Response of larvalXenopus laevisto atrazine: Assessment of growth, metamorphosis, and gonadal and laryngeal morphology (original) (raw)
Related papers
Environmental Toxicology and Chemistry, 2003
Larval Xenopus laevis were exposed to one of four concentrations of atrazine (0, 1, 10, or 25 g/L, 11 replicate tanks per treatment, 60-65 larvae per replicate) dissolved in an artificial pond water (frog embryo teratogenesis assay-Xenopus [FETAX]) medium beginning 48 h after hatching until the completion of metamorphosis. Separate groups of larvae (six replicate tanks per treatment, 60-65 larvae per replicate) were exposed to estradiol (100 g/L), dihydrotestosterone (100 g/L), or ethanol vehicle control dissolved in FETAX medium. None of the treatments affected posthatch mortality, larval growth, or metamorphosis. There were no treatment effects on sex ratios except for estradiol, which produced a greater percentage of female offspring. Exposure to either estradiol or 25 g atrazine/L increased the incidence of intersex animals based on assessment of gonadal morphology. Atrazine did not reduce the size of the laryngeal dilator muscle, a sexually dimorphic muscle in this species. We conclude that environmentally relevant concentrations of atrazine do not influence metamorphosis or sex ratios and do not inhibit sexually dimorphic larynx growth in X. laevis. The incidence of atrazine-induced intersex animals was small (Ͻ5%) and occurred only at the greatest concentration of atrazine tested, a concentration that is rarely observed in surface waters in the United States.
Does Atrazine Influence Larval Development and Sexual Differentiation in Xenopus laevis?
Toxicological Sciences, 2008
Debate and controversy exists concerning the potential for the herbicide atrazine to cause gonadal malformations in developing Xenopus laevis. Following review of the existing literature the U.S. Environmental Protection Agency required a rigorous investigation conducted under standardized procedures. X. laevis tadpoles were exposed to atrazine at concentrations of 0.01, 0.1, 1, 25, or 100 mg/l from day 8 postfertilization (dpf) until completion of metamorphosis or dpf 83, whichever came first. Nearly identical experiments were performed in two independent laboratories: experiment 1 at Wildlife International, Ltd. and experiment 2 at the Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB). Both experiments employed optimized animal husbandry procedures and environmental conditions in validated flowthrough exposure systems. The two experiments demonstrated consistent survival, growth, and development of X. laevis tadpoles, and all measured parameters were within the expected ranges and were comparable in negative control and atrazine-treated groups. Atrazine, at concentrations up to 100 mg/l, had no effect in either experiment on the percentage of males or the incidence of mixed sex as determined by histological evaluation. In contrast, exposure of larval X. laevis to 0.2 mg 17b-estradiol/l as the positive control resulted in gonadal feminization. Instead of an even distribution of male and female phenotypes, percentages of males:females:mixed sex were 19:75:6 and 22:60:18 in experiments 1 and 2, respectively. These studies demonstrate that long-term exposure of larval X. laevis to atrazine at concentrations ranging from 0.01 to 100 mg/l does not affect growth, larval development, or sexual differentiation.
Proceedings of the National Academy of Sciences of the United States of America, 2010
The herbicide atrazine is one of the most commonly applied pesticides in the world. As a result, atrazine is the most commonly detected pesticide contaminant of ground, surface, and drinking water. Atrazine is also a potent endocrine disruptor that is active at low, ecologically relevant concentrations. Previous studies showed that atrazine adversely affects amphibian larval development. The present study demonstrates the reproductive consequences of atrazine exposure in adult amphibians. Atrazineexposed males were both demasculinized (chemically castrated) and completely feminized as adults. Ten percent of the exposed genetic males developed into functional females that copulated with unexposed males and produced viable eggs. Atrazineexposed males suffered from depressed testosterone, decreased breeding gland size, demasculinized/feminized laryngeal development, suppressed mating behavior, reduced spermatogenesis, and decreased fertility. These data are consistent with effects of atrazine observed in other vertebrate classes. The present findings exemplify the role that atrazine and other endocrine-disrupting pesticides likely play in global amphibian declines.
