生物为什么需要性?

性是我们的动物本能之一。但是 ,别说对天真烂漫的学童 ,就是对生物学家来说 ,性也是自然界最神秘的谜题。我们为什么需要性?直到20世纪60年代 ,生物学家一直认为 ,是为了得到基因的多样性 ,因此它对生物进化意义深远。无性物种的下一代是在没有雄性的干预下 ,由雌性单独繁殖出     

桑德森和小型猫科动物

鲜红的太阳从柬埔寨豆蔻山升起，吉姆·桑德森出发寻找一种毛色斑驳的树栖猫的踪迹。这种美丽的小型猫科动物十分罕见，桑德森的使命是找到这种动物，把它用摄像机拍录下来，让人们了解它们的生活习性和生存环境，保护它们，使它们繁衍兴盛。     

绒山羊增绒技术

我国有许多优良山羊是产绒山羊中最优良的品种。它们的特点是：产绒量、绒白、绒细及净绒率都较高且品质好。可以引进原种饲养繁殖，也可采用与本地羊杂交改良，使山羊绒产量增加。     

它们从陆地走到海洋

寻找会走路的鲸鱼早在上世纪60年代,科学家们就提出了鲸鱼是从陆地上的原蹄类动物转化而来的说法,但始终没有确凿的证据。这种说法最早是科学家凡威伦提出的,他研究原蹄类动物化石后认为鲸鱼与偶蹄类动物源自同一祖先,因为在美国自然史博物馆,他发现几个鲸鱼化石的牙齿与有蹄目极为相似。凡威伦的结论是,鲸鱼是从肉食、似狼的中爪兽演化来的,因此与偶蹄类动物一样,部源自原蹄类动物。     

院校食堂如何预防食物中毒

食物中毒，即健康人吃了有毒物质而引起的以急性中毒症状为主的一类疾病。有毒物质有以下几种：被细菌、真菌等微生物污染的食物，被致病微生物污染并在繁殖过程中产生了大量毒素的食物；被有毒化学物质污染并达到中毒剂量的食物，本身就含有有毒物质而在加工过程中毒素未被除去的食物，在贮存过程中或增加了有毒成份的食物，外形与有毒食物难以区别而实际有毒的食物。食物中毒，一年四季都可发生。     

猪的繁殖障碍疾病的诊断要点及防制对策

随着养猪业的发展,我国各地种猪场发展较快,但是猪的繁殖障碍疾病在猪场都有不同程度的存在,有的猪场比较严重.据郑明球1999年对江苏某猪场调查,该场1998年母猪产仔1000窝,由于母猪流产、产死胎及木乃伊胎占465窝(46.5%);据杨宜生在湖北调查资料,在8235头次生产母猪中,有繁殖障碍的有3390头次(41.2%),产出仔猪84392头,而流产、死胎、木乃伊胎达10849头(21.8%).由此可见,猪的繁殖障碍病己严重影响养猪业的发展,应当引起高度重视及认真对待.     

Reproductive Biology and Prospects for Conservation of Caldesia parnassifolia (Alismataceae)——A Threatened Monocot in China

Caldesia parnassifolia (Bassi ex Linn.) Parl. in China has declined in number in recent years and is increasingly faced with the risk of extirpation arising from anthropogenic changes associated with rapid urbanization and expansion of both agriculture and infrastructure. To aid in provision of the data needed for effective conservation of the species, studies on the habitat, pollination ecology, and breeding system of C.parnassifolia were carried out on natural populations occurring in Southeastern China. Flowering in the study populations extended for more than eighty days beginning in early summer. Floral anthesis occurred in the morning hours and proceeded rapidly, lasting about 45 min. Flowers lasted ca.8h. Caldesia parnassifolia is self-compatible; however autogamy resulted in lower seed set than geitonogamy and xenogamy as well as free pollination. The data on pollen/ovule (P:O) ratio is consistent with a partially selfing and outcrossing mating system. Interpopulational crosses yielded similar seed set to within-population crosses. Agamospermy did not occur in the study populations. Propagation is achieved through seeds as well as through turions which commonly occur in the inflorescences. Flies (Insecta; Diptera) were the most frequent visitors to the flowers of C.parnassifolia; however bees (Insecta;Hymenoptera )composed a larger proportion of effective pollinators. The Syrphidae species Sphaerophoria indiana (Bigot) presents evidence of oligolectic foraging behavior. Recommendations are made on the immediate steps necessary for conservation of Caldesia species in China.