Chronic effects of environmentally-relevant concentrations of lead in Pelophylax nigromaculata tadpoles: Threshold dose and adverse effects.

Lead (Pb) is a common heavy metal in the natural environment, but its concentration has been increasing alongside widespread industrial and agricultural development in China. The dark-spotted frog Pelophylax (formerly Rana) nigromaculata (Anura: Ranidae) is distributed across East Asia and inhabits anthropogenic habitats such as farmland. Here, P. nigromaculata tadpoles (Gosner stage 19-46) were exposed to Pb at different concentrations (0, 40, 80, 160, 320, 640 and 1280µg/L) and Pb-induced survival, metamorphosis time, development, malformations, mobility and gonad structure were monitored. The results showed that above the threshold concentration of Pb, adverse effects were obvious. As the concentration of Pb increased, the adverse effects on different traits followed different patterns: the effects on hindlimb length, survival rate, metamorphosis rate, total malformation rate, swimming speed and jumping speed largely exhibited a linear pattern; the effects on snout-vent length, body mass and forelimb length largely exhibited a bimodal pattern. Sex ratio and gonadal histology were not affected by Pb, suggesting that Pb is not strongly estrogenic in P. nigromaculata.

The effect of atrazine on intestinal histology, microbial community and short chain fatty acids in Pelophylax nigromaculatus tadpoles.

The intestine is the main organ for nutrient absorption in amphibians. It is sensitive to atrazine, which is a herbicide widely used in agricultural areas. At present, there is a lack of systematic research on the effect of atrazine on the amphibian intestine. In this study, we evaluated the effects of atrazine exposure (0, 50 µg/L, 100 µg/L, and 500 µg/L) for 20 days on intestinal histology, microbiota and short chain fatty acids in Pelophylax nigromaculatus tadpoles. Our research showed that 500 µg/L atrazine exposure significantly decreased the height of microvilli and epithelial cells, and altered the composition and diversity of intestinal microbiota in P. nigromaculatus tadpoles compared to the control. At the phylum level, the abundance of Bacteroidetes and Fusobacteria increased significantly, while that of Verrucomicrobia and Firmicutes decreased significantly in the 500 µg/L atrazine treatment group. At the genus level, Akkermansia and Lactococcus had significantly lower abundance in the 100 µg/L and 500 µg/L atrazine exposure group, while Cetobacterium was only detected in the 100 µg/L and 500 µg/L atrazine treated group. Also, function prediction of intestinal microbiota showed that atrazine treatment significantly changed the metabolism pathways of P. nigromaculatus tadpoles. In addition, 500 µg/L atrazine exposure changed the content of short chain fatty acids by significantly increasing the content of total SFCAs, butyric acid, and valeric acid, and decreasing the content of isovaleric acid in the intestine. Taken together, atrazine exposure could affect the intestinal histology and induce intestinal microbiota imbalance and metabolic disorder in amphibian tadpoles.

The influence of long-term cadmium exposure on the male advertisement call of Xenopus laevis.

Cadmium (Cd) is a non-essential environmental endocrine-disrupting compound found in water and a potential threat to aquatic habitats. Cd has been shown to have various short-term effects on aquatic animals; however, evidence for long-term effects of Cd on vocal communications in amphibians is lacking. To better understand the long-term effects of low-dose Cd on acoustic communication in amphibians, male Xenopus laevis individuals were treated with low Cd concentrations (0.1, 1, and 10 µg/L) via aqueous exposure for 24 months. At the end of the exposure, the acoustic spectrum characteristics of male advertisement calls and male movement behaviors in response to female calls were recorded. The gene and protein expressions of the androgen receptor (AR) were determined using Western blot and RT-PCR. The results showed that long-term Cd treatment affected the spectrogram and formant of the advertisement call. Compared with the control group, 10 µg/L Cd significantly decreased the first and second formant frequency, and the fundamental and main frequency, and increased the third formant frequency. One and 10-µg/L Cd treatments significantly reduced the proportion of individuals responding to female calls and prolonged the time of first movement of the male. Long-term Cd treatment induced a downregulation in the AR protein. Treatments of 0.1, 1, and 10 µg/L Cd significantly decreased the expression of AR mRNA in the brain. These findings indicate that long-term exposure of Cd has negative effects on advertisement calls in male X. laevis.

