中国北方树木秋季物候的过程模拟及其区域分异归因

揭示温带落叶树木秋季物候的发生机理对提高生态系统固碳量和植被生产力的预估精度具有重要意义。该研究利用低温和光周期乘积模型模拟了1981-2014年中国北方温带90余个站点6个树种的叶始变色期和落叶末期, 并对逐站点-物种的最优模型进行了模拟精度评价, 分析了最优模型模拟精度的时空差异及其随水分梯度的空间变化。主要结果如下: (1)在诱导叶片衰老方面, 光周期缩短的影响通常大于温度降低的影响。据此建立的叶始变色期和落叶末期最优模型模拟的平均均方根误差分别为6.9 d和6.0 d, 模拟与观测时间序列呈显著正相关关系的比例分别为71.4%和83.6%; (2)最优模型对区域平均和多年平均叶始变色期和落叶末期模拟的绝对误差小于2.4 d, 但模拟日期的时空变幅通常小于观测日期, 这与秋季物候发生日期的高度时间变异性密切相关; (3)水分条件在一定程度上影响叶片衰老诱导途径的选择, 表现为光周期缩短诱导叶片衰老的叶始变色期最优模型所占比例在干旱和半干旱区大于湿润和半湿润区, 而最优模型的模拟精度在湿润和半湿润区高于干旱和半干旱区。该研究验证了低温和光周期乘积模型在中国温带地区的适用性, 并揭示了水分条件对秋季物候发生机理和模拟精度的影响。     

A rural–urban latitudinal study of the distributions of Culex quinquefasciatus and Culex pipiens bioforms in their southernmost sympatric fringe

Mosquitoes grouped in the complex Culex pipiens L. (Diptera: Culicidae) are important vectors of medical and veterinary diseases. In the South American sympatric region, Cx. pipiens and Culex quinquefasciatus Say coexist and potentially hybridize. To identify key drivers of their geographical distribution, mosquito immatures were collected from flower vases of eight urban/rural cemetery pairs within a 5° latitudinal transect along Buenos Aires Province, Argentina. The specimens were identified by molecular methods and their relative proportion modelled as a function of environmental variables. At the beginning of the warm season, northern and southern cemeteries presented exclusively Cx. quinquefasciatus and Cx. pipiens, respectively, with different proportions of both at mid latitudes. By the end of the summer, Cx. quinquefasciatus was present throughout the study area, exclusively in 11 of the 16 cemeteries both rural and urban, whereas Cx. pipiens was predominant only in the southernmost pair. Mean annual temperature, photoperiod variability and time of the season were key drivers of their distributions. All specimens of Cx. pipiens were identified as form molestus and no hybrids were recognized. The reported distribution patterns and the potential absence of Cx. pipiens f. pipiens and hybrids are discussed, along with their implications in disease transmission.     

Advancing breeding in stickleback (Gasterosteus aculeatus) to produce two reproductive cycles per year

The effects of photoperiod and temperature manipulation on reproductive cycles in threespine stickleback Gasterosteus aculeatus were examined. The experimental “advanced group” conditions were adjusted to simulate two reproductive seasons within a calendar year by adjusting light and temperature cycles. G. aculeatus subject to advanced conditions had two reproductive cycles per year, grew at normal rates and suffered little additional mortality. The research of many stickleback scientists would benefit from faster generation times and our methods could potentially shorten the time required to produce fish for genetic, behavioural and morphological work.     

Attractive male sticklebacks carry more oxidative DNA damage in the soma and germline

Trade‐offs between the expression of sexual signals and the maintenance of somatic and germline tissues are expected when these depend upon the same resources. Despite the importance of sperm DNA integrity, its trade‐off with sexual signalling has rarely been explored. We experimentally tested the trade‐off between carotenoid‐based sexual coloration and oxidative DNA damage in skeletal muscle, testis and sperm by manipulating reproductive schedule (early vs. late onset of breeding) in male three‐spined sticklebacks. Oxidative DNA damage was measured as the amount of 8‐hydroxy‐2‐deoxyguanosine in genomic DNA. Irrespective of the experimentally manipulated reproductive schedule, individuals investing more in red coloration showed higher levels of oxidative DNA damage in muscle, testis and sperm during the peak breeding season. Our results show that the expression of red coloration traded off against the level of oxidative DNA damage possibly due to the competing functions of carotenoids as colorants and antioxidants. Thus, female sticklebacks may risk fertility and viability of offspring by choosing redder, more deteriorated partners with decreased sperm DNA integrity. The evolution of sexual signal may be constrained by oxidative DNA damage in the soma and germline.     

