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 31 毫秒
1.
The present paper reports on the study of French and Danish strains of Acinetospora crinita (Harvey) Kornmann and their responses in growth and reproduction to various combinations of temperature and salinity. The distribution of the species in both hemispheres may be explained by the temperature requirements for growth and reproduction. The limit at lower latitudes in both hemispheres is a lethal limit, at higher latitudes it is probably a growth and reproduction limit. Acinetospora crinita is a stenohaline species and only occurs in high salinity areas in Danish waters. This paper also discusses the status of the genus Acinetospora, which has been considered to be a phase in the life history of some Feldmannia and Hincksia species. We conclude that there are several characters that justify independent status at the genus and species level. The large variation in reproductive patterns is enigmatic and adds to the taxonomic confusion. In A. crinita various reproductive structures occur: megasporangia/acinetosporangia, unilocular sporangia (some are apomeiotic), monosporangia, plurilocular sporangia which are presured to be gametangia, and a strain is known from the United States with reproduction solely by fragmentation. The combination of reproductive structures appears to be unique to specific strains.  相似文献   

2.
We have characterized Tdr1, a family of Tc1-like transposable elements found in the genome of zebrafish (Danio rerio). The copy number and distribution of the sequence in the zebrafish genome have been determined, and by these criteria Tdr1 can be classified as a moderately repetitive, interspersed element. Examination of the sequences and structures of several copies of Tdr1 revealed that a particular deletion derivative, 1250 by long, of the transposon has been amplified to become the dominant form of Tdr1. The deletion in these elements encompasses sequences encoding the N-terminal portion of the putative Tdr1 transposase. Sequences corresponding to the deleted region were also detected, and thus allowed prediction of the nucleotide sequence of a hypothetical full-length element. Well conserved segments of Tc1-like transposons were found in the flanking regions of known fish genes, suggesting that these elements have a long evolutionary history in piscine genomes. Tdr1 elements have long, 208 by inverted repeats, with a short DNA motif repeated four times at the termini of the inverted repeats. Although different from that of the prototype C. elegans transposon Tc1, this inverted repeat structure is shared by transposable elements from salmonid fish species and two Drosophila species. We propose that these transposons form a subgroup within the Tc1-like family. Comparison of Tc1-like transposons supports the hypothesis that the transposase genes and their flanking sequences have been shaped by independent evolutionary constraints. Although Tc1-like sequences are present in the genomes of several strains of zebrafish and in salmonid fishes, these sequences are not conserved in the genus Danio, thus raising the possibility that these elements can be exploited for gene tagging and genome mapping.  相似文献   

3.
Comparative investigations of hormone concentration and pattern during ontogeny can offer insight regarding the evolution of growth trajectories. Anubis (Papio anubis) and hamadryas (P. hamadryas) baboons exemplify primate populations at a crucial stage of phylogenetic divergence. Though not reproductively isolated, the species are distinguished by consistent morphological, behavioral, and physiological differences, including trajectories of growth and maturation associated with divergent male reproductive strategies. As a step toward understanding the proximate causes of these differences, we tested several hypotheses regarding the relationship of growth-regulatory hormones and binding proteins (insulin-like growth factor-I, insulin-like growth factor binding protein-3 [IGFBP-3], growth hormone binding protein, and testosterone) to growth in several measurements. We collected samples (N = 559) across 13 field seasons, from 7 different social groups. Samples came from 398 different individuals. We sampled 285 once; 76, twice; 29, three times; 5, four times; and 3, five times. Although ages at peak hormone concentrations were not significantly different, concentrations of all hormones and binding proteins measured, except testosterone, were higher in hamadryas than in anubis. All factors measured correlated positively with growth in both species, and IGFBP-3 and testosterone in particular correlated significantly with growth in all measurements. Overall, our findings suggest a role for the growth hormone/insulin-like growth factor axis in producing distinctive patterns of growth in these species.  相似文献   

