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 46 毫秒
1.
《Comptes Rendus Palevol》2008,7(8):557-569
New observations on the Late Miocene and Earliest Pliocene mustelids from the Middle Awash of Ethiopia are presented. The Middle Awash study area samples the last six million years of African vertebrate evolutionary history. Its Latest Miocene (Asa Koma Member of the Adu-Asa Formation, 5.54–5.77 Ma) and Earliest Pliocene (Kuseralee and Gawto Members of the Sagantole Formation, 5.2 and 4.85 Ma, respectively) deposits sample a number of large and small carnivore taxa among which mustelids are numerically abundant. Among the known Late Miocene and Early Pliocene mustelid genera, the Middle Awash Late Miocene documents the earliest Mellivora in eastern Africa and its likely first appearance in Africa, a new species of Plesiogulo, and a species of Vishnuonyx. The latter possibly represents the last appearance of this genus in Africa. Torolutra ougandensis is known from both the Late Miocene and Early Pliocene deposits of the Middle Awash. The genus Sivaonyx is represented by at least two species: S. ekecaman and S. aff. S. soriae. Most of the lutrine genera documented in the Middle Awash Late Miocene/Early Pliocene are also documented in contemporaneous sites of eastern Africa. The new observations presented here show that mustelids were more diverse in the Middle Awash Late Miocene and Early Pliocene than previously documented.  相似文献   

2.
In the last few million years, tropical Africa has experienced pronounced climatic shifts with progressive aridification. Such changes must have had a great impact on freshwater biota, such as Odonata. With about forty species, Trithemis dominates dragonfly communities across Africa, from rain-pools to streams, deserts to rainforests, and lowlands to highlands. Red-bodied species tend to favor exposed, standing and often temporary waters, have strong dispersal capacities, and some of the largest geographic ranges in the genus. Those in cooler habitats, like forest streams, are generally dark-bodied and more sedentary. We combined molecular analyses of ND1, 16S, and ITS (ITSI, 5.8S, and ITSII) with morphological, ecological, and geographical data for 81% of known Trithemis species, including three Asian and two Madagascan endemics. Using molecular clock analyses, the genus’s origin was estimated 6–9 Mya, with multiple lineages arising suddenly around 4 Mya. Open stagnant habitats were inferred to be ancestral and the rise of Trithemis may have coincided with savannah-expansion in the late Miocene. The adaptation of red species to more ephemeral conditions leads to large ranges and limited radiation within those lineages. By contrast, three clades of dark species radiated in the Plio-Pleistocene, each within distinct ecological confines: (1) lowland streams, (2) highland streams, and (3) swampy habitats on alternating sides of the Congo-Zambezi watershed divide; together giving rise to the majority of species diversity in the genus. During Trithemis evolution, multiple shifts from open to more forested habitats and from standing to running waters occurred. Allopatry by habitat fragmentation may be the dominant force in speciation, but possibly genetic divergence across habitat gradients was also involved. The study demonstrates the importance of combining ecological and phylogenetic data to understand the origin of biological diversity under great environmental change.  相似文献   

3.
The Silvertree (Leucadendron argenteum (L.) R.Br.) is an iconic tree to South Africans and tourists alike. This endangered species is endemic to the Cape Peninsula, the most southwestern part of Africa. Despite its visual presence, no population genetic data of L. argenteum are currently available, but such information is crucial for effective conservation management. A historical question is whether the inland populations are natural or planted? This study aimed to reveal the genetic structure and possible differences of L. argenteum populations on the Cape Peninsula and inland at Helderberg, Paarl Mountain and Simonsberg. It was expected that inland populations would exhibit reduced genetic variation due to their isolation from each other and the main Cape Peninsula gene pool. Furthermore, genetic differences between populations were expected to be higher at inland populations because they are further apart from each other, relative to the Peninsula populations. Plant leaf material was collected and AFLP was used to assess the genetic variation. In general, low genetic variation was present within all populations (mean Nei's gene diversity 0.11 ± 0.01) and no significant differences between Peninsula and inland populations were found. Minor differences in molecular variances were found between Peninsula and inland populations (PhiPt = 0.11), being double between Peninsula populations (PhiPt = 0.08) than between inland populations (PhiPt = 0.04). This supports a possible anthropogenic origin of inland populations. Although the genetic variation of populations is very similar, they should not be managed as a single gene pool. Inland populations are more similar to each other compared to the Peninsula ones and therefore might be managed as one genetic entity. In contrast, Peninsula populations show a higher degree of differentiation and should be managed to maintain genetic integrity by minimizing further cross planting.  相似文献   

