Divergent mechanisms for regulating growth and development after imaginal disc damage in the tobacco hornworm, Manduca sexta.

Holometabolous insects have been able to radiate to vast ecological niches as adults through the evolution of adult-specific structures such as wings, antennae and eyes. These structures arise from imaginal discs that show regenerative capacity when damaged. During imaginal disc regeneration, development has been shown to be delayed in the fruit fly Drosophila melanogaster, but how conserved the delay-inducing mechanisms are across holometabolous insects has not been assessed. The goal of this research was to develop the hornworm Manduca sexta as an alternative model organism to study such damage-induced mechanisms, with the advantage of a larger hemolymph volume enabling access to the hormonal responses to imaginal disc damage. Upon whole-body X-ray exposure, we noted that the imaginal discs were selectively damaged, as assessed by TUNEL and Acridine Orange stains. Moreover, development was delayed, predominantly at the pupal-to-adult transition, with a concomitant delay in the prepupal ecdysteroid peak. The delays to eclosion were dose dependent, with some ability for repair of damaged tissues. We noted a shift in critical weight, as assessed by the point at which starvation no longer impacted developmental timing, without a change in growth rate, which was uncoupled from juvenile hormone clearance in the body. The developmental profile was different from that of D. melanogaster, which suggests species differences may exist in the mechanisms delaying development.

Effect of gamma radiation as a post-harvest disinfestation treatment against life stages of the coffee berry borer, Hypothenemus hampei (Ferrari) (Coleoptera: Curculionidae).

Purpose: Gamma radiation is mainly used for disinfesting insect pests as an alternative for harmful fumigants. The specific dose of radiation is known to affect different developmental stages of insect pests. The study was conducted to determine the effective irradiation doses for inhibition of developmental stages and adult longevity of the coffee berry borer, Hypothenemus hampei (Ferrari). Materials and methods: Irradiation was carried with the following doses: five levels between 0.01 and 0.16 kGy for eggs, seven levels between 0.10 and 2.00 kGy for larva and prepupa, six levels between 0.10 and 1.60 kGy for pupa and ten levels between 0.10 and 3.20 kGy for adults. Results: Egg development was completely arrested at 0.160 kGy. A dose of 2.00 kGy caused 100% mortality in the first and second instar larva and 98.99% mortality in prepupa. The dose of 1.60 kGy prevented adult eclosion from the irradiated pupa. The adult mortality was 100% at 3.20 kGy. Conclusion: A dose of 3.20 kGy could successfully provide complete security from all developmental stages of H. hampei and prevent yield loss in green coffee as well as the spread of the pest.

Concomitant changes in radiation resistance and trehalose levels during life stages of Drosophila melanogaster suggest radio-protective function of trehalose.

PURPOSE: During development, various life stages of Drosophila melanogaster (D. melanogaster) show different levels of resistance to gamma irradiation, with the early pupal stage being the most radiation sensitive. This provides us an opportunity to explore the biochemical basis of such variations. The present study was carried out to understand the mechanisms underlying radiation resistance during life stages of D. melanogaster. MATERIALS AND METHODS: Homogenates from all the life stages of D. melanogaster were prepared at stipulated age. These homogenates were used for the determination of (1) enzymatic antioxidants: superoxide dismutase (SOD), catalase, D. melanogaster glutathione peroxidase (DmGPx), and glutathione S-transferase (GST); (2) reducing non-enzymatic antioxidants: total antioxidant capacity (TAC), reduced glutathione (GSH) and non-reducing non-enzymatic antioxidant trehalose; and (3) levels of protein carbonyl (PC) content. Age-dependent changes in radiation resistance and associated biochemical changes were also studied in young (2 d) and old (20 and 30 d) flies. RESULTS: TAC and GSH were found high in the early pupal stage, whereas catalase and DmGPx were found to increase in the early pupal stage. The non-feeding third instar (NFTI) larvae were found to have high levels of SOD and GST, besides NFTI larvae showed high levels of trehalose. A remarkable decrease was observed in radiation resistance and trehalose levels during the early pupal stage. The PC level was the highest during early pupal stage and was the lowest in NFTI larvae. Older flies showed high level of PC compared with young flies. CONCLUSION: In vitro increments in trehalose concentration correspond to reduced formation of PCs, suggesting a protective role of trehalose against free radicals. A strong correlation between levels of trehalose and PC formation suggests amelioration of proteome damage due to ionizing radiation (IR). Stages with high trehalose levels showed protected proteome and high radiation resistance, suggesting a significant role for this disaccharide in radiation resistance.

