Venoms from six species of marine fish: lethal and hemolytic activities and their neutralization by commercial stonefish antivenom

A specimen of the stonefish Synanceja verrucosa was captured in Okinawa in March 1988. Live specimens of the scorpionfish Inimicus japonicus were purchased from the Tokyo Central Wholesale Market in November 1988 and those of four species of zebrafish Pterois lumulata, P. volitans, P. antennata and Dendrochirus zebra from an aquarium in December 1988. Crude venoms were extracted from dorsal spines of the six species. All venoms exhibited lethal activity against mice and hemolytic activity specific for rabbit erythrocytes. The lethal activity (or hemolytic activity) of each venom was very unstable to freezing, lyophilization and heating. Both lethal and hemolytic activities of S. verrucosa venom were remarkably neutralized by the commerical stonefish (Synanceja trachynis) antivenom. This antivenom was also effective, to some extent, in counteracting the other venom activities. The neutralizing capacities of the antivenom were calculated to be 7310 LD₅₀ ml^-1 for S. verrucosa venom and 1 220 to 2 990 LD₅₀ ml^-1 for the other venoms. Results of neutralization tests suggest that venoms from the six species were comparable in terms of antigenecity.     

Light-dependency of nitrate uptake by phytoplankton over the spring bloom in Auke Bay,Alaska

The effect of light intensity on nitrate uptake by natural populations of phytoplankton was examined by ¹⁵N traceruptake experiments during the spring (March–May 1987) in Auke Bay, Alaska. The data were fit to a rectangular hyperbolic model which included a term for dark uptake. Three types of curves described nitrate uptake as a function of light intensity. The first (Type I) had a low half-saturation light intensity (K _I), low chlorophyll-specific uptakes rates, no dark uptake and occasional photoinhibition. These were observed during a period of biomass decrease, accompanied by low daily light and strong wind, prior to the major bloom. The second type (Type II) had relatively high K _I, high chlorophyll-specific uptake rates, and no dark uptake. Type II curves were observed during most of the period prior to nitrate depletion in the surface waters. Types I and II both appeared prior to nitrate depletion in the water and reflected variations in the light history of the phytoplankton population. The third type (Type III) occurred in nitrate-deplete conditions, when nitrate uptake was less dependent on light intensity (i.e., high rates of dark uptake and lower K _I). Decreased light-dependency during this period was coupled with physiological nitrogen deficiency in the population. Comparing these parameters to those of photosynthetic carbon fixation, K _Ivalues of nitrate uptake were generally higher than those of photosynthesis prior to nitrate depletion, and lower during nutrient-deplete conditions.     

Paternity assurance by “helpful” males: adaptations to sperm competition in burying beetles

Summary Male burying beetles invest parentally by participating in the burial of a carcass and in provisioning and guarding the larvae that come to the carcass. Since most of the females arriving at a carcass have stored fertile sperm within their spermathecae, sperm transferred by such helpful males must compete with other males' ejaculates for the fertilization of the female's eggs. We showed that these males are able to achieve a high level of paternity (mean=92%). The mechanism they employ is a repeat-mating tactic, i.e., the female is mated very frequently shortly before and during oviposition. Repeated matings are essential for a high reliability of paternity, since single copulations result in the fertilization of only a very small proportion of the female's eggs.     

The echolocation and hunting behavior of Daubenton's bat,Myotis daubentoni

Summary The echolocation and hunting behavior of Daubenton's bat (Myotis daubentoni) were studied in the field under completely natural conditions using a multiflash photographic system synchronized with high-speed tape recordings. The hunting behavior of M. daubentoni is separated into four stages. In the search flight stage Daubenton's bat flies with an average speed of 3.4±0.6 m/s SD usually within 30 cm over water surfaces searching for insects. After the detection of potential prey, the approach flight stage occurs, during which the bat approaches the target in a goal-directed flight. The stage tail down indicates that M. daubentoni is close to the potential prey (approximately 10–22 cm) and is preparing for the catch. The insects are caught with the interfemoral membrane, the feet, and sometimes with the additional aid of a wing. In the stage head down, the bat seizes the prey during flight. Immediately afterwards, Daubenton's bat returns to search flight. M. daubentoni shows the typical echolocation behavior of a vespertilionid bat, emitting frequency-modulated (FM) echolocation signals. The three behavioral stages search, approach, and terminal phase (Griffin et al. 1960) are used to describe the pulse pattern of foraging M. daubentoni in the field. The terminal phase (or buzz) of Daubenton's bat is separated into two parts: buzz I and buzz II. Buzz II is distinguished from buzz I by the following characteristics: a sharp drop in terminal frequency, a distinct reduction in the bandwidth of the first harmonic, a continuous high repetition rate throughout the phase in the range 155–210 Hz, very short pulses (0,25–0.3 ms) and interpulse intervals (4.5–5.0 ms) at the end of the phase, and a distinct decrease in duty cycle. A pause in echolocation separates the end of the terminal phase from the ongoing search phase. The reduction in sound duration after the detection of a target and during pursuits with successfull or attempted catches is discussed in relation to the actual distance of the bat to the target at each stage. It is likely that Daubenton's bat reduces sound duration during approach and terminal phase in order to prevent an overlap of an outgoing pulse with the returning echo from the target. It is argued that the minimum detection distance can be estimated from the sound duration during search flight. Estimates of detection and reaction distances of M. daubentoni based upon synchronized photos and echolocation sequences are given to corroborate this hypothesis. An average detection distance of 128 cm and an average reaction distance of 112 cm were determined. Each behavioral stage of foraging M. daubentoni is characterized by a distinct pattern of echolocation signals and a distinct stage in hunting behavior. The approach flight in hunting behavior coincides with the approach phase and with buzz I in echolocation behavior. The stage tail down corresponds to buzz II. The stage head down is correlated with a pause in echolocation. Immediately afterwards, the bat returns into search flight and into the search phase, emitting search signals.     

