A fast algorithm for computing geodesic distances in tree space.

Comparing and computing distances between phylogenetic trees are important biological problems, especially for models where edge lengths play an important role. The geodesic distance measure between two phylogenetic trees with edge lengths is the length of the shortest path between them in the continuous tree space introduced by Billera, Holmes, and Vogtmann. This tree space provides a powerful tool for studying and comparing phylogenetic trees, both in exhibiting a natural distance measure and in providing a euclidean-like structure for solving optimization problems on trees. An important open problem is to find a polynomial time algorithm for finding geodesics in tree space. This paper gives such an algorithm, which starts with a simple initial path and moves through a series of successively shorter paths until the geodesic is attained.

A set of primers for plastid indels and nuclear microsatellites in the invasive plant Heracleum mantegazzianum (Apiaceae) and their transferability to Heracleum sphondylium.

This study reports the isolation and polymorphism characterization of four plastid indels and six nuclear microsatellite loci in the invasive plant Heracleum mantegazzianum. These markers were tested in 27 individuals from two distant H. mantegazzianum populations. Plastid indels revealed the presence of five chlorotypes while five nuclear microsatellite loci rendered polymorphism. Applications of these markers include population genetics and phylogeography of H. mantegazzianum. A very good transferability of markers to Heracleum sphondylium was demonstrated.

High-resolution organellar genome analysis of Triticum and Aegilops sheds new light on cytoplasm evolution in wheat.

We have utilised polymorphic chloroplast microsatellites to analyse cytoplasmic relationships between accessions in the genera Triticum and Aegilops. Sequencing of PCR products revealed point mutations and insertions/deletions in addition to the standard repeat length expansion/contraction which most likely represent ancient synapomorphies. Phylogenetic analyses revealed three distinct groups of accessions. One of these contained all the non- Aegilops speltoides S-type cytoplasm species, another comprised almost exclusively A, C, D, M, N, T and U cytoplasm-type accessions and the third contained the polyploid Triticum species and all the Ae. speltoides accessions, further confirming that Ae. speltoides or a closely related but now extinct species was the original B-genome donor of cultivated polyploid wheat. Successive decreases in levels of genetic diversity due to domestication were also observed. Finally, we highlight the importance of elucidating longer-term evolutionary processes operating at microsatellite repeat loci.

Long-term population isolation in the endangered tropical tree species Caesalpinia echinata Lam. revealed by chloroplast microsatellites.

Habitat fragmentation represents the single most serious threat to the survival of tropical ecosystems. In formulating strategies to counteract the detrimental effects of fragmentation, knowledge of the levels and patterns of genetic diversity within and between natural populations is vital to the establishment of any conservation programme. We utilized polymorphic chloroplast microsatellite markers to analyse genetic diversity in populations of the endangered tropical tree Caesalpinia echinata Lam. representing the entire extant range of the species. Levels of within-population diversity were low, with only two of seven populations studied displaying any variation. The vast majority of the genetic variation was partitioned between geographical regions (36%) and between populations within regions (55%). These levels of genetic structuring, coupled with a calculated pollen-to-seed flow ratio of approximately 6.7:1, suggest that there has been little gene flow between the three major geographical regions over an extended period. Thus, the current tripartite distribution of the species is more consistent with the existence of separate glacial refugia, rather than reflecting any anthropogenic effects.

rbcL sequences reveal multiple cryptic introductions of the Japanese red alga Polysiphonia harveyi.

In Europe, the last 20 years have seen a spectacular increase in accidental introductions of marine species, but it has recently been suggested that both the actual number of invaders and their impacts have been seriously underestimated because of the prevalence of sibling species in marine habitats. The red alga Polysiphonia harveyi is regarded as an alien in the British Isles and Atlantic Europe, having appeared in various locations there during the past 170 years. Similar or conspecific populations are known from Atlantic North America and Japan. To choose between three competing hypotheses concerning the origin of P. harveyi in Europe, we employed rbcL sequence analysis in conjunction with karyological and interbreeding data for samples and isolates of P. harveyi and various congeners from the Pacific and North Atlantic Oceans. All cultured isolates of P. harveyi were completely interfertile, and there was no evidence of polyploidy or aneuploidy. Thus, this biological species is both morphologically and genetically variable: intraspecific rbcL divergences of up to 2.1% are high even for red algae. Seven rbcL haplotypes were identified. The four most divergent haplotypes were observed in Japanese samples from Hokkaido and south-central Honshu, which are linked by hypothetical 'missing' haplotypes that may be located in northern Honshu. These data are consistent with Japan being the centre of diversity and origin for P. harveyi. Two non-Japanese lineages were linked to Hokkaido and Honshu, respectively. A single haplotype was found in all North Atlantic and Mediterranean accessions, except for North Carolina, where the haplotype found was the same as that invading in New Zealand and California. The introduction of P. harveyi into New Zealand has gone unnoticed because P. strictissima is a morphologically indistinguishable native sibling species. The sequence divergence between them is 4-5%, greater than between some morphologically distinct red algal species. Two different types of cryptic invasions of P. harveyi have therefore occurred. In addition to its introduction as a cryptic sibling species in New Zealand, P. harveyi has been introduced at least twice into the North Atlantic from presumed different source populations. These two introductions are genetically and probably also physiologically divergent but completely interfertile.

