Population Structure, Genetic Connectivity, and Signatures of Local Adaptation of the Giant Black Tiger Shrimp (Penaeus monodon) throughout the Indo-Pacific Region

Experimentalinfection study reveals differential susceptibilities of Penaeus monodon and Penaeus vannamei to Enterocytozoon hepatopenaei

Enterocytozoon hepatopenaei (EHP) is a significant pathogen affecting penaeid shrimp, particularly farmed whiteleg shrimp Penaeus vannamei, causing hepatopancreatic microsporidiosis (HPM). Although initially reported in tiger shrimp P. monodon, limited data exists on its current impact and pathogenic potential of EHP infection in tiger shrimp due to the shift toward farming P. vannamei. This study aimed to compare the susceptibility of P. monodon and P. vannamei via experimental oral EHP challenge. Challenge group shrimps were fed commercial feed mixed with minced EHP-infected hepatopancreatic tissue (1:1) containing 10⁶ copies/ng DNA for four days, while control groups received commercial pellet feed. Over 90 days, hepatopancreas and fecal samples were aseptically sampled and PCR-tested for EHP presence on days 7, 15, 30, 60, and 90 post-challenge (dpc). EHP loads, quantified using qPCR, were higher in P. vannamei (1.5-5.3 × 105 copies/μL DNA) compared to P. monodon (5.6-10.3 × 103 copies/μL DNA). Challenged P. monodon tested EHP-positive only in nested step SWP-PCR till 90 dpc. Further, infection was confirmed through wet mount, calcofluor white stain, histology, and in situ hybridization. EHP-challenged P. monodon had a higher survival rate (75 %) than P. vannamei (37.5 %). This first experimental report on EHP in P. monodon indicates it is less susceptible than P. vannamei, suggesting that the reintroduction of P. monodon can help deal with the EHP crisis the shrimp industry is currently going through.

Complete mitochondrial genome sequence of giant tiger prawn, Penaeus monodon, of Bangladesh

We report the complete mitochondrial genome sequence of the giant tiger prawn (Penaeus monodon) from Bangladesh. The circular genome spans 15,979 base pairs, with a GC content of 29.04%, and encodes 13 protein-coding genes, 22 tRNAs, 2 rRNAs, and 1 control region.

A Possible More Precise Management Unit Delineation Based on Epigenomic Differentiation of a Long-Distance-Migratory Marine Fish Scomberomorus niphonius

Understanding population structure and adaptive history is critical for designing appropriate management regulations for fisheries and conserving adaptive potential for the future. However, this is not easy for marine fish, especially those with long-distance migration abilities. In this study, we constructed a high-quality reference genome for Japanese Spanish mackerel (Scomberomorus niphonius) and explored its population structure using whole genomic and epigenomic data. Despite the high depth of the sequence data, we failed to identify geographical genetic differentiation of Japanese Spanish mackerel across Chinese coastal waters. However, whole-genome bisulphite sequencing can classify this species into the Bohai-Yellow Sea group and the East China Sea-South China Sea group. Genes involved in embryonic skeletal system development, limb morphogenesis functions, and adult locomotory behaviour were differentially methylated in the southern (Zhanjiang, ZJ) and northern (Western Dalian, WDL) populations and may play important roles as drivers of population structure in Japanese Spanish mackerel. Our study not only provides the first reference genome of the Japanese Spanish mackerel and sheds light on population differentiation at the epigenomic level, but also provides a methylome-based framework for population structure analyses of marine fish with long-distance migration ability. These findings are expected to facilitate the development of scientific programmes for the successful conservation of marine fishery resources.

A Seascape Genomics Perspective on Restrictive Genetic Connectivity Overcoming Signals of Local Adaptations in the Green Abalone (Haliotis fulgens) of the California Current System

