首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
The study of samples from various waterbodies (rivers, lakes, reservoirs, and seas) has shown that S. agassizensis manifests a significant morphological variability of qualitative and quantitative characters (the valve diameter and its relief, the mantle height, and the presence and arrangement valve face fultoportulae) which distinguish this species from other species with similar a morphology (S. neoastraea, S. heterostylus, S. alpinus, and S. maximus). Original and literature data on the morphology, ecology, and distribution of S. agassizensis has allowed the author to specify its taxonomic position, refer the species to the synonymy of S. neoastraea, and extend the diagnosis of the latter.  相似文献   

2.
Despite the great economic importance of citrus, its phylogeny and taxonomy remain a matter of controversy. Moreover pathogens of increased virulence and dramatic environmental changes are currently spreading or emerging. The objectives of the present paper, measuring genetic variability and studying its pattern of distribution, are crucial steps to optimize sampling strategies in the search of genotypes that tolerate or resist these threatening factors within the huge array of Citrus and Citrus related species. Their intraspecific and intrageneric variability was studied comparatively by means of ten enzymatic systems using eight different measures. The analysis of ten enzymatic systems allowed us to distinguish all the species and all but one artificial hybrid. The species with the lowest genotypic variability are C. myrtifolia, C. deliciosa (willow leaf mandarin), C. paradisi (grapefruit), C. limon (lemon) and C. sinensis (sweet orange), while Severinia buxifolia shows the highest value. A broad spectrum of heterozygosity values was found in the collection. Lemons (C. limon, C. meyeri, C. karna, C. volkameriana), limes (C. aurantifolia, C. limettioides, C. lattifolia) and C. bergamia show a very high percentage of heterozygosity which indicates an origin through interspecific hybridization. Two main factors limit genetic intraspecific variability: apomictic reproduction, where nucellar embryos are much more vigorous than the zygotic ones, and nurserymen selecting against variability in the seedling stage of the rootstocks or in propagating the scion cultivars vegetatively. Additionally, self-pollination appears in some species mainly used as rootstocks which would explain their low heterozygosity values. Genetic differences between species and genera are in general high, which suggests that adaptation might have played an important role during the evolution of the orange subfamily.  相似文献   

3.
A new halophilous–gypsicolous species of Corynopuntia, C. halophila (Cactaceae), is described and illustrated from the state of Coahuila, north-eastern Mexico. It is morphologically similar to the diploid Corynopuntia moelleri, but it differs by some traits, such as body size and some unusual morphological features which are here reported for the first time; there are also ecological and karyological differences, as the latter study revealed that C. halophila is a polyploid with 2n = 44 chromosomes. Diagnostic morphological characters from similar taxa are discussed and arranged in a taxonomic key. Knowledge of the species ecology, biogeography, demography and conservation status is also provided.  相似文献   

4.
A small thecate dinoflagellate was encountered during winter and spring in the phytoplankton community of a shallow, brackish and hypertrophic pond in the South of France. The abundance of material permitted its identification, using scanning electron microscopy, as Oblea rotunda Balech ex Sournia. However, morphological features showed some discrepancies with the typical characteristics of O. rotunda. Environmental hydrographic parameters in the pond were very different from marine ecosystems where O. rotunda is usually reported. In this polluted and alkaline pond, salinity was low, ranging from 1.1 to 6.2 p.s.u.; the maximum densities of O. rotunda (greater than 1?×?105 cells l???1) were observed at temperatures around 13°C, after a Cylindrotheca closterium?–?Heterocapsa rotundata bloom in early spring. These two species and other abundant taxa of the phytoplankton had seasonal patterns that could explain the presence of O. rotunda, since they could have been a food for this heterotrophic species. As this population showed most of the morphological criteria of O. rotunda, but with some variability and a different ecology, it is better considered as a variant of the marine species, rather than as a new species. This study provides additional data on the ecological and morphological features of this poorly known small peridinioid species, previously only reported from open seas and oceans.  相似文献   

