Host Mussels Research Articles

Chronic polystyrene microplastics exposure-induced changes in thick-shell mussel (Mytilus coruscus) metaorganism: A holistic perspective

Microplastics have emerged as a significant global concern, particularly in marine ecosystems. While extensive research has focused on the toxicological effects of microplastics on marine animals and/or their associated microorganisms as two separate entities, the holistic perspective of the adaptability and fitness of a marine animal metaorganism—comprising the animal host and its microbiome—remains largely unexplored. In this study, mussel metaorganisms subjected chronic PS-MPs exposure experienced acute mortality but rapidly adapted. We investigated the response of innate immunity, digestive enzymes and their associated microbiomes to chronic PS-MPs exposure. We found that PS-MPs directly and indirectly interacted with the host and microbe within the exposure system. The adaptation was a joint effort between the physiological adjustments of mussel host and genetic adaptation of its microbiome. The mussel hosts exhibited increased antioxidant activity, denser gill filaments and increased immune cells, enhancing their innate immunity. Concurrently, the gill microbiome and the digestive gland microbiome respective selectively enriched for plastic-degrading bacteria and particulate organic matter-utilizing bacteria, facilitating the microbiome’s adaptation. The microbial adaptation to chronic PS-MPs exposure altered the ecological roles of mussel microbiome, as evidenced by alterations in microbial interactions and nutrient cycling functions. These findings provided new insights into the ecotoxicological impact of microplastics on marine organisms from a metaorganism perspective.

Reproductive Strategies and Embryonic Development of Autumn-Spawning Bitterling (Acheilognathus rhombeus) within the Mussel Host.

We investigated the reproductive strategies and embryonic development of Acheilognathus rhombeus (a bitterling species that spawns in autumn) within its freshwater mussel host in the Bongseo Stream, South Korea. By focusing on survival mechanisms during critical stages of embryonic development, the selective use of mussel gill demibranchs by the bitterlings and associated adaptive traits were observed over 1 year. A significant diapause phase occurs at developmental stage D, which lasts for approximately 7 months, allowing embryos to survive winter. Development resumes when the temperature exceeds 10 °C. Minute tubercles on the embryos (crucial for anchoring within the host gill demibranchs and preventing premature ejection) exhibit the largest height during diapause, and the height decreases when developmental stage E is reached, when growth resumes. Acheilognathus rhombeus embryos were observed in 30.5% of the mussels, mostly within the inner gills, thereby maximizing spatial use and oxygen access to enhance survival. These results highlight the intricate relationship between A. rhombeus and its mussel hosts, demonstrating the evolutionary adaptations that enhance reproductive success and survival. This study provides valuable insights into the ecological dynamics and conservation requirements of such symbiotic relationships.

The reproductive costs of bitterling fish and zebra mussel parasitism to a unionid mussel

Unionid mussels are one of the most vulnerable groups of animals, with multitude of factors responsible for the decline of their populations in the freshwater ecosystems. Many of those causes stem from interspecific relationships. Direct data on the reproductive costs incurred to unionids through parasitism by fish and other mussel species are incomplete. We used field experiments to test whether reproduction of the swollen river mussel (Unio tumidus) is affected by parasitism by the European bitterling fish (Rhodeus amarus) and zebra mussel (Dreissena polymorpha). We documented that bitterling brood can develop in the gills of female, male and hermaphrodite mussels. Our research showed that male mussels carried more fish offspring than female U. tumidus and bitterling embryo survival appeared higher in the outer gill demibranchs. Parasitised female U. tumidus suffered reduced fecundity in terms of a reduced number of mature ovulated oocytes and increased oocyte degeneration. Our data lend clear support to the hypothesis that bitterling fish embryos parasitizing mussel gills and epibiont zebra mussel fouling unionid shells represent a major cost to the reproductive success of their host mussels. Extended gonadal activity (multiple spawning) of U. tumidus spreads their spawning time over a longer period, which may mitigate the costs of parasitism.

Deciphering deep-sea chemosynthetic symbiosis by single-nucleus RNA-sequencing

Bathymodioline mussels dominate deep-sea methane seep and hydrothermal vent habitats and obtain nutrients and energy primarily through chemosynthetic endosymbiotic bacteria in the bacteriocytes of their gill. However, the molecular mechanisms that orchestrate mussel host–symbiont interactions remain unclear. Here, we constructed a comprehensive cell atlas of the gill in the mussel Gigantidas platifrons from the South China Sea methane seeps (1100 m depth) using single-nucleus RNA-sequencing (snRNA-seq) and whole-mount in situ hybridisation. We identified 13 types of cells, including three previously unknown ones, and uncovered unknown tissue heterogeneity. Every cell type has a designated function in supporting the gill’s structure and function, creating an optimal environment for chemosynthesis, and effectively acquiring nutrients from the endosymbiotic bacteria. Analysis of snRNA-seq of in situ transplanted mussels clearly showed the shifts in cell state in response to environmental oscillations. Our findings provide insight into the principles of host–symbiont interaction and the bivalves' environmental adaption mechanisms.

