Reproductive Ability of Hybrids between Japanese Pond Turtle (Mauremys japonica) and Reeves' Pond Turtle (Mauremys reevesii).

Hybridization induced by human activities, such as crossbreeding between invasive and native species, can adversely affect the natural biodiversity of an ecosystem. In Japan, the endemic turtle species Mauremys japonica is known to hybridize with the alien species Mauremys reevesii, and putative hybrids have been encountered in the wild. If M. japonica × M. reevesii hybrids can readily crossbreed with M. japonica, the hybridization with M. reevesii could lead to the extinction of pure M. japonica populations. However, information on the reproductive ability of M. japonica × M. reevesii hybrids is limited. In this study, we collected wild-caught hybrids from across western Japan to assess their reproductive ability. We investigated the nesting season timing, clutch size, embryonic development, hatching success, and sperm viability. The results showed that female hybrids nested during the same months as the parental species and had similar clutch sizes and hatching success. No embryonic development abnormalities were detected, and viable sperm were observed in all hybrid male semen samples. In conclusion, the fertility of M. japonica × M. reevesii hybrids appears to be similar to the fertilities of the parental species, posing a potential challenge for M. japonica conservation.

Random PCR-based genotyping by sequencing technology GRAS-Di (genotyping by random amplicon sequencing, direct) reveals genetic structure of mangrove fishes.

While various technologies for high-throughput genotyping have been developed for ecological studies, simple methods tolerant to low-quality DNA samples are still limited. In this study, we tested the availability of a random PCR-based genotyping-by-sequencing technology, genotyping by random amplicon sequencing, direct (GRAS-Di). We focused on population genetic analysis of estuarine mangrove fishes, including two resident species, the Amboina cardinalfish (Fibramia amboinensis, Bleeker, 1853) and the Duncker's river garfish (Zenarchopterus dunckeri, Mohr, 1926), and a marine migrant, the blacktail snapper (Lutjanus fulvus, Forster, 1801). Collections were from the Ryukyu Islands, southern Japan. PCR amplicons derived from ~130 individuals were pooled and sequenced in a single lane on a HiSeq2500 platform, and an average of three million reads was obtained per individual. Consensus contigs were assembled for each species and used for genotyping of single nucleotide polymorphisms by mapping trimmed reads onto the contigs. After quality filtering steps, 4,000-9,000 putative single nucleotide polymorphisms were detected for each species. Although DNA fragmentation can diminish genotyping performance when analysed on next-generation sequencing technology, the effect was small. Genetic differentiation and a clear pattern of isolation-by-distance was observed in F. amboinensis and Z. dunckeri by means of principal component analysis, FST and the admixture analysis. By contrast, L. fulvus comprised a genetically homogeneous population with directional recent gene flow. These genetic differentiation patterns reflect patterns of estuary use through life history. These results showed the power of GRAS-Di for fine-grained genetic analysis using field samples, including mangrove fishes.

Effects of dietary supplementation of ferulic acid and gamma-oryzanol on integument color and suppression of oxidative stress in cultured red sea bream, Pagrus major.

The effects of ferulic acid (FA) and gamma-oryzanol (OZ) supplementation on cultured red sea bream were examined. Commercial brown fish meal diets supplemented with FA (0.01-0.5%) or OZ (0.05-0.5%) were given to zero-year, cultured red sea bream for 98 days. After the experiment, the brightness of the integument color ("L" value) of FA- and OZ-administrated fish was higher than that of control fish. Furthermore, 2-Thiobarbituric acid reactive substances (TBARS) in the liver of FA- and OZ-administrated fish was lower than in control fish. These results indicate that FA and OZ suppressed not only dark-color pigmentation but also oxidative stress in cultured red sea bream.