Radiation biology of a serious tropical pigeon pea pest, Maruca vitrata (Fabricius) (Lepidoptera: Crambidae) and potential of radiation mediated 'inherited (F1) sterility technique' for the pest suppression.

Purpose: The impact of gamma radiation on the reproductive biology of the spotted pod borer, Maruca vitrata (Fabr.) (Lepidoptera: Crambidae) was ascertained to explore the potential of the radio-genetic 'Inherited (F1) Sterility' technique (modified Sterile Insect technique) to control this serious pigeonpea pest in India.Materials and methods: Radio-biological investigations involved dose-response studies, at a range of 100-250 Gy, with respect to radiation induced adverse effects on reproductive behavior in substerilized parent (P1) moths, inheritance of sterility and associated metamorphic disruption in F1 progeny. The reproductive competence of P1 male moths and their F1 progeny was evaluated by ascertaining the survival, mating success, sperm transfer and amphimixis of gametes from irradiated male parents and their F1 progeny. Daily ovipositional and egg fertility profile were evaluated as crucial parameters for simulation modeling for this radio-genetic technique.Results: Radiation-induced check in insemination rate and sterility in P1 and F1 generation had a positive correlation with gamma dose. The metamorphic adverse effects in F1 progeny of substerilized P1 males were influenced by P1 irradiation. A higher dose of 200 Gy that resulted in 21.1% fertility in parent cross (P1♂x N♀) could form only 14.4% F1 adults that were all malformed. A gamma dose of 150 Gy (administered to P1 males) could be considered as a suitable dose for F1 sterility, that induced 57.4% control of reproduction in parent generation, followed by 72-85% control of reproduction in F1 progeny involved in three crosses -F1♂xN♀, N♂xF1♀, F1♂xF1♀. Daily fertility profile of the eggs laid indicated a marked reduction on 4th day onwards during the ovipositional span in P1 and F1 generation. High degree of mating competitiveness value (CV) was noticed for 150 Gy irradiated male P1 moths (0.78-0.93), and their F1 male progeny (0.70-0.89), released in different sex ratios in the field cages having untreated moths. Reduced relative damage to the pigeon pea plants by the released F1 progeny in the field cages was observed in comparison to control.Conclusion: The present study indicated the potential use of a dose of 150 Gy to apply the 'F1 sterility' technique for parabiological suppression of the pigeon pea pod borer. The present findings and reproductive performance of the irradiated moths in F2 generation along with other compatible biorational pest control tactics (that are in progress), might help in formulating an effective integrated pest management module, including the F1 sterility technique as an integral component.

Live fast, die young: Behavioural and physiological impacts of light pollution on a marine fish during larval recruitment.

Artificial light at night (ALAN) is a recently acknowledged form of anthropogenic pollution of growing concern to the biology and ecology of exposed organisms. Though ALAN can have detrimental effects on physiology and behaviour, we have little understanding of how marine organisms in coastal areas may be impacted. Here, we investigated the effects of ALAN exposure on coral reef fish larvae during the critical recruitment stage, encompassing settlement, metamorphosis, and post-settlement survival. We found that larvae avoided illuminated settlement habitats, however those living under ALAN conditions for 10 days post-settlement experienced changes in swimming behaviour and higher susceptibility to nocturnal predation. Although ALAN-exposed fish grew faster and heavier than control fish, they also experienced significantly higher mortality rates by the end of the experimental period. This is the first study on the ecological impacts of ALAN during the early life history of marine fish.

The effect of intensified illuminance and artificial light at night on fitness and susceptibility to abiotic and biotic stressors.