Under the cover of ice: Trematode infections affect survival and growth of wintering mussels

Parasites play many regulating roles that are increasingly recognized in different ecosystems. In coastal ecosystems, the trematode Himasthla elongata infects blue mussel Mytilus edulis, a foundation species that shapes the functioning of intertidal communities. Although the largest impacts of infections occur during the summer months, the parasites form long-lived cysts that can be harmful to their host mussels under winter conditions. Here, we experimentally show that even moderate levels of infection by H. elongata have a detrimental effect on the survival and growth rate of wintering blue mussels. These parasite-induced costs during winter may potentially affect populations of blue mussels in coastal habitats, with ramifications for the whole ecosystem.

Host size matters for reproduction: Evolution of spawning preference and female reproductive phenotypes in mussel-symbiotic freshwater bitterling fishes.

Bitterling fishes evolve an idiosyncratic symbiosis with freshwater mussels, in which they are obligated to spawn in the gills of mussels for reproduction. In recent years, freshwater mussel populations have been drastically diminishing, due to accelerating anthropogenic impacts, which can be large threats to the risk of bitterling's extinction cascade (i.e. 'coextinction'). The host mussel size may be an important factor driving the adaptation and evolution of bitterling's reproductive phenotypes. Here we examined the host size preference and morphological adaptation of female bitterling to the host size from 17 localities at the Han River in Korea. Using our developed molecular-based species identification for bitterling's eggs/larvae inside the mussels, we further determined the spawning patterns of seven bitterling species. Mean length of spawned mussels (N = 453) was significantly larger than that of unspawned mussels (N = 1814), suggesting that bitterling prefers to use larger hosts as a spawning ground. Spawning probability was clearly greater as mussel size increases. Results of our reciprocal transplant experiments do provide some evidence supporting the 'bitterling's larger host preference' hypothesis. Interspecific competition appeared to be intense as two fish species often spawned eggs in the same mussel individuals simultaneously. Longer ovipositor and more elongated egg may evolve in females of Tanakia signifer in response to larger host environments. The observed bitterling's spawning preference for large-sized mussels may evolve perhaps because of the fitness advantage in relation to the offspring survival. Our findings further inform on the development of effective conservation and management strategy for the endangered bitterling fishes.

Trophic relationship between mussels and scale worms under various seepage intensities in the haima cold seep: Insights from stable isotopes (δ13C and δ15N) and C:N:P stoichiometry

The deep-sea mussels Gigantidas haimaensis (Mytilidae: Bathymodiolinae) usually contain one scale worm Branchipolynoe pettiboneae in their mantle cavity in the Haima cold seep, South China Sea. To explore their environmental adaptation and coexistence mechanisms, the stable isotopes (δ13C and δ15N) and C:N:P ecological stoichiometry of G. haimaensis and the associated B. pettiboneae were investigated under different methane seepage intensities. In the presence of seepage, most mussels harbored one scale worm in their mantle cavity. However, under seepage cease, the physiological status of mussels looked unhealthy, and no scale worm appeared in their bodies. The variation in δ13C values was great among different mussel tissues, ranging from −49.7‰ to −57.8‰. The δ13C values of mussel tissues followed the order of foot > gill > mantle under active seepage, while no regular trend was found under seepage cease. The δ13C and δ15N of scale worms were averagely enriched by 2.9 ‰ and 3.2 ‰ relative to their mussel hosts, and the trophic niche separation between scale worms and mussels was more significant under active seepage. The δ13C value of mussel foot was significantly higher under active seepage (average −50.8‰) than under seepage cease (average −55.1‰), indicating that mussels might ingest and assimilate more 13C-rich suspended particulate organic matter (POM) under active seepage. In mantle tissues, the high C:N ratio and low δ13C value should be attributed to the high content of energy storage substances. The C:N ratio of mantle dramatically declined with the exhaustion of energy storage materials under seepage cease. The variation of P content was most significant in the gill, which might be regulated by the abundance of symbiotic bacteria. It can be speculated that the dramatic decline of P content in the gill was attributed to the loss of high-P bacterial symbionts under seepage cease. Both the C:P and N:P ratios of gill tissues significantly increased under seepage cease, which suggested the decline of food quality for scale worms. Mussel-dwelling scale worms might detect the change of food quality and abandon their starving mussel host. Our results help to better understand the environmental adaptation of chemoautotrophic mussels and scale worms under unstable seepage intensity in cold seep ecosystems.

