Variable prey development time suppresses predator–prey cycles and enhances stability

Although theoretical models have demonstrated that predator–prey population dynamics can depend critically on age (stage) structure and the duration and variability in development times of different life stages, experimental support for this theory is non‐existent. We conducted an experiment with a host–parasitoid system to test the prediction that increased variability in the development time of the vulnerable host stage can promote interaction stability. Host–parasitoid microcosms were subjected to two treatments: Normal and High variance in the duration of the vulnerable host stage. In control and Normal‐variance microcosms, hosts and parasitoids exhibited distinct population cycles. In contrast, insect abundances were 18–24% less variable in High‐ than Normal‐variance microcosms. More significantly, periodicity in host–parasitoid population dynamics disappeared in the High‐variance microcosms. Simulation models confirmed that stability in High‐variance microcosms was sufficient to prevent extinction. We conclude that developmental variability is critical to predator–prey population dynamics and could be exploited in pest‐management programs.     

变温和恒温对沙葱萤叶甲发育速率的影响

沙葱萤叶甲为近年来在内蒙古草原猖獗成灾的新害虫,为明确温度对其发育速率的影响,分别设置5个变温组合(8/20℃,11/23℃,14/26℃,17/29℃和20/32℃)和6个恒温(13℃,17℃,21℃,25℃,29℃和33℃),比较了变温和恒温对沙葱萤叶甲幼虫和蛹发育速率的影响。结果表明,不同变温组合和恒温对沙葱萤叶甲幼虫和蛹的发育速率有显著的影响。发育历期随温度的升高而缩短,在变温条件下,1龄幼虫期、2龄幼虫期、3龄幼虫期、总幼虫期和蛹期分别从最低温度组合(8/20℃,平均15℃)的11.00,13.44,23.18,46.42和16.89 d,缩短至最高温度组合(20/32℃,平均27℃)的4.92,4.63,9.17,17.83和5.83 d;在恒温条件下,13℃下幼虫不能发育和存活,1龄幼虫期、2龄幼虫期、3龄幼虫期、总幼虫期和蛹期分别从17℃的14.50,10.75,20.63,45.50和11.00 d,缩短至33℃的6.10,5.47,10.60,22.17和5.33 d。在变温条件下,幼虫和蛹的发育起点温度分别为7.44℃和8.48℃,有效积温分别为344.82日度和113.52日度;在恒温条件下,幼虫和蛹的发育起点温度分别为0.64℃和5.11℃,有效积温分别为714.28日度和147.06日度。变温促进了沙葱萤叶甲幼虫和蛹的发育,本研究结果为沙葱萤叶甲的预测预报及综合防控提供了科学依据。     

Phase response curve to 1 h light pulses for the European rabbit (Oryctolagus cuniculus)

While much is known about the circadian systems of rodents, chronobiological studies of other mammalian groups have been limited. One of the most extensively studied nonrodent species, both in the laboratory and in the wild, is the European rabbit. The aim of this study was to extend knowledge of the rabbit circadian system by examining its phasic response to light. Twelve Dutch-Himalayan cross rabbits of both sexes were allowed to free-run in constant darkness and then administered 1 h light pulses (1000 lux) at multiple predetermined circadian times. Changes in the phase of the rabbits’ circadian wheel-running rhythms were measured after each light pulse and used to construct a phase–response curve (PRC). The rabbits’ PRC and free-running period (τ) conformed to the empirical regularities reported for other predominantly nocturnal animals, including rodents and predatory marsupials. The results of the study are thus consistent with reports that the rabbit is essentially a nocturnal animal and show that it can entrain to light/dark (LD) cycles via discrete phase shifts. Knowledge about the rabbit’s circadian range of entrainment to LD cycles gained in this study will be useful for examining the putative circadian processes believed to underlie the unusual rhythm of very brief, once-daily nest visits by nursing rabbit mothers and other nursing lagomorphs.     

Trend in Pacific walrus (Odobenus rosmarus divergens) tusk asymmetry, 1990–2014

We used the basal circumference of Pacific walrus (Odobenus rosmarus divergens) tusks (upper canine teeth, n = 21,068 pairs) to estimate fluctuating asymmetry (FA1 index) from 1990 to 2014. The mean difference in circumference between paired tusks was ?0.006 (SEM = 0.002) cm and approximately normally distributed. Measurement error was 0.6 (0.02)%, similar between biologists and lay persons (P = 0.83), and ≤15% of FA1. Tusk FA1 was greatest in 1990 then declined by 56% (P = 0.0001) through 2014. Male and female trends differed (P = 0.0001) and male FA1 was 40% greater (P = 0.0001) and the rate of decline 28% steeper (P = 0.3) than females. A quartic polynomial model (r² = 0.66, w_i = 0.685) fit the trend for female data better than simpler forms, whereas a linear model (r² = 0.55, w_i = 0.693) was a better fit for male data. Walrus tusk FA1 reflected periods when the population was stressed due to food limitations and then recovered, and perhaps when females began to experience the loss of preferred sea ice habitat in summer and FA1 is an easily monitored indicator. More work is needed to confirm the link between FA1, individual fitness, and adaptive potential.     

