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1.
An increasing diversity of highly specialized pollination systems are being discovered, many of which are likely to be vulnerable to anthropogenic landscape modification. Here, we investigate if a specialized pollination system limits the persistence of C aladenia huegelii (Orchidaceae), an endangered species pollinated by sexual deception of thynnine wasps. Once locally common in part of its geographical range, C. huegelii is now largely restricted to small habitat remnants in urban areas. Pollinator surveys coupled with DNA barcoding detected a single pollinator taxon, a small form of Macrothynnus insignis. Phylogenetic analysis revealed that small M. insignis from within the range of C. huegelii are strongly divergent from other wasp populations, suggesting that some reproductive isolation may exist. Although common in intact landscapes outside the range of C. huegelli, small M. insignis individuals were recorded at only 4% of sites in suitable C. huegelii habitat. Accordingly, reproductive success in C. huegelii was low compared with related Caladenia spp., with 33–60% of populations failing to set fruit in any given year. As such, populations are likely to now persist primarily through individual plant longevity rather than reproduction. Due to the low reproductive success of C. huegelii, ongoing human intervention will almost certainly be needed to sustain the species. Future research will need to focus on optimizing hand pollination to maintain reproduction and high seed fitness. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 179 , 511–525. 相似文献
2.
Comparative studies of tree-building methods have shown minimum evolution to be in general an accurate criterion for selecting
a true tree. To improve the use of this criterion, this paper proposes a method for rapidly and directly calculating a length
of a dichotomous tree without having to resort to branch length calculations. This direct calculation (DC) method applies
to the complete final topology, giving equal importance to each branch after a dichotomy. According to this method, the tree
length S
DC
is S
DC
=∑
i
∑
j
( D
ij
/2
Bij
) = (∑
i<j
∑ D
ij
2
Bmax−Bij
)/2
Bmax
−1 where D
ij
is the observed distance between taxa i and j,
B
ij
is the number of branches connecting i and j,
Bmax is the greatest B
ij
in the tree, and the powers of two are due to the dichotomy of the tree. This tree length expression may be used as a rapid
method for selecting the shortest tree from a set of hypothetical or subobtimal trees.
Received: 2 March 2000 / Accepted: 24 March 2000 相似文献
3.
A DNA fragment (ADG2, 310 bp) 77% homologous to the gene N (resistance to tobacco mosaic virus in Nicotiana glutinosa) and 53% homologous to RPP5 (resistance to Peronospora parasitica in Arabidopsis thaliana) was amplified by PCR from the diploid potato genotype 2 x(v-2)7 that carries the gene Ry
adg
located on chromosome XI and conferring extreme resistance to potato virus Y(PVY). Sequence comparison revealed that ADG2
spans a region corresponding to the predicted kinase-2 and kinase-3a motifs in N and RPP5. One of the 12 nucleotide differences detected between ADG2 and a homologous fragment from a PVY-susceptible potato genotype
was located within the predicted kinase-3a motif. This single nucleotide substitution of G→C, resulting in an amino-acid substitution
Ser→Thr, abolished the BbvI recognition site of ADG2, which was shown to distinguish all tested potato genotypes carrying Ry
adg
from those lacking this gene, irrespective of the genetic background and ploidy level. This PCR-based resistance marker,
developed using a resistance gene analogue as a target, is the first example of a PCR-based marker that is generally applicable
for selection of an economically important trait in potato.
Received: 28 November 1998 / Accepted: 28 December 1998 相似文献
4.
