Cyanobacterial blooms have emerged as a significant environmental issue worldwide in recent decades. However, the toxic effects of microcystin-LR (MC-LR) on aquatic organisms, such as frogs, have remained poorly understood. In this study, frogs (Pelophylax nigromaculatus) were exposed to environmentally relevant concentrations of MC-LR (0, 1, and 10 μg/L) for 21 days. Subsequently, we assessed the impact of MC-LR on the histomorphology of the frogs\' livers and conducted a global MS-based nontarget metabolomics analysis, followed by the determination of substances involved in lipid metabolism. Results showed that MC-LR significantly induced histological alterations in the frogs\' hepatopancreas. Over 200 differentially expressed metabolites were identified, primarily enriched in lipid metabolism. Biochemical analysis further confirmed that MC-LR exposure led to a disorder in lipid metabolism in the frogs. This study laid the groundwork for a mechanistic understanding of MC-LR toxicity in frogs and potentially other aquatic organisms.

Amphibian skin contains wound-healing peptides, antimicrobial peptides, and insulin-releasing peptides, which give their skin a strong regeneration ability to adapt to a complex and harsh living environment. In the current research, a novel wound-healing promoting peptide, PM-7, was identified from the skin secretions of Polypedates megacephalus, which has an amino acid sequence of FLNWRRILFLKVVR and shares no structural similarity with any peptides described before. It displays the activity of promoting wound healing in mice. Moreover, PM-7 exhibits the function of enhancing proliferation and migration in HUVEC and HSF cells by affecting the MAPK signaling pathway. Considering its favorable traits as a novel peptide that significantly promotes wound healing, PM-7 can be a potential candidate in the development of novel wound-repairing drugs.

Alarm signals and cues are crucial to animal survival and vary greatly across species. Eavesdropping on heterospecific alarm signals and cues can provide eavesdroppers with information about potential threats. In addition to acoustic alarm signals, evidence has accumulated that chemical alarm cues and disturbance cues can also play a role in alerting conspecifics to potential danger in adult anurans (frogs and toads). However, there is very little known about whether disturbance cues are exploited by heterospecifics. In the present study, we conducted a binary choice experiment and a prey chemical discrimination experiment, respectively, to test the responses of a sympatric anuran species (red webbed treefrogs, Rhacophorus rhodopus) and a sympatric predator species (Chinese green tree vipers, Trimeresurus stejnegeri) to disturbance odors emitted by serrate-legged small treefrogs (Kurixalus odontotarsus). In the binary choice experiment, we found that the presence of disturbance odors did not significantly trigger the avoidance behavior of R. rhodopus. In the prey chemical discrimination experiment, compared with odors from undisturbed K. odontotarsus (control odors) and odorless control, T. stejnegeri showed a significantly higher tongue-flick rate in response to disturbance odors. This result implies that disturbance odor cues of K. odontotarsus can be exploited by eavesdropping predators to detect prey. Our study provides partial evidence for heterospecific eavesdropping on disturbance cues and has an important implication for understanding heterospecific eavesdropping on chemical cues of adult anurans.

Integrated Rice-frog Ecosystem (IRFE) has the potential to reduce methane (CH4) emission and maintain yields from paddy fields. However, the quantitative relationship between rice morphological traits and CH4 emission remains to be explored. In this study, a 2-year field experiment was conducted to evaluate the effect of IRFE on rice morphological traits and CH4 emission from paddy fields and the ecological mechanisms. This study was conducted to analyze twelve aboveground and eight underground rice morphological traits, rice yields, and CH4 flux and emission from the paddy fields with six frog densities (0, 3750, 7500, 15,000, 30,000, and 60,000 frogs ha-1). The results showed that IRFE reduced CH4 emission by 24.70%-41.75% and 21.68%-51.21% in the 2018 and 2019 rice growth seasons, respectively. Moreover, CH4 emission decreased with the increase of frogs. Frogs also increased the diameter, biomass, and volume of rice roots, thus promoting rice growth. Root biomass, thousand-grain weight, and harvest index were also closely related to the yield. Root porosity and oxygen secretion capacity were negatively correlated with CH4 flux. Frogs increased root porosity and oxygen secretion, thereby reducing CH4 emission. The present study demonstrated that reducing CH4 emission and improving rice yields could be simultaneously achieved by altering rice morphological traits in IRFE.

