Microsporidia of mammals--widespread pathogens or opportunistic curiosities?

The microsporidia are primitive eukaryotic parasites - well known in some invertebrates and in fish, and increasingly recognized in mammals. One species, Encephalitozoon cuniculi is widespread in rodents, lagomorphs and carnivores and has been reported in human and non-human primates. But although clinical expressions of E. cuniculi infections are well substantiated in carnivores, evidence for its pathogeniciry in primates is less clear. Indeed, serological evidence suggests that latent infections may be quite common in man. Another species, Enterocytozoon bieneusi has now been reported several times from AIDS patients, associated with a severe, intractable diarrhoea. Other records of microsporidia in mammals have also been associated with an immunoprivileged site or immunocompromized host. In this article Elizabeth Canning and Wafaa Hollister discuss the recent findings, and consider the likelihood that microsporidial infections of man will be increasingly revealed following immunosuppressive therapy. But will they be opportunistic infections, or manifestations of common parasites that are otherwise held at sub-patent levels?     

Microsporidia infecting Apis mellifera: coexistence or competition. Is Nosema ceranae replacing Nosema apis?

Nosema ceranae has been suggested to be replacing Nosema apis in some populations of Apis mellifera honeybees. However, this replacement from one to the other is not supported when studying the distribution and prevalence of both microsporidia in professional apiaries in Spanish territories (transverse study), their seasonal pattern in experimental hives with co-infection or their prevalence at individual level (either in worker bees or drones). Nevertheless, N.ceranae has shown to present a higher prevalence at all the studied levels that could indicate any advantage for its development over N.apis or that it is more adapted to Spanish conditions. Also, both microsporidia show a different pattern of preference for its development according to the prevalence in the different Spanish bioclimatic belts studied. Finally, the fact that all analyses were carried out using an Internal PCR Control (IPC) newly developed guarantees the confidence of the data extracted from the PCR analyses. This IPC provides a useful tool for laboratory detection of honeybee pathogens.     

Paramyxean–microsporidian co-infection in amphipods: Is the consensus that Microsporidia can feminise their hosts presumptive?

The current consensus is that Microsporidia belong to a select group of parasites capable of causing both intersexuality and complete sex reversal in their hosts. Indeed, species such as Nosema granulosis and Dictyocoela duebenum, which infect amphipod crustaceans, are regularly referred to as 'feminising microsporidians'. This categorisation is based on a combination of findings: that these species are vertically transmitted and occur at a high prevalence of infection in intersex and female amphipods, that infected amphipod populations are female-biased, and that infected females have significantly female-biased broods with no concurrent increase in mortality. In this study, we report on a population of the amphipod Echinogammarus marinus presenting both female bias and high levels of intersexuality, which are infected with D. deubenum. In keeping with its feminising classification, infection is prevalent in animals presenting female and intersex phenotypes. However, a further screen revealed the presence of a previously unknown paramyxean parasite related to organisms of the genus Marteilia, a group known to cause catastrophic sexual dysfunction in bivalves. We found that the paramyxean parasite was also vertically transmitted, with infections being more prevalent in females and intersex animals. Critically, every animal infected with D. deubenum was also co-infected with the paramyxean, with few animals presenting an independent paramyxean infection. In contrast, co-infection of E. marinus with a paramyxean and the non-feminising microsporidian Dictyocoela berillonum rarely occurred. These observations raise a new hypothesis, namely, that D. duebenum and other feminising microsporidians are not actually capable of host feminisation but instead 'hitch-hike' together with a feminising paramyxean parasite.     

Horizontal transmission of Amblyospora albifasciati García and Becnel, 1994 (Microsporidia: amblyosporidae), to a copepod intermediate host and the neotropical mosquito, Aedes albifasciatus (Macquart, 1837)

The life cycle of Amblyospora albifasciati is characterized by three sporulation sequences involving the definitive mosquito host and a copepod intermediate host. Meiospores of A. albifasciati were infectious per os to adult females of the copepod Mesocyclops annulatus. All developmental stages in the copepod had unpaired nuclei, with sporulation involving the formation of a sporontogenic interfacial envelope and the production of a second type of uninucleate spore. These spores, formed in the ovaries of M. annulatus, were large, pyriform, and measured 10.4 x 4.8 microm. They infected Aedes albifasciatus larvae when ingested to initiate a sequence that involves schizogony and gametogony and ends with plasmogamy and nuclear association to form diplokaryotic meronts. Oval binucleate spores (9.3 x 3.1 microm) are formed in the adult mosquito and are responsible for vertical transmission to the filial generation.     

