Mode of zooxanthella transmission does not affect zooxanthella diversity in acroporid corals

Two distinct modes of algal endosymbiont acquisition exist in corals, a direct transmission from the parental colony to the eggs and a larval or post-larval uptake from the environment. The former, maternal-transmission mode is expected to be a more closed system, while the latter is believed to be an open system. Here we test the hypothesis that the diversity of symbionts in closed systems is lower than that in open systems. We examine the identity and diversity of the algal endosymbionts (zooxanthellae) in 25 Montipora species sampled from Irian Jaya (Indonesia) and Magnetic Island (central Great Barrier Reef) and compare the results with those previously obtained from Acropora species, which belong to the same family. All Montipora colonies examined harbour clade C zooxanthellae, with two colonies harbouring both clade C and D zooxanthellae simultaneously. Two algal strains (named C· and D· in this study) present in Montipora have not been observed in Acropora, and may have co-evolved with Montipora. Symbiodinium C· shows approximately 5% sequence divergence from C strains observed in Acropora spp. and occurs in 76% of the colonies examined. Nevertheless, several other C strains commonly found in other corals occur in some of the Montipora colonies. Montipora species transmit their algal endosymbionts directly to the eggs, while Acropora species have to acquire zooxanthellae from the environment every generation. Contrary to our expectations, the diversity of zooxanthellae is similar for the two genera, indicating that the mode of symbiont transmission (i.e. maternal versus horizontal) does not affect symbiont diversity in acroporid corals.Communicated by M.S. Johnson, Crawley     

Testosterone stress does not increase asymmetry of a hormonally mediated sexual ornament in a lizard

The theory that fluctuating asymmetry is sensitive to both environmental and genetic stress is gaining acceptance among evolutionary biologists. Most empirical work has focused on ornamental traits on the assumption that they are more susceptible to stress. In tegumentary coloration is a common ornament in nature, and frequently has a hormonal basis. Earlier studies in the lizard Psammodromus algirus indicate that testosterone induces the development of head nuptial coloration in large males and, at the same time, produces an increase of the ectoparasite load and higher mortality. Hence, the manipulation of testosterone levels may be a way to increase ornament expression and simultaneously create conditions that may make symmetrical development difficult. This positive covariation between character size and symmetry is opposite to that expected in theory for sexually selected traits, so the predicted elevation of asymmetry due to the treatment cannot be confounded by any intrinsic association between symmetry and character size. We firstly consider the effect that testosterone supplementation has on two variables that reflect the symmetry of bilateral throat nuptial coloration in large P. algirus males. Also, we examine whether ornament symmetry is positively associated with reproductive success, a prediction of theory of sexually selected symmetry. Testosterone treatment did not increase the fluctuating asymmetry of throat coloration. Size asymmetry increased with character size in individuals with a fragmented colour pattern, but changed suddenly to a highly symmetric pattern in individuals with non-fragmented coloration. Mirror asymmetry decreased steadily with character size. These results suggest that the development of coloration on both sides of the throat midline follows a random pattern. Asymmetry did not correlate with variables that estimated reproductive success, suggesting that asymmetry is not affected by physiological stress and that this trait is not a sexually selected signal in P. algirus. Received: 1 July 1996 / Accepted after revision: 4 May 1997     

Between discrete and continuous: consumer-resource dynamics with synchronized reproduction

In many consumer-resource systems the consumer population has synchronized reproduction at regular intervals (e.g., years) but consumes the resource and dies continuously, while the resource population grows continuously or has overlapping generations that are short relative to the time between consumer reproductive events. Such systems require "semi-discrete" models that have both discrete and continuous components. This paper defines and analyzes a canonical, semi-discrete model for a widespread class of consumer-resource interactions in which the consumer is a discrete breeder and the resource reproduction can be described continuously. The model is the analog of the Nicholson-Bailey and Lotka-Volterra models for discrete and continuous systems, respectively. It thereby develops the basis for understanding more realistic, and hence more complex, semi-discrete models. The model can display stable equilibria, consumer-resource cycles, and single-species-like overcompensation cycles. Cycles are induced by high maximum fecundity in the consumer. If the resource grows rapidly and the consumer has high maximum fecundity, the model reduces to a single-species discrete-time model of the consumer, which can exhibit overcompensation cycles. By contrast, such cycles in discrete consumer-resource models typically occur only in the resource once the consumer is extinct. Also unlike a common class of discrete models that do not display consumer-resource cycles with periods below four years, semi-discrete models can exhibit consumer-resource cycles with periods as short as two years.     