Parasitic fish embryos do a “front-flip” on the yolk to resist expulsion from the host

Embryonic development is often considered shielded from the effects of natural selection, being selected primarily for reliable development. However, embryos sometimes represent virulent parasites, triggering a coevolutionary "arms race" with their host. We have examined embryonic adaptations to a parasitic lifestyle in the bitterling fish. Bitterlings are brood parasites that lay their eggs in the gill chamber of host mussels. Bitterling eggs and embryos have adaptations to resist being flushed out by the mussel. These include a pair of projections from the yolk sac that act as an anchor. Furthermore, bitterling eggs all adopt a head-down position in the mussel gills which further increases their chances of survival. To examine these adaptations in detail, we have studied development in the rosy bitterling (Rhodeus ocellatus) using molecular markers, X-ray tomography, and time-lapse imaging. We describe a suite of developmental adaptations to brood parasitism in this species. We show that the mechanism underlying these adaptions is a modified pattern of blastokinesis-a process unique, among fish, to bitterlings. Tissue movements during blastokinesis cause the embryo to do an extraordinary "front-flip" on the yolk. We suggest that this movement determines the spatial orientation of the other developmental adaptations to parasitism, ensuring that they are optimally positioned to help resist the ejection of the embryo from the mussel. Our study supports the notion that natural selection can drive the evolution of a suite of adaptations, both embryonic and extra-embryonic, via modifications in early development.

A multi-study analysis of gut microbiome data from the blue mussel (Mytilus edulis) emphasises the impact of depuration on biological interpretation.

The blue mussel (Mytilus edulis) is a suspension feeder which has been used in gut-microbiome surveys. Although raw 16S sequence data are often publicly available, unifying secondary analyses are lacking. The present work analysed raw data from seven projects conducted by one group over 7 years. Although each project had different motivations, experimental designs and conclusions, all selected samples were from the guts of M. edulis collected from a single location in Long Island Sound. The goal of this analysis was to determine which independent factors (e.g., collection date, depuration status) were responsible for governing composition and diversity in the gut microbiomes. Results indicated that whether mussels had undergone depuration, defined here as voidance of faeces in a controlled, no-food period, was the primary factor that governed gut microbiome composition. Gut microbiomes from non-depurated mussels were mixtures of resident and transient communities and were influenced by temporal factors. Resident communities from depurated mussels were influenced by the final food source and length of time host mussels were held under laboratory conditions. These findings reinforce the paradigm that gut microbiota are divided into resident and transient components and suggest that depuration status should be taken into consideration when designing and interpreting future experiments.

Spawning patterns of three bitterling fish species (Pisces: Acheilognathinae) in host mussels and the first report of their spawning in Asian clam (<i>Corbicula fluminae</i>) from Korea

Spawning patterns of three bitterling fish species (Pisces: Acheilognathinae) in host mussels and the first report of their spawning in Asian clam (<i>Corbicula fluminae</i>) from Korea

MTORC1 regulates phagosome digestion of symbiotic bacteria for intracellular nutritional symbiosis in a deep-sea mussel.

Phagocytosis is one of the methods used to acquire symbiotic bacteria to establish intracellular symbiosis. A deep-sea mussel, Bathymodiolus japonicus, acquires its symbiont from the environment by phagocytosis of gill epithelial cells and receives nutrients from them. However, the manner by which mussels retain the symbiont without phagosome digestion remains unknown. Here, we show that controlling the mechanistic target of rapamycin complex 1 (mTORC1) in mussels leads to retaining symbionts in gill cells. The symbiont is essential for the host mussel nutrition; however, depleting the symbiont's energy source triggers the phagosome digestion of symbionts. Meanwhile, the inhibition of mTORC1 by rapamycin prevented the digestion of the resident symbionts and of the engulfed exogenous dead symbionts in gill cells. This indicates that mTORC1 promotes phagosome digestion of symbionts under reduced nutrient supply from the symbiont. The regulation mechanism of phagosome digestion by mTORC1 through nutrient signaling with symbionts is key for maintaining animal-microbe intracellular nutritional symbiosis.

Feeding of mussel-associated leeches Hemiclepsis kasmiana on bitterling embryos: novel interaction between parasites in a shared host.

