Metamorphosis Rate Research Articles

Stimulation of inactivated Metschnikowia bicuspidata promotes the growth, and immunity of Eriocheir sinensis larvae

The Chinese mitten crab (Eriocheir sinensis) is an economically essential crustacean specie in China. The outbreak of disease caused by Metschnikowia bicuspidata has resulted in high mortality and huge economic loss in the E. sinensis aquaculture industry. Immune priming can protect invertebrates against pathogens in the second exposure, which has been reported in adult E. sinensis and provides a novel approach for disease control. This study evaluated the effects of treatment with formalin-killed M. bicuspidata on the growth, development, and immunity of E. sinensis embryos and larvae. Stimulation of E. sinensis embryos with inactivated M. bicuspidata (Mb group) did not significantly affect the mass and size of embryos. While the carapace width, abdominal length, and tail length of larvae in the Mb group were significantly longer than those of control group in most stages. At 120 h and 144 h after embryo hatching, the metamorphosis rate of larvae in the Mb group was 24.59-fold (p < 0.05) and 16.07-fold (p < 0.001) higher than that in the control group. Moreover, after the larvae suffered alive M. bicuspidata challenge, the mortality in the Mb group significantly decreased (0.48-fold, p < 0.05) compared with that in the control group, and the mRNA expression levels of genes related to immunity (MAPK, Toll2, and STAT), growth (ATGL, Chi, Chymotrypsin, and mTOR), and development (Ubx) were significantly increased in the Mb group. These results suggested that stimulation of E. sinensis embryos with inactivated M. bicuspidata significantly promoted the growth and development of larvae and endowed them with stronger resistant capacity to M. bicuspidate. This finding may provide a novel and safe approach for preventing disease and improving larvae quality in E. sinensis aquaculture.

The Impact of Polychlorinated Biphenyls on the Development of Zebrafish (Danio rerio).

Polychlorinated biphenyls (PCBs) are a group of 209 highly stable molecules that were used extensively in industry. Although their commercial use ceased in 1979, they are still present in many aquatic ecosystems due to improper disposal, oceanic currents, atmospheric deposition, and hydrophobic nature. PCBs pose a significant and ongoing threat to the development and sustainability of aquatic organisms. In areas with PCB exposure high mortality rates of organisms inhabiting them are still seen today, posing a significant threat to local species. Zebrafish were exposed to a standard PCB mixture (Aroclor 1254) for the first 5 days post fertilization, as there is a gap in knowledge during this important developmental period for fish (i.e., organization of the body). This PCB mixture was formally available commercially and has a high prevalence in PCB-contaminated sites. We tested for the effects of PCB dosage (control (embryo water only; 0 mg/L), methanol (solvent control; 0 mg/L); PCB 1 (0.125 mg/L), PCB 2 (0.25 mg/L), PCB 3 (0.35 mg/L), and PCB 4 (0.40 mg/L)) on zebrafish survival, rate of metamorphosis, feeding efficiency, and growth. We found significant, dose-dependent effects of PCB exposure on mortality, feeding efficiency, and growth, but no clear effect of PCBs on the rate of zebrafish metamorphosis. We identified a concentration in which there were no observable effects (NOEC), PCB concentration above the NOEC had a significant impact on life-critical processes. This can further inform local management decisions in environments experiencing PCB contamination.

Effect of diet on larval settlement, growth, and spat survival of the oyster Crassostrea gigas (Thunberg, 1793)

This study aimed to assess the impact of microalgal concentrations in diets on the settlement and metamorphosis stages of pediveliger larvae and spat of Crassostrea gigas oysters. Diets containing microalgal concentrations of 8, 12, and 16×104 cells mL-1 were administered for seven days during the larval settlement phase of pediveliger larvae. In the metamorphosis and postlarval cultivation phases, diets with microalgal concentrations of 8, 16, 24, and 32×104 cells mL-1 and a control group without food were tested for 14 and 21 days, respectively. Growth, yield, and survival were assessed every seven days. The diet comprised 30% Isochrysis galbana and 70% Chaetoceros muelleri microalgae. In the metamorphosis phase, the results revealed no significant differences in larval metamorphosis rate and survival across the tested diets. The concentrations exhibited similar survival in the spat with an initial average shell height of 0.657 ± 0.05 mm, with a significant difference only in growth. In the spat with an initial average shell height of 0.830 ± 0.12 mm, no differences in survival were observed among the tested concentrations. We concluded that diets of 12 and 16×104 cells mL-1 provide high rates of larval metamorphosis and spat yield during the larval settlement and metamorphosis phases. During the spat cultivation phases, diets of 32 and 24×104 cells mL-1 could optimize the cultivation time and yield of C. gigas spat in the laboratory. However, when considering survival alone, no advantage was found in providing a diet with a microalgal concentration above 8×104 cells mL-1 across all C. gigas oyster cultivation phases.