Changing light conditions due to human activities represents an important emerging environmental concern. Although changes to natural light conditions can be independently detrimental, in nature, organisms commonly face multiple stressors. To understand the consequences of altered light conditions, we exposed a model amphibian (wood frog; Lithobates sylvaticus) to a control and two anthropogenic light conditions: intensified daytime illuminance and artificial light at night - ALAN (intensified daytime illuminance + extended photoperiod). We measured (1) metrics of fitness (hatching success as well as survival to, size at, and time to metamorphosis) (2) susceptibility (time to death) to a commonly co-occurring anthropogenic stressor, road salt (NaCl) and (3) susceptibility (infection load) to a common parasite (trematode). We also explored behavioral (swimming activity) and physiological (baseline corticosterone (CORT) release rates) changes induced by these light conditions, which may mediate changes in the other measured parameters. We found that both intensified daytime illuminance and ALAN reduced hatching success. In contrast, for amphibians that successfully hatched, neither treatment affected amphibian survival or time to metamorphosis but individuals exposed to ALAN were larger at metamorphosis. The light treatments also had marginal effects; individuals in ALAN treatments were more susceptible to NaCl and trematodes. Finally, tadpoles exposed to ALAN moved significantly less than tadpoles in the control and intensified daytime illuminance treatments, while light had no effect on CORT release rate. Overall, changes in light conditions, in particular ALAN, significantly impacted an amphibian model in laboratory conditions. This work underscores the importance of considering not only the direct effects of light on fitness metrics but also the indirect effects of light with other abiotic and biotic stressors. Anthropogenic-induced changes to light conditions are expected to continue increasing over time so understanding the diverse consequences of shifting light conditions will be paramount to protecting wildlife populations.

Artificial light at night decreases metamorphic duration and juvenile growth in a widespread amphibian.

Artificial light at night (ALAN) affects over 20% of the earth's surface and is estimated to increase 6% per year. Most studies of ALAN have focused on a single mechanism or life stage. We tested for indirect and direct ALAN effects that occurred by altering American toads' (Anaxyrus americanus) ecological interactions or by altering toad development and growth, respectively. We conducted an experiment over two life stages using outdoor mesocosms and indoor terraria. In the first phase, the presence of ALAN reduced metamorphic duration and periphyton biomass. The effects of ALAN appeared to be mediated through direct effects on toad development, and we found no evidence for indirect effects of ALAN acting through altered ecological interactions or colonization. In the second phase, post-metamorphic toad growth was reduced by 15% in the ALAN treatment. Juvenile-stage ALAN also affected toad activity: in natural light, toads retreated into leaf litter at night whereas ALAN toads did not change behaviour. Carry-over effects of ALAN were also present; juvenile toads that had been exposed to larval ALAN exhibited marginally increased activity. In this time frame and system, our experiments suggested ALAN's effects act primarily through direct effects, rather than indirect effects, and can persist across life stages.

UVB Radiation Delays Tribolium castaneum Metamorphosis by Influencing Ecdysteroid Metabolism.

Ultraviolet B (UVB) radiation is an important environmental factor. It is generally known that UVB exhibits high genotoxicity due to causing DNA damage, potentially leading to skin carcinogenesis and aging in mammals. However, little is known about the effects of UVB on the development and metamorphosis of insects, which are the most abundant terrestrial animals. In the present study, we performed dose-response analyses of the effects UVB irradiation on Tribolium castaneum metamorphosis, assessed the function of the T. castaneum prothoracicotropic hormone gene (Trcptth), and analyzed ecdysteroid pathway gene expression profile and ecdysterone titers post-UVB irradiation. The results showed that UVB not only caused death of T. castaneum larvae, but also delayed larval-pupal metamorphosis and reduced the size and emergence rate of pupae. In addition, we verified the function of Trcptth, which is responsible for regulating metamorphosis. It was also found that the expression profiles of Trcptth as well as ecdysteroidogenesis and response genes were influenced by UVB radiation. Therefore, a disturbance pulse of ecdysteroid may be involved in delaying development under exposure to irradiation. To our knowledge, this is the first report indicating that UVB can influence the metamorphosis of insects. This study will contribute to a better understanding of the impact of UVB on signaling mechanisms in insect metamorphosis.

External control of the Drosophila melanogaster egg to imago development period by specific combinations of 3D low-frequency electric and magnetic fields.

We report that the duration of the egg-to-imago development period of the Drosophila melanogaster, and the imago longevity, are both controllable by combinations of external 3-dimensional (3D) low-frequency electric and magnetic fields (LFEMFs). Both these periods may be reduced or increased by applying an appropriate configuration of external 3D LFEMFs. We report that the longevity of D. melanogaster imagoes correlates with the duration of the egg-to-imago development period of the respective eggs. We infer that metabolic processes in both eggs and imago are either accelerated (resulting in reduced time periods) or slowed down (resulting in increased time periods). We propose that external 3D LFEMFs induce electric currents in live systems as well as mechanical vibrations on sub-cell, whole-cell and cell-group levels. These external fields induce media polarization due to ionic motion and orientation of electric dipoles that could moderate the observed effects. We found that the longevity of D. melanogaster imagoes is affected by action of 3D LFEMFs on the respective eggs in the embryonic development period (EDP). We interpret this effect as resulting from changes in the regulation mechanism of metabolic processes in D. melanogaster eggs, inherited by the resulting imagoes. We also tested separate effects of either 3D electric or 3D magnetic fields, which were significantly weaker.