4.
We diagnose new subfossil specimens belonging to the extinct palaeopropithecid, Mesopropithecus,from several caves at the Ankarana massif in northern Madagascar. They include three partial crania with mandibles, and the first vertebrae, ribs, clavicle, pelvis, ulna, and hand and foot bones of Mesopropithecusever found. Several other postcranial elements are known for this northern variant of Mesopropithecusand for previously described species from central and southern Madagascar. The new materials cannot be accommodated in either currently recognized species of this genus and are,hereby, given the name Mesopropithecus dolichobrachion. M. dolichobrachionis the second new species of extinct subfossil lemur to be found in the caves of Ankarana. It is unlike the two previously described species of this genus primarily in its larger size, different limb proportions, and aspects of its long bone morphology. Most notable is the fact that this is the only species of Mesopropithecuswith the forelimb longer than the hind limb— hence the name, the “long-armed” Mesopropithecus.Various characteristics place M. dolichobrachionphenetically closest (of species belonging to Mesopropithecus)to Babakotia radofilai, Archaeoindris,and Palaeopropithecus.If these similarities are derived specializations rather than primitive for palaeopropithecids, a new generic name will be required.  相似文献   

5.
We describe a distinct type of heteromorphic basal frond element in four species of the seed-fern foliage Dicroidium, based principally on a survey of plant-fossil collections from the Triassic of Antarctica. The modified foliar elements are conspicuously enlarged, and arise at wide angles and obliquely to the frond plane. Those of D. elongatum and D. crassinerve arise more or less directly from the petiole base; they are overall wedge- to fan-shaped with variably dissected margins and fan-shaped venation. Those of D. odontopteroides and D. dubium are (sub)circular, reniform, or obcordate, also with fan-shaped venation, or divided into narrow tongue-shaped segments with alethopteroid venation. The basal elements of some species commonly occur isolated. By analogy with comparable structures among other plant groups, we conclude that the basal elements represent a distinct, early leaf-ontogenetic architectural unit in the frond bauplan of Dicroidium, which provides an important additional character for a more accurate delimitation and systematic classification. Similar structures also occur on the corystosperm reproductive organs Umkomasia and Pteruchus. It appears that the basal elements were particularly common among high-latitude Dicroidium trees that flourished in a strongly seasonal light regime. We hypothesize that the modified elements may represent the initial foliar outgrowths during spring flush, ensuring a rapid re-initiation of sap flow and metabolic activity after the extended period of winter dormancy.  相似文献   

6.
Trichosporon (Dikarya: Basidiomycota) is a genus of anamorphic yeasts typically associated with soil and water, although many species are causative agents of diseases in animals and man. Here we provide the first compelling evidence that spiders can be occasionally colonized by at least two Trichosporon species. Trichosporon dulcitum (Berkhout) Weijman 1979 was isolated from the exoskeleton of purse-web spider Atypus piceus, while Trichosporon porosum (Stautz) Middelhoven, Scorzetti & Fell 2001 was isolated from the exoskeleton of purse-web spider Atypus affinis. Both of the species were identified based on DNA sequence analysis of the host specimens displaying macroscopic signs of the superficial white mycosis on their exoskeleton. Only two specimens with macroscopic signs of superficial yeast growth were identified among the 125 individuals of A. affinis, A. piceus and Atypus muralis examined that were collected at various sites throughout the Czech Republic. The consistent burrow microclimate, uninterrupted occupancy of the single burrow for several subsequent years, and presence of prey remnants in the burrow below the purse-web may play a role in the course of infection of the mygalomorphs examined. The phylogenetic relationships of Trichosporon species are analyzed, concluding that association with invertebrates clusters predominantly among four groups of closely related species in independent Trichosporon clades.  相似文献   

