2 resultados para Bull semen
em Brock University, Canada
Resumo:
Sperm competition is the competition for fertilizations between ejaculates, within a female, following multiple mating. There are four sperm utilization or precedence patterns: first male precedence, where the first male to mate fertilizes most of the eggs laid by a female; last male precedence, where the last male to mate fertilizes most of the eggs laid by a female; "all-or-none" pattern, where sperm from either male fertilizes all the eggs laid by a female but which male's sperm that is used is random; or sperm mixing, where sperm from each male is used equally in fertilizing eggs laid by a female. Intermediate utilization patterns are also possible. Sperm competition occurs in a wide variety of insect species as well as other animals. This study was undertaken to study sperm competition in the field cricket, Gryllus integer. Four experiments were conducted: a radiation and sterilization experiment, a diapause experiment, and 2 competition experiments. It was found that 7,000 rad of gamma radiation sterilized adult ~ integer males. There was no diapause in the laboratory in ~ integer eggs. In the first competition experiment, three groups of females were used: females mated with a normal male, then with a second normal male (NN group); females mated with a normal male, and then with a sterile male (NR group); and females mated with a sterile male, and then with a normal male (RN group). The results obtained from this experiment showed that the mean proportion of eggs hatched was significantly different between 3 groups of females, with the proportion hatched much greater in the NN group than in either the NR or RN groups. The pattern for the proportion of eggs hatched following a double mating most closely resembled a pattern expected if sperm mixing is occurring. Results obtained in the replicate competition experiment showed that the mean proportion of eggs hatched for the females in the NR group was significantly lower than the proportion hatched in the other two groups. This also supports a model of sperm mixing as a precedence pattern. Values calculated following Boorman and Parker (1976), for the proportion of eggs fertilized by the second male to mate following a double mating, were 0.57 in competition experiment 1 and 0.62 in the replicate. These values indicate that sperm mixing occurs in~ integer.
Resumo:
In order for young people to meaningfully participate in the criminal justice system they must possess an understanding of their rights and legal procedures. To examine their understanding, 50 young people between the ages of 13-17 who received an extrajudicial sanction or were sentenced to probation, were recruited from the Finch Courthouse in Toronto, Ontario. Semi-structured interviews were conducted with participants regarding their understanding of their due process rights and their rights under the United Nations Convention on the Rights of the Child. Youth who indicated involvement in plea bargaining were also asked about their experiences during this procedure. In addition, the present study examined youths' perceptions of power differences in their interactions with criminal justice officials working within an institution that has tremendous control over offenders' lives. The results indicate that while youth seem to have some understanding oftheir rights and legal procedures, they nevertheless feel ill-equipped to invoke their rights in an adult-led criminal justice system. Furthermore, while past literature has often conceptualized youth understanding based on age (e.g., Crawford & Bull, 2006) the findings of the present study demonstrate that while age plays some role, the lack of power experienced by youth vis-a-vis adults, and specifically criminal justice professionals, has the most bearing on the inability of youth to exercise their rights.