Ontogenetic transfer of microplastics in natural populations of malaria mosquitoes in Western Siberia

AbstractThe uptake, accumulation, and ontogenetic transfer of microplastics (MPs) in bloodsucking mosquitoes of the genus Anopheles, vectors of helminth and protozoa parasites in humans and animals, were studied under laboratory conditions. In the experiment, 2‐μm‐diameter fluorescent polystyrene spheres were counted in mosquitoes of all stages, from larvae to adults. Larvae from a natural population readily ingested MPs with food, accumulating on average 3.9 × 106 particles per larva within 3 days. The concentration of MPs decreased significantly in mosquitoes during their transition from stage to stage. The average number of detected MPs attained 110 particles per pupa and 3.0 particles per adult. MP uptake by mosquitoes did not affect their survival, whereas the rate of metamorphosis in MP‐consuming mosquitoes was slightly higher. Our data confirmed that MPs can be transferred from feeding larvae to non‐feeding pupae and adult flying Anopheles mosquitoes from natural populations in aquatic ecosystems.

Larval feeding activity and use of embryonic resources determine juvenile performance of the common prawn Palaemonserratus

Phenotypic links are the potential for “carryover” of effects of experience during one life history stage into performance and selection at subsequent stages. They reflect plastic responses to the environment experienced during an early phase on the phenotype of subsequent phases. We are studying these effects by following individuals of the shrimp Palaemon serratus from the embryonic (eggs carried by females) through the larval phase (pelagic) to the juvenile phase (benthic). In experiment 1, we investigated the effects of larval prey concentration (10, 4 and 2 Artemia/mL) and larval incubation temperature (16 and 22 °C) on larval performance (metamorphosis rate, developmental duration and growth) and then on juvenile performance (survival and Specific Growth Rate, SGR, at 18 and 24 °C in 14 days). In experiment 2, we investigated the effects of embryonic incubation temperature (larval biomass and lipid content of newly hatched larvae from embryos incubated at 12 and 18 °C) and larval prey concentration on larval performance and then on juvenile performance. In both experiments, the larvae plastically increased their development time in response to the reduction in temperature and prey concentration, whereas their survival decreased with temperature and prey concentration. The quantity of lipids available at hatching decreased with decreasing embryonic incubation temperature, which reduced the larval performance, particularly with a low concentration of prey. Survival at 14 days post-metamorphosis was significantly reduced when the embryos were incubated at 12 °C compared with those incubated at 18 °C, regardless of the subsequent larval incubation conditions, revealing phenotypic links between overconsumption of embryonic yolk reserves and post-metamorphic fitness. Overall, juveniles had a better SGR at 24 than at 18 °C, and even better when incubated under stressful embryo-larval conditions (temperature and prey concentration). This study highlighted phenotypic links between developmental stages and over developmental periods of several months.