Developmental experience with anthropogenic noise hinders adult mate location in an acoustically signalling invertebrate.

Phenotypic plasticity facilitates survival and reproduction in rapidly changing and novel environments. Traffic noise spectrally overlaps with (i.e. masks) the sounds used by many acoustically signalling organisms to locate and secure mates. To determine if pre-reproductive exposure to noise improves adult performance in noisy environments, we reared field crickets (Teleogryllus oceanicus) in one of three noise environments: masking traffic noise, traffic noise from which frequencies that spectrally overlap with the crickets' song were removed (non-masking), or silence. At reproductive maturity, we tested female mate location ability under one of the same three acoustic conditions. We found that exposure to noise during rearing hindered female location of mates, regardless of the acoustic environment at testing. Females reared in masking noise took 80% longer than females reared in silence to locate a simulated singing male who was less than 1 m away. Impaired mate location ability can be added to a growing list of fitness costs associated with anthropogenic noise, alongside reductions in pairing success, nesting success and offspring survival.

Evaluation of methylene blue as photosensitizer in promastigotes of Leishmania major and Leishmania braziliensis.

The cutaneous leishmaniasis is caused by the protozoan of the genus Leishmania. It is considered by WHO as a public health issue and a neglected disease, which affects rural workers and it is also a risk to travelers in endemic areas. The conventional treatment is toxic and leads to severe side effects. The photodynamic therapy has been studied as an alternative treatment to cutaneous leishmaniasis. This study aimed to evaluate the methylene blue internalization and the impact of the PDT in the viability and morphology of Leishmania major and Leishmania braziliensis promastigote in culture medium. The fluorescence microscopy was used to determine the MB localization. To evaluate the mitochondrial activity (MTT), viability (Trypan blue test) and the morphological alterations both species were incubated with the MB in concentrations starting in 500µg/ml, in serial dilution, until 7,8µg/ml. The fluorescence microscopy demonstrated that the MB is internalized by both species after one hour of incubation. The MB presented low toxicity at the dark and the PDT was capable of decreasing the viability in more than 70% in the higher concentrations tested. The PDT also triggered significant morphological alterations in the Leishmania promastigotes. The results presented in this study are an indicative that the MB is a photosensitizer with promising potential to clinical application, besides its low cost.

Effect of ionising (gamma) radiation on female Anopheles arabiensis.

Background: In a mosquito sterile insect technique programme the ideal scenario is to release male mosquitoes only. However, because there are currently no sex separation strategies which guarantee total female elimination, this study investigated the effect of irradiation on physiological and reproductive fitness of females of an Anopheles arabiensis genetic sexing strain. Methods: Female pupae were irradiated at 70 Gy and the effects of irradiation on adult emergence, longevity, blood-feeding capability, mating ability, fecundity and fertility were assessed. Results and conclusion: Irradiation reduced adult emergence and fecundity but did not affect adult survivorship, mating and blood feeding ability, which suggests that irradiated female mosquitoes can transmit disease pathogens.

Ultraviolet B radiation induces impaired lifecycle traits and modulates expression of cytochrome P450 (CYP) genes in the copepod Tigriopus japonicus.

To evaluate the effects of ultraviolet B (UV-B) radiation at the developmental, reproductive, and molecular levels in aquatic invertebrates, we measured UV-B-induced acute toxicity, impairments in developmental and reproductive traits, and UV-B interaction with the entire family of cytochrome P450 (CYP) genes in the intertidal benthic copepod Tigriopus japonicus. We found a significant, dose-dependent reduction (P<0.05) in the survival of T. japonicus that began as a developmental delay and decreased fecundity. The 48h LD10 and LD50 were 1.35 and 1.84kJ/m2, and the CYP inhibitor (PBO) elevated mortality, confirming the involvement of CYP genes in UV-B induced toxicity. Low-dose UV-B (1.5kJ/m2) induced developmental delays, and higher doses (6-18kJ/m2) caused reproductive impairments in ovigerous females. The significant up-regulation of CYP genes belonging to clans 2/3/MT/4/20 in T. japonicus exposed to UV-B (12kJ/m2) confirmed molecular interaction between UV-B and CYP genes. Moreover, orphan CYPs, such as CYP20A1, provide good insight on the deorphanization of invertebrate CYPs. Overall, these results demonstrate the involvement of UV-B radiation in the expression of all the CYP genes in T. japonicus and their susceptibility to UV-B radiation. This will provide a better understanding of the mechanistic effects of UV-B in copepods through the predicted AhR-mediated up-regulation of CYP genes.

