The Site and Time of Expression of MIF in Frog Development

A ventrally localized melanization-inhibiting factor (MIF) has been suggested to play a role in the expression of dorsal-ventral pigment patterns in amphibia. Here we investigate the onset and localization of MIF appearance in frog development. The expression of MIF was analyzed in the wild-type and gray-eyed mutant (g/g) of Rana japonica by immunoblotting and immunohistochemistry using an anti-MIF neutralizing monoclonal antibody. Western blot analysis revealed that the anti-MIF antibody recognized ～51 kDa and ～58 kDa bands. The 51 kDa band first appeared at the external gill stage, while 58 kDa band was additionally detected at the hindlimb bud stage. With the use of immunohistochemistry, it was found that the anti-MIF antibody stained the whole epidermis of the embryos at the external gill stage; however, the staining was stronger in lateral and ventral epidermis than in dorsal. Staining with the anti-MIF antibody was observed only in the outer epidermis of the ventral skin, but not in the dorsal skin during and after metamorphosis. The spatial expression of MIF in the wild-type was the same as that in the gray-eyed mutant. The same immunohistochemical result was obtained in the adults of R. nigromaculata. These results suggest that MIF is involved in the formation of the dorsal-ventral pigment pattern.     

A two‐step mechanism controls the timing of behaviour leading to emergence from soil in adult males of the scarab beetle Dasylepida ishigakiensis

Adults of the white grub beetle Dasylepida ishigakiensis Niijima et Kinoshita (Coleoptera: Scarabaeidae) emerge from the soil around dusk for mating on subtropical islands. The present study examines the factors controlling the emergence of males in the laboratory. There are two steps involved. Standby behaviour (i.e. insect head appears at the soil surface) can be observed for several hours before the beetles actually emerge for mating. The standby behaviour is facilitated by warm conditions, although the proportion of standby individuals is influenced not only by the temperature on that day, but also by that on the previous day. Experiments in which beetles are exposed to photoperiod and thermoperiod combinations, in and out of phase, show that temperature is more important in inducing standby and emerging behaviour than light alone. For the second step, factors such as temperature, light and the presence of the female sex pheromone determine whether males will leave the standby position and emerge onto the ground. The female sex pheromone stimulates standby beetles to exhibit emerging and wing vibration behaviours, although the effect depends on when it is presented to beetles. Beetles burrow back into the soil; this behaviour is influenced by illumination and time of the day but not by temperature. The results suggest that D. ishigakiensis possesses a sophisticated mechanism controlling male emergence from the soil.     

Presence of larval and adult diapauses in a subtropical scarab beetle: graded thermal response for synchronized sexual maturation and reproduction

Abstract The white grub Dasylepida ishigakiensis has a 2‐year life cycle and spends approximately 9 months as a nonfeeding larva, pupa and adult on a subtropical island. Evidence is presented indicating that this beetle has two diapauses that appear to synchronize this long life cycle with the seasons. Larvae exposed to 20, 22.5, 25 and 27.5 °C late in the third (last) stadium pupate rapidly except for some individuals kept at the highest temperature. The latter pupate upon transfer to 22.5 °C, indicating that larval diapause is maintained at high temperature but terminates upon transfer to a lower temperature. Pupal development is directly temperature‐dependent in the range 20–30 °C. Adults develop reproductive organs (i.e. the ovary in females and the seminal vesicles and accessory glands in males) rapidly at 15 and 20 °C, whereas those kept at 25 °C take a long time to do so. Ovarian development is completely suppressed at 30 °C but initiated upon transfer to 20 °C. In the laboratory, males with well‐developed reproductive organs mate even with sexually immature females , whereas females with undeveloped ovaries show no sexual behaviour. Although the two diapauses of this species are thermally regulated (i.e. a characteristic commonly expressed by insects in summer diapause), adults of this beetle emerge from pupae late in the autumn and remain in the soil for 2 months. Adult diapause effectively serves to synchronize the time of sexual maturation with the coldest month of the year.     