Effect of atrazine on metamorphosis and sexual differentiation in Xenopus laevis
Aquatic Toxicology, 2008
There is a growing international concern that commonly used environmental contaminants have the potential to disrupt the development and functioning of the reproductive system in amphibians. One such chemical of interests is the herbicide atrazine. Effects of atrazine on sex differentiation were studied using wild-type Xenopus laevis tadpoles and all-ZZ male cohorts of X. laevis tadpoles, produced by mating wild-type ZZ male to sex-reversed ZZ male (female phenotype). Stage 49 tadpoles were exposed to 0.1-100 ppb atrazine or 0.27 ppb (1 nM) 17-estradiol (E 2) until all larvae completed metamorphosis (stage 66). Metamorphosis, gonadal morphology and histology, CYP19 (P450 aromatase) mRNA induction, and hepatic vitellogenin (VTG) induction were investigated. Effects of atrazine on VTG-induction were also assessed in vitro in primarycultured X. laevis hepatocytes. Atrazine had no effect on metamorphosis of developing wild-type or all-male X. laevis larvae. Statistical increase in female ratios was observed in 10 and 100 ppb atrazine groups in comparison with control group. While no hermaphroditic froglet was observed in all atrazine groups. In ZZ males, sex reversal was induced by 0.27 ppb E 2 , but not by atrazine at concentrations of 0.1 and 1.0 ppb. In addition, neither P450 aromatase mRNA in the gonad nor hepatic VTG were induced by atrazine. Furthermore, VTG was not induced by 1000 ppb atrazine in primary-cultured hepatocytes. Our results indicate that female ratios in developing X. laevis tadpoles were increased by 10 and 100 ppb atrazine under the present experimental conditions. While the other endpoints showed no effect in the range of 0.1-100 ppb atrazine. These results suggest that effect of atrazine on sexual differentiation was not caused by estrogenic action and has no induction ability of P450 aromatase gene in gonad.
Environmental Science & Technology, 2005
The potential effects of atrazine on gonadal development in metamorphs and subadults of the African clawed frog (Xenopus laevis) were studied under conditions of natural photoperiod and temperatures in outdoor microcosms from August 2002 to June 2003 in South Africa. Triplicate 1100 L microcosms for each nominal concentration of 0.0, 1, 10, and 25 µg of atrazine/L were used. Measured atrazine concentrations varied <25% throughout the study, and no atrazine was detected in the control microcosms. Tadpoles developed well at all concentrations. On the basis of histological examination of testes of recently metamorphosed stage 66 frogs, 57% of the individuals in the reference group exhibited testicular oocytes as compared with 57, 59, and 39% of the 1, 10, and 25 µg/L atrazine groups, respectively. The average prevalence of testicular oocytes for all of the treatments including the controls was 54% in a single testis, while, in 35% of individuals, testicular oocytes were observed in both testes. The number of testicular oocytes per individual ranged from 0 to 58 with means of 9. 5, 9.8, 8.5, and 11.1 for the 0.0, 1, 10, and 25 µg of atrazine/L groups, respectively. Ten months after metamorphosis, another subset of juveniles was examined, and the maximum number of testicular oocytes observed was five in one animal. The presence of testicular oocytes was not related to exposure to atrazine and may be a natural phenomenon during ontogeny.
