Diapause Response Research Articles

RNA-Seq reveals early distinctions and late convergence of gene expression between diapause and quiescence in the Asian tiger mosquito,Aedes albopictus

Dormancy is a crucial adaptation allowing insects to withstand harsh environmental conditions. The pre-programmed developmental arrest of diapause is a form of dormancy that is distinct from quiescence, in which development arrests in immediate response to hardship. Much progress has been made in understanding the environmental and hormonal controls of diapause. However, studies identifying transcriptional changes unique to diapause, rather than quiescence, are lacking, making it difficult to disentangle the transcriptional profiles of diapause from dormancy in general. The Asian tiger mosquito, Aedes albopictus, presents an ideal model for such a study, as diapausing and quiescent eggs can be staged and collected for global gene expression profiling using a newly developed transcriptome. Here, we use RNA-Seq to contrast gene expression during diapause with quiescence to identify transcriptional changes specific to the diapause response. We identify global trends in gene expression that show gradual convergence of diapause gene expression upon gene expression during quiescence. Functionally, early diapause A. albopictus show strong expression differences of genes involved in metabolism, which diminish over time. Of these, only expression of lipid metabolism genes remained distinct in late diapause. We identify several genes putatively related to hormonal control of development that are persistently differentially expressed throughout diapause, suggesting these might be involved in the maintenance of diapause. Our results identify key biological differences between diapausing and quiescent pharate larvae, and suggest candidate pathways for studying metabolism and the hormonal control of development during diapause in other species.

Effects of photoperiod and temperature on diapause induction in Conogethes punctiferalis (Lepidoptera: Pyralidae)

The yellow peach moth, Conogethes punctiferalis (Guenée), a multivoltine species that overwinters as diapausing larvae, is one of the most serious insect pests on maize in China. Effect of photoperiod and temperature on larval diapause was examined under empirical laboratory conditions. Short-day treatments caused larval diapause at 25°C, and the critical photoperiod was between 12 and 13 h (or 12 h 51 min) light per day. No sensitive instar was identified for diapause induction under alternated short- (L : D 11 : 13 h) and long-day (L : D 14 : 10 h) treatments at different larval stages. However, accumulative treatment of three instars and 10 d under short-day treatment was required for the induction of 50% larval diapause. All larvae entered diapause at 20°C, whereas less than 3% did so at 30°C, irrespective of the long- or short-day treatment. Furthermore, under the short-day treatment, more than 90% of larvae went into diapause with temperatures ≤ 25°C, but less than 17% did so at 28°C. In contrast, under the long-day treatment, less than 19% of larvae went into diapause with temperatures ≥ 23°C. The forward shift (5°C) of critical temperature under the long-day regime demonstrated the compensatory effect of temperature and photoperiod on diapause induction. In conclusion, C. punctiferalis had a temperature-dependent type I photoperiodic diapause response; there was no sensitive instar for diapause determination, but the photoperiodic accumulation time countermeasures both of the short-day cycles and the number of instars exposed, and the photoperiodic diapause response, was a temperature-compensated phenomenon.

Inheritance of photoperiodic control of pupal diapause in the cotton bollworm, Helicoverpa armigera (Hübner)

Pupae of the cotton bollworm, Helicoverpa armigera display a diapause in response to the exposure of their larvae to short photoperiods and relatively low temperatures. Due to geographic variation in photoperiodic response, moths from a northern population, Langfang (39°32′N, 116°41′E), enter diapause in response to short daylengths (D strain) while moths from a southern population, Ledong (18°28′N, 108°53′E), exhibit no diapause under the same conditions (N strain). In the present study, crosses between the two strains are utilized to evaluate the inheritance of diapause under different photoperiods at temperatures 20, 22 and 25°C. The moths in both reciprocal crosses and backcrosses to D strain showed a clear long-day response, similar to that of the D strain, suggesting that the photoperiodic response controlling diapause in this moth is heritable. The incidences of diapause for all F1 hybrids were intermediate between those of their parents. However, the incidences of diapause at 20°C in F1 (N×D) strain were significantly higher than those in F1 (D×N) strain, indicating that the male parent plays a more important role in the determination of diapause. The N strain also showed a short-day photoperiodic response at the lower temperature of 20°C, indicating that the N strain still has the capability to enter a photoperiodically induced diapause, depending on the rearing temperature. Results from all crosses under photoperiods LD 12:12 or LD 13:11 at 22°C showed that inheritance of diapause in H. armigera did not fit an additive hypothesis and that the capacity for diapause was transmitted genetically in the manner of incomplete dominance with non-diapause characteristic partially dominant over the diapausing. Diapause duration in hybrid pupae was also influenced by their inheritance from both parents. Diapause duration in hybrid pupae was intermediate between those of their parents. These results reveal that both diapause induction and duration are under the control of polygene.