5.
A mimic scale-worm was found associated with the athecate hydroid Solanderia secunda, commonly found on reefs of the NW coast of North Sulawesi, Indonesia. The species resembled Medioantenna clavata Imajima 1997, which was originally described without any reference to a symbiotic mode of life and later reported to be living on a solanderiid hydroid both in Japanese waters. A detailed morphological analysis led us to consider the Indonesian specimens as a new species, namely Medioantenna variopinta sp. nov., which is congeneric with the Japanese species. The new species differs from the type material of M. clavata as it has elytra with one prominent finger-like papilla and all neurochaetae with unidentate tip, instead of an elytral lump and both unidentate and bidentate neurochaetae on segment two. In turn, the Japanese worms associated with Solanderia are here referred to our new species. Two morphological features in M. variopinta sp. nov. are rather unusual among scale-worms. One of them is its extremely high level of bilateral asymmetry and antero-posterior variability in elytral distribution and the other one is its elongated, upwardly directed nephridial papillae. The morphology and geographical distribution of the host together with the known characteristics of the symbiotic association have also been highlighted.  相似文献   

6.
The diatom flora of the Salton Sea, California   总被引:1,自引:0,他引:1  
We report on diatom species of the Salton Sea, a highly saline (43 g l–1) inland lake in California. We identified and photographed all diatom taxa encountered in the phytoplankton and benthos of the Salton Sea and its immediate tributaries. Ninety-four taxa were distinguished based on their morphological features using light- and electron microscopy. In the Salton Sea, there are four general categories of diatom assemblages related to their habitats: (1) A planktonic assemblage composed of Chaetoceros muelleri var. subsalsum, Cyclotella choctawhatcheeana, Cyclotella sp., Cylindrotheca closterium, Pleurosigma ambrosianum, Thalassionema sp.; (2) a benthic assemblage with diatoms that live on the bottom (e.g. genera Caloneis, Diploneis, Entomoneis, Gyrosigma, Plagiotropis, Pleurosigma, Surirella and Tryblionella), or in algal mats (Proschkinia bulnheimii, several species of Navicula and Seminavis gracilenta); (3) an epiphytic community attached to the macroscopic green algae which grow on the rocks and other hard surfaces near shore (e.g. Achnanthes brevipes, Licmophora ehrenbergii, Tabularia parva); and (4) a freshwater assemblage composed of species that get washed in by the rivers and other inflows discharging into the Sea (e.g. Achnanthidium minutissimum, Cocconeis pediculus, Cyclotella atomus, C. scaldensis, Nitzschia elegantula, T. weissflogii). The most striking feature of the phytoplankton is the abundance of species formerly known only from marine environments; this is not surprising given the high salinity and the peculiar history of the lake.  相似文献   

7.
Long‐term data sets, covering several decades, could help to reveal the effects of observed climate change on herbivore damage to plants. However, sufficiently long time series in ecology are scarce. The research presented here analyzes a long‐term data set collected by the Hungarian Forest Research Institute over the period 1961–2009. The number of hectares with visible defoliation was estimated and documented for several forest insect pest species. This resulted in a unique time series that provides us with the opportunity to compare insect damage trends with trends in weather patterns. Data were analyzed for six lepidopteran species: Thaumetopoea processionea, Tortrix viridana, Rhyacionia buoliana, Malacosoma neustria, Euproctis chrysorrhoea, and Lymantria dispar. All these species exhibit outbreak dynamics in Hungary. Five of these species prefer deciduous tree species as their host plants, whereas R. buoliana is a specialist on Pinus spp. The data were analyzed using general linear models and generalized least squares regression in relation to mean monthly temperature and precipitation. Temperature increased considerably, especially over the last 25 years (+1.6°C), whereas precipitation exhibited no trend over the period. No change in weather variability over time was observed. There was increased damage caused by two species on deciduous trees. The area of damage attributed to R. buoliana decreased over the study period. There was no evidence of increased variability in damage. We conclude that species exhibiting a trend toward outbreak‐level damage over a greater geographical area may be positively affected by changes in weather conditions coinciding with important life stages. Strong associations between the geographical extent of severe damage and monthly temperature and precipitation are difficult to confirm, studying the life‐history traits of species could help to increase understanding of responses to climate change.  相似文献   