We assessed the potential for microbial interactions influencing a well-documented host–pathogen system. Mycoplasma agassizii is the known etiological agent of upper respiratory tract disease in Mojave desert tortoises (Gopherus agassizii), but disease in wild animals is extremely heterogeneous. For example, a much larger proportion of animals harbor M. agassizii than those that develop disease. With the availability of a new quantitative PCR assay for a microbe that had previously been implicated in disease, Pasteurella testudinis, we tested 389 previously collected samples of nasal microbes from tortoise populations across the Mojave desert. We showed that P. testudinis is a common commensal microbe. However, we did find that its presence was associated with higher levels of M. agassizii among the tortoises positive for this pathogen. The best predictor of P. testudinis prevalence in tortoise populations was average size of tortoises, suggesting that older populations have higher levels of P. testudinis. The prevalence of co-infection in populations was associated with the prevalence of URTD, providing additional evidence for an indirect interaction between the two microbes and inflammatory disease. We showed that URTD, like many chronic, polymicrobial diseases involving mucosal surfaces, shows patterns of a polymicrobial etiology. 相似文献
5.
Zebrafish embryos demonstrate robust swimming behavior, which consists of smooth, alternating body bends. In contrast, several motility mutants have been identified that perform sustained, bilateral trunk muscle contractions which result in abnormal body shortening. Unlike most of these mutants, accordion ( acc) dta5 demonstrates a semidominant effect: Heterozygotes exhibit a distinct but less severe phenotype than homozygotes. Using molecular‐genetic mapping and candidate gene analysis, we determined that accdta5 mutants harbor a novel mutation in atp2a1, which encodes SERCA1, a calcium pump important for muscle relaxation. Previous studies have shown that eight other acc alleles compromise SERCA1 function, but these alleles were all reported to be recessive. Quantitative behavioral assays, complementation testing, and analysis of molecular models all indicate that the accdta5 mutation diminishes SERCA1 function to a greater degree than other acc alleles through either haploinsufficient or dominant‐negative molecular mechanisms. Since mutation of human ATP2A1 results in Brody disease, an exercise‐induced impairment of muscle relaxation, accdta5 mutants may provide a particularly sensitive model of this disorder. genesis, 48:354–361, 2010. © 2010 Wiley‐Liss, Inc. 相似文献
6.
Localization of nanos ( nos) mRNA to the posterior pole of the Drosophila oocyte is essential for abdominal segmentation and germline development during embryogenesis. Posterior localization is mediated by a complex cis-acting localization signal in the nos 3' untranslated region that comprises multiple partially redundant elements. Genetic analysis suggests that this signal is recognized by RNA-binding proteins and associated factors that package nos mRNA into a localization competent ribonucleoprotein complex. However, functional redundancy among localization elements has made the identification of individual localization factors difficult. Indeed, only a single direct-acting nos localization factor, Rumpelstiltskin (Rump), has been identified thus far. Through a sensitized genetic screen, we have now identified the Argonaute family member Aubergine (Aub) as a nos localization factor. Aub interacts with nos mRNA in vivo and co-purifies with Rump in an RNA-dependent manner. Our results support a role for Aub, independent of its function in RNA silencing, as a component of a nos mRNA localization complex. 相似文献
7.
A morphological account on the endosymbiosis between Amphiscolops sp and Amphidinium sp is given, based on scanning and transmission electron microscopy observations. The algal symbionts (15–20 µm in diameter) are found among cells of the peripheral parenchyma. Amphidinium sp. has a single pyrenoid of the multiple-stalked type, with several chloroplast lobes radiating from it. A comparison with A. klebsii is made. Our observations reinforce the assumption of selectivity of Amphiscolops for the symbiotic genus Amphidinium. 相似文献
8.
Consider the two linear regression models of Y ij on X ij, namely Y ij = β io + β il X ij + ε ij, j = 1,2,…, ni, i = 1,2, where ε ij are assumed to be normally distributed with zero mean and common unknown variance σ 2. The estimated value of a mean of Y 1 for a given value of X 1 is made to depend on a preliminary test of significance of the hypothesis β 11 = β 21. The bias and the mean square error of the estimator for the conditional mean of Y 1 are given. The relative efficiency of the estimator to the usual estimator is computed and is used to determine a proper choice of the significance level of the preliminary test. 相似文献
9.
