162 resultados para Sexual reproduction


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From an evolutionary standpoint, the production of offspring is the single most important aspect of an animal's life. Offspring carry an individual's genes into the next generation and it is the differential representation of genes in a population that drives evolutionary change. There are a variety of ways in which animals create offspring, ranging from cases where parents make identical copies of themselves by budding or parthenogenesis, to the standard case in vertebrates where gametes from a male and female fuse in sexual reproduction to produce the next generation. In this article we describe an usual variant of sexual reproduction, polyembryony.

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Existing in suboptimal conditions is a frequent occurrence for species inhabiting the cusp of their ecological range. In range-edge populations of plants, the scarcity of suitable habitat may be reflected in small population sizes which may result in increased self-pollination and/or inbreeding and an increase in the incidence of clonal reproduction. These factors may result in a decrease in levels of genetic diversity and a loss of potential adaptive variation that may compromise species' ability to cope with changes in their environment, an issue that is particularly relevant today with the current concern surrounding global climate change and its effect on species' distributional ranges. In the present study, we have compared the levels of clonal reproduction in the one-sided wintergreen Orthilia secunda (L.) House in (1) populations from its main continuous distribution range, (2) populations occurring on the limits of the continuous range, and (3) peripheral populations outwith the species' continuous distribution range. Range-edge populations in Scotland and Sweden displayed significantly lower genotypic richness and diversity than those from the main area of the species' distribution in these countries. Populations from Ireland, which occur in the temperate zone rather than the boreal conditions that are the preferred habitat for the species, and which represent relict populations left over from cooler periods in the Earth's history, displayed no within-population genetic diversity, suggesting a complete lack of sexual reproduction. Furthermore, the genetic distinctiveness of the Irish populations, which contained alleles not found in either the Scottish or the Swedish populations, highlights the value of 'trailing edge' populations and supports the concept of 'parochial conservation', namely the conservation of species that are locally rare but globally common.

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Background. The assembly of the tree of life has seen significant progress in recent years but algae and protists have been largely overlooked in this effort. Many groups of algae and protists have ancient roots and it is unclear how much data will be required to resolve their phylogenetic relationships for incorporation in the tree of life. The red algae, a group of primary photosynthetic eukaryotes of more than a billion years old, provide the earliest fossil evidence for eukaryotic multicellularity and sexual reproduction. Despite this evolutionary significance, their phylogenetic relationships are understudied. This study aims to infer a comprehensive red algal tree of life at the family level from a supermatrix containing data mined from GenBank. We aim to locate remaining regions of low support in the topology, evaluate their causes and estimate the amount of data required to resolve them. Results. Phylogenetic analysis of a supermatrix of 14 loci and 98 red algal families yielded the most complete red algal tree of life to date. Visualization of statistical support showed the presence of five poorly supported regions. Causes for low support were identified with statistics about the age of the region, data availability and node density, showing that poor support has different origins in different parts of the tree. Parametric simulation experiments yielded optimistic estimates of how much data will be needed to resolve the poorly supported regions (ca. 103 to ca. 104 nucleotides for the different regions). Nonparametric simulations gave a markedly more pessimistic image, some regions requiring more than 2.8 105 nucleotides or not achieving the desired level of support at all. The discrepancies between parametric and nonparametric simulations are discussed in light of our dataset and known attributes of both approaches. Conclusions. Our study takes the red algae one step closer to meaningful inclusion in the tree of life. In addition to the recovery of stable relationships, the recognition of five regions in need of further study is a significant outcome of this work. Based on our analyses of current availability and future requirements of data, we make clear recommendations for forthcoming research.

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Different reproductive strategies of males and females may lead to the evolution of differences in their energetic costs of reproduction, overall energetic requirements and physiological performances. Sexual dimorphism is often associated with costly behaviours (e.g. large males might have a competitive advantage in fighting, which is energetically expensive). However, few studies of mammals have directly compared the energy costs of reproductive activities between sexes. We compared the daily energy expenditure (DEE) and resting metabolic rate (RMR) of males and females of two species of mole-rat, Bathyergus janetta and Georychus capensis (the former is sexually dimorphic in body size and the latter is not) during a period of intense digging when males seek females. We hypothesized that large body size might be indicative of greater digging or fighting capabilities, and hence greater mass-independent DEE values in males of the sexually dimorphic species. In contrast to this prediction, although absolute values of DEE were greater in B. janetta males, mass-independent values were not. No differences were apparent between sexes in G. capensis. By comparison, although RMR values were greater in B. janetta than G. capensis, no differences were apparent between the sexes for either species. The energy cost of dimorphism is most likely to be the cost of maintenance of a large body size, and not the cost of behaviours performed when an individual is large.

