Structural and functional effects of early exposure to estradiol-17β and 17α-ethynylestradiol on the gonads of the gonochoristic teleost Dicentrarchus labrax

This study investigated the effects of estrogens on sexual differentiation in sea bass (Dicentrarchus labrax L.), a gonochoristic marine teleost that under culture conditions has a histologically sexual undifferentiated period that covers most of the first year of life, after which most individuals develop as males. Sea bass that had no noticeable histological sign of sex differentiation were fed estrogens at two doses (5 or 10 mg kg^-1 food) and for different periods ranging from 48 to 426 days post fertilization (DPF). Exposure to the synthetic estrogen 17-ethynylestradiol (EE₂) at 10 mg kg^-1 food from 60 to 260 DPF, including the sensitive period to equivalent doses of synthetic androgens previously determined for this species (126-226 DPF), significantly (p < 0.05) more than doubled the number of juvenile females to 80%, compared to the control value of 33%, and completely suppressed gonadal development in the remaining 20% of the population. This suggests that the period during which sea bass gonads exhibit high sensitivity to androgens is also very sensitive to estrogens. A comparable exposure to the natural estrogen estradiol-17 (E₂) resulted in 13% of the fish having suppressed gonadal development, but induced 57% of the fish to develop gonads with germinal tissue of both sexes, suggesting a pivotal role for E₂ during this sensitive period. Earlier exposure to EE₂ at 10 mg kg^-1 food from 48-88 DPF, significantly (p < 0.05) increased the number of females to 62% from 36% in the control group, allowing for the normal testicular development in the remaining fish. In contrast, a later chronic exposure (226-426 DPF) to E₂, at either 5 or 10 mg kg^-1 food, starting when the gonads showed no sign of sexual differentiation but past the critical sensitive period, had no effect on the resulting overall sex ratios, indicating that after this period responsiveness of the gonads to estrogens decreases as gonadal sexual differentiation progresses. However, the consequences of this apparently innocuous exposure were later manifested in adults, exemplified by a significant dose-dependent reduction in the number of mature males at 626 DPF, coinciding with the second reproductive season, the time when males normally reach sexual maturation in cultured sea bass. This suggests that chronic exposure to E₂ past the critical sensitive period may not affect the sex ratio, but could result in alterations in the male reproductive organs. This was later verified by histological analysis which revealed a significant (p < 0.05) dose-dependent reduction of the surface of the testicular lobules in the remaining males that did not mature. Together, these experiments illustrate both readily observable and subtle effects of estrogens on sex proportions, gonadal morphology and maturation rates, providing evidence that estrogen exposure can have delayed action in a teleost in a manner similar to the effects described for mammalian species. The possible existence of effects of this latter type in adult fish could be considered when evaluating the consequences of deliberate or accidental exposure to estrogens or putative estrogenic chemicals, particularly if such exposure had taken place during sex differentiation.     

Differential response to soil drought among co-occurring broad-leaved tree species growing in a 15- to 25-year-old mixed stand

? Introduction

In the context of global environmental changes, better understanding of tree response to soil drought in young mixed species stands is needed to anticipate forest adaptation and management practices for the future.

? Materials and methods

We investigated the functional response of five co-occurring broad-leaved tree species growing in a 15- to 25-year-old mixed stand in northeastern France during the 2006 summer drought. We measured functional traits related to water acquisition (phenology, rooting pattern and vulnerability of xylem to cavitation) and the ecophysiological response (sap flux density, leaf water potential) of these species to soil water shortage.

? Results

Our study highlights contrasted drought response strategies among these species and a trade-off between leaf phenology, resistance of xylem to cavitation and root system depth.

? Conclusion

At this site, a deep root system seemed to be a key functional trait for the species to cope with drought. Quercus robur and Salix capreae can be characterised as drought-avoidance species as they possess a deep root system and therefore did not strongly experience soil drought. Despite deep rooting capacity, Betula pendula did not really avoid soil drought and strongly regulated transpiration during dry periods. Nevertheless, the earliness of budburst of this species contributes to high annual growth rate. In contrast, Carpinus betulus and Fagus sylvatica both displayed typical characteristics of drought-sensitive species.     