Inheritance of photoperiodic induction of larval diapause in the Asian corn borer Ostrinia furnacalis

The Asian corn borer Ostrinia furnacalis (Guenée) enters facultative diapause as fully‐developed larvae in response to short‐day conditions. As a consequence of geographical variation in photoperiodic response, moths from Nanchang (28°46′N, 115°50′E) enter diapause in response to short day‐lengths (D strain), even at the high temperatures whereas moths from Ledong (18°47′N, 108°89′E) exhibit almost no diapause under the same conditions (N strain). In the present study, crosses between the two strains are used to evaluate the inheritance of diapause under different photoperiods at temperatures of 22, 25 and 28 °C. The moths, both reciprocal crosses and backcrosses, show a clear long‐day response, similar to that of the D strain, suggesting that the photoperiodic response controlling diapause in this moth is heritable. However, the critical day‐length for induction of diapause is shorter in hybrids than in the D strain. The N strain also shows a short‐day photoperiodic response at the lower temperature of 22 °C, indicating that the N strain still has the capacity to enter a photoperiodically‐induced diapause, depending on the rearing temperature. The incidence of diapause in all crosses is highest with D strain fathers or grandfathers and lowest with N strain fathers or grandfathers, indicating that the male parent has significantly more influence on the incidence of diapause of subsequent progeny than the female. The results obtained from all crosses under LD 12 : 12 h or LD 13 : 11 h photocycles at 25 °C show that inheritance of diapause in O. furnacalis does not fit an additive hypothesis and that the capacity for diapause is transmitted genetically in the manner of incomplete dominance.

Metabolic and Proteomic Profiling of Diapause in the Aphid Parasitoid Praon volucre

BackgroundDiapause, a condition of developmental arrest and metabolic depression exhibited by a wide range of animals is accompanied by complex physiological and biochemical changes that generally enhance environmental stress tolerance and synchronize reproduction. Even though some aspects of diapause have been well characterized, very little is known about the full range of molecular and biochemical modifications underlying diapause in non-model organisms.Methodology/Principal FindingsIn this study we focused on the parasitic wasp, Praon volucre that exhibits a pupal diapause in response to environmental signals. System-wide metabolic changes occurring during diapause were investigated using GC-MS metabolic fingerprinting. Moreover, proteomic changes were studied in diapausing versus non-diapausing phenotypes using a combination of two-dimensional differential gel electrophoresis (2D-DIGE) and mass spectrometry. We found a reduction of Krebs cycle intermediates which most likely resulted from the metabolic depression. Glycolysis was galvanized, probably to favor polyols biosynthesis. Diapausing parasitoids accumulated high levels of cryoprotective polyols, especially sorbitol. A large set of proteins were modulated during diapause and these were involved in various functions such as remodeling of cytoskeleton and cuticle, stress tolerance, protein turnover, lipid metabolism and various metabolic enzymes.Conclusions/SignificanceThe results presented here provide some first clues about the molecular and biochemical events that characterize the diapause syndrome in aphid parasitoids. These data are useful for probing potential commonality of parasitoids diapause with other taxa and they will help creating a general understanding of diapause underpinnings and a background for future interpretations.