4.
The ability of vertical flow (VF) constructed wetland systems to treat high-strength (ca. 300 mg L?1 of COD and ca. 300 mg L?1 total-nitrogen) wastewater under tropical climatic conditions was studied during a 5-month period. Nine 0.8-m diameter experimental VF units (depth 0.6 m) were used: three units were planted with Typha angustifolia L., another three units were planted with Cyperus involucratus Rottb and three units were unplanted. Each set of units were operated at hydraulic loading rates (HLRs) of 20, 50 and 80 mm d?1. Cyperus produced more shoots and biomass than the Typha, which was probably stressed because of lack of water. The high evapotranspirative water loss from the Cyperus systems resulted in higher effluent concentrations of COD and total-P, but the mass removal of COD did not differ significantly between planted and unplanted systems. Average mass removal rates of COD, TKN and total-P at a HLR of 80 mm d?1 were 17.8, 15.4 and 0.69 g m?2 d?1. The first-order removal rate constants at a HLR of 80 mm d?1 for COD, TKN and total-P were 49.8, 30.1 and 13.5 m year?1, respectively, which is in the higher range of k-values reported in the literature. The oxygen transfer rates were ca. 80 g m?2 d?1 in the planted systems as opposed to ca. 60 g m?2 d?1 in the unplanted systems. The number of Nitrosomonas was two to three orders of magnitude higher in the planted systems compared to the unplanted systems. Planted systems thus had significantly higher removal rates of nitrogen and phosphorus, higher oxygen transfer rates, and higher quantities of ammonia-oxidizing bacteria. None of the systems did, however, fully nitrify the wastewater, even at low loading rates. The vertical filters did not provide sufficient contact time between the wastewater and the biofilm on the gravel medium of the filters probably because of the shallow bed depth (0.6 m) and the coarse texture of the gravel. It is concluded that vertical flow constructed wetland systems have a high capacity to treat high-strength wastewater in tropical climates. The gravel and sand matrix of the vertical filter must, however, be designed in a way so that the pulse-loaded wastewater can pass through the filter medium at a speed that will allow the water to drain before the next dose arrives whilst at the same time holding the water back long enough to allow sufficient contact with the biofilm on the filter medium.  相似文献   

5.
Physical size has been critical in the evolutionary success of the genus Homo over the past 2.4 million-years. An acceleration in the expansion of savannah grasslands in Africa from 1.6 Ma to 1.2 Ma witnessed concomitant increases in physical stature (150–170 cm), weight (50–70 kg), and brain size (750–900 cm3). With the onset of 100,000 year Middle Pleistocene glacial cycles (“ice ages”) some 780,000 years ago, large-bodied Homo groups had reached modern size and had successfully dispersed from equatorial Africa, Central, and Southeast Asia to high-latitude localities in Atlantic Europe and North East Asia. While there is support for incursions of multiple Homo lineages to West Asia and Continental Europe at this time, data does not favour a persistence of Homo erectus beyond ~400,000 years ago in Africa, west and Central Asia, and Europe. Novel Middle Pleistocene Homo forms (780,000–400,000 years) may not have been substantially taller (150–170 cm) than earlier Homo (1.6 Ma–800,000 years), yet brain size exceeded 1000 cm3 and body mass approached 80 kg in some males. Later Pleistocene Homo (400,000–138,000 years) were ‘massive’ in their height (160–190 cm) and mass (70–90 kg) and consistently exceed recent humans. Relative brain size exceeds earlier Homo, yet is substantially lower than in final glacial H. sapiens and Homo neanderthalensis. A final leap in absolute and relative brain size in Homo (300,000–138,000 years) occurred independent of any observed increase in body mass and implies a different selective mediator to that operating on brain size increases observed in earlier Homo.  相似文献   