The occurrence of Xylosandrus compactus and its associated fungi on cacao from South Sulawesi,Indonesia: A preliminary study of an emerging threat to the cacao industry

Journal of Plant Diseases and Protection - Xylosandrus compactus is one of the significant beetle pests on perennial crops, which has become an increasing problem on cacao productivity and...     

Prevalence of antibodies to Leptospira interrogans serovar hardjoin bulk tank milk from unvaccinated irish dairy herds

: Bulk tank milk samples, collected from 347 herds throughout the Republic of Ireland using a sampling frame based on seven milk-recording organisations, were tested by ELISA for antibodies to Leptospira interrogans serovar hardjo. These herds, which had not been vaccinated against leptospirosis within the previous five years, were categorised according to their province, milk-recording organisation and size. Two-hundred-and-seventy-three herds (79%) had a positive ELISA titre. Both the probability of a herd being seropositive and the antibody level in the herd milk sample were affected by the province (P < 0.05 and P < 0.01, respectively) and the herd size category (P < 0.05 and P < 0.01, respectively). Larger herds were significantly more likely to have positive reactions and higher mean concentrations of antibody. It was concluded that a high proportion of unvaccinated Irish dairy herds have been exposed to infection with Leptospira hardjo.     

Antimicrobial resistance in generic fecal Escherichia coli obtained from beef cattle on arrival at the feedlot and prior to slaughter, and associations with volume of total individual cattle antimicrobial treatments in one western Canadian feedlot

A prospective observational study was carried out to examine antimicrobial resistance patterns of fecal Escherichia coli isolates of calves on arrival at the feedlot, and then evaluate the associations between the total volume of antimicrobial used for disease treatment and changes in antimicrobial resistance, during the feeding period. No macrolides or tetracyclines were administered in the feed during this study. On arrival, at the animal level, all 3 isolates obtained from 36.6% [95% confidence interval (CI): 29.0 to 44.8] of all cattle sampled (n = 153), were susceptible to all antimicrobials, while 5.9% (95% CI: 2.7 to 10.9) of cattle had at least 1 isolate that was resistant to ≥ 3 antimicrobials out of the 7 antimicrobials tested. The most frequent antimicrobials for which resistance was observed were sulphamethoxazole, ampicillin, and tetracycline where, of all cattle, 44.4% (95% CI: 36.4 to 52.7), 20.3% (95% CI: 14.2 to 27.5), and 17.7% (95% CI: 12.0 to 24.6), respectively had at least 1 resistant isolate. All cattle received antimicrobial metaphylaxis on arrival at the feedlot. Antimicrobial use was described for a cohort of 95 cattle. Antimicrobials were given to 42 of the 95 cattle during the feeding period, to treat disease. Amongst the 42 treated cattle, there were a total of 133 animal daily doses (ADD_Feedlot), where 1 ADD_Feedlot represented 1 day of antimicrobial treatment received by a feedlot animal at the approved dose. Only 1 ADD_Feedlot was given in the 100 days immediately prior to slaughter. There were no associations found between antimicrobial use and antimicrobial resistance in this study.     

Antimicrobial resistance of fecal Salmonella spp. isolated from all phases of pig production in 20 herds in Alberta and Saskatchewan

Salmonella spp. (n = 468), isolated from the feces of sows, nursery, and grow-finish pigs in 20 farrow-to-finish herds in Alberta and Saskatchewan, were tested for susceptibility to 16 antimicrobials. No resistance was identified to amikacin, amoxicillin-clavulanic acid, ceftiofur, ceftriaxone, ciprofloxacin or nalidixic acid, and less than 1% of the isolates were resistant to cefoxitin and gentamicin. Isolates were most commonly resistant to tetracycline (35%) and sulfamethoxazole (27%). Overall, 59% of the Salmonella were susceptible to all 16 drugs (pansusceptible). Isolates from sows were more likely to be pansusceptible than isolates from nursery or grow-finish pigs. Resistance to 2 or more drugs occurred in 29% of the isolates and was significantly more likely to occur in Salmonella from nursery pigs than from sows. The odds of resistance to 4 of the drugs, streptomycin, ampicillin, kanamycin and cephalothin, were significantly higher in isolates from nursery pigs than grow-finish pigs, while the odds of resistance to 2 drugs, tetracycline and streptomycin, were higher in Salmonella from nursery pigs than from sows. More age-specific risk factor studies are needed to investigate these differences between production phases.