暗期干扰对棉铃虫两个不同地理种群滞育抑制作用的比较

至今,所测试昆虫的光周期反应均表明,光周期反应对暗期干扰高度敏感,短暂的光脉冲都可在不同程度上逆转长夜效应,抑制滞育的发生。在研究了棉铃虫<em>Helicoverpa armigera</em>泰安种群(36.15°N, 116.59°E)和喀佐种群(41.34°N, 120.27°E)光周期反应的基础上,在滞育诱导的短光周期下(L12:D12 和L9:D15),分别测试了暗期不同时段1h光脉冲对这两个不同地理种群滞育抑制的影响。25和22℃下的光周期反应显示了泰安种群在长暗期11-14 h 的滞育率均显著低于喀佐种群;泰安种群的临界暗长分别为11.7 h和11.5 h,喀佐种群分别为10.5 h和10.3 h,泰安种群均比喀佐种群长1.2 h。在所测试的暗期干扰实验中,除了极少数光脉冲干扰点外,泰安种群蛹滞育率显著低于喀佐种群,但两者的滞育反应曲线基本相似。在短光周期L9:D15下,泰安种群和喀佐种群均显示了光脉冲落入暗期的第9-11小时最有效地抑制了滞育的发生。在短光周期L12∶D12下,泰安种群和喀佐种群在25℃时均显示了光脉冲落入暗期的第3-4小时和第10小时导致了最低的滞育发生;但在22℃时,喀佐种群只在暗期的第3-4小时显示了最高的滞育抑制。这些结果揭示了偏南的泰安种群对暗期干扰的敏感性强于偏北的喀佐种群,但这两个地理种群的最高光敏感位点基本相同。;Photoperiodic time measurement in insects can be affected by interrupting the dark phase of the light dark cycle with short supplementary light pulses. All the photoperiodic responses tested are highly sensitive to night interruption, and the long night effect is reversed by a light break. Most past studies revealed two points of apparent light sensitivity (the so-called A and B peaks), but the response pattern varied considerably among different species. Some species had only one peak (or trough), either A or B. Even the same species may have different patterns of response depending on the experimental conditions. However, it is still not clear whether differences exist in the effect of night-interruption on diapause-averting among different geographic populations. The cotton bollworm, <em>Helicoverpa armigera </em>(Hübner) is one of the most serious crop pests in Asia, Australia, Africa and Europe. The species is distributed across much of China and attacks many host plants. The widely distributed<em> H. armigera</em> encounters a great diversity in climatic conditions in different places and shows different critical day lengths or night lengths (the day length that elicits 50% diapause response) among different geographic populations. In the present study, the photoperiodic response and effects of night-interruption on diapause-averting, in which the scotophases of L9:D15 (Light 9 h:Dark 15 h) and L12∶D12 were interrupted by 1 h light pulse, were investigated at 22℃ and 25℃ in Taian (TA, 36.15°N, 116.59°E) and Kazuo (KZ, 41.34°N, 120.27°E) populations of the cotton bollworm<em> H. armigera</em>. The photoperiodic response curves showed that the incidences of diapause in the scotophases of 11-14 h were significantly lower in the Taian population than in the Kazuo population. The critical night length in the Taian population at 25℃ and 22℃ was 11 h 42 min and 11 h 30 min, respectively, and 1h 20 min longer than that in Kazuo population (10 h 30 min and 10 h 18min). In all night-interruption experiments, the incidences of diapause in almost all positions of light pulse in the Taian population were significantly lower than that in the Kazuo population. However, the diapause response curves were similar in the two populations. Under L9: D15, the incidence of diapause was inhibited most effectively in both the Taian population and the Kazuo populations when the light pulses were placed at 9-11 h in the darkness. Under L12:D12 the incidence of diapause was lowest at 25℃ in both Taian population and Kazuo population when the light pulses were placed at 3-4 h and 10 h in the darkness. However, the Kazuo population only showed a peak of diapaus-averting occurring in 3-4 h in the darkness at 22℃. <br> Our results reveal that effect of night-interruption on diapause-averting is different among different geographic population. The southern Taian population is more sensitive to night-interruption than the northern Kazuo populations, but the most highly photosensitive position is similar for both populations.<br> A light pulse plays two possible roles in photoperiodic time measurement. First it ‘initiates’ or ‘resets’ the clock; this has been called the ‘entraining agent’ or ‘priming agent’. Second it ‘measures’ a critical duration of day or night; this has been called the ‘inductive agent’ or ‘terminating agent’. The present study in <em>H. armigera</em> reveals that a light pulse can reset the process measuring night length, and thus influences the incidence of diapause.

Retention and adaptiveness of photoperiodic EGG diapause in Florida populations of invasive Aedes albopictus.

Female Aedes albopictus, F2-F3 descendents from individuals collected as immatures at 6 geographic sites in the USA during 2008, exposed to short daylengths (10 h of light and 14 h of darkness at 21 degrees C) laid eggs in diapause, whose frequency depended upon population origin. Diapause responses in northern Florida and Illinois were strong, as had been reported approximately 10 years earlier for Ae. albopictus from these regions. For southern Florida, the diapause response was polymorphic, and its mean incidence decreased at 2 of 3 collection sites compared to 10 years earlier. Exposure in the field for 2- to 4-wk intervals in Vero Beach (lat 27 degrees 35'N) during January 2009 revealed that eggs laid by short-day females had significantly higher survivorship, even though <50% were estimated, from laboratory results, to be in diapause. Enhanced desiccation resistance may select for retention of diapause in southern Florida.