6.
The phylogeny of the family Sciaridae is reconstructed, based on maximum likelihood, maximum parsimony, and Bayesian analyses of 4809 bp from two mitochondrial (COI and 16S) and two nuclear (18S and 28S) genes for 100 taxa including the outgroup taxa. According to the present phylogenetic analyses, Sciaridae comprise three subfamilies and two genus groups: Sciarinae, Chaetosciara group, Cratyninae, and Pseudolycoriella group + Megalosphyinae. Our molecular results are largely congruent with one of the former hypotheses based on morphological data with respect to the monophyly of genera and subfamilies (Sciarinae, Megalosphyinae, and part of postulated “new subfamily”); however, the subfamily Cratyninae is shown to be polyphyletic, and the genera Bradysia, Corynoptera, Leptosciarella, Lycoriella, and Phytosciara are also recognized as non-monophyletic groups. While the ancestral larval habitat state of the family Sciaridae, based on Bayesian inference, is dead plant material (plant litter + rotten wood), the common ancestors of Phytosciara and Bradysia are inferred to living plants habitat. Therefore, shifts in larval habitats from dead plant material to living plants may have occurred within the Sciaridae at least once. Based on the results, we discuss phylogenetic relationships within the family, and present an evolutionary scenario of development of larval habitats.  相似文献   

7.
《Small Ruminant Research》2009,85(1-3):132-134
A longitudinal survey was conducted to determine the prevalence and loads of gastrointestinal parasites in goats raised by communal farmers of Qaukeni (QA) and Nkosana (NK) communities of Eastern Cape Province of South Africa between June 2007 and April 2008. One hundred and seventy one goats were weighed and had faecal samples collected from their recta in four seasons; cold-dry, hot-dry, hot-wet and the post-rainy seasons. The samples were examined by the modified McMaster technique for nematode egg types. Goats in QA weighed more (P < 0.05) than those in NK in the post-rainy, cold-dry and hot-dry seasons. However, in the hot-wet season, goats in NK had higher (P < 0.05) weights than those in QA. The most frequently detected gastrointestinal eggs were the strongyle egg type (68.4 ± 8.49 in QA and 96.1 ± 12.01 in NK), followed by coccidial oocysts (53.3 ± 8.76 in QA and 68.8 ± 8.00 in NK). The other identified nematodes were Strongyloides and Trichostrongylus egg types. Higher loads (P < 0.05) of strongyle eggs were observed in the hot-wet and post-rainy seasons, whilst the other egg types showed a peak in the hot-wet season. Strongyle egg counts were higher (P < 0.05) in NK compared to QA. The results indicate that strongyles are the major gastrointestinal egg types negatively affecting body weights of goats.  相似文献   

8.
《Process Biochemistry》2010,45(10):1638-1644
An open reading frame (XylX) with 1131 nucleotides from Paenibacillus campinasensis BL11 was cloned and expressed in E. coli. It encodes a family 11 endoxylanase, designated as XylX, of 41 kDa. The homology of the amino acid sequence deduced from XylX is only 73% identical to the next closest sequence. XylX contains a family 11 catalytic domain of the glycoside hydrolase and a family 6 cellulose-binding module. The recombinant xylanase was fused to a His-tag for affinity purification. The XylX activity was 2392 IU/mg, with a Km of 6.78 mg/ml and a Vmax of 4953 mol/min/mg under optimal conditions (pH 7, 60 °C). At pH 11, 60 °C, the activity was still as high as 517 IU/mg. Xylanase activities at 60 °C under pH 5 to pH 9 remained at more than 69.4% of the initial activity level for 8 h. The addition of Hg2+ at 5 mM almost completely inhibited xylanase activity, whereas the addition of tris-(2-carboxyethyl)-phosphine (TCEP) and 2-mercaptoethanol stimulated xylanase activity. No relative activities for Avicel, CMC and d-(+)-cellobiose were found. Xylotriose constitutes the majority of the hydrolyzed products from oat spelt and birchwood xylan. Broad pH and temperature stability shows its application potentials for biomass conversion, food and pulp/paper industries.  相似文献   

