A single ancient origin of brood parasitism in African finches: implications for host-parasite coevolution.

Robust phylogenies for brood-parasitic birds, their hosts, and nearest nesting relatives provide the framework to address historical questions about host-parasite coevolution and the origins of parasitic behavior. We tested phylogenetic hypotheses for the two genera of African brood-parasitic finches, Anomalospiza and Vidua, using mitochondrial DNA sequence data from 43 passeriform species. Our analyses strongly support a sister relationship between Vidua and Anomalospiza, leading to the conclusion that obligate brood parasitism evolved only once in African finches rather than twice, as has been the conventional view. In addition, the parasitic finches (Viduidae) are not recently derived from either weavers (Ploceidae) or grassfinches (Estrildidae), but represent a third distinct lineage. Among these three groups, the parasitic finches and estrildids, which includes the hosts of all 19 Vidua species, are sister taxa in all analyses of our full dataset. Many characters shared by Vidua and estrildids, including elaborate mouth markings in nestlings, unusual begging behavior, and immaculate white eggs, can therefore be attributed to common ancestry rather than convergent evolution. The host-specificity of mouth mimicry in Vidua species, however, is clearly the product of subsequent host-parasite coevolution. The lineage leading to Anomalospiza switched to parasitizing more distantly related Old World warblers (Sylviidae) and subsequently lost these characteristics. Substantial sequence divergence between Vidua and Anomalospiza indicates that the origin of parasitic behavior in this clade is ancient (approximately 20 million years ago), a striking contrast to the recent radiation of extant Vidua. We suggest that the parasitic finch lineage has experienced repeated cycles of host colonization, speciation, and extinction through their long history as brood parasites and that extant Vidua species represent only the latest iterations of this process. This dynamic process may account for a significantly faster rate of DNA sequence evolution in parasitic finches as compared to estrildids and other passerines. Our study reduces by one the tally of avian lineages in which obligate brood parasitism has evolved and suggests an origin of parasitism that involved relatively closely related species likely to accept and provide appropriate care to parasitic young. Given the ancient origin of parasitism in African finches, ancestral estrildids must have been parasitized well before the diversification of extant Vidua, suggesting a long history of coevolution between these lineages preceding more recent interactions between specific hosts and parasites.

Adjustment of serum total calcium for albumin concentration: effects of non-linearity and of regression differences between laboratories.

It has been reported that the relationship between serum total calcium and albumin concentrations in hospital patients deviates from linearity at low albumin concentrations. We searched a large laboratory computer data base for adult patients with discretionary requests for serum calcium analysis but with no other data suggestive of disturbances of calcium homeostasis, and collected a minimum of 100 calcium values at each of a wide range of albumin concentrations. We confirmed the earlier observation, but found that the use of a single regression to derive an adjustment of total calcium for albumin gave only small differences of no clinical significance. To investigate whether equations to adjust total calcium for albumin can be transferred between laboratories, three laboratory computers were searched for calcium requests from patients likely to have a low prevalence of calcium disturbances. The regressions of total calcium on albumin differed significantly between laboratories, but within each laboratory gave adjusted calcium values identical with those in health. Although the errors resulting from applying an equation from one laboratory to another were small and unlikely to be of major clinical significance, we recommend that where possible laboratories should derive adjustment equations from their own data.

Adjustment of serum total calcium for albumin concentration: values change with age in women but not in men.

A total of 669 women and 609 men were selected from a laboratory computer data base in such a way that they would be expected to have a low prevalence of disturbances of calcium homeostasis but a wide range of serum albumin concentrations. The least squares regression coefficients of total calcium on albumin did not differ between men and women, nor did they differ at different ages. Mean serum albumin-adjusted calcium concentrations did not change with age in men from 1 to 90 years, and values were similar in women aged 1-20 years. However, adjusted calcium concentrations were significantly lower in women aged 21-50 and higher in women aged 61-90 than in younger women and all men. The differences were small and are unlikely to affect clinical interpretation.

Motivational effects of anxiety on psychomotor performance.

The Hull-Spence theory of anxiety drive (A) was tested in a psychomotor learning situation in which both correct responses (R+) and competing responses (R-) were evoked by the task. Measures of A-Trait and A-State were obtained from 151 women and 52 men, all of whom were then exposed to a sequence of 16 trials on a mirror-tracking task presented either continuously or with 2-min. intertrial intervals. Analyses of the effects of A were then performed on samples of 68 women and 16 men drawn from the tails of the A distributions. Theoretical predictions about the effects of A on initial scores and performance trends of both R+ and R- were strongly supported, somewhat more so within the A-State classification than within the A-Trait classification owing to the larger amount of variance accounted for. Analyses involving intermediate levels of A showed that R+ was a monotonic and essentially linear function of A.

