Life history traits and damage potential of an invasive pest Brontispa longissima (Coleoptera: Chrysomelidae) on Satakentia liukiuensis

The coconut hispine beetle Brontispa longissima has been causing serious damage to the coconut palm Cocos nucifera in the Pacific, and Southeast and East Asia. This beetle also attacks Satakentia liukiuensis, an endemic palm on Ishigaki and Iriomote Islands, Japan. To assess the potential impact of B. longissima on S. liukiuensis, we examined the development period, survival rate, egg production and body size of B. longissima on S. liukiuensis at 22–31°C and consumption of S. liukiuensis leaf at 28°C. We also examined these life history traits on C. nucifera at 28°C to compare with those on S. liukiuensis. Brontispa longissima completed their development and reproduced on S. liukiuensis at 22–30°C. Linear regression analysis was used to estimate the effective cumulative temperature (k) as 891.2 degree‐days, and the lower developmental threshold as 13.3°C. On the basis of these values and monthly average temperatures on Ishigaki Island, it was estimated that B. longissima has four generations per year on the island. Satakentia liukiuensis was less suitable for B. longissima than C. nucifera in terms of immature survival, development time, resultant adult size and reproduction. The low quality of S. liukiuensis as a host‐plant may prevent the outbreak of B. longissima, which has not occurred yet on Ishigaki and Iriomote Islands.     

Evaluating the relationship between basin‐scale fish species richness and ecologically relevant flow characteristics in rivers worldwide

1. River flow alterations due to climate change and increasing water usage affect freshwater biodiversity including fish species richness. Here, we statistically explored the relationships of fish species richness to 14 ecologically relevant flow metrics as well as basin area and latitude in 72 rivers worldwide. 2. The statistical models best supported by the data included three variables with positive coefficients (mean river discharge, basin area and the maximum proportion of no‐flooding period) and three variables with negative coefficients (latitude, coefficients of variation in the frequency of low flow and the Julian date of annual minimum flow). 3. The model outputs have provided the first empirical indication that specific low‐ and high‐flow characteristics may be important in explaining variations in basin‐scale fish species richness. Our findings can be useful in identifying high‐risk basins for conservation of fish species diversity. 4. The results not only support the adoption of mean discharge as a predictor, but also suggest the importance of basin area in predicting basin‐scale fish species richness around the world.     

Steroid Producing Cells during Ovarian Differentiation of the Tilapia, Sarotherodon niloticus

In order to examine the initial appearance and development of the steroid producing cells (SPCs) during the process of ovarian differentiation, histology and ultrastructure of tilapia ( Sarotherodon niloticus ) ovaries were investigated from 10 to 50 days after hatching. In gonads of fry at 23–26 days after hatching, initial ovarian differentiation was confirmed by the differentiation of stromal aggregations in the proximal and distal region of the gonad on the side facing the lateral wall. This represents the initial formation of the ovarian cavity. At the same time as ovarian differentiation, a few large cells appeared initially in the vicinity of blood vessels. They have some of the ultrastructural features characteristic of SPCs such as a moderate number of mitochondria with tubular cristae, a large amount of smooth endoplasmic reticulum and many free ribosomes. Based on these ultrastructural criteria, together with the present finding that these cells further differentiated into the typical SPCs at older stages, these cells were identified as SPCs. Thereafter, by 30–50 days, SPCs increased gradually in number in the area enclosing the blood vessels of ovaries. The increase in SPCs coincided with the development of germ cells, including the multiplication of oogonia and the transformation from oogonia to oocytes.     

The Ontogeny of Thymic Myoid Cells in the Chicken

The ontogeny of thymic myoid cells in the chick was studied electron microscopically and immunohistochemically. An anticreatine kinase antibody which reacts specifically to skeletal muscle cells was used. This antibody reacts only to myoid cells in the thymus. Myoid cells were found in the medulla or in the interlobular region, though the number of the myoid cells was small. Immunohistochemically, myoid cells were detected on the 18th day of incubation. Mature myoid cells showed clear cross striations after immunohistochemical staining around the time of hatching. Electron microscopically, myoid cells were detectable on the 19th day of incubation. The discrepancy between immunohistochemical and electron microscopical detection may be due to the low number of myoid cells.