9.
Among several highly fossiliferous localities in the Bloubank Valley (Gauteng, South Africa), the Cooper's Cave System has been known since 1938 and has produced a rich fossil assemblage, including some remains of the early hominin Paranthropus robustus. In 2001, excavations began at a new locality, Cooper's D, which dates to ~1.4-1.5 Ma. Although hominins are relatively rare in the assemblage, remains of cercopithecoid primates are much more common. Craniodental fossils currently indicate the possible presence of at least three large-bodied cercopithecoid primate genera at Cooper's D: Gorgopithecus, Papio, and Theropithecus. In this study, we identify and describe > 100 cercopithecoid primate postcranial fossils representing all regions of the appendicular skeleton. The specimens come from several age classes and size morphs; more than one third of the fossils described are from sub-adult and juvenile individuals. The adult postcranial fossils vary substantially in size, with body masses estimated between 30 and 60 kg (from 16 of the better preserved specimens). The functional morphology of the postcranial remains indicate that these elements come from animals that likely utilized terrestrial substrates, but they remain difficult to definitively attribute to Gorgopithecus, Theropithecus, or Papio given the absence of associated skeletons. The smaller specimens likely belong to Papio while the larger ones can be attributed to the other two genera. Because Cooper's D has also yielded fossils of the early hominin Paranthropus robustus, this raises the question of how these four large-bodied, mostly terrestrial primates sympatrically utilized the landscape.  相似文献   

10.
The new species Pelargonium saxatile is a local endemic of sandstone rock pavement in the Elandskloofberge near Wellington in Western Cape Province, South Africa. One of just seven species of sect. Hoarea that have only the posterior two petals developed, it most closely resembles Pelargonium dipetalum from the southern Cape coastal lowlands but is distinguised by its rosette of numerous, small, mainly simple leaves, glabrous above and strigose beneath only along the midrib and sometimes also the veins. In addition, the pink flowers have the dorsal filament shorter, 4–5 mm long. We include a key to the species of the P. dipetalum group.  相似文献   

11.
《Comptes Rendus Palevol》2008,7(8):645-656
This study analyses the carnivore component of African fossil faunas from three time slices: 7–5 Ma, 4–3 Ma, and 2.5–1.2 Ma, using cluster analysis and principal coordinate analysis (PCO) of presence/absence data on genera. The faunas mostly cluster by time slice, with the exception of Laetoli (Tanzania) and Ahl al Oughlam (Morocco), which differ from all other faunas. The separation during the Late Miocene of a Chado–Libyan bioprovince from the remainder of Africa is supported. No such distinctions are present in the other time slices. Taxonomic distance is not generally correlated with geographic distance, though if Langebaanweg is removed from the 7–5 Ma time slice, the correlation at that time is significant. Comparison of these paleontological results with phylogeographic studies of modern species leads to some general comments on the analytic power of the fossil record with regard to interregional migrations.  相似文献   

12.
A molecular phylogeny is used to analyze the diversification history of Adesmia ser. psoraleoides, and its implications for understanding the historical assembly of the grasslands in the highlands of southern Brazil. All species of A. ser. psoraleoides were sampled, including multiple accessions for each species, plus representative species of the rest of Adesmia covering its geographic distribution. Phylogenetic analyses were based on nuclear and plastid DNA sequences, and a plastid matK phylogeny was dated. A. ser. psoraleoides is a well-supported monophyletic group, nested within the series bicolores, muricatae, subnudae, longisetae and candidae. The stem of A. ser. psoraleoides is c. 11 Mya, but most extant species diversified c. 3–5 Mya, suggesting that the flora of the subtropical grasslands of southern Brazil was assembled recently, co-incident with the expansion of other tropical grassland systems globally.  相似文献   

