Shape shifting predicts ontogenetic changes in metabolic scaling in diverse aquatic invertebrates

Metabolism fuels all biological activities, and thus understanding its variation is fundamentally important. Much of this variation is related to body size, which is commonly believed to follow a 3/4-power scaling law. However, during ontogeny, many kinds of animals and plants show marked shifts in metabolic scaling that deviate from 3/4-power scaling predicted by general models. Here, we show that in diverse aquatic invertebrates, ontogenetic shifts in the scaling of routine metabolic rate from near isometry (b_R = scaling exponent approx. 1) to negative allometry (b_R < 1), or the reverse, are associated with significant changes in body shape (indexed by b_L = the scaling exponent of the relationship between body mass and body length). The observed inverse correlations between b_R and b_L are predicted by metabolic scaling theory that emphasizes resource/waste fluxes across external body surfaces, but contradict theory that emphasizes resource transport through internal networks. Geometric estimates of the scaling of surface area (SA) with body mass (b_A) further show that ontogenetic shifts in b_R and b_A are positively correlated. These results support new metabolic scaling theory based on SA influences that may be applied to ontogenetic shifts in b_R shown by many kinds of animals and plants.     

Tracing dietary origins of aphids and the predatory beetle Propylea japonica in agricultural systems using stable isotope analyses

Tracing dietary origins of the predatory beetle Propylea japonica (Thunberg) (Coleoptera: Coccinellidae) aids understanding their roles in the food web and provides information to develop strategies for effective conservation in agroecosystems comprised of wheat [Triticum aestivum L. (Poaceae)], cotton [Hirsutum spp. (Malvaceae)], and maize [Zea mays L. (Poaceae)]. Intrinsic markers of carbon and nitrogen stable isotope ratios (δ¹³C and δ¹⁵N) in P. japonica need to be developed to ascertain the source(s) of diet. Experiments were carried out to examine the changes of δ¹³C and δ¹⁵N among the three crops, pests (wheat, cotton, and maize aphids; all Hemiptera: Aphididae), and P. japonica fed on aphids of each of the three crops. Results indicated that δ¹³C values in P. japonica fed on wheat, cotton, and maize aphids were ?27.2 to ?26.5‰, ?24.2 to ?23.9‰, and ?11.0 to ?10.7‰, respectively, whereas their δ¹⁵N values were 1.1 to 2.9‰, 6.0 to 7.4‰, and ?0.6 to 0.1‰, respectively. δ¹³C and δ¹⁵N plots clearly identify the three crops, the dietary origins of the aphids, and the host origins of the aphid prey consumed by the ladybird beetles, as each pathway displays a non‐overlapping pattern. Based on the values of δ¹³C and δ¹⁵N of the three food webs, dietary origins can be traced in the predatory beetle P. japonica derived from wheat, cotton, and maize crops.     

Trace Metal Mixture Toxicity in Aquatic Organism Reviewed from a Biotoxicity Perspective

Biotoxicity of individual metals is well investigated but that of metal mixture, an environmental reality, in the developing metal mixture, is relatively obscure. Experimental evidences had shown that this mixture could give rise to combined effects that were different from the effect of metals one by one. This review provides an overview of recent research on metal mixture toxicity and the methods employed to predict their toxic combined effects. The two established reference models, the concentration-addition model and the independent-addition model, were used for evaluating the combined effect from the biological activities of the metal mixtures. While the reference models had provided reasonable tools for analyzing the combined effects, the actual predictions for binary metal mixtures showed often somewhat less than additive combined effects compared to what has been observed. As the metal bioavailability is oriented by several environmental factors as well as the toxicodynamics of metals is highly compound-specific, the non-interactive combined effects may be confused with different processes of the interactions. Thus, for improving the predictability of combined effects in metal mixture toxicity, numerous qualitative and quantitative analysis are required for the processes governing the toxicokinetics and dynamics of metals in aquatic organisms.     

Use of stable carbon and nitrogen isotopes in insect trophic ecology

Insects are the most diverse organisms and often the most abundant animals in some ecosystems. Despite the importance of their functional roles and of the knowledge for conservation, the trophic ecology of many insect species is not fully understood. In this review, I present how stable carbon (C) and nitrogen (N) isotopes have been used to reveal the trophic ecology of insects over the last 30 years. The isotopic studies on insects have used differences in C isotope ratios between C₃ and C₄ plants, along vertical profiles of temperate and tropical forest stands, and between terrestrial and aquatic resources. These differences enable exploration of the relative importance of the food resources, as well as movement and dispersal of insects across habitats. The ¹³C‐enrichment (approximately 3‰) caused by saprotrophic fungi can allow the estimation of the importance of fungi in insect diets. Stable N isotopes have revealed food resource partitioning across diverse insect species above and belowground. Detritivorous insects often show a large trophic enrichment in ¹³C (up to 3‰) and ¹⁵N (up to 10‰) relative to the food substrates, soil organic matter. These values are greater than those commonly used for estimation of trophic level. This enrichment likely reflects the prevalence of soil microbial processes, such as fungal development and humification, influencing the isotopic signatures of diets in detritivores. Isotope analysis can become an essential tool in the exploration of insect trophic ecology in terms of biogeochemical C and N cycles, including trophic interactions, plant physiological and soil microbial processes.     

