Females from resting eggs and parthenogenetic eggs in the rotifer Brachionus calyciflorus: lipid droplets, starvation resistance and reproduction

1. In the heterogonic life cycle of monogonont rotifers, amictic (female‐producing) females develop from two types of eggs: fertilised resting (diapausing) eggs and parthenogenetic subitaneous eggs. Females hatched from resting eggs initiate clonal populations by female parthenogenesis and are called stem females. This study compares females from resting and parthenogenetic eggs that were produced under identical culture conditions and were of similar birth order. 2. Newborn stem females had many more lipid droplets in their tissues than similar‐sized, newborn females from parthenogenetic eggs. When neonates were stained with Nile Red and viewed under epifluorescent illumination, these droplets were shown to be sites of neutral‐lipid storage products. 3. Stem females had no posterolateral spines and short anterior spines, while their mothers and offspring in subsequent, parthenogenetic generations typically had long posterolateral spines and elongated anterior spines. 4. Newborn stem females survived starvation significantly longer than newborn females from parthenogenetic eggs. 5. When females from resting and parthenogenetic eggs were cultured from birth to death at a high food concentration, the reproductive potential (r day^?1) of the stem females was significantly higher (0.82–0.88 versus 0.70), primarily because of egg production at an earlier age. The mean lifetime fecundity (R_o) of stem females was significantly greater than that of females from parthenogenetic eggs. 6. Extensive lipid reserves should increase the ability of stem females to colonise new habitats. Firstly, compared with females from parthenogenetic eggs, stem females are more likely to experience starvation or food limitation. Resting eggs hatch in response to physical and chemical factors that are not directly related to food availability, and from sediments that may be far from food‐rich surface waters. Secondly, when food is abundant, stem females have a greater reproductive potential.     

Adaptive significance of the recurrent photoperiodic response in a spring‐breeding carabid beetle,Carabus yaconinus

Seasonal changes in the photoperiodic sensitivity for reproduction in adults of a spring‐breeding carabid beetle, Carabus yaconinus (Coleoptera: Carabidae), were examined by transferring adults from outdoor to photoperiodic conditions in various seasons. Newly‐emerged adults transferred to the laboratory in September to December showed a long‐day photoperiodic response, but lost photoperiodic sensitivity gradually during winter. In late April, overwintered adults were not sensitive to the photoperiod, with females continuing to have mature eggs under both long‐day and short‐day conditions. In contrast, in late June and late July, the adults were sensitive to the photoperiod, with only those kept under short‐day conditions re‐entering reproductive diapause. This recovery of photoperiodic sensitivity appears to play a definitive role in maintenance of diapause in autumn for adults that have reproduced. The adults collected in late April regained photoperiodic sensitivity in two months even after being kept under unchanged conditions. Therefore, no environmental cue is required for recovery of photoperiodic sensitivity, which apparently recovers with the lapse of time. Our results suggest that the recurrent photoperiodic response is required in long‐living adults of C. yaconinus to regulate the timing of reproduction, and also indicate a difference in photoperiodic sensitivity in summer between overwintered and newly‐emerged adults.     

亚洲玉米螟两个不同地理种群对暗期干扰的滞育反应

为了探明亚洲玉米螟Ostrinia furnacalis (Guenée)不同地理种群对暗期干扰的滞育反应, 本文在研究了亚洲玉米螟南昌种群（28°41′N, 115°53′E）和哈尔滨种群（44°56′N, 127°10′E）光周期反应的基础上, 在室内分别测试了25℃和28℃温度下1 h的光脉冲干扰光周期L9∶D15和L12∶D12对这两个不同地理种群幼虫滞育抑制的影响。结果表明： 在25℃和28℃下, 哈尔滨种群的临界日长分别比南昌种群延长了1 h 40 min和2 h; 在所有测试的暗期干扰实验中, 除了极少数光脉冲干扰点外, 南昌种群幼虫滞育的发生率显著低于哈尔滨种群; 1 h光脉冲干扰光周期L9∶D15的滞育发生率明显低于干扰光周期L12∶D12, 且前者表现了暗期的中间对光脉冲最敏感, 而后者显示了暗期的初期对光脉冲最敏感; 28℃下光脉冲对滞育的抑制效果强于25℃。这些结果进一步提示, 即使在同种昆虫中, 如果地理种群和实验条件不同, 暗期干扰对滞育抑制的效果也可能不同。     

