Nest architecture, fungus gardens, queen, males and larvae of the fungus-growing ant Mycetagroicus inflatus Brandão & Mayhé-Nunes.

All known fungus-growing ants (tribe Attini) are obligately symbiotic with their cultivated fungi. The fungal cultivars of "lower" attine ants are facultative symbionts, capable of living apart from ants, whereas the fungal cultivars of "higher" attine ants, including leaf-cutting genera Atta and Acromyrmex, are highly specialized, obligate symbionts. Since higher attine ants and fungi are derived from lower attine ants and fungi, understanding the evolutionary transition from lower to higher attine agriculture requires understanding the historical sequence of change in both ants and fungi. The biology of the poorly known ant genus Mycetagroicus is of special interest in this regard because it occupies a phylogenetic position intermediate between lower and higher ant agriculture. Here, based on the excavations of four nests in Pará, Brazil, we report the first biological data for the recently described species Mycetagroicus inflatus, including the first descriptions of Mycetagroicus males and larvae. Like M. cerradensis, the only other species in the genus for which nesting biology is known, the garden chambers of M.inflatus are unusually deep and the garden is most likely relocated vertically in rainy and dry seasons. Due to the proximity of nests to the Araguaia River, it is likely that even the uppermost chambers and nest entrances of M. inflatus are submerged during the rainy season. Most remarkably, all three examined colonies of M. inflatus cultivate the same fungal species as their congener, M. cerradensis, over 1,000 km away, raising the possibility of long-term symbiont fidelity spanning speciation events within the genus.

Weaning children from mechanical ventilation: a prospective randomized trial of protocol-directed versus physician-directed weaning.

OBJECTIVE: Compare outcomes between physician-directed and protocol-directed weaning from mechanical ventilation in pediatric patients. DESIGN: Prospective-randomized. SETTING: Pediatric and cardiac intensive care units in a 307-bed tertiary referral hospital for children. INTERVENTIONS: The control group (physician-directed) was weaned according to individual physician order for reduction in minute ventilation, positive end-expiratory pressure, and ordered oxygen saturation parameters for reduction in fraction of inspired oxygen (F(IO)(2)). The study group (protocol-directed) was weaned according to a predetermined algorithm developed for the purpose of this investigation. METHODS: The study enrolled 223 patients (116 physician-directed, 107 protocol-directed). All patients were monitored for hemodynamics, ventilator parameters, arterial blood gas values when available, oxygen saturation, weaning time, pre-weaning time, extubation time, and time on F(IO)(2) > or = 0.40. We also monitored the incidence of reintubation, subglottic stenosis, tracheitis, and pneumonia. The protocol-directed group had additional measurements of actual versus predicted minute volume, comparisons of respiratory rate (actual versus predicted for age), and presence of spontaneous breathing effort for 10 consecutive minutes. Data analysis was done according to intent to treat. RESULTS: There was no significant difference in 12-hour and 24-hour pediatric risk of mortality (PRISM III) scores between groups. The protocol-directed group overall had shorter total ventilation time, weaning time, pre-weaning time, time to extubation, and time on F(IO)(2) >0.40, although after stratification for respiratory diagnosis, only the difference in weaning time remained significant. There was no difference in the incidence of reintubation, new-onset tracheitis, subglottic stenosis, or pneumonia. CONCLUSIONS: Protocol-directed weaning resulted in a shorter weaning time than physician-directed weaning in these pediatric patients.

The origin of the attine ant-fungus mutualism.

