Microplastics Prevalence in Different Cetaceans Stranded along the Western Taiwan Strait.

Microplastics (MPs) pollution is of global concern, which poses serious threats to various marine organisms, including many threatened apex predators. In this study, MPs were investigated from nine cetaceans of four different species, comprising one common dolphin (Delphinus delphis), two pygmy sperm whales (Kogia breviceps), one ginkgo-toothed beaked whale (Mesoplodon ginkgodens), and five Indo-Pacific humpback dolphins (Sousa chinensis) stranded along the western coast of the Taiwan Strait from the East China Sea based on Fourier transform infrared (FTIR) spectroscopy analysis. Mean abundances of 778 identified MPs items were 86.44 ± 12.22 items individual-1 and 0.43 ± 0.19 items g-1 wet weight of intestine contents, which were found predominantly to be transparent, fiber-shaped polyethylene terephthalate (PET) items usually between 0.5 and 5 mm. The abundance of MPs was found at a slightly higher level and significantly correlated with intestine contents mass (p = 0.0004*). The MPs source was mainly likely from synthetic fibers-laden sewage discharged from intense textile industries. Our report represents the first study of MPs in pelagic and deep-diving cetaceans in China, which not only adds baseline data on MPs for cetaceans in Asian waters but also highlights the further risk assessment of MPs consumption in these threatened species.

High genetic differentiation of Indo-Pacific humpback dolphins (Sousa chinensis) along the Asian Coast of the Pacific Ocean.

The Indo-Pacific humpback dolphin (Sousa chinensis) is a vulnerable marine mammal species that inhabits shallow, coastal waters from Southeast China, southward throughout Southeast Asia, and westward around the Bay of Bengal to eastern India. Polymorphic microsatellites are useful for elucidating ecological and population genetics-related questions. Here, 18 new polymorphic microsatellites were developed from S. chinensis genomic DNA by Illumina MiSeq sequencing. Population genetic analyses were conducted on 42 S. chinensis individuals from three geographic locations, including the Xiamen Bay of China, the Western Gulf of Thailand, and Andaman Sea. Our microsatellite data revealed a strong and significant population structure among the three sampling regions (overall F ST = 0.371, p = .001). Pairwise mutual information index also demonstrated high levels of genetic differentiation between different region pairs (values range from 0.272 to 0.339, p < .001). Moreover, Structure analysis inferred three genetic clusters, with the high assignment probabilities of 95.92%, 99.47%, and 99.68%, respectively. Principal coordinate analysis plots of individuals divided entire genotypes into three clusters, indicating high level of genetic differentiation. Our results indicated the strong genetic structure in S. chinensis populations is a result of geographic distances. Other factors such as environmental variables, anthropogenic interference, and social behavior may also have contributed to population differentiation.

The prevalence and potential implications of microplastic contamination in marine fishes from Xiamen Bay, China.

The wide presence of microplastics (MPs) in the ocean leads their exposure on marine fish. MP contamination was reported for the gastrointestinal tracts and gills of 117 marine fishes attributed to nine species from Xiamen Bay, a special economic zone in China. Among species, MP abundance ranged from 1.07 items individual-1 to 8.00 items individual -1. Fibers dominated MP shapes, accounting for 59.03% of all MPs. Polymer composition was dominated by polyamide (26.97%) and rayon (17.56%). MPs were most commonly (55.22%) transparent, and most (77.61%) were < 1 mm in size. Our report represents the first of MP contamination in wild marine fish from Xiamen Bay, which we determine to be at an intermediate to slightly higher level compared with levels reported elsewhere, and provides further insights into potential risks of MPs pose to fish and human health.

Linear polyketides produced by co-culture of Penicillium crustosum and Penicillium fellutanum.

Two new polyketides, penifellutins A (1) and B (2), possessing a 22 carbon linear skeleton, were isolated from a co-culture of the deep-sea-derived fungi Penicillium crustosum PRB-2 and Penicillium fellutanum HDN14-323. Meanwhile, two esterification products of 1, penifellutins C (3) and D (4), were obtained because compound 1 could be esterified spontaneously when stored in methanol. Their configurations were difficult to determine because of chiral central crowdedness, structural flexibility and instability. As such, we solved this issue by comprehensively using Mo2(OAc)4-based CD experiments, density functional theory calculation of 13C NMR, DP4 + probability analysis and many chemical reactions, including making acetonide derivative, Mosher's method, PGME method, etc. Compounds 1 and 2 show obvious inhibitory activity on the liver hyperplasia of zebrafish larvae at a concentration of 10 µmol/L, while 3 and 4 show no activity, indicating that two carboxyls in the structure are important active sites. Supplementary Information: The online version contains supplementary material available at 10.1007/s42995-021-00125-8.

Genetic structure of the endangered Irrawaddy dolphin (Orcaella brevirostris) in the Gulf of Thailand.

