LAURENCIA MARILZAE SP. NOV. (CERAMIALES,RHODOPHYTA) FROM THE CANARY ISLANDS,SPAIN, BASED ON MORPHOLOGICAL AND MOLECULAR EVIDENCE1

Laurencia marilzae Gil‐Rodríguez, Sentíes et M.T. Fujii sp. nov. is described based on specimens that have been collected from the Canary Islands. This new species is characterized by distinctive yellow–orange as its natural habitat color, a terete thallus, four pericentral cells per vegetative axial segment, presence of secondary pit‐connections between adjacent cortical cells, markedly projecting cortical cells, and also by the presence of corps en cerise (one per cell) present in all cells of the thallus (cortical, medullary, including pericentral and axial cells, and trichoblasts). It also has a procarp‐bearing segment with five pericentral cells and tetrasporangia that are produced from the third and fourth pericentral cells, which are arranged in a parallel manner in relation to fertile branchlets. The phylogenetic position of this taxon was inferred based on chloroplast‐encoded rbcL gene sequence analyses. Within the Laurencia assemblage, L. marilzae formed a distinctive lineage sister to all other Laurencia species analyzed. Previously, a large number of unique diterpenes dactylomelane derivatives were isolated and identified from this taxon. L. marilzae is morphologically, genetically, and chemically distinct from all other related species of the Laurencia complex described.     

Thermal plasticity is independent of environmental history in an intertidal seaweed

Organisms inhabiting the intertidal zone have been used to study natural ecophysiological responses and adaptations to thermal stress because these organisms are routinely exposed to high‐temperature conditions for hours at a time. While intertidal organisms may be inherently better at withstanding temperature stress due to regular exposure and acclimation, they could be more vulnerable to temperature stress, already living near the edge of their thermal limits. Strong gradients in thermal stress across the intertidal zone present an opportunity to test whether thermal tolerance is a plastic or canalized trait in intertidal organisms. Here, we studied the intertidal pool‐dwelling calcified alga, Ellisolandia elongata, under near‐future temperature regimes, and the dependence of its thermal acclimatization response on environmental history. Two timescales of environmental history were tested during this experiment. The intertidal pool of origin was representative of long‐term environmental history over the alga's life (including settlement and development), while the pool it was transplanted into accounted for recent environmental history (acclimation over many months). Unexpectedly, neither long‐term nor short‐term environmental history, nor ambient conditions, affected photosynthetic rates in E. elongata. Individuals were plastic in their photosynthetic response to laboratory temperature treatments (mean 13.2°C, 15.7°C, and 17.7°C). Further, replicate ramets from the same individual were not always consistent in their photosynthetic performance from one experimental time point to another or between treatments and exhibited no clear trend in variability over experimental time. High variability in climate change responses between individuals may indicate the potential for resilience to future conditions and, thus, may play a compensatory role at the population or species level over time.     

Closely related freshwater macrophyte species,Ceratophyllum demersum and C. submersum,differ in temperature response

相似文献   

Population‐dependent acclimatization capacity of thermal tolerance in larvae of the rocky‐shore barnacle Pollicipes elegans

As environmental temperatures increase and become more seasonally variable, the ability of individuals to plastically alter their physiological responses to temperature (=acclimatize) may affect the potential for species persistence. Among marine organisms, the larval stage is often the most physiologically sensitive; larvae are also often the main dispersal stage in the life history. However, studies that address the acclimatization of marine larvae are rare. We investigated whether larvae of the gooseneck barnacle Pollicipes elegans from two temperate populations, one from the Northern Hemisphere (Mexico) and one from the Southern Hemisphere (Peru), show patterns of seasonal acclimatization to temperature. We compared the effects of temperature on swimming activity, oxygen consumption, and mortality of larvae from the two populations in both warm and cold seasons. Larvae from Mexico had higher thermal tolerances when collected in the boreal summer compared to the boreal winter, while no similar indication of seasonal acclimatization was seen in larvae from Peru. The lack of acclimatization in larvae of P. elegans from Peru may be related to recent thermal history, low selection for acclimatization due to irregular patterns of seasonal temperature change during ENSO events, or to different phylogeographic histories of Northern‐ and Southern‐hemisphere populations.     