The complete chloroplast genome of the invasive and Cd-hyperaccumulator herb Bidens pilosa L. (Asteraceae).

Bidens pilosa is an annual invasive and Cd-hyperaccumulator herb. The complete chloroplast genome sequence of the B. pilosa is 150,542 bp in length, which is composed of a large single-copy region of 83,542 bp, a small single-copy region of 17,624 bp and a pair of inverted repeat regions of 24,688 bp. It encodes a set of 114 genes, consisting of 80 protein coding, 30 tRNA and 4 rRNA genes. Among all of these genes, 2 genes possess double introns, and 16 genes have a single intron. Phylogenetic analysis showed that B. pilosa clustered together with Marshallia obovata.

Individual and mixture toxicity of chromium and copper in development, oxidative stress, lipid metabolism and apoptosis of Bufo gargarizans embryos.

In natural ecosystems, living organisms are always subjected to a mixture of multiple heavy metals exposure, yet it is more common to study the effect of individual, rather than combined exposure. This study assessed the impacts of single or combined exposure to Cr and Cu on embryonic development, oxidative stress, lipid metabolism and apoptosis in the early development of Bufo gargarizans embryos. The total length, development stage and malformations of embryos were measured, and the mRNA expression of genes related to oxidative stress, lipid metabolism and apoptosis at Gs 18 and Gs 22 were determined by RT-qPCR. The results showed that all treatments significantly reduced the total length of embryos, delayed the stage of embryonic development and increased the proportion of malformed embryos. The Cr-Cu mixture treatment showed the greatest suppression of embryonic development and induced the highest rate of embryo malformation, compared to individual Cr and Cu treatments. In addition, the expression levels of oxidative stress genes (HSP90, SOD and GPx) and fatty acid ß-oxidation-related genes (ACOXL, ECHS1 and SCP) showed an up-regulated trend in treatments compared to control groups. Conversely, the lipid synthesis-related mRNA gene expressions (KAR, TECR, ACSL3 and ACSL4) were down-regulated. Among them, the Cr-Cu mixture had the greatest impact on lipid metabolism gene expression. The treatments showed significant effects on the expression of apoptosis genes (Bcl-1 and Bax), with Bcl-1 mRNA expression increasing and Bax mRNA expression decreasing. These results indicated that exposure to individual Cr, Cu and a Cr-Cu mixture can lead to oxidative stress, disrupt lipid metabolism and promote apoptosis, and the Cr-Cu mixture could cause more serious negative effects on B. gargarizans embryos than Cr or Cu individually.

The influence of low-dose cadmium on the laryngeal microstructure and ultrastructure of Pelophylax nigromaculata.

Cadmium (Cd) is one of the common heavy metals dispersed throughout the modern environment that disrupts the development of aquatic organisms. Amphibians appear to be particularly vulnerable to this heavy metal contaminant since their eggs and aquatic larvae live in aquatic habitats and have permeable skin. During this critical sensitive period, amphibians live primarily in the water and are thus susceptible to the effects of environmental pollutants in water. Pelophylax nigromaculata completes their laryngeal development from Gosner stage 19 (GS 19, embryonic stage) to GS 46 (metamorphosis stage). To study whether long-term (from GS 19 to GS 46) exposure to low Cd concentrations (0, 4, 8, 16, 32, 64, and 128 µg/L) affects the development of the larynx in P. nigromaculata, a comparative study of microstructures and ultrastructures of female and male P. nigromaculata larynges was carried out. In histological structure, the larynx was composed of epithelial tissue, skeletal muscle, and hyaline cartilage, and there were no differences between male and female frogs except that males had a larger cross-section area than females. In contrast to controls, 64 and 128 µg/L Cd treatments caused a significant decrease in cross-sectional area, while other treatments showed no significant differences. Under the scanning electron microscope, the surface of the larynx could be seen to be attached to developed and evenly distributed cilia, with no significant differences between young male and female frogs, even among the Cd treatments. Under transmission electron microscopy, developed laryngeal epithelial cells could be observed, with obvious cross striations of skeletal muscle cells and mitochondria distributed around the muscle and skeletal muscle satellite cells. Compared with the control group, mitochondria around the skeletal muscle grew in size and decreased in number in the high-concentration treatment.

