Genetic effects on sperm design in the zebra finch

Sperm design and function are important determinants of male reproductive success and are expected to be under strong selection. The way that spermatozoa phenotypes evolve is poorly understood, because there have been few studies of the quantitative genetics of sperm. Here we show, in the zebra finch Taeniopygia guttata, an extraordinary degree of inter-male variation in sperm design that is independent of sperm swimming velocity. A quantitative genetics study using data from over 900 zebra finches in a complex breeding experiment showed that sperm head, mid-piece and flagellum length are heritable, that negative genetic correlations exist between sperm traits, and that significant indirect (maternal) genetic effects exist. Selection on the zebra finch sperm phenotype may be low because sperm competition is infrequent in this species, and this, in combination with negative genetic correlations and maternal genetic effects, may account for the variation in sperm phenotype between males. These results have important implications for the evolution of sperm in other taxa.     

Neuronal growth, atrophy and death in a sexually dimorphic song nucleus in the zebra finch brain

The song control nuclei of the zebra finch brain contain more neurones of larger diameter in the male than in the female. This sexual dimorphism is thought to result from differential growth of neurones in the two sexes. Using neurohistological techniques and radioactive tracers, we have studied the development of several forebrain nuclei involved in the control of song and find that the dimorphism arises from neuronal atrophy and death in the female brain as well as from an increase in cell-body size and afferent terminals from other forebrain nuclei in the male. Although the timing of these events varies from nucleus to nucleus, the sequence is essentially similar in all of them except area X. Here we describe the events in one of these nuclei, the robust nucleus of archistriatum (RA), as an example.     

Male mammals respond to a risk of sperm competition conveyed by odours of conspecific males

Sperm competition occurs when a female copulates with two or more males and the sperm of those males compete within the female's reproductive tract to fertilize her eggs. The frequent occurrence of sperm competition has forced males of many species to develop different strategies to overcome the sperm of competing males. A prevalent strategy is for males to increase their sperm investment (total number of sperm allocated by a male to a particular female) after detecting a risk of sperm competition. It has been shown that the proportion of sperm that one male contributes to the sperm pool of a female is correlated with the proportion of offspring sired by that male. Therefore, by increasing his sperm investment a male may bias a potential sperm competition in his favour. Here we show that male meadow voles, Microtus pennsylvanicus, increase their sperm investment when they mate in the presence of another male's odours. Such an increase in sperm investment does not occur by augmenting the frequency of ejaculations, but by increasing the amount of sperm in a similar number of ejaculations.     

Sexual conflict reduces offspring fitness in zebra finches

Parental care is often costly; hence, in sexually reproducing species where both male and female parents rear their offspring (biparental care), sexual conflict over parental investment can arise. Such conflict occurs because each care-giver would benefit from withholding parental investment for use with another partner, leading to a reduction in the amount of care given by one parent at the expense of the other. Here we report experiments to explore the prediction from theory that parents rearing offspring alone may provide greater parental investment than when rearing offspring together with a partner. We found that when the number of offspring per parent, and hence the potential workload, were kept constant, offspring received a greater per capita parental investment from single females than from both parents working together, and that males reared by single mothers were more sexually attractive as adults than their biparentally reared siblings. This difference between single- and two-parent families is due to a reduction in care provided by females when they care together with a male, rather than laziness by males or differences in the begging behaviour of chicks, supporting the claim that sexual conflict in biparental care can reduce the quality of offspring raised.     

青藏高原异质栖息地棕颈雪雀和白腰雪雀的分布研究

大型有蹄类动物的放牧和小型哺乳动物的挖掘行为,会改变它们栖息地的植物群落,从而影响物种分布和种群大小.高原鼠兔的分布与高山雪雀之间存在正相关性,牦牛的放牧与高山雪雀的分布间则存在未知的关系.在拉萨墨竹工卡县日多镇念村,研究者采用了最新的野生动物监测和研究方法(占据模型中的多物种多季节模型)来探索这一问题.研究目的集中在观察牦牛放牧和土地利用与高山雪雀分布的关系.结果发现,白腰雪雀对高原鼠兔洞穴的平均利用率为82％;棕颈雪雀和白腰雪雀对高原鼠兔洞穴的占据率随着离牦牛夜宿地距离变远而显著减少.在研究地点,白腰雪雀对牦牛夜宿地的利用率高,而棕颈雪雀无法确定.     