Cultivation of fungus for food originated about 45-65 million years ago in the ancestor of fungus-growing ants (Formicidae, tribe Attini), representing an evolutionary transition from the life of a hunter-gatherer of arthropod prey, nectar, and other plant juices, to the life of a farmer subsisting on cultivated fungi. Seven hypotheses have been suggested for the origin of attine fungiculture, each differing with respect to the substrate used by the ancestral attine ants for fungal cultivation. Phylogenetic information on the cultivated fungi, in conjunction with information on the nesting biology of extant attine ants and their presumed closest relatives, reveal that the attine ancestors probably did not encounter their cultivars-to-be in seed stores (von Ihering 1894), in rotting wood (Forel 1902), as mycorrhizae (Garling 1979), on arthropod corpses (von Ihering 1894) or ant faeces in nest middens (Wheeler 1907). Rather, the attine ant-fungus mutualism probably arose from adventitious interactions with fungi that grew on walls of nests built in leaf litter (Emery 1899), or from a system of fungal myrmecochory in which specialized fungi relied on ants for dispersal (Bailey 1920) and in which the ants fortuitously vectored these fungi from parent to offspring nests prior to a true fungicultural stage. Reliance on fungi as a dominant food source has evolved only twice in ants: first in the attine ants, and second in some ant species in the solenopsidine genus Megalomyrmex that either coexist as trophic parasites in gardens of attine hosts or aggressively usurp gardens from them. All other known ant-fungus associations are either adventitious or have nonnutritional functions (e.g., strengthening of carton-walls in ant nests). There exist no unambiguous reports of facultative mycophagy in ants, but such trophic ant-fungus interactions would most likely occur underground or in leaf litter and thus escape easy observation. Indirect evidence of fungivory can be deduced from contents of the ant alimentary canal and particularly from the contents of the infrabuccal pocket, a pharyngeal device that filters out solids before liquids pass into the intestine. Infrabuccal pocket contents reveal that ants routinely ingest fungal spores and hyphal material. Infrabuccal contents are eventually expelled as a pellet on nest middens or away from the nest by foragers, suggesting that the pellet provides fungi with a means for the dispersal of spores and hyphae. Associations between such "buccophilous" fungi and ants may have originated multiple times and may have become elaborated and externalized in the case of the attine ant-fungus mutualism. Thus, contrary to the traditional model in which attine fungi are viewed as passive symbionts that happened to come under ant control, this alternative model of a myrmecochorous origin of the attine mutualism attributes an important role to evolutionary modifications of the fungi that preceded the ant transition from hunter-gatherer to fungus farmer.

Molecular phylogenetic analysis of the dragonfly genera Libellula, Ladona, and Plathemis (Odonata: Libellulidae) based on mitochondrial cytochrome oxidase I and 16S rRNA sequence data.

Molecular phylogenetic relationships among members of the odonate genus Libellula (Odonata: Anisoptera: Libellulidae) were examined using 735 bp of mitochondrial COI and 416 bp of 16S ribosomal RNA gene sequences. Considerable debate exists over several relationships within Libellula, as well over the status of two putative genera often placed as subgenera within Libellula: Ladona and Plathemis. Parsimony and maximum-likelihood analyses of the separate and combined data sets indicate that Plathemis is basal and monophyletic and that Ladona is the sister clade to the remainder of Libellula sensu stricto (s.s.) (all species within the genus Libellula, excluding Plathemis and Ladona). Moreover, two European taxa, Libellula fulva and L. depressa, were found to occupy a sister group relationship within the Ladona clade. Relationships within Libellula s.s. are less well resolved. However, monophyletic lineages within the genus are largely consistent with morphologically based subgeneric classifications. Although tree topologies from each analysis differed in some details, the differences were in no case statistically significant. The analysis of the combined COI and 16S data yielded trees with overall stronger support than analyses of either gene alone. Several analyses failed to support the monophyly of Libellula sensu lato due to the inclusion of one or more outgroup species. However, statistical comparisons of topologies produced by unconstrained analyses and analyses in which the monophyly of Libellula was constrained indicate that any differences are nonsignificant. Based on morphological data, we therefore reject the paraphyly of Libellula and accept the outgroup status of Orthemis ferruginea and Pachydiplax longipennis.

Airway pressure release ventilation in pediatrics.