Detrimental effects of electron beam irradiation on the cowpea bruchid Callosobruchus maculatus.

BACKGROUND: Electron beam (eBeam) irradiation technology is an environmentally friendly, chemical-free alternative for disinfesting insect pests of stored grains. The underlying hypothesis is that specific doses of eBeam will have defined detrimental effects on the different life stages. We evaluated the effects of eBeam exposure in a range of doses (0.03-0.12 kGy) on the development of the cowpea bruchid (Callosobruchus maculatus) at various stages of its life cycle. RESULTS: Differential radiosensitivity was detected during egg development. Early and intermediate stages of eggs never hatched after exposure to a dose of 0.03 kGy, whereas a substantial portion of black-headed (i.e. late) eggs survived irradiation even at 0.12 kGy. However, further development of the hatched larvae was inhibited. Although midgut protein digestion remained intact, irradiated larvae (0.06 kGy or higher) failed to develop into normal living adults; rather, they died as pupae or abnormally eclosed adults, suggesting a detrimental effect of eBeam on metamorphosis. Emerged irradiated pupae had shorter longevity and were unable to produce any eggs at 0.06 kGy or higher. At this dose range, eggs laid by irradiated adults were not viable. eBeam treatment shortened adult longevity in a dose-dependent manner. Reciprocal crosses indicated that females were more sensitive to eBeam exposure than their male counterparts. Dissection of the female reproductive system revealed that eBeam treatment prevented formation of oocytes. CONCLUSION: eBeam irradiation has very defined effects on cowpea bruchid development and reproduction. A dose of 0.06 kGy could successfully impede cowpea burchid population expansion. This information can be exploited for post-harvest insect control of stored grains.

Pro-apoptotic gene regulation and its activation by gamma-irradiation in the Caribbean fruit fly, Anastrepha suspensa.

Transcriptional activation of pro-apoptotic genes in response to cytotoxic stimuli is a conserved feature of the cell death pathway in metazoans. However, understanding the extent of this conservation in insects has been limited by the lack of known pro-apoptotic genes in non-drosophilids. Recently, we described the pro-apoptotic genes, Asrpr and Ashid, from the tephritid, Anastrepha suspensa, that now allow us to explore the conservation of pro-apoptotic gene regulation between a tephritid and drosophilids. In this study, we determined the developmental profiles of Asrpr and Ashid transcripts during embryogenesis and in embryos exposed to γ-irradiation. Transcript levels of both genes determined by qRT-PCR were low throughout embryogenesis, with strong Ashid expression occurring during early to mid-embryogenesis and Asrpr expression peaking in late embryogenesis. This correlated to acridine orange stained apoptotic cells first appearing at 17 h and increasing over time. However, when irradiated at 16 h post-oviposition embryos exhibited significant levels of apoptosis consistent with strong induction of Asrpr and Ashid transcript levels by γ-irradiation in young embryos <24 h post-oviposition. Furthermore, embryos irradiated <24 h post-oviposition failed to hatch, those irradiated between 24 and 32 h had increased hatching rates, but between 48 and 72 h irradiation had no effect on egg hatching. This indicates a transition of embryos from an irradiation-sensitive to irradiation-resistance stage between 24 and 48 h. Throughout post-embryonic development, the two pro-apoptotic genes share similar patterns of up-regulated gene expression, which correlate to ecdysone-induced developmental events, especially during metamorphosis. Together these results provide the first direct evidence for a conserved molecular mechanism of the programmed cell death pathway in insects.

Extreme tolerance and developmental buffering of UV-C induced DNA damage in embryos of the annual killifish Austrofundulus limnaeus.

