A maternal effect that eliminates pupal diapause in progeny of the flesh fly, Sarcophaga bullata

Flesh flies that have experienced pupal diapause produce progeny that will not enter diapause even when reared in a strongly diapause-inducing environment. The effect is determined, not by diapause itself, but by the short days previously received by the larvae during the programming of pupal diapause. Reciprocal cross matings indicate that the effect is transmitted solely by the female parent. Though the embryos develop within the uterus of the female, the maternal effect is transmitted prior to the onset of embryogenesis, probably during oögenesis. Only by rearing a generation in long-day (nondiapausing) conditions can the capacity for pupal diapause be restored in the progeny. The effect is likely to provide an adaptive mechanism for preventing an untimely diapause response among the progeny of overwintering females that emerge early in the spring.     

Puparial wax restricts passive movement of water during diapause in the flesh fly

Abstract. To determine whether the capacity of diapausing pupae of the flesh fly ( Sarcophaga crassipalpis Macquart) to absorb water from drier air than non-diapausing pupae is due to a simple passive process, we examined water flux in empty puparia. Empty puparia from both types of fly absorb and lose water passively, but those from diapause pupae do so to a lesser degree. The impervious nature of such puparia is attributed to an extra layer of cuticular wax not found in the non-diapause group.     

Deuterium oxide alters pupal diapause response in the flesh fly, Sarcophaga crassipalpis

ABSTRACT. Deuterium oxide averts pupal diapause in the flesh fly Sarcophaga crassipalpis Macquart when fed to larvae or when applied topically to photosensitive embryos exposed to short daylength. Deuterium oxide was not effective in promoting diapause when presented to embryos or larvae reared at long daylength. The effect of deuterium oxide appears to be cumulative in the larval state: increasing exposure time progressively reduces diapause response. If flies reared on deuterium oxide are exposed to continuous darkness, the diapause response remains high, thus implying that the physiological capacity for diapause is not disrupted. We suggest that deuterium oxide exerts its effect on the circadian rhythm controlling diapause induction.     

Photoperiodic induction of pupal diapause in Sarcophaga argyrostoma: Temperature effects on circadian resonance

Larval cultures of the flesh-fly Sarcophaga argyrostoma maintained in circadian ‘resonance’ experiments produced a high incidence of pupal diapause when the period of the light cycle was close to (T) 24, 48 or 72 hr, but a low incidence of diapause at T 36, 60 or 84 hr. Cultures pre-programmed for diapause by exposing pregnant females to long nights indicated the induction of non-diapause development at T 36, 60 and 84, whereas cultures pre-programmed for diapause-free development by exposing females to continuous light indicated the induction of diapause at T 24, 48 and 72.Raising the temperature reduced the heights of the diapause peaks whereas lowering the temperature raised them. With progeny from long-night-reared flies the lowest temperature tested (18°C) produced a result indistinguishable from an ‘hour-glass’ response, warning that ‘negative’ resonance experiments may merely indicate non-permissive conditions for demonstrating the involvement of circadian rhythmicity in insect photoperiodism.The results of the ‘resonance’ experiments and the effects of temperature are interpreted in terms of a multioscillator ‘external coincidence-photoperiodic counter’ model for the clock.     

Length variation in a specific region of the period gene correlates with differences in pupal diapause incidence in the flesh fly, Sarcophaga bullata

We report differences in the length of a specific region of the circadian clock gene period (per) that correlate with different capacities for pupal diapause in the flesh fly, Sarcophaga bullata. The conspicuous difference is located in a region we refer to as the putative C-terminal photoperiodic (CP) region. The length of the CP region correlates inversely with the incidence of diapause. A deletion of 33 amino acids in this region correlates with a significant increase in the incidence of diapause, from 78.1% to 93.0%, and an insertion of 9 amino acids in the same area correlates with a drop in the diapause incidence to 4.0%. This correlation suggests a possible functional role for this region of per in photoperiodism.     

Influence of maternal age on incidence of pupal diapause in the flesh fly, Sarcophaga bullata

ABSTRACT. Females of the flesh fly, Sarcophaga bullata Parker, produce an increasingly higher number of diapausing progeny in successive broods. Though a maternal effect completely eliminates the capacity for diapause in the first brood of females with an embryonic and larval history of short day, diapause is restored at low levels in later broods. Exposure to long daylength at the onset of adult life does not alter the diapause response of later broods, thus suggesting that the age effect cannot be modified by daylength manipulation. The age response implies that changes in maternal physiology exert an important regulatory control on the diapause fate of the pupa.     

