Fixation times and probabilities for an independent loci model in genetics

Assuming that two genetic loci evolve independently and that there is no mutation and selection, formulae are obtained for mean first and final fixation times and first fixation probabilities. These results, together with known results for the case of complete linkage, give some indication of the effect of linkage on these quantities.     

Ecological cues, gestation length, and birth timing in African buffalo (Syncerus caffer)

We examined annual variation in the timing of conception andparturition in the African buffalo (Syncerus caffer) and thesynchrony of birth timing with resource cues, using 8 yearsof monthly birth, rainfall, and vegetation data, measured asNormalized Difference Vegetation Index (NDVI). Monthly birthshad the strongest significant correlations with NDVI and rainfalllevels 12 and 13 months in the past, respectively. In addition,the synchrony of current year births corresponds most stronglyto the synchrony of the previous year's NDVI distribution. Becausethe gestation period of buffalo has been estimated to be around11 months, these findings suggest that improved protein levels,occurring approximately a month after the first green flushof the wet season, are either a trigger for conception or conceptionhas evolved to be synchronous with correlated environmentalcues that ensure females enter a period of peak body conditionaround the time of conception and/or parturition. With a gestationperiod of approximately 340 days, parturition occurs to takeadvantage of the period when forage has its highest proteincontent. A comparative analysis of gestation periods withinthe subfamily Bovinae indicates that African buffalo have aprotracted gestation for their body size, which we suggest isan adaptation to their seasonal environment. We also found thatinterannual variation in the birth distribution suggests a degreeof plasticity in the date of conception, and variation in thenumber of calves born each year suggest further synchrony ata timescale longer than a single year.     

A low-cost chromatograph data-collection system

A data collection system has been constructed, based on the low-cost BBC microcomputer, which provides for the digitization and storage of the data from one or more g.l.c. or h.p.l.c. instruments, or from other data sources with similar data rates. The data can be observed during collection on the graphics screen, and are then stored on disk for subsequent processing. This processing is designed to be interactive, so that the operator can influence decisions about base-line drifts, peak separations, etc. when integrating the peaks, and can decide which peaks are to be stored in a time/intensity record, on the basis of a visual display of the trace. A low cost multi-channel precision ADC, using isolated voltage-to-frequency transducers sited at the sources of data, and multiple counters at the computer, may be used to measure several signals simultaneously even when they originate at some distance from the computer, and extra memory can also be added to the BBC microcomputer to allow temporary storage of data. The software is written in machine code (for the data collection) and BASIC (for the analysis routines) so that modifications to the latter routines can be made easily. The user interface is suitable for routine users who have no computing experience.     

Deep-water rhodolith distribution, productivity, and growth history at sites of formation and subsequent degradation

This study provides the first quantitative measures of deep-water (i.e., below scuba depths) rhodolith development, distribution, abundance, and primary productivity at sites of both active formation and breakdown. The 1.27-km² upper platform surface of San Salvador Seamount, Bahamas, ranges in depth from 67 to 91 m and averages 95.8% cover of rhodoliths that contribute an estimated 391 t organic C·yr⁻¹ to deep-sea productivity. The predominant nongeniculate coralline alga of the slope environment has an extremely narrow PI curve (photosynthesis vs. irradiance) of net primary production (0.005) to slightly beyond 0.24 μmol·m⁻²·⁻¹ PAR) suggesting that some deep-water benthic algae may be acclimated to restricted light ranges. Platform areas contain up to fice-deep accumulations (≈45 cm thick) of rhodoliths with their visible, planar (2-D), crustose algal cover (68.5%) composed of 41% Lithophyllum sp., 14.9% average nongeniculate corallines, and 12.6% Peyssonnelia sp. Platform rhodoliths also contain ≈25% average planar cover of the foraminiferan Gypsina sp. overlying the rock-penetrating chlorophyte Ostreobium sp.

On the steep slopes of the seamount, to a depth of 290 m, rhodoliths that have spilled down from the relatively flat platform average 17.4% cover. These nodules tend to be concentrated in fan-shaped deposits that are most prevalent (33.3% cover) on the west side (leeward) of the mount where they are more abundant near the top of the slope than on the other three sides. Cover of living crustose algae on the deeper slope rhodoliths averages only 22.8% and is made up of 14.8% unidentified nongeniculate corallines, 6% Lithophyllum sp., and 2% Peyssonnelia. Gypsina sp. is not an important component of the slope nodules. Biotic overstory on the seamout slopes is greatly reduced relative to the platform, restricted mainly to bedrock, and consists mostly of Halimeda, gorgonians, and sponges along with scattered patches of small frondose algae.

Over platform depths from 67 to 91 m, rhodoliths are fairly uniform in composition and abundance. Ranging from 4 to 15 cm in diameter, with an average of ≈ 9 cm, they are roughly spherical with smooth living surfaces. The rhodoliths spilling down the steep slopes of the seamount to depths below 200 m are characteristically smaller (mean of ≈5 cm diameter), much rougher, and pittend by boring organisms. As shown by cross sections through the centers of the platform nodules, outer, relatively thin (1–3 cm thick), well-preserved envelopes overlie dead laminated crustose layerse. These layers surround much thicker cores of biotically altered carbonate (mostly coralline, foraminiferan, and coral) that have been extensively reworked by boring sponges, algae, polychaetes, and pelecypods. Borings have been infilled with carbonate detritus and are lithified to various degrees ranging from porous to dense and stony.

Radiocarbon dates indicate that the outermost unaltered envelopes that underlie actively growing crusts are 112–880 yr old ( ), while the innermost unaltered layers average 731 ybp (range = 200–1100 ybp). The consistently abrupt transitions from the intact underlying layers of living.