CHEMOTAXONOMY IN MARINE ALGAE: CHEMICAL SEPARATION OF SOME LAURENCIA SPECIES (RHODOPHYTA) FROM THE GULF OF CALIFORNIA1

Species separation in the genus Laurencia (Rhodomelaceae, Rhodophyta) is complicated by the high degree of morphological variation within the species. Chemical investigations on a worldwide basis of over 15 species indicate that 1 or more of the halogenated natural products synthesized by Laurencia are unique to each species. Our chemical investigations of Laurencia pacifica, as presently understood from the Gulf of California, indicate that more than 1 species had been included under this name. Thin layer chromatographic (TLC) comparisons of the halogenated components of 3 recognizable forms of “L. pacifica” were completed. The results revealed 3 distinct forms, with halogenated products unique to each form. In each form the observed chemical characters had been previously isolated and identified and could now be positively assigned to their algal source. Comparisons were also conducted with L. pacifica Kylin (1941) from the type locality of the species, La Jolla, California, and revealed that it contained another halogenated product different from those isolated from the Gulf species. We conclude that 3 species of Laurencia have been elucidated in the Gulf of California and these are separate from L. pacifica Kylin. Each species can be distinguished by its characteristic array of halogenated compounds. Comparative thin layer chromatography of the lipid components of morphologically similar Laurencia species should prove to be a useful new taxonomic aid.     

The persistence of short‐term cold acclimation in Drosophila melanogaster (Diptera: Drosophilidae)

Daily and seasonal fluctuations in temperature present significant challenges for the survival of many ectothermic species that can be tempered via thermal acclimation. In the present study, we use multiple naturally derived genotypes of Drosophila melanogaster to determine the persistence of beneficial short‐term thermal acclimation on subsequent survival after cold shock. We found that the benefit of short‐term acclimation persisted for 2 h in most genotypes after a rapid cold hardening treatment. Genotype did not directly influence the persistence of short‐term acclimation benefits, indicating that environmental variation may be more important for the persistence of acclimation benefits rather than genetic capacity for acclimation. The present study extends the current understanding of the limits and importance of short‐term acclimation events, providing greater detail on the timing of the loss of short‐term acclimation benefits in a genetically variable natural population.     

LIFE HISTORY AND GROWTH OF LAURENCIA BRACHYCLADOS (RHODOPHYTA,CERAMIALES)1

Laurencia brachyclados Pilger from Hawai'i completed a “Polysiphonia-type” tri-phasic life history in 21 weeks in laboratory culture. Tetraspores developed into gametophytes in a nearly 1:1:1 ratio of females: males: non-reproductive. Carpospores were released as early as 21 days after mixing virgin female and male gametophytes. Cultured thalli showed a “guerilla type” growth form. Other Hawaiian Laurencia species in culture had longer maturation times or remained non-reproductive. Variation in life history schedules may influence Laurencia species coexistence and algal community structure.     

The photobiology of Heterosigma akashiwo. Photoacclimation,diurnal periodicity,and its ability to rapidly exploit exposure to high light

Periodic and seasonal exposure to high light is a common occurrence for many near‐shore and estuarine phytoplankton. Rapid acclimatization to shifts in light may provide an axis by which some species of phytoplankton can outcompete other microalgae. Patterns of photoacclimation and photosynthetic capacity in the raphidophyte Heterosigma akashiwo (Hada) Hada ex Hara et Chihara isolated from the mid‐Atlantic of the United States were followed in continuous cultures at low‐ and high‐light intensities, followed by reciprocal shifts to the opposite light level. The maximum quantum yield (F_v/F_m) as well as the photosynthetic cross‐section (σ_PSII) of photosystem II was higher in high‐light cultures compared to low‐light cultures. Significant diurnal variability in photochemistry and photoprotection was noted at both light levels, and high‐light‐acclimated cultures displayed greater variability in photoprotective pathways. When shifted from low to high light, there was only a slight and temporary decline in maximum quantum yield, while cell specific growth more than doubled within 24 h. Rapid acclimation to high light was facilitated by short‐term photoprotection (nonphotochemical quenching), reduced PSII reaction center connectivity, and electron transport. Short‐term increases in de‐epoxidated xanthophyll pigments contributed to nonphotochemical protection, but lagged behind initial increases in nonphotochemical quenching and were not the primary pathway of photoprotection in this alga. By 48 h, photochemistry of cultures shifted from low to high light resembled long‐term high‐light‐acclimated cultures. This isolate of H. akashiwo appears well poised to exploit rapid shifts in light by using unique cellular adjustments in light harvesting and photochemistry.     

