Frog call transmission in forestry monocultures: Are there drawbacks?

Anuran males emit advertisement calls for the purpose of attracting females and repelling conspecific males. Call transmission is influenced by the acoustics of the propagation environment, including vegetation. Thus, forestry monocultures of non-native trees represent artificial environments that could modify call transmission. These monocultures have substituted large areas of Atlantic Forest in southern Brazil, representing a conservation challenge. Considering this context, we hypothesized that anurans have calls that are less attenuated in their native environment than in forest plantations. To test it, we performed sound transmission experiments using calls of three anuran species native to southern Brazil: Boana bischoffi, B. leptolineata, and Hylodes meridionalis. We compared sound attenuation between the native forest and forestry monocultures (Eucalyptus sp. and Pinus sp. forests), and included distance from the sound source, air temperature, humidity, and vegetation density as cofactors in linear mixed models. Our results show that the advertisement calls of the two tree frogs (Boana) attenuate less in tree plantations than in native forests, while the third species shows either no differences or less attenuation in native forests. Our results can be understood according to differences in natural history and microhabitat use among the studied species. The two tree frog species vocalize perched from vegetation so their calls become better transmitted in forestry monocultures, which have fewer trees than the native forest. On the other hand, H. meridionalis calls from rocks on streams and the propagation is finely tuned to this peculiar microhabitat. We discuss the conservation implications of our findings for anurans and for the Atlantic Forest. Abstract in Portuguese and Spanish are available with online material.     

Responses of the desert green algae,Chlorella sp. to drought stress

Desert algae are important components of the desert soil crust and play an essential role in desert soil ecosystem development. Owing to their special habitat, desert algae are often exposed to harsh environments, among which drought represents the most common stress. Green algae are considered to have drought tolerance potential; however, only a few studies have investigated this. In this study, we selected the green alga Chlorella sp., which was isolated from desert soil, and studied its physiological response to polyethylene glycol (PEG) 6000-induced drought stress. The results showed that drought stress can affect the photosynthetic efficiency of Chlorella sp., reduce its water retention ability, and destroy its ultrastructure. However, Chlorella sp. can cope with drought stress through a series of physiological regulatory strategies. Protective strategies include quick recovery of photosynthetic efficiency and increased chlorophyll content. In addition, induced synthesis of soluble proteins, lipids, and extracellular polysaccharide (EPS), and accumulation of osmotic regulatory substances, such as sucrose and trehalose, also contribute to improving drought tolerance in Chlorella sp. This study provides insights into the physiological responses of Chlorella sp. to drought stress, which may be valuable for understanding the underlying drought adaptation mechanisms of desert green algae.     

An ancient enzyme finds a new home: Prevalence and neofunctionalization of trypsin in marine phytoplankton

Trypsin is an ancient protease best known as a digestive enzyme in animals, and traditionally believed to be absent in plants and protists. However, our recent studies have revealed its wide presence and important roles in marine phytoplankton. Here, to gain a better understanding on the importance of trypsin in phytoplankton, we further surveyed the distribution, diversity, evolution and potential ecological roles of trypsin in global ocean phytoplankton. Our analysis indicated that trypsin is widely distributed both taxonomically and geographically in marine phytoplankton. Furthermore, by systematic comparative analyses we found that algal trypsin could be classified into two subfamilies (trypsin I and trypsin II) and exhibited highly duplicated and diversified during evolution. We also observed markedly different domain sequences and organizations between and within the subfamilies, suggesting potential neofunctionalization. Diatoms contain both subfamilies of trypsin, with higher numbers of genes and more environment-responsive expression of trypsin than other lineages. The duplication and subsequent neofunctionalization of the trypsin family may be important in diatoms for adapting to dynamical environmental conditions, contributing to diatoms' dominance in the coastal oceans. This work advances our knowledge on the distribution and neofunctionalization of this ancient enzyme and creates a new window of research on phytoplankton biology.     

Effects of oxygen level on metabolism and development of seedlings of Trapa natans and two ecologically related species

Seeds of the water plant Trapa natans L. (water chestnut) can germinate in strict anoxia. The seedlings show seminal roots growing upwards while shoot buds remain quiescent until O₂ becomes available. Trapa seedlings are highly tolerant to anoxia. The rate of ethanol fermentation was 21.2 μmol (g FW)⁻¹ h⁻¹, while production of lactate was negligible and lower than that of succinate. The seminal root of Trapa compares better to the rice coleoptile rather than to the rice root, both functionally and as to the metabolic response to anoxia. The anaerobic germination of Nuphar luteum L. and Scirpus mucronatus L. was also characterized by a limited developmental program.     