人类生态学(七):野生动物管理(1)

地球上的生物已有大约40亿年的进化史,而人类的起源和进化大约只经历了400万年,约占整个生物进化史的1‰。人类是地球上最晚出现的一种智慧生物,人类起源于生物界,而又离不开生物界。在人类进化历史的绝大部分时期内,人类几乎完全依赖野生生物为生(靠狩猎和采集野生植物),只是在1万多年以前,当农业和畜牧业产生以后,人类才逐渐减少了对野生生物的依赖性(目前仍有许多国     

人类生态学(八):野生动物管理(2)

栖息地遭受破坏和污染随着人类人口的增长和对自然资源需求的增加,人类一直在不断地砍伐森林、扩大耕地、建立城市、修筑道路、开采矿山、竖立井架、建设发电站等。热带雨林是保护生物遗传多样性最理想的地方,但地球上热带雨林的面积正在急剧缩小,顶极植被的破坏是对野生动物生存的最大威胁。每一种动物对于周围环境都有自己特定的忍受限度,栖息地的改变和破坏将使很多动物失去生存场所和必需的资源,造成这些动物的生存危机。虽然很多野生动     

行为生态学(十七):栖息地选择(2)

栖息地选择的遗传与获得据目前研究所知,动物对栖息地的选择具有一定的遗传性和后天获得性(即可借助于早期生活经验和学习而改进)。如果把两种动物饲养在同一环境中,发现它们对栖息地的选择有所不同,那么这种差异大都是由遗传所决定的。例如:把从未在自然植被中生活过的蓝山雀和煤山雀关在同一个鸟舍中,鸟舍内放有栎树枝和松树枝,观察记录表明,煤山雀大部分时间都停栖在松树枝上,而蓝山雀则主要停栖在栎树枝上。这种不同的选择同这两种山雀在自然状态下对栖息地的不同偏爱是一致的(蓝山雀偏爱阔叶林,而煤山雀偏爱针叶林)。     

行为生态学(十六):栖息地选择(1)

栖息地选择是指动物对生活地点类型的选择或偏爱,显然,所有的动物都只能生活在环境中的一定空间范围之内。但是,每一种动物的现实分布状况是通过怎样的过程而完成的,目前生态学家还了解得很少,现在只知道同动物对栖息地的选择有关。栖息地选择常常可以产生深远影响。动物对一个特定栖息地的选择可使动物只生活在某一特定环境之中,这有利于动物的表现型的定向改造。因此,同一种动物对栖息地的不同选择往往会引起它们之间基因频率的差异,而不同种动物对栖息地的不同选择又往往能增加种     

行为生态学(二):最优觅食行为(1)

动物觅食时经常面临着各种不同的选择,如猎取什么食物?到哪里去猎食?采取怎样的猎食路线?自然选择总是使动物的觅食效率尽可能地加以改进,因为只要捕食者能够借助于更有效的觅食,使其存活和繁殖成功的机会增加,自然选择就会对它有利。这个道理对山雀属鸟类来说是很明显的,这些食虫小鸟在冬季白天必须每隔三秒钟就捕食一只昆虫才能维持自己的生存(J.A.Gibb,1960)。     

行为生态学(三):最优觅食行为(2)

3.对模型的检验通过测定生态小区内的食物摄取曲线和各生态小区间的旅行时间,就可以对图8中的模型进行检验。有了可靠的模型,我们就可以预测捕食者在每一个生态小区内的搜寻时间、食物摄取量和边界值。下面我们举两个研究实例: (1)大山雀大山雀试验是对上述模型所进行的最严格检验之一。R.J.Cowie(1977)为了研究大山雀的觅食行为,在室内大鸟舍中建立了五棵人工     

人类生态学(四):人类与环境(1)