Development of an artificial propagation and breeding method for the beehorn snail (Clithon diadema)

Beehorn snail (Clithon diadema), known for its vibrant colors, is threatened with extinction due to excessive field collection. Therefore, this study investigated the effects of different diets and salinity (0‰–35‰) on the gonadal development, capsule productivity, embryonic development, and larval survival and growth of C. diadema. Adult snails (shell length: 9.09 ± 0.87 mm) were fed diatoms, including pennate marine diatom (Nitzschia grossestriata), boat-shaped diatom algae (Navicula sp.) and Cylindrotheca sp., along with giant tiger prawn (Penaeus monodon) commercial feed, sea lettuce (Ulva lactuca), or Cladophora fascicularis, while snail larvae (shell length: 154.85 ± 6.03 μm) were fed Isochrysis galbana or Chaetoceros muelleri. The diatom group outperformed commercial feed and U. lactuca groups. The highest capsule productivity, yielding 79–82 capsules in 4 weeks, occurred at 15‰-20‰ salinity for diatom-fed adults. Embryos thrived at 0‰ but didn't hatch; hatching required salinities above 0‰, highlighting saline necessity. In addition, acute salinity changes (0‰ to 30‰) can deform embryo. Embryonic development at 15‰–20‰ salinity lasted 13.56–14.33 days with 100% larval hatching. However, larvae hatched at >20‰ salinity exhibit improved the percentage of survival without feeding (longer median lethal times). I. galbana-fed larvae survived 68 days with a 75% rate, outlasting C. muelleri-fed larvae which perished within 28 days. I. galbana-fed larvae, raised for 68 days at 25‰ salinity, showed 100% survival, 44.44% metamorphosis, and a 3.1 times growth increase. Metamorphosis rates were highest at 25‰ salinity with I. galbana, exceeding the 20‰ group by 3.2 times. Mucus of C. diadema boosts larval metamorphosis to 50.00%, 9 times higher than without inducers. Based on previous results, we developed an artificial propagation and breeding method for C. diadema. Artificially propagating C. diadema in large quantities could reduce the need for wild harvesting, thereby mitigating negative ecological impacts from excessive collection.

Comparative analysis on growth performance, survival and harvest traits between offspring from wild and mass-selected populations of Crassostrea nippona

Crassostrea nippona has recently been recognized as a preferred alternative to C. gigas in summer due to its firm flesh and high glycogen content. To promote industrial development, the mass selective breeding program was initiated to improve growth performance of C. nippona in 2014. Although a steady genetic gain of approximately 10% for growth traits was achieved in each of the first three generations of the selected strains, little is known about the cumulative genetic progress in desired traits contributed by the selective breeding in the genetic improvement program. In this study, the aquaculture performance of the selected population was comprehensively evaluated by comparing the production performance and reproductive traits of the progeny (WF1 and SF4) from the wild population and the third-generation selected line in commercial farming environments. The results showed that the diameters of eggs from both populations were at similar levels, but the fertilization and hatching rates of the progeny from the selected lines were significantly higher than those of the wild population (P < 0.05). At larval stages, the shell height and cumulative survival rate (CSR) of individuals from SF4 were consistently superior to that of WF1, especially on day 6 post-fertilization, in which CSR of the improved C. nippona was increased by 25.08% compared to that of wild oysters. Meanwhile, a significant 12.10% enhancement in the metamorphosis rate was observed in SF4 when compared with WF1. During the grow-out stage, SF4 displayed distinct advantages in growth performance and survival compared to the wild strain, with 23.19, 33.48, 34.18 and 79.11% improvement in shell height, body weight, CSR and final yield at harvest on day 800, respectively. Meanwhile, relative brood amount (RBA) associated with initial development of offspring was found to be significantly higher in SF4 compared with WF1 (P < 0.05). Remarkably, the gonadal development, sex ratios and biochemical composition of oysters from both populations were at similar levels at final harvest, implying that high-intensity artificial selection had no significant effect on reproductive characteristics and nutritional quality of C. nippona. The encouraging results in the present study suggest that the overall genetic progress contributed by genetic breeding is considerable in the fast-growing strain of C. nippona, and such gains are expected to continue to increase with further selective breeding.

Bacterial c-di-GMP signaling gene affects mussel larval metamorphosis through outer membrane vesicles and lipopolysaccharides

Biofilms serve as crucial cues for settlement and metamorphosis in marine invertebrates. Within bacterial systems, c-di-GMP functions as a pivotal signaling molecule regulating both biofilm formation and dispersion. However, the molecular mechanism of how c-di-GMP modulates biofilm-induced larval metamorphosis remains elusive. Our study reveals that the deletion of a c-di-GMP related gene in Pseudoalteromonas marina led to an increase in the level of bacterial c-di-GMP by knockout technique, and the mutant strain had an enhanced ability to produce more outer membrane vesicles (OMVs) and lipopolysaccharides (LPS). The mutant biofilms had higher induction activity for larval metamorphosis in mussels Mytilus coruscus, and OMVs play a major role in the induction activity. We further explored the function of LPS in OMVs. Extracted LPS induced high larval metamorphosis rate, and LPS content were subject to c-di-GMP and LPS-biosynthesis gene. Thus, we postulate that the impact of c-di-GMP on biofilm-induced metamorphosis is mediated through OMVs and LPS.