Seascape genomics facilitates integrative research on eco-evolutionary forces, such as migration and natural selection, which shape genomic connectivity and structure and provide critical insights for conservation strategies. The green abalone (Haliotis fulgens) is distributed from California, United States, to Baja California Sur, Mexico, and exposed to a latitudinal environmental gradient in the California Current System. This study aimed to investigate genomic population structure and potential local adaptations of green abalone across its distribution. The green abalone exhibits a distinctive neutral genetic structuring influenced by geographic distance and marine currents rather than local adaptations. Analyses using 9100 neutral and 17 outlier SNPs revealed three distinct populations: the North group (California to Ensenada, Baja California), a population on Guadalupe Island, and the South group (coastal locations of the Baja California peninsula). The research underscores the significance of life history traits and larval dispersal in shaping genetic connectivity. Connectivity appears to be influenced by geographic distance on neutral genetic structure, overshadowing natural selection's role. Furthermore, no genome-environment associations to sea surface temperature values were found. Future research should integrate genetic data with ocean circulation modeling to better understand the mechanisms and outcomes of larval dispersal and genetic connectivity. This study emphasizes the importance of both local and binational (USA-Mexico) conservation efforts, suggesting the development of SNP marker panels for traceability and management. Collaborative strategies could serve as models for binational conservation initiatives in other ecoregions, promoting sustainable management and conservation of green abalone populations and other exploited species across national borders.

Development of DNA Markers for Acute Hepatopancreatic Necrosis Disease Tolerance in Litopenaeus vannamei through a Genome-Wide Association Study

Shrimp aquaculture is facing a serious disease, acute hepatopancreatic necrosis disease (AHPND), caused by Vibrio paraheamolyticus (VpAPHND). For sustainable shrimp aquaculture, massive losses of shrimp infected with VpAPHND must be prevented. Research and selection of shrimp tolerant to VpAPHND infection is a sustainable approach to reducing the risk of AHPND. This study focused on the identification and development of potential DNA markers associated with AHPND using DArT sequencing (DArTSeq) and a genome-wide association study. Three populations of post-larval Litopenaeus vannamei were immersed in VpAPHND to collect susceptible (D) and tolerant (S) samples. The 45 D and 48 S shrimp had their genotypes analyzed using DArTSeq. A total of 108,983 SNPs and 17,212 InDels were obtained from the DArTseq data, while the biallelic 516 SNPs and 2293 InDels were finally filtered with PIC < 0.1, MAF < 0.05, and a call rate ≥ 80%. The filtered variants were analyzed for their association with AHPND tolerance. Although there were no significantly associated SNPs and InDels above the Bonferroni correction threshold, candidate variants, four SNPs and 17 InDels corresponding to p < 0.01, were provided for further validation of the AHPND tolerance trait. The candidate SNPs are located on an exon of the zinc finger protein 239-like gene, an intron of an uncharacterized gene, and in intergenic regions. Most of the candidate InDels are in the intergenic regions, with fewer in the intronic and exonic regions. This study provides information on SNPs and InDels for white shrimp. These markers will support the variant database of shrimp and be useful in shrimp aquaculture for breeding selection.

Asymmetric genetic population structures at the range edges of a mangrove whelk

Many marine species are distributed across incredibly wide geographical ranges spanning thousands of kilometers often due to movement along prevailing ocean currents. However, data are lacking on genetic connectivity among populations of such widespread species within or among ecoregions, possibly due to the lack of appropriate datasets. In this study, we investigated the genetic structure of populations of the mangrove whelk, Terebralia palustris, using mitochondrial cytochrome oxidase subunit I (COI) sequences. Sequences generated for this study from Okinawa, Japan, were compared to samples from the coast of East Africa analyzed in a previous study. Interestingly, despite considerable distance separating them, the African and Japanese populations share major haplotypes and do not show clear genetic differentiation. At lower latitudes, core African populations exhibited higher genetic diversity than either the more southerly African and Japanese populations. Genetic β-diversity revealed that the northern edge population in Japan has a greater proportion of βSNE (the nestedness-resultant component), indicating contemporary migration, whereas the southern edge population in Africa is characterized by a predominant βSIM (the turnover component), suggesting historical demography. A potential cause of this dissimilarity could be due to the strong Kuroshio Current along the Ryukyu Islands, which may promote larval dispersal. These differing patterns suggest that there may be divergent responses to future climate change at the population level at the periphery of the range of T. palustris.