Free-living aquatic embryos are often at risk of exposure to ultraviolet radiation (UV-R). Successful completion of embryonic development depends on efficient removal of DNA lesions, and thus many aquatic embryos have mechanisms to reverse DNA lesions induced by UV-R. However, little is known of how embryos that are able to enter embryonic dormancy may respond to UV-R exposure and subsequent DNA damage. Embryos of the annual killifish Austrofundulus limnaeus are unique among vertebrates because their normal embryonic development includes (1) a complete dispersion of embryonic blastomeres prior to formation of the definitive embryonic axis, and (2) entry into a state of metabolic depression and developmental arrest termed diapause. Here, we show that developing and diapausing embryos of A. limnaeus have exceptional tolerance of UV-C radiation and can successfully complete embryonic development after receiving substantial doses of UV-C, especially if allowed to recover in full-spectrum light. Recovery in full-spectrum light permits efficient removal of the most common type of DNA lesion induced by UV-R: cyclobutane pyrimidine dimers. Interestingly, whole-mount embryo TUNEL assays suggest that apoptosis may not be a major contributor to cell death in embryos UV-C irradiated during dispersion/reaggregation or diapause. We also observed embryo mortality to be significantly delayed by several weeks in diapausing embryos irradiated and allowed to recover in the dark. These atypical responses to UV-R induced DNA damage may be due to the unique annual killifish life history and provide insight into DNA damage repair and recognition mechanisms during embryonic dormancy.

Effects of radiation on inherited sterility in the European grapevine moth (Lobesia botrana).

BACKGROUND: The sterile insect technique (SIT) is an alternative, environmentally friendly method for controlling insect pests. In the Lepidoptera, a low dose of gamma irradiation causes inherited sterility (SIT-IS), leading to full sterility in females but only partial sterility in males, which successfully compete with wild males for mates. This study examined the effect of a low radiation dose (150 Gy) on the fitness parameters of male and female Lobesia botrana, a polyphagous and major pest of vineyards found in the Middle East, Europe and the Americas. RESULTS: Irradiation of the pupae did not affect their emergence rate, flight ability out of a cylinder, male response to sex pheromone in a field cage or male or female mating success. A major effect of irradiation was observed in the significantly reduced number of irradiated females' offspring reaching pupation, and as a consequence a limited number of F2 offspring. The effect of irradiation on male partial sterility (also called inherited sterility) was reflected in the male-biased sex ratio of F1 offspring of irradiated males, the reduced number of F1 offspring and the very low number of F2 descendants. CONCLUSION: This study demonstrates the feasibility of controlling L. botrana using SIT-IS. Adding this method to the arsenal of environmentally friendly tools to control this pest may assist in further reducing the use of insecticides on edible crops.

Diapause induction and termination in the small brown planthopper, Laodelphax striatellus (Hemiptera: Delphacidae).

The small brown planthopper, Laodelphax striatellus (Fallén) enters the photoperiodic induction of diapause as 3rd or 4th instar nymphs. The photoperiodic response curves in this planthopper showed a typical long-day response type with a critical daylength of approximately 11 h at 25 °C, 12 h at 22 and 20 °C and 12.5 h at 18 °C, and diapause induction was almost abrogated at 28 °C. The third stage was the most sensitive stage to photoperiod. The photoperiodic response curve at 20 °C showed a gradual decline in diapause incidence in ultra-long nights, and continuous darkness resulted in 100% development. The required number of days for a 50% response was distinctly different between the short- and long-night cycles, showing that the effect of one short night was equivalent to the effect of three long nights at 18 °C. The rearing day length of 12 h evoked a weaker intensity of diapause than did 10 and 11 h. The duration of diapause was significantly longer under the short daylength of 11 h than it was under the long daylength of 15 h. The optimal temperature for diapause termination was 26 and 28 °C. Chilling at 5 °C for different times did not shorten the duration of diapause but significantly lengthened it when chilling period was included. In autumn, 50% of the nymphs that hatched from late September to mid-October entered diapause in response to temperatures below 20 °C. The critical daylength in the field was between 12 h 10 min and 12 h 32 min (including twilight), which was nearly identical to the critical daylength of 12.5 h at 18 °C. In spring, overwintering nymphs began to emerge in early March-late March when the mean daily temperature rose to 10 °C or higher.

Anthropogenic noise causes body malformations and delays development in marine larvae.