Examination of Parental Effect on the Progeny Diapause by Reciprocal Cross Test in the Cabbage Beetle,Colaphellus bowringi

The cabbage beetle, Colaphellus bowringi Baly (Coleoptera: Chrysomelidae), a serious pest of crucifers in China, undergoes summer or winter diapause in the soil as an adult. In the present study, the incidence of diapause were measured in reciprocal crosses between a high—diapause strain (HD strain) and a laboratory—selected nondiapausing strain (ND strain) under different photoperiods and temperatures, to explore parental influences on the progeny diapause. Sensitivity to photoperiod in the selected nondiapausing strain was nearly eliminated at 25 °C, whereas sensitivity to temperature of the selected nondiapausing strain was retained under continuous darkness at 20 and 22 °C. Reciprocal crosses between the HD strain and the ND strain showed that the incidence of diapause in the progeny was always intermediate to that of the parents under different photoperiods and temperatures, suggesting that diapause induction was determined by both female and male parents. There was a significant effect of temperature; temperature interacted with reciprocal cross on diapause induction, whereas no significant effect of reciprocal cross was demonstrated. The incidence of diapause in ♀ND × ♂HD was the same as in ♀HD × ♂ND under continuous darkness at 18 °C (100%) and 26 °C (0%), but the former was higher than that in ♀HD × ♂ND under continuous darkness at 22 °C, suggesting that female parent does not exhibit strong influence on the diapause response to temperature. There was a significant effect of photoperiod and reciprocal cross on diapause induction, whereas no significant interactive effect on diapause induction was demonstrated. Incidence of diapause in ♀HD × ♂ND was always higher than in ♀ND × ♂HD at 25 °C and 12:12 L:D, 14:10 L:D, and 16:8 L:D, suggesting a strong maternal influence on the diapause response to photoperiod, though a significant difference was observed only at 14:10 L:D. Our results support the idea that diapause induction is determined by both female and male parents. However, results also indicated that a strong maternal influence on diapause was exhibited only in response to photoperiod.

Geographic Variation of Photoperiodic Diapause but Not Adult Survival or Reproduction of the Invasive MosquitoAedes albopictus(Diptera: Culicidae) in North America

Climate differences across latitude can result in seasonal constraints and selection on life-history characters. Because Aedes albopictus (Skuse) invaded North America in the mid-1980s, it has spread across a range of ≈14° latitude and populations in the north experience complete adult mortality because of cold winter temperatures that are absent in the south. Life-table experiments were conducted to test for differences in the adult survival and reproductive schedules of Ae. albopictus females from three populations from the northern (Salem, NJ; Springfield, IL; Eureka, MO; ≈39° N) and southern (Palm Beach, Palmetto, Tampa, FL; ≈27-28° N) extremes of the species distribution in North America. There were consistent differences between northern and southern populations in incidence of photoperiodically-induced egg diapause. Under short daylength, diapause eggs constituted twice the proportion of total viable eggs from northern females (81.9-92.1%) than southern females (35.9-42.7%). There were no consistent differences between northern and southern populations in resource allocation between reproduction and maintenance, reproduction over time, and reproductive investment among offspring, and no apparent trade-offs between diapause incidence with reproduction or longevity. Our results suggest that the main response of North American Ae. albopictus to unfavorable winter climates is via the life history strategy of producing diapausing eggs, rather than quantitative variation in reproduction, and that there are no detectable costs to adult survival. Inherent geographic variation in the expression of diapause, consistent with the latitudinal extremes of A. albopictus, indicates evolutionary loss of diapause response in southern populations because of the invasion of A. albopictus in North America.

