Sea turtles represent an ancient lineage of marine vertebrates that evolved from terrestrial ancestors over 100 Mya. The genomic basis of the unique physiological and ecological traits enabling these species to thrive in diverse marine habitats remains largely unknown. Additionally, many populations have drastically declined due to anthropogenic activities over the past two centuries, and their recovery is a high global conservation priority. We generated and analyzed high-quality reference genomes for the leatherback ( Dermochelys coriacea ) and green ( Chelonia mydas ) turtles, representing the two extant sea turtle families. These genomes are highly syntenic and homologous, but localized regions of noncollinearity were associated with higher copy numbers of immune, zinc-finger, and olfactory receptor (OR) genes in green turtles, with ORs related to waterborne odorants greatly expanded in green turtles. Our findings suggest that divergent evolution of these key gene families may underlie immunological and sensory adaptations assisting navigation, occupancy of neritic versus pelagic environments, and diet specialization. Reduced collinearity was especially prevalent in microchromosomes, with greater gene content, heterozygosity, and genetic distances between species, supporting their critical role in vertebrate evolutionary adaptation. Finally, diversity and demographic histories starkly contrasted between species, indicating that leatherback turtles have had a low yet stable effective population size, exhibit extremely low diversity compared with other reptiles, and harbor a higher genetic load compared with green turtles, reinforcing concern over their persistence under future climate scenarios. These genomes provide invaluable resources for advancing our understanding of evolution and conservation best practices in an imperiled vertebrate lineage.

Saurida lessepsianus a new species of lizardfish (Pisces: Synodontidae) from the Red Sea and Mediterranean Sea, with a key to Saurida species in the Red Sea

The augmentation of traditional taxonomy by the addition of genetic methods, particularly DNA analysis, has revealed that many species that appeared identical morphologically throughout their distribution range are actually divided into two or more genetically distinct species. The whiting, Sillago sihama, is a fish that was considered to be of a wide Indo-Pacific distribution. Not long ago, what was considered to be S. sihama invaded the Mediterranean from the Red Sea via the Suez Canal. In our study we sequenced a 655-bp region of the mitochondrial cytochrome c oxidase subunit I gene (COI) from Hong Kong, southern Red Sea and Mediterranean populations of Sillago. We discovered that the first two (HK and southern Red Sea) are genetically similar while the sequencing of the Mediterranean population shows a significant divergence, confirming the existence of two distinct species. We further sequenced a segment of 178 bp (of the 655 bp) from a formaldehyde-fixed specimen from the northern Red Sea (Gulf of Suez) and found it to be identical to that of the Mediterranean population. We were thus able to confirm that the northern Red Sea population is the source for the invading population. The mitochondrial control region (D-loop) analysis of the Mediterranean population revealed that all 38 specimens have a single mitochondrial haplotype.

A total of six Red Sea inshore fish species with wide Indo-Pacific distribution, including Lessepsian migrants that reached the Mediterranean Sea via the Suez Canal, were studied and compared genetically to conspecific populations from Japan and the Seychelles. Examination of the cytochrome c oxidase 1 (COI) gene of Apogon cyanosoma, Sargocentron rubrum, Upeneus moluccensis, Spratelloide sdelicatulus, Gerres oyena and Terapon jarbua from Japan, the Red Sea, the Seychelles and the Mediterranean revealed that in five out of six fish species, a difference greater than 4% was found. These results indicate the importance of DNA genetic analysis in revealing possible cryptic species and supplementing classic taxonomic studies, as well as contributing to a reappraisal of the zoogeography and evolution of Indo-Pacific ichthyofauna and enhancing our understanding of fish biodiversity.