Predicting ecosystem carbon balance in a warming Arctic: the importance of long‐term thermal acclimation potential and inhibitory effects of light on respiration

The carbon balance of Arctic ecosystems is particularly sensitive to global environmental change. Leaf respiration (R), a temperature‐dependent key process in determining the carbon balance, is not well‐understood in Arctic plants. The potential for plants to acclimate to warmer conditions could strongly impact future global carbon balance. Two key unanswered questions are (1) whether short‐term temperature responses can predict long‐term respiratory responses to growth in elevated temperatures and (2) to what extent the constant daylight conditions of the Arctic growing season inhibit leaf respiration. In two dominant Arctic species E riophorum vaginatum (tussock grass) and B etula nana (woody shrub), we assessed the extent of respiratory inhibition in the light (R _L/R _D), respiratory response to short‐term temperature change, and respiratory acclimation to long‐term warming treatments. We found that R of both species is strongly inhibited by light (averaging 35% across all measurement temperatures). In E . vaginatum both R _L and R _D acclimated to the long‐term warming treatment, reducing the magnitude of respiratory response relative to the short‐term response to temperature increase. In B . nana, both R _L and R _D responded to short‐term temperature increase but showed no acclimation to the long‐term warming. The ability to predict plant respiratory response to global warming with short‐term temperature responses will depend on species‐specific acclimation potential and the differential response of R _L and R _D to temperature. With projected woody shrub encroachment in Arctic tundra and continued warming, changing species dominance between these two functional groups, may impact ecosystem respiratory response and carbon balance.     

Within‐generation variation of critical thermal limits in adult Mediterranean and Natal fruit flies Ceratitis capitata and Ceratitis rosa: thermal history affects short‐term responses to temperature

Insect thermal tolerance shows a range of responses to thermal history depending on the duration and severity of exposure. However, few studies have investigated these effects under relatively modest temperature variation or the interactions between short‐ and longer‐term exposures. In the present study, using a full‐factorial design, 1 week‐long acclimation responses of critical thermal minimum (CT_min) and critical thermal maximum (CT_max) to temperatures of 20, 25 and 30 °C are investigated, as well as their interactions with short‐term (2 h) sub‐lethal temperature exposures to these same conditions (20, 25 and 30 °C), in two fruit fly species Ceratitis capitata (Wiedemann) and Ceratitis rosa Karsch from South Africa. Flies generally improve heat tolerance with high temperature acclimation and resist low temperatures better after acclimation to cooler conditions. However, in several cases, significant interaction effects are evident for CT_max and CT_min between short‐ and long‐term temperature treatments. Furthermore, to better comprehend the flies' responses to natural microclimate conditions, the effects of variation in heating and cooling rates on CT_max and CT_min are explored. Slower heating rates result in higher CT_max, whereas slower cooling rates elicit lower CT_min, although more variation is detected in CT_min than in CT_max (approximately 1.2 versus 0.5 °C). Critical thermal limits estimated under conditions that most closely approximate natural diurnal temperature fluctuations (rate: 0.06 °C min^?1) indicate a CT_max of approximately 42 °C and a CT_min of approximately 6 °C for these species in the wild, although some variation between these species has been found previously in CT_max. In conclusion, the results suggest critical thermal limits of adult fruit flies are moderated by temperature variation at both short and long time scales and may comprise both reversible and irreversible components.     

