EVIDENCE FOR A MOSAIC HYBRID ZONE IN THE GRASS SHRIMP PALAEMONETES KADIAKENSIS (PALAEMONIDAE) AS REVEALED BY MULTIPLE GENETIC MARKERS

Molecular techniques provide powerful tools for studying the geographic structure of hybrid zones and the dynamics of gene exchange between incipient species. We examined allozyme variation at five loci (PGM, GPI, MDH-1, MDH-2, and LDH) for 27 populations of Palaemonetes kadiakensis from the central, coastal, and eastern regions of Texas. Central Texas populations of P. kadiakensis exhibited highly significant linkage disequilibrium and departures from Hardy-Weinberg genotype proportions. In populations with linkage disequilibrium, allelic differences at GPI defined two types of P. kadiakensis, designated A and B. Both types existed in central Texas with little or no evidence of interbreeding, whereas the populations from all other localities showed complete introgression of type B alleles into the type A gene pool. We also examined ribosomal DNA (rDNA) and mitochondrial DNA (mtDNA) variation in a subset of populations, chosen to cover a range of geographic locations and levels of linkage disequilibrium. Two groups of mtDNA haplotypes and two restriction fragment patterns for the rDNA corresponded to allozyme type A and B individuals in populations exhibiting linkage disequilibrium. In populations with ongoing hybridization, all hybrid animals (N= 15) exhibited type A mtDNA. Exhibition of type A mtDNA indicated that type A females had mated successfully with type B males, but type B females had not mated successfully with type A males. Genotype distributions suggest reduced reproduction by hybrid offspring in central Texas populations. These patterns are consistent with a mosaic model of hybrid zone dynamics.     

Mitochondrial phylogeography and population history of pine martens Martes martes compared with polecats Mustela putorius

The flora and fauna of Europe are linked by a common biogeographic history, most recently the Pleistocene glaciations that restricted the range of most species to southern refugial populations. Changes in population size and migration, as well as selection, have all left a signature on the genetic differentiation. Thus, three paradigms of postglacial recolonization have been described, inferred from the patterns of DNA differentiation. Yet some species, especially wide-ranging carnivores, exhibit little population structuring between the proposed refugia, although relatively few have been studied due to the difficulty of obtaining samples. Therefore, we investigated mitochondrial variation in pine martens, Martes martes, in order to understand the extent to which they were affected by glacial cycles, and compared the results with an analysis of sequences from polecats, Mustela putorius. A general lack of ancient lineages, and a mismatch distribution that is consistent with an expanding population, is evidence that the present-day M. martes and Mu. putorius in central and northern Europe colonized from a single European refugium following a recent glaciation. There has also been interspecific mitochondrial introgression between M. martes and the sable M. zibellina in Fennoscandia.     

Up- and down-regulation of membrane receptors as possible mechanisms related to the antiulcer actions of milk in rat gastric mucosa

The effects of a cow's milk diet on receptor activity and histamine metabolism in gastric glands and mucosa isolated from adult rats were examined. The milk diet was associated with (1) a decreased mobilization of H₂ receptors by histamine and (2) an increased mobilization of PGE₂ (prostaglandin E₂) receptors in mucous cells (cytoprotective effect) and parietal cells (antiacid effect). These changes are not observed for the receptors reducing pentagastrin- and histamine-induced gastric acid secretion (pancreatic/enteroglucagons, somatostatin) and stimulating mucus, bicarbonate and pepsin secretions in the rat (secretin). Cimetidine produced a parallel displacement of the histamine dose-response curve, suggesting competitive inhibition between this classical H₂ receptor antagonist and histamine in the two experimental groups. Prostaglandins and other components in milk such as EGF (epidermal growth factor) and somatostatin might therefore protect gastric mucosa by a differential control of PGE₂ and histamine H₂ receptor activity eitherdirectly (PGE₂ in milk) orindirectly (inhibition of endogeneous histamine synthesis/release and stimulation of PGE-I synthesis/release).     

Molecular cloning and physical characterization of a Brassica linear mitochondrial plasmid

Summary A linear mitochondrial plasmid reported to be associated with cytoplasmic male sterility in the genus Brassica was analyzed. A protein was found to be associated with the 5 ends of the plasmid. The entire plasmid was cloned by the homopolymer tailing technique via free hydroxyl groups present at its 3 ends. DNA sequence analysis of the cloned plasmid revealed a perfect terminal inverted repeat of 325 base pairs. Southern hybridization and restriction enzyme mapping analysis confirmed colinearity of the native plasmid and the clone, which showed significant homology with organelle DNA but not with nuclear DNA. Under high-stringency hybridization conditions, an internal 4.6 kb fragment of the 11.5 kb plasmid hybridized to the main mitochondrial genome in several species. Although the hybridization signal was weaker, the chloroplast genome also showed homology to the mitochondrial plasmid. The plasmid was undetectable at a molar ratio of less than 1/10 000 of the main mitochondrial genome in some lines of Brassica and Raphanus that contain the Ogura male sterile cytoplasm (cms). The absence of the plasmid in these sterile lines demonstrates that the plasmid is not required for the expression and maternal inheritance of male sterility.     