7.
The Tc1 transposable element is the most widespread family among animal transposon and these elements consist of an inverted repeat (IR) sequence flanking a transposase gene that belongs to Class II type transposon, which is highly conserved in the genome of the nematode C. elegans. In order to characterize Tc1-like transposable elements from several fishes, PPTN (Tc1-like transposon was isolated from Pleuronectes platessa, marine flatfish species) IR primer-specific amplified elements were cloned from the genomic DNA of several fishes. Transposable elements were found in ridged-eye flounder (Pleuronichthys cornutus) and inshore hagfish (Eptatretus burgeri) and named as PCTN and EBTN, respectively. Amino acid sequence alignment and phylogenetic analysis confirmed that the PPTN-like transposons belonged to the Tc1 superfamily of transposons, but they comprised a unique clade of Tc1-like transposons. The IR-PCR analysis using MMTS-IR and PPTN-IR specific primers from Paralichthys olivaceus (Paralichthyidae), Paraplagusia japonica (Cynoglossidae), P. yokohamae (Pleuronectidae) and Pagurus cornutus (Pleuronectidae) (within the same order, Pleuronectiformes but different families) exhibited mutually exclusive distribution of Tc1 family-derived PPTN and MMTS-like transposons in these fish genomes. These results indicate that Tc1 family-derived PPTN and MMTS related Tc1-like transposable elements have uniquely evolved in piscine genome, and can be used as phylogenetic markers for the distribution of subfamilies of Tc1-like transposon and the involvement of horizontal and vertical transmission in the evolution of fish genome.  相似文献   

8.
Traditionally, biostratigraphy of the terminal Famennian (Upper Devonian) and lower part of the Tournaisian (Mississippian) is based on phylogeny of the conodont genus Siphonodella Branson and Mehl. This study is focused on a Siphonodella species with a long taxonomical history. For the last three decades it was known as S. hassi Ji, 1985 and was used as a zonal index for the eponymic hassi Zone, used worldwide. However, this species faces several taxonomical problems. The main issue is the homonymy of S. hassi and S. cooperi hassi Thompson and Fellows, 1970. However, S. cooperi hassi is a subjective junior synonym of S. obsoleta Hass, 1959. The oldest junior synonym of S. hassi is S. wilberti Bardasheva, Bardashev, Weddige and Ziegler, 2004, and, according to a statement by the International Commission on Zoological Nomenclature, the latter represents the only available name for this species. An additional problem is the similar morphology of early ontogenetic stages of S. wilberti and S. quadruplicata Branson and Mehl, 1944, the youngest stratigraphically important siphonodellid species. In advanced ontogenetic stages, P1 elements that possess two rostral ridges belong to S. wilberti only. The smaller P1 elements having two or less rostral ridges comprise the S. wilberti- S. quadruplicata plexus. Maintenance of the wilberti Zone in the Tournaisian global zonation is suggested.  相似文献   

9.
Our study concerns 10 genera and 26 species of cyprinodontid fish. In the cytoplasm of spermatids tubulin polymerizes in various forms according to species. We have demonstrated the presence of classic microtubules with a diameter of 24 nm and also of tubules of smaller diameter (15 run) and greater diameter (30 to 50 nm). Microtubules are very numerous in the cytoplasm of certain species. They may be arranged without any order or form bundles which may contain several hundred parallel elements. They never form a manchette. In two species (Aplocheilichthys normani and Epiplatys fasciolatus) only spermatids that degenerate show this peculiarity. The microtubules present two kinds of decorations. The first type are small elements composed of MAP which enable two or more microtubules to link up. The second type are curved tubulin elements that give the microtubule that bear them the appearance of an incomplete doublet. Doublets and triplets may also be formed. Cyprinodontidae spermatocytes and spermatids probably synthesize a very large quantity of tubulin which polymerizes in certain species.  相似文献   