2000
African clawed frogs (Xenopus laevis) were exposed to one of eight nominal waterborne concentrations including 0, 0.1, 1.0, 10, or 25mg/L atrazine, 0.005% ethanol (EtOH), or 0.1 mg/L estradiol (E2) or dihydrotestosterone (DHT) containing 0.005% EtOH. Frogs were exposed,from 72 h posthatch,until 2–3 months,postmetamorphosis via a 3-day static renewal exposure,regimen. Atrazine at concentrations between 0.1 and 25mg/L did not
Gonadal Development of Larval Male Xenopus laevis Exposed to Atrazine in Outdoor Microcosms
Environmental Science & Technology, 2005
The potential effects of atrazine on gonadal development in metamorphs and subadults of the African clawed frog (Xenopus laevis) were studied under conditions of natural photoperiod and temperatures in outdoor microcosms from August 2002 to June 2003 in South Africa. Triplicate 1100 L microcosms for each nominal concentration of 0.0, 1, 10, and 25 µg of atrazine/L were used. Measured atrazine concentrations varied <25% throughout the study, and no atrazine was detected in the control microcosms. Tadpoles developed well at all concentrations. On the basis of histological examination of testes of recently metamorphosed stage 66 frogs, 57% of the individuals in the reference group exhibited testicular oocytes as compared with 57, 59, and 39% of the 1, 10, and 25 µg/L atrazine groups, respectively. The average prevalence of testicular oocytes for all of the treatments including the controls was 54% in a single testis, while, in 35% of individuals, testicular oocytes were observed in both testes. The number of testicular oocytes per individual ranged from 0 to 58 with means of 9. 5, 9.8, 8.5, and 11.1 for the 0.0, 1, 10, and 25 µg of atrazine/L groups, respectively. Ten months after metamorphosis, another subset of juveniles was examined, and the maximum number of testicular oocytes observed was five in one animal. The presence of testicular oocytes was not related to exposure to atrazine and may be a natural phenomenon during ontogeny.
Environmental Health Perspectives, 2006
Atrazine is a potent endocrine disruptor that both chemically castrates and feminizes male amphibians. It depletes androgens in adult frogs and reduces androgen-dependent growth of the larynx in developing male larvae. It also disrupts normal gonadal development and feminizes the gonads of developing males. Gonadal malformations induced by atrazine include hermaphrodites and males with multiple testes [single sex polygonadism (SSP)], and effects occur at concentrations as low as 0.1 ppb (µg/L). Here, we describe the frequencies at which these malformations occur and compare them with morphologies induced by the estrogen, 17β-estradiol (E 2), and the antiandrogen cyproterone acetate, as a first step in testing the hypothesis that the effects of atrazine are a combination of demasculinization and feminization. The various forms of hermaphroditism did not occur in controls. Nonpigmented ovaries, which occurred at relatively high frequencies in atrazine-treated larvae, were found in four individuals out of more than 400 controls examined (1%). Further, we show that several types of gonadal malformations (SSP and three forms of hermaphroditism) are produced by E 2 exposure during gonadal differentiation, whereas a final morphology (nonpigmented ovaries) appears to be the result of chemical castration (disruption of androgen synthesis and/or activity) by atrazine. These experimental findings suggest that atrazine-induced gonadal malformations result from the depletion of androgens and production of estrogens, perhaps subsequent to the induction of aromatase by atrazine, a mechanism established in fish, amphibians, reptiles, and mammals (rodents and humans).
Does Atrazine Affect Larval Development and Sexual Differentiation of South African Clawed Frogs?
Annals of the New York Academy of Sciences, 2009
The potential impact of atrazine (ATZ) on gonadal malformations in larval Xenopus laevis has been controversially discussed, and a hypothesis has been generated that ATZ might induce the estrogen-synthesizing enzyme aromatase, leading to feminization or demasculinization. Recently, extensive long-term studies clearly indicate that no adverse effect of ATZ on larval development and sexual differentiation could be found. Therefore, to determine potential transient impacts of ATZ on sexual differentiation processes, short-term exposures were conducted using tadpoles treated for 4 days with ATZ at 25 μg/L. The expression levels of the key players for sexual differentiation in amphibians were determined in the brain, assessing aromatase, 5α-reductase type 1 (S1) and type 2 (S2), and the gonadotropins luteinizing hormone and follicle-stimulating hormone, and in the gonads, measuring aromatase, S1, and S2, by means of quantitative RT-PCR. No significant changes in any of these parameters have been found, implicating, in accordance with recent long-term exposures, that no aromatase induction by ATZ could be observed, and it seems likely that no further endocrine mechanism of ATZ affecting sexual differentiation in X. laevis exists.