OBJECTIVES: The purpose of this study was to determine the effectiveness of airway pressure release ventilation in children. DESIGN: Prospective, randomized, crossover clinical trial. SETTING: This study was conducted in our 33-bed pediatric intensive care unit at The Children's Hospital of Philadelphia. PATIENTS: Patients requiring mechanical ventilatory support and weighing >8 kg were considered for enrollment. Patients were excluded if they required mechanical ventilatory support for >7 days or required >.50 Fio(2) for >7 days before enrollment. Patients with documented obstructive airway disease and congenital or acquired heart disease were excluded as well. INTERVENTIONS: Each patient received both volume-controlled synchronized intermittent mechanical ventilation (SIMV) and airway pressure release ventilation (APRV) via the Drager Evita ventilator (Drager, Lubeck, Germany). Measurements were obtained after the patient was stabilized on each ventilation mode. Stabilization was defined as oxygenation, ventilation, hemodynamic variables, and patient comfort within the acceptable range for each patient as determined by the bedside physician. After measurements were obtained on the initial mode of ventilation, the subjects crossed over to the alternative study mode. Stabilization was again achieved, and measurements were repeated. After completion of the second study measurements, patients were placed on the ventilation modality preferred by the bedside clinician and were followed through weaning and extubation. Measurements: Vital signs, airway pressures, minute ventilation, Spo(2), and E(T)CO(2) were recorded at enrollment and at each study condition. MAIN RESULTS: APRV provided similar ventilation, oxygenation, mean airway pressure, hemodynamics, and patient comfort as SIMV. Inspiratory airway pressures were lower with APRV when compared with SIMV. CONCLUSIONS: Using APRV in children with mild to moderate lung disease resulted in comparable levels of ventilation and oxygenation at significantly lower inspiratory peak and plateau pressures. Based on these findings, we plan to evaluate APRV in children with significant lung disease.

Agro-predation: usurpation of attine fungus gardens by Megalomyrmex ants.

A new ant species of Megalomyrmex conducts mass raids to usurp gardens of the fungus-growing ant Cyphomyrmex longiscapus, then lives in the gardens and consumes the cultivated fungus. Unlike attine ants, however, Megalomyrmex sp. does not forage for substrate to manure the gardens; therefore, when gardens become depleted, Megalomyrmex sp. must locate and usurp new gardens. Megalomyrmex sp. workers feed their larvae with attine brood, but only after removing the fungal mycelium that covers the attine larval integument, suggesting that this fungal coat may provide partial protection against other predators. Unlike other known Megalomyrmex species, which coexist as social parasites in attine colonies, Megalomyrmex sp. expels its attine hosts during the garden raids. Megalomyrmex sp. thus maintains a unique agro-predatory lifestyle that is described here for the first time.

Effects of article retraction on citation and practice in medicine.

At times, there are reasons for authors to make a formal statement of retraction of work they publish in biomedical journals. This study examines 235 retracted articles and looks at the reasons for these retractions and citations to the articles subsequent to retraction. The primary reasons for retraction are error of various kinds (such as problems with method or sample, including contamination of samples) and misconduct. The 235 articles are cited a total of 2,034 times after retraction. This set of citations can be divided into two groups: citations that appear in journals included in the Abridged Index Medicus and those that appear in other journals included in MEDLINE. While most of the citations in these two groups of journals can be categorized as "implicitly positive," 275 make explicitly positive mention of retracted articles. The implications for continued citation for biomedical research and clinical practice are discussed.

Phenomena of retraction: reasons for retraction and citations to the publications.

