Acclimation Response and Ability of Growth and Photosynthesis of Terrestrial Cyanobacterium Cylindrospermum sp. Strain FS 64 Under Combined Environmental Factors

This investigation tested the hypothesis that the native cyanobacteria can acclimatize and grow under the combination of environmental factors and/or how does their process change with the age of culture? Here, we tried to combine multiple factors to simulated what happens in natural ecosystems. We analyzed the physiological response of terrestrial cyanobacterium, Cylindrospermum sp. FS 64 under combination effect of different salinity (17, 80, and 160 mM) and alkaline pHs (9 and 11) at extremely limited carbon dioxide concentration (no aeration) up to 96h. Our evidence showed that growth, biomass, photosystem II, and phycobilisome activity significantly increased under 80 mM salinity and pH 11. In addition, this combined condition led to a significant increase in maximum light-saturated photosynthesis activity and photosynthetic efficiency. While phycobilisomes and photosystem activity decreased by increasing salinity (160 mM) which caused decreased growth rates after 96h. The single-cell study (CLMS microscopy) which illustrated the physiological state of the individual and active-cell confirmed the efficiency and effectiveness of both photosystems and phycobilisome under the combined effect of 80 mM salinity and pH 11.

New Insights From Transcriptomic Data Reveal Differential Effects of CO2 Acidification Stress on Photosynthesis of an Endosymbiotic Dinoflagellate in hospite

Ocean acidification (OA) has both detrimental as well as beneficial effects on marine life; it negatively affects calcifiers while enhancing the productivity of photosynthetic organisms. To date, many studies have focused on the impacts of OA on calcification in reef-building corals, a process particularly susceptible to acidification. However, little is known about the effects of OA on their photosynthetic algal partners, with some studies suggesting potential benefits for symbiont productivity. Here, we investigated the transcriptomic response of the endosymbiont Symbiodinium microadriaticum (CCMP2467) in the Red Sea coral Stylophora pistillata subjected to different long-term (2 years) OA treatments (pH 8.0, 7.8, 7.4, 7.2). Transcriptomic analyses revealed that symbionts from corals under lower pH treatments responded to acidification by increasing the expression of genes related to photosynthesis and carbon-concentrating mechanisms. These processes were mostly up-regulated and associated metabolic pathways were significantly enriched, suggesting an overall positive effect of OA on the expression of photosynthesis-related genes. To test this conclusion on a physiological level, we analyzed the symbiont’s photochemical performance across treatments. However, in contrast to the beneficial effects suggested by the observed gene expression changes, we found significant impairment of photosynthesis with increasing pCO2. Collectively, our data suggest that over-expression of photosynthesis-related genes is not a beneficial effect of OA but rather an acclimation response of the holobiont to different water chemistries. Our study highlights the complex effects of ocean acidification on these symbiotic organisms and the role of the host in determining symbiont productivity and performance.

Could plasticity mediate highlands lizards’ resilience to climate change? A case study of the leopard iguana (Diplolaemus leopardinus) in central andes of Argentina

The rising temperature predicted is of main concern for ectotherms because its direct impact on their behavior and physiology. Since physiological performance mediates a species’ resilience to warming exposure, physiological plasticity could greatly reduce the susceptibility to climate change. We studied the degree to which Diplolaemus leopardinus’ lizards are able to adjust behavioral and physiological traits in response to short periods of temperature change. We used a split cross design to measure acclimation response of preferred body temperature (Tp), and thermal performance curve of resting metabolic rate (RMR) and evaporative water loss (EWL). Our results showed that plasticity differs among traits; whereas Tp and EWL showed lower values in warm conditions, RMR increased the temperature at which its value is highest. Moreover, RMR was affected by thermal history, showing a great increase in response to cold exposure in the group initially acclimated to warm. The reduction of EWL and the increase in optimal temperature will give lizards the potential to partially mitigate the impact of rising temperatures in the energy cost and water balance. However, the decrease in Tp and the sensitivity to the warm thermal history in RMR could be detrimental to the energy net gain increasing the species vulnerability, especially considering the increase of heat waves predicted for the next fifty years. The integration of acclimation responses in behavioral and physiological traits provides a better understanding of the range of possible responses of lizards to cope with the upcoming climatic and environmental modifications expected due to climate change.

