变化光周期对丽斗蟋(Velarifictonus ornatus)若虫发育的影响

为弄清湖南株洲丽斗蟋若虫的季节适应策略,研究了恒定及变化光周期对其若虫发育的调控.结果表明,丽斗蟋若虫发育明显受变化光周期的影响.25℃温度条件下,3个光周期条件下的若虫发育都较慢,羽化也极不整齐,长日条件(LD 16:8h)、中间日照条件(LD 14:10h)和短日条件(LD 12:12h)的若虫发育历期(mean±SD)分别为(206.2±44.0)d、(236.6±93.3)d和(230.3±47.4)d,若虫从开始羽化到供试个体全部完成羽化所需时间分别为216、301和156d,经历短日条件的若虫转移至长日条件后能够促进其快速发育,羽化也很整齐,反方向转移则会抑制若虫发育,且羽化也不整齐.30℃温度条件下,恒定长日条件下的若虫发育明显快于短日条件,变化光周期对若虫发育的调控与25℃相类似.变化光周期对若虫发育的影响与光周期的变化方向及低龄若虫感受的光周期类型有关.丽斗蟋若虫复杂的光周期反应模式的生态意义在于调节其生活史与季节同步.     

Antioxidant defense in mitochondria during diapause and postdiapause development of European corn borer (Ostrinia nubilalis, Hubn.)

Antioxidant enzymes (CAT, catalase; GPx, selenium nondependent glutathione peroxidase; GST, glutathione-S-transferase; GR, glutathione reductase; DHAR, dehydroascorbate reductase) were determined in the mitochondria of diapausing and non-diapausing larvae and pupae of both diapausing and non-diapausing larvae of the European corn borer (Ostrinia nubilalis, Hubn., Lepidoptera: Pyralidae). CAT, GST, and DHAR activity in mitochondria of diapausing larvae were reduced compared to non-diapausing larvae. Pupae of diapaused-larvae possessed lower GST, but higher DHAR activities compared to pupae of non-diapaused individuals. Comparison between larvae and pupae revealed lower GPx activity in the mitochondria of pupae. CAT activity in the mitochondria of pupae was higher compared to diapausing larvae, but lower than in non-diapausing ones. Correlation and canonical discriminant analyses revealed different antioxidant enzyme compositions for a particular stage and developmental pattern. Our results show that antioxidant enzymes have a similar role in the regulation of energetics in mitochondria as that in diapause and metamorphosis.     

Differentiation in sex investment by clones and populations of Daphnia

Dormancy is an ecological strategy by which organisms avoid stressful environments, but it also can have genetic consequences. Many facultative parthenogens shift from asexual to sexual reproduction to enter dormancy. Hence, conditions that favour dormancy are predicted to select for more sex, which should increase clonal diversity. We examined lake populations of Daphnia that face different ecological risks to remaining active year‐round, and quantified the extent to which they have differentiated in their investment in dormancy and sex. There was substantial genetic variation among populations and clones for sex induction and production of dormant eggs, and striking evidence of gender specialization. We also observed a positive association between the magnitudes of population‐level investment in dormancy and of variance among clones in sex induction. These results document an ecological gradient in dormancy that is manifest as a genetic gradient in clonal variation for the propensity to engage in sex.     

Maternal source of variability in the embryo development of an annual killifish

Organisms inhabiting unpredictable environments often evolve diversified reproductive bet‐hedging strategies, expressed as production of multiple offspring phenotypes, thereby avoiding complete reproductive failure. To cope with unpredictable rainfall, African annual killifish from temporary savannah pools lay drought‐resistant eggs that vary widely in the duration of embryo development. We examined the sources of variability in the duration of individual embryo development, egg production and fertilization rate in Nothobranchius furzeri. Using a quantitative genetics approach (North Carolina type II design), we found support for maternal effects rather than polyandrous mating as the primary source of the variability in the duration of embryo development. The number of previously laid eggs appeared to serve as an internal physiological cue initiating a shift from rapid‐to‐slow embryo developmental mode. In annual killifish, extensive phenotypic variability in progeny traits is adaptive, as the conditions experienced by parents have limited relevance to the offspring generation. In contrast to genetic control, with high phenotypic expression and heritability, maternal control of traits under natural selection prevents standing genetic diversity from potentially detrimental effects of selection in fluctuating environments.     

