English Sexe Matures
It has been suggested that mating behaviours require high levels of cognitive ability. However, since investment into mating and the brain both are costly features, their relationship is likely characterized by energetic trade-offs. Empirical data on the subject remains equivocal. We investigated if early sexual maturation was associated with brain development in Atlantic salmon (Salmo salar), in which males can either stay in the river and sexually mature at a small size (sneaker males) or migrate to the sea and delay sexual maturation until they have grown much larger (anadromous males). Specifically, we tested how sexual maturation may induce plastic changes in brain development by rearing juveniles on either natural or ad libitum feeding levels. After their first season we compared brain size and brain region volumes across both types of male mating tactics and females. Body growth increased greatly across both male mating tactics and females during ad libitum feeding as compared to natural feeding levels. However, despite similar relative increases in body size, early maturing sneaker males maintained larger relative brain size during ad libitum feeding levels as compared to anadromous males and females. We also detected several differences in the relative size of separate brain regions across feeding treatments, sexes and mating strategies. For instance, the relative size of the cognitive centre of the brain, the telencephalon, was largest in sneaker males. Our data support that a large relative brain size is maintained in individuals that start reproduction early also during fast body growth. We propose that the cognitive demands during complex mating behaviours maintain a high level of investment into brain development in reproducing individuals.
english sexe matures
The results showed that boys did more daily physical activity than girls overall, as well as within each age group, this agrees with previous research3,5,16,36,37. The major difference in age was observed at 8 years, where boys were more active that girls. These results are similar to a recent study38, where the daily physical activity was measured with accelerometers. Some studies have reported that maturity differences between sexes (females mature earlier than males) may be one reason why results consistently show that females are less active than males of the same chronological age39. However this study observed less daily physical activity levels in girls at younger ages, which suggest maturity may not be the only factor for the lower physical activity levels reported by girls.
In the current study, no differences were found in daily physical activity or recess physical activity across age groups in boys. This finding is in contrast to studies that indicate that after age 9 there is a reduction in daily physical activity in boys32. On the other hand, 11-year old girls reported more daily physical activity than their 8-year old peers. However this difference was not reflected in their recess physical activity. This could be explained by physical activity for this age group occurring outside the playground40. On the other hand playground physical activity levels in both sexes are low, which is in agreement with previous research36. Another study38 suggest a decline in objectively measured overall physical activity levels between the ages of 6 and 9 years. This decline might be explained by increased time spend in scheduled time in school and non-sporting extracurricular activities (e.g. extra tuition, music lessons). It is possible that increased screen time (television, computer, console) such as that reported in the present study could at least partly explain this decline in physical activity. Too much screen time has been shown to influence the appearance of diseases such as obesity41. Therefore, the family environment might be considered an area of intervention to increasing physical activity in this age group, although a lack of high quality evaluations of interventions in such a setting hampers conclusions concerning effectiveness14.
On the other hand, school playgrounds provide important settings and opportunities for children to engage in physical activity. In the present study, from the age of nine, boys were more active than girls during recess. Reasons that explain these differences in playground physical activity are not completely clear42,43. Differences have been observed between the type of activity in which boys and girls participate5,37,44. For example boys often participate in team activities such as handball, football, and basketball of moderate to high intensity, which often contained a competitive element, whereas girls generally participated in lower intensity activity such as talking, walking or skipping16. Generally, boys take part in more competitive activities and girls showed a preference for activities of cooperative character and view recess time as an opportunity to socialize with friends20. Another explanation of the differences found between the amount of physical activity engaged in during recess, might be that the accelerometer is more sensitive to the type and intensity of activities participated in by boys, this would exaggerate the differences found between sexes when using this measure40. Furthermore, the type of physical activity engaged in during recess time, might also be affected by cultural and environmental factors45. The analysis of recess PA revealed that there were no differences across age groups except among the group of schoolchildren aged 8 and 11. This finding is in disagreement with other studies that have found a decrease in physical activity levels from the age of nine23,32. One study40 explained this decrease in physical activity to a reluctance of wearing accelerometers. Likewise, according to previous research38, gender differences in physical activities were most pronounced during school recess. These differences could also be due to the fact that some of the accelerometry studies focused on vigorous activity14,22, whereas the present data and other studies represent the total volume of physical activity accumulated during recess time, regardless of intensity16. Thus, this study suggests that strategies should be developed to increase physical activity at recess for girls over nine years of age. So, recess must be perceived not only as a leisure time, but also as an opportunity to promote a healthy and active lifestyle. Recess could be used by teachers to organize activities to suit the respective age, gender and interests groups of schoolchildren.
17. Mota J, Silva P, Santos MP, Ribeiro JC, Oliveira J and Duarte JA. Physical activity and school recess time: differences between the sexes and the relationship between children's playground physical activity and habitual physical activity. J Sports Sci. 2005; 23:269-275.
In the case of the boy, there have not been demonstrated symptoms of the development of mature spermatozoa comparable to the girl's menstruation, hence, it is apparently impossible to compare these phases of maturity in the two sexes. It is popularly believed, and taught by many texts, that girls as a rule "mature" earlier than boys, but the significance of such statements is as yet conjectural. Even if it is true that as a rule, mature ova in the female appear at an earlier age than that at which mature spermatozoa appear in the male (and we do not yet know this to be true), the fact means little. "Maturity," or the more limited "sexual maturity," is a complex matter of which we know little. Girls may "mature" in some details earlier than boys; and boys may "mature" in some details earlier than girls. Emotionally, it is possible that men mature earlier than women; but even of this we cannot be certain as yet.
The physical growth of boys does not keep pace with that of girls. Although male infants are on the average larger and heavier than girls, girls exceed boys in absolute stature and weight during the pubertal period, and are again exceeded by boys from sixteen on. In relation to the norms for the adults of both sexes, however, females are taller and heavier than males during both infancy and the pubertal period. Adult stature is attained by females at about twenty, by males at about twenty-three. The increase in weight, however, is said to continue until the age of forty in men, and fifty in women, although this difference may be due to accumulation of fat by the woman between forty and fifty.
In logical memory (as distinguished from rote memory), where the significance of what has been studied is to be retained, regardless of form, there is no clear differentiation of the sexes; although it is sometimes assumed that males are superior in this. Women may be relatively deficient in the application of what has been learned; if this were true it would explain their inferiority to men in the solving of problems, in arithmetic as in other matters, which has been reported by some experimenters. Girls are said to find geometry relatively harder than algebra (as compared with boys), presumably for this reason. In schools and colleges, women seem to do best in linguistic, literary, and historical subjects, where memory (not necessarily rote memory) is the important factor; and they are said to be at a disadvantage in mathematics and scientific topics in which problem-solving is involved. The fact that in coeducational schools and colleges girls and women have in certain cases made better average grades than boys and men, has been said to be due in part to the pre-dominant selection of languages, literature, and history by the females, and in part to their more serious application to the curriculum. It is probably true that until recently the male students have been more distracted by school and college "life" and by other extraneous activities, although the female students are rapidly growing toward the same neglect of the curriculum as has been characteristic of the males, and perhaps in some institutions have outstripped the male students in this respect. 041b061a72