Nectar secondary compounds affect self-pollen transfer: implications for female and male reproduction

Pollen movement within and among plants affects inbreeding, plant fitness, and the spatial scale of genetic differentiation. Although a number of studies have assessed how plant and floral traits influence pollen movement via changes in pollinator behavior, few have explored how nectar chemical composition affects pollen transfer. As many as 55% of plants produce secondary compounds in their nectar, which is surprising given that nectar is typically thought to attract pollinators. We tested the hypothesis that nectar with secondary compounds may benefit plants by encouraging pollinators to leave plants after visiting only a few flowers, thus reducing self-pollen transfer. We used Gelsemium sempervirens, a plant whose nectar contains the alkaloid gelsemine, which has been shown to be a deterrent to foraging bee pollinators. We found that high nectar alkaloids reduced the total and proportion of self-pollen received by one-half and one-third, respectively. However, nectar alkaloids did not affect female reproduction when we removed the potential for self-pollination (by emasculating all flowers on plants). We then tested the assumption that self-pollen in combination with outcrossed pollen depresses seed set. We found that plants were weakly self-compatible, but self-pollen with outcrossed pollen did not reduce seed set relative to solely outcrossed flowers. Finally, an exponential model of pollen carryover suggests that high nectar alkaloids could benefit plants via increased pollen export (an estimate of male function), but only when pollinators were efficient and abundant and plants had large floral displays. Results suggest that high nectar alkaloids may benefit plants via increased pollen export under a restricted set of ecological conditions, but in general, the costs of high nectar alkaloids in reducing pollination balanced or outweighed the benefits of reducing self-pollen transfer for estimates of female and male reproduction.     

Organophosphorous compounds and oxidative stress: a review

Organophosphorous compounds (OP) have largely been used as pesticides globally. These chemicals induce oxidative stress as a possible mechanism of action, which has been a focus of toxicological research for the last decade. This review evaluated the presence of oxidative stress, balance between total antioxidant capacity, and oxygen free radicals associated with OP compound exposure. Oxidative stress induced by OP leads to disturbances in function of different organs and tissues. Evidence indicates that stimulation of free radical production, induction of lipid peroxidation, and disturbance of the total antioxidant capacity are mechanisms of toxicity induced by most OP. Thus, use of antioxidants may be beneficial in treatment of OP poisoning, which remains to be elucidated with further clinical trials.     

Predator guild does not influence orangutan alarm call rates and combinations

Monkey alarm calls have shown that in the primate clade, combinatorial rules in acoustic communication are not exclusive to humans. A recent hypothesis suggests that the number of different call combinations in monkeys increases with increased number of predator species. However, the existence of combinatorial rules in great ape alarm calls remains largely unstudied, despite its obvious relevance to ideas about the evolution of human speech. In this paper, we examine the potential use of combinatorial rules in the alarm calls of the only Asian great ape: the orangutan. Alarm calls in orangutans are composed of syllables (with either one or two distinct elements), which in turn are organized into sequences. Tigers and clouded leopards are predators for Sumatran orangutans, but in Borneo, tigers are extinct. Thus, orangutans make a suitable great ape model to assess alarm call composition in relation to the size of the predator guild. We exposed orangutans on both islands to a tiger and control model. Response compositionality was analyzed at two levels (i.e., syllable and syllable sequences) between models and populations. Results were corroborated using information theory algorithms. We made specific, directed predictions for the variation expected if orangutans used combinatorial rules. None of these predictions were met, indicating that monkey alarm call combinatorial rules do not have direct homologues in orangutans. If these results are replicated in other great apes, this indicates that predation did not drive selection towards ever more combinatorial rules in the human lineage.     