人类是大自然进化的产物,因而也是大自然不可分割的一个组成部分。人类和其他生物一样,自身的生存离不开它们的生存环境。据计算,人在一生中(按60年计算)要从外界环境吸收324吨空气、54吨水和32.4吨食物,同时要向环境排出数量大致相同的废物。因此,对人类的生存来讲,新鲜的空气、清洁的淡水和足够的食物是最起码的物质基础。但仅仅通过新陈代谢活动     

人类生态学(五):人类与环境(2)

二氧化硫和酸雨1982年人类环境国际会议所讨论的另一个重要问题是酸雨。同年6月在瑞典斯德哥尔摩还专门召开了有33国代表参加的酸雨问题国际会议,可见这个问题已经引起了人们多么大的重视。如果现在有人把酸雨说成是八十年代最     

行为生态学(二十四):动物的信号(1)

动物的很多醒目特征、很多行为方式、分泌的很多化学物质以及由动物发出的大多数声音都可以被解释为是为了影响其他动物的行为而发展起来的一种适应,并经常被看作是动物的信号。正如翅膀借助于在空气中搏击来完成其正常的飞行功能一样,一个信号是借助于影响另一个动物(经由感觉器官)而完成其正常     

长效尿素(专利号:85109580.1)

长效尿素这一尿素新品种是在尿素中添加了脲酶抑制剂,使土壤脲酶活性得到适度抑制,减缓了尿素的分解速度,从而使尿素的肥效期由原来的50天延长到110天以上,氮紊利用率由40％提高到52％,对各类作物平均增产11.3％,相当节肥20％以上,同时减免追肥用工,解放了劳力,为农业免中耕提供了条件。 所选用的脲酶抑制剂,抑制效率高,添加剂量低,在自然界中的百合科、茄科、越桔科、杜鹃花科和鼠李科的某     

能量生态学(一):绪论

在生态学形成和发展过程中,生态学的分科,有过三次大的分化。从形成初期起一直到现在,生态学的主要分科依据是生物类型与生物栖息地的类型。如动物生态、植物生态、微生物生态、湖沼生态、陆地生态和海洋生态等等。这实际上也清楚表明生态学源于生物学和自然地理学。只要生物学与自然地理学存在,上述生态学分支也将生存并发展下去。本世纪30年代以来,生态学的研究逐步受到人们的重视。许多生态学家注重于研究生态系统各层次的结构与功能。美国著名的生态     

行为生态学(一):导论

什么是行为生态学行为学和生态学是生物科学中两个正在蓬勃发展的分支学科,而行为生态学则是这两个学科的交叉领域。行为学和生态学一方面各自独立地发展,一方面又日益相互渗透,形成了行为生态学这一新的研究领域。     

中国小(鱼巴)属的分类整理及小(鱼巴)属的分类学讨论(鲤形目:鲤科:(鱼巴)亚科)

Puntius是典型的热带和亚热带鱼类类群,主要生活在山涧溪流及敞水环境.Hamilton(1822)建立此分类单元时将它作为Cyprinus属的一个亚属.Bleeker(1863)用Puntius Hamilton属名代替Systomus Mc'Clelland,确立了其属的地位,并分成3个亚属:Barbodes Bleeker, Capoeta Cuvier et Valencience和Puntius Hamilton,分别包括4须、2须和无须的种类.此后许多学者对Puntius属进行过研究,但其属级概念仍然模糊不清,该属的界限和命名的有效性还存在争议.现在较多将它用于亚洲的种类.     

行为生态学(九):昆虫社会的经济学(1)

当我们研究昆虫社会中的经济学原理时,必须注意昆虫同脊椎动物相比时的某些特殊性。在脊椎动物中,合作行为和社会性主要是建立在社群生活和保卫资源的基础上,但是在昆虫社会中,亲缘关系和亲代操纵(parental manipulation)却起着重要的作用。一个雌性个体的生殖力可以借助于女儿们(不育的)的帮助而大大提高。但是,要靠这种关系形成一个社会还必须具备下列几个先决条件:1)必须有足够的食物喂养后代;2)后代必须同它们的母亲有足够密切的联系,以便于亲代操纵;3)后代必须干愿忍受操纵并予以合作,无疑,后代只有从亲代操纵中也得到某些好处,它们才会这样做。