Water quality during egg incubation influences yolk-sac fry sodium kinetics in Atlantic salmon, Salmo salar L.: a possible mechanism of adaptation to acid waters

Atlantic salmon ( Salmo salar L.) fry hatched from eggs transferred from high-Na to low-Na water during the eyed stage of development had a significantly higher V_max and lower K_m (P <0.01) of the sodium uptake mechanism than fry hatched from eggs incubated entirely in low-Na or high-Na water.
Fry hatched from eggs transferred to acid, high aluminium water during the eyed stage of development had a similar V_max and K_m to fry hatched from eggs incubated entirely in high- or low-Na water. Eggs incubated continuously in acid, high aluminium (low-Na) water produced fry with significantly lower K_m and V_max values than fry hatched from eggs incubated continuously in low-Na water. Eggs and fry in acid, high aluminium water continually lost sodium and mortality was 100% at 5 5 M O degree-days (2–3 weeks after hatching).
The results are discussed with respect to the influence of perivitelline fluid ion activities in eggs in acid, high aluminium water on the kinetic characteristics of sodium uptake in yolk-sac fry. A possible mechanism for the long-term adaptation of teleosts in acidified natural waters is also proposed.     

MULTIVARIATE ANALYSIS OF SELECTION IN EXPERIMENTAL POPULATIONS DERIVED FROM HYBRIDIZATION OF TWO ECOTYPES OF THE ANNUAL PLANT DIODIA TERES W. (RUBIACEAE)

Morphologically variable F₂ genotypes derived from hybridization of coastal and inland ecotypes of the annual plant Diodia teres were used to identify selection on morphological traits in the natural habitat of each ecotype. These ecotypes occur in very different habitats, and have evolved pronounced morphological differentiation. Selection analysis can suggest whether present patterns of selection can explain morphological differences between ecotypes. F₂ genotypes were characterized morphologically, clonally replicated, and transplanted into the habitat of each ecotype. Selection was measured on six morphological traits. Directional and stabilizing selection occurred on many traits; direction and strength of selection varied sharply at different stages of growth, as revealed by a path-analysis approach that divided selection into a set of independent components. Directional selection favored traits of the native population at the coastal habitat, but less so at the inland habitat. Selection was of sufficient strength to create the observed morphological differences between ecotypes in 25–100 generations, given constant selection and sufficient genetic variation. In effects on fitness, most traits were neither independent nor consistently interactive with other traits. Rather, many traits entered into strong but evanescent interactions affecting particular components of fitness. Observed interactions did not support the hypothesis that the morphology of each ecotype was functionally integrated to a high degree.     

EFFECTS OF LONG TERM EXPOSURE TO LOW TEMPERATURE ON THE PHOTOSYNTHETIC APPARATUS OF DUNALIELLA TERTIOLECTA (CHLOROPHYCEAE)1

The effects of long term exposure to suboptimal growth temperature on the photosynthetic apparatus of Dunaliella tertiolecta Butcher were investigated using carbon fixation rate versus irradiance curves and the variable fluorescence induction method. Carbon fixation rates per unite chlorophyll a at saturating (p^B_m) and subsaturating (α^B) irradiances were 55% and 39% lower, respectively, at 12° C than at 20° C. Chlorophyll a quotas and the spectrally averaged in vivo absorption cross section normalized to chlorophyll a (a^*) were not significantly different at these two temperatures. Analysis of the fluorescence kinetics revealed 1) no significant variations of the amount of PSII photoactive reaction centers per unit chlorophyll a, 2) a 14% decrease of the PSII quantum yield(+) and 3) a 29% decrease of the energy transfer efficiency between the light harvesting chlorophyll a pigment bed and the PSII reaction centers. The decrease in energy transfer efficiency between the antennae and the PSII reaction centers at 12° C was interpreted as a mechanism to avoid photoinhibition.     