基于形态及分子特征的鳖扁蜡蝉长翅型研究

研究了鳖扁蜡蝉属Cixiopsis Matsumura长翅型雌虫的形态和分子特征.通过和该属的模式种,即鳖扁蜡蝉Cixiopsis punctatus Matsumura,1900短翅型的形态比较,发现该长翅型雌虫在形态学方面存在某些差异.为了明确该长翅型雌虫的归属,还测定了该长翅型雌虫和鳖扁蜡蝉短翅型的COI序列,结...     

Carnivorous Utricularia: The buckling scenario

We review recent results about the functioning of aquatic carnivorous traps from the genus Utricularia. The use of high speed cameras has helped to elucidate the mechanism at the origin of the ultra fast capture process of Utricularia, at a millisecond time scale. As water is pumped out of the trap, pressure decreases inside the trap and elastic energy is stored due to the change of shape of the trap body. This energy is suddenly released when the trap is fired: the trap door undergoes an elastical instability: buckling, which allows its fast and passive opening and closure. This mechanism is used by Utricularia both to catch preys touching its trigger hairs and to fire spontaneously at regular time intervals. The results leading to this interpretation are reviewed and discussed and suggestions for further work are briefly presented.     

Synergistic effects of water temperature and dissolved nutrients on litter decomposition and associated fungi

In woodland streams, the decomposition of allochthonous organic matter constitutes a fundamental ecosystem process, where aquatic hyphomycetes play a pivotal role. It is therefore greatly affected by water temperature and nutrient concentrations. The individual effects of these factors on the decomposition of litter have been studied previously. However, in the climate warming scenario predicted for this century, water temperature and nutrient concentrations are expected to increase simultaneously, and their combined effects on litter decomposition and associated biological activity remains unevaluated. In this study, we addressed the individual and combined effects of water temperature (three levels) and nutrient concentrations (two levels) on the decomposition of alder leaves and associated aquatic hyphomycetes in microcosms. Decomposition rates across treatments varied between 0.0041 day^?1 at 5 °C and low nutrient level and 0.0100 day^?1 at 15 °C and high nutrient level. The stimulation of biological variables at high nutrients and temperatures indicates that nutrient enrichment of streams might have a higher stimulatory effect on fungal performance and decomposition rates under a warming scenario than at present. The stimulation of fungal biomass and sporulation with increasing temperature at both nutrient levels shows that increases in water temperature might enhance fungal growth and reproduction in both oligotrophic and eutrophic streams. The stimulation of fungal respiration and litter decomposition with increasing temperature at high nutrients indicates that stimulation of carbon mineralization will probably occur at eutrophied streams, while oligotrophic conditions seem to be ‘protected’ from warming. All biological variables were stimulated when both factors increased, as a result of synergistic interactions between factors. Increased water temperature and nutrient level also affected the structure of aquatic hyphomycete assemblages. It is plausible that if water quality of presently eutrophied streams is improved, the potential stimulatory effects of future increases in water temperature on aquatic biota and processes might be mitigated.     

Use of a mitochondrial COI sequence to identify species of the subtribe Aphidina (Hemiptera, Aphididae)

Aphids of the subtribe Aphidina are found mainly in the North Temperate Zone. The relative lack of diagnostic morphological characteristics has hindered the identification of species in this group. However, DNA-based taxonomic methods can clarify species relationships within this group. Sequence variation in a partial segment of the mitochondrial COI gene was highly effective for identifying species within Aphidina. Thirty-six species of Aphidina were identified in a neighbor-joining tree. Mean intraspecific sequence divergence in Aphidina was 0.52%, with a range of 0.00% to 2.95%, and the divergences of most species were less than 1%. Mean interspecific divergence within previously recognized genera or morphologically similar species groups was 6.80%, with a range of 0.68% to 11.40%, with variation mainly in the range of 3.50% to 8.00%. Possible reasons for anomalous levels of mean nucleotide divergence within or between some taxa are discussed.