Waterlogging responses in dune,swale and marsh populations of Spartina patens under field conditions

Summary Soil waterlogging responses were examined in three Spartina patens populations along a steep flooding gradient in coastal Louisiana. Root anatomy and physiological indicators of anaerobic metabolism were examined to identify and compare flooding responses in dune, swale and marsh populations, while soil physicochemical factors were measured to characterize the three habitats. Soil waterlogging increased along the gradient from dune to marsh habitats and was accompanied by increases in root porosity (aerenchyma). Aerenchyma in marsh roots was apparently insufficient to provide enough oxygen for aerobic respiratory demand, as indicated by high root alcohol dehydrogenase activities and low energy charge ratios. Patterns of root metabolic indicators suggest that dune and swale roots generally respired aerobically, while anaerobic metabolism was important in marsh roots. However, in each population, relatively greater soil waterloging was accompanied by differences in enzyme activities leading to malate accumulation. In dune and swale roots under these circumstances, depressed adenylate energy charge ratios may have been the result of an absence of increased ethanol fermentation. These trends suggest that: 1) Aerenchyma formation was an important, albeit incomplete, long-term adaptation to the prevalent degree of soil waterlogging. 2) All populations adjusted root metabolism in response to a relative (short-term) increase in soil waterlogging.     

Uptake and metabolism of taurine in the green alga Chlorella fusca

Taurine entered the alga Chlorella fusca Shihira et Krauss strain 21l-8b via a pH and energy-dependent system ("permease"). Transport followed triphasic kinetics from 10⁻⁶ to 10⁻² M with K_m values for taurine of 5.4 × 10⁻⁵, 4.1 × l0⁻⁴ and l.5 × 10⁻³ M. This uptake system was specific for sulfonic acids and showed no affinity for α- and β -amino acids or Na⁺; thus the permease of C. fusca is different from all known taurine transport systems with respect to structural specificity and lack of Na⁺ -dependence. Uptake was not observed in sulfate-grown algae but developed as a response to sulfate limitation within 2 h. Sulfate addition caused a rapid decline in taurine transport capacity. Labeled taurine was rapidly metabolized in C. fusca to sulfate and ethanolamine, suggesting oxidative hydrolysis as the mechanism of C-S bond cleavage. Further incorporation of these catabolic products in C - and S -metabolism was demonstrated. Taurine catabolism was also detected in other green algae and some cyanobacteria.     

Twenty-four-hour variations in activity,core temperature,metabolic rate,and respiratory quotient in captive chinese pangolins

The circadian rhythms in activity, core temperature (T_c), O₂ consumption, CO₂ production, and respiratory quotient (RQ) were monitored in four captive Chinese pangolins (Manis pentadactyla). The pangolins were strictly nocturnal, never emerging from their nest before 1600 h, and their intermittent activity continued no later than 0230. As is usual in nocturnal mammals, the highest values observed in T_c, O₂ consumption, and CO₂ production occurred during the night; the lowest values occurred during the day. The magnitude of the variation in T_c, O₂ consumption, CO₂ production, and RQ averaged 1.2°C, 1.3 ml O₂ kg^?1 min^?1, 1.2 ml CO₂ kg^?1 min^?1, and 0.24, respectively. The circadian pattern in RQ was independent of activity, T_c, and the metabolic parameters and was of a different character than the patterns exhibited in the other variables. RQ remained constant at either a high or low level for long periods (8–10 h) and then increased or decreased relatively rapidly (1–2h) to the other level as in a square wave, whereas the rhythms in the other variables are similar to sine waves. The sharp increase in RQ was followed by a slow decline in T_c, and the sharp decline in RQ was followed by a slow increase in T_c.     

The metabolism of deoxyguanosine in mitochondria. Characterization of the uptake process

Summary The uptake of deoxyguanosine by rat liver mitochondria was characterized. The process required an intact mitochondrial membrane and exhibited a dependence on added phosphate. Deoxyguanosine uptake was minimally influenced by Mg²⁺ or Mn²⁺, but Ca²⁺ at concentrations above 0.5 mM were detrimental. Of the deoxynucleosides tested, only deoxyinosine inhibited the uptake of deoxyguanosine. The ribonucleoside guanosine was not observed to compete with its deoxynucleoside analog. Known inhibitors of nucleoside transport, cytochalasin B and NBMPR, did not block deoxyguanosine uptake, but the sulfhydryl reagents NEM and pCMB were both inhibitory. The uptake of deoxyguanosine was shown to be a saturable process and an apparent Km of 0.64 M was calculated from a Hanes plot.