A simple bioassay for feeding-stimulants for the young seahare Aplysia juliana

Water extracts of a green alga (Ulva sp.) are known to elicit phagostimulatory responses against a seahare Aplysia sp. In 1984 we happened, however, to find that a seahare shows its feeding preference for filter paper on which an ether extract of Ulva sp. had been absorbed. We succeeded in establishing a simple and reliable bioassay procedure for the feeding-stimulants for the seahare A. juliana, which is applicable to isolation of the active principles.Chemical Studies on Phagostimulants for Marine Gastropods, Part V. For Part IV, see Sakata et al. (1985)     

Determination of photosynthetic pigment composition in an individual phytoplankton cell in seas and lakes using fluorescence microscopy; properties of the fluorescence emitted from picophytoplankton cells

To develop a method for the determination of photosynthetic pigment species in individual phytoplankton cells, especially natural picophytoplankton cells, the fluorescence spectra of intact cells were studied with cultured phytoplankton. The study was made mainly with phycoerythrin-containing picophytoplankton collected off Japan in 1982 with reference to diatomal species and phycoerythrin-free cyanophycean species. The spectra were measured for cell suspensions with an ordinary spectrofluorometer, and for individual cells with a microscope spectrofluorometer, paying special attention to the effect of cell-fixation. Results indicated that: (1) the cell-fixation with the glutaraldehyde and paraformaldehyde mixture modified phycoerythrin emission from picophytoplankton markedly in its wavelength location and intensity, but (2) the emission from phycocyanin was affected far less, and (3) the emission from chlorophyll a was not altered. However, the phycoerythrin emission modified by the fixation was found to be easily distinguished from other emissions, and kept its intensity high enough for detection with a fluorescence microscope. The fluorescence properties after the fixation were kept unaltered for a long period of time. Based on the results, we propose a simple method for the determination of photosynthetic pigments in individual phytoplankton cells in seas and lakes using fluorescence microscopy. Results of our tests with natural samples of phytoplankton are presented, and problems for further improvement are also discussed.     

Vertical distribution and feeding patterns of midwater fish in the central equatorial Atlantic II. Sternoptychidae

The vertical distribution of seven sternoptychid species was examined from RMT 1+8 samples collected aboard R. V. Meteor in March-April 1979 and from Royal Research Ship R.R.S. Discovery in July 1974 in the central equatorial Atlantic. During daytime sternoptychids occupied depths between 200 and 1250 m, with Sternoptyx pseudobscura living deepest, centering between 800 and 900 m, and Argyropelecus sladeni most shallow, aggregating predominantly at 300 and 400 m. They are all considered limited or partial migrants, ascending only some 100 and 200 m towards the surface at night. Only A. sladeni was observed to enter the epipelagic zone (0 and 200 m).-Feeding patterns were investigated from stomach content analyses of Sternoptyx diaphana, S. pseudobscura, Argyropelecus sladeni and A. affinis. Additional stomach contents were analysed from samples of S. diaphana, A. hemigymnus and A. olfersi collected in June 1985 from F.R.V. Walther Herwig in the temperate NE Atlantic at 46°N, 17°W by means of the Engel Trawl. The food spectrum of the six species is generally described, and additional dietary evidence regarding calanoid copepod prey is provided for four of these taxa. All sternoptychid species investigated were planktivorous, feeding predominantly on copepods and ostracods, except for the largest size class, which preyed heavily on euphausiids and amphipods. The relationship of predator size towards prey type and prey size is analysed for both Sternoptyx species. Of these, S. pseudobscura in particular exhibits taxonomic selectivity towards polychaete prey. The diet of both species of Sternoptyx included a number of epipelagic or even neustonic calanoid copepod species which contributed more than 50% of the total copepod population by numbers. So far it is not known how the predators find access to prey organisms of the upper 200 m, as netfeeding is considered unlikely. Cyclopoid copepods of the genus Sapphirina were observed as dietary component particular of S. diaphana.