The Adaptive Significance of the Tadpole Stage with Comments on the Maintenance of Complex Life Cycles in Anurans

Istock (1967) argued on theoretical grounds that "complex lifecycles are inherently unstable over evolutionary time," yetthe vast majority of frogs have distinct adult and larval forms.The maintenance of complex life cycles in anurans seems relatedto the unusual morphology and feeding ecology of the larvalstage. An argument is presented that tadpoles are highly specializedsuspension feeders adapted for utilizing rapid rises in primaryproduction as a food source. Such resources are likely coupledto environmental fluctuations and available for only a limitedamount of time during any year. In being adapted to feed ona temporary resource, tadpoles are obliged to change their feedinghabits after a certain length of time. From a general considerationof matters such as predator susceptibility, feeding behavior,and growth patterns for suspension feeders, a case is made forwhy neotenic tadpoles have never been found and are unlikelyto occur. The argument presented here links complex life cycles with shortterm environmental perturbation. Frog species with direct developmenttend to occur in relatively aseasonal environments, supportingthis conclusion. The oldest known fossil frog is found in aseasonal rock formation. There has been a gradual trend towardincreased seasonality since the early Mesozoic, apparently dueto continental drift. This phenomenon may have some indirectand long-term bearing on the general maintenance of complexlife cycles throughevolutionary time. Understanding larval ecology is fundamental to understandingthe process of metamorphosis and the maintenance of complexlife cycles.     

水洞沟遗址第3、4、5地点发掘简报

水洞沟遗址第3、4、5地点位于水洞沟盆地西南边缘,自1923年发现以来,这三个地点尚未经过正式发掘。2004年夏秋季节,宁东重化工基地引黄管道的修建要穿越盆地的边缘,遂对这三个地点进行了抢救性发掘。发掘共揭露110m2,出土和采集了上千件石制品和鸵鸟蛋皮。下文化层的石制品主体呈现出与水洞沟第1地点相同的文化面貌;上文化层石制品和采集品特征则与第6地点表现出较强的一致性,其中包含大量的细石器制品。另外,在水洞沟盆地首次发现了两面器类型。此次发掘出土的文化遗物丰富了水洞沟遗址的文化内涵,对研究水洞沟文化与华北相邻区域古文化关系有重要意义。     

Primary Carcinoma of the Liver in Alberta

A survey was made to determine the incidence and to elucidate the manifestations of primary carcinoma of the liver in Alberta. The findings were compared with other reported series. Ninety-six cases were identified: 69 hepatomas, 25 cholangiomas and two cholangiohepatomas. Seventy-four of the patients were male and 22 were female, a male preponderance of greater than 3:1. Ages ranged from 7 days to 92 years, but the majority of the patients (58%) were in the seventh and eighth decades. The incidence of associated cirrhosis (38.5%) was lower than that noted in most series.Hepatomegaly, abdominal pain, weight loss and ascites were the outstanding clinical features. Gastrointestinal hemorrhage was frequent and second only to hepatic failure as the immediate cause of death. An abdominal mass and pleural effusion occurred in higher frequency than that cited in the literature. Associated disorders included peptic ulceration and cholelithiasis.Surgical biopsy was superior to needle biopsy in establishing the diagnosis. Laboratory tests and routine radiographs may be of diagnostic aid.     

Excavations into the active-site gorge of cholinesterases.

Acetyl- and butyrylcholinesterase (ACHE, BCHE) from evolutionarily distant species display a high degree of primary sequence homology and have biochemically similar catalytic properties, yet they differ in substrate specificity and affinity for various inhibitors. The biochemical information derived from analyses of ACHE and BCHE from human, Torpedo, mouse, and Drosophila, as well as that from the recombinant forms of their natural variants and site-directed mutants, can currently be re-examined in view of the recent X-ray crystallography data revealing the three-dimensional structure of Torpedo ACHE. The picture that emerges deepens the insight into the biochemical basis for choline ester catalysis and the complex mechanism of interaction between cholinesterases and their numerous ligands.     