Comparison of hypertonic and isotonic reference electrode junctions for measuring ionized calcium in whole blood: a clinical study.

We measured ionized calcium concentrations in whole blood from 91 patients who had no clinical or biochemical evidence of disturbed calcium homeostasis and who had a wide range of serum albumin concentrations. We used both a standard Ciba-Corning 634 analyzer, which has a membrane-restricted saturated KCl reference electrode bridge, and a modified instrument with a 150 mmol/L NaCl bridge. After adjusting the externally standardized values from each instrument for their least-squares regressions on pH, there was a significant correlation between ionized calcium and albumin only with the standard analyzer. In contrast, only values from the modified instrument correlated with serum chloride; this was not explained by ionic strength or organic anion interferences. We conclude that there is unlikely to be any major advantage in using a membrane-restricted isotonic NaCl reference electrode for in vitro clinical measurements, although it may be of value for in vivo monitoring. The importance of measuring serum albumin when using most commercial ionized calcium analyzers is emphasized.

Mnemonic coding system for clinical data entry into laboratory computers: its effect on quality and efficiency.

A simplified coding method for entering the clinical details found on pathology request cards was developed. The method uses a basic four letter code, derived from the initial character of the first four words in a clinical detail, being expanded to four characters with letters from the final word if the number of words is less than four. Rules were devised to cope with common medical terminology. In excess of 90% of clinical details on request cards are readily input by clerical staff using our coding system, and 8% of clinical details are used intelligently by the computer in scheduling further tests or automatically commenting on results. A carefully designed coding system such as the one outlined above could greatly facilitate input of clinical detail without the penalty of reduced throughput.

Effects of ionic strength on ionized calcium measured using reference electrode liquid junctions of varying design and composition.

Five commercial analysers were used to measure ionized calcium in aqueous and protein solutions which contained the same amount of calcium but had sodium chloride concentrations ranging from 100 to 150 mmol/L. In aqueous solutions measured activity fell significantly with increasing ionic strength while in protein solutions it increased. When isotonic sodium chloride was substituted for the hypertonic potassium chloride reference electrode liquid junction of an analyser with an open junction, there was a marked positive change in the effect of ionic strength in both aqueous and protein solutions. In contrast, when either isotonic sodium chloride or potassium chloride was substituted for the hypertonic potassium chloride of an instrument with a membrane-restricted junction, there was no effect on the change of measured values with ionic strength. Increasing the protein concentration by ultrafiltration did not change ionized calcium values when isotonic reference solutions were used with either open or membrane-restricted junctions. Because membrane-restricted isotonic junctions respond like hypertonic junctions to changes in sample ionic strength but do not exhibit protein interference, they may prove to have advantages over both open isotonic junctions and all configurations of hypertonic junction for measurements in patients.

Protein interference with ion-selective electrode measurement depends on reference electrode composition and design.

There is controversy about whether protein interferes with ion measurements using ion-selective electrodes. We have investigated the effects of changes in the salt-bridge composition of five commercially available analysers with open, membrane-restricted or porous frit-restricted reference electrode junctions on measurements of an albumin solution prepared by gel filtration. When the manufacturers' salt bridges were used, instruments with open or membrane-restricted junctions showed apparent increases in the activity of ionized calcium, sodium and potassium in the presence of protein. When the hypertonic bridge solutions were replaced with 150 mmol/L potassium chloride this increase disappeared. The instrument with a porous frit-restricted junction showed no protein effect, but its response to changes in sample sodium chloride concentration in protein-free solution suggested that its junction was functionally equivalent to that formed with an isotonic sodium chloride bridge. Our results emphasize that liquid junction design and composition affect ion measurements in protein-containing solutions and suggest that the use of hypertonic bridge solutions for biological samples needs to be re-examined.

Albumin-adjusted calcium concentration in serum increases during normal pregnancy.

Concentrations of total calcium and albumin were measured in serum specimens from 41 women at intervals before, during, and after 42 pregnancies. The albumin concentration decreased but the calcium decreased more slowly, so that the albumin-adjusted calcium concentration increased from conception to term. These findings, taken in conjunction with published observations of hypercalciuria, increased concentrations of 1,25-dihydroxycholecalciferol and calcitonin in serum, and decreased concentrations of intact parathyrin in serum, strongly suggest that maternal ionized calcium increases throughout normal pregnancy.