Life-History Variation inChrysoperla carnea:Implications for Rearing and Storing a Mexican Population

A population ofChrysoperla carneafrom San Pedro, Coahuila, Mexico, showed phenological responses that differ from those of previously studied North American biotypes. Short daylengths that induce diapause in other biotypes resulted in low incidences of diapause in the San Pedro population. Diapause induction required a decrease in daylength (from long to short days). Constant long days produced variable reproductive responses, whereas an increase in daylength (from short to long day) resulted in high incidences of reproduction. Providing prey to adults that had been reared under short days consistently increased the incidences of reproduction. Storage of either diapausing or nondiapausing adults at low temperature (5°C) for 13 weeks yielded better survivorship and reproductive performance than in unstored (24°C) controls. For efficient production, the San Pedro population ofC. carneamay be reared either with an increase in daylength or with the regular intervention of a storage period. To induce diapause in individuals destined for storage, larvae may be reared under long-day photoperiod and the prepupae transferred to short days.     

Completion of diapause in field populations of the cabbage root fly (Delia radicum)

The various diapause and post-diapause stages entered by cabbage root fly pupae during the overwintering period are shown schematically. Although diapause induction started in mid-Aug., the early-pupating insects did not develop further but were maintained in diapause by the warm autumn temperatures. Therefore, diapause development was simultaneous in all Wellesbourne pupae, whether of second or third generation origin. Diapause development started only in mid-Oct., when mean soil temperatures fell below 10°. In the field, 90% of the overwintering population of cabbage root fly pupae had completed pleted diapause by 5 March 1980, 17 Feb. 1981 and 18 Feb. 1982. This was equivalent to a duration of 19 weeks from mid-Oct. onwards, during the winters of 1979–80, 1980–81 and 1981–82 respectively. A further break between the completion of diapause and the warm conditions required to start post-diapause development also helps to condense the emergence of flies in the spring. Hence, an accurate forecast of the time of spring attack by populations of flies similar to those at Wellesbourne should be possible.This study was financed partly by the Commission of the European Communities as CEC Contract No. 0771.     

Diapause induction in the codling moth, Cydia pomonella: effect of prediapause temperatures

The effect of four prediapause temperatures (18, 22, 26 and 30°C) on the photoperiodic response of the codling moth, Cydia pomonella (L.), was studied under controlled conditions. The highest rates of diapause were recorded, for all day-lengths, at temperatures of 22 and 26°C while relatively lower rates of diapause were elicited at 18 and 30°C. The same trend was demonstrated by projecting the values of the critical photoperiod which induces 50% diapause (=CPhP₅₀) over the prediapause temperature. The change in diapause incidence as a function of photoperiod, at all prediapause temperatures, exhibited a response characteristic of long-day insects, i.e. high rates of diapause at short days (12–13.5 h) and a decrease in diapause incidence at long days (14–15 h). The results for temperatures 22, 26 and 30°C support the view that lower prediapause temperatures enhance diapause induction, at a give photoperiod, while higher temperatures tend to avert or diminish the process. On the other hand, the low rates of diapause obtained at 18°C contradict this view. Nevertheless, high correlation was found between the laboratory evidence and field data, indicating the adaptability of the Israeli codling moth to subtropical climate.     

Photoperiodic induction of larval diapause and temperature-dependent termination in a wild multivoltine bruchid,Kytorhinus sharpianus

A wild bean weevil,Kytorhinus sharpianus Bridwell (Coleoptera: Bruchidae), has a multivoltine life cycle and enters a hibernal larval diapause at the fourth instar under a short daylength (Shimada & Ishihara, 1991). Here, we investigated their diapause incidence under different photoperiods at 24°C and 27°C. The critical photoperiods for diapause induction were 14.5 h at 24°C and 14 h at 27°C. The stages susceptible to diapause-inducing stimuli were estimated by transferring larvae of various instars from long days to short days and vice versa. Then we investigated the incidence of larval diapause. The sensitive stage was estimated to be from the third to early fourth instar. Though larval diapause, which was induced under a short daylength, was terminated only by increasing the daylength, the termination was more synchronized by an exposure to a low temperature followed by increasing temperature, irrespective of photoperiod.