8.
Abstract: Palaeophis maghrebianus belongs to the Palaeophiinae (Palaeophiidae). This snake subfamily is relatively poorly known, and it is mainly represented by disarticulated vertebrae and ribs and by a few vertebral segments. Its intracolumnar variability remains also poorly understood. The discovery of new isolated vertebrae and vertebral segments of Palaeophis maghrebianus in the Ypresian (Lower Eocene) Phosphates of Morocco enables us to provide a more detailed diagnosis of this species and to describe its intracolumnar variability. Moreover, the new material reveals that this species could reach gigantic size being, with Palaeophis colossaeus, one of the two longer palaeophiids. The microanatomical and histological analysis of some vertebrae illustrating diverse positions along the vertebral column reveals the presence of osteosclerosis, especially in the anterior and mid‐precloacal regions. The occurrence of this osseous specialization implies a role in buoyancy and body trim control in this taxon, which is considered a shallow marine dweller based on its anatomical features and geological data. Palaeophis maghrebianus also displays a dense vascular network suggesting a growth speed, and thus a metabolic rate, much higher than in the biggest extant snakes.  相似文献   

9.
Candida dubliniensis pathogenic species, which shares many phenotypic features with C. albicans, may be misidentified in the microbiology laboratory. The growth on DRBC agar at 25 °C was shown to be a new tool for differentiation between C. dubliniensis and C. albicans. All 27 isolates of C. dubliniensis showed in this medium rough colonies (peripheral hyphal fringes) and abundant chlamydospore production, while all 103 isolates of C. albicans showed smooth colonies without fringes or chlamydospores. DRBC agar allowed the differentiation of C. albicans from C. dubliniensis with 100 % sensitivity and specificity.  相似文献   

10.
Exceptional chromosomal variability makesCtenomys an excellent model for evolutionary cytogenetic analysis. Six species belonging to three evolutionary lineages were studied by means of restriction endonuclease and C-chromosome banding. The resulting banding patterns were used for comparative analysis of heterochromatin distribution on chromosomes. This combined analysis allowed intra- and inter-specific heterochromatin variability to be detected, groups of species belonging to different lineages to be characterized, and phylogenetic relationships hypothesized from other data to be supported. The “ancestral group”,Ctenomys pundti andC. talarum, share three types of heterochromatin, the most abundant of which was also found in C. aff.C. opimus, suggesting that the latter species also belongs to the “ancestral group”. Additionally, within the subspeciesC. t. talarum, putative chromosomal rearrangements distinguishing two of the three chromosomal races were identified. Two species belong to an “eastern lineage”,C. osvaldoreigi andC. rosendopascuali, and share only one type of heterochromatin homogeneously distributed across their karyotypes.C. latro, the only analyzed species from the “chacoan” lineage, showed three types of heterochromatin, one of them being that which characterizes the “eastern lineage”.C. aff.C. opimus, because of its low heterochromatin content, is the most primitive karyotype of the genus yet described. The heterochromatin variability showed by these species, reflecting the evolutionary divergence toward different heterochromatin types, may have diverged since the origin of the genus. Heterochromatin amplification is proposed as a trend withinCtenomys, occurring independently of chromosomal change in diploid numbers.  相似文献   

11.
Abstract

We measured some aspects of the population ecology of an arboreal aphid, Paradoxaphis plagianthi, that might contribute to its rarity. Models were fitted to data on the development rate and variability of solitary aphids in the laboratory, from larviposition to maturity, which were similar to those of several common European tree‐dwelling aphids. Life tables suggested that the intrinsic rate of population increase increases linearly with temperature to a maximum of 0.123/day at 20°C. Aphid colonies raised in controlled environments showed a lower rate of increase, presumably due to crowding effects. The rate of increase of field colonies was further depressed, probably reflecting the action of other background mortality factors. New data for seasonal population trends in the field matched previously published results, showing an increase in spring followed by a rapid decline and low summer populations. A caging experiment failed to detect any differences in host suitability in late spring between Plagianthus regius, the main host, and Hoheria angustifolia or Parsonsia heterophylla, which may act as “spill‐over” hosts in some circumstances. While the results do not explain the rarity of P. plagianthi, they suggest new hypotheses to target future work.  相似文献   

12.
In 2001 and 2003, several occipital fragments of a single mature skull were unearthed on the site of les Pradelles (Marillac-le-Franc, Charente). The archaeological context of the deposit allowed us to provisionally assign the remains to the Neandertal taxon. A morphometric study of this piece was conducted in order to confirm its placement in this lineage. Some features observed on this specimen and commonly described among Neandertals (e.g. the presence of a suprainiac fossa) as well as dimensional data locate the les Pradelles occipital within the morphological variability of Neandertals.  相似文献   

