Home About us Contact
|
Home About us Contact | ||
|
|
||
Mixed Sex (mixed + sex)
Selected AbstractsEffects of 17 ,-estradiol exposure on Xenopus laevis gonadal histopathologyENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 5 2010Jeffrey C. Wolf Abstract The natural estrogen 17 ,-estradiol (E2) is a potential environmental contaminant commonly employed as a positive control substance in bioassays involving estrogenic effects. The aquatic anuran Xenopus laevis is a frequent subject of reproductive endocrine disruptor research; however, histopathological investigations have tended to be less than comprehensive. Consequently, a study was designed to characterize gross and microscopic changes in the gonads of X. laevis as a result of E2 exposure. Additional goals of this study, which consisted of three separate experiments, included the standardization of diagnostic terminology and criteria, the validation of statistical methodology, and the establishment of a half maximal effective concentration (EC50) for E2 as defined by an approximately 50% conversion of presumptive genotypic males to phenotypic females. In the first experiment, frogs were exposed to nominal concentrations of 0, 0.2, 1.5, or 6.0,µg/L E2. From these experimental results and those of a subsequent range finding trial, the EC50 for E2 was determined to be approximately 0.2,µg/L. This E2 concentration was utilized in the other two experiments, which were performed at different facilities to confirm the reproducibility of results. Experiments were conducted according to Good Laboratory Practice guidelines, and the histopathologic evaluations were peer reviewed by an independent pathologist. Among the three trials, the histopathological findings that were strongly associated with E2-exposure (p,<,0.001 to 0.0001) included an increase in the proportion of phenotypic females, mixed sex, dilated testis tubules, dividing gonocytes in the testis, and dilated ovarian cavities in phenotypic ovaries. A comparison of the gross and microscopic evaluations suggested that some morphologic changes in the gonads may potentially be missed if studies rely entirely on macroscopic assessment. Environ. Toxicol. Chem. 2010;29:1091,1105. © 2010 SETAC [source] Growth performance of mixed sex, hormonally sex reversed and progeny of YY male tilapia of the GIFT strain, Oreochromis niloticusAQUACULTURE RESEARCH, Issue 6 2009Norhidayat Kamaruzzaman Abstract The growth performance of three experimental groups consisting of mixed sex fish (control), hormone-treated fish and progeny of YY male tilapia, all originated from the genetically improved farmed tilapia (GIFT) strain was evaluated. Masculinization of sexually undifferentiated fry was achieved by providing a supplement of 5 mg of 17-,-methyltestosterone per kg of feed over a period of 21 days (after sac absorption). Both mixed sex and progeny of YY male groups were fed a standard commercial ration. Mixed sex fish did not deviate significantly (P>0.05) from the 1:1 male to female ratio. Percentages of male averaged 75% in hormone-treated fish and 95% in YY male group over the sampling periods and at final harvest. The effect of sex on weight and length was statistically significant (P<0.001). The model used to analyse weight and length included experimental group and sex in each culture period as the fixed effects, and replicate cages as the random effect. Over the culture period of 141 days, there were no statistical differences (P>0.05) in body weight and length between mixed sex, hormonally treated and progeny of YY males. There were also no significant differences in level of variability in harvest weight between three groups of fish when the data were classified into five categories (=<100, 100 to <150, 150 to <200, 200 to <250 and ,250 g). It is concluded that monosex culture of all male tilapia would be of no advantage over mixed sex culture for the GIFT strain under conditions of cages suspended in earthen ponds. [source] Spatial and temporal habitat use of kob antelopes (Kobus kob kob, Erxleben 1777) in the Comoé National Park, Ivory Coast as revealed by radio trackingAFRICAN JOURNAL OF ECOLOGY, Issue 3 2001Frauke Fischer Abstract Spatial and temporal habitat use of kob antelopes (Kobus kob kob) have been investigated in the Comoé National Park (Ivory Coast, West Africa) by use of radio telemetry. A total of 23 kob were equipped with radio collars and radio tracked for up to 15 months. Home ranges of males were smaller and those of females larger than expected from theoretical models. Adult males used smaller areas than adult females and did not show seasonal home range shifts. Daily distances travelled did not differ between sexes. Kob walked less during the night than by day and covered shorter distances in the wet season. Whereas an increase in home range overlap between females resulted in higher rates of association among individuals, association of adults of mixed sexes was not correlated with the degree of home range overlap. Territorial behaviour of males and predator avoidance by females are suggested to explain the sex-specific differences in home range size of adults and the deviation from the predicted sizes. Predator avoidance is presumed as the main reason for the reduced walking distances at night as well as in the wet season. Reproductive behaviour and feeding ecology are assumed to determine the degree of association of conspecifics. Résumé On a étudié par radio-télémétrie l'utilisation spatiale et temporelle de l'habitat par les cobes (Kobus kob kob) au Parc National de Comoé (en Côte d'Ivoire, Afrique de l'Ouest). On a équipé un total de 23 cobes de colliers radio et on les a suivis pendant 15 mois (pour certains). L'espace vital des mâles était plus petit et celui des femelles plus grand que ce à quoi on s'attendait d'après les modèles théoriques. Les mâles adultes couvraient une zone plus réduite que les femelles adultes et ne déplaçaient pas leur espace vital en fonction des saisons. Les distances parcourues chaque jour étaient les mêmes pour les deux sexes. Les cobes se déplaçaient moins la nuit que le jour, et couvraient de plus courtes distances pendant la saison des pluies. Alors qu'une augmentation du recouvrement entre espaces vitaux des femelles aboutissait à un taux supérieur d'associations entre individus, l'association d'adultes des deux sexes n'était pas liée au taux de recouvrement des espaces vitaux. On suggère que le comportement territorial des mâles et l'évitement des prédateurs par les femelles pourraient expliquer les différences, spécifiques au sexe, de la dimension de l'espace vital des adultes et la déviation par rapport aux dimensions prévues. On suppose que l'évitement des prédateurs est la raison principale de la limitation des déplacements de nuit ainsi qu'en saison des pluies. On suppose que le comportement reproducteur et l'écologie alimentaire déterminent le degré d'association entre membres de la même espèce. [source] | ||||||||||