The adaptability of organisms to novel environmental conditions depends on the amount of genetic variance present in the population as well as on the ability of individuals to adjust their phenotype ...through phenotypic plasticity. Here, we investigated the phenotypic plasticity induced by a single generation's exposure to three different temperature regimes with respect to several life‐history and stress‐resistance traits in a natural population of Drosophila simulans. We studied a constant as well as a predictably and an unpredictably fluctuating temperature regime. We found high levels of phenotypic plasticity among all temperature regimes, suggesting a strong influence of both temperature fluctuations and their predictability. Increased heat tolerance was observed for flies developed in both types of fluctuating thermal environments compared with flies developed in a constant environment. We suggest that this was due to beneficial hardening when developing in either fluctuating temperature environment. To our surprise, flies that developed in constant and predictably changing environments were similar to each other in most traits when compared to flies from the unpredictably fluctuating environment. The unpredictably changing thermal environment imposed the most stressful condition, resulting in the lowest performance for stress‐related traits, even though the absolute temperature changes never exceeded that of the predictably fluctuating environment. The overall decreased stress resistance of flies in the unpredictably fluctuating environment may be the consequence of maladaptive phenotypic plasticity in this setting, indicating that the adaptive value of plasticity depends on the predictability of the environment.
The selective past of populations is presumed to affect the levels of phenotypic plasticity. Experimental evolution at constant temperatures is generally expected to lead to a decreased level of ...plasticity due to presumed costs associated with phenotypic plasticity when not needed. In this study, we investigated the effect of experimental evolution in constant, predictable and unpredictable daily fluctuating temperature regimes on the levels of phenotype plasticity in several life history and stress resistance traits in Drosophila simulans. Contrary to the expectation, evolution in the different regimes did not affect the levels of plasticity in any of the traits investigated even though the populations from the different thermal regimes had evolved different stress resistance and fitness trait means. Although costs associated with phenotypic plasticity are known, our results suggest that the maintenance of phenotypic plasticity might come at low and negligible costs, and thus, the potential of phenotypic plasticity to evolve in populations exposed to different environmental conditions might be limited.
Laboratory selection in thermal regimes that differed in the amplitude and the predictability of daily fluctuations had a marked effect on stress resistance and life history traits in Drosophila ...simulans. The observed evolutionary changes are expected to be the result of both direct and correlated responses to selection. Thus, a given trait might not evolve independently from other traits because of genetic correlations among these traits. Moreover, different test environments can induce novel genetic correlations because of the activation of environmentally dependent genes. To test whether and how genetic correlations among stress resistance and life history traits constrain evolutionary adaptation, we used three populations of D. simulans selected for 20 generations in constant, predictable and unpredictable daily fluctuating thermal regimes and tested each of these selected populations in the same three thermal regimes. We explored the relationship between genetic correlations between traits and the evolutionary potential of D. simulans by comparing genetic correlation matrices in flies selected and tested in different thermal test regimes. We observed genetic correlations mainly between productivity, body size, starvation and desiccation tolerance, suggesting that adaptation to the three thermal regimes was affected by correlations between these traits. We also found that the correlations between some traits such as body size and productivity or starvation tolerance and productivity were determined by test regime rather than selection regime that is expected to limit genetic adaptation to thermal regimes in these traits. The results of this study suggest that several traits and several environments are needed to explore adaptive responses, as genetic and environmentally induced correlations between traits as results obtained in one environment cannot be used to predict the response of the same population in another environment.
Populations ofDrosophila melanogaster, as well as of otherDrosophilaspecies, show body size differences according to their geographic origin. Thermal selection is considered to be the most likely ...cause explaining these differences. We investigated wing size, wing shape and their relationship in 3 different geographic populations ofD. melanogaster, 1 population ofD. simulans, and their interspecific hybrids grown at 18, 21, 25 and 28°C. The aim was to explore how the past adaptive history of 2 related species, or populations of the same species, modulates the plastic response to the environment. The wing size plasticity of hybrids between the temperateD. simulans(Bologna) and the 2 tropicalD. melanogasterpopulations (Belém and Rio de Janeiro) was higher than that of parental species, probably as a side effect of a decanalized and compromised development at higher temperatures. The wing size plasticity of Bologna hybrids was the same as the parents, suggesting that the 2 species are subjected to the same plasticity selection. Wing shape was typical of each species, population and temperature. Shape differences increased in hybrids at higher temperatures as a consequence of developmental perturbation. The allometric relationship between size and shape changed among temperatures and among species, suggesting that the wing development is differently regulated in the 2 species and can be altered by natural selection. The allometry changed between populations of different geographic origin ofD. melanogaster, but was similar in the 2 species that shared the same selective environment. Two species would have been subjected to the same plasticity selection, so the breakdown of the plastic response is avoided in hybrids. As a whole, these data suggest that thermal plasticity is a trait under selection and that similar mechanisms are at work in different species.