Choosing source populations for conservation reintroductions: lessons from variation in thermal tolerance among populations of the imperilled redside dace

Reintroduction is an increasingly common conservation tool to recover populations of imperilled species, but success depends on the suitability of the introduced animals’ phenotype for their new habitat. For fishes, thermal tolerance may be a key trait in urbanized habitats. We compared thermal tolerance (CTmax) among three lineages (western, central, eastern) of imperilled redside dace Clinostomus elongatus. CTmax of eastern adults was 3-4°C lower than the other lineages, but adults of each lineage had similar thermal acclimation responses. In contrast, the acclimation response of juveniles differed by ~80% between the central and western lineages. Using this data, we predicted how each lineage would fare in a hypothetical reintroduction to relatively warm urbanized habitats. Due to the differences in juvenile acclimation responses, predicted thermal safety margins for the central lineage were double those predicted for the western lineage. Overall, we suggest that CTmax is a useful trait to incorporate into the source population selection process. However, there is an urgent need for the establishment of captive experimental research populations of imperilled species to address remaining uncertainties.

Biomass and Leaf Acclimations to Ultraviolet Solar Radiation in Juvenile Plants of Coffea arabica and C. canephora

Despite the negative impacts of increased ultraviolet radiation intensity on plants, these organisms continue to grow and produce under the increased environmental UV levels. We hypothesized that ambient UV intensity can generate acclimations in plant growth, leaf morphology, and photochemical functioning in modern genotypes of Coffea arabica and C. canephora. Coffee plants were cultivated for ca. six months in a mini greenhouse under either near ambient (UVam) or reduced (UVre) ultraviolet regimes. At the plant scale, C. canephora was substantially more impacted by UVam when compared to C. arabica, investing more carbon in all juvenile plant components than under UVre. When subjected to UVam, both species showed anatomic adjustments at the leaf scale, such as increases in stomatal density in C. canephora, at the abaxial and adaxial cuticles in both species, and abaxial epidermal thickening in C. arabica, although without apparent impact on the thickness of palisade and spongy parenchyma. Surprisingly, C. arabica showed more efficient energy dissipation mechanism under UVam than C. canephora. UVam promoted elevated protective carotenoid content and a greater use of energy through photochemistry in both species, as reflected in the photochemical quenching increases. This was associated with an altered chlorophyll a/b ratio (significantly only in C. arabica) that likely promoted a greater capability to light energy capture. Therefore, UV levels promoted different modifications between the two Coffea sp. regarding plant biomass production and leaf morphology, including a few photochemical differences between species, suggesting that modifications at plant and leaf scale acted as an acclimation response to actual UV intensity.

Cuticle Hydrocarbons Show Plastic Variation under Desiccation in Saline Aquatic Beetles

In the context of aridification in Mediterranean regions, desiccation resistance and physiological plasticity will be key traits for the persistence of aquatic insects exposed to increasing desiccation stress. Control of cuticular transpiration through changes in the quantity and composition of epicuticular hydrocarbons (CHCs) is one of the main mechanisms of desiccation resistance in insects, but it remains largely unexplored in aquatic ones. We studied acclimation responses to desiccation in adults of two endemic water beetles from distant lineages living in Mediterranean intermittent saline streams: Enochrus jesusarribasi (Hydrophilidae) and Nebrioporus baeticus (Dytiscidae). Cuticular water loss and CHC composition were measured in specimens exposed to a prior non-lethal desiccation stress, allowed to recover and exposed to a subsequent desiccation treatment. E. jesusarribasi showed a beneficial acclimation response to desiccation: pre-desiccated individuals reduced cuticular water loss rate in a subsequent exposure by increasing the relative abundance of cuticular methyl-branched compounds, longer chain alkanes and branched alkanes. In contrast, N. baeticus lacked acclimation capacity for controlling water loss and therefore may have a lower physiological capacity to cope with increasing aridity. These results are relevant to understanding biochemical adaptations to drought stress in inland waters in an evolutionary and ecological context.