The potential effects of climate change on amphibian distribution, range fragmentation and turnover in China.

Many studies predict that climate change will cause species movement and turnover, but few have considered the effect of climate change on range fragmentation for current species and/or populations. We used MaxEnt to predict suitable habitat, fragmentation and turnover for 134 amphibian species in China under 40 future climate change scenarios spanning four pathways (RCP2.6, RCP4.5, RCP6 and RCP8.5) and two time periods (the 2050s and 2070s). Our results show that climate change may cause a major shift in spatial patterns of amphibian diversity. Amphibians in China would lose 20% of their original ranges on average; the distribution outside current ranges would increase by 15%. Suitable habitats for over 90% of species will be located in the north of their current range, for over 95% of species in higher altitudes (from currently 137-4,124 m to 286-4,396 m in the 2050s or 314-4,448 m in the 2070s), and for over 75% of species in the west of their current range. Also, our results predict two different general responses to the climate change: some species contract their ranges while moving westwards, southwards and to higher altitudes, while others expand their ranges. Finally, our analyses indicate that range dynamics and fragmentation are related, which means that the effects of climate change on Chinese amphibians might be two-folded.

The influence of long-term cadmium exposure on phonotaxis in male Pelophylax nigromaculata.

Cadmium (Cd) is a common industrial and agricultural heavy metal found in the natural environment that disrupts the endocrine systems of vertebrates. Amphibians are particularly vulnerable to endocrine disruptors because of their aquatic habitats and permeable skin. Endocrine disruptors are known to negatively affect amphibian acoustic behavior, but whether and how the ubiquitous pollutant Cd impacts this crucial amphibian signaling system remains unknown. Male black-spotted frogs (Pelophylax nigromaculata) show phonotactic responses to female receptive calls by emitting advertisement calls and moving towards females during the mating season, essential for reproductive success. To study whether long-term (60 d) exposure to low Cd concentrations (10(-8), 10(-7) and 10(-6) M) affects male phonotaxis, we recorded male responses to female calls following Cd exposure during the breeding season. We found that Cd adversely affected advertisement call characteristics (call latency, call duration and call rate), the proportion of individuals that responded and the time to first movement of the male. These results indicate that long-term exposure to Cd at environmentally relevant concentrations alters phonotaxis in male P. nigromaculata.

The predictive performance and stability of six species distribution models.

BACKGROUND: Predicting species' potential geographical range by species distribution models (SDMs) is central to understand their ecological requirements. However, the effects of using different modeling techniques need further investigation. In order to improve the prediction effect, we need to assess the predictive performance and stability of different SDMs. METHODOLOGY: We collected the distribution data of five common tree species (Pinus massoniana, Betula platyphylla, Quercus wutaishanica, Quercus mongolica and Quercus variabilis) and simulated their potential distribution area using 13 environmental variables and six widely used SDMs: BIOCLIM, DOMAIN, MAHAL, RF, MAXENT, and SVM. Each model run was repeated 100 times (trials). We compared the predictive performance by testing the consistency between observations and simulated distributions and assessed the stability by the standard deviation, coefficient of variation, and the 99% confidence interval of Kappa and AUC values. RESULTS: The mean values of AUC and Kappa from MAHAL, RF, MAXENT, and SVM trials were similar and significantly higher than those from BIOCLIM and DOMAIN trials (p<0.05), while the associated standard deviations and coefficients of variation were larger for BIOCLIM and DOMAIN trials (p<0.05), and the 99% confidence intervals for AUC and Kappa values were narrower for MAHAL, RF, MAXENT, and SVM. Compared to BIOCLIM and DOMAIN, other SDMs (MAHAL, RF, MAXENT, and SVM) had higher prediction accuracy, smaller confidence intervals, and were more stable and less affected by the random variable (randomly selected pseudo-absence points). CONCLUSIONS: According to the prediction performance and stability of SDMs, we can divide these six SDMs into two categories: a high performance and stability group including MAHAL, RF, MAXENT, and SVM, and a low performance and stability group consisting of BIOCLIM, and DOMAIN. We highlight that choosing appropriate SDMs to address a specific problem is an important part of the modeling process.