Gamma radiation tolerance in different life stages of the fruit fly Drosophila melanogaster.

PURPOSE: Insects are known to have higher levels of radiation tolerance than mammals. The fruit fly Drosophila provides opportunities for genetic analysis of radiation tolerance in insects. A knowledge of stage-specific sensitivity is required to understand the mechanisms and test the existing hypothesis of insect radiation tolerance. MATERIALS AND METHODS: Drosophila melanogaster were irradiated using gamma rays at different life stages. Irradiation doses were chosen to start from 100-2200 Gy with increments of 100 Gy, with a dose rate of 12.5 and 25 Gy/min. The threshold of mortality, LD50 and LD100 1 h post-irradiation was recorded for larvae and adults and 24 h post-irradiation for eggs and after 2-3 days for early and late pupae. Total antioxidant capacity for all the life stages was measured using the phosphomolybdenum method. RESULTS: Twenty-four hours post-irradiation, 100% mortality was recorded for eggs at 1000 Gy. One hour post irradiation 100% mortality was recorded at 1300 Gy for first instar larvae, 1700 Gy for second instar larvae, 1900 Gy for feeding third instar larvae and 2200 Gy for non-feeding third instar larvae. Post-irradiation complete failure of emergence (100% mortality) was observed at 130 Gy for early pupae and 1500 Gy for late pupae; 100% mortality was observed at 1500 Gy for adults. The values of LD50 were recorded as 452 Gy for eggs, 1049 Gy for first instar larvae, 1350 Gy for second instar larvae, 1265 Gy for feeding third instar larvae, 1590 Gy for non-feeding third instar larvae, 50 Gy for early pupae, 969 Gy for late pupae, 1228 Gy for adult males and 1250 Gy for adult females. CONCLUSIONS: Early pupae were found to be prone to radiation, whereas the non-feeding third instar larvae were most resistant among all stages. The chromosome number being constant and total antioxidant capacity being nearly constant in all stages, we suggest that high rate of cell division during early pupae makes this stage sensitive to radiation.

X-ray radiation and developmental inhibition of Drosophila suzukii (Matsumura) (Diptera: Drosophilidae).

PURPOSE: Different doses of X-ray radiation were tested to assess the developmental inhibition effects on different stages of Drosophila suzukii, spotted wing drosophila (SWD). Efficacy of a potential quarantine treatment dose was evaluated for its practicality by a small scale-up validation test at a commercial facility. MATERIALS AND METHODS: X-ray treatments at different doses of 50, 100, 200, and 300 Gy were carried out with eggs, larvae, pupae and adults of SWD. The trial at the commercial facility was performed with pupae at 150 Gy. RESULTS: X-ray radiation inhibited development of all stages of SWD, and the estimated dose to cause 99% mortality or to prevent emergence (ED99) are reported here. Irradiation to eggs inhibited hatching, pupariation and adult emergence at 1962, 649 and 31 Gy, respectively. The inhibition of irradiated larvae to adult emergence was 66 Gy. Irradiation to pupae could not inhibit adult emergence completely even at 300 Gy. However, irradiation at 100 Gy and above induced complete adult sterility. Irradiation to pupae inhibited hatching of F1 eggs at 73 Gy, while for adults, total inhibition of F1 egg hatching was observed at 822 Gy. In the trial at the commercial facility, radiation at 150 Gy to pupae induced complete adult sterility in all combinations of cross-mating between treated or untreated males and females. CONCLUSION: This study suggests that X-ray radiation can be recommended as an alternative to methyl bromide as phytosanitary treatment for quarantine purpose.

Model biases in rice phenology under warmer climates.

Climate-induced crop yields model projections are constrained by the accuracy of the phenology simulation in crop models. Here, we use phenology observations from 775 trials with 19 rice cultivars in 5 Asian countries to compare the performance of four rice phenology models (growing-degree-day (GDD), exponential, beta and bilinear models) when applied to warmer climates. For a given cultivar, the difference in growing season temperature (GST) varied between 2.2 and 8.2 °C in different trials, which allowed us to calibrate the models for lower GST and validate under higher GST, with three calibration experiments. The results show that in warmer climates the bilinear and beta phenology models resulted in gradually increasing bias for phenology predication and double yield bias per percent increase in phenology simulation bias, while the GDD and exponential models maintained a comparatively constant bias. The phenology biases were primarily attributed to varying phenological patterns to temperature in models, rather than on the size of the calibration dataset. Additionally, results suggest that model simulations based on multiple cultivars provide better predictability than using one cultivar. Therefore, to accurately capture climate change impacts on rice phenology, we recommend simulations based on multiple cultivars using the GDD and exponential phenology models.