Role of natural day-length and temperature in determination of summer and winter diapause in Pieris melete (Lepidoptera: Pieridae)

Under field conditions, the cabbage butterfly, Pieris melete, displays a pupal summer diapause in response to relatively low daily temperatures and gradually increasing day-length during spring and a pupal winter diapause in response to the progressively shorter day-length. To determine whether photoperiod is 'more' important than temperature in the determination of summer and winter diapause, or vice versa, the effects of naturally changing day-length and temperature on the initiation of summer and winter diapause were systematically investigated under field conditions for five successive years. Field results showed that the incidence of summer diapause significantly declined with the naturally increasing temperature in spring and summer generations. Path coefficient analysis showed that the effect of temperature was much greater than photoperiod in the determination of summer diapause. In autumn, the incidence of diapause was extremely low when larvae developed under gradually shortening day-length and high temperatures. The incidence of winter diapause increased to 60-90% or higher with gradually shortening day-length combined with temperatures between 20.0°C and 22.0°C. Decreasing day-length played a more important role in the determination of winter diapause induction than temperature. The eco-adaptive significance of changing day-length and temperature in the determination of summer and winter diapause was discussed.

The prevalence of diapause response to risk of size-selective predation in small- and large-bodied prey species

The prevalence of diapause response to the simulated threat of fish predation was compared in three species of planktonic crustaceans of the genus Daphnia (D. magna, D. pulicaria and D. longispina), which due to their different body size vary in vulnerability to fish predation pressure in natural conditions. Higher incidence of diapause response was presumed in the larger-bodied species, which due to their higher conspicuousness and higher energetic content experience the greatest size-selective pressure from visually foraging fish. Small-bodied species were expected to utilize less costly yet less effective active defences, e.g. lower conspicuousness achieved due to slower body growth when facing risk of size-selective predation. Proportions of females forming diapausing structures as well as females body size at the maturation period were compared in experimental beakers containing or not containing fish kairomones (chemical cues of fish predation) in a few clonal lineages of 3 species of Daphnia derived from a single lake inhabited by fish. The highest incidence of diapause response to fish kairomones was observed in D. magna (when measured both as proportion of sensitive individuals and as proportion of inductive clones), the largest of the tested Daphnia species. The lowest proportion of individuals and clones that employed diapause was reported in the smallest tested species, D. longispina. In addition, the large-bodied Daphnia (D. magna) showed a greater reduction in body size in response to fish kairomones than the small-bodied species (D. longispina). The results of the present study support the assumption of higher prevalence of diapause response to the threat of selective predation in larger and more vulnerable prey species.

Diapause induction and photoperiodic clock in Chilo suppressalis (Walker) (Lepidoptera: Crambidae)

AbstractThe mature larvae of the rice stem borer, Chilo suppressalis Walker (Lepidoptera: Crambidae) enters facultative diapause in response to short‐day conditions in the autumn (August–September). Diapause induction and photoperiodic clock mechanism were investigated in C. suppressalis larvae reared on an artificial diet in the present study. The critical night length for diapause induction was about 9 h 53 min to 10 h 39 min at 22 to 28°C. The third‐instar larvae were found to be relatively sensitive to diapause induction. Photoperiodic response under non‐24‐h light–dark cycles showed that scotophase length played an essential role in the induction of larval diapause in C. suppressalis, and consecutive exposure to long‐night cycles was necessary for a high diapause incidence. In the Nanda–Hamner experiment, diapause incidence peaked at scotophase of 12 h and dropped rapidly at scotophases &gt; 24 h. In the Bünsow experiment, diapause incidence was clearly suppressed, especially at the light pulse located 8 h in the scotophase. Both the Nanda–Hamner and Bünsow experiments showed no rhythmic fluctuations with a period of about 24 h; thus the photoperiodic clock in C. suppressalis is a non‐oscillatory hourglass timer or a rapidly damping circadian oscillator.

Genetic Variation and Inheritance of Diapause Induction in Two Distinct Voltine Ecotypes of Ostrinia nubilalis (Lepidoptera: Crambidae)

Abstract European corn borer, Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae), displays a larval diapause in response to short photoperiods and is adapted to a variety of local conditions throughout North America. Hence, the effective photoperiod inducing larval diapause will differ among geographic ecotypes. This study considers the inheritance of photoperiodic larval diapause induction by hybridization and backcrossing two latitudinally distinct ecotypes of the European corn borer collected between 41° N, 96° W and 48° N, 96° W and under a range of photoperiods representative of their respective locations: from 14:10 to16:8 (L:D) h. The ecotype adapted to a bivoltine habitat (southeastern Nebraska) exhibited a shorter critical photoperiod (1480 h) than the ecotype (1533 h), originating from a univoltine habitat (northwestern Minnesota). Reciprocal F1 crosses exhibited intermediate values with indication of sex-linked inheritance. In addition, the male parent had significantly more influence on diapause incidence of subsequent progeny than the female. The F2 and backcross progeny further supported the supposition that diapause response is a sex-linked inheritance. The minimum number of genes estimates, and the response from backcross progeny, suggest that diapause response of European corn borer larva may be controlled by only a few loci. The overall results indicated that both ecotypes had adopted unique diapause responses, which ultimately lead to seasonal synchrony in their ecosystems.