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.     

Allocation from capital and income sources to reproduction shift from first to second clutch in the flesh fly, Sarcophaga crassipalpis

Understanding how resources are allocated between survival and reproduction is fundamental to the study of the evolution of life histories. Reproductive resources can come from two intrinsic resource pools, stored reserves (capital) acquired before reproduction or income acquired during reproduction. The variety of reproductive strategies in insects is remarkable and reproductive allocation encompasses the complete range of allocation strategies from pure capital breeders to pure income breeders. However, most organisms probably use a blend of capital and income and this blend is likely dynamic, changing between reproductive bouts in response to internal and external conditions. We used stable isotopes to quantify the allocation of capital and income resources to reproduction in the flesh fly, Sarcopha crassipalpis and assessed how allocation patterns change over multiple bouts of reproduction. Sarcophaga crassipalpis shifts from a slight investment of capital in the first clutch to an almost pure income breeder in the second clutch. We discuss the relationship between activity and allocation, and the potential for this system to understand how allocation patterns change in response to environmental stress.     

Possible involvement of distinct photoreceptors in the photoperiodic induction of diapause in the flesh fly Sarcophaga similis

Physiological characteristics of the photoreceptors involved in the photoperiodic induction of diapause were investigated in the flesh fly Sarcophaga similis. Both the early and late phases of scotophase were sensitive to light and a light pulse during each of these phases prevented diapause. Certain physiological differences between the phases were, nevertheless, detected. Compared with early scotophase, late scotophase required a light pulse with a long period and a large number of night interruption photoperiodic cycles in order to effectively prevent diapause. The diapause-averting effects of a light pulse during early scotophase were canceled by an additional long dark period, but those during late scotophase were not. Thus, the diapause-averting effects produced during early scotophase are different to those produced during late scotophase. The early scotophase was sensitive to light at wavelengths of 470 nm or shorter, but not to light of 583 nm or longer. In contrast, the late scotophase was sensitive to light of a broad range of wavelengths, ranging from 395 to 660 nm. Furthermore, the early scotophase was considerably more sensitive to monochromatic light with low photon flux density than the late scotophase. These results suggest that different types of photoreceptor are involved in the photoperiodic response.     

Genetic analysis of diapause capability and association between larval and pupal photoperiodic responses in the flesh fly Sarcophaga similis

Abstract A variant of the flesh fly Sarcophaga similis, which does not enter pupal diapause even under diapause‐inducing conditions, is established by artificial selection. Interline crosses of the wild‐type and the variant revealed that the diapause capability is inherited in an incomplete dominant manner. Neither sex linkage nor a maternal factor is involved in the mode of inheritance. Genetic and genetic–environmental interactions are involved in the induction of diapause. In the wild‐type, the post‐feeding larval period is prolonged in response to short days. However, in the variant, the duration of the larval period under short‐day conditions is identical to that under long‐day conditions. Long‐day responses under short‐day conditions at both the larval and pupal stages in the variant indicate that the responses are established by common factors in both stages. The factors causing the long‐day responses under short‐day conditions at different developmental stages in the variant remain to be identified. However, it is plausible to hypothesize that common factors regulate ecdysteroid release at both the larval and pupal stages, and that malfunction of the system regulating these factors triggers such ecdysteroid release, irrespective of the photoperiod. Hence, the photoperiodic responses disappear in the variant in both stages. The adult stage of the variant has a functional circadian clock, suggesting that the nondiapause phenotype is not necessarily involved in malfunction of the circadian clock.     

Mendelian inheritance of pupal diapause in the flesh fly, Sarcophaga bullata

Pupal diapause (dormancy) in the flesh fly, Sarcophaga bullata, is induced by short-day photoperiods and low temperature. In this study, the inheritance mode of diapause was investigated by crossing a nondiapausing (nd) strain of S. bullata with 2 diapausing strains having different diapause capacities. The results consistently indicated that diapause incidence is inherited in a simple Mendelian pattern, thus a single gene or a small gene cluster linked to the photoperiodic clock controls the seasonal response of diapause. The fact that the nd strain lacked daily rhythmicity in adult eclosion and showed altered expression of 2 circadian clock genes suggests that the photoperiodic and circadian clocks are related through a shared molecular component in S. bullata.     