Evaluation of Phytochemical Compositions and Biological Properties of Achillea gypsicola at Different Phenological Stages

Phytochemicals, which are commonly found at different levels in many medicinal plants, are natural strong antioxidants used in traditional medicine. In this research, determination of differences of phytochemical compositions and biological properties were aimed as periodically (pre‐, full and post flowering) and daily (6 am, 1 pm and 8 pm) in Achillea gypsicola Hub.‐Mor . The volatile oils belonging to A. gypsicola were obtained by hydrodistillation and analyzed by gas chromatography‐flame ionization detection (GC‐FID) and gas chromatography‐mass spectrometry (GC/MS). The antimicrobial activities of the volatile oils were determined with disc diffusion method. The microdilution method was used to determine minimum inhibitory concentration (MIC). Total phenolic and flavonoid contents were determined by spectrophotometric methods and antioxidant capacities were evaluated by 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) free radical, reducing power (RP) and metal chelating activity (MCA) assay. In addition, the phenolic acid and flavonoid compositions were evaluated by reversed phase‐high‐performance liquid chromatography (RP‐HPLC). This study presented a comprehensive report for the first time on evaluation of the phytochemical composition and the biological properties of A. gypsicola at different phenological stages. Thirty‐two compounds, containing the major component as camphor, 1,8‐cineole and borneol, were detected. Designated harvest time for the highest yield of volatile oils was found to be at full flowering stage‐1 pm. It has been observed that the volatile oil composition changes periodically and even daily. Also, in this research, menthol and menthone were found as the composition of volatile oil in Achillea species for the first time. Full flowering stage was found as the richest period in terms of phenolic acid and flavonoid compositions of A. gypsicola for the first time. The species examined in this research showed a high antioxidant and antimicrobial activity in comparison to other studies with Achillea species. The volatile oils exhibited high performances with range of inhibition zones (8.3–42.3 mm) and minimum inhibitory concentration values (2.25—144 μg/ml). Besides, a high correlation between antioxidant activity and phenolic content of A. gypsicola was found. These results suggest that A. gypsicola can be used as a safe source in the cosmetic, food and pharmaceutical industries.     

Economic weights of maternal and direct traits of pigs calculated by applying gene flow methods

Multiple trait selection indexes in pig breeding programmes should take into account the population structure and time delay between parent selection and expressions of traits in all production levels next to the trait impacts on economic efficiency of production systems. Gene flow procedures could be used for the correct evaluation of maternal and direct traits of pig breeds involved in breeding or crossbreeding systems. Therefore, the aim of this study was to expand a previously developed bioeconomic model and computer program to calculate the marginal economic values by including a gene flow procedure to calculate the economic weights for maternal and direct traits in pig breeds. The new program was then applied to the three-way crossbreeding system of the Czech National Programme for Pig Breeding. Using this program, the marginal economic values of traits for dam breeds Czech Large White in the dam position and Czech Landrace in the sire position, and for the sire breed Pietrain were weighted by the number of discounted gene expressions of selected parents of each breed summarised within all links of the crossbreeding system during the 8-year investment period. Economic weights calculated in this way were compared with the approximate economic weights calculated previously without a gene flow procedure. Taking into account the time delay between parent selection and trait expression (using discounting with half-year discount rates of 2% or 5%) and including more than one generation of parent progeny had little impact on the relative economic importance of maternal and direct traits of breeds involved in the evaluated three-way crossbreeding system. These results indicated that this gene-flow method could be foregone when estimating the relative economic weights of traits in pig crossbreeding systems applying artificial insemination at all production levels.     

Developmental effects of trichloroacetate in Zebrafish embryos: Association with the production of superoxide anion

To assess the developmental toxicity of trichloroacetate (TCA), zebrafish embryos were exposed to 8 to 48 mM of TCA and evaluated for developmental milestones from 8‐ to 144‐hour postfertilization (hpf). All developmental toxicities are reported in this paper. Embryos were found to have developed edema in response to 16 to 48 mM of TCA exposure at 32‐ to 80‐hpf, experienced delay in hatching success in response to 24 to 48 mM at 80‐hpf. Lordosis was observed in developing embryos exposed to 40 to 48 mM at 55‐ to 144‐hpf. The observed toxic effects of TCA exposure were found to be concentration and exposure period independent. Effects were found to be associated with increases in superoxide anion production, but these increases were also found to be concentration and time independent. TCA resulted in concentration‐dependent increases in embryonic lethality at 144‐hpf, with an LC₅₀ determined to be 29.7 mM.