14
448.75
-210.38
24.32
6
< 0.001***
11
466.77
-222.38
0.29
3
0.960
M d.f. AIC
Llike
8
489.24
-222.53
1
9
461.85
(Bt2 | ID)
1
11
4
((Bt+Bt2) | ID)
1
5
(AT | ID)
1
p-value
Models including water bath as random effect always were less informative with AIC values higher than 500. *P < 0.05; **P < 0.01; ***P < 0.001 1
Diel thermal fluctuating conditions reduced maximal swimming speed of tadpoles and triggered a flatter curve. This finding gives partial evidence to support the “faster-slower” and “generalist-specialist trade offs“ hypothesis. Alternatively, the reduction of maximal performance can be explained by Jensen’s inequality, a mathematical property of non-linear functions. Jensen’s inequality states that temperature variability is predicted to consistently elevate or depress performance in relation to acquired performance at the same mean temperature in a constant regime. Performance only depend on whether or not the function is accelerating or decelerating. Locomotion is a relevant trait because determines if an organism is able to escape from predators, catch prey, or disperse. Our results suggest that individual variation of thermal sensitivity on maximal swimming speed could represent additional substrate for natural selection to act, but more field and laboratory studies should be conducted. Our simple laboratory experiment demonstrates that a minimal diel variation in temperature can reduce maximal performance; therefore, the widespread use of constant acclimation temperatures in laboratory experiments may overestimate what actually occurs in nature.
Quadratic, Gaussian an Weibull functions was analyzed using the Akaike Information Criterion. We used general linear mixed models (LMM) with a quadratic function. Figure 2. thermal bath with a swimming track and video recording system.
Acknowledgements All experimental procedures were approved by the Universidad Austral de Chile animal care committee and followed Chilean legal requirements. Funded by FONDECYT N° 3140243.