Vocalization during copulation behavior in greater horseshoe bats, Rhinolophus ferrumequinum

Vocal communication plays an important role for individual recognition and male-female interaction during mating in greater horseshoe bats,especially in respect to mate fidelity,which ensures that the bats can maintain a stable social organization.Few studies,however,have addressed the calling behavior during copulating in bats.Here,we initially report the copulation vocalizations and behaviors of both male and female greater horseshoe bats.During copulation,the male assumed a dorsal position and arched his back,arming around the female using his feet and thumbs.The male repeatedly produced very short constant frequency(SCF) syllables with high intensity and repetition rate(male 1:16.48±4.8 ms,male 2:17.79±4.03 ms) when he tried to insert the penis into the female,and then long syllables(male 1:42.08±12.67 ms,male 2:43.02±11.44 ms) after penile insertion.The female bats sometime refused the male bats in the early phase of copulations as emitting noise bursts and broad-band vocalizations,but kept silence during actual copulation.We also found that the SCF copulation calls of one male remained stable peak frequencies on different copulation days although its echolocation call frequency varied each day.Moreover,different male individuals maintained their own "private frequency" in the SCF copulation calls.Therefore,we predicted that the SCF copulation calls may serve as an indicator for female greater horseshoe bats to recognize the mating males in order to maintain mate fidelity because horseshoe bats exhibit sexual segregation before mating.Our results stipulate further studies on mating system and copulation strategies in polygynous bats.Such work may also aid in promoting the preservation of greater horseshoe bats.     

Sperm competition: motility and the midpiece in primates

In animals with multiple-partner mating systems, the gametes of two or more males must compete to fertilize a given set of ova. Here we show that the volume of the midpiece in individual sperm is significantly greater in primate species in which the females mate with multiple partners, and in which males have larger testes in relation to their body weight, than in those species that mate with only one partner and have relatively small testes. Our results indicate that sexual selection by sperm competition has influenced the evolution of a specific component of male-gamete morphology, the volume of the sperm midpiece.     

Cooperation and competition in pathogenic bacteria

Explaining altruistic cooperation is one of the greatest challenges for evolutionary biology. One solution to this problem is if costly cooperative behaviours are directed towards relatives. This idea of kin selection has been hugely influential and applied widely from microorganisms to vertebrates. However, a problem arises if there is local competition for resources, because this leads to competition between relatives, reducing selection for cooperation. Here we use an experimental evolution approach to test the effect of the scale of competition, and how it interacts with relatedness. The cooperative trait that we examine is the production of siderophores, iron-scavenging agents, in the pathogenic bacterium Pseudomonas aeruginosa. As expected, our results show that higher levels of cooperative siderophore production evolve in the higher relatedness treatments. However, our results also show that more local competition selects for lower levels of siderophore production and that there is a significant interaction between relatedness and the scale of competition, with relatedness having less effect when the scale of competition is more local. More generally, the scale of competition is likely to be of particular importance for the evolution of cooperation in microorganisms, and also the virulence of pathogenic microorganisms, because cooperative traits such as siderophore production have an important role in determining virulence.     