We investigated an interaction between bitterlings and a parasitic leech Hemiclepsis kasmiana in freshwater mussel hosts. We found that leeches fed on bitterling eggs and embryos; this may exert a considerable negative effect on bitterling fitness. Host choices by females of three bitterling species may be differently affected by the presence of leeches within mussels; Tanakia limbata apparently avoided laying eggs in infested mussels while T. lanceolata and Acheilognathus rhombeus did not. Our novel findings suggest that relationships among the parasitic leech and the host mussel may be context dependent. This article is protected by copyright. All rights reserved.

A regulatory hydrogenase gene cluster observed in the thioautotrophic symbiont of Bathymodiolus mussel in the East Pacific Rise

The mytilid mussel Bathymodiolus thermophilus lives in the deep-sea hydrothermal vent regions due to its relationship with chemosynthetic symbiotic bacteria. It is well established that symbionts reside in the gill bacteriocytes of the mussel and can utilize hydrogen sulfide, methane, and hydrogen from the surrounding environment. However, it is observed that some mussel symbionts either possess or lack genes for hydrogen metabolism within the single-ribotype population and host mussel species level. Here, we found a hydrogenase cluster consisting of additional H2-sensing hydrogenase subunits in a complete genome of B. thermophilus symbiont sampled from an individual mussel from the East Pacific Rise (EPR9N). Also, we found methylated regions sparsely distributed throughout the EPR9N genome, mainly in the transposase regions and densely present in the rRNA gene regions. CRISPR diversity analysis confirmed that this genome originated from a single symbiont strain. Furthermore, from the comparative analysis, we observed variation in genome size, gene content, and genome re-arrangements across individual hosts suggesting multiple symbiont strains can associate with B. thermophilus. The ability to acquire locally adaptive various symbiotic strains may serve as an effective mechanism for successfully colonizing different chemosynthetic environments across the global oceans by host mussels.

Factors at multiple scales drive parasite community structure.

Understanding how ecological communities are assembled remains a key goal of ecosystem ecology. Because communities are hierarchical, factors acting at multiple scales can contribute to patterns of community structure. Parasites provide a natural system to explore this idea, as they exist as discrete communities within host individuals, which are themselves part of a community and metacommunity. We aimed to understand the relative contribution of multi-scale drivers in parasite community assembly and assess how patterns at one level may mask those occurring at another. Specifically, we wanted to disentangle patterns caused by passive sampling from those determined by ecological drivers, and how these vary with scale. We applied a Markov Random Fields model and assessed measures of β-diversity and nestedness for 420 replicate parasite infracommunities (parasite assemblages in host individuals) across two freshwater mussel host species, three sites and two time periods, comparing our results to simulations from four different ecologically relevant null models. We showed that β-diversity between sites (explaining 25% of variation in parasite distribution) and host species (41%) is greater than expected, and β-diversity between individual hosts is smaller than expected, even after accounting for parasite prevalence and characteristics of host individuals. Furthermore, parasite communities were significantly less nested than expected once parasite prevalence and host characteristics were both accounted for, but more nested than expected otherwise, suggesting a degree of modularity at the within-host level that is masked if underlying host and parasite characteristics are not taken into account. The Markov Random Fields model provided evidence for possible competitive within-host parasite interactions, providing a mechanism for the observed infracommunity modularity. An integrative approach that examines factors at multiple scales is necessary to understand the composition of ecological communities. Furthermore, patterns at one level can alter the interpretation of ecologically important drivers at another if variation at higher scales is not accounted for.

Insights into symbiotic interactions from metatranscriptome analysis of deep-sea mussel Gigantidas platifrons under long-term laboratory maintenance.

Symbioses between invertebrates and chemosynthetic bacteria are of fundamental importance in deep-sea ecosystems, but the mechanisms that enable their symbiont associations are still largely undescribed, owing to the culturable difficulties of deep-sea lives. Bathymodiolinae mussels are remarkable in their ability to overcome decompression and can be maintained successfully for an extended period under atmospheric pressure, thus providing a model for investigating the molecular basis of symbiotic interactions. Herein, we conducted metatranscriptome sequencing and gene co-expression network analysis of Gigantidas platifrons under laboratory maintenance with gradual loss of symbionts. The results revealed that one-day short-term maintenance triggered global transcriptional perturbation in symbionts, but little gene expression changes in mussel hosts, which were mainly involved in responses to environmental changes. Long-term maintenance with depleted symbionts induced a metabolic shift in the mussel host. The most notable changes were the suppression of sterol biosynthesis and the complementary activation of terpenoid backbone synthesis in response to the reduction of bacteria-derived terpenoid sources. In addition, we detected the upregulation of host proteasomes responsible for amino acid deprivation caused by symbiont depletion. Additionally, a significant correlation between host microtubule motor activity and symbiont abundance was revealed, suggesting the possible function of microtubule-based intracellular trafficking in the nutritional interaction of symbiosis. Overall, by analyzing the dynamic transcriptomic changes during the loss of symbionts, our study highlights the nutritional importance of symbionts in supplementing terpenoid compounds and essential amino acids and provides insight into the molecular mechanisms and strategies underlying the symbiotic interactions in deep-sea ecosystems.