The effects of cell adhesion on leukemia cell proliferationremain poorly documented and somehow controversial. Inthis work, we investigated the effect of adhesion to fibronectinon the proliferation ...of acute myeloid leukemia (AML) celllines (U937 and KG1a) and CD34+ normal or leukemic primarycells. We observed an increased rate of proliferation of AMLcells when adhered to fibronectin, concomitant with acceleratedS-phase entry and accumulation of CDC25A. Conversely,normal CD34+ cell proliferation was decreased by adhesion tofibronectin with a concomitant drop in CDC25A expression.Importantly, we showed that both small interfering RNA(siRNA)–mediated CDC25A down-regulation and a recentlydeveloped CDC25 pharmacologic inhibitor impaired thisadhesion-dependent proliferation, establishing a functionallink between CDC25A accumulation and adhesion-dependentproliferation in leukemic cells. CDC25A accumulation wasfound only slightly dependent on transcriptional regulationand essentially due to modifications of the proteasomaldegradation of the protein as shown using proteasomeinhibitors and reverse transcription-PCR. Interestingly, CDC25Aregulation was Chk1 dependent in these cells as suggestedby siRNA-mediated down-regulation of this protein. Finally,we identified activation of the phosphatidylinositol 3-kinase/Akt pathway as an adhesion-dependent regulation mechanismof CDC25A protein expression. Altogether, our data show thatin leukemic cells adhesion to fibronectin increases CDC25Aexpression through proteasome- and Chk1-dependent mechanisms,resulting in enhanced proliferation. They also suggestthat these adhesion-dependent proliferation properties ofhematopoietic cells may be modified during leukemogenesis.
The effects of cell adhesion on leukemia cell proliferationremain poorly documented and somehow controversial. Inthis work, we investigated the effect of adhesion to fibronectinon the proliferation ...of acute myeloid leukemia (AML) celllines (U937 and KG1a) and CD34+ normal or leukemic primarycells. We observed an increased rate of proliferation of AMLcells when adhered to fibronectin, concomitant with acceleratedS-phase entry and accumulation of CDC25A. Conversely,normal CD34+ cell proliferation was decreased by adhesion tofibronectin with a concomitant drop in CDC25A expression.Importantly, we showed that both small interfering RNA(siRNA)–mediated CDC25A down-regulation and a recentlydeveloped CDC25 pharmacologic inhibitor impaired thisadhesion-dependent proliferation, establishing a functionallink between CDC25A accumulation and adhesion-dependentproliferation in leukemic cells. CDC25A accumulation wasfound only slightly dependent on transcriptional regulationand essentially due to modifications of the proteasomaldegradation of the protein as shown using proteasomeinhibitors and reverse transcription-PCR. Interestingly, CDC25Aregulation was Chk1 dependent in these cells as suggestedby siRNA-mediated down-regulation of this protein. Finally,we identified activation of the phosphatidylinositol 3-kinase/Akt pathway as an adhesion-dependent regulation mechanismof CDC25A protein expression. Altogether, our data show thatin leukemic cells adhesion to fibronectin increases CDC25Aexpression through proteasome- and Chk1-dependent mechanisms,resulting in enhanced proliferation. They also suggestthat these adhesion-dependent proliferation properties ofhematopoietic cells may be modified during leukemogenesis.
Thermal CFTs in momentum space Manenti, Andrea
The journal of high energy physics,
01/2020, Letnik:
2020, Številka:
1
Journal Article
Recenzirano
Odprti dostop
A
bstract
We study some aspects of conformal field theories at finite temperature in momentum space. We provide a formula for the Fourier transform of a thermal conformal block and study its analytic ...properties. In particular we show that the Fourier transform vanishes when the conformal dimension and spin are those of a “double twist” operator ∆ = 2∆
ϕ
+
ℓ
+ 2
n
. By analytically continuing to Lorentzian signature we show that the spectral density at high spatial momenta has support on the spectrum condition |
ω
| > |
k
|. This leads to a series of sum rules. Finally, we explicitly match the thermal block expansion with the momentum space Green’s function at finite temperature in several examples.
A
bstract
We present a systematic method to expand in components four dimensional superconformal multiplets. The results cover all possible
N
= 1 multiplets and some cases of interest for
N
= 2. As ...an application of the formalism we prove that certain
N
= 2 spinning chiral operators (also known as “exotic” chiral primaries) do not admit a consistent three-point function with the stress tensor and therefore cannot be present in any local SCFT. This extends a previous proof in the literature which only applies to certain classes of theories. To each superdescendant we associate a superconformally covariant differential operator, which can then be applied to any correlator in superspace. In the case of three- point functions, we introduce a convenient representation of the differential operators that considerably simplifies their action. As a consequence it is possible to efficiently obtain the linear relations between the OPE coefficients of the operators in the same superconformal multiplet and in turn streamline the computation of superconformal blocks. We also introduce a Mathematica package to work with four dimensional superspace.
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