Takashi Haramura

Spanwise coherence characteristics of surface pressure field on 2-D bluff bodies

In order to clarify the mechanism of the high coherent structure of surface pressure in spanwise direction on bluff body surface, its coherence as well as cross-spectrum are evaluated for a 2-D rectangular and a 2-D hexagonal cross sections in smooth flow, in turbulent flow and in 2-D sinusoidal vertically fluctuating flow. The pressure coherence was confirmed to be higher than that of the approaching flow. It was found that the pressure fluctuation at slightly upstream from the reattaching point plays the most significant role in the evaluation of buffeting force.

Salinity Tolerance of Eggs of Buergeria japonica (Amphibia, Anura) Inhabiting Coastal Areas

Abstract Buergeria japonica is one of a few frogs that breed in coastal areas. To understand why this species can breed in coastal areas, I tested the salinity tolerance of eggs of B. japonica collected from a coastal area of Okinawa Island, Japan. All eggs hatched within four days after oviposition. At 0‰ salinity (control), over 94% of eggs hatched normally, and even at 1‰ salinity over 85% of eggs hatched. Survival rate of eggs was low at 2, 3, and 4‰, and no eggs hatched at 5‰ salinity. These results indicate that low salinity, close to pure water, is necessary for successful egg development, even for populations of B. japonica that breed in coastal areas. Future studies are necessary to examine whether females of B. japonica breeding in coastal areas select appropriate oviposition sites where the environmental salinity level is sufficiently low for eggs.

Activity Rhythm of Drosophila Kept in Complete Darkness for 1300 Generations

Locomotor activity rhythms of dark stock flies of Drosophila melanogaster kept in complete darkness for 700 to 1340 generations were examined. The stock was established by the late Prof. S. Mori in November 1954 to investigate long-term effects of darkness on organisms. The activity of flies was recorded under three types of light conditions: DD after LD12:12, and DD after exposure to a 3.5 h (P3) or 7.5 h (P7) light pulse. In all of these conditions, the experimental dark flies exhibited clear circadian rhythms similar to those of control light flies. We compare our results with those of various studies on troglobites.

Preliminary Survey on the Turtle Community in a Lotic Environment of the Kizu River

Abstract A mark-recapture study was conducted for turtles of the Kizu River, Kyoto Prefecture, Japan, from 1999 to 2002. We captured 179 individuals and recorded 745 recaptures, involving four species (Chinemys reevesii, Mauremys japonica, Trachemys scripta elegans, and Pelodiscus sinensis) and the hybrid between C. reevesii and M. japonica. Of these, C. reevesii occupied 63% of the whole sample in individual number. In all four microhabitats (main stream, branch, pools, and irrigation canal), this species was most dominant. In both C. reevesii and M. japonica, females were significantly larger than males in carapace length and body mass. Analysis of age structure suggested that females live longer than males in these two species, as well as in T. scripta elegans. The movement distance estimated from recaptured turtles did not differ between sexes in any species with the maximum distance being 675 m, 375 m, and 734 m in C. reevesii, M. japonica, and T. scripta elegans, respectively. Species composition of the turtle community in the present study site distinctly differed from that in a nearby (<2 km) lentic habitat, where M. japonica was reported to be dominant. Such difference in species composition may reflect the difference in habitat preference between C. reevesii and M. japonica.

Microhabitat selection by tadpoles of Buergeria japonica inhabiting the coastal area

Microhabitat selection is particularly important to increase the survival rate and reproductive success of animals inhabiting heterogeneous environments. I investigated microhabitat selection of Buergeria japonica tadpoles inhabiting the stream in a coastal area to reveal how animals select their appropriate habitat under heterogeneous and unstable environments on the subtropical Okinawa Island of Japan. Tadpoles are sensitive to subtle environmental changes, and the mouths of streams in coastal areas that have intense environmental fluctuations such as desiccation and sudden changes in current velocity would be risky habitat for tadpoles. Tadpoles of B. japonica can inhabit both lotic and lentic systems. Field observations showed that, among six physical factors (water depth, water temperature, salinity, pH, current velocity, and substrate), current velocity and water temperature were key factors in microhabitat selection by tadpoles. It is likely that tadpoles stay at low current velocity sites to reduce the probability of being washed out to the sea by a sudden squall and that selection of warmer sites would accelerate development of tadpoles so as to escape the heterogeneous aquatic habitat sooner.

Compound Eyes of Dark-fly

The ultrastructure of the compound eye of Dark- and control flies was examined. Flies of both groups reared with nutrient-poor Pearl’s medium exhibited a considerable degree of degeneration of the rhabdomeres. When they were reared with nutrient-rich standard cornmeal medium, the rhabdomeres of Dark-fly showed partial degeneration, while those of the control fly showed no degeneration. Thus, nutrients showed a far larger effect on the morphology of the eye than environmental light conditions, which slightly affected on eyes of flies that had experienced many generations of life without light.

Radiotelemetric Study of Movement Patterns of Lotic Freshwater Turtles during Breeding and Hibernation Seasons

ABSTRACT We conducted a radio tracking study to assess movement patterns and microhabitat use of lotic turtles during their nesting and hibernation seasons. During the nesting season, female turtles moved from the sandbank along the river to the outer-embankment and/or inner-embankment that includes rice fields. The maximum movement distance was over 2.5 km. Turtles frequently utilized terrestrial microhabitats for basking but also for other activities such as feeding and resting. Calm, deep aquatic sites near banks were used for hibernation. These results indicate that large areas that include different microhabitat type (both aquatic and terrestrial) are essential for freshwater turtles inhabiting river environments.

History of the “Dark-fly” Project

We summarize the history of the “Dark-fly” project here. We describe the method of maintenance and results of experiments performed by Shuiti Mori, who initially started this project about 60 years ago. We also conducted statistical re-examination of some data. As a result, we concluded that differences between the “Dark-fly” and a control fly were apparent in response to light, olfactory sense, and length of sensory hairs. Finally, we discuss future prospects of this project.

Genome Features of Dark-fly

Recent progress in genome science enables us to determine the whole genome sequences of laboratory-evolved organisms and to address the molecular mechanisms underlying environmental adaptation. We determined the whole genome sequence of Dark-fly and identified many genomic alterations in its genome. Analysis of the population genome structure revealed that about 5 % of genome regions were possibly selected during the Dark-fly history, and that 241 genes in those regions carry mutations. In addition, we identified 28 nonsense mutations in the Dark-fly genome, which probably disrupt or severely affect the function of the gene product. These results revealed unique features of the Dark-fly genome and provided a list of potential candidate genes involved in environmental adaptation. These candidate genes include a light receptor, olfactory receptors, and enzymes related to detoxification and neural development.

Circadian Rhythm of Dark-fly

Locomotor activity rhythms of Dark-stock flies of Drosophila melanogaster kept in complete darkness for 700–1,340 generations were examined. The activity of flies was recorded under the conditions of continuous darkness and of light–dark cycling. The activity rhythm of the experimental dark stock flies observed in continuous darkness was not weakened at 1,340 generations or at 700–900 generations. The degree of diurnality, measured by the ratio of daytime activity to the total activity per day under light–dark cycling, did not differ between the Dark-fly of 700–900 generations and the control fly subjected to normal daylight conditions for the same number of generations. Dark-flies showed a slightly weaker depression of activity in the daytime than control flies did. The possibility of alteration of circadian rhythm in Dark-fly is discussed.