Sexual differences in the total content of ribosomal RNA, established by cytophotometric measurements in neurones from selected brain regions, were studied in rats of the Wistar strain. In females of reproductive age, cyclic changes of RNA were synchronized with their oestrous cycle, the values being higher in the oestrous phase than in dioestrus. These changes were observed in pyramidal cells of the hippocampus and of the frontal cortex, in cells of anterior thalamus, of ventromedial and lateral hypothalamus and of tuberculi olfactorii. However, cycling cells were not disclosed in septum and thalamus posterior. A dependence upon the actual level of ovarial hormones was found in ventromedial hypothalamic cells only. In general, the RNA values in males of the same age corresponded to values of dioestrous females. The differences between newborn and 7-day-old pups were not marked enough and did not allow to define the critical period responsible for initiation of this sexual difference. In senescent rats, this difference persisted. During the stable phase of long-lasting dioestrus, the total RNA content in cells of the frontal cortex, hippocampus and hypothalamus was higher in females than in males of the same age which may suggest a faster reduction of this substance in aged males. The prolonged influence of oestrogens in the oestrous phase of the climacteric period (preceding the permanent dioestrus) decreased the RNA values in hippocampal and hypothalamic neurones even below the level established during the permanent dioestrus (and thus reached male values). On the contrary, in frontal cortical neurones, the female values remained higher in the permanent dioestrus as well as during long-lasting oestrus. A discussion concerns the possible participation of genetic determination and of the actual state of ovarial hormones in the manifestation of sexual differences in brain cells of the rat.
Circadian rhythms play an essential role in the adaptation of organisms to the environment and may show species-specific or sex-specific differences even within a closely related taxonomic group. Although spiders (Araneae) are sexually dimorphic in several morphological and behavioural features, there are very few studies on the sex-specific differences in their biological rhythms. This study evaluated the circadian rhythm in the locomotor activity of two agrobiont hunting species of spider, Carrhotus xanthogramma (Latreille, 1819) (Salticidae) and Philodromus cespitum (Walckenaer, 1802) (Philodromidae), under natural photoperiod conditions. Particular attention was paid to possible differences between the sexes in both species. We found that C. xanthogramma is a strictly diurnal species with a mean activity peak in the morning in both sexes and the females are more active than males. The locomotor activity rhythm of males was richer in ultradian (shorter than a day but longer than an hour) components, although the relative power of these components was negligible compared to the main, 24-h period component. In accordance with these results, the diel pattern of locomotor activity of C. xanthogramma can be described by a unimodal cosine curve. In contrast to C. xanthogramma, both sexes of Ph. cespitum showed cathemeral activity (i.e., activity occur within both the light and dark portions of the daily cycle) and females and males follow quite different activity schedules: females were most active at night, shortly before nautical dawn, whereas males were most active early in the morning. Unlike C. xanthogramma, Ph. cespitum has more ultradian components, with higher relative power especially in females, where besides the 24-h circadian component there is a particularly strong 12-h ultradian period. Based on these factors, females of Ph. cespitum show a bimodal and males a unimodal pattern.
We examined the reliability of laboratory-derived calibration curves for age determination of field individuals of the common vole, Microtus arvalis. The sex-specific calibration curves for age determination based on the relationship between eye lens mass and age derived in the laboratory were applied to a live-trapped field population of common vole. When comparing the individual’s age to the length of its trapping history, we found a slight tendency for underestimation of real age. These errors were observed slightly more in females than in males and in individuals captured over a longer time. This could mean that growth rates in captive animals, especially older ones, and in females are greater than those from the field. The month of first trapping has no effect on the presence of the error. We suggest that, in population studies with a special concern for ageing individuals over the whole life span, other methods should be examined, such as those measuring insoluble eye lens proteins or calibration curves based on more than one predictor.