Antimony induces oxidative stress and cell death in normal hepatocytes

Antimony (Sb) accumulates in the liver which is one of the target organs for metal-mediated toxicity. Although toxicity of Sb was previously investigated, the precise mechanism of Sb-induced hepatotoxicity remains to be determined. The aim of this study was to examine the role of oxidative stress, and mitochondria in the induction of cell death by Sb. Our results showed that liver cell lysis induced by Sb is mediated by reactive oxygen species (ROS) formation, lipid peroxidation and decline of mitochondrial membrane potential (MMP). Antimony-induced ROS formation, lipid peroxidation and reduction of MMP were significantly diminished by antioxidants and ROS scavengers such as dimethyl sulfoxide and mannitol; mitochondrial permeability transition (MPT) pore sealing agents such as carnitine and trifluoperazine; and adenosine triphosphate (ATP) generator, L-glutamine. Antimony-induced ROS formation, lipid peroxidation and fall in MMP were potentiated by glutathione (GSH) depletion via n-bromoheptane. MPT pore sealing agents and ATP generator inhibited hepatotoxicity, indicating Sb-activated cell death via mitochondrial pathway. Pretreatment of hepatocytes with antioxidants and ROS scavengers also blocked cell death induced by Sb, whereas GSH depletion enhances Sb-induced cell death, suggesting that oxidative stress may be directly involved in the reduction of MMP. These findings contribute to a better understanding of the mechanisms that mediate Sb-induced cell death in isolated rat hepatocytes.     

Oleuropein alleviates malathion-induced oxidative stress and DNA damage in rats

The effects of acute exposure to 250 mg/kg malathion and the protective effects of 20 mg/kg oleuropein, both administered intraperitoneally, were evaluated in Wistar male rats. Malathion administration increased malondialdehyde, nitric oxide, 8-hydroxy-2′-deoxyguanosine, total oxidant status, and DNA damage, yet decreased total antioxidant activity, superoxide dismutase, and catalase activities in blood, liver, and kidney. Administration of oleuropein reversed malathion-induced oxidative stress, lipid peroxidation, DNA damage, and antioxidant enzyme activity.     

Competition and cooperation: bumblebee spatial organization and division of labor may affect worker reproduction late in life

Within-group conflict may influence the degree to which individuals within a group cooperate. For example, the most dominant individuals within a group often gain access to the best resources and may be less inclined to perform risky tasks. We monitored space use and division of labor among all workers in three colonies of bumblebees, Bombus impatiens, during the ergonomic and queenless phases of their colony cycle. We then measured the two largest oocytes in each worker to estimate each individual's reproductive potential at the end of the colony cycle. We show that workers that remained farther from the queen while inside the nest and avoided risky or more energy-expensive tasks during the ergonomic phase developed larger oocytes by the end of the colony cycle. These individuals also tended to be the largest, oldest workers. After the queen died, these workers were more likely than their nestmates to increase brood incubation. Our results suggest that inactive bumblebees may be storing fat reserves to later develop reproductive organs and that the spatial organization of workers inside the nest, particularly the distance workers maintain from the queen, may predict which individuals will later have the greatest reproductive potential in the colony.     

Permethrin induced oxidative stress and neurotoxicity on the freshwater beetle Laccophilus minutus

Biomonitoring has become a useful tool in environmental risk assessment of anthropogenic activities releasing disturbing pollutants. Permethrin, used worldwide to control a wide range of pest insects, can threaten aquatic biota, potentially useful as precocious bioindicators in ecotoxicology. This study seeks to assess the acute toxicity permethrin to the freshwater beetle, its availability in water, as well as, its uptake. The acute toxicity of permethrin to non-target species was studied under laboratory conditions to assess its effect, after the exposure 48 h, on the freshwater beetle Laccophilus minitus considering changes in some enzymatic activities; a specific biomarker of neurotoxicity (acetylcholinesterase) and a non-specific biomarker of oxidative stress (superoxide dismutase and catalase). The rates of permethrin in water and insects were determined using gas chromatography. The low measured concentration of the pesticide 0.0013 μg/L didńt modify the SOD and CAT activities in comparison with controls, only the high concentrations (0.023 and 0.18 μg/L) induced a significant increase in the enzyme activity. A similar profile was recorded for the H₂O₂ level. The permethrin treatment induced a drastic depletion of AChE activity. As outcomes, uptake at a low level (<6.8 ± 0.43 ng/g dry weight) showed to be the factor underlying the alterations in the beetles exposed to permethrin. Such findings provide information on the behaviour of permethrin within the environment and its biological target through its neurotoxicity and induction of oxidative stress in a freshwater beetle.     

Health risk assessment and oxidative stress in workers exposed to welding fumes

The aim of this study was designed to determine the influence of welding fumes on oxidative stress in humans and the role of metals. A questionnaire was designed to collect information regarding personal characteristics, including age, weight, height, and medical history; life style such as smoking status and exercise habits; and occupational history such as working history, working environment, employment duration, and use of protective equipment. Body mass index (BMI) in kg/m² was then calculated for each participant. Blood samples were also drawn to determine malondialdehyde (MDA) levels and various metals in plasma. Significantly higher plasma MDA (4.08 µg/L) was observed as compared to controls (1.61 µg/L). Blood metal analysis also showed elevated level of metals in welders for cadmium, chromium, lead,and nickel. Data indicated that workers occupationally exposed to welding fumes for prolong periods possessed higher metal levels associated with increased oxidative stress as evidenced by elevated MDA levels.     

