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.     

Inhibitory effect of cortisone acetate on the stimulation of rat liver cytosol l-serine Pyruvate aminotransferase by dibutyryl adenosine 3′,5′-monophosphate

An injection of cortisone acetate at a dose of 5 mg/100 g body weight concomitant with dibutryl cyclic AMP prevents the increase in the activity of rat liver cytosol serine aminotransferase (L-serine: pyruvate aminotransferase, EC 2.6.1.51) elicited by the nucleotide with a lag of about 2 h. If the glucocorticoid is given 2 h prior to the nucleotide inducer, the lag disappears. The inhibitory effect of cortisone acetate gradually decays and is no longer detectable 12 h following its administration. Theophylline, insulin and glucose at doses which affect significantly the level of tyrosine aminotransferase, have no effect on the level of serine aminotransferase and on the cortisone inhibition. The inhibitory effect of the glucocorticoid on the dibutyryl cyclic AMP-mediated increase in serine aminotransferase diminishes with the age of animals. Increase in the enzyme activity by a single dose of glucagon can also be inhibited by cortisone acetate and actinomycin D as in the case with dibutyrl cyclic AMP as an inducer. The possibility of the existence of a specific inhibitory factor which is formed in response to cortisone acetate is discussed.     

The haemagglutination activity in the different developmental stages and changes of this activity caused by analogues of insect hormones in two members of the Culex pipiens complex of mosquitoes

Abstract. Haemagglutination activity was studied in last larval instars, pupae and adults of both sexes of the Culex pipiens mosquito complex. In females of Culex pipiens quinquefasciatus Say, an anautogenous member of C. pipiens complex, activity was detected in the homogenate of the head‐thorax complex, gut and remaining abdomen (after removing the gut), before and after sucking water, glucose solution or blood. Similar investigations were made in females of autogenous Culex pipiens molestus Forskal, a member of the same mosquito complex. The results were compared with data obtained for males of these subspecies, plus the larvae and pupae. The results show that haemagglutination activity in adult females depends not on the sucking of blood, but on the age of the females. In newly emerged females, the level of activity was very low, but after 24 h or 48 h of activity was highly enhanced, even in females that had no possibility to suck water or other liquids including blood. Furthermore, in C. p. molestus, the haemagglutination activity does not change in hungry or engorged females, and a high level of activity was found in the gut of last larval instars, a developmental stage that never takes blood. Treatment with methoprene reduces haemagglutination activity in both sexes, but 20‐hydroxycdysone application decreased activity in the gut of females. It is suggested that haemagglutination activity may be regulated indirectly by the endocrine system. The possibility that haemagglutination activity may depend on some aspect of the digestive system that has no direct connection to blood uptake is discussed. In addition, the activity may be important not only for the elimination of infections, but also for the processing of food and the utilization and transport of nutrients.     

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.     

Presence of haemocyte-like cells in coccinellid reflex blood

Abstract.  Contrary to current assumptions, the reflex blood of two-spot ladybirds, Adalia bipunctata , and seven-spot ladybirds, Coccinella septempunctata , contains haemocyte-like cells. Furthermore, DNA can be extracted and amplified from coccinellid reflex blood, confirming the presence of haemocyte-like cells and demonstrating a nondestructive method of DNA extraction.     

Response of muscle-based biochemical condition indices to short-term variations in food availability in post-flexion reared sea bass Dicentrarchus labrax (L.) larvae

Six condition indices based on RNA, total soluble protein and two metabolic enzymes [lactate dehydrogenase (LDH) and citrate synthase (CS)] were analysed in muscle tissue of individual larvae, post-flexion reared sea bass Dicentrarchus labrax using DNA and total soluble protein as standards for size. In addition, the effect of 2 days of food deprivation on the cell proliferation rates was assessed. The RNA:DNA best reflected short-term changes in feeding conditions. If standardized by DNA content, LDH activity was a better indicator of condition than any other index but RNA:DNA. Further, the analysis of cell proliferation rates in muscle from 26 day-old larvae proved useful in distinguishing continuously fed larvae from individuals subjected to 2 days of fast.     

Transfection of a DNA/protein complex into nuclei of mammalian cells using polyoma capsids and electroporation

We used empty capsids ofpolyoma virus to transfer DNA fragments and DNA/protein complexes into human cells. We encapsulated labeled and unlabeled single stranded DNA fragments by viral capsids. A complex of DNA with a DNA binding protein, recA, will also be taken up by the capsids, whereas the free protein is not incorporated. We further compared this gentle biological method of DNA transfection with a well-established physical method, electroporation. Electroporation also allows the transfer of DNA as well as protein into cells, although there is no proof that a DNA/protein complex can survive the procedure functionally. Whereas the viability of capsid transfected cells is unaffected (100%), electroporation reduces the viability to 90–95%. On the other hand, the amount of DNA found in the nucleus of electroporated cells is higher than for cells treated with loaded viral capsids.     

Neutral mutations and repetitive DNA

We have previously shown that computer simulations of processes that generate selectively advantageous changes together with random duplications and deletions give rise to genomes with many different genes embedded in a large amount of dispensable DNA sequence. We now explore the consequences of neutral changes on the evolution of genomes. We follow the consequences of sequence divergences that are neutral when they occur in dispensable sequences or extra copies of genes present in multigene families. We find that when divergence occurs at about the same frequency as duplication/deletion events, genomes carry repetitive sequences in proportion to their size. Inspection of the genomes as they evolved showed that multigene families were generated by relatively recent duplications of single genes and so would be expected to be highly homogeneous.     

Tomato protoplast DNA transformation: physical linkage and recombination of exogenous DNA sequences

Tomato protoplasts have been transformed with plasmid DNA's, containing a chimeric kanamycin resistance gene and putative tomato origins of replication. A calcium phosphate-DNA mediated transformation procedure was employed in combination with either polyethylene glycol or polyvinyl alcohol. There were no indications that the tomato DNA inserts conferred autonomous replication on the plasmids. Instead, Southern blot hybridization analysis of seven kanamycin resistant calli revealed the presence of at least one kanamycin resistance locus per transformant integrated in the tomato nuclear DNA. Generally one to three truncated plasmid copies were found integrated into the tomato nuclear DNA, often physically linked to each other. For one transformant we have been able to use the bacterial ampicillin resistance marker of the vector plasmid pUC9 to rescue a recombinant plasmid from the tomato genome. Analysis of the foreign sequences included in the rescued plasmid showed that integration had occurred in a non-repetitive DNA region. Calf-thymus DNA, used as a carrier in transformation procedure, was found to be covalently linked to plasmid DNA sequences in the genomic DNA of one transformant. A model is presented describing the fate of exogenously added DNA during the transformation of a plant cell. The results are discussed in reference to the possibility of isolating DNA sequences responsible for autonomous replication in tomato.