Subfossil Chironomidae from Lake Tanganyika, East Africa. 2. Chironominae (Chironomini and Tanytarsini)

Analysis of subfossil remains of larval Chironomidae in 38 surface-sediment samples from between 53 and 189 meter depth in Lake Tanganyika (East Africa) yielded 77 morphotypes, among which 7 Tanypodinae, 19 Orthocladiinae, and 51 Chironominae. Character-state differences between these morphotypes resemble differences at the species level in the better-known Holarctic fauna, hence we consider most of our Lake Tanganyika morphotypes equivalent to morphological species. Individual morphotypes were identified to species, genus, or tribe level depending on current alpha-taxonomic knowledge on the larvae of the group concerned, and the taxonomic resolution of preserved diagnostic features. This paper presents taxon diagnoses and an illustrated key to the Chironominae (Chironomini and Tanytarsini) in this collection. As the living chironomid fauna of Lake Tanganyika has never been comprehensively studied, we also briefly discuss faunistic aspects, and the ecology of the recovered species and genera in relation to benthic habitat diversity in Lake Tanganyika.     

三角褐指藻(Phaeodactylum tricornutum)形态及其变异现象的研究

分别对青岛、浙江、上海和厦门四地的三角褐指藻藻种及单个细胞克隆后多个藻株的形态及其变异现象进行了比较研究。青岛、上海藻种短期培养后，培养液细胞基本由梭形细胞组成；浙江和厦门藻种则基本由三出放射形细胞组成。正常培养液中卵形细胞比例均在0.1%以下。特定条件下，梭形和三出放射形细胞均能产生卵形细胞，卵形细胞也能发育成梭形或三出放射形细胞；三出放射形细胞可能经“突变”或“定向变异”转变成梭形细胞，而梭形细胞培养液中没有出现三出放射形细胞。培养液比重、温度及光照条件的改变短期内对细胞形态类型的转变没有明显影响；淡水和低温(4℃～8℃)的长期胁迫能使梭形和三出放射形藻株发生高比例的卵形细胞。     

Biological soil crusts exhibit a dynamic response to seasonal rain and release from grazing with implications for soil stability

In Northern Mexico, long-term grazing has substantially degraded semiarid landscapes. In semiarid systems, ecological and hydrological processes are strongly coupled by patchy plant distribution and biological soil crust (BSC) cover in plant-free interspaces. In this study, we asked: 1) how responsive are BSC cover/composition to a drying/wetting cycle and two-year grazing removal, and 2) what are the implications for soil erosion? We characterized BSC morphotypes and their influence on soil stability under grazed/non-grazed conditions during a dry and wet season. Light- and dark-colored cyanobacteria were dominant at the plant tussock and community level. Cover changes in these two groups differed after a rainy season and in response to grazing removal. Lichens with continuous thalli were more vulnerable to grazing than those with semi-continuous/discontinuous thalli after the dry season. Microsites around tussocks facilitated BSC colonization compared to interspaces. Lichen and cyanobacteria morphotypes differentially enhanced resistance to soil erosion; consequently, surface soil stability depends on the spatial distribution of BSC morphotypes, suggesting soil stability may be as dynamic as changes in the type of BSC cover. Longer-term spatially detailed studies are necessary to elicit spatiotemporal dynamics of BSC communities and their functional role in biotically and abiotically variable environments.     

罗氏沼虾(Macrobrachium rosenbergii)雌雄虾不同形态阈值性状的遗传变异分析

氏沼虾(Macrobrachium rosenbergii)雄虾有四种不同形态:小雄虾(SM)、橙色螯(OC)、蓝色螯(BC)和老蓝色螯(OBC)雄虾;雌虾分为四种:性腺未发育(IF)、性腺成熟(MOF)、抱卵(BF)和已产幼体(SF)的雌虾。已有研究表明不同形态的雌雄虾的体重存在显著差异,为了探讨是否可以对罗氏沼虾不同形态雌雄虾所占比例开展选择来间接提高产量,首次对上述性状的遗传参数及其与收获体重的遗传相关进行了评估。记录了罗氏沼虾核心育种群体两代共计40 935尾个体的形态和体重信息,使用父母本育种分析模型和阈值统计模型估计不同形态二分类(0和1)阈值性状在世代间和世代内的遗传参数,并使用两性状模型估计其与体重性状的遗传相关。方差组分估计结果表明,雄、雌虾不同形态阈值性状的遗传力估计值分别为0.08~0.12和0.04~0.22。雄虾形态OC、BC阈值性状与收获体重间为低度正相关(0.01~0.43)。雌虾形态IF、BF、SF阈值性状和收获体重性状之间为中等程度相关(–0.61~0.53)。在我国土塘养殖模式下,罗氏沼虾雌雄个体不同形态阈值性状存在可利用的加性遗传变异,具有较大的改良空间;选择OC形态雄虾并增加其在育种群体中比例,并不会降低其生长速度;选择IF形态雌虾并增加其在育种群体中的比例,可能会降低其生长速度。     

苏皖早二叠世孤峰组的Ruzhencevispongus uralicus的形态变化

本文详细研究了苏皖地区早二叠世孤峰组上部的放射虫Ruzhencevispongus uralicus化石。根据其形态的变化,认为该种可以分成3种形态型,即m. triradiatus. m. subtriangulus和m. uralicus。文章对这3种形态型进行了描述,同时还讨论了它们的相互关系,演化以及Ruzhencevispongus uralicus的生物地层学意义。     

Ecological implications of biomass and morphotype variations of bacterioplankton: an example in a coastal zone of the Northern Adriatic Sea (Mediterranean)

This study had the objective of quantifying the variability in abundance, cell volume, morphology and C content of a natural bacterioplankton community in a coastal zone of the North Adriatic Sea during two periods (February and June) of two consequent years (1996 and 1997). We used epifluorescence microscopy with Acridine Orange staining procedures and a microphotographic technique. Low variability in bacterial abundance (range 0.3–3.1 × 10⁵ cells ml^?1) occurred between summer and winter periods. Conversely, the cell volume and the calculated carbon content changed greatly with warm and cold periods (ranges: 0.015–0.303 μm³ and 5.83–42.17 fg C cell^?1, respectively). Elongated bacteria were dominant while coccoid cells prevailed only in February 1997. Biomass showed high variability (range 0.12–10.21 μg C l^?1) whilst the abundance did not show noticeable differences among the sampling periods. As a consequence, quantification of bacterial biomass based solely on cell abundance must be considered with caution because the true biomass could depend on variability in cell volumes and morphotypes.     

Subfossil Chironomidae from Lake Tanganyika, East Africa 1. Tanypodinae and Orthocladiinae

Analysis of subfossil remains of larval Chironomidae in 38 surface-sediment samples from between 53 and 189 m depth in Lake Tanganyika (East Africa) yielded 77 different morphotypes, including 7 Tanypodinae, 19 Orthocladiinae, and 51 Chironominae. Character-state differences between these morphotypes resemble differences at the species level in the better-known Holarctic fauna, hence we consider most of our Lake Tanganyika morphotypes equivalent to morphological species. Individual morphotypes were identified to species, genus, or tribe level depending on current alpha-taxonomic knowledge on the larvae of the group concerned, and the taxonomic resolution of preserved diagnostic features. This paper presents taxon diagnoses and an illustrated key to the Tanypodinae and Orthocladiinae in this Lake Tanganyika collection, with the aim to promote consistency of identification in studies using African Chironomidae as biological indicators of natural and anthropogenic environmental change in lacustrine ecosystems.