10.
11.
Linepithema micans (Forel) (Hymenoptera: Formicidae) is reported to occur from eastern Brazil to central Argentina in pasture or grassland, forest and second growth riparian forest, nesting under stones, rotting wood, and sandy soil. However, information on this species is poor and its ecological interactions and role as pests are unknown. Linepithema humile (Mayr), a closely related species to L. micans, known as the Argentine ant, is native to South America, and was accidentally introduced to several regions of the world. Recent studies have shown that other related species, such as L. micans, could become as pestiferous as L. humile because of its phylogenetic proximity. Samples of L. micans from different habitats in Southern Brazil were characterized by sequencing of the mitochondrial DNA. Sequences were compared to previously obtained sequences from samples of L. humile and the genetic distance and differences in the tRNALeu structure were investigated. Our data identified three haplotypes of L. micans, two of which were observed in ant populations closely associated with the Brazilian ground pearl Eurhizococcus brasiliensis (Hempel) (Hemiptera: Margarodidae), a soil scale that is a serious pest of vineyards. The third haplotype was identified in ants from populations invading residences in urban habitats.  相似文献   

12.
The occurrence of Archaeopsittacus sp. (Psittaciformes) in the fossil deposits of Sansan (France) is reported, testifying to a survival of this genus in the Middle Miocene, as Archaeopsittacus verreauxi was described from the Early Miocene of Saint-Gérand-le-Puy (France) and was recorded only from its type locality. The data discussed here indicate the presence of two parrot species from Sansan, as it is the type locality of another parrot species, Pararallus dispar, only known from this locality. The differences between the humeri of these two taxa are described in detail, together with the differences from the other European fossil parrot species. The presence of more than one species of parrot in the same locality is not rare, but in Europe it is recorded in Sansan for the second time. Evidence for parrots also confirms the paleoenvironmental reconstruction of Sansan, as parrots are primarily arboreal species. Archaeopsittacus also represents one of the few common elements between the Early and Middle Miocene European bird assemblages.  相似文献   

13.
《Comptes Rendus Palevol》2019,18(4):442-448
The Rhinocerotidae material from the latest Miocene of Sahabi (Libya) is here revised in detail in order to clarify its systematic position and the paleobiogeographic implications. The family is represented by four specimens only at Sahabi, a phalanx, a mandible, a second upper molar (M2), and a second upper premolar (P2). Except for the phalanx, which can be only identified at the family level, the morphology and the dimensions of these specimens have revealed the presence of three taxa: Aceratheriini vel Teleoceratina, Brachypotherium lewisi and ‘Diceros’ sp. The presence of the large-sized Blewisi has been suggested in several papers, but without a detailed comparison or critical revision. The Brachypotherium from Sahabi also resembles Brachypotherium heinzelini, suggesting a probable synonymy between this species and Blewisi. A P2 from Sahabi differs from several species belonging to Ceratotherium, including Ceratotherium neumayri, and it resembles the genus Diceros. The rhinoceros association (Brachypotherium and a dicerotine) recognized at Sahabi has been recorded at Lothagam (Kenya), suggesting a biogeographic affinity with the eastern Africa assemblage.  相似文献   

14.
Populations of three coexisting intertidal gastropods, Nerita atramentosa Reeve, Bembicium nanum (Lamarck) and Cellana tramoserica (Sowerby), were sampled from a shore in Botany Bay, New South Wales, from July 1972 to September 1973. The recruitment and growth rates of each species were analysed from size frequency distributions. Mortality of each age cohort, and longevity, were estimated from analyses of the densities of Nerita atramentosa and Bembicium nanum.Nerita atramentosa showed no significant mortality during the first two years on the shore, but high mortality (at an instantaneous rate of 0.084 deaths/individual/month) after reaching the age of reproductive maturity, which was 20 months from settlement and at a mean shell-length of 13.5 mm. No growth could be detected after reproductive maturity was reached. Longevity of N. atramentosa was estimated as 3–5.5 years. Bembicium nanum juveniles showed higher mortality (at an instantaneous rate of 0.233 deaths/individual/month) than reproductively mature animals (0.060 deaths/individual/month). Reproductive maturity was reached at a mean shell-breadth of 11.0mm, i.e., about ten months after settlement on the shore. Longevity was estimated as from 4–8 years. Cellana tramoserica showed different growth patterns depending on the time of settlement.The three species showed different patterns of growth and life history relating to variable recruitment (which was demonstrated in all three species) and different rates of mortality of age cohorts.  相似文献   