Transcriptomic Insights and the Development of Microsatellite Markers to Assess Genetic Diversity in the Broodstock Management of Litopenaeus stylirostris

The Pacific blue shrimp (Litopenaeus stylirostris) is a premium product in the international seafood market. However, intensified farming has increased disease incidence and reduced genetic diversity. In this study, we developed a transcriptome database for L. stylirostris and mined microsatellite markers to analyze their genetic diversity. Using the Illumina HiSeq 4000 platform, we identified 53,263 unigenes from muscle, hepatopancreas, the intestine, and lymphoid tissues. Microsatellite analysis identified 36,415 markers from 18,657 unigenes, predominantly dinucleotide repeats. Functional annotation highlighted key disease resistance pathways and enriched categories. The screening and PCR testing of 42 transcriptome-based and 58 literature-based markers identified 40 with successful amplification. The genotyping of 200 broodstock samples revealed that Na, Ho, He, PIC, and FIS values were 3, 0.54 ± 0.05, 0.43 ± 0.09, 0.41 ± 0.22, and 0.17 ± 0.27, respectively, indicating moderate genetic variability and significant inbreeding. Four universal microsatellite markers (CL1472.Contig13, CL517.Contig2, Unigene5692, and Unigene7147) were identified for precise diversity analysis in Pacific blue, Pacific white (Litopenaeus vannamei), and black tiger shrimps (Penaeus monodon). The transcriptome database supports the development of markers and functional gene analysis for selective breeding programs. Our findings underscore the need for an appropriate genetic management system to mitigate inbreeding depression, reduce disease susceptibility, and preserve genetic diversity in farmed shrimp populations.

Variation in Shrimp Allergens: Place of Origin Effects on Food Safety Assessment

Due to the widespread use of shellfish ingredients in food products, accurate food labelling is urgently needed for consumers with shellfish allergies. Most crustacean allergen detection systems target the immunorecognition of the allergenic protein tropomyosin. However, this mode of detection may be affected by an origin-dependent protein composition. This study determined if the geographic location of capture, or aquaculture, influenced the allergenic protein profiles of Black Tiger Shrimp (Penaeus monodon), one of the most farmed and consumed shrimp species worldwide. Protein composition was analysed in shrimp from nine different locations in the Asia-Pacific by SDS-PAGE, immunoblotting, and mass spectrometry. Ten of the twelve known shrimp allergens were detected, but with considerable differences between locations. Sarcoplasmic calcium-binding protein, myosin light chain, and tropomyosin were the most abundant allergens in all locations. Hemocyanin-specific antibodies could identify up to six different isoforms, depending on the location of origin. Similarly, tropomyosin abundance varied by up to 13 times between locations. These findings suggest that allergen abundance may be related to shrimp origin and, thus, shrimp origin might directly impact the readout of commercial crustacean allergen detection kits, most of which target tropomyosin, and this should be considered in food safety assessments.

Genome assembly of the Australian black tiger shrimp (Penaeus monodon) reveals a novel fragmented IHHNV EVE sequence

Shrimp are a valuable aquaculture species globally; however, disease remains a major hindrance to shrimp aquaculture sustainability and growth. Mechanisms mediated by endogenous viral elements have been proposed as a means by which shrimp that encounter a new virus start to accommodate rather than succumb to infection over time. However, evidence on the nature of such endogenous viral elements and how they mediate viral accommodation is limited. More extensive genomic data on Penaeid shrimp from different geographical locations should assist in exposing the diversity of endogenous viral elements. In this context, reported here is a PacBio Sequel-based draft genome assembly of an Australian black tiger shrimp (Penaeus monodon) inbred for 1 generation. The 1.89 Gbp draft genome is comprised of 31,922 scaffolds (N50: 496,398 bp) covering 85.9% of the projected genome size. The genome repeat content (61.8% with 30% representing simple sequence repeats) is almost the highest identified for any species. The functional annotation identified 35,517 gene models, of which 25,809 were protein-coding and 17,158 were annotated using interproscan. Scaffold scanning for specific endogenous viral elements identified an element comprised of a 9,045-bp stretch of repeated, inverted, and jumbled genome fragments of infectious hypodermal and hematopoietic necrosis virus bounded by a repeated 591/590 bp host sequence. As only near complete linear ∼4 kb infectious hypodermal and hematopoietic necrosis virus genomes have been found integrated in the genome of P. monodon previously, its discovery has implications regarding the validity of PCR tests designed to specifically detect such linear endogenous viral element types. The existence of joined inverted infectious hypodermal and hematopoietic necrosis virus genome fragments also provides a means by which hairpin double-stranded RNA could be expressed and processed by the shrimp RNA interference machinery.