Understanding the impact of noise on marine fauna at the population level requires knowledge about the vulnerability of different life-stages. Here we provide the first evidence that noise exposure during larval development produces body malformations in marine invertebrates. Scallop larvae exposed to playbacks of seismic pulses showed significant developmental delays and 46% developed body abnormalities. Similar effects were observed in all independent samples exposed to noise while no malformations were found in the control groups (4881 larvae examined). Malformations appeared in the D-veliger larval phase, perhaps due to the cumulative exposure attained by this stage or to a greater vulnerability of D-veliger to sound-mediated physiological or mechanical stress. Such strong impacts suggest that abnormalities and growth delays may also result from lower sound levels or discrete exposures during the D-stage, increasing the potential for routinely-occurring anthropogenic noise sources to affect recruitment of wild scallop larvae in natural stocks.

Population dependent effects of photoperiod on diapause related physiological traits in an invasive beetle (Leptinotarsa decemlineata).

Organisms undergoing latitudinal range expansion face a change in the photoperiod which can lead to a mismatch between the timing of seasonal changes in physiological and life history traits with seasonal environmental changes. This mismatch can lead to lowered survival, for example, due to unsynchronized diapause timing. Successful range expansion even in recent introductions requires that organisms which use the photoperiod for seasonal predictions should show interpopulational differences in photoperiodic responses at different latitudes, as the photoperiod is a function of latitude. We investigated among population differences in photoperiodic responses of life history and physiological traits linked to diapause in the invasive beetle Leptinotarsa decemlineata. Beetles from a northern marginal and a southern European population were reared under short day (12:12L:D) and long day (18:6L:D) photoperiods. Both populations reacted similarly to the short day photoperiod. Their abdominal total lipid content increased and water content decreased which suggests that the beetles prepared for diapause. This was also indicated by low mortality during diapause. In the long day photoperiod large interpopulational differences were found, the southern population ceased lipid accumulation after 5 days, while the northern population continued lipid accumulation as beetles in the short day photoperiod. This indicates that the northern population has a longer critical photoperiod than the southern one. Abdominal total lipid stores in 10 day old beetles were shown to be predominantly composed of neutral lipids (85%), most likely representing storage triacylglycerols. Fatty acid profiles of both the neutral lipids and the phospholipids showed large shifts during the first 10 day of adult life, predominantly in the fractions of 18:0, 18:1ω9, 18:2ω6 and 18:3ω3. Although the degree of unsaturation increased with age, it was not higher in diapausing than non-diapausing beetles. This indicates that this species does not increase diapause related cold tolerance via homeoviscous adaptation, and might have developed other means to cope with suboptimal temperatures, such as behavioral adaptations.

Effects of two stressors on amphibian larval development.

In parallel with a renewed interest in nuclear power and its possible environmental impacts, a new environmental radiation protection system calls for environmental indicators of radiological stress. However, because environmental stressors seldom occur alone, this study investigated the combined effects of an ecological stressor (larval density) and an anthropogenic stressor (ionizing radiation) on amphibians. Scaphiopus holbrookii tadpoles reared at different larval densities were exposed to four low irradiation dose rates (0.13, 2.4, 21, and 222 mGy d(-1)) from (137)Cs during the sensitive period prior to and throughout metamorphosis. Body size at metamorphosis and development rate served as fitness correlates related to population dynamics. Results showed that increased larval density decreased body size but did not affect development rate. Low dose rate radiation had no impact on either endpoint.

Preexposure to ultraviolet B radiation and 4-tert-octylphenol affects the response of Rana pipiens tadpoles to 3,5,3'-triiodothyronine.