13.
Magnesium (Mg2 +) plays a critical role in many physiological processes. Mg2 + transport systems in Salmonella have been well documented, but those in Escherichia coli have not been fully elucidated. We examined the effects of corA, mgtA, yhiD and corC gene deletion on Mg2 + transport in E. coli. We obtained every combination of double, triple and quadruple mutants. The corA and mgtA double mutant required addition of 10 mM Mg2 + to Luria-Bertani (LB) medium for growth, and the corA, mgtA and yhiD triple mutant TM2 required a higher Mg2 + concentration. The Mg2 + requirement of the quadruple mutant was similar to that of TM2. The results demonstrated that either CorA or MgtA is necessary for normal E. coli growth in LB medium and that YhiD plays a role in Mg2 + transport under high Mg2 + growth conditions in E. coli. The Arabidopsis Mg2 + transporters, AtMRS2-10 and AtMRS2-11, were heterologously expressed in TM2 cells. TM2 cells expressing AtMRS2-10 and AtMRS2-11 could grow in LB medium that had been supplemented with 1 mM Mg2 + and without Mg2 + supplementation, respectively, and cell growth was inhibited by 2 mM AlCl3. The results indicated that the growth of TM2 expressing AtMRS2-10 and AtMRS2-11 reflected these AtMRS2 function for Mg2 + and aluminum. The E. coli TM2 cells are useful for functional analysis of Arabidopsis MRS2 proteins.  相似文献   

14.
《Endocrine practice》2015,21(3):226-230
ObjectiveWe investigated the correlation between the severity of diabetic retinopathy (DR) and carotid intima media thickness (IMT) as a marker of atherosclerosis in patients with type 2 diabetes.MethodsThe study group consisted of 140 normo-tensive Egyptian patients (68 males and 72 females) with type 2 diabetes and DR. Carotid IMT was evaluated using high-resolution B-mode ultrasonography. DR was assessed and graded using colored fundus photography and fundus fluorescein angiography, as either nonproliferative DR (NPDR) or proliferative DR (PDR).ResultsCarotid IMT was greater in patients with PDR compared to those with NPDR (1.094 ± 0.142 mm vs. 0.842 ± 0.134 mm; P < .001). Carotid IMT showed positive correlation with diabetes duration (P < .01), systolic blood pressure (P < .001), diastolic blood pressure (P < .01), fasting blood glucose (P < .01), postprandial blood glucose (PPBG) (P < .001), glycated hemoglobin (P < .01), total cholesterol (P < .01), triglycerides (TGs) (P < .001), and DR (P < .0001). No significant difference was found between males and females in any of the studied parameters. Multiple regression analysis revealed that the determinants of carotid IMT in the studied group were age (P < .01), PPBG (P < .01), TGs (P < .001), and DR (P < .0001).ConclusionOur study proves that both NPDR and PDR are strong determinants of carotid IMT and atherosclerosis in patients with type 2 diabetes. (Endocr Pract. 2015;21:226-230)  相似文献   

15.
Rhodacaridae are cosmopolitan mites mentioned as predators, although nothing is known about their potential as biological control agents. One of the objectives of the work reported in this paper was to evaluate the potential of Protogamasellopsis posnaniensis (Acari: Rhodacaridae) as predator of representative species of insects of the families Sciaridae (Bradysia matogrossensis (Lane)) and Thripidae (Frankliniella occidentalis (Pergande)), of mites of the family Acaridae (Tyrophagus putrescentiae (Schrank) and Rhizoglyphus echinopus (Fumouze & Robin) and of nematodes of the family Rhabditidae (Protorhabditis sp.). Another objective was to determine the biological cycle of P. posnaniensis when fed the prey on which it performed best in the preceding predation test. The study was conducted in a laboratory where the experimental units were maintained at 25 ± 1 °C, 97 ± 3% RH and in the dark. Although the predator was able to kill all prey species considered in this study, the most favorable prey were T. putrescentiae, F. occidentalis and Protorhabditis sp. Survivorship of the predator in predation tests was always 98% or higher. Life table biological parameters when the predator was fed T. putrescentiae were: Ro = 109.29; T = 19.06 days; λ = 1.28 e rm = 0.32 female/female/day. Despite preying upon larvae of B. matogrossensis, eggs of the former can also be killed by the latter. The results indicated that P. posnaniensis is a promising biological control agent, deserving additional studies on its possible use for the control of soil pests.  相似文献   

