Results
Maximum and minimum critical thermal limits were differentially affected
by the thermal environment experienced by flies.CTmax was significantly higher in flies from
parental generation reared at variable thermal environment (V) than
those reared at constant temperature (C), whileCTmin was not different between parental thermal
environments (Figures 2A, 2B and Supplementary Figure S1).
Interestingly, whereas CTmax was significantly
higher in females than males, CTmin did not vary
between sex (Table 1, Supplementary Figure S1). With regards to the F1,
the thermal environment experienced by parental generation affected the
critical thermal limits of their offspring (Table 1, Figure 3). More
specifically, F1 flies raised under variable conditions whose parents
were also maintained in this environment (i.e., VV) exhibited a
significantly higher CTmax than all other F1
groups (including flies from CV, see Figure 2 and Supplementary Figure
S1). Also, CTmax of F1 flies reared under
constant environment, whose parents were reared in the alternative
treatment (i.e., VC) had significant lower CTmaxthan F1 flies from a constant environment whose parents were maintained
in a constant environment (CC). Besides, cold tolerance of F1 flies
reared in a variable thermal environment (i.e., VV and CV) were lower
than those reared at C (i.e., CC and VC).
Changing now to demographic descriptors of fitness, both survival and
fecundity per female was lower in P flies reared at variable
environments (Figure 3, detailed analyses in Supplementary Table S2),
resulting in substantially lower \(R_{0}\) and \(T_{g}\) in C in
comparison to V (Figure 2, Supplementary Table S3). In contrast, the
variation in survival and fecundity was substantially reduced in the F1
regardless of the thermal treatment, which suggests some sort of
compensation across generations (Figures 2 and 3). In fact, flies from
the second generation exposed to a variable thermal environment showed a
significant increase of \(R_{0}\) and \(T_{g}\) values compared with
their parents (Figure 2)\(.\) Effects of the parental environment were
still evident, however, with both \(R_{0}\) and \(T_{g}\ \)being on
average lower in F1 lines derived from parents subjected to a variable
environment (i.e., VC and VV groups), indicating that the apparent
compensatory response to a stressful parental environment was only
partial (Figure 2). Interestingly, flies whose parents were maintained
at a constant temperature (CC and CV) did not show differences in\(R_{0}\) and \(T_{g}\) between them or their parents regardless of the
thermal environment in which they were raised (Figure 2).
Results from our GAM analyses in conjunction with a model comparison
approach support the observations listed above (Table 2, Supplementary
Table S3). Thermal treatment had a major effect in these fitness
components, explaining up to 53.6% and 34.9% of the variance in\(R_{0}\) and \(T_{g}\), respectively, after controlling for density
(density effects on demographic variables are represented in
Supplementary Figure S2). Furthermore, the models with the lowest AIC in
both cases included the treatment factor (see Methods), which
encapsulates the thermal environment of the parents
(TP ), the offspring (TF1 )
and their interaction, and resulted in a model with a better fit than
those where these factors were included separately (Table 1).
Interestingly \(R_{0}\) and CTmax were negative
and significantly correlated (r=-0.8, T=-2.69, df=4,
P=0.027 ) but, we did not find significant correlations among\(T_{g}\)and CTmax (r=-0.55, T=-1.32, df=4,
P=0.12 ).