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This article explores the use of shaming mechanisms with sexual offenders, particularly those who offend against children. Shaming, a central concept in the broader theory of restorative justice, may be of two varieties. The first, ‘disintegrative shaming’, characterises the traditional retributive framework of justice and is evident in recent state led and popular responses to the risk posed by released sexual offenders. Far from ensuring offender integration, the net result is often labelling, stigmatisation, ostracism and a return to offending behaviour. The second, ‘reintegrative shaming’, affirms the offender’s membership within law abiding society. This has been used in several jurisdictions as the basis of restorative support and treatment networks for sexual offenders where the community works in partnership with state and voluntary agencies. Contrary to arguments put forward by critics of restorative justice, this article argues that such cases may be particularly suitable for a restorative approach.

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The term ‘grooming’ has been used to describe the offender’s actions during the preparatory stage of sexual abuse. This paper will argue that current discourses on grooming have created ambiguities and misunderstandings about child sexual abuse. In particular, the popular focus on ‘stranger danger’ belies the fact that the majority of children are abused by someone well known to them, where grooming can also occur. Current discourses also neglect other important facets of the sex offending pattern. They fail to consider that offenders may groom not only the child but also their family and even the local community who may act as the gatekeepers of access. They also ignore what can be termed ‘institutional grooming’ – that sex offenders may groom criminal justice and other institutions into believing that they present no risk to children. A key variable in the grooming process is the creation and subsequent abuse of trust. Given that the criminal law may be somewhat limited in its response to this type of behaviour, ultimately concerted efforts must be made to foster social and organisational awareness of such processes in order to reduce the offender’s opportunity for abuse.

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Two National Surveys of Sexual Attitudes and Lifestyles in Britain (Natsal) were conducted, one in 1990 and one in 2000. Northern Ireland was excluded from both studies. Now, for the first time, comparable data about sexual attitudes and lifestyles of young people (14- to 25-year-olds) in Northern Ireland are available. Data were collected through self-administered questionnaires, one-to-one interviews and focus-group discussions. As in Natsal 1990 and 2000, young people were asked about their sexual attitudes towards sex, experiences of sex education, knowledge of sexually transmitted infections (STIs) and, if sexually active, about the circumstances in which sexual intercourse occurred. A total of 1013 young people in the target age group completed the self-administered questionnaire. Young people in Northern Ireland do not differ significantly from their counterparts in Britain in terms of sexual lifestyles and attitudes. Some 53.3% of all respondents reported that they had had sexual intercourse. Condom use at first sex was reported by 64% of sexually active respondents; 27.4% said they used no contraception; 26.7% of all respondents said they had sex before age 16. Respondents who first had sex when they were 15 or 16 years were more likely than other respondents to say that 'being drunk' was the main reason why intercourse occurred. Peer pressure to engage in sex was more prevalent among males than females. Young people in Northern Ireland regard friends as their most important source of sex education. School is the second most important source but most respondents wanted more sex education in school. It is important that it is needs focused and includes potentially sensitive and contentious information.

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Abortion politics are contentious and divisive in many parts of the world, but nowhere more so than in Ireland. Abortion and Nation examines the connection between abortion politics and hegemonic struggles over national identity and the nation-state in the Irish Republic. Situating the abortion question in the global context of human rights politics, as well as international social movements, Lisa Smyth analyses the formation and transformation of abortion politics in Ireland from the early 1980s to the present day. She considers whether or not the shifting connections between morality, rights and nationhood promise a new era of gender equality in the context of nation-state citizenship.
The book provides a new sociological framework through which the significance of conflict over abortion and reproductive freedom is connected to conflict over national identity. It also offers a distinctive in-depth consideration of the connection between gender and nationhood, particularly in terms of its impact on women's status as citizens; within the nation-state; within the European Union; and as members of a global civil society.