Chloroplast microsatellites: new tools for studies in plant ecology and evolution.

The nonrecombinant, uniparentally inherited nature of organelle genomes makes them useful tools for evolutionary studies. However, in plants, detecting useful polymorphism at the population level is often difficult because of the low level of substitutions in the chloroplast genome, and because of the slow substitution rates and intramolecular recombination of mtDNA. Chloroplast microsatellites represent potentially useful markers to circumvent this problem and, to date, studies have demonstrated high levels of intraspecific variability. Here, we discuss the use of these markers in ecological and evolutionary studies of plants, as well as highlighting some of the potential problems associated with such use.

Genetic differentiation of Euterpe edulis Mart. populations estimated by AFLP analysis.

Heart-of-palm (Euterpe edulis Mart.) is a wild palm with a wide distribution throughout the Atlantic Rainforest. Populations of E. edulis represent important renewable natural resources but are currently under threat from predatory exploitation. Furthermore, because the species is indigenous to the Atlantic Rainforest, which is located in the most economically developed and populated region of Brazil, social and economic pressures have devastated heart-of-palm forests. In order to estimate the partitioning of genetic variation of endangered E. edulis populations, 429 AFLP markers were used to analyse 150 plants representing 11 populations of the species distribution range. Analysis of the genetic structure of populations carried out using analysis of molecular variance (AMOVA) revealed moderate genetic variation within populations (57. 4%). Genetic differentiation between populations (FST = 0.426) was positively correlated with geographical distance. These results could be explained by the historical fragmentation of the Atlantic coastal region, together with the life cycle and mating system. The data obtained in this work should have important implications for conservation and future breeding programmes of E. edulis.

Patterns of variation at a mitochondrial sequence-tagged-site locus provides new insights into the postglacial history of European Pinus sylvestris populations.

Due to their maternal mode of inheritance, mitochondrial markers can be regarded as almost 'ideal' tools in evolutionary studies of conifer populations. In the present study, polymorphism was analysed at one mitochondrial intron (nad 1, exon B/C) in 23 native European Pinus sylvestris populations. In a preliminary screening for variation using a polymerase chain reaction-restriction fragment length polymorphism approach, two length variants were identified. By fully sequencing the 2.5 kb region, the observed length polymorphism was found to result from the insertion of a 31 bp sequence, with no other mutations observed within the intron. A set of primers was designed flanking the observed mutation, which identified a novel sequence-tagged-site mitochondrial marker for P. sylvestris. Analysis of 747 trees from the 23 populations using these primers revealed the occurrence of two distinct haplotypes in Europe. Within the Iberian Peninsula, the two haplotypes exhibited extensive population differentiation (PhiST = 0.59; P < or = 0.001) and a marked geographical structuring. In the populations of central and northern Europe, one haplotype largely predominated, with the second being found in only one individual of one population.

Postoperative tonsillectomy pain in pediatric patients: electrocautery (hot) vs cold dissection and snare tonsillectomy--a randomized trial.

OBJECTIVE: To determine the effect of the method of tonsillectomy on postoperative pain in pediatric patients. DESIGN: Prospective, randomized, single-blind, controlled clinical trial. SETTING: A university pediatric hospital in Aberdeen, Scotland. PATIENTS: A volunteer sample of 54 children, aged 3 to 12 years, with recurrent tonsillitis or symptomatic adenotonsillar hypertrophy. Two patients withdrew consent. INTERVENTIONS: Twenty-six children underwent a nonelectrical (ie, cold) dissection tonsillectomy with cold steel instruments, 5 of whom also had adenoidectomy by curettage. Monopolar diathermy forceps were used for tonsillar bed hemostasis. Twenty-four children had electrocautery (ie, hot) dissection tonsillectomy, 7 of whom underwent adenoidectomy by curettage without a suction coagulator. MAIN OUTCOME MEASURES: Postoperative analgesic consumption, time to regain normal diet and activity levels, and complications. RESULTS: Patients who underwent hot dissection tonsillectomy showed no difference in time to first drink or analgesic use within the first 24 postoperative hours compared with children undergoing cold nonelectrical dissection tonsillectomy. The hot dissection tonsillectomy group took 7.5 (95% confidence interval [CI], 1-14.1) more doses of analgesics than the cold dissection group over the next 12 days (P<.05). The hot dissection tonsillectomy group took 2.5 more days than the cold dissection tonsillectomy group to regain normal diet (P<.05). Thirteen children (54%; 95% CI, 34-74) in the hot dissection tonsillectomy group and 6 (23%; 95% CI, 7-39) in the cold dissection tonsillectomy group sought outpatient care for throat pain, otalgia, poor diet, pyrexia, and/or bleeding (P<.05). Throat pain delayed in onset or of prolonged duration affected 9 children (38%; 95% CI, 19-57) in the hot dissection tonsillectomy group as opposed to 3 children (12%; 95% CI, 0-24) in the cold dissection tonsillectomy group (P<.05). CONCLUSION: Hot dissection tonsillectomy increases morbidity in pediatric patients in the recovery period following hospital discharge.