The Irrawaddy dolphin (Orcaella brevirostris) is an endangered, small cetacean species which is widely distributed in rivers, estuaries, and coastal waters throughout the tropical and subtropical Indo-Pacific. Despite the extensive distribution of this species, little is known of individual movements or genetic exchange among regions in Thailand. Here, we evaluate the genetic diversity and genetic structure of O. brevirostris in the eastern, northern and western Gulf of Thailand, and Andaman Sea. Although phylogenetic relationships and network analysis based on 15 haplotypes obtained from 32 individuals reveal no obvious divergence, significant genetic differentiation in mitochondrial DNA (overall FST = 0.226, P < 0.001; ΦST = 0.252, P < 0.001) is apparent among regions. Of 18 tested microsatellite loci, 10 are polymorphic and successfully characterized in 28 individuals, revealing significant genetic differentiation (overall FST = 0.077, P < 0.05) among the four sampling sites. Structure analysis reveals two inferred genetic clusters. Additionally, Mantel analysis demonstrates individual-by-individual genetic distances and geographic distances follow an isolation-by-distance model. We speculate that the significant genetic structure of O. brevirostris in Thailand is associated with a combination of geographical distribution patterns, environmental and anthropogenic factors, and local adaptations.

Early divergence and differential population histories of the Indo-Pacific humpback dolphin in the Pacific and Indian Oceans.

The currently recognized Indo-Pacific humpback dolphin occurs in estuaries and surrounding shallow waters from the South China Sea to the Asian coast of the Indian Ocean. However, a recent study suggested that the humpback dolphin from the Bay of Bengal may represent a distinct phylogenetic species. In this study, we sequenced 915-bp mtDNA segments from five geographic populations in both Chinese and Thai waters; together with previously published sequences, these data revealed that the ancestral Indo-Pacific humpback dolphin might have split during the transition from the Oligocene to Miocene (23.45 Mya, 95% HPD: 16.65-26.55 Mya), and then dispersed along the Pacific and Indian Ocean coasts of Asia. Genetic differentiation was detected between most of the examined populations, except for only a few pairwise populations in the northern South China Sea. Genetic differentiation/distance between the humpback dolphins from the northern and southern South China Sea met the sub-species threshold value proposed for marine mammals, whereas that between the humpback dolphins in the Pacific and the Indian Ocean was above the species threshold. Bayesian inference of historic gene flow indicated low but constant northward gene flow along the Indian Ocean coast; however, there was a recent abrupt increase in gene flow in the Pacific region, likely due to the shortening coastline at the low stand of sea level. Our results revealed that the current taxonomic classification of Indo-Pacific humpback dolphins may not reflect their phylogeography.

Integrated Full-Length Transcriptome and RNA-Seq to Identify Immune System Genes from the Skin of Sperm Whale (Physeter macrocephalus).

Cetaceans are a group of secondary aquatic mammals whose ancestors returned to the ocean from land, and during evolution, their immune systems adapted to the aquatic environment. Their skin, as the primary barrier to environmental pathogens, supposedly evolved to adapt to a new living environment. However, the immune system in the skin of cetaceans and the associated molecular mechanisms are still largely unknown. To better understand the immune system, we extracted RNA from the sperm whale's (Physeter macrocephalus) skin and performed PacBio full-length sequencing and RNA-seq sequencing. We obtained a total of 96,350 full-length transcripts with an average length of 1705 bp and detected 5150 genes that were associated with 21 immune-related pathways by gene annotation enrichment analysis. Moreover, we found 89 encoding genes corresponding to 33 proteins were annotated in the NOD-like receptor (NLR)-signaling pathway, including NOD1, NOD2, RIP2, and NF-kB genes, which were discussed in detail and predicted to play essential roles in the immune system of the sperm whale. Furthermore, NOD1 was highly conservative during evolution by the sequence comparison and phylogenetic tree. These results provide new information about the immune system in the skin of cetaceans, as well as the evolution of immune-related genes.

Characterization of Insulin and Glucagon Genes and Their Producing Endocrine Cells From Pygmy Sperm Whale (Kogia breviceps).

Insulin and glucagon are hormones secreted by pancreatic ß and α cells, respectively, which together regulate glucose homeostasis. Dysregulation of insulin or glucagon can result in loss of blood glucose control, characterized by hyperglycemia or hypoglycemia. To better understand the endocrine physiology of cetaceans, we cloned and characterized the insulin and glucagon genes from pygmy sperm whale (Kogia breviceps). We obtained the complete coding sequences of the preproinsulin and preproglucagon genes, which encodes the preproinsulin protein of 110 amino acid (aa) residues and encodes the preproglucagon protein of 179 aa residues, respectively. Sequence comparison and phylogenetic analyses demonstrate that protein structures were similar to other mammalian orthologs. Immunohistochemistry and immunofluorescence staining using insulin, glucagon, and somatostatin antibodies allowed analysis of pygmy sperm whale islet distribution, architecture, and composition. Our results showed the pygmy sperm whale islet was irregularly shaped and randomly distributed throughout the pancreas. The architecture of α, ß, and δ cells of the pygmy sperm whale was similar to that of artiodactyls species. This is the first report about insulin and glucagon genes in cetaceans, which provides new information about the structural conservation of the insulin and glucagon genes. Furthermore, offers novel information on the properties of endocrine cells in cetacean for further studies.