Effect of photoperiod on immature development and diapause induction in the Kanzawa spider mite, Tetranychus kanzawai (Acari: Tetranychidae)

The diapause response of the Kanzawa spider mite (KSM), Tetranychus kanzawai, was examined. KSMs were reared in aluminum bottles at 18°C with different combinations of light and dark periods created by the light-control unit. The developmental periods for all immature stages tended to decrease as the light period increased. The photoperiodic response curve for diapause induction showed that the critical (=50% diapause) light period was around 13 h days(-1). No diapause induction was observed when the light period was longer than 13.5 h days(-1) or under continuous light. At 13-h days(-1) light period, the developmental period for deutonymphal stage as well as for the total immature stages was longer in diapaused females than in non-diapaused females. These results indicate that immature development as well as diapause induction are affected by photoperiod and further suggest that diapause-inducing stimuli prolong the developmental period especially for the deutonymphal stage of KSMs.

Population Dynamics and Diapause Response of the Springtail Pest Sminthurus viridis (Collembola: Sminthuridae) in Southeastern Australia

The springtail, Sminthurus viridis (L.) (Collembola: Sminthuridae), is an important agricultural pest across southern Australia. We investigated the seasonal abundance patterns and summer diapause response of S. viridis in southeastern Australia by using field and shadehouse (a greenhouse that offers seedlings shade) experiments. Seasonal activity patterns of S. viridis were largely consistent with previous studies, with the pest active from autumn to spring. In addition, the timing and pattern of the summer-diapausing egg stage was established, with multiple generations probably producing diapause eggs. A strong relationship between soil moisture and temperature with autumn emergence also was observed. These results suggest that S. viridis autumn pest pressure can be predicted and indicate that late-season spraying strategies currently used for a sympatric agricultural pest are unlikely to be as effective against S. viridis.

Inheritance of the photoperiodic response controlling imaginal summer diapause in the cabbage beetle, Colaphellus bowringi

Adults of the cabbage beetle Colaphellus bowringi display a summer diapause in response to the exposure of their larvae to long photoperiods. In the present study, the inheritance of the photoperiodic response controlling summer diapause in C. bowringi by crossing a high diapause strain (D strain) with a laboratory selected nondiapause strain (N strain) was investigated under different photoperiods at 22, 25 and 28 °C. The beetles in both reciprocal crosses and backcrosses showed a clear short-day response for the induction of diapause at all temperatures, similar to that of the D strain, suggesting that photoperiodic response of this beetle is heritable. The diapause incidences in the progeny from all the crosses under LD 15:9 or LD 12:12 at 25 °C suggest that genetic and genetic–environmental interactions are involved in diapause induction. The incidence of diapauses in F 1 progeny was significantly lower than that in the D × D strain but significantly higher than that in the N × N strain, indicating that the diapause capability is inherited in an incomplete dominant manner. The incidence of diapause was greater among the offspring of hybrid females when those females had a D strain mother or grandmother rather than a N strain mother or grandmother, indicating that maternal effects on diapause induction are stronger than paternal effects. The laboratory selected nondiapause strain also showed a short-day photoperiodic response at a low temperature of 22 °C, indicating that the photoperiodic photoreceptor and photoperiodic clock still function in the nondiapause strain.

