Towards a conceptual and operational union of bacterial systematics, ecology, and evolution

To completely understand the ecology of a bacterial community, we need to identify its ecologically distinct populations (ecotypes). The greatest promise for enumerating a community's constituent ecotypes is held by molecular approaches that identify bacterial ecotypes as DNA sequence clusters. These approaches succeed when ecotypes correspond with sequence clusters, but some models of bacterial speciation predict a one-to-many and others a many-to-one relationship between ecotypes and sequence clusters. A further challenge is that sequence-based phylogenies often contain a hierarchy of clusters and subclusters within clusters, and there is no widely accepted theory to guide systematists and ecologists to the size of cluster most likely to correspond to ecotypes. While present systematics attempts to use universal thresholds of sequence divergence to help demarcate species, the recently developed ‘community phylogeny’ approach assumes no universal thresholds, but demarcates ecotypes based on the analysis of a lineage's evolutionary dynamics. Theory-based approaches like this one can give a conceptual framework as well as operational criteria for hypothesizing the identity and membership of ecotypes from sequence data; ecology-based approaches can then confirm that the putative ecotypes are actually ecologically distinct. Bacterial ecotypes that are demonstrated to have a history of coexistence as ecologically distinct lineages (based on sequence analysis) and as a prognosis of future coexistence (based on ecological differences), are the fundamental units of bacterial ecology and evolution, and should be recognized by bacterial systematics

Sleep phase and gastro-oesophageal reflux in infants at possible risk of SIDS.

The association between gastro-oesophageal reflux and sleep state in 24 infants with confirmed or suspected gastro-oesophageal reflux was studied by monitoring both the pH in the lower oesophagus and polygraphic tracings made during sleep at night. Gastro-oesophageal reflux during the night was confirmed in 20 infants. Three hundred and sixteen precipitous drops of more than one unit of pH were recorded during the studies, 186 during periods of wakefulness. Of 130 drops in pH during sleep, 62 (48%) began during active sleep and 62 during indeterminate sleep. Of the latter, 56 (90%) were associated with brief gross body movements. Only five of the drops in pH (4%) began during quiet sleep. Gastro-oesophageal reflux stopped during active sleep on 56 occasions (43%), in indeterminate sleep in 62 (47%), and in quiet sleep in 12 (9%). Episodes of gastro-oesophageal reflux starting or ending in quiet sleep were uncommon. The occurrence of gastro-oesophageal reflux during active sleep may partly explain why reflux during sleep is a risk factor for pulmonary disease