Effects of dietary lipid and protein levels on metamorphosis, growth, metabolism and gut microbiota of tadpole (Lithobates catesbeianus)

Tadpole cultivation is a crucial step in the artificial production of bullfrogs (Lithobates catesbeiana), but its feed nutrition is poorly understood. This study examined how dietary lipid and protein levels affect metamorphosis, growth and intestinal health of tadpole. Six groups of tadpoles were fed six diets with two lipid levels (7% and 10%) and three protein levels (36%, 40% and 44%) for 70 days. The results showed that at 7% lipid level, increasing protein enhanced metamorphosis rate and mean weight of tadpoles, reaching the optimal value at 40% protein (P < 0.05). At 10% lipid level, increasing protein also improved mean weight, peaking at 40% protein. Dietary nutrition also influenced liver amino acid and lipid metabolism directly. At 7% lipid level, increasing protein significantly increased the activities of hepatic enzymes GLS, PDH, ALT, AST, etc. (P < 0.05), and up-regulated the expression of hepatic genes fas, accb, fadd6 and cpt1a involved in lipid metabolism (P < 0.05). At 10% lipid level, increasing protein also up-regulated fadd6 and cpt1a genes (P < 0.05), but down-regulated acadl gene. Meanwhile, increasing dietary lipid level elevated TG and T-CHO levels in liver. Increasing dietary protein enhanced gut microbiota richness, while increasing lipid reduced it. Moreover, different gut microbiota groups had distinct biomarkers, such as Rikenellaceae, Desulfovibrionaceae, Burkholderiales and Bacteroidales, which were related to amino acid or lipid metabolism. In summary, under the test conditions, 7% lipid and 40% protein in diet are suitable levels, which can promote metamorphosis, growth and metabolism of tadpoles, and are more economical than high-lipid and high-protein diets.

Heritability Estimates for Growth Traits and Correlation Analysis between Weight and Metamorphosis Rate in the Bullfrog Rana (Aquarana) catesbeiana

Metamorphosis is a crucial process in the life cycle of Rana (Aquarana) catesbeiana. R. catesbeiana tadpoles, in their short larval period, possess a high survival rate and also a highly competitive ability in the amphibious stage. In actual seed production, the economic traits of larval period and metamorphosis rate are used as quantifiable indicators of quality for individuals and populations, respectively. However, studies of these economic traits in larval cultivation and production are still lacking. In this study, we constructed 40 full-sib families of R. catesbeiana and measured the weight and metamorphosis rate of tadpoles at different developmental stages. Subsequently, we calculated the phenotypic and genetic association between weight and metamorphosis rate in tadpoles and assessed the heritability of these two traits. The heritabilities of weight at three developmental stages were all higher than 0.40 and decreased with advancement of the developmental stage; the heritability of the metamorphosis rate was 0.18 ± 0.20, a moderate level. Correlation analysis of weight and metamorphosis rate at each developmental stage in each tadpole family showed that weight at stages 25-I, 25-II, and 25-III was significantly correlated at the phenotypic level but non-significantly at the genetic level. The metamorphosis rate was only moderately associated with stage 25-III weight (0.38, p &lt; 0.05). The results of this study confirm the importance and transportability of tadpole weight in actual seed production and provide basic data and a potentially optimized direction for the selective breeding of high-metamorphosis-rate bullfrogs.