Exposure to solar radiation drives organismal vulnerability to climate: Evidence from an intertidal limpet

Understanding the physiological abilities of organisms to cope with heat stress is critical for predictions of species’ distributions in response to climate change. We investigated physiological responses (respiration and heart beat rate) of the ectotherm limpet Patella vulgata to heat stress events during emersion and the role of seasonal and microclimatic acclimatization for individual thermal tolerance limits. Individuals were collected from 5 microhabitats characterized by different exposure to solar radiation in the high intertidal zone of a semi-exposed rocky shore in winter and summer of 2014. Upper thermal tolerance limits (heat coma temperatures – HCTs, and heart rate Arrhenius break temperatures - ABTs) were determined for individuals from each microhabitat in both seasons under laboratory conditions. While we found a clear seasonal acclimatization, i.e., higher HCTs and ABTs in summer than in winter, we did not find evidence for microhabitat-specific responses that would suggest microclimatic acclimatization. However, operative limpet temperatures derived from in-situ temperature measurements suggest that individuals from sun exposed microhabitats have a much narrower thermal safety margins than those from less exposed surfaces or within crevices. Microhabitat specific thermal safety margins caused by high thermal heterogeneity at small spatial scales and the lack of short term acclimatization will likely shape small scale distribution patterns of intertidal species in response to the predicted increase in the frequency and intensity of heat waves.     

THE EFFECTS OF TEMPERATURE ON THE PHOTOSYNTHETIC PARAMETERS AND RECOVERY OF TWO TEMPERATE BENTHIC MICROALGAE,AMPHORA CF. COFFEAEFORMIS AND COCCONEIS CF. SUBLITTORALIS (BACILLARIOPHYCEAE)1

Temperature and irradiance are the most important factors affecting marine benthic microalgal photosynthetic rates in temperate intertidal areas. Two temperate benthic diatoms species, Amphora cf. coffeaeformis (C. Agardh) Kütz. and Cocconeis cf. sublittoralis Hendey, were investigated to determine how their photosynthesis responded to temperatures ranging from 5°C to 50°C after short‐term exposure (1 h) to a range of irradiance levels (0, 500, and 1,100 μmol photons · m^?2 · s^?1). Significant differences were observed between the temperature responses of maximum relative electron transport rate (rETRmax), photoacclimation index (E_k), photosynthetic efficiency (α), and effective quantum yield (ΔF/F_m’) in both species. A. coffeaeformis had a greater tolerance to higher temperatures than C. sublittoralis, with nonphotochemical quenching (NPQ) activated at temperatures of 45°C and 50°C. C. sublittoralis, however, demonstrated a more rapid rate of recovery at ambient temperatures. Temperatures between 10°C and 20°C were determined to be optimal for photosynthesis for both species. High temperatures and irradiances caused a greater decrease in ΔF/F_m’ values. These results suggest that the effects of temperature are species specific and that short‐term exposure to adverse temperature slows the recovery process, which subsequently leads to photoinhibition.     

Contrasting effects of high‐intensity photosynthetically active radiation on two bloom‐forming dinoflagellates

While light limitation can inhibit bloom formation in dinoflagellates, the potential for high‐intensity photosynthetically active radiation (PAR) to inhibit blooms by causing stress or damage has not been well‐studied. We measured the effects of high‐intensity PAR on the bloom‐forming dinoflagellates Alexandrium fundyense and Heterocapsa rotundata. Various physiological parameters (photosynthetic efficiency F_v/F_m, cell permeability, dimethylsulfoniopropionate [DMSP], cell volume, and chlorophyll‐a content) were measured before and after exposure to high‐intensity natural sunlight in short‐term light stress experiments. In addition, photosynthesis‐irradiance (P‐E) responses were compared for cells grown at different light levels to assess the capacity for photophysiological acclimation in each species. Experiments revealed distinct species‐specific responses to high PAR. While high light decreased F_v/F_m in both species, A. fundyense showed little additional evidence of light stress in short‐term experiments, although increased membrane permeability and intracellular DMSP indicated a response to handling. P‐E responses further indicated a high light‐adapted species with Chl‐a inversely proportional to growth irradiance and no evidence of photoinhibition; reduced maximum per‐cell photosynthesis rates suggest a trade‐off between photoprotection and C fixation in high light‐acclimated cells. Heterocapsa rotundata cells, in contrast, swelled in response to high light and sometimes lysed in short‐term experiments, releasing DMSP. P‐E responses confirmed a low light‐adapted species with high photosynthetic efficiencies associated with trade‐offs in the form of substantial photoinhibition and a lack of plasticity in Chl‐a content. These contrasting responses illustrate that high light constrains dinoflagellate community composition through species‐specific stress effects, with consequences for bloom formation and ecological interactions within the plankton.     