The effect of γ-radiation on resting eggs and life cycle of cladoceran Moina macrocopa.

We investigated the effects of γ-irradiation on the survival of resting eggs of the cladoceran Moina macrocopa and on the parameters of the life cycle of neonates hatched from the irradiated eggs. It was shown that γ-irradiation in a wide range of doses (from the background level to 100 Gy) had no effect on survival of eggs and mortality of neonates hatched from the irradiated eggs. However, exceeding the absorbed dose of 40 Gy sharply decreased the reproductive potential of the neonates hatched from irradiated eggs.

Irradiation of rainbow trout at early life stages results in trans-generational effects including the induction of a bystander effect in non-irradiated fish.

The bystander effect, a non-targeted effect (NTE) of radiation, which describes the response by non-irradiated organisms to signals emitted by irradiated organisms, has been documented in a number of fish species. However transgenerational effects of radiation (including NTE) have yet to be studied in fish. Therefore rainbow trout, which were irradiated as eggs at 48h after fertilisation, eyed eggs, yolk sac larvae or first feeders, were bred to generate a F1 generation and these F1 fish were bred to generate a F2 generation. F1 and F2 fish were swam with non-irradiated bystander fish. Media from explants of F1 eyed eggs, F1 one year old fish gill and F1 two year old fish gill and spleen samples, and F2 two year old gill and spleen samples, as well as from bystander eggs/fish, was used to treat a reporter cell line, which was then assayed for changes in cellular survival/growth. The results were complex and dependent on irradiation history, age (in the case of the F1 generation), and were tissue specific. For example, irradiation of one parent often resulted in effects not seen with irradiation of both parents. This suggests that, unlike mammals, in certain circumstances maternal and paternal irradiation may be equally important. This study also showed that trout can induce a bystander effect 2 generations after irradiation, which further emphasises the importance of the bystander effect in aquatic radiobiology. Given the complex community structure in aquatic ecosystems, these results may have significant implications for environmental radiological protection.

Exposure to acute levels of waterborne aluminium modifies the legacy of early life stage irradiation, including the communication of radiation-induced bystander signals, in adult rainbow trout.

PURPOSE: To determine if the legacy of early life stage irradiation seen in rainbow trout is modified in adult fish by acute exposure to waterborne aluminium (Al). METHODS: Two-year-old trout which had been irradiated as either eggs 48 h after fertilization, eyed eggs, yolk sac larvae or as first feeders, were exposed to 100 or 200 µg l(-1) Al. These fish were then paired with untreated fish. Gill and skin samples from both the irradiated and Al-exposed, and the untreated bystander fish, were then assayed for the production of toxic or pro-death signals, using the HPV-G reporter cell line. RESULTS: Depending on the life stage, irradiated and the tissue assayed acute Al exposure modified both the radiation legacy, and the radiation-induced bystander effect in untreated fish, either by reducing reporter cell survival or increasing reporter cell growth. CONCLUSIONS: The effects of early irradiation and adult Al exposure were complex but clearly demonstrated that both the direct radiation effects and the communication of a radiation-induced bystander effect can be modified by a second environmental stressor.

Retinal Development and Ommin Pigment in the Cranchiid Squid Teuthowenia pellucida (Cephalopoda: Oegopsida).

The cranchiid Teuthowenia pellucida, like many deep-sea squid species, possesses large eyes that maximise light sensitivity in a nearly aphotic environment. To assess ontogenetic changes in the visual system, we conducted morphometric and histological analyses of the eyes using specimens from New Zealand collections. While the ratio between eye diameter and mantle length maintained a linear relationship throughout development, histological sections of the retina revealed that the outer photoreceptor layer became proportionally longer as the animal aged, coincident with a habitat shift into deeper, darker ocean strata. Other retinal layers maintained the same absolute thickness as was observed in paralarvae. Granules of the pigment ommin, normally located in the screening layer positioned at the base of the photoreceptors, were also observed at the outer end of the photoreceptor segments throughout the retina in young and mid-sized specimens. Early developmental stages of this species, dwelling in shallow waters, may therefore rely on migratory ommin to help shield photoreceptors from excess light and prevent over-stimulation. The oldest, deeper-dwelling specimens of T. pellucida examined had longer photoreceptors, and little or no migrated ommin was observed; we suggest therefore that short-term adaptive mechanisms for bright light conditions may be used primarily during epipelagic, early life stages in this species.