15.
A new sample of 65 specimens representing a minimum number of 15 individuals of the Eurasian antelope Gazellospira torticornis is described from the Lower Pleistocene fossil sites of Dafnero (DFN, N. Greece). The intrapopulation comparisons highlight that several cranial (frontal sinuses, inter-frontal sutures, longitudinal grooves, degree of the horn-cores torsion, and development of anterior keel) and postcranial features are likely subject to sexual dimorphism, suggesting a mixed-herd DFN population of both males and females with a social distribution estimated at a ∼1:2 ratio (seven females and three presumed males). The analysis also reveals that both cranial and postcranial elements of G. torticornis are subjected to a strong temporal linear regression during the Villafranchian; this trend appears more evident in western than eastern European territories. Furthermore, for contemporaneous samples, the metapodials of G. torticornis show higher dimensions in northern (above ca. 42.5° of latitude) than in meridional latitudes. A preliminary ecomorphological study suggests that open landscapes with plains and quite homogeneous substrates was the preferred habitat of Gazellospira from Dafnero. A revision of Eurasian specimens and taxa referred to several genera and species of heteronymous spiral horned antelopes spanning from the Late Pliocene to the Early Pleistocene, allows us to propose synonymizing Gazellospira gromovae with Antilospira? zdanskyi, and to recognize Parastrepsiceros sokolovi as an early eastern subspecies of G. torticornis. Our morphological analysis does not support recent results about close phylogenetic relationships of Gazellospira with either Antilospira or Spirocerus. A biogeographic scenario is proposed, in which Gazellospira originates in the peri-Black Sea region with a radiation westwards and eastwards during the early Villafranchian.  相似文献   

16.
Insects face several (environmental) abiotic stressors, including low temperature, which cause the failure of neuromuscular function. Such exposure leads insects toa reversible comatose state termed chill-coma, but the consequences of this state for the organism biology were little explored. Here, the consequences of the chill-coma phase were investigated in two of the main stored product pest species – the red flour beetle Tribolium castaneum (larvae and adults) and the rice weevil Sitophilus oryzae (adults). For this purpose, a series of low-temperature shocks were used to estimate the chill-coma recovery time (CCRT), survival, nutrition and weight gain/growth of T. castaneum (larvae and adults) and S. oryzae, as well as the development of T. castaneum life stages. The relatively long CCRT was characteristic of beetle larvae, at different low-temperature shocks, and CCRT increased with decreasing temperatures and increasing exposure intervals for both pest species. The survival was little affected by the low-temperature shocks applied, but such shocks affected insect feeding and growth. Tribolium castaneum larvae was more sensitive than adults of both insect species. Moreover, the relative consumption and weight gain of S. oryzae adults were lower than those of T. castaneum adults and mainly larvae, while feeding deterrence was not affected by low temperature shocks, unlike food conversion efficiency. Low-temperature shocks, even under short duration at some temperatures, significantly delayed development. The lower the temperature and the higher the exposure period, the more delayed the development. Thus, the physiological costs of chill-coma are translated into life-history consequences, with potential implications for the management of this insect pest species in stored products and even more so on red flour beetles and rice weevils.  相似文献   