To avoid detrimental interactions with intestinal microbes, the human epithelium is covered with a protective mucus layer that traps host defence molecules. Microbial properties such as adhesion to mucus further result in a unique mucosal microbiota with a great potential to interact with the host. As mucosal microbes are difficult to study in vivo, we incorporated mucin‐covered microcosms in a dynamic in vitro gut model, the simulator of the human intestinal microbial ecosystem (SHIME). We assessed the importance of the mucosal environment in this M‐SHIME (mucosal‐SHIME) for the colonization of lactobacilli, a group for which the mucus binding domain was recently discovered. Whereas the two dominant resident Lactobacilli, Lactobacillus mucosae and Pediococcus acidilactici, were both present in the lumen, L. mucosae was strongly enriched in mucus. As a possible explanation, the gene encoding a mucus binding ( mub) protein was detected by PCR in L. mucosae. Also the strongly adherent Lactobacillus rhamnosus GG (LGG) specifically colonized mucus upon inoculation. Short‐term assays confirmed the strong mucin‐binding of both L. mucosae and LGG compared with P. acidilactici. The mucosal environment also increased long‐term colonization of L. mucosae and enhanced its stability upon antibiotic treatment (tetracycline, amoxicillin and ciprofloxacin). Incorporating a mucosal environment thus allowed colonization of specific microbes such as L. mucosae and LGG, in correspondence with the in vivo situation. This may lead to more in vivo‐like microbial communities in such dynamic, long‐term in vitro simulations and allow the study of the unique mucosal microbiota in health and disease. 相似文献
10.
We investigated directly an early stage of the development of an endosymbiosis between an alga and a ciliate, beginning from
a non-associated stage by conducting a long-term microcosm culture composed of a green alga ( Chlorella vulgaris), a bacterium ( Escherichia coli) and a ciliate ( Tetrahymena thermophila) for three years. During this culture, Chlorella-harboring Tetrahymena appeared and increased in frequency. We examined the adaptive characteristics of the T. thermophila in association with the C. vulgaris derived from a well-established microcosm culture maintained for 1164–1400 days, and compared it with the original culture
of T. thermophila. The T. thermophila with the associated, intracellular C. vulgaris grew at a lower density of E. coli than the original T. thermophila with the original C. vulgaris, and the former survived longer than the latter in the absence of E. coli. These results suggest that this induced algal-ciliate association confers some fitness advantage at least to the host under
the conditions of less or no available food such as E. coli. Although the algal-ciliate association is not completely stable, this quasi-stable association may enable the host to exploit
a new niche through the advantages of mixotrophy. 相似文献
11.
An “empirical” distribution function F?(x, y) is estimated from measured points ( xi, yi), i =1(1) n, of a continuous two-dimensional random variable ( X, Y) with unknown continuous density function f(x, y). The density function F?(x, y) of F?(x, y) is a mixture of n two-dimensional normal densities. The first order moments of F?(x, y) are the sample means x and y, whilst the second order moments are only proportional to the sample variances and the sample covariance. This “empirical” distribution F?(x, y) is used for evaluation of an empirical regression curve where a free parameter has to be fixed by an optimality criterion. The procedure is demonstrated by an example from morphometrical research. 相似文献
12.
Starting from a stochastic model for the spread of a parasitic infection in a spatially distributed host population we describe the way to a continuum formulation by a deterministic model in terms of a nonlinear partial differential equation and an integro-differential equation. The hosts are assumed to occupy fixed spatial positions, whereas the parasites are mobile, however can propagate only within the hosts. To perform the continuum limit we suppose that the size N
h
of the host population, the size N
p
of the parasite population, and the ratio N
p
/N
h
tend to infinity. Accordingly, the parameters determining the time evolution of the host and parasite populations are rescaled suitably.Parts of this work have been elaborated during a stay at the Institute of Applied Mathematics at the University of Zürich 相似文献
13.