权力场上的人性角逐--论刘震云早期中篇系列小说

刘震云早期的中篇小说《新兵连》、《单位》、《一地鸡毛》、《官人》、《官场》、《头人》等系列作品都渗透出一种有关权力的思考,作品刻画了一个个在权力重压下被扭曲的“官”或“民”的人物形象。这些人物为获取权力或为权力所驱使,在权力的角斗场上疫于奔命,成为主体意识沦丧的灰色人群。通过对灰色人群生存状态的审视,刘的“新写实”叙事文本极大丰富了当代文学对人性内涵的表达,揭示了国人真实的文化心理和当前面临的精神困境。同时,这些作品蕴含的矛盾也表明作家思想的犹疑及其对传统现实主义写作观念的新思考。     

Exceptional sperm cooperation in the wood mouse

Spermatozoa from a single male will compete for fertilization of ova with spermatozoa from another male when present in the female reproductive tract at the same time. Close genetic relatedness predisposes individuals towards altruism, and as haploid germ cells of an ejaculate will have genotypic similarity of 50%, it is predicted that spermatozoa may display cooperation and altruism to gain an advantage when inter-male sperm competition is intense. We report here the probable altruistic behaviour of spermatozoa in an eutherian mammal. Spermatozoa of the common wood mouse, Apodemus sylvaticus, displayed a unique morphological transformation resulting in cooperation in distinctive aggregations or 'trains' of hundreds or thousands of cells, which significantly increased sperm progressive motility. Eventual dispersal of sperm trains was associated with most of the spermatozoa undergoing a premature acrosome reaction. Cells undergoing an acrosome reaction in aggregations remote from the egg are altruistic in that they help sperm transport to the egg but compromise their own fertilizing ability.     

Retinotopic order in the absence of axon competition

The retinotectal projection has long been studied experimentally and theoretically, as a model for the formation of topographic brain maps. Neighbouring retinal ganglion cells (RGCs) project their axons to neighbouring positions in the optic tectum, thus re-establishing a continuous neural representation of visual space. Mapping along this axis requires chemorepellent signalling from tectal cells, expressing ephrin-A ligands, to retinal growth cones, expressing EphA receptors. High concentrations of ephrin A, increasing from anterior to posterior, prevent temporal axons from invading the posterior tectum. However, the force that drives nasal axons to extend past the anterior tectum and terminate in posterior regions remains to be identified. We tested whether axon-axon interactions, such as competition, are required for posterior tectum innervation. By transplanting blastomeres from a wild-type (WT) zebrafish into a lakritz (lak) mutant, which lacks all RGCs, we created chimaeras with eyes that contained single RGCs. These solitary RGCs often extended axons into the tectum, where they branched to form a terminal arbor. Here we show that the distal tips of these arbors were positioned at retinotopically appropriate positions, ruling out an essential role for competition in innervation of the ephrin-A-rich posterior tectum. However, solitary arbors were larger and more complex than under normal, crowded conditions, owing to a lack of pruning of proximal branches during refinement of the retinotectal projection. We conclude that dense innervation is not required for targeting of retinal axons within the zebrafish tectum but serves to restrict arbor size and shape.     

A sperm ion channel required for sperm motility and male fertility

Calcium and cyclic nucleotides have crucial roles in mammalian fertilization, but the molecules comprising the Ca2+-permeation pathway in sperm motility are poorly understood. Here we describe a putative sperm cation channel, CatSper, whose amino-acid sequence most closely resembles a single, six-transmembrane-spanning repeat of the voltage-dependent Ca2+-channel four-repeat structure. CatSper is located specifically in the principal piece of the sperm tail. Targeted disruption of the gene results in male sterility in otherwise normal mice. Sperm motility is decreased markedly in CatSper-/- mice, and CatSper-/- sperm are unable to fertilize intact eggs. In addition, the cyclic-AMP-induced Ca2+ influx is abolished in the sperm of mutant mice. CatSper is thus vital to cAMP-mediated Ca2+ influx in sperm, sperm motility and fertilization. CatSper represents an excellent target for non-hormonal contraceptives for both men and women.     

试论现代科学研究中的合作与竞争

在现代科学研究中既有和谐的合作 ,也有激烈的竞争 ,合作与竞争已经成为科学研究和科学发展的主要方式和动力。本文结合现代科学的发展特点 ,着重探讨了科学研究中的合作与竞争问题 ,并指出确立良好的合作与竞争意识的重要意义