Fitness costs associated with Cry1F resistance in the European corn borer

Crops producing insecticidal toxins derived from the bacterium Bacillus thuringiensis (Bt) are widely planted to manage insect pests. Bt crops can provide an effective tool for pest management; however, the evolution of Bt resistance can diminish this benefit. The European corn borer, Ostrinia nubilalis Hübner, is a significant pest of maize and is widely managed with Bt maize in the Midwest of the United States. When Bt crops are grown in conjunction with non‐Bt refuges, fitness costs of Bt resistance can delay the evolution of resistance. Importantly, fitness costs often vary with ecological factors, including host‐plant genotype and diapause. In this study, we examined fitness costs associated with Cry1F resistance in O. nubilalis when insects were reared on three maize lines. Fitness costs were tested in two experiments. One experiment assessed the fitness costs when Cry1F‐resistant and Cry1F‐susceptible insects were reared on plants as larvae and experienced diapause. The second experiment tested resistant, susceptible and F1 heterozygotes that were reared on plants but did not experience diapause. Despite some evidence of greater adult longevity for Cry1F‐resistant insects, these insects produced fewer fertile eggs than Cry1F‐susceptible insects, and this occurred independent of diapause. Reduced fecundity was not detected among heterozygous individuals, which indicated that this fitness cost was recessive. Additionally, maize lines did not affect the magnitude of this fitness cost. The lower fitness of Cry1F‐resistant O. nubilalis may contribute to the maintenance of Cry1F susceptibility in field populations more than a decade after Cry1F maize was commercialized.     

Non‐genetic polymorphisms in rotifers: environmental and endogenous controls,development, and features for predictable or unpredictable environments

Pronounced non‐genetic polymorphisms, or polyphenisms, occur in some monogonont rotifers reproducing by diploid, female parthenogenesis. In many brachionids, there is great variation in spine length. In trimorphic species of Asplanchna, females can vary in size and shape, from a small saccate morph to giant cruciform and campanulate morphs. In species that also reproduce sexually, diploid eggs can develop into two types of females. Amictic females produce diploid eggs that develop parthenogenetically into females; mictic females produce haploid eggs that develop parthenogenetically into males or, if fertilized, into resting eggs. In a species of Synchaeta, amictic females produce diploid eggs that can be either thin‐shelled and subitaneous or thicker‐shelled and diapausing. In all cases, morph determination occurs during the oogenesis or embryological development of diploid eggs in the maternal body cavity. For the first time, these polymorphisms are reviewed together and compared regarding a number of features associated with transitions from default to induced morphs: (i) type of variation (morphological, physiological, or both; continuous or discrete); (ii) inducing signal (environmental, endogenous, or both); (iii) universality of response to that signal (all or only some individuals); (iv) fitness cost; (v) reversibility; and (vi) ecological significance. Most of the polymorphisms fall into two major categories regarding these features. Transitions suitable for predictable environments involve: universal responses to environmental signals; continuous morphological variation; low reproductive cost; rapid reversibility; and adaptations for defence, hydrodynamics or prey ingestion. Transitions suitable for unpredictable environments are bet‐hedging strategies and usually involve: partial (stochastic) responses to environmental or endogenous signals; discontinuous physiological variation; initiation of diapause, and thus high reproductive cost and slow reversibility. Two cases of morphological variation also involve the simultaneous production of different morphs and likely are adaptations for an uncertain future: continuous spine‐length variation due to maternal age in Brachionus calyciflorus, and production of discrete cruciform and campanulate females in Asplanchna spp.     