Exposure to multiple environmental stressors is negatively impacting the health of amphibians worldwide. Increased exposure to ultraviolet B radiation (UVBR) and chemical pollutants may affect amphibian populations by disrupting metamorphosis; however, the actual mechanisms by which these stressors affect development remain unknown. Because amphibian metamorphosis is controlled by thyroid hormones (TH), changes in developmental rates by environmental stress suggest a disruption of the thyroid system. Tadpoles were chronically exposed to environmental levels of UVBR (average of 0.15 W/m2) and 4-tert-octylphenol (OP; 10 nM), alone and combined, prior to being challenged to exogenous TH triiodothyronine (T3; 5 or 50 nM). This experimental approach was taken to determine whether exposure to these stressors affects the ability of T3 to elicit specific molecular and morphological responses. Exposure to OP increased mRNA levels of thyroid receptors (TRs) alpha and beta, deiodinase type 2 (D2), and corticotropin releasing hormone in the brain and of D2 in the tail of tadpoles. 4-tert-octylphenol also enhanced T3-induced expression of D2 in the brain. The combination of UVBR and OP affected the expression of TR alpha in the brain and the responses of TR alpha and beta genes to T3 in the tail, demonstrating the importance of considering the effects of multiple stressors on amphibians. Tadpoles exposed to UVBR were developmentally delayed and exhibited slowed tail resorption and accelerated hindlimb development following exposure to T3. Together, these findings indicate that UVBR alters the rate of development and TH-dependent morphological changes at metamorphosis, and that exposure to UVBR and/or OP disrupts the expression of genes important for development and the biological action of T3 in peripheral tissues. Our group is the first to demonstrate that environmental levels of UVBR and/or OP can affect the thyroid system of amphibians.

Changes in the distribution of corticotropin-releasing factor (CRF)-like immunoreactivity in the larval bullfrog brain and the involvement of CRF in the cessation of food intake during metamorphosis.

In submammalian vertebrates, corticotropin-releasing factor (CRF) acts as an anorexigenic neuropeptide as well as a potent stimulator of corticotropin and thyrotropin release from the pituitary. As a step for demonstrating the involvement of CRF in the feeding regulation of anuran larvae, which are known to stop feeding toward the metamorphic climax, we studied firstly the changes in the distribution of CRF-like immunoreactivity (CRF-LI) in the brain of metamorphosing bullfrog larvae. Neuronal cell bodies showing CRF-LI were invariably present in the thalamic regions throughout larval development. Cells with CRF-LI were also found in the hypothalamus. The number of cells with CRF-LI in the hypothalamus, but not in the thalamus, showed a significant increase as metamorphosis progressed. Immunoreactive nerve fibers were observed mainly in the median eminence, and became abundant as metamorphosis proceeded. The number of cells showing CRF-LI in the hypothalamus as well as the density of immunoreactive fibers in the median eminence decreased at the end of metamorphosis. Secondly, we examined the effect of intracerebroventricular (ICV) injection of CRF on the food intake in the premetamorphic larvae. ICV injection of CRF at 10 pmol/g body weight (BW) induced a significant decrease of food intake during 15 min. The CRF-induced anorexigenic action was blocked by the treatment with a CRF receptor antagonist [alpha-helical CRF(9-41)] at 100 pmol/g BW. The results suggest the involvement of CRF in the accomplishment of metamorphosis through the pituitary and in the feeding restriction that occurs during the later stages of metamorphosis through the central nervous system.

Metamorphosis delay in Xenopus laevis (Daudin) tadpoles exposed to a 50 Hz weak magnetic field.

PURPOSE: The experiment was performed to prove that exposure to a relatively weak extremely low frequency (ELF) magnetic field retards tadpoles' development. METHODS: Two cohorts of Xenopus laevis laevis (Daudin) tadpoles were exposed during their immature period ( approximately 60 days) to a 50 Hz magnetic field of 63.9 < or = B < or = 76.4 microT rms (root mean square, average values) magnetic flux density in a solenoid. At the same time, as controls, two comparable cohorts were reared in two aquariums remote from the solenoid. Cohorts' degree of development was quantified by daily inspections of animal limbs and attributing them to a stage of the Nieuwkoop and Faber ( 1956 ) classification. The experiment was replicated three times. RESULTS: (a) Mean developmental rate of exposed cohorts was reduced with respect to controls (0.43 vs. 0.48 stages/day, p < 0.001) starting from early larval stages; (b) Exposure increased the mean metamorphosis period of tadpoles by 2.4 days compared with the controls (p < 0.001); (c) Maturation rates of exposed and control tadpoles changed during maturation period; and (d) Important mortality, malformations or teratogenic effects were not observed in exposed matured tadpoles. CONCLUSION: A long-term exposure of X. laevis tadpoles to a relatively weak 50 Hz magnetic field causes a sub-lethal effect that slows down their larval developmental rate and delays their metamorphosis.

Photoperiodism of diapause induction in Thyrassia penangae (Lepidoptera: Zygaenidae).