The role of adaptive resistance in a widespread freshwater mussel species

Abstract Organism features, such as size, weight, sex and age, among others, can influence the success of parasitism. For species that depend on a host to complete their life cycle, such as freshwater mussels (Bivalvia, Unionida), understanding how these traits influence parasitism can help guide management actions aimed at improving their reproductive success, ultimately benefitting their conservation. In this study, the physiological compatibility between the duck mussel Anodonta anatina and its host fish was investigated in a simultaneous infestation experiment on four (three native and one non‐native) fish species using sympatric and allopatric host strains. The success of glochidia metamorphosis in juvenile mussels was evaluated as a function of host species, strain and fish length. Successful metamorphosis was achieved in almost all fish species tested and differences were detected between allopatric and sympatric strains, with higher values found in allopatric hosts. Allopatric strains of primary hosts produce more juveniles than marginal hosts and non‐native species. In addition, larger fish have lower rates of metamorphosis. The results confirm recent findings showing high variation in the metamorphosis success of A. anatina glochidia among different native and non‐native hosts, both in the natural environment and in artificial laboratory infestations. Allopatric hosts were more suitable for encystment, demonstrating potential adaptive immunity, not yet observed in A. anatina. Nevertheless, A. anatina may temporarily exploit the naivety of smaller fish regardless of strain. Overall, the results suggest that mussel propagation, reproduction and reintroduction efforts should consider the mechanisms that influence adaptive immunity in fish, including differences in compatibility within and between populations of sympatric and allopatric host strains. This situation should be taken into account, as successful metamorphosis is an important factor in the selection of hosts for juvenile development, especially in efforts to propagate endangered mussel species.

Effects of Thyroid Powder on Tadpole (Lithobates catesbeiana) Metamorphosis and Growth: The Role of Lipid Metabolism and Gut Microbiota.

A low metamorphosis rate of amphibian larvae, commonly known as tadpoles, limits the farming production of bullfrogs (Lithobates catesbeiana). This study aimed to examine the effects of processed thyroid powder as a feed additive on tadpole metamorphosis, lipid metabolism, and gut microbiota. Five groups of tadpoles were fed with diets containing 0 g/kg (TH0), 1.5 g/kg (TH1.5), 3 g/kg (TH3), 4.5 g/kg (TH4.5), and 6 g/kg (TH6) thyroid powder for 70 days. The results showed that TH increased the average weight of tadpoles during metamorphosis, with the TH6 group having the highest values. The TH4.5 group had the highest metamorphosis rate (p < 0.05). Biochemical tests and Oil Red O staining showed that the lipid (triglyceride) content in the liver decreased after TH supplementation, especially at doses higher than 1.5 g/kg. RT-qPCR revealed that TH at doses higher than 4.5 g/kg significantly up-regulated the transcriptional expression of the pparα, accb, fas, fadd6, acadl, and lcat genes, which are related to lipid metabolism (p < 0.05). These results showed that TH seems to simultaneously promote the synthesis and decomposition of lipid and fatty acids, but ultimately show a decrease in lipids. As for the gut microbiota, it is noteworthy that Verrucomicrobia increased significantly in the TH4.5 and TH6 groups, and the Akkermansia (classified as Verrucomicrobia) was the corresponding genus, which is related to lipid metabolism. Specifically, the metabolic pathways of the gut microbiota were mainly enriched in metabolic-related functions (such as lipid metabolism), and there were significant differences in metabolic and immune pathways between the TH4.5 and TH0 groups (p < 0.05). In summary, TH may enhance lipid metabolism by modulating the gut microbiota (especially Akkermansia), thereby promoting the growth of tadpoles. Consequently, a supplementation of 4.5 g/kg or 6 g/kg of TH is recommended for promoting the metamorphosis and growth of tadpoles.

Growth, Feed Utilization, Lipid Metabolism, and Metamorphosis of Bullfrog (Aquarana catesbeianus) Tadpoles Fed Diets With Different Lipid Levels