Cycles of protein synthesis during pupal diapause in the flesh fly,Sarcophaga crassipalpis

Protein synthesis is cyclic during pupal diapause in Sarcophaga crassipalpis. These cycles are in phase with infradian MO₂ cycles, which have a periodicity of about 4 days at 25°C. Mean incorporation of [³⁵S]methionine by diapausing pupae was 5.4% during the 2 days of highest MO₂ but dropped to 1.7% during the 2 days of low MO₂. Diapausing pupae treated with a juvenile hormone analog prior to pupariation had a constant high MO₂ similar to peak values observed in untreated pupae, and such pupae consistently incorporated [³⁵S]methionine at a high rate (7.7%). [³⁵S]Methionine incorporation by nondiapausing pupae and pharate adults was eightfold higher than the peak rates observed during diapause. Autoradiography of in vivo labeled proteins indicated quantitative and qualitative changes in the synthesis of proteins by diapausing pupae during different phases of the MO₂ cycle. Brains from diapausing pupae labeled in vitro showed higher incorporation at the peak of the MO₂ cycle than at the nadir of the cycle, but no such differences were detected for integument, fat body, or fat body supernatant. Theses differences in tissue response indicate that control of protein synthesis during diapause is not cell autonomous, but is a function of the metabolism of the intact organism.     

Reversal of pupal diapause in Sarcophaga argyrostoma by temperature shifts after puparium formation

Puparia from Sarcophaga argyrostoma larvae reared under short days were collected daily within 24 hr of their formation and divided into two groups: one which remained at the larval rearing temperature, and one which was transferred to a different temperature. Such temperature shifts after puparium formation can modify the subsequent incidence of pupal diapause. Temperature step-ups decrease the percentage of diapause; temperature step-downs increase it. The degree of this effect increases with the size of the temperature step. The effectiveness of a temperature step-up declines with increasing time after puparium formation.The percentage of diapause finally achieved in any group is a function of both the number of inductive (short-day) photoperiods experienced during larval life and the magnitude and direction of the subsequent temperature step. Temperature step-ups can permit the expression of photoperiodic information which would otherwise be masked. A model is presented to account for these findings.     

Geographic variation in the incidence of pupal diapause in Asian and Oceanian species of the flesh fly Boettcherisca (Diptera: Sarcophagidae)

ABSTRACT. The incidence of pupal diapause was examined in nine species of the genus Boettcherisca Rohdendorf ( B.peregrina, B.javanica, B.nathani, B.septentrionalis, B. karnyi, B. koimani, B. timorensis, B. formosensis and B.invaria ) collected from various localities in East Asia and Oceanian islands.
Colonies of B.septenrionalis, B. nathani and B.peregrina obtained from temperate regions of Asia and those of B. formosensis and B.peregrina from the continental subtropics entered pupal diapause in response to photoperiod at 20C.
The incidence of pupal diapause showed a geographic gradient in B.peregrina. No photoperiodically induced diapause was observed in the other five species which are indigenous to the tropical or subtropical habitats.
Different species of Boettcherisca seem to have evolved their pupal diapause independently of one another as an ecophysiological mechanism which enabled those species to expand from the tropical to temperate region.     

Reduction in the critical number of short days for pupal diapause in Papilio machaon with precocious metamorphosis

Normal and allatectomized larvae of Papilio machaon were transferred from short (light:dark 10:14) to long (light:dark 16:8), or long to short days, on successive days of larval development to examine the critical number of short days necessary for diapause induction. The reciprocal transfer revealed that the normal larvae required 12 consecutive short days during the early instars to raise the incidence of pupal diapause to 50%. The critical number of short days was reduced to 9.5 days when the length of the larval period was cut due to precocious pupation induced by allatectomy. The reduction in the critical number of short days with precocious metamorphosis was less remarkable when the larvae were exposed to short days during the late instars. A possible summation mechanism of photoperiodic information for diapause induction in P. machaon is presented to explain the results obtained.     

