Model analysis of the effect of environmental fluctuation on the species replacement pattern of pelagic fishes under interspecific competition

There are two factors affecting long-term fluctuation of planktotrophic pelagic fish: environmental fluctuation and interspecific competition. Long-term catch data of planktotrophic pelagic fishes in Japan suggest that the chub mackerel (species B) was replaced by the sardine (A), A was replaced by the anchovy, Pacific saury and horse mackerel (Group C), and species in group C were replaced by species B. If species A defeats B, B defeats C, and C defeats A in interspecific competitive ability, then the abundance of these three groups fluctuate forever and dominate in the same order. We call this cyclic advantage hypothesis for species replacement. In this model, environmental fluctuation affects the species replacement as a trigger. Environmental fluctuation does not determine the next dominant species but greatly affects when the next replacement occurs.     

Method for distinguishingLimnodrilus hoffmeisteri andLimnodrilus claparedeianus (Oligochaeta,Tubificidae) and its applicability in Lake Suwa

It is still next to impossible to distinguish species using immature worms of theLimnodrilus genus. A method was developed to separate mixed immature populations ofLimnodrilus hoffmeisteri andLimnodrilus claparedeianus into each species. The ratio of setal upper tooth length to lower tooth length, inL. hoffmeisteri andL. claparedeianus, ranged from 0.9 to 1.6 and from 1.3 to 2.1, respectively. Even if the median value of the frequency overlapped, this indistinguishable portion did not exceed 6% of each population.     

dnaA suppressor (dasF) mutants of Escherichia coli are stable DNA replication (sdrA/rnh) mutants

Summary The possible allelic relationship between dasF (dnaA suppressor) and sdrA/rnh (stable DNA replication/RNase H) mutations was examined. dasF mutations could not only suppress various dnaA(ts) mutations, but also the insertional inactivation of the dnaA gene or deletion of the oriC sequence, as could sdrA mutations. dasF mutants were found to exhibit the stable DNA replication phenotype, and the sensitivity to rich media, of sdrA mutants. The dasF and sdrA mutations were mapped very closely between metD and proA on the E. coli genetic map. The mutations were recessive to the wild-type allele for all the above phenotypes. It was concluded that dasF is allelic to sdrA/mh.     

The First Symbiont-Free Genome Sequence of Marine Red Alga,Susabi-nori (Pyropia yezoensis)

Nori, a marine red alga, is one of the most profitable mariculture crops in the world. However, the biological properties of this macroalga are poorly understood at the molecular level. In this study, we determined the draft genome sequence of susabi-nori (Pyropia yezoensis) using next-generation sequencing platforms. For sequencing, thalli of P. yezoensis were washed to remove bacteria attached on the cell surface and enzymatically prepared as purified protoplasts. The assembled contig size of the P. yezoensis nuclear genome was approximately 43 megabases (Mb), which is an order of magnitude smaller than the previously estimated genome size. A total of 10,327 gene models were predicted and about 60% of the genes validated lack introns and the other genes have shorter introns compared to large-genome algae, which is consistent with the compact size of the P. yezoensis genome. A sequence homology search showed that 3,611 genes (35%) are functionally unknown and only 2,069 gene groups are in common with those of the unicellular red alga, Cyanidioschyzon merolae. As color trait determinants of red algae, light-harvesting genes involved in the phycobilisome were predicted from the P. yezoensis nuclear genome. In particular, we found a second homolog of phycobilisome-degradation gene, which is usually chloroplast-encoded, possibly providing a novel target for color fading of susabi-nori in aquaculture. These findings shed light on unexplained features of macroalgal genes and genomes, and suggest that the genome of P. yezoensis is a promising model genome of marine red algae.     

Alternative models for species replacement of pelagic fishes

It is well known that the stock abundance of a pelagic fish usually fluctuates and a species of pelagic fish which was dominant in abundance is often taken over by another species. Several alternative models for species replacement among pelagic fishes are presented and analyzed: (A) environmental fluctuation, (B) strong density-dependent reproduction rate, (C) a two-species system with phase variation (density-dependent change of life history traits), (D) a two-species competition system with environmental fluctuation, (E) cyclic advantage relationship among three competitive species, and (F) a two-prey, one-predator system. Different model requires different number of species for the occurrence of species replacement. Three criteria to test each hypothesis from qualitative properties of species replacement are proposed. Possible management policies to decrease the amplitude of stock fluctuations are discussed. As a result, if the catching effort to mackerels which is rare now is large, or if the catching effort to the sardine is still large when it begins to decline in stock abundance, fisheries may be strong destabilizing effect on the stock abundance.     

Size of Paramecium bursaria individuals under cold and dark conditions

The photobiont-containing ciliate, Paramecium bursaria, was cultured for a week under three treatments: 25°C with light (25 L), 10°C without light (10 D), and 10°C with light (10 L). Cells of two strains under the 10 D treatment were enlarged relative to those under the 25 L treatment. This effect was very pronounced in that the length of enlarged cells was on average 130–140% of that of normal cells, and also reversible, as cells showed the opposite pattern within a week after switching treatments. In addition, many achromic drops were observed in cells cultured under the 10 D treatment. These drops are probably lipids produced by the photobiont, Chlorella variabilis.     

Phosphorylation at Tyr-694 of Nogo-A by Src-family kinases

Nogo-A is a neurite outgrowth inhibitor protein associated with myelin in the central nervous system. Unexpectedly, targeted disruption of Nogo-A in mice results in little or no improvement of axonal regeneration, suggesting that Nogo-A has other functions and/or receives complex regulations to exert its inhibitory functions. Here, we have found that Nogo-A becomes phosphorylated at Tyr-694 in the N-terminal region. The phosphorylation is mediated co-operatively by Src-family tyrosine kinases, which play many important roles in the nervous system. Levels of tyrosine phosphorylation of Nogo-A seem to be irrelevant to developmental stages of oligodendrocytes, and might be regulated by specific extracellular stimuli. Identification of tyrosine phosphorylation of Nogo-A will introduce an additional level of complexity into Nogo-A functions.