This study investigated the effect of dietary lipid levels on growth performance, lipid metabolism, antioxidant capacity, digestive enzyme activity, and metamorphosis rate of bullfrog (Aquarana catesbeianus) tadpoles. A total of six isonitrogenous diets were prepared, each containing 4.46% (L5), 6.95% (L7), 9.10% (L9), 10.90% (L11), 12.34% (L13), and 15.00% (L15) crude lipid content. The experimental diets were administered to triplicates of tadpoles (stage 25, 0.007 g) twice daily for 75 days with a daily feeding rate of 6.50% of their body weight. Weight gain (WG), specific growth rate (SGR), crude protein content of the whole body, apparent digestibility of dry matter and gross energy, intestinal lipase (LPS) capacity, lipoprotein lipase (LPL), and carnitine palmitoyltransferase‐I (CPT‐I) and contents of growth hormone (GH) and insulin‐like growth factor‐1 (IGF‐1) in the liver, high‐density lipoprotein cholesterol (HDL‐C) content in the serum, and metamorphosis rate at stages 40 and 41 increased as the dietary lipid level increased from 4.46% to 12.34% and then decreased. As the dietary lipid level increased from 4.46% to 10.90%, the protein efficiency ratio (PER), protein deposition rate (PDR), lipid deposition rate (LDR), crude lipid content and gross energy of the whole body, apparent digestibility of the crude lipid, superoxide dismutase (SOD), catalase (CAT) activities in the liver, and the intestinal trypsin (TPS) activity all increased and then decreased. According to the second‐order polynomial regression analysis of the WG and metamorphosis rate at stage 41 to the dietary lipid level, the ideal dietary lipid content for tadpoles was 11.08% and 10.72%, respectively. Overall, the appropriate dietary lipid level for bullfrog tadpoles was found to be 10.72%–11.08% of the diet.

Persistent exposure to artificial light at night (ALAN) accelerates metamorphosis and colonization in larvae of marine shellfish

The ongoing course of urbanization has led to excessive use of artificial light at night (ALAN), which has rapidly become an important source of pollution in many cities. The Pacific abalone (Haliotis discus hannai) Larvae were kept under a 12/12 h light/dark photoperiod (DD) in order to determine the effects of ALAN on embryonic development. To simulate the street lighting conditions at night, the artificial light was switched on from 18:00 until midnight (AD) or until 06:00 the next day (ND). Moreover, Groups AD and ND had a considerably greater hatching success rate and metamorphosis rate than Group DD (P < 0.05), whereas Group DD had a significantly longer hatching period and course to complete the metamorphosis of the larvae (P < 0.05). Transcriptomic analyses showed that members of Groups AD and DD had considerably higher expression levels of genes involved in ribosome biogenesis, spliceosome function, and the mRNA surveillance pathway. Prostaglandin B2, L-palmitoylcarnitine, stearic acid, palmitic acid, leukotriene C4, and arachidonic acid were screened by non-targeted metabolomics as differential metabolic markers that played a vital role in the response of larvae to different ALAN conditions. Multi-omics correlation analysis suggested that five pathways related to fatty acid synthesis, catabolism, and metabolism, such as biosynthesis of unsaturated fatty acids and arachidonic acid metabolism, were enriched in each comparison. Further quantitative analysis showed that compared to Group DD, 33 out of 50 fatty acids were upregulated in Group AD, and the levels of almost all fatty acids were increased in Group ND, which in turn suggested that fatty acids played a vital role in the physiological response of larvae to illumination changes. The findings of this work were significant for the unbiased and full-scale assessment of the ecological effects of ALAN, as well as the structural stability of the marine benthic community.

Optimal dietary protein level for the growth and metamorphosis of bullfrog (Lithobates catesbeianus) tadpoles

This study investigated the effects of dietary protein levels on growth performance, antioxidant capacity, digestive enzyme activity, and metamorphosis rate of the bullfrog (Lithobates catesbeianus) tadpoles. Seven isolipidic and isoenergetic diets were formulated with 24.61%, 28.49%, 33.74%, 37.50%, 44.06%, 48.39% and 53.92% crude protein. Triplicate replicates of tadpoles (growth stage 25 and 0.009 g) were fed with experimental diets two times daily for 11 weeks, and the daily feeding amount was 6.50% of the tadpole's body weight. Weight gain (WG), specific growth rate (SGR), the total antioxidant capacity (T-AOC) and catalase (CAT) activity in the liver, the intestinal trypsin activity (TPS) and metamorphosis rate at stage 42 of bullfrog tadpoles all increased with increasing dietary protein level from 24.61% to 44.06% and then decreased. Based on the second-order polynomial regression analysis of the weight gain and metamorphosis rate at stage 41 vs. dietary protein level, the optimal dietary protein level for bullfrog tadpoles was 42.49% and 46.50%, respectively. In conclusion, the optimum dietary protein level of bullfrog tadpoles was estimated to be 42.49%–46.50% of the diet.