Seasonal variation in basal and plastic cold tolerance: Adaptation is influenced by both long‐ and short‐term phenotypic plasticity

Understanding how thermal selection affects phenotypic distributions across different time scales will allow us to predict the effect of climate change on the fitness of ectotherms. We tested how seasonal temperature variation affects basal levels of cold tolerance and two types of phenotypic plasticity in Drosophila melanogaster. Developmental acclimation occurs as developmental stages of an organism are exposed to seasonal changes in temperature and its effect is irreversible, while reversible short‐term acclimation occurs daily in response to diurnal changes in temperature. We collected wild flies from a temperate population across seasons and measured two cold tolerance metrics (chill‐coma recovery and cold stress survival) and their responses to developmental and short‐term acclimation. Chill‐coma recovery responded to seasonal shifts in temperature, and phenotypic plasticity following both short‐term and developmental acclimation improved cold tolerance. This improvement indicated that both types of plasticity are adaptive, and that plasticity can compensate for genetic variation in basal cold tolerance during warmer parts of the season when flies tend to be less cold tolerant. We also observed a significantly stronger trade‐off between basal cold tolerance and short‐term acclimation during warmer months. For the longer‐term developmental acclimation, a trade‐off persisted regardless of season. A relationship between the two types of plasticity may provide additional insight into why some measures of thermal tolerance are more sensitive to seasonal variation than others.     

Seasonal patterns of leaf photosynthetic and secondary xylem vascular traits in current‐year stems of three Sorbus species with contrasting growth habits

Seasonal effects of environmental variables on photosynthetic activity and secondary xylem formation provide data to demonstrate how environmental factors together with leaf ageing during the season control tree growth. In this study, we assessed physiological responses in photosynthetic behaviour to seasonal climate changes, and also identified seasonal differences in vascular traits within differentiating secondary xylem tissue from three diploid species of the taxonomically complex genus Sorbus. From sampling day 150, a clear physiological segregation of S. chamaemespilus from S. torminalis and S. aria was evident. The shrubby species S. chamaemespilus could be distinguished by a higher photosynthetic capacity between days 150 and 206. This was reflected in its associations with net CO₂ assimilation rate (P_N), maximum photochemical efficiency of PSII (F_v/F_m), variable‐to‐initial fluorescence ratio (F_v/F₀), potential electron acceptor capacity (‘area’) in multivariate space, and also its associations with log‐transformed vessel area and log‐transformed relative conductivity between days 239 and 268. The maximum segregation and differentiation among the examined Sorbus species was on sampling day 206. The largest differences between S. torminalis and S. aria were found on day 115, when the latter species clearly showed closer associations with high values of vessel density and transpiration (E). Sampling day clusters were arranged along an arch‐like gradient that reflected the positioning of the entire growing season in multivariate space. This arch‐like pattern was most apparent in the case of S. chamaemespilus, but was also observed in S. torminalis and S. aria.     

Short‐term acclimation to warmer temperatures accelerates leaf carbon exchange processes across plant types