The evolution of complex organisms such as animals requires a large expansion of the number of genes controlling developmental
events. In addition, it is thought that domains are shuffled between genes to further increase the complexity and generate
new types of genes and functions. Working with the Caenorhabditis elegans homeobox gene ceh-43, the orthologue of fly Distal-less ( Dll), we observed sequence similarity to the C. elegans gene fkh-1. Now, with the complete genomic sequence available, we examined this similarity in detail. The region of similarity is confined
essentially to one exon in the carboxy terminus of the two genes. Based on the gene structure, we think that an exon of fkh-1 was duplicated to the carboxy terminus of ceh-43, where it was incorporated as the last exon. This duplication event seems to have happened recently since the similarity
on the nucleotide level is higher than the sequence similarity between fkh-1 of C. elegans and C. briggsae. Potentially the duplication event was mediated via a short region of sequence similarity between the two open reading frames
of the genes. This duplication event clear shows that a part of a gene can successfully be juxtaposed to another gene. These
events may perhaps not be rare.
Received: 28 March 1999 / Accepted: 8 June 1999 相似文献
14.
Sinorhizobium fredii USDA191 is a Gram-negative bacterium capable of forming nitrogen-fixing nodules on soybean roots. The USDA191 idhA gene encoding myo-inositol dehydrogenase, an enzyme necessary for myo-inositol utilization, is known to be involved in competitive nodulation and nitrogen fixation. In Bacillus subtilis, myo-inositol dehydrogenase catalyzes the first step of the myo-inositol catabolic pathway. Recently iolE was identified as the gene encoding 2-keto- myo-inositol dehydratase, which catalyzes the second step in the pathway. Here we report the presence of 2-keto- myo-inositol dehydratase activity in free-living USDA191 cells cultured in a medium containing myo-inositol. An iolE ortholog was cloned from USDA191. USDA191 iolE was expressed in Escherichia coli as a His 6-tag fusion and purified to exhibit 2-keto- myo-inositol dehydratase activity. Inactivation of USDA191 iolE led to defective myo-inositol utilization. USDA191 iolE partially complemented a B. subtilis iolE deficient mutant. These results suggest that S. fredii USDA191 utilizes a myo-inositol catabolic pathway, analogous to that of B. subtilis, involving at least idhA and iolE. 相似文献
15.
We have developed a genetic transformation system for a freeze-tolerant yeast Kluyveromyces thermotolerans. K. thermotolerans spheroplasts could be transformed with a YRp-type vector containing an autonomously replicating sequence (ARS) of Saccharomyces cerevisiae. However, transformation with a YEp-type vector containing a replication origin of S. cerevisiae 2 μM DNA was not successful. The cycloheximide resistance gene (RIM-C) of Candida maltosa and the URA3 gene of S. cerevisiae were successfully used to transform a prototrophic strain of K. thermotolerans and an Ura ? mutant of this yeast isolated in this study, respectively. Transformation was also possible by using intact cells treated with lithium salts or thiol compounds. The YRp-type vectors were maintained as plasmids in the transformants under selective conditions. This is the first report of successful transformation of K. thermotolerans. 相似文献
16.
DNA sequencing has been used to construct two molecular phylogenies at the intrafamily and intrageneric level within the Rutaceae. Analysis of trnL- trnF sequence data for five Rutaceae subfamilies has shown that there is no molecular support for the current subfamily classifications within the Rutaceae. The Dictyolomatoideae and Spathelioideae belong to a clade separate from the clades containing the remaining Rutaceae subfamilies. Rutoideae and Citroideae do not form discrete clades which suggests a reassessment of the subfamily classification is necessary, particularly as Ruta falls within the majority Citroideae clade. Flindersioideae forms a clade within the Rutaceae and does not form a separate family or form a clade with Meliaceae.Sequencing of 17 Flindersia species produces a similar phylogeny to that proposed by other authors using morphological methods with two exceptions. The molecular phylogeny indicates F. amboinensis is associated with F. fournieri and F. laevicarpa and, in addition, F. oppositifolia and F. pimenteliana were found to be genetically identical. 相似文献
17.