Photoperiodic induction of pupal diapause in the flesh fly,Sarcophaga crassipalpis: embryonic sensitivity

Summary The last two days of embryonic development are crucial in programming pupal diapause in the flesh fly,Sarcophaga crassipalpis. Short daylength (greater than 10 1/2h of darkness) during this interval permits expression of diapause while long daylength during this brief sensitive stage eliminates the potential for diapause. Length of scotophase rather than photophase programs the diapause although three hours of light is needed to separate tandem dark periods. Early in the scotophase, photosensitivity is restricted to blue light (less than 540 nm). The scotophase can be divided into 4 phases according to the effect of light breaks on diapause expression. During Phase I (0–6 h after scotophase onset) embryos are highly sensitive to light interruption and diapause is effectively eliminated. A period of insensitivity to light, Phase II, extends from 6–hh after onset of scotophase. Light breaks at 10–11h coincide with the critical scotophase length and result in a partial reduction of diapause. In Phase IV, the scotophase reaction is complete and diapause competence is preserved even in the presence of light. Although light breaks result in elimination of diapause throughout Phase I, recovery time from a 1 h light break (length of darkness needed to counter the effect of a light break) differs dramatically depending upon when the light break is presented. Early in Phase I (0–3h) recovery from light interruption is rapid, while late in Phase I (4–6h), the effects of light are not readily reversible. The scotophase reaction thus appears to follow a step-wise progression rather than represent a simple linear response. We present a molecular model that could account for the dynamics of the scotophase reaction.     

Clock genes period and timeless are rhythmically expressed in brains of newly hatched, photosensitive larvae of the fly, Sarcophaga crassipalpis

While roles of the clock genes period (per) and timeless (tim) are relatively well understood in relation to circadian clocks, their potential roles in insect photoperiodism remain enigmatic. In this study, the expression of per and tim genes under two contrasting photoperiods is described in the central nervous system of photoperiodically sensitive, newly hatched first instar larvae of the flesh fly, Sarcophaga crassipalpis. Using qPCR, diel oscillations were observed in the mRNA levels of both genes under long-day (15 h light:9 h dark, promotes direct development) and short-day conditions (11 h light:13 h dark, induces pupal diapause). Peak per and tim mRNA oscillations were closely associated with the light/dark transition. The conspicuous difference between the two photoperiodic conditions was that the sharp increase in per and tim mRNA abundance occurred during the light phase under long days but during the dark phase under short days. The diel oscillations were, at least in part, driven by an endogenous component, as demonstrated by transferring larvae to continuous darkness. The cells displaying Tim- and Per-like immunoreactivities (Tim- and Per-LIRs) were localized using anti-Drosophila-Per and anti-Chymomyza-Tim antibodies. Per-LIR and Tim-LIR co-localized in three groups of cells in each brain hemisphere. Two other groups, one in the brain hemispheres and the other in the fused ventral nerve ganglion, expressed only the Per-LIR.     

Selection for late pupariation affects diapause incidence and duration in the flesh fly, Sarcophaga bullata

ABSTRACT. This artificial selection study with the flesh fly, Sarcophaga bullata Parker, tested the hypothesis that phenotypic variability in the length of the larval stage (under non-diapause conditions) is largely a consequence of genetic variability. Selection for late pupariation resulted in a line that pupariated significantly later and also developed more slowly during other stages of the life cycle. In a diapause-inducing environment, the selected line pupariated later, showed a higher incidence of pupal diapause, and remained in diapause longer than the unselected line. This is the first experimental evidence in S.bullata to show that diapause incidence and duration are related. The relationship between developmental rate and diapause traits may stem from the pleiotropic effects of genes associated with late pupariation, or from one or more genes associated with late pupariation being closely linked to genes that affect diapause.     

Photoperiodic sensitivity and diapause induction during ovarian,embryonic and larval development of the flesh fly,Sarcophaga argyrostoma

Sensitivity to the daily photoperiod, particularly with respect to pupal diapause induction, was studied during ovarian, embryonic, and larval development of the flesh flySarcophaga argyrostoma. Large flies were shown to have a greater number of primary follicles in their ovaries and to be capable of limited ovarian maturation in the absence of exogenous protein (autogeny). Such ovarian development occurred independently of photoperiod. However, long days experienced during embryogenesis caused more rapid development, and earlier larviposition, than short days. Short days during embryonic and subsequent larval development also induced pupal diapause, whereas long days led to continuous or non-diapause development of the pupae. Pupal diapause could not be induced by photoperiods during the vitellogenic phase of ovarian development. InSarcophaga argyrostoma, a maternal effect preventing pupal diapause among the progeny of files with a diapause history was not observed.