Opalinids are a large group of anaerobic protists, mainly inhabiting the cloacae of amphibians (frogs and toads). The classification of this group has not been fully resolved, because of a lack of molecular information. Here, we give a redescription of Opalina triangulata Metcalf, 1923, collected from the rectum of the frog Fejervarya limnocharis, based on detailed morphological and molecular data. Our phylogenetic analyses confirmed the monophyly of Opalinata. Within it, Opalinea were monophyletic with O. triangulata and O. undulata as well as two Protoopalina species grouping together. Karotomorpha and Proteromonas did not group together confirming the paraphyly of Proteromonadea. Meanwhile, the ITS2 secondary structural similarities as well as G-C content revealed greater similitudes between Opalina species and P. lacertae than with Blastocystis hominis, which is in accordance with their position as sister clades in the SSU rDNA-based phylogenies.

Multiple pathogens coexist in nature, and hence, host species often encounter several pathogens simultaneously. The sequence in which the host encounters the parasites influences interactions between parasites and host pathology. Here, the effects of infection by two cercaria (larvae of trematodes) types, pleurolophocercous cercaria of Acanthostomum burminis and a furcocercous cercaria, on the tadpoles of common hourglass tree frog (Polypedates cruciger) were examined. Ten days posthatch, tadpoles (Gosner stage 27/28) were used for infection exposures. First, in a single infection each cercaria type was introduced to the tadpoles separately. Second, coinfection of the two cercaria was carried out by alternating the sequences of exposure. For all the experiments, appropriate controls were instituted. Tadpoles of all groups exposed to parasites had lower survival levels compared to controls. Among the four groups exposed, the highest survival was observed in the coinfection when furcocercous was introduced first (82.5%). The lowest survival was observed in the coinfection when the A. burminis cercaria was introduced first (65.0%). In the coinfections, when A. burminis was introduced prior to furcocercous, survival of the tadpoles was reduced by 17.0% compared to the exposures of furcocercous prior to A. burminis. Prior infection with A. burminis induced negative effect on the host with an increased infection severity, while prior infection with furcocercous had reduced infection severity than lone exposures. These results suggest that furcocercous infections can be beneficial for hosts challenged with A. burminis provided that A. burminis exposure occurs second. None of the treatments had an effect on the growth of the tadpoles, but lengthening of developmental period was observed in some exposures. All exposed tadpoles developed malformations which were exclusively axial-kyphosis and scoliosis. However, there was no difference in the number of malformed individuals in the single infection (19.0%-25.0%) compared to coinfection (20.0%-22.5%) or between coinfections. The results suggest that the sequence of parasite exposure affects host-parasite interactions and hence the disease outcomes. Understanding the effects of coinfection on disease outcomes for hosts provides insight into disease dynamics.

Mitochondrial genome (mito-genome) introgression among metazoans is commonplace, and several biological processes may promote such introgression. We examined two proposed processes for the mito-genome introgression between Rana chensinensis and R. kukunoris: natural hybridization and sex-biased dispersal. We sampled 477 individuals from 28 sites in the potential hybrid zone in the western Tsinling Mountains. Mitochondrial gene (cyt-b) trees were used to examine the introgression events. Microsatellite DNA loci, cyt-b and morphological data were used to identify hybrids and to examine the extent of natural hybridization. We detected rampant bidirectional introgressions, both ancient and recent, between the two species. Furthermore, we found a wide hybrid zone, and frequent and asymmetric hybridization. The hybrid zone cline analysis revealed a clear mitochondrial-nuclear discordance; while most nuclear markers displayed similar and steep clines, cyt-b had a displaced cline centre and a more gradual and wider cline. We also detected strong and asymmetric historical maternal gene flow across the hybrid zone. This widespread hybridization and detected low mito-nuclear conflicts may, at least partially, explain the high frequency of introgression. Lastly, microsatellite data and population genetic methods were used to assess sex-biased dispersal. A weak pattern of female-biased dispersal was detected in both species, suggesting it may not play an important role in the observed introgression. Our data are consistent with the hybridization hypothesis, but support for the sex-biased dispersal hypothesis is weak. We further suggest that selective advantages of the R. kukunoris-type mito-genome in thermal adaptation may also contribute to the introgression between the two species.