Use of microsatellite DNA markers to investigate the level of genetic diversity and population genetic structure of coconut (Cocos nucifera L.).

We have used eight pairs of simple sequence repeat (SSR) primers to analyse the genetic diversity in 130 individuals of coconut (Cocos nucifera L.) comprising 75 tall individuals and 55 dwarf individuals, representing 94 different coconut ecotypes throughout the world. A total of 51 alleles were detected, with an average of 6.4 alleles per locus. Fifty alleles were detected in tall coconuts (talls; mean alleles/locus 6.3) compared with only 26 (mean/locus 3.3) in dwarfs, and the average diversity value in talls (0.589) was also significantly higher than that in dwarfs (0.348). Using the eight SSRs we were able to uniquely discriminate 116 of the 130 individuals. A phenetic tree based on DAD (absolute distance) values clustered individuals into five groups, each mainly composed of either talls or dwarfs. These results provide evidence in support of previous hypotheses concerning the dissemination of coconut, as well as important new information for conservation and breeding purposes.

A low mutation rate for chloroplast microsatellites.

We used chloroplast simple sequence repeats (cpSSRs) to examine whether there is any variation present in the chloroplast genome of Pinus torreyana (Parry ex Carrière) that may previously not have been detected using RFLPs. Analysis of 17 cpSSR loci showed no variation, which is consistent with previous cpRFLP work and confirms that the species is descended from an original, highly monomorphic population following a bottleneck. This lack of biological variation in the chloroplast genome of P. torreyana allowed us to estimate the mutation rates at cpSSR loci as between 3. 2 x 10(-5) and 7.9 x 10(-5). This estimate is lower than published mutation rates at nuclear SSR loci but higher than substitution rates elsewhere in the chloroplast genome.

The urology work force in Ontario for the 21st century: feast or famine?

OBJECTIVE: To address the issues of work-force planning and modelling in the 21st century for the specialty of urology in the Province of Ontario. DESIGN: Data (from 1991 to 1995) regarding urology physician resources were gathered from Health Canada, the Royal College of Physicians and Surgeons of Canada, the Ontario Physician Human Resources Data Centre, the Canadian Post-M.D. Education Registry, the System for Health Area Resource Planning (SHARP) database, the Canadian Institute for Health Information and the National Physician Database. Specifically, the age and gender breakdown of currently active Ontario urologists, measures of urologist clinical activity (from Ontario Hospital Insurance Plan billings and questionnaires), inputs into and exits from the active urologist population were gathered, and estimates of future needs for urologist services, based on current population and demographic models, were made. A model to predict the balance between future needs for urology services and future supply of urologists was then created and validated against data drawn from the SHARP database. RESULTS: The model revealed that there will be a significant shortage of urologists in Ontario in the immediate and long-term future; by the year 2010 there will be a shortfall of 101 urologists in Ontario, or 51% of the total needed. CONCLUSIONS: Enlarging the urology training programs in Ontario would help to minimize the estimated shortfall. Systematic modelling of physician work-force needs for the future is necessary for the optimal allocation of health care resources. The methodology of the urology work-force model is generalizable to physician work-force planning for other specialty groups on a provincial or national basis.

An example of microsatellite length variation in the mitochondrial genome of conifers.

In the present study, the intergenic region between the mitochondrial genes encoding subunit 3 of NADH dehydrogenase (nad3) and ribosomal protein S12 (rps12) was shown to contain a Gn mononucleotide microsatellite repeat. This region was analysed in 15 species belonging to the genus Pinus and interspecific variation was detected in the form of repeat length polymorphism. Sequence analysis of a 576-bp region containing the microsatellite confirmed that the variability was due to expansion and contraction of the repeat motif and that no point mutations were present in the coding regions of the two genes. This is the first report of the occurrence of a microsatellite polymorphism in plant mitochondria.