SAT013 Characterization Of CRISPR/Cas9 Induced RXR Isotype Mutants In Xenopus Laevis

Abstract Disclosure: J.D. Furlow: None. S. Saini: None. B.J. Mengeling: None. M.E. Horb: None. Retinoid-X receptors (RXRs) occupy a unique position in the nuclear receptor (NR) superfamily. While some actions of the highly conserved RXRs may be independent, RXRs most often are heterodimer partners for several NRs that regulate development, reproduction and metabolism. As such, environmental chemicals interfering with the activity of RXRs and their partners may have significant deleterious effects on human health, often in developmental window, cell-type, and gene selective ways. The frog Xenopus has long served as an excellent model for studying vertebrate development including thyroid hormone action, and recent advances in genome editing have greatly enhanced its utility for investigating basic cell and organismal biology as well as human disease processes. To determine isotype specific roles in response to natural and synthetic ligands as well as candidate environmental chemicals interacting with RXRs in vivo, we created targeted germline mutations in the Xenopus tropicalis RXRα (rxra), RXRβ (rxrb), and RXRγ (rxrg) genes. For CRISPR/Cas9 mediated genome editing, guide RNAs were designed to target sequences just prior to or within the first RXR DNA binding domains. We raised all three RXR homozygous null mutants up to and through metamorphosis. The rxrb and rxrg homozygous null mutants completed metamorphosis and allowed us to establish adult null lines, but the rxra homozygous null mutants die at metamorphic climax, reminiscent of the thyroid hormone receptor (thra/thrb) double mutants. Some rxra mutant froglets also lack forearms or have forelimb defects, implying a role for rxra in RA mediated forelimb specification. The X. tropicalis rxrg homozygous null mutants show a trend toward an increased rate of metamorphosis versus matched wild-type controls, with significantly elevated tshb gene expression as newly metamorphosed froglets suggesting impaired negative feedback by TH. Significantly altered opsin gene expression in the froglet eye was also observed in rxrg mutant retinas: elevated short wave opsins opn1sw1 and opn1sw2 and sharply reduced long wave opsin opn1lw. This elevated tshb and opn1sw1 expression is highly similar to what is found in mouse rxrg null mutants; thus RXRγ action in the eye and pituitary appears to be highly conserved between mammals and amphibians. The establishment of these new RXR isotype mutant specific lines will support the expanded use of Xenopus to study basic biology and environmental toxicology involving TR-RXR and other NR-RXR partnerships. Presentation: Saturday, June 17, 2023

Earthworm as a Better Feed Component for Growth And Metamorphosis of &lt;i&gt;Bufo stomaticus&lt;/i&gt;

Laboratory rearing of Bufo stomaticus tadpoles indicated that change In food types affected larval growth rate and duration of metamorphosis. Tadpoles fed with only earthworm tissue of its combination grew better and metamorphosed earlier than those fed only goat meat or its combination. Hence utilisation of earthworm tissue in place of goat meat ts suggested to prepare the mixed diet for laboratory culture of anuran tadpoles.

Metabolic and Developmental Changes in Insects as Stress-Related Response to Electromagnetic Field Exposure

(1) Background: The growing ubiquity of electromagnetic fields (EMF) due to rapid technological progress raises concerns about potential health implications. While laboratory experiments have generated inconclusive findings about adverse effects, EMFs have demonstrated efficacy in magnetotherapy. Earlier studies indicate that an EMF can trigger stress responses in organisms, the outcomes of which are dependent on the intensity of the EMF. (2) Methods: This study aims to explore the effects of extremely low-frequency EMF (50 Hz, 1 mT, or 7 mT) on metamorphosis and metabolism rates, which are indicators of stress, across different developmental stages of Tenebrio molitor, including adults, pupae, and larvae. (3) Results: Our findings reveal that exposure to EMF leads to accelerated weight loss, increased adult metabolism, and higher mortality; however, EMF exposure appears to have no impact on sugar levels or the rate and success of metamorphosis. Notably, significant changes were only observed under the influence of a strong EMF (7 mT), while the weaker EMF (1 mT) did not yield statistically significant outcomes. (4) Conclusion: The obtained results suggest that an extremely low-frequency EMF can be considered a stressor, with its effects contingent upon the specific parameters of exposure and the developmental stage of the experimental model.