Inbreeding level does not induce female discrimination between sibs and unrelated males in guppies

Significant empirical evidence has demonstrated the importance of discriminative mate choice as a mechanism to avoid inbreeding. Incestuous mating can be avoided by recognition of kin. The guppy, Poecilia reticulata, is a livebearer with a polygamous mating system and active female choice. Despite potential inbreeding costs in the guppy, Viken et al. (Ethology 112:716–723, 2006) and Pitcher et al. (Genetica 134:137–146, 2008) have found that females do not discriminate between sibs and unrelated males. However, populations experiencing different inbreeding histories can have different levels of inbreeding avoidance, and it is possible that the lack of inbreeding avoidance observed in guppies is a consequence of using outbred fish only. Here we tested the preference of female guppies with different inbreeding coefficients, for olfactory cues of males that were either unrelated but had the same inbreeding coefficient, or were related (i.e. brother) with the same inbreeding coefficient. We found no evidence that female guppies preferred unrelated males with the same inbreeding coefficient. Moreover, inbreeding level did not influence female preference for unrelated males, suggesting that inbreeding history in a population has no influence on female discrimination of unrelated males in guppies.     

Single walled carbon nanotubes induce cytotoxicity and oxidative stress in HEK293 cells

The aim of the present study was to evaluate the potential toxicity and general mechanisms involved in single walled carbon nanotubes (SWCNTs)-induced cytotoxicity using human embryonic kidney cell line (HEK293) cells. Carbon nanotubes (coded as CNT) used in this study were synthesized by the chemical vapor deposition method. To elucidate the possible mechanisms underlying SWCNT-induced cytotoxicity, cell viability, cell membrane damage (lactate dehydrogenase activity (LDH) assay), reduced glutathione (GSH), interleukin-8 (IL-8) and lipid peroxidation products levels were quantitatively assessed following SWCNT exposure for 48 hr using HEK293 cells. Exposure of cells to SWCNT at 3–300 μg/ml produced significant reduction in cell viability in a concentration-dependent manner. The IC₅₀ value of SWCNT was found to be 87.58 μg/ml. Exposure of HEK cells to SWCNT at 10–100 μg/ml resulted in concentration-dependent cell membrane damage, increased production of IL-8, elevated levels of thiobarbituric acid reactive substances like malondialdehyde and decreased intracellular GSH levels. In summary, exposure to SWCNT resulted in a concentration-dependent cytotoxicity in cultured HEK293 cells that was associated with increased oxidative stress.     

Nanosilica exerts cytotoxicity and apoptotic response via oxidative stress in mouse embryonic fibroblasts

Nanoscale silica is an important industrial material and extensively used in medicines. The objective of this study was to determine potential cytotoxicity and genotoxic effects attributed to nanosilica exposure in mouse embryonic fibroblasts (L929) cells. Nanosilica produced mild cytotoxicity in L929 cells. Results showed that nanosilica increased thiobarbituric acid reactive substance levels and enhanced superoxide dismutase activity but decreased levels of glutathione. This was accompanied by a concomitant generation of reactive oxygen species, loss of mitochondrial membrane potential, and activation of caspase-3 activity. In addition, in the single-cell gel test, nanosilica (50–300 μg/ml) at two treatment times 24 and 48 hr produced concentration- and time-dependent increase of DNA damage. Therefore, the obtained results indicate that nanosilica may induce genotoxic effects in cultured L929 cells associated with induction of oxidative stress.     

环境污染物导致氧化应激的关键信号通路及其检测方法

环境污染物能够以多种途径进入生物体内,在体内产生含氧自由基等活性氧物质,并通过多种信号通路及酶反应引起氧化应激,造成生物体内的脂质过氧化、蛋白质损伤、DNA表达改变、酶失活等,从而引发心血管疾病、风湿类疾病、感染及癌症等的发生。本文对环境污染物致氧化应激产生的原因、涉及的信号通路及酶反应、造成的危害,以及常见的基于细胞模型的氧化应激检测方法进行了综述,期望为评价环境污染物和检测氧化损伤提供参考。