Multi-Level Effects of Low Dose Rate Ionizing Radiation on Southern Toad, Anaxyrus [Bufo] terrestris.

Despite their potential vulnerability to contaminants from exposure at multiple life stages, amphibians are one of the least studied groups of vertebrates in ecotoxicology, and research on radiation effects in amphibians is scarce. We used multiple endpoints to assess the radiosensitivity of the southern toad (Anaxyrus [Bufo] terrestris) during its pre-terrestrial stages of development -embryonic, larval, and metamorphic. Toads were exposed, from several hours after oviposition through metamorphosis (up to 77 days later), to four low dose rates of 137Cs at 0.13, 2.4, 21, and 222 mGy d-1, resulting in total doses up to 15.8 Gy. Radiation treatments did not affect hatching success of embryos, larval survival, or the length of the larval period. The individual family variation in hatching success of embryos was larger than the radiation response. In contrast, newly metamorphosed individuals from the higher dose-rate treatments had higher mass and mass/length body indices, a measure which may relate to higher post-metamorphic survival. The increased mass and index at higher dose rates may indicate that the chronic, low dose rate radiation exposures triggered secondary responses. Additionally, the increases in growth were linked to a decrease in DNA damage (as measured by the Comet Assay) in red blood cells at a dose rate of 21 mGy d-1 and a total dose of 1.1 Gy. In conclusion, the complex effects of low dose rates of ionizing radiation may trigger growth and cellular repair mechanisms in amphibian larvae.

Gamma rays induce DNA damage and oxidative stress associated with impaired growth and reproduction in the copepod Tigriopus japonicus.

Nuclear radioisotope accidents are potentially ecologically devastating due to their impact on marine organisms. To examine the effects of exposure of a marine organism to radioisotopes, we irradiated the intertidal copepod Tigriopus japonicus with several doses of gamma radiation and analyzed the effects on mortality, fecundity, and molting by assessing antioxidant enzyme activities and gene expression patterns. No mortality was observed at 96h, even in response to exposure to a high dose (800Gy) of radiation, but mortality rate was significantly increased 120h (5 days) after exposure to 600 or 800Gy gamma ray radiation. We observed a dose-dependent reduction in fecundity of ovigerous females; even the group irradiated with 50Gy showed a significant reduction in fecundity, suggesting that gamma rays are likely to have a population level effect. In addition, we observed growth retardation, particularly at the nauplius stage, in individuals after gamma irradiation. In fact, nauplii irradiated with more than 200Gy, though able to molt to copepodite stage 1, did not develop into adults. Upon gamma radiation, T. japonicus showed a dose-dependent increase in reactive oxygen species (ROS) levels, the activities of several antioxidant enzymes, and expression of double-stranded DNA break damage genes (e.g. DNA-PK, Ku70, Ku80). At a low level (sub-lethal dose) of gamma irradiation, we found dose-dependent upregulation of p53, implying cellular damage in T. japonicus in response to sub-lethal doses of gamma irradiation, suggesting that T. japonicus is not susceptible to sub-lethal doses of gamma irradiation. Additionally, antioxidant genes, phase II enzyme (e.g. GSTs), and cellular chaperone genes (e.g. Hsps) that are involved in cellular defense mechanisms also showed the same expression patterns for sublethal doses of gamma irradiation (50-200Gy). These findings indicate that sublethal doses of gamma radiation can induce oxidative stress-mediated DNA damage and increase the expression of antioxidant enzymes and proteins with chaperone-related functions, thereby significantly affecting life history parameters such as fecundity and molting in the copepod T. japonicus.

Gamma radiation induces growth retardation, impaired egg production, and oxidative stress in the marine copepod Paracyclopina nana.