CONTEXT: This study examined the impact of retracted articles on biomedical communication. OBJECTIVE: To examine publications identified in the biomedical literature as having been retracted, to ascertain why and by whom the publications were retracted and to what extent citations of later-retracted articles continue to be incorporated in subsequent work. DESIGN: A search of MEDLINE from 1966 through August 1997 for articles that had been retracted. MAIN OUTCOME MEASURES: Characteristics of retractions and citations to articles after retraction. RESULTS: A total of 235 articles had been retracted. Error was acknowledged in relation to 91 articles; results could not be replicated in 38; misconduct was evident in 86; and no clear reason was given in 20. Of the 235 articles, 190 were retracted by some or all of the authors; 45 were retracted by a person or organization other than the author(s). The 235 retracted articles were cited 2034 times after the retraction notice. Examination of 299 of those citations reveals that in only 19 instances was the retraction noted; the remaining 280 citations treated the retracted article either explicitly (n = 17) or implicitly (n = 263) as though it were valid research. CONCLUSION: Retracted articles continue to be cited as valid work in the biomedical literature after publication of the retraction; these citations signal potential problems for biomedical science.

Phylogeny of fungus-growing ants (Tribe Attini) based on mtDNA sequence and morphology.

We examined the phylogenetic relationships among taxa of attine or "fungus-growing" ants (Tribe Attini) using parsimony analyses of molecular and morphological data. We sequenced a region of mitochondrial DNA from 13 taxa of attines and from one closely related outgroup species, Wasmannia auropunctata. Our study sequence included the 3' end of the cytochrome c oxidase subunit I (CO I) locus (183 to 198 total sites; 91 informative sites), an intergenic spacer region of variable size (0 to 152 sites), the tRNA leucine locus (65 to 74 sites), and the 5' end of the cytochrome c oxidase subunit II (co II) locus (292 total sites; 140 informative sites). The inferred relationships among the attine taxa based on an unweighted analysis of the nucleotide sequence data closely matched the relationships inferred from an analysis of larval morphological characters from 11 of the taxa. In fact, the inferred relationships were completely congruent among the protein parsimony analysis of amino acid data, the morphology analysis, and "total evidence" analysis combining the amino acid and morphology data. The congruent conclusions we obtained from two independent data sets increases our confidence in the reliability of our analyses.

The use of verbal expectancy in reducing pain associated with arteriotomies.

Hospitalized patients (n = 25) receiving arteriotomies were given one of two verbal instructions one hour apart prior to each incision. In the first arteriotomy, the right radial artery was prepped with alcohol without mention and administered non-expectancy instruction-A, "You may or may not feel pain. everyone is different." One hour later, prior to the second incision, prepping the left radial artery with alcohol was brought to the patient's attention while providing expectancy instruction-B, "Notice how cool this feels, it's interesting how coldness numbs the skin." Analysis of variance revealed that administration of expectancy instruction-B significantly reduced pain (p value, < .005, determined by paired t-test) associated with arteriotomies.

Evolutionary history of the symbiosis between fungus-growing ants and their fungi.

The evolutionary history of the symbiosis between fungus-growing ants (Attini) and their fungi was elucidated by comparing phylogenies of both symbionts. The fungal phylogeny based on cladistic analyses of nuclear 28S ribosomal DNA indicates that, in contrast with the monophyly of the ants, the attine fungi are polyphyletic. Most cultivated fungi belong to the basidiomycete family Lepiotaceae; however, one ant genus, Apterostigma, has acquired a distantly related basidiomycete lineage. Phylogenetic patterns suggest that some primitive attines may have repeatedly acquired lepiotaceous symbionts. In contrast, the most derived attines have clonally propagated the same fungal lineage for at least 23 million years.

Phylogeny of the attine ant fungi based on analysis of small subunit ribosomal RNA gene sequences.

Complete 16S-like ribosomal RNA coding regions were obtained from the fungal symbiont of five genera of attine (leaf-cutting) ants and two free-living fungi. Phylogenetic analyses with distance matrix, maximum likelihood, and parsimony methods revealed that the attine fungal symbionts are homobasidiomycetes in the order Agaricales. Comparison of the topology of the attine fungal symbiont phylogenetic tree with a tree based on attine ant morphology revealed a congruent branching pattern of the more derived attine ants and their fungal symbionts. The parallel branching pattern suggests a long-term coevolution of derived leaf-cutting attine ants and their fungal symbionts.