Connectivity and divergence of symbiotic bacteria of deep-sea hydrothermal vent mussels in relation to the structure and dynamics of mid-ocean ridges

The population divergence process of deep-sea vent invertebrates is driven by both biotic (e.g., dispersal during the larval stage) and abiotic factors such as deep-ocean currents, depth, and the geological setting of vents. However, little is known regarding the divergence of hydrothermal vent microorganisms. Therefore, our study sought to investigate the influence of geological and geographic factors on the divergence of symbiotic bacteria of Bathymodiolus vent mussels. The genetic differentiation patterns of symbionts were examined using next-generation sequencing DNA data in two ocean basins with distinct geological features: the slow-spreading Central Indian Ridge (CIR) and the fast- or superfast-spreading eastern Pacific Ridges. Our findings showed that the degree of differentiation of symbiont populations was geographically hierarchical: the highest between ocean basins, followed by inter-ridge sites between the East Pacific Rise and the Pacific Antarctic Ridge. The Easter Microplate intervening these two ridges acted as a biogeographic physical barrier for both symbionts and their host mussels. On a scale of intra-ridge, symbionts showed isolation by distance in the CIR but not in the eastern Pacific ridges. These contrasting genetic patterns relate to different ridge spreading rates determining most of the geological characteristics of mid-ocean ridges that affect the connectivity of vent habitats in space and time. At the intra-ridge geographic scale of the CIR, population divergence processes of both symbionts and hosts from separate three ridge segments were analyzed in detail using a genetic model of isolation with migration (IM). The phylogenetic topology of symbiont populations was congruent with the host populations, indicating the influence of common historical and physical constraints for habitats and dispersal between vents in the Central Indian Ridge. Collectively, our findings provide key insights into the dynamics of microbial population divergence in deep-sea vents.

Mussel parasite richness and risk of extinction.

Parasite conservation is important for the maintenance of ecosystem diversity and function. Conserving parasites relies first on understanding parasite biodiversity and second on estimating the extinction risk to that biodiversity. Although steps have been taken independently in both these areas, previous studies have overwhelmingly focused on helminths in vertebrate hosts over broad scales, providing low resolution and excluding a large proportion of possible host and parasite diversity. We estimated both total obligate parasite richness and parasite extinction risk in freshwater mussels (Unionidae and Margaritiferidae) from Europe and the United States to provide a case study for considering parasite conservation in a severely understudied system. We used currently reported host-parasite relationships to extrapolate parasite diversity to all possible mussel hosts and then used the threat levels of those hosts to estimate the extinction risk for both described and undescribed parasites. An estimated 67% of parasite richness in freshwater mussels is undescribed and over 80% of the most host-specific groups (digenean trematodes and ciliates) are undescribed. We estimated that 21% of this total parasite fauna is at immediate risk of extinction, corresponding to 60 unique species, many of which will likely go extinct before being described. Given the important roles parasites play in community structure and function and the strong ecosystem engineering capacities of freshwater mussels, such extinctions are likely to severely affect freshwater ecosystems. Our detailed study of mussel parasites provides compelling evidence for the hidden conservation threat to parasites through extinction cascades and shows parasites are deserving of immediate attention.

Effects of scale worm parasitism on interactions between the symbiotic gill microbiome and gene regulation in deep sea mussel hosts.

Diverse adaptations to the challenging deep sea environment are expected to be found across all deep sea organisms. Scale worms Branchipolynoe pettiboneae are believed to adapt to the deep sea environment by parasitizing deep sea mussels; this biotic interaction is one of most known in the deep sea chemosynthetic ecosystem. However, the mechanisms underlying the effects of scale worm parasitism on hosts are unclear. Previous studies have revealed that the microbiota plays an important role in host adaptability. Here, we compared gill-microbiota, gene expression and host-microorganism interactions in a group of deep sea mussels (Gigantidas haimaensis) parasitized by scale worm (PA group) and a no parasitic control