While temperature responses of photosynthesis and plant respiration are known to acclimate over time in many species, few studies have been designed to directly compare process‐level differences in acclimation capacity among plant types. We assessed short‐term (7 day) temperature acclimation of the maximum rate of Rubisco carboxylation (V_cmax), the maximum rate of electron transport (J_max), the maximum rate of phosphoenolpyruvate carboxylase carboxylation (V_pmax), and foliar dark respiration (R_d) in 22 plant species that varied in lifespan (annual and perennial), photosynthetic pathway (C₃ and C₄), and climate of origin (tropical and nontropical) grown under fertilized, well‐watered conditions. In general, acclimation to warmer temperatures increased the rate of each process. The relative increase in different photosynthetic processes varied by plant type, with C₃ species tending to preferentially accelerate CO₂‐limited photosynthetic processes and respiration and C₄ species tending to preferentially accelerate light‐limited photosynthetic processes under warmer conditions. R_d acclimation to warmer temperatures caused a reduction in temperature sensitivity that resulted in slower rates at high leaf temperatures. R_d acclimation was similar across plant types. These results suggest that temperature acclimation of the biochemical processes that underlie plant carbon exchange is common across different plant types, but that acclimation to warmer temperatures tends to have a relatively greater positive effect on the processes most limiting to carbon assimilation, which differ by plant type. The acclimation responses observed here suggest that warmer conditions should lead to increased rates of carbon assimilation when water and nutrients are not limiting.     

Quantifying the effects of drought on abrupt growth decreases of major tree species in Switzerland

Drought entails important effects on tree physiology, which may result in short‐ to long‐term radial growth decreases. While the majority of studies have focused on annual drought‐related variability of growth, relatively little is known about sustained growth decreases following drought years. We apply a statistical framework to identify climatic factors that induce abrupt growth decreases and may eventually result in tree mortality. We used tree‐ring data from almost 500 standing dead trees and 200 living trees in eight sites of the Swiss network of strict forest reserves, including four of the most important Central European tree species (Abies alba, Picea abies, Fagus sylvatica and Quercus spp.). First, to assess short‐term growth responses to drought under various climate and site conditions, we calculated correlations and linear mixed‐effects models between ring‐width indices (RWIs) and drought based on the Standardized Precipitation Evapotranspiration Index (SPEI). Second, to quantify drought effects on abrupt growth decreases, we applied distributed lag nonlinear models (DLNMs), which account for both delayed effects and the nonlinear relationship between the SPEI and the occurrence of abrupt growth decreases. Positive correlations between RWIs and the SPEI indicated short‐term growth responses of all species, particularly at arid sites. Results of the DLNMs revealed species‐specific growth responses to drought. For Quercus spp., abrupt growth decreases were more likely to occur several years following severe drought, whereas for P. abies, A. alba, and F. sylvatica abrupt growth decreases started frequently immediately in the drought year. We conclude that the statistical framework allows for quantifying the effects of drought intensity on the probability of abrupt growth decreases, which ultimately contributes to an improved understanding of climate impacts on forest community dynamics.     

Photoacclimatory and photoprotective responses to cold versus heat stress in high latitude reef corals

Corals at the world's southernmost coral reef of Lord Howe Island (LHI) experience large temperature and light fluctuations and need to deal with periods of cold temperature (<18°C), but few studies have investigated how corals are able to cope with these conditions. Our study characterized the response of key photophysiological parameters, as well as photoacclimatory and photoprotective pigments (chlorophylls, xanthophylls, and β‐carotene), to short‐term (5‐d) cold stress (~15°C; 7°C below control) in three LHI coral species hosting distinct Symbiodinium ITS2 types, and compared the coral–symbiont response to that under elevated temperature (~29°C; 7°C above control). Under cold stress, Stylophora sp. hosting Symbiodinium C118 showed the strongest effects with regard to losses of photochemical performance and symbionts. Pocillopora damicornis hosting Symbiodinium C100/C118 showed less severe bleaching responses to reduced temperature than to elevated temperature, while Porites heronensis hosting Symbiodinium C111* withstood both reduced and elevated temperature. Under cold stress, photoprotection in the form of xanthophyll de‐epoxidation increased in unbleached P. heronensis (by 178%) and bleached Stylophora sp. (by 225%), while under heat stress this parameter increased in unbleached P. heronensis (by 182%) and in bleached P. damicornis (by 286%). The xanthophyll pool size was stable in all species at all temperatures. Our comparative study demonstrates high variability in the bleaching vulnerability of these coral species to low and high thermal extremes and shows that this variability is not solely determined by the ability to activate xanthophyll de‐epoxidation.