NEGATIVE FREQUENCY‐DEPENDENT SELECTION IN FEMALE COLOR POLYMORPHISM OF A DAMSELFLY

Negative frequency‐dependent selection (NFDS) is one of the most powerful selective forces maintaining genetic polymorphisms in nature. Recently many prospective cases of polymorphisms by NFDS have been reported. Some of them are very complicated, although strongly supportive of the NFDS. Here we investigate NFDS in wild populations of the dimorphic damselfly Ischnura senegalensis, in which females occur as andromorphs and gynomorphs. Specifically, we (1) test fitness responses to morph frequencies, (2) built a simple population genetic model, and (3) compare the observed and predicted morph‐frequency dynamics. Fitnesses of the two morphs are an inverse function of its own frequency in a population, and are about equal when their frequencies are similar. Thus the conditions necessary for NFDS are satisfied. The long‐term field surveys show that the morph frequencies oscillate with a period of two generations. Morph frequencies in a small population undergo large oscillations whereas those in a large population do small oscillations. The demographic properties of the observed dynamics agree well with those of our model. This example is one of the simplest confirmed cases of NFDS maintaining genetic polymorphisms in nature.     

Deterioration of cichlid habitat by increased sedimentation in the rocky littoral zone of Lake Malawi

Lake Malawi has been affected by soil erosion across the catchment area. We experimentally investigated habitat preferences of cichlids in the rocky littoral zone to examine the influence of increased sedimentation on bottom-dwelling cichlids. Numbers of individuals and species, as well as the feeding rate of some of these cichlids, increased following the clearing of sediment. The results showed that these cichlids preferred sediment-free bottom and that the sedimentation causes deterioration of their habitats. Studies on the consequences of the habitat deterioration caused by increased sedimentation are needed in the management of these most diverse freshwater fish communities.     

Disturbed secretion of mutant adiponectin associated with the metabolic syndrome

Adiponectin, an adipocyte-derived protein, consists of collagen-like fibrous and complement C1q-like globular domains, and circulates in human plasma in a multimeric form. The protein exhibits anti-diabetic and anti-atherogenic activities. However, adiponectin plasma concentrations are low in obese subjects, and hypoadiponectinemia is associated with the metabolic syndrome, which is a cluster of insulin resistance, type 2 diabetes mellitus, hypertension, and dyslipidemia. We have recently reported a missense mutation in the adiponectin gene, in which isoleucine at position 164 in the globular domain is substituted with threonine (I164T). Subjects with this mutation showed markedly low level of plasma adiponectin and clinical features of the metabolic syndrome. Here, we examined the molecular characteristics of the mutant protein associated with a genetic cause of hypoadiponectinemia. The current study revealed (1) the mutant protein showed an oligomerization state similar to the wild-type as determined by gel filtration chromatography and, (2) the mutant protein exhibited normal insulin-sensitizing activity, but (3) pulse-chase study showed abnormal secretion of the mutant protein from adipose tissues. Our results suggest that I164T mutation is associated with hypoadiponectinemia through disturbed secretion into plasma, which may contribute to the development of the metabolic syndrome.     

Effects of anthropogenic shoreline alteration on fish emigration from small lakes

Limnology - In lentic ecosystems (e.g., lakes and ponds), anthropogenic shoreline alterations, such as concrete embankments, severely degrade habitat, affecting fish assemblage structure. Since...     

A unique primary structure, cDNA cloning and function of a galactose-specific lectin from ascidian plasma.

The complete amino acid sequence of a galactose-specific lectin from the plasma of the ascidian Halocynthia roretzi has been determined by sequential Edman degradation analysis of peptide fragments derived by proteolytic fragmentation and chemical cleavage of the reductive S-pyridylethylated lectin. Peptide fragments were separated by reverse-phase HPLC. The N-terminal and C-terminal amino acid sequences were determined by Edman degradation and enzymatic digestion. The H. roretzi plasma lectin is a single-chain protein consisting of 327 amino acids and four disulfide bonds, one of which was found to be cross-linked intramolecularly. A comparison of the amino acid sequence of the H. roretzi plasma lectin with the sequences of other proteins reveals that the H. roretzi lectin has a structure consisting of a twice-repeated sequence, a fibrinogen-related sequence and a C-type lectin-homologous sequence. The above amino acid sequence was verified by cDNA cloning of this lectin. Three cDNA clones that have single ORFs encoding the lectin precursor were isolated from an H. roretzi hepatopancreas cDNA library. The deduced amino acid sequences in the three cDNA clones contain the same sequence of the mature lectin molecule and the same putative signal sequence. In addition, it was demonstrated that this lectin can enhance phagocytosis by H. roretzi hemocytes. Thus, the plasma lectin is constructed into an oligomer structure via intermolecular disulfide bonds and plays a role in the biological defense of H. roretzi as a defense molecule.     

Telecytology in Hokkaido Island, Japan: results of primary telecytodiagnosis of routine cases

In 1997, an Internet-based static image telepathology system was built at Sapporo National Hospital, Japan. We can exchange high-resolution microscopical images through a file transfer protocol server and discuss cytological findings and diagnosis on an electronic mailing list. We applied the system to primary telecytodiagnosis. From May 1997 to April 1999 we have made diagnoses of 614 daily cases only by looking at the video monitor images transmitted from the cytotechnologist of Wakkanai Municipal Hospital 300 km distant from Sapporo. The concordance between telecytodiagnosis and glass slide diagnosis was 88.6%. Kappa statistics for cervical smears was 0.919 and that for specimens other than uterine cervix was 0.810. The accuracy of telecytodiagnosis was 91.4%, and was not substantially different from that of the conventional mail-based cytology in a previous year. We had five cases with a severely inappropriate diagnosis in telecytology, all of which however were quickly corrected by follow-up histological or cytological specimens. With the use of an electronic mailing list the participants had quick and sufficient discussions. We conclude that telecytology is very useful for primary cytodiagnosis in regional medicine and that it may raise the accuracy of cytodiagnosis in future, if we make consistent efforts to reflect the benefits of telecytology in daily practices. This is the first report of clinical results of telecytology from Japan.     

Differential display analysis reveals the expression of glutathione S-transferase ω and novel genes through an ITAM-containing receptor in ascidian immunocytes

The immunoreceptor tyrosine-based activation motif (ITAM) plays an important role in signal transduction through antigen receptors in mammalian lymphocytes. We previously reported that an ITAM-containing receptor, ascidian hemocyte ITAM-containing receptor 1 (AhITAMR1), exists on the hemocyte surfaces of the ascidian Halocynthia roretzi, and is involved in both phagocytosis and hemocyte aggregation. In this study, we carried out differential display screening of upregulated genes during H. roretzi hemocyte aggregation and found that at least three genes are upregulated. One encodes glutathione S-transferase ω (GSTω), while the other two encode novel proteins. The expression of all three genes was induced by treatment with a specific monoclonal antibody against AhITAMR1, while their expression was inhibited by wortmannin, BAPTA-AM, and cyclosporin A. We also found that the expression of GSTω was induced by treatment with anti-T cell receptor antibody in mouse peripheral T cells. We propose that signal transduction pathways mediated by ITAM-containing receptors are conserved from ascidian hemocytes to mammalian T cells. The nucleotide sequence data reported in this study have been submitted to the DNA Data Bank of Japan (DDBJ) with accession numbers AB187220 for 18A-1, AB187221 for 20A, and AB187222 for 20G-1.