Aim Previous work on the tidepool copepod Tigriopus californicus revealed a curious case of incipient speciation at the southern end of the species' range in Baja California, Mexico. The present study expands on the geography of this pattern and tests for congruence between reproductive and phylogenetic patterns.Location The Pacific coast of North America, from central Baja California to south-eastern Alaska (27-57°N), including the full range of T. californicus.Methods Primary techniques included mating experiments (> 4000 crosses), phylogeny reconstruction (mitochondrial cytochrome c oxidase subunit I) and screening of single nucleotide polymorphisms (SNPs, 42 loci). Analyses used > 8000 copepods for the mating experiments, 86 copepods for the phylogeny and 41 copepods for the SNP assays. Phylogenies were constructed using Bayesian, maximum likelihood and maximum parsimony methods. ResultsPopulations were found to fall into three reproductive groups: northern and southern groups that were reproductively isolated from each other, and an intermediate group that could serve as a conduit for gene flow. The northern and intermediate populations fell into one clade while all southern populations fell into a second clade. These two clades are now separated by less than 12 km at latitude 29.35°N. Nuclear SNP data for a subset of locations confirmed striking divergence between populations on either side of this boundary. The second (southern) clade was further subdivided into two clades separated by the lagoon region of Guerrero Negro (latitude 28°N).Main conclusions Reproductive assays and molecular data (both mitochondrial and nuclear) reveal a sharp break at 29.35°N, a region with no obvious barriers to dispersal, with no evidence for mixing across this narrow transition zone. Results also showed a milder break at the Guerrero Negro Lagoon (28°N), a location where breaks have been reported for other taxa.

For the intertidal copepod Tigriopus californicus, outbreeding depression for a variety of fitness measures is typically observed in early-generation interpopulation hybrids. We examined both controlled crosses and longterm, freely mating experimental hybrid swarms composed of individuals from Baja California (Mexico) populations Playa Altamira and Punta Morro. In controlled crosses, F1 and F2 hybrids showed large and significant declines in hatching numbers compared to parentals, while reciprocal backcrosses produced no offspring at all. For long-term studies, four treatment groups were initiated: 100%PA, 100%PM, 50%PA: 50%PM, and 80%PA: 20%PM. Replicates were surveyed at 3-month intervals for morphometric, census and fitness measures. The PA and 80PA:20PM treatments had initial fitness below the PM treatment, and went extinct within the first 12 months of the experiment. The 50:50 treatment had fitness below the PM parent at the 3-and 6-month time points, recovered to equivalent or superior fitness from months 9 to 18, and dropped again below PM at month 21. Limited genotyping of diagnostic microsatellites was consistent with PM alleles going nearly to fixation in hybrid replicates and male morphological data were concordant with a shift toward PM values. Results were strikingly different from a recent study of a different pair of populations showing extensive introgression and superior fitness in hybrid populations. This demonstrates how longterm consequences of population mixing depend on the relative fitness and level of compatibility between hybridizing populations.

Eleven microsatellite loci were isolated and characterized for the intertidal copepod Tigriopus californicus. Primers reliably amplify alleles in inbred lines derived from two divergent populations previously shown to have genetic distances of 18% for the mitochondrial cytochrome oxidase I gene. The 11 loci provided markers for eight of the species’ 12 chromosomes.

Although the utility of the base deficit as an indicator of hypoperfusion and physiologic derangement in adults is well established, its value in the assessment of children is not as clear. The purpose of this study was to evaluate this tool with regard to injury severity, infectious morbidity, and outcome in a pediatric trauma population. A retrospective review of a 6-year period of the database of our level 1 pediatric trauma center was performed. One hundred seventeen severely injured children requiring mechanical ventilation were identified. Initial base deficit, Injury Severity Score, time to correction of this abnormality, ventilator days, infectious morbidity, and mortality were obtained and compared. Of the 117 patients included in this study, 30 patients were identified with an initial BD of less than or equal to -8 mEq/L and were placed into group 1. Group 2 consisted of the remaining 87 patients who presented with a base deficit (BD) of greater than -8 mEq/L. An admission base deficit of -8 mEq/L or less corresponded to a probability of mortality of 23 per cent as opposed to only 6 per cent with a BD greater than -8. Patients in group 1 remained on mechanical ventilation 9.4 ± 8.1 days, whereas patients in group 2 remained ventilated 6.5 ± 6.4 days; an increase of nearly 145 per cent. Likewise, the number of infectious complications rose 26 per cent with a worsening initial base deficit from 17 per cent of group 2 patients to 43 per cent of group 1 patients. We conclude that a high initial base deficit in injured children predicts a higher incidence of infectious complications and a less favorable outcome. This readily available laboratory study can identify those children most at risk of potentially preventable complications.