Accidental nuclear radioisotope release into the ocean from nuclear power plants is of concern due to ecological and health risks. In this study, we used the marine copepod Paracyclopina nana to examine the effects of radioisotopes on marine organisms upon gamma radiation, and to measure the effects on growth and fecundity, which affect population and community structure. Upon gamma radiation, mortality (LD50 - 96 h=172 Gy) in P. nana was significantly increased in a dose-dependent manner in ovigerous P. nana females. For developmental impairment of gamma-irradiated nauplii, we observed growth retardation; in over 30 Gy-irradiated groups, offspring did not grow to adults. Particularly, over 50 Gy-irradiated ovigerous P. nana females did not have normal bilateral egg sacs, and their offspring did not develop normally to adulthood. Additionally, at over 30 Gy, we found dose-dependent increases in oxidative levels with elevated antioxidant enzyme activities and DNA repair activities. These findings indicate that gamma radiation can induce oxidative stress and DNA damage with growth retardation and impaired reproduction.

Involvement of circadian oscillation(s) in the photoperiodic time measurement and the induction of reproductive diapause in a northern Drosophila species.

An ability to predict forthcoming changes in environmental conditions and get prepared for them in advance is crucial for the survival and reproduction of organisms living in a seasonally changing environment. We have studied the possible involvement of circadian oscillator(s) in the photoperiodic timer controlling seasonal responses by tracing Drosophila montana females' diapause induction in constant darkness and in a classical Nanda-Hamner experiment. Nearly all females developed ovaries in continuous darkness, which shows the direct development to be their default developmental pathway in the absence of photoperiods. In Nanda-Hamner experiment the females' diapause incidence was close to zero in light:dark cycle 12:4 (photoperiod 16 h) and increased to nearly 100% in 12:8 and 12:12 (photoperiods 20 and 24 h). In longer photoperiods (28-72 h) the females' diapause percentages decreased gradually along with an increase in the length of the dark period, showing no peaks of high diapause incidence in the multiples of 24h. These findings suggest that the photoperiodic timer of D. montana is based on heavily damping circadian oscillator(s) or that it lacks strong oscillators. Damping of the photoperiodic timer under prolonged nights and constant darkness fits well with our earlier finding that these flies lose their locomotor activity rhythm in constant darkness, and suggests that the mechanisms underlying females' photoperiodic diapause response and their free-running locomotor activity rhythm may be partly based on same oscillators.

Effects of salinity and ultraviolet radiation on the bioaccumulation of mycosporine-like amino acids in Artemia from Lake Urmia (Iran).

We investigated the effects of salinity and artificial UV radiation on the accumulation of mycosporine-like amino acids (MAAs) in sexual and parthenogenetic Artemia from Lake Urmia. The nauplii hatched from the cysts were cultured until adulthood under two salinities (150 and 250 g L(-1) ) and two light treatments (PAR and PAR+UVR) in the laboratory. Finally, the Artemia were analyzed for their concentration of MAAs. In most of the cases, the higher salinity level applied was found to increase the MAA concentrations in both Artemia populations significantly. The acquisition efficiency of MAAs in both Artemia populations increased under exposure to UVR-supplemented photosynthetically active radiation (PAR) compared to those raised under PAR, except for Porphyra-334. It was observed that combination of UV radiation and elevated salinity significantly increased the bioaccumulation of MAAs. Thus, the presence of these compounds in these populations of Artemia may increase their adaptability for living in high-UV and high-salinity conditions prevailing in Lake Urmia. Higher concentrations of MAAs in the parthenogenetic population of Artemia could be probably attributed to its mono sex nature and higher adaptation capacities to extreme environmental conditions.

Stable photosymbiotic relationship under CO2-induced acidification in the acoel worm Symsagittifera roscoffensis.

As a consequence of anthropogenic CO2 emissions, oceans are becoming more acidic, a phenomenon known as ocean acidification. Many marine species predicted to be sensitive to this stressor are photosymbiotic, including corals and foraminifera. However, the direct impact of ocean acidification on the relationship between the photosynthetic and nonphotosynthetic organism remains unclear and is complicated by other physiological processes known to be sensitive to ocean acidification (e.g. calcification and feeding). We have studied the impact of extreme pH decrease/pCO2 increase on the complete life cycle of the photosymbiotic, non-calcifying and pure autotrophic acoel worm, Symsagittifera roscoffensis. Our results show that this species is resistant to high pCO2 with no negative or even positive effects on fitness (survival, growth, fertility) and/or photosymbiotic relationship till pCO2 up to 54 K µatm. Some sub-lethal bleaching is only observed at pCO2 up to 270 K µatm when seawater is saturated by CO2. This indicates that photosymbiosis can be resistant to high pCO2. If such a finding would be confirmed in other photosymbiotic species, we could then hypothesize that negative impact of high pCO2 observed on other photosymbiotic species such as corals and foraminifera could occur through indirect impacts at other levels (calcification, feeding).