Ontogenetic and seasonal changes in the diet of the halfbeak <Emphasis Type="Italic">Zenarchopterus dunckeri</Emphasis> at Iriomote Island,southern Japan

Ontogenetic and seasonal changes in the diet of the halfbeak Zenarchopterus dunckeri were examined in the Urauchi River estuary, Iriomote Island, southern Japan, using gut content analysis. The diet of this species changed dramatically with growth. Smaller juveniles fed mostly on small zooplankton and small gastropods, with a shift to the consumption of terrestrial insects, such as ants and flies, by larger individuals. Seasonal dietary differences were also apparent in adults. Ants were the most dominant prey item in the spring to fall months, whereas flies were abundant in the diet in the winter and early summer months.     

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, F_ST 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.     

Fish assemblage structure response to seagrass bed degradation due to overgrazing by the green sea turtle Chelonia mydas at Iriomote Island,southern Japan

Ichthyological Research - The fish assemblage structure response to rapid degradation of Enhalus acoroides seagrass beds due to overgrazing by green sea turtles (Chelonia mydas) was investigated at...