Variability in diapause propensity within populations of a temperate insect species: interactions between insecticide resistance genes and photoperiodism

Temperate insects generally use day length as a reliable cue for long-term seasonal changes in their environment. Significant variation in photoperiodism between and within populations is thought to be associated with genetic variation resulting from local adaptation. In this study, we investigated whether genetic variation associated with selection for insecticide resistance may be a source of divergence in the photoperiodic timing of diapause through pleiotropic interactions. Critical photoperiods for diapause induction were estimated in one susceptible and two insecticide-resistant homozygous strains of the codling moth Cydia pomonella , as well as in their reciprocal F₁ progeny. Diapause responses to naturally decreasing day length were subsequently followed in the laboratory strains and in two field populations of C. pomonella in south-eastern France. We found higher critical photoperiods for diapause induction in homozygous resistant individuals than in both homozygous susceptible and heterozygous ones. This partly explained the significantly earlier timings of diapause found in homozygous resistant individuals of both laboratory and field populations of C. pomonella under natural photoperiods, relative to those found in both homozygous susceptible and heterozygous ones. We assume that adaptive genetic changes associated with selection for insecticide resistance may generate substantial variation in the seasonal timing of diapause, an essential ecological feature of the fitness of insecticide resistance genes in this species.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 83 , 341–351.     

Cold-induced purpling of Pinus contorta seedlings depends on previous daylength treatment

The characteristic cold-induced foliar accumulation of anthocyanin (‘purpling’) seen in many species of pine seedlings in the autumn can be contingent upon photoperiod received months previously. In nursery-grown seedlings of Pinus contorta Dougl. var. latifolia Engelm., a 4-week exposure during August of 10-h days followed by return to ambient photoperiod diminished the frequency of purpling following the November onset of cold weather (21% compared to 71% of the untreated controls). Anthocyanin accumulation (primarily cyanidin 3-glucoside) was controlled differently than general phenolic metabolism, and involved the integration of two temporally separated environmental signals.     

Monoterpene content in Origanum syriacum as affected by environmental conditions and flowering

A high content of essential oil in the foliage of two chemotypes of field-grown Origanum syriacum L. was found between August and October. The content of phenolic monoterpenes in the essential oil was low from November to January, while the content of p -cymene was high. The effect of environmental conditions and flowering on the two chemotypes was similar. Controlled experiments revealed that under long photoperiods the content of essential oils in the foliage and of phenolic monoterpenes in the oil increased, while that of p -cymene decreased. A similar effect was observed when an 8 h natural light day was extended by 8 h low-intensity incandescent light. When the 16 h day was composed of 12 h natural light, the effect on oil content and composition was intensified. Under short-day photoperiods, increasing temperature or light intensity enhanced the relative content of p -cymene, while that of phenolic monoterpenes and the γ-terpinene generally decreased. Flowering decreased the essential oil content in the leaves and the relative content of the phenolic monoterpenes in the essential oil. Since environmental conditions influence flowering, they had both direct and indirect effects on the essential oil content and composition.     

Phytochrome action and frost hardening in black spruce seedlings

Black spruce [ Picea mariana (Mill.) B.S.P.] development is sensitive to photoperiod. To date the implication of photoperiod, and especially phytochrome, in the frost hardening process of black spruce has not been fully tested. Two light fluence rates, night interruption of darkness, and red vs far-red radiation treatments were applied to black spruce seedlings, followed by freezing at –6°C. Parallel to the freezing test, growth measurements, bud formation and the xylem water potential estimates of the seedlings were done. While dry weight accumulation depends on the irradiation energy level, bud formation and freezing tolerance are photoperiodically sensitive. Furthermore, bud formation and frost hardening are dependent upon whether phytochrome is in the active form or inactive form, as demonstrated by the positive effect of short days, far-red radiation and the reversal of the red effect by far-red radiation. Also, xylem water potential appears to be influenced by short day and far-red conditioning.     

The phenology of seed‐propagated globe artichoke

The ability of globe artichoke to produce inflorescences (capitula) during the autumn when the market price is highest is lost when plants are propagated from seed, as are most F₁ hybrid cultivars. To gain an understanding of the phenology of seed‐propagated globe artichoke, both vernalised and non‐vernalised seedlings grown from open pollinated progeny of ‘Spinoso sardo’ plants were transplanted into the field at two monthly intervals covering a whole year. Final leaf number and the date of unfolding of each leaf were used to calculate the phyllochrons. The average final leaf number increased from 24 to 88 in response to increasing daylength above an approximately 11 h threshold during the first 30 days after emergence, and this variate explained about 90% of the variation in the thermal time taken to reach the bolting stage. The average phyllochron ranged from 56 to 96°Cd among the six emergence dates and was the major underlying physiological cause of the loss of early flowering shown by seed‐propagated plants. Genotypic variation for phyllochron within an emergence date was strongly associated with variation for the length of the emergence to bolting stage period. The limited effect of vernalisation on development indicated that the late flowering tendency of seed‐propagated plants cannot be attributed to an unfulfilled cold requirement.