Role of temperature in diapause response to fish kairomones in crustacean Daphnia

The effect of non-lethal thermal conditions on the diapause response to a simulated threat of fish predation was tested in the freshwater planktonic crustacean Daphnia magna. From an early developmental stage, female Daphnia were either exposed or not exposed to fish kairomones that notified of the threat of fish predation at the benign growth temperatures of 18, 22 or 26 °C. The proportion of females switching from the production of subitaneous to diapausing eggs and their rate of reproduction were recorded. Besides the faster development and more intense reproduction observed at higher temperatures, a smaller proportion of the females formed protective, diapausing eggs when exposed to fish kairomones than was the case in colder conditions. The production of diapausing eggs was not observed when the threat of fish predation was absent. These results indicate an interactive effect of fish kairomones and thermal conditions on diapause induction in D. magna. We interpret these findings in the context of strategies for the maximisation of reproductive success. The production of well protected diapausing eggs (which assures low yet stable gains under diverse thermal conditions) may be a more beneficial life history strategy at lower temperatures, where the chances of survival of active individuals until maturation and successful reproduction are low. Higher temperatures permit faster maturation and more intensive reproduction that may surpass numerical losses of active descendants due to predation, making diapause a less rewarding option.

Geographic Variation in Diapause Induction: The Grape Berry Moth (Lepidoptera: Tortricidae)

Diapause in insects occurs in response to environmental cues, such as changes in photoperiod, and it is a major adaptation by which insects synchronize their activity with biotic resources and environmental constraints. For multivoltine agricultural insect pests, diapause initiation is an important consideration in management decisions, particularly toward the end of the growing season. The grape berry moth, Paralobesia viteana (Clemens), is the main insect pest affecting viticulture, and this insect responds to postsummer solstice photoperiods to initiate diapause. Because the range of grape berry moth extends from southern Canada to the southern United States, different populations are exposed to different photoperiodic regimes. We quantified the diapause response in grape berry moth populations from Arkansas, Michigan, New York, Pennsylvania, Texas, and Virginia, and observed latitudinal variation in diapause initiation. Populations from Michigan, New York, and Pennsylvania responded significantly different than those from Arkansas, Texas, and Virginia. We also observed, as a consequence of our experiments, that the timing of our laboratory studies influenced grape berry moth's response to photoperiod, ceteris paribus. Experiments that were conducted when grape berry moth would be naturally in diapause resulted in a significant higher proportion of diapausing pupae at photoperiods (i.e., >15 h) that generally do not induce diapause, suggesting that attention should be paid to the timing of behavioral and physiological experiments on insects. This relationship between photoperiod and diapause induction in grape berry moth across geographic regions will provide applicable knowledge to improve pest management decisions.

Stem Cell Dynamics in Response to Nutrient Availability

When nutrient availability becomes limited, animals must actively adjust their metabolism to allocate limited resources and maintain tissue homeostasis. However, it is poorly understood how tissues maintained by adult stem cells respond to chronic changes in metabolism. To begin to address this question, we fed flies a diet lacking protein (protein starvation) and assayed both germline and intestinal stem cells. Our results revealed a decrease in stem cell proliferation and a reduction in stem cell number; however, a small pool of active stem cells remained. Upon refeeding, stem cell number increased dramatically, indicating that the remaining stem cells are competent to respond quickly to changes in nutritional status. Stem cell maintenance is critically dependent upon intrinsic and extrinsic factors that act to regulate stem cell behavior. Activation of the insulin/IGF signaling pathway in stem cells and adjacent support cells in the germline was sufficient to suppress stem cell loss during starvation. Therefore, our data indicate that stem cells can directly sense changes in the systemic environment to coordinate their behavior with the nutritional status of the animal, providing a paradigm for maintaining tissue homeostasis under metabolic stress.

Sexual difference in the photoperiodic induction of pupal diapause in the flesh fly Sarcophaga similis

The flesh fly Sarcophaga similis enters pupal diapause in response to short days, but averts diapause under long days. This species shows a sexual difference in the photoperiodic induction of diapause, with females having shorter critical daylength than males. Here, we proposed two hypotheses to explain this sexual difference. First, we proposed a sexual difference in the qualitative evaluation of photoperiods. This hypothesis assumes under the external coincidence model that although the photoinducible phase of both sexes locates at late scotophase, in males, it locates at a slightly earlier phase. However, the results of night interruption experiments clearly ruled out this hypothesis. Because we verified that S. similis evaluated photoperiods quantitatively, we next proposed a sexual difference in the quantitative evaluation of photoperiods. This hypothesis incorporates concepts of a hypothetical substance accumulation that shows a diapause-inducing effect and an internal threshold that serves as a reference to determine the diapause/nondiapause developmental program. In long-day exposure experiments and night interruption experiments, females consistently showed a lower incidence of diapause than males. Thus, the present study data satisfactorily meet the second hypothesis, that is a sexual difference in the quantitative evaluation of photoperiods exists in S. similis.