Ecological benefits of artificial light at night (ALAN): Accelerating the development and metamorphosis of marine shellfish larvae

Urbanization has led to increasing use of artificial light at night (ALAN), which has rapidly become an important source of pollution in many cities. To identify the ALAN effects on the embryonic development of the Pacific abalone Haliotis discus hannai, we first exposed larvae to natural light with a light period of 12 L:12D (control, Group CTR). We then exposed larvae to three different light regimes. Larvae in Group NL were exposed to full spectrum artificial light from 18:00 to 00:00 to simulate the lighting condition at night, whereas Groups BL and YL were illuminated at the same time interval with 450 nm of short-wavelength blue light and 560 nm of long-wavelength orange light, respectively, to simulate billboard lighting at night. There were significantly higher hatching success and metamorphosis rates of larvae in Group BL than in Group YL or CTR (P < 0.05). The larvae in Group YL had the highest abnormality rate and took the longest time to complete metamorphosis. Transcriptomic studies revealed significantly higher expression levels of genes related to RNA transport, DNA replication, and protein processing in endoplasmic reticulum pathways in Group BL compared to the other groups. In the metabolomic analysis, we identified prostaglandin B1, tyramine, d-fructose 6-phosphate, L-adrenaline, leukotriene C4, and arachidonic acid as differential metabolic markers, as they play a vital part in helping larvae adapt to different ALAN conditions. Multi-omics correlation analysis of pairwise comparisons between all of the groups suggested that the biosynthesis of unsaturated fatty acids (FAs) and arachidonic acid metabolism pathways were significantly enriched (P < 0.05). Further quantitative analysis of the fatty acid (FA) contents revealed that 42 out of 50 FAs were down-regulated in Group BL and up-regulated in Group YL, which suggested that the synthesis, catabolism, and metabolism of FAs are crucial for the larval response to different spectral components of ALAN. For the first time, we report positive rather than negative effects of artificial blue light at night on the embryonic development of a benthic marine species. These results are significant for unbiased and full-scale assessment of the ecological effects of ALAN and for understanding the structural stability of the marine benthic community.

Assessment of Larval Health and Metamorphosis of the Giant Freshwater Prawn Macrobrachium rosenbergii Larvae during Acute Exposure to Imidacloprid

An acute toxicity study of imidacloprid on the larval health and metamorphosis of the giant freshwater prawn Macrobrachium rosenbergii larvae were carried out during the months of January–August 2021 at the aquatic animal raring and experimenting facility in the Cochin University of Science and Technology, Kerala, India. Imidacloprid is a broad-spectrum neonicotinoid insecticide used against sucking pests infecting agricultural crops as both contact poison and stomach poison. The present study investigated the adverse effects of imidacloprid on the survival rate, feeding behaviour, larval quality and incidence of metamorphosis in Macrobrachium rosenbergii larvae. The 48 h median lethal concentrations (LC50 values) and safe concentration of imidacloprid determined for different larval stages (Zoea I–XI) of M. rosenbergii ranged between 0.000635–0.001388 mg l-1 and 0.000055–0.000191 mg l-1, respectively. Larvae exposed to imidacloprid for 48 h showed decrease in survival rate with increase in concentration of imidacloprid. The results of larval condition index (LCI) that indicates the larval quality showed that imidacloprid reduced the larval health significantly (p&lt;0.05) at high concentrations and is potent to delay the incidence of metamorphosis. The feeding rate of larvae exposed to different concentrations of imidacloprid were found to be significantly (p&lt;0.05) reduced due to paralytic effect of imidacloprid. The present work provides relevant data beneficial for the risk assessment of imidacloprid in M. rosenbergii.