Hormonal control of reproduction in small ruminants

Reproduction of small ruminants can be controlled by several methods developed in recent decades. Some of these involve administration of hormones that modify the physiological chain of events involved in the sexual cycle. Methods which utilise progesterone or its analogues are based on their effects in the luteal phase of the cycle, simulating the action of natural progesterone produced by the corpus luteum after ovulation, which is responsible for controlling LH secretion from the pituitary. Use of prostaglandins is an alternative method for controlling reproduction by eliminating the corpus luteum and inducing a subsequent follicular phase with ovulation. Finally, the discovery of the properties of melatonin in photoperiod-dependent breeding animals opened up a new methodology to control reproduction in these species, inducing changes in the perception of photoperiod and the annual pattern of reproduction. Use of hormones to induce oestrus has allowed increased use of artificial insemination in small ruminants, a very useful management tool, considering the difficulty of detecting oestrus in these species. At commercial level, synchronisation of oestrus allows control of lambing and kidding, with subsequent synchronisation of weaning of young animals for slaughter. Also, it allows more efficient use of labour and animal facilities. Multiple ovulation and embryo transfer programmes are also possible with the use of oestrus synchronisation and artificial insemination. Finally, hormonal treatments have also been used to induce puberty in ewe-lambs and doelings.     

Active role of small peptides in Arabidopsis reproduction: Expression evidence

<正>Dear Editor,Successful sexual reproduction in plants requires extensive communication between male and female gametophytes,their gametes,and with the surrounding sporophytic tissues(Dresselhaus and Franklin-Tong 2013).Over the past two decades,many peptides including small cysteine-rich peptides(CRPs)and non-CRPs were found to play key roles in plant reproduction,mainly acting as signaling cues in this male–the Editor     

The physiological costs of reproduction in small mammals

Life-history trade-offs between components of fitness arise because reproduction entails both gains and costs. Costs of reproduction can be divided into ecological and physiological costs. The latter have been rarely studied yet are probably a dominant component of the effect. A deeper understanding of life-history evolution will only come about once these physiological costs are better understood. Physiological costs may be direct or indirect. Direct costs include the energy and nutrient demands of the reproductive event, and the morphological changes that are necessary to facilitate achieving these demands. Indirect costs may be optional 'compensatory costs' whereby the animal chooses to reduce investment in some other aspect of its physiology to maximize the input of resource to reproduction. Such costs may be distinguished from consequential costs that are an inescapable consequence of the reproductive event. In small mammals, the direct costs of reproduction involve increased energy, protein and calcium demands during pregnancy, but most particularly during lactation. Organ remodelling is necessary to achieve the high demands of lactation and involves growth of the alimentary tract and associated organs such as the liver and pancreas. Compensatory indirect costs include reductions in thermogenesis, immune function and physical activity. Obligatory consequential costs include hyperthermia, bone loss, disruption of sleep patterns and oxidative stress. This is unlikely to be a complete list. Our knowledge of these physiological costs is currently at best described as rudimentary. For some, we do not even know whether they are compensatory or obligatory. For almost all of them, we have no idea of exact mechanisms or how these costs translate into fitness trade-offs.     

小型啮齿动物的繁殖能量代价

繁殖是动物向后代传递和保持遗传信息的方式。因此繁殖的意义是显而易见的,但也需要付出代价。主要代价是能量需求增加。在对小家鼠繁殖能量需求的研究中发现,能量摄入在妊娠期只是稍微增加,而在哺乳期则急剧增加。尽管在妊娠期增加的幅度很小,但这可能反映了消化道和发育的胎儿之间在动物腹中的空间竞争,从而可能使能量摄入受到限制进而影响到繁殖过程。哺乳期间,能量摄入急剧增加,在哺乳后期达到高峰并趋于稳定。对野生鼠的研究也表明,野生鼠妊娠期和哺乳期的能量摄入模式与小家鼠是基本相同的,这样我们在小家鼠研究工作中的发现就具有更普遍的适应意义。对哺乳后期能量摄入的限制机制研究至少已经进行了15 年。能量摄入受消化道消化能力的限制(中心限制假说)或者受乳腺泌乳能力限制(外周限制假说) 的假说,都不能合理地解释一些现有的结果。我们提出了一个新的假说,即能量摄入可能受啮齿动物散热能力的限制(热耗散限制假说)。很久以来,一直认为散热能力是对大型哺乳动物哺乳的一个限制因素,但它在小型啮齿动物中的意义尚不清楚。传统观点认为,啮齿动物哺乳期对褐色脂肪组织产热水平的调节是为了重新分配能量以满足哺乳所需;但现在看来,实际上可能是动物为了避免体温过高而降低其基本的产热水平。我们在这个领域已经有了一些进展,但要利用这些知识来理解即使很简单的生活史权衡等问题也还有很多的工作需要做。     

Keeping a low profile: small hive beetle reproduction in African honeybee colonies

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Multiple roles for small RNAs during plant reproduction

Germline development and early embryogenesis in eukaryotes are characterized by large-scale genome reprogramming events. In companion cells of the Arabidopsis male gametophyte, epigenome reorganization leads to loss of heterochromatin and production of a distinct small RNA (sRNA) population. A specific class of sRNA derived from transposons appears to be mobile and can accumulate in germ cells. In the germline of maize, rice, and Arabidopsis, specific ARGONAUTE-sRNA silencing complexes appear to play key roles in reproductive development, including meiosis and regulation of germ cell fate. These results reveal new roles for sRNAs during plant reproduction and suggest that mobility of sRNAs could be critical for some of these functions.     