Effect of salinisation of soil on growth and macro- and micro-nutrient accumulation in seedlings of Acacia catechu (Mimosaceae)

The effects of salinisation of soil on Acacia catechu (Mimosaceae) were studied by means of emergence and growth of seedlings and pattern of mineral accumulation. A mixture of chlorides and sulphates of Na, K, Ca and Mg was added to the soil and salinity was maintained at 4.1, 6.3, 8.2,10.1 and 12.2 dSm⁻¹. A negative relationship between proportion of seed germination and salt concentration was obtained. Seedlings did not emerge when soil salinity exceeded 10.1 dSm⁻¹. Results suggested that this tree species is salt tolerant at the seed germination stage. Seedlings survived and grew up to soil salinity of 10.1 dSm⁻¹, which suggests that this species is salt tolerant at the seedling stage too. Elongation of stem and root was retarded by increasing salt stress. Among the tissues, young roots and stem were most tolerant to salt stress and were followed by old roots and leaves, successively. Leaf tissue exhibited maximum reduction in dry mass production in response to increasing salt stress. However, production of young roots and death of old roots were found to be continuous and plants apparently use this process as an avoidance mechanism to remove excess ions and delay onset of ion accumulation in this tissue. This phenomenon, designated “fine root turnover”, is of importance to the mechanisms of salt tolerance. Plants accumulated Na in roots and were able to regulate transfer of Na ions to leaves. Stem tissues were a barrier for translocation of Na from root to leaf. Moreover, K was affected in response to salinity; it rapidly decreased in root tissues with increased salinisation. Nitrogen content decreased in all tissues (leaf, stem and root) in response to low water treatment and salinisation of soil. Phosphorus content significantly decreased, while Ca increased in leaves as soil salinity increased. Changes in tissue and whole plant accumulation patterns of the other elements tested, as well as possible mechanisms for avoidance of Na toxicity in this tree species during salinisation, are discussed.     

Comparative ultrastructural properties of pallisade tissue and spongy tissue chloroplasts from normal and mutant leaves of Pisum sativum L.*

Abstract. The ultrastructure of chloroplasts from palisade and spongy tissue was studied in order to analyse the adaptation of chloroplasts to the light gradient within the bifacial leaves of pea. Chloroplasts of two nuclear gene mutants of Pisum sativum (chlorotica-29 and chlorophyll b-less 130A), grown under normal light conditions, were compared with the wild type (WT) garden-pea cv. ‘Dippes Gelbe Viktoria’. The differentiation of the thylakoid membrane system of plastids from normal pea leaves exhibited nearly the same degree of grana formation in palisade and in spongy tissue. Using morphometrical measurements, only a slight increase in grana stacking capacity was found in chloroplasts of spongy tissue. In contrast, chloroplasts of mutant leaves differed in grana development in palisade and spongy tissue, respectively. Their thylakoid systems appeared to be disorganized and not developed as much as in chloroplasts from normal pea leaves. Grana contained fewer lamellae per granum, the number of grana per chloroplast section was reduced and the length of appressed thylakoid regions was decreased. Nevertheless, chloroplasts of the mutants were always differentiated into grana and stroma thylakoids. The structural changes observed and the reduction of the total chlorophyll content correlated with alterations in the polypeptide composition of thylakoid membrane preparations from mutant chloroplasts. In sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE), polypeptide bands with a relative molecular mass of 27 and 26 kilodalton (kD) were markedly reduced in mutant chloroplasts. These two polypeptides represented the major apoproteins of the light harvesting chlorophyll a/b complex from photosystem II (LHC-II) as inferred from a comparison with the electrophoretic mobility of polypeptides isolated from the LHC-II.     

贺兰山不同生境旱生灌木的解剖学研究

贺兰山荒漠地带三种不同基质生境的２０种旱生灌木的营养器官的比较解剖学研究表明：其共同特点是叶片的表面积／体积的比值小,叶表具厚的角质层、表皮毛,气孔下陷、并具孔下室,叶向中栅栏组织发达;轴器官中木栓层细胞层数多,皮层较厚,机械组织发达,木薄壁组织及髓部细胞的细胞壁术化加厚,根内都具周皮、木质部的导管分子大小不一、频率较高。此外,根、茎、叶中普遍存在粘液细胞和草酸钙结晶,部分植物的根和茎内有异常维管组织。这些结构特征都与早生环境相关,而不同基质生境中生长的植物尚存在一定差异。