State transitions and photosystems spatially resolved in individual cells of the cyanobacterium Synechococcus elongatus

State transitions are a low-light acclimation response through which the excitation of Photosystem I (PSI) and Photosystem II (PSII) is balanced; however, our understanding of this process in cyanobacteria remains poor. Here, picosecond fluorescence kinetics was recorded for the cyanobacterium Synechococcus elongatus using fluorescence lifetime imaging microscopy (FLIM), both upon chlorophyll a and phycobilisome (PBS) excitation. Fluorescence kinetics of single cells obtained using FLIM were compared with those of ensembles of cells obtained with time-resolved fluorescence spectroscopy. The global distribution of PSI and PSII and PBSs was mapped making use of their fluorescence kinetics. Both radial and lateral heterogeneity were found in the distribution of the photosystems. State transitions were studied at the level of single cells. FLIM results show that PSII quenching occurs in all cells, irrespective of their state (I or II). In S. elongatus cells, this quenching is enhanced in State II. Furthermore, the decrease of PSII fluorescence in State II was homogeneous throughout the cells, despite the inhomogeneous PSI/PSII ratio. Finally, some disconnected PBSs were resolved in most State II cells. Taken together our data show that PSI is enriched in the inner thylakoid, while state transitions occur homogeneously throughout the cell.

What can physiological capacity and behavioural choice tell us about thermal adaptation?

To date, behavioural responses and their role in thermal adaptation have largely been overlooked in small ectotherms. Here, we measure reproductive output using four adult acclimation temperatures in Drosophila melanogaster and quantify egg-laying at restricted temperatures (thermal capacity) and across a thermal gradient (thermal preference). We demonstrate that different conclusions about insect responses to changing environmental temperatures can be drawn based on whether individuals are temperature restricted or allowed a behavioural choice of temperature. When measuring physiological capacity at forced temperatures, we find an acclimation response to increasing temperatures. In contrast, when measuring behavioural choice, we find limited variation in thermal preference regardless of the acclimation temperature. Although flies are physiologically capable of increased performance at higher temperatures, these benefits might not be realized in heterogeneous environments. Our data serve as an example to illustrate why it is important to understand how behaviour and physiology contribute to thermal biology and, ultimately, the ecology of organisms. To do this, we should consider the behavioural avenues available to the organism when estimating ecologically relevant fitness consequences in varying thermal environments.

Divergent strategies to reduce stomatal pore index during water deficit in perennial angiosperms

Summary⍰ Modulation of stomatal development may be an acclimation response to low water availability. However, stomatal development plasticity has been assessed in very few species.⍰ We quantified leaf anatomy traits, including stomatal index (SI), density (SD), size (SS), and pore index (SPI), in response to water-deficit stress in river birch (Betula nigra L.), eastern redbud (Cercis canadensis L.), and silver maple (Acer saccharinum L.).⍰ Birch and redbud, but not maple, had reduced SPI in response to water deficit. The mechanism by which SPI reduction occurred (via SD or SS) varied among species and with severity of water stress. Despite reduced SPI in birch and redbud, anatomical changes were relatively small and had a minor to no effect on the theoretical maximum stomatal conductance. Furthermore, gas-exchange rates were equivalent to well-watered plants following media re-irrigation.⍰ In some tree species, stomatal development is downregulated in response to water deficit conditions. Stomatal development plasticity is facilitated by smaller or fewer stomata, depending upon the species and the intensity of the stress. Water-deficit-induced plasticity in stomatal development is species-specific, likely due to species adaptation to ecological niches.

A photosynthesis operon in the chloroplast genome drives speciation in evening primroses

Incompatibility between the cytoplasm and the nucleus is considered as major factor in species formation, but mechanistic understanding is poor. In evening primroses, a model plant for organelle genetics and population biology, hybrid offspring regularly displays chloroplast-nuclear incompatibility. These incompatibilities affect photosynthesis, a trait under selection in changing environments. Here we show that light-dependent misregulation of the plastid psbB operon (encoding core subunits of photosystem II and the cytochrome b6f complex), can lead to hybrid incompatibility, thus ultimately driving speciation. This misregulation results in an impaired light acclimation response in incompatible plants. Moreover, as a result of their different chloroplast genotypes, the parental lines differ in their photosynthesis performance upon exposure to different light conditions. Significantly, the incompatible chloroplast genome is naturally found in xeric habitats with high light intensities, whereas the compatible one is limited to mesic habitats. Consequently, our data raise the possibility that the hybridization barrier evolved as a result of adaptation to specific climatic conditions.