Interspecific variation in the defensive responses of ant mutualists to plant volatiles

In ant–plant mutualist systems, ants patrol their host plants and search for herbivores. Such patrolling can be inefficient, however, because herbivore activity is spatio-temporally unpredictable. It has been proposed that rapid and efficient systems of communication between ants and plants, such as volatile compounds released following herbivory, both elicit defensive responses and direct workers to sites of herbivore activity. We performed bioassays in which we challenged colonies of two Amazonian plant-ants, Azteca sp. and Pheidole minutula , with extracts of leaf tissue from (1) their respective host-plant species ( Tococa bullifera and Maieta guianensis , both Melastomataceae), (2) sympatric ant-plants from the Melastomataceae, and (3) two sympatric but non-myrmecophytic Melastomataceae. We found that ants of both species responded dramatically to host-plant extracts, and that these responses are greater than those to sympatric myrmecophytes. Azteca sp. also responded to non-myrmecophytes with an intensity similar to that of sympatric ant-plants. By contrast, the response of P. minutula to any non-myrmecophytic extracts was limited. These differences may be driven in part by interspecific differences in nesting behaviour; although P. minutula only nests in host plants, Azteca sp. will establish carton satellite nests on nearby plants. We hypothesize that Azteca sp. must therefore recognize and defend a wider array of species than P. minutula .  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 241–249.     

Melanosome Formation in Cultured Amelanotic Melanophores of Rana brevipoda by a Frog Tyrosinase cDNA Transfection

A cDNA encoding tyrosinase of Rana nigromaculata was introduced into cultured, tyrosinase-negative amelanotic melanophores of R. brevipoda by a calcium phosphate precipitation method. Within a few days following transfection, dark pigmentation became visible in a small number of cells. Light microscopic observation revealed that the morphology of these transformed cells was comparable to that of normal melanophores in culture, and their proliferative activity was lower than that of amelanotic cells. Ultrastructural examination verified that amelanotic melanophores possessed a relatively small number of premelanosomes while the transformants contained numerous melanosomes at various stages of pigment deposition. The result indicated that tyrosinase cDNA of R. nigromaculata was expressed in amelanotic melanophores of R. brevipoda inducing the maturation of premelanosomes. It was also suggested that the expression of transfected tyrosinase cDNA had promoted differentiation of the amelanotic cells into fully developed melanophores.     

Survey of Evidence for Neurosecretion in Gastropod Molluscs

In gastropods that have been studied, there is some indicationof the presence of neurons with specialized staining propertiesthat are possibly neurosecretory. However, there are no stainsspecific for neurosecretion, and certain cellular inclusionscan simulate secretory products. The presence of elementaryneurosecretory granules does not as such determine neurosecretorystatus since such granules may represent neurotransmitters. Evidence of cyclical secretory activity of so-called neurosecretoryneurons is most frequently related to reproductive phenomena,but there are also instances of control of water balance andhibernation. The existence of neurohemal organs within nerves and commissureshas been described in several species. So-called neuroglandularcomplexes have been reported in association with the nervoussystem. Vesicles incorporated in the central nervous systemmay be sensory rather than glandular. Some caution is neededin estimating secretory activity of these complexes. Possible non-neural endocrine glands adjacent to the centralganglia have been described. In pulmonates granule-laden fibersare associated with the mediodorsal bodies; however, the natureof the neurosecretomotor or neurosecretory-neuropil controlis still unclear, both morphologically and physiologically.     

CELLULAR DIFFERENTIATION IN THE URINARY BLADDER OF A EURYHALINE MARINE FISH, GILLICHTHYS MIRABILIS, IN RESPONSE TO ENVIRONMENTAL SALINITY CHANGE

The urinary bladder of a euryhaline marine teleost, Gillichthys mirabilis , was studied by light and electron microscopy. An enlargement of the mesonephric ducts forms a sac-like structure lined by an epithelium composed of two major cell types. Tall columnar cells continuous with the duct epithelium are characterized by a large number of mitochondria and well-developed rough and smooth endoplasmic reticulum. Tubular smooth endoplasmic reticulum is more developed in the basal cytoplasm and often opens into the extracellular space. A second cell type, the low cuboidal cells, forming most of the bladder epithelium, has fewer mitochondria. Basal cells are rarely observed and mucous cells are absent.
In seawater Gillichthys , cells of both types are separated by narrow intercellular spaces. In 5% seawater fish, the columnar cells show functional activation, as evidenced by an increased number of mitochondria and more extensive tubular smooth endoplasmic reticulum. No such changes were noted in the cuboidal cells; however, the lateral intercellular spaces are dilated probably owing to hypotonicity of the urine in the hypotonic environment. A functional difference between the two cell types is strongly suggested. The columnar cells may be responsible for active sodium uptake in hypotonic seawater environments.