Centromeres: old tales and new tools

The centromere is a specialised region of the eukaryotic chromosome that directs the equal segregation of sister chromatids into two daughter cells during mitosis. In mitosis, the kinetochores mediate (1) microtubule capture and chromosome alignment at a metaphase plate; (2) the correction of improper microtubule attachments; (3) the maintenance of an active checkpoint until bi-orientation is achieved by the whole complement of chromosomes; (4) the establishment of tension within the centromere which, in turn, contributes to silencing of the spindle checkpoint and triggers the onset of anaphase. In this review, we will analyse how centromeres are organised with respect to chromatin types and arrangements.     

Strange Craft, Strange History, Strange Folks: Cultural Amnesia and the Case for Lesbian and Gay Studies

The academy today is only vaguely aware that its racial, ethnic, gender, and sexual makeup does not reflect the diversity of the society that surrounds it. When the university fails to encompass lesbian and gay studies, it loses not only knowledge of the presence of homosexuality in history and culture but analysis of homophobia and the role it has played in constructing the present. What is at stake is the integrity of the Western tradition of scholarship. The question is whether its studies can be objective, thorough, accurate, and complete-in a word, scholarly-as long as subjects like homosexuality, homosexual persons, and homophobia are systematically excluded.     

Prior specification in Bayesian statistics: three cautionary tales

One of the most important differences between Bayesian and traditional techniques is that the former combines information available beforehand-captured in the prior distribution and reflecting the subjective state of belief before an experiment is carried out-and what the data teach us, as expressed in the likelihood function. Bayesian inference is based on the combination of prior and current information which is reflected in the posterior distribution. The fast growing implementation of Bayesian analysis techniques can be attributed to the development of fast computers and the availability of easy to use software. It has long been established that the specification of prior distributions should receive a lot of attention. Unfortunately, flat distributions are often (inappropriately) used in an automatic fashion in a wide range of types of models. We reiterate that the specification of the prior distribution should be done with great care and support this through three examples. Even in the absence of strong prior information, prior specification should be done at the appropriate scale of biological interest. This often requires incorporation of (weak) prior information based on common biological sense. Very weak and uninformative priors at one scale of the model may result in relatively strong priors at other levels affecting the posterior distribution. We present three different examples intu?vely illustrating this phenomenon indicating that this bias can be substantial (especially in small samples) and is widely present. We argue that complete ignorance or absence of prior information may not exist. Because the central theme of the Bayesian paradigm is to combine prior information with current data, authors should be encouraged to publish their raw data such that every scientist is able to perform an analysis incorporating his/her own (subjective) prior distributions.     

Mycoplasma hominis: growth, reproduction, and isolation of small viable cells.

Improved methods for studying the growth of Mycoplasma hominis (ATCC 14027) have been developed, involving modified growth conditions and preparation of the organisms under minimally distorting conditions. Cells so prepared from batch cultures show relatively uniform exponential growth and appear to be dividing by binary fission; but pleomorphic forms appear upon further incubation. Similar behavior was demonstrated by another laboratory-adapted strain and by three clinical isolates, and therefore seems characteristic of the species. The pleomorphic populations contain small forms having diameters within the 100- to 250-nm size range reported for "elementary bodies." Such forms were isolated from this strain of M. hominis by sequential filtration using gravity alone, after cell aggregates were dispersed by Pronase treatment. Of the small bodies which traversed membranes of 220-nm pore size, a negligible number grew in liquid or on solid media, suggesting that these were not essential reproductive units in a life cycle, but involution forms due to growth in an altered environment.     

Hypermutation in stationary-phaseE. coli: tales from thelac operon

Escherichia coli cells are capable of complex regulatory responses to environmental conditions and stresses. In some circumstances, the response includes an increase in the mutation rate, effectively mutagenizing the genome. The classic example is the SOS response to DNA damage. Recent work indicates that other environmental stresses can also result in mutation of the genome. Modulation of mutation rate may be a more prevalent stress response than previously thought. In this review we focus on genome-wide mutation inE. coli cells subjected to a nonlethal genetic selection for reversion of alac frameshift allele. Reversion of thelac frameshift allele occurs via a novel mechanism that requires homologous recombination functions, and is enhanced by transiently diminished postsynthesis mismatch repair. A model for recombination-dependent stationary-phase mutation will be presented and its relevance for genome-wide mutation discussed.     

Ancestors and variants: tales from the cryptic

SUMMARY Those who work at the interface of development and evolution are united by the conviction that developmental comparisons can shed light on both the evolution of specific morphologies and the macroevolutionary process itself. In practice, however, the field comprises a diversity of approaches. As the field grows and practitioners attempt to digest a growing mountain of comparative data, the various approaches of "Evo Devo" have themselves evolved. A meeting organized by the authors and held at the University of Chicago in the Spring of 1999 illustrated some of these changes. This review will draw on its content to discuss recent developments in two areas: the reconstruction of common ancestors and the developmental basis of evolutionary change.