Thyrassia penangae enters winter diapause as a prepupa in a cocoon. Photoperiodism of diapause induction was systematically investigated in this moth. The photoperiodic response curves under 24-h light-dark cycles showed that this insect is a typical long-day species. The critical daylength was 13h 30min at 25 degrees C, 13h at 30 degrees C and 12h 20min at 28 degrees C. Transferring experiments from a short day (LD 12:12) to a long day (LD 15:9) or vice versa indicated that photoperiodic sensitivity mainly occurs during the larval period. In experiments using non-24-h light-dark cycles, when the length of photophase exceeded the critical daylength (13.5h), was diapause inhibited effectively, even when the length of scotophase exceeded the critical nightlength (10.5h). Only when a long scotophase was combined with a short photophase, diapause was induced effectively. This result suggests that daylength measurement is more important than nightlength measurement in T. penangae. Night interruption experiments under 24-h light-dark cycles exhibited two points of apparent light sensitivity, but the photosensitive position was highly influenced by temperature and the length of scotophase. Nanda-Hamner experiments failed to reveal the involvement of a circadian system in this photoperiodic time measurement. All light-dark cycles from LD 12:12 to LD 12:72 resulted in a short day response, and all cycles from LD 14:4 to LD 14:72 resulted in a long day response, suggesting that photoperiodic time measurement in this moth is performed by a day-interval timer or an hourglass-like clock.

Global increases in ultraviolet B radiation: potential impacts on amphibian development and metamorphosis.

Levels of ultraviolet B radiation (UVBR) reaching the Earth's surface have increased since the 1970s as a result of stratospheric ozone depletion caused by the emission of ozone-depleting substances (ODSs) such as chlorofluorocarbons. Despite international agreements to phase out harmful ODSs, these substances are persistent, and even under the most optimistic scenarios, stratospheric ozone levels will not return to pre-1980 levels for several decades. Furthermore, climate change may enhance chemical stratospheric ozone depletion. Global phenomena such as climate change, ozone depletion, and acidification of aquatic ecosystems interact to modify dissolved organic carbon levels in aquatic systems, thereby increasing the penetration of UVBR. Since amphibians inhabit both aquatic and terrestrial habitats and have unshelled eggs and permeable skin, they are vulnerable to changes in environmental conditions and habitat quality. Increased exposure of amphibians to UVBR can produce lethal and sublethal effects, especially in individuals that do not possess adequate defense mechanisms to protect themselves. In this article, we discuss worldwide increases in UVBR and the adverse effects of UVBR exposure on amphibians. Specifically, studies on the effects of UVBR on amphibian development and metamorphosis are summarized, and possible mechanisms of thyroid system disruption caused by UVBR exposure are considered.

Pigmented and nonpigmented ocelli in the brain vesicle of the ascidian larva.

The vertebrate-type opsin, Ci-opsin1, is localized in the outer segments of the photoreceptor cells of larvae of the ascidian Ciona intestinalis. The absorption spectrum of the photopigment reconstituted from Ci-opsin1 and 11-cis-retinal suggested that the photopigment is responsible for photic behavior of the larvae. The structure and function of Ci-opsin1-positive photoreceptor cells were examined by immunohistochemistry, confocal microscopy, electron microscopy, laser ablation, and behavioral analysis. Ciona larvae have three morphologically distinct groups of photoreceptor cells in the brain vesicle. Group I and group II photoreceptor cells are associated with the ocellus pigment cell on the right side of the brain vesicle. The outer segments of the group I photoreceptor cells are regularly arranged inside the small cavity encircled by the cup-shaped pigment cell. The outer segments of the group II photoreceptor cells are located outside the pigment cavity and exposed to the lumen of the brain vesicle. The outer segments of the group III photoreceptor cells are located near the otolith on the left ventral side of the brain vesicle. Thus, the brain vesicle of the ascidian larva has two ocelli: a 'conventional' pigmented ocellus containing the group I and group II photoreceptor cells and a novel nonpigmented ocellus solely consisting of the group III photoreceptor cells. Laser ablation experiments suggest that the pigmented ocellus is responsible for the photic swimming behavior. The nonpigmented ocellus might relate to later developmental or physiological events, such as metamorphosis, because Ci-opsin1 immunoreactivity appears in the late larval stage and becomes intense just before the onset of metamorphosis.