13.
A new ammonia fungus, Coprinopsis austrophlyctidospora, is described from Nothofagus and Pinus forests in New Zealand and from Eucalyptus forest in Australia. In ecology and macro-morphology, this species is similar to the Northern Hemisphere species C. phlyctidospora, but the new species differs in morphological characters of the basidiospore, i.e., in having a plage, more minute surface warts, and the smaller size of the basidiospore.  相似文献   

14.
Most nominal fan worm species belonging to the genus Parasabella Bush, 1905, and Sabellomma Nogueira, Fitzhugh & Silva‐Rossi, 2010 (Sabellidae, Annelida) lack unique morphological diagnostic features. Species diagnoses rely on a combination of attributes, often making reference to characters that are qualitatively or quantitatively continuous. This, together with a lack of knowledge about phenotypic intraspecific variation in most species, suggests that the sole use of morphological features is insufficient to identify and characterize some of these species. Examination of collections revealed that Parasabella is a common and diverse group of sabellids along the Australian coastline, although it had only been recorded here twice. The genus Sabellomma is here reported in Australia for the first time. Comparison of morphological data and nuclear (internal transcribed spacer) and mitochondrial (cytochrome oxidase I) DNA sequence data of 30 terminals in a range of analyses allowed us to assess the monophyly of Parasabella and its sister‐group relationship with Sabellomma and to examine some of the species boundaries and genetic diversity within lineages. The combined sequence data results indicate the presence of seven distinct genetic Parasabella lineages in Australia, four of which are assigned to previously described species (three are new records for Australia), and two are considered as a complex of species sharing a unique combination of characters, one of which is described as new. Another Parasabella species with distinct atypical radiolar eyes and a species of Sabellomma are also described as new. © 2015 The Linnean Society of London  相似文献   

15.
16.
Sponges are the dominant invertebrates in many Antarctic communities, where they play a decisive structural function thanks to their abundance and large sizes. However, current knowledge on Antarctic sponges remains poor even with respect to basic aspects such as taxonomy. Here, we report on an Antarctic species of the genus Stylocordyla, which has been recorded for a long time under the name of the boreal S. borealis due to spicule and growth habit similarities. A thorough study of dense populations of the only Stylocordyla species known up to now from the eastern zone of the Weddell Sea as well as the re-examination of several specimens (including the type material) of S. borealis has allowed us to assess the variability of the boreal species and to confirm that the austral species is not S. borealis (Lovén, 1868) but a new species of Stylocordyla, different from the other congeners recorded from southern latitudes. The new species S. chupachups commonly dwells on horizontal or slighted sloped hard bottoms of the continental shelf of Weddell Sea, from 100 m to below 400 m depth, although the densest populations usually occur between 150 and 300 m. It is a pioneer species in areas that have been scoured by icebergs, and thus its presence may be considered an indicator of recent colonisation.  相似文献   

17.
Cephaloziella tahora, a new species of Cephaloziella is described and illustrated from a lowland forest habitat in eastern Taranaki in the North Island of New Zealand. It has similarities to six other New Zealand species of Cephaloziella, and appears closest in New Zealand to Cephaloziella aenigmatica R.M.Schust. It is defined by a unique combination of features and distinguished from C. aenigmatica and other New Zealand species by having entire, distant leaves that reach the dorsal stem mid-line, and have large conspicuous hemispherical and hemi-ellipsoidal papillae, underleaves on gemmiparous and gynoecial shoots, and by its dioecy. The addition brings the number of New Zealand species of Cephaloziella to 18, 12 of which are endemic to New Zealand.  相似文献   

18.
A new species, Bilacunaria anatolica A. Duran (Apiaceae) is described and illustrated from southwest Turkey. The species grows on eroded marly stony slopes and in openings of Pinus brutia forest in Fethiye district (C2 Mu?la province). Bilacunaria anatolica, an endemic confined to southwest Anatolia, is related to B. microcarpa and B. scabra. It is also similar to the Mediterranean species Cachrys crassiloba and C. cristata in terms of habit, but differs in fruit characteristics. Diagnostic morphological and carpo‐anatomical characters are discussed. Notes are also presented on ecology and conservation status. In addition, pollen characteristics and mericarp surface features are examined by SEM. The geographical distribution of the new species and related species is mapped.  相似文献   

19.
20.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号