Amplified fragment length polymorphism (AFLP) analysis of genetic variation in Moringa oleifera Lam

Moringa oleifera is an important multipurpose tree introduced to Africa from India at the turn of this century. Despite limited knowledge of the levels of genetic diversity and relatedness of introduced populations, their utilization as a source of seed for planting is widespread. In order to facilitate reasoned scientific decisions on its management and conservation and prepare for a selective breeding programme, genetic analysis of seven populations was performed using amplified fragment length polymorphism (AFLP) markers. The four pairs of AFLP primers (PstI/MseI) generated a total of 236 amplification products of which 157 (66.5%) were polymorphic between or within populations. Analysis of molecular variance (AMOVA) revealed significant differences between regions and populations, even though outcrossing perennial plants are expected to maintain most variation within populations. A phenetic tree illustrating relationships between populations suggested at least two sources of germplasm introductions of Kenya. The high levels of population differentiation detected suggest that provenance source is an important factor in the conservation and exploitation of M. oleifera genetic resources.

Polymorphic chloroplast simple sequence repeat primers for systematic and population studies in the genus Hordeum

In this study we report the development of primers to amplify polymorphic chloroplast simple sequence repeats in the genus Hordeum, which includes cultivated barley (H. vulgare ssp. vulgare) and its wild progenitor H. vulgare ssp. spontaneum. Polymorphic products were amplified in a wide range of Hordeum spp. and intraspecific variation was detected in both cultivated and wild barley. A decrease in cytoplasmic diversity was observed between sspp. spontaneum and vulgare as well as between ssp. vulgare landraces and cultivars, which is characteristic of domestication processes in many corp species. We also observed possible evidence for reticulate evolution of H. brachyantherum polyploids, with apparent multiple cytoplasmic introgressions during successive polyploidization events.

Gene-pool variation in caledonian and European Scots pine (Pinus sylvestris L.) revealed by chloroplast simple-sequence repeats.

We have used polymorphic chloroplast simple-sequence repeats to analyse levels of genetic variation within and between seven native Scottish and eight mainland European populations of Scots pine (Pinus sylvestris L.). Diversity levels for the Scottish populations based on haplotype frequency were far in excess of those previously obtained using monoterpenes and isozymes and confirmed lower levels of genetic variation within the derelict population at Glen Falloch. The diversity levels were higher than those reported in similar studies in other Pinus species. An analysis of molecular variance (AMOVA) showed that small (3.24-8.81%) but significant (p < or = 0.001) portions of the variation existed between the populations and that there was no significant difference between the Scottish and the mainland European populations. Evidence of population substructure was found in the Rannoch population, which exhibited two subgroups. Finally, one of the loci studied exhibited an allele distribution uncharacteristic of the stepwise mutation model of evolution of simple-sequence repeats, and sequencing of the PCR products revealed that this was due to a duplication rather than slippage in the repeat region. An examination of the distribution of this mutation suggests that it may have occurred fairly recently in the Wester Ross region or that it may be evidence of a refugial population.

Canadian human resource needs in vascular surgery.

OBJECTIVE: To outline the distribution of vascular surgeons in Canada and to determine the present and future human resource needs in vascular surgery practice in Canada. DESIGN: Voluntary questionnaires sent to all members of the Canadian Society for Vascular Surgery (CSVS), the administrators of hospitals in Canada with more than 100 beds, and interrogation of the membership database of the CSVS. MAIN OUTCOME MEASURES: The perceived present and future needs for full-time and part-time vascular surgeons, determined by a variety of methods. PARTICIPANTS: One hundred and forty active members of the CSVS and administrators of 120 hospitals. MAIN RESULTS: From the CSVS members 62 responses were received from those residing in Canada, revealing 47 full-time vascular (more than 75% of the practice) surgeons working with 0 to 5 colleagues (mean 1.8 [SD 1.3]). Fifteen responding surgeons combined the practice of vascular surgery with another specialty. Perceived immediate needs were 24 surgeons, with 42 required in 4.8 (1.8) years. Of 120 hospitals offering vascular surgery services, 90 stated that they met the needs of their community; however, additional immediate manpower requirements totalled 27 surgeons. Hospital administrators predicted a need of 55 additional vascular surgeons in a mean of 5.5 (4.6) years. Over 85% of hospitals stated that they had the resources to support the currently practising surgeons and their immediately required additions. CONCLUSIONS: Prediction of the need for additional vascular surgeons should be based on an estimated retirement age of 65 years, with an adjustment for the increasing percentage of the Canadian population reaching the age of 60 years. All methodologies used in this study predict the need for additional human resources in vascular surgery. The need for continued training of new vascular surgeons is apparent, but the optimal number of trainees per year is less clear.