Picea-Abies forests in the highlands of Northern Alberta

Summary Thirty stands of Picea-Abies dominated forest in highland areas of northern Alberta were studied quantitatively. The highlands are cooler and receive more precipitation than the adjacent lowlands in summer. Orthic Grey Luvisols are the most common soil type.Based on morphological criteria the Picea was basically P. glauca, the Abies mostly A. balsamea, and the Pinus nearly all P. contorta var. latifolia. The boreal floristic element in stands increases from west to east and from high to low altitude.Four Picea-Abies community types were recognized using ordination and cluster analysis: Rubus pedatus/Ptilium crista-castrensis, Cornus canadensis-Linnaea borealis, Viburnum edule/Hylocomium splendens, Calamagrostis canadensis. The 4 community types are well correlated with altitude, soil nutrient status, and 2 groups of correlated floristic and structural variables.The floristic and structural affinities of the 4 community types to those of adjacent regions are discussed.The Picea-Abies stands studied are considered to belong to a group of climax community types, with Abies dominance indicated at higher altitudes, shifting to Picea dominance at lower altitudes.Nomenclature follows Moss (1959) for vascular plants, with the exception of Dryopteris (Britton 1972) and Betula (Dugle 1966); Lawton (1971) for mosses; Schofield (1968) for hepatics; and Hale & Culberson (1970) for lichens.We thank E. M. Achuff and T. P. Achuff for field assistance; D. M. Britton, M. Dumais, M. Ostafichuk, W. Peterson and D. H. Vitt for taxonomic assistance; the Dept of Soil Science, University of Alberta and the Research Branch, Agriculture Canada for the use of laboratory equipment, Financial support was received from the Boreal Institute for Northern Studies and the National Research Council of Canada (A-2570 La Roi).     

The Impact of Roads on the Demography of Grizzly Bears in Alberta

One of the principal factors that have reduced grizzly bear populations has been the creation of human access into grizzly bear habitat by roads built for resource extraction. Past studies have documented mortality and distributional changes of bears relative to roads but none have attempted to estimate the direct demographic impact of roads in terms of both survival rates, reproductive rates, and the interaction of reproductive state of female bears with survival rate. We applied a combination of survival and reproductive models to estimate demographic parameters for threatened grizzly bear populations in Alberta. Instead of attempting to estimate mean trend we explored factors which caused biological and spatial variation in population trend. We found that sex and age class survival was related to road density with subadult bears being most vulnerable to road-based mortality. A multi-state reproduction model found that females accompanied by cubs of the year and/or yearling cubs had lower survival rates compared to females with two year olds or no cubs. A demographic model found strong spatial gradients in population trend based upon road density. Threshold road densities needed to ensure population stability were estimated to further refine targets for population recovery of grizzly bears in Alberta. Models that considered lowered survival of females with dependant offspring resulted in lower road density thresholds to ensure stable bear populations. Our results demonstrate likely spatial variation in population trend and provide an example how demographic analysis can be used to refine and direct conservation measures for threatened species.     

Effect of screening on the incidence of cervical cancer in Alberta.

The rates of registration of cases of in-situ and invasive cancer of the cervix in Alberta have fallen for women aged 35 and over since the introduction of screening in the early 1960s, as predicted by theory and described in Finland. However, for women aged 15 to 34 years of age the predicted pattern was followed only initially: the registration rate for in-situ and probably also invasive cancer increased after 1973. This could be due to an actual increase in the incidence of in-situ cancer of the cervix among younger women, as might be expected from the epidemiologic aspects of the disease, but it might also be due to increased recruitment of younger women to the screening program.     

毛叶粉背蕨配子体的泌粉现象及其系统学意义

为探讨蕨类配子体泌粉现象的系统学意义,对5种粉背蕨属(Aleuritopteris)植物的配子体发育过程进行了观察。结果表明,毛叶粉背蕨(A.squamosa)的配子体(通常是雌配子体)也具有泌粉现象,而其他4种的配子体不具粉状分泌物。基于叶绿体rbc L序列的证据表明,毛叶粉背蕨与粉背蕨属其他植物、中国蕨属(Sinopteris)等构成一个具有强烈支持率的单系,即Hemionitids支,该支与美洲分布的隐囊蕨类互为姐妹群。因此,配子体泌粉现象在碎米蕨类中并非隐囊蕨类植物所特有,泌粉现象的产生,在系统发育上至少涉及2次独立的演化事件。毛叶粉背蕨的泌粉现象多发生在雌性配子体上,暗示配子体的泌粉可能与配子体的雌性分化和胚发生发育相关。     

滇蛙和昭觉林蛙的形态差异及其潜在的适应意义

以比较解剖学的方法,观察和比较了采自1997年8月-2000年9月的滇蛙(♂16,♀14)和昭觉林蛙(♂17,♀17)标本的外部形态、肌肉和骨骼。结果显示,两种蛙的皮肤颜色不同;滇蛙的鳞骨比昭觉林蛙的发达;滇蛙雄性个体具声囊,而昭觉林蛙则无;滇蛙和昭觉林蛙的肱三头肌、股三头肌和胫部的肌肉有显著或极显著差异;昭觉林蛙的四肢骨骼较滇蛙的细长,腰带坐骨结节较突出,髋臼也较大;两种蛙头部扩大的骨骼不同;滇蛙腹直肌具腱划4条,昭觉林蛙5条。两种蛙的这些形态差异与其栖息的小生境及生活方式的差异相适应。