PCR‐RFLP markers detect 29 mitochondrial haplotypes in Pacific lamprey (Entosphenus tridentatus)

We developed five polymerase chain reaction‐based markers that detect variation in the mitochondrial genome of the Pacific lamprey, Entosphenus tridentatus, across most of its range. Two gene fragments (ND2 and ND5) were amplified and digested with three and two restriction enzymes, respectively, detecting sequence variation at 18 sites (ND2 = 13; ND5 = 5) and yielding 29 composite haplotypes among 1246 lampreys. These sequence‐based markers will be useful in a range of phylogeographical and population genetic studies.     

Factors Controlling the Abundance and Size Distribution of the Phototrophic Ciliate Myrionecta rubra in Open Waters of the North Atlantic

ABSTRACT. Myrionecta rubra, a ubiquitous planktonic ciliate, has received much attention due to its wide distribution, occurrence as a red tide organism, and unusual cryptophyte endosymbiont. Although well studied in coastal waters, M. rubra is poorly examined in the open ocean. In the Irminger Basin, North Atlantic, the abundance of M. rubra was 0–5 cells/ml, which is low compared with that found in coastal areas. Distinct patchiness (100 km) was revealed by geostatistical analysis. Multiple regression indicated there was little relationship between M. rubra abundance and a number of environmental factors, with the exception of temperature and phytoplankton biomass, which influenced abundance in the spring. We also improve on studies that indicate distinct size classes of M. rubra; we statistically recognise four significantly distinct width classes (5–16, 12–23, 18–27, 21–33 μm), which decrease in abundance with increasing size. A multinomial logistic regression revealed the main variable correlated with this size distribution was ambient nitrate concentration. Finally, we propose a hypothesis for the distribution of sizes, involving nutrients, feeding, and dividing of the endosymbiont.     

Studies in Stomatal Behaviour: VIII. STOMATAL RESPONSES TO TEMPERATURE AND CARBON DIOXIDE CONCENTRATION IN ALLIUM CEPA L., AND THEIR RELEVANCE TO MID-DAY CLOSURE

It has been reported in the literature that onion leaf stomatatend to close at noon (Loftfield, 1921) and that the minimumcarbon dioxide concentration () in onion leaf tissue rises from0.012 per cent to 0.024 per cent. When the leaf temperatureincreases from 30°C. to 35°C (light intensity 900.f.c.)(Heath and Orchard, 1957). Experiments were therefore carried out of test the hypothesisthat raising the left temperature above about 30°C. causesstomatal closing movements in onion leaves (e.g. mid-day closure)by increasing the carbon dioxide concentration in the leaf tissue.This hypothesis has been supported by the results of these experiments.Another and diametrically opposed effect of temperature on stomatalmovements in onion leaves has, however, been discovered, Namelythat, provided the final width of stomatal pores.