棉铃虫转录因子c-Myc基因在滞育和非滞育蛹脑中的表达分析及多克隆抗体制备

【目的】c-Myc是近年来研究较多的转录因子,也是受Wnt/β-catenin信号通路调节的重要靶标。本研究旨在克隆棉铃虫 Helicoverpa armigera c-Myc基因,从核酸水平初步调查 c-myc 在滞育和非滞育蛹脑中的表达情况,同时制备其蛋白的多克隆抗体。【方法】通过RACE方法克隆棉铃虫 c-myc 基因的cDNA,运用RT-PCR方法比较滞育和非滞育蛹脑中Har-c-myc基因的表达情况。根据获取的序列构建原核表达载体,在大肠杆菌 Escherichia coli 中进行表达,纯化后免疫新西兰兔,制备了多克隆抗体。【结果】克隆了棉铃虫 c-myc 基因,核酸水平的研究表明滞育蛹脑中 c-myc 表达水平明显低于非滞育蛹脑。成功地在大肠杆菌中表达了c-Myc部分肽段并通过镍柱纯化获得了较纯的重组蛋白。制备的c-Myc抗体效价达到了1:125 000。【结论】滞育蛹脑中 Har-c-myc 的表达下调。获得了抗棉铃虫c-Myc的多克隆抗体。本研究的成果为后续进一步深入研究棉铃虫Wnt/β-catenin信号通路在棉铃虫发育中的作用奠定了基础。     

Reproductive cycle and maternal–embryonic nutritional relationship of shovelnose guitarfish Pseudobatos productus in the Gulf of California

Samples of the shovelnose guitarfish Pseudobatos productus were collected on board a vessel and at landings of artisanal commercial fisheries in the Gulf of California from May 2004 to June 2007. Samples of 650 females, 2047 embryos and 484 uterine eggs were examined. The reproductive cycle is annual, ovulation and parturition occur in July, the uterine eggs are in diapause for 9 months (July–March) before an accelerated growth of embryos of 3 months. Histological analyses of the uterine wall of pregnant females suggested that no secretions were used for embryo nourishment. The standard percentage of water content was 48·6% in fertilized eggs and 80·75% in full‐term embryos. Dry mass loss during embryonic development was 16·3% and the chemical balance of development was 0·84. This indicates that P. productus is a strictly lecithotrophic, viviparous species, that makes no maternal contribution of nutrients during embryonic development.     

Obligate annual and successive facultative diapause establish a bet‐hedging strategy of Rhagoletis cerasi (Diptera: Tephritidae) in seasonally unpredictable environments

To cope with temporal and spatial heterogeneity of habitats, herbivorous insects in the temperate zone usually enter diapause that facilitates synchronization of their life cycle with specific stages of host plants, such as fruit ripening. In the present study, we address those factors regulating dormancy responses as part of a ‘longer strategy’ to persist and thrive in temperate environments, focusing on Rhagoletis cerasi, a univoltine, oligophagous species, which overwinters as pupae and emerges when host fruits are available for oviposition at local scale. To ensure population survival and reproduction at habitats with ecological heterogeneity, R. cerasi has evolved a sophisticated diapause strategy based on a combination of local adaptation and diversified bet‐hedging strategies. Diapause duration is determined both by (i) the adaptive response to local host fruit phenology patterns (annual diapause) and (ii) the plastic responses to unpredictable inter‐annual (temporal) climatic variability that drives a proportion of the populations to extend dormancy by entering a second, successive, facultative cycle of prolonged diapause as part of a bet‐hedging strategy. Besides the dormant periods, post‐diapause development (which varies among populations) exerts ‘fine tune’ adjustments that assure synchronization and may correct possible errors. Adults emerging from pupae with prolonged diapause are larger in body size compared with counterparts emerging during the first year of diapause. However, female fecundity rates are reduced, followed by an extended post‐oviposition period, whereas adult longevity remains unaffected. Overall, it appears that R. cerasi populations are adapted to ecological conditions of local habitats and respond plastically to unpredictable environmental (climatic) conditions.