The production of unicellular algae is laborious and is a major constraint for the culturing of aquatic filter-feeders. Because
of their small particle size and their high protein content yeasts are considered as a promising substitute for micro-algae.
Furthermore, recent work has shown that baker's yeast can be converted into a digestible diet for Artemia by chemical treatment. The present study documents the use at laboratory scale of this manipulated yeast as an algal substitute
for the culture of two anostracan species.
The experiments were conducted with the brine shrimp artemia franciscana and the fairy shrimp Streptocephalus proboscideus. A similar experimental set-up was used for both species. The algal diet, consisting of Dunaliella tertiolecta for A. franciscana and Selenastrum capricornutum for S. proboscideus, was substituted at various levels by two types of treated baker's yeast: a fresh form and a dried product which was rich
in highly unsaturated fatty acids (HUFA).
The chemically-treated yeast offers promising possibilities as an algal substitute for Artemia; i.e. replacing 75% of the algae by the dried yeast resulted in similar survival and even higher growth rates in comparison with
the reference algal diet; for the treated fresh yeast similar results could be achieved by up to 95% substitution. For S. proboscideus, a substitution of 75% by either of the yeast products resulted in good survival, though growth did not exceed 80% of the
observed growth in the algal control. A diet consisting solely of yeast resulted in poor survival for larvae of both species.
Experiments were run to investigate whether this was due to a sub-optimal feeding regime, nutritional deficiencies, or deterioration
of the water quality. 相似文献
18.
In the course of our examination for the alkaloid productivities of Streptomyces strains, Streptomyces sp. NA–15 was found to produce a new alkaloid, pyrindicin, in the culture medium. The strain NA–15 was found to be a variant of Streptomyces griseoflavus and was designated as S. griseoflavus var. pyr indie us nov. var.After the culture conditions for pyrindicin production were studied, pyrindicin was obtained as its hydrochloride (mp 145°C, decomp.) from the cultured broth. The compound was shown to possess weak antimicrobial and several pharmacological activities. The LD 50 of the hydrochloride (ip, in mice) was 87 mg/kg. 相似文献
19.
A DNA fragment containing a Klebsiella oxytoca gene for polygalacturonate trans-eliminase was cloned into the kanamycin resistance transposon Tn 5. This new transposon, designated Tn 5-Pga
+, had a transposition frequency of 1×10 -6. The broad host range plasmid pR751::Tn 5-Pga
+ was conjugally transferred to a variety of genetic backgrounds. The ability to degrade polygalacturonate was expressed in Aeromonas hydrophila, Alcaligenes eutrophus, Azotomonas insolita, Escherichia coli, Pseudomonas putida and Rhodopseudomonas sphaeroides, but not in Zymomonas mobilis.Abbreviations PGA
polygalacturonate
- UGA
unsaturated galacturonic acid
- PATE
polygalacturonate trans-eliminase
- PG
polygalacturonase
- CVP
crystal-violet pectate 相似文献
20.
From a pollen tube cDNA library of Petunia inflata, we isolated cDNA clones encoding a protein, PPE1, which exhibits sequence similarity with plant, bacterial, and fungal pectin esterases. Genomic clones containing the PPE1 gene were isolated using cDNA for PPE1 as a probe, and comparison of the cDNA and genomic sequences revealed the presence of a single intron in the PPE1 gene. During pollen development, PPE1 mRNA was first detected in anthers containing uninucleate microspores; it reached the highest level in mature pollen and persisted at a high level in in vitro germinated pollen tubes. The observed expression pattern of the PPE1 gene suggests that its product may play a role in pollen germination and/or tube growth. 相似文献
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