17.
Flavonoid compounds from 36 of the 38 known taxa of the genusArceuthobium (dwarf mistletoes) were examined. The flavonoid chemistry of the genus is rather uniform, all taxa producing 3-O-glycosides of the flavonols quercetin and myricetin. No infraspecific chemical variation was encountered, and in those instances where subspecific taxa are recognized, their chemistry was uniform. At the subgeneric level, members of subgenusArceuthobium synthesize primarily glucosides, whereas galactosides are more common in subgenusVaginata. In two of the four Old World species of subgenusArceuthobium (A. juniperi- procerae andA. oxycedri) only myricetin 3-O-glucoside was detected. There are no absolute flavonoid differences between subgenera, sections, or series. On the other hand, flavonoids are useful in several instances at the species level. In several cases, chemical data lend support to the recognition of species which in the past have been considered doubtfully distinct on the basis of morphology.  相似文献   

18.
Genus Macaca (Cercopithecidae: Papionini) is one of the most successful primate radiations. Despite previous studies on morphology and mitochondrial DNA analysis, a number of issues regarding the details of macaque evolution remain unsolved. Alu elements are a class of non-autonomous retroposons belonging to short interspersed elements that are specific to the primate lineage. Because retroposon insertions show very little homoplasy, and because the ancestral state (absence of the SINE) is known, Alu elements are useful genetic markers and have been utilized for analyzing primate phylogenentic relationships and human population genetic relationships. Using PCR display methodology, 298 new Alu insertions have been identified from ten species of macaques. Together with 60 loci reported previously, a total of 358 loci are used to infer the phylogenetic relationships of genus Macaca. With regard to earlier unresolved issues on the macaque evolution, the topology of our tree suggests that: 1) genus Macaca contains four monophyletic species groups; 2) within the Asian macaques, the silenus group diverged first, and members of the sinica and fascicularis groups share a common ancestor; 3) Macaca arctoides are classified in the sinica group. Our results provide a robust molecular phylogeny for genus Macaca with stronger statistical support than previous studies. The present study also illustrates that SINE-based approaches are a powerful tool in primate phylogenetic studies and can be used to successfully resolve evolutionary relationships between taxa at scales from the ordinal level to closely related species within one genus.  相似文献   

19.
Since the discovery of the extinct species Halitherium schinzii in the Mainz Basin, sirenian remains from the German Oligocene are usually assigned to this taxon according to the assumption that this would be the only sea cow species there. The attempts of several authors to determine morphological distinctions on the species level remain unconsidered until today. The new find of a partial sea cow skeleton from the lower Oligocene of Bottrop-Kirchheller Heide (western Germany) stirs up the debate on splitting the species currently referred to as H. schinzii. The Bottrop specimen morphologically corresponds to skullcaps from the Mainz Basin and the Belgian Oligocene, which were the basis for the introduction of new species in the past, but are considered synonymous with H. schinzii today. Despite its fragmentary preservation, the new sirenian record reveals shared morphological features mainly referring to the supraoccipital, such as a distinctly rostrad indenting nuchal crest and a reduced external occipital protuberance. These features are in contrast to the prominent morphology of the specimens generally associated with H. schinzii and support the assumed presence of at least two morphotypes in the Oligocene of Central Europe. Additionally, the sea cow from Bottrop-Kirchheller Heide represents the first occurrence of skeletal elements, which are not preserved in the known specimens from this morphotype so far and may contribute to a better understanding of intra- and/or interspecific differences within Sirenia.  相似文献   

20.
Species of Laccaria are described from the eastern Himalayas, in the Xizang Autonomous Region of China, more commonly known as Tibet. Specimens were collected during several expeditions over a 12-year time span. Nuclear ribosomal internally transcribed spacer regions 1 and 2 including and 5.8S (ITS) as well as the 5' end of the large subunit (28S) sequence data were generated for 22 specimens from Tibet and analyzed in a dataset of 115 Laccaria samples. The results documented seven species from this region, five of which represent currently undescribed species. The taxonomy of Tibetan Laccaria is discussed, five new species are proposed, and an artificial key that includes extralimital species from Asia is provided.  相似文献   

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