16.
Agricultural intensification is altering biodiversity patterns worldwide. Rapid and effective methods are needed to monitor these changes in farmland biodiversity, but it becomes both a cost- and time-prohibitive task, particularly for hyper-diverse groups such as arthropods. We evaluated the effectiveness of surrogates in irrigated and rainfed wheat fields in a Mediterranean farmland in NW Spain in order to get a rapid tool to assess arthropod biodiversity. We studied six groups with different ecological needs (i.e. Aphididae, Aphidiinae, Coccinellidae, Formicidae, Heteroptera and Syrphidae) at species level (147 species), genus (105), family (10, only Heteroptera) and order (19) level. Higher taxa, cross-taxa and subset-taxa or total richness approaches were tested as well as the correlation in composition between levels for the selected groups, and the influence of farming regime. Genus richness was a good surrogate of species richness in all six groups studied (R2 = 0.38–0.60), like family and order were for Heteroptera (R2 = 0.37 and 0.29, respectively). Cross-taxa analyses showed that Aphididae and Aphidiinae genera (R2 = 0.19 and 0.30, respectively) and species (R2 = 0.20 and 0.28, respectively) were good surrogates for Aphidiinae and Aphididae species respectively. Coccinellidae genera (R2 = 0.26) and species (R2 = 0.25) were good surrogates for Heteroptera species. Finally, Aphididae and Coccinellidae both at genera (R2 = 0.14 and 0.20, respectively) and at species levels (R2 = 0.12–0.22, respectively) were good surrogates for total species richness of all groups. Genera composition was the best surrogate for the species composition within each group. Farming regime had no influence on the relationships between surrogates and species patterns in most cases. Our results suggest that genera level is a useful surrogate for all the studied groups and family is appropriate for Heteroptera. Genus level provided a saving of 15% of identification time in Aphididae and 80% for Coccinellidae. This proves its usefulness to asses and monitor biodiversity in wheat croplands and the possibility to reduce costs.  相似文献   

17.
The astronomically tuned marls of the Monte Gibliscemi section, Sicily, constitute an archive to trace the late Miocene palaeoenvironmental conditions (~ 9.7–7.0 Ma) in North Africa. Here we have utilised carbonate content and Al-normalised geochemical proxies to trace changes in terrigenous source area and bottom-water ventilation. The terrigenous input into the section is dominated by North African river systems draining into the Eastern Mediterranean. The proxy parameters indicate that the palaeoenvironmental conditions in North Africa were humid from 9.5 Ma onward with high fluvial input to the Mediterranean. Increases in the Si/Al and Mg/Al ratios occurred from 8.4 to 8.2 Ma and from 8.05 to 7.75 Ma, with maximum values similar to those of Messinian diatomites. These peaks indicate conditions of enhanced biosiliceous productivity and the presence of authigenic clay formation. Sluggish water circulation in the Mediterranean during those times is inferred from the Mn/Al and V/Al behaviour. Late Miocene changes of the Betic (southern Spain) and Rifian (Morocco) Mediterranean–Atlantic gateways are interpreted as the driving force for the changes in water circulation and the transgression associated with the opening of the Rifian corridor is interpreted to occur at 7.8 Ma.  相似文献   

18.
Terrein has potential application in the fields of medicine, cosmetology and agriculture, however, the chemical synthesis of terrein with single configuration is a difficult task, and the biosynthesis of terrein always results in low production (ca. 0.33–400 mg/L). In this study, we reported an Aspergillus terreus strain PF26 which could produce (+)-terrein on a high level. After the selection of a suitable basic medium, the component concentrations were optimized using Plackett–Burman design and response surface methodology. Consequently, an optimal medium containing 28.41 g glucose, 23.18 g maltose, 20.00 g mannitol, 8.52 g malt extract, 10.00 g monosodium glutamate 10.00 g NH4Cl in 1 L ASW was obtained, and a high (+)-terrein production of 3.71 g/L fermentation broth was achieved, which represents the highest fermentation production of (+)-terrein to date. The result highlighted the industry's potential of A. terreus strain PF26 in the production of bioactive (+)-terrein on a large-scale.  相似文献   

19.
The tailed frog Ascaphus truei Stejneger, 1899 is the most primitive extant anuran and the sister taxon to the clade of all other living frogs. The species occupies two disjunct ranges in the Northwest region of North America: the Cascade Mountains and coastal area from British Columbia to Northern California, and an inland range in the northern Rocky Mountains and the Blue and Wallowa mountains. A previous study led to the isolation of eight peptides with antimicrobial activity (termed the ascaphins) from skin secretions of A. truei from the coastal range. The present study has used peptidomic analysis to identify the products of orthologous ascaphin genes in electrically-stimulated skin secretions from inland range specimens. Structural characterization of the peptides demonstrated that ascaphins from the inland range contained the following amino acid substitutions compared with orthologs from the coastal range frogs: ascaphin-1 (Ala12  Glu), ascaphin-3 (Asp4  Glu), ascaphin-4 (Ala19  Ser), ascaphin-5 (Lys12  Thr), and ascaphin-7 (Gly8  Ser and Ser20  Asn). Orthologs of ascaphins-2, -6, and -8 were not identified but a paralog of ascaphin-5, identical to ascaphin-5 from coastal range frogs, was found. The data support the claims, derived from analysis of the nucleotide sequences of mitochondrial genes, that the inland populations of the tailed frog should be recognized as a distinct species, the Rocky Mountain tailed frog Ascaphus montanus and that the divergence of the species from A. truei probably occurred in the late Miocene (approximately 10 Mya).  相似文献   

20.
Croton macrostachyus Hochst. ex Del. (Euphorbiaceae) is a multipurpose, deciduous, and medium sized tree of pantropic occurrence. Because the species has numerous useful qualities (e.g., establishment and growth in disturbed sites, drought tolerance, fast growth rate, copious litter/necromass production, suitability for agroforestry, and ability to attract avian frugivores), its speedy restoration has become increasingly critical. Germination studies were therefore conducted on seeds pooled from five widely located provenances with a view to supporting efforts geared toward the speedy propagation and restoration of this valuable tree species. Seed pretreatments were achieved using various dilution levels of plant-derived smoke–water (1:1, 1:10, 1:100 and 1:1000), as well as gibberellic acid (GA3) or potassium nitrate (KNO3) ranging in concentration from 0.1 to 100 μmol. The control was to use distilled water for seed pretreatment. Seeds were germinated under either illuminated (ca 60 μmol m 2 s 1; cool-white fluorescent lamp) or non-illuminated conditions. Experiments on the impact of seed storage durations, as well as storage temperatures were also conducted. The study found that germination percentage (GP: ca 90%), and mean germination time (MGT: 14 days) were significantly (P < 0.001) better when seeds were pretreated with smoke–water and germinated under non-illuminated conditions, than when these were pretreated with various concentrations of GA3 or KNO3 (GP and MGT of ca 65% and 20 days, respectively). Germination percentage (GP) and germination vigor (GV) declined with increasing storage-time for all storage temperatures, but GV's decline was faster for seeds stored at 22 °C than for those stored at 5 and 15 °C. On the other hand, mean germination time (MGT) increased significantly (P < 0.01) with seed storage-time of up to 8 months at 5, 15, and 22 °C, but the increase was more marked for seeds stored at 22 °C than for those stored at 5 and 15 °C. From these investigations, it is concluded that germination of C. macrostachyus seeds through use of smoke–water is faster, cheaper, and technically less demanding, compared to that of either GA3 or KNO3. The study also concludes that C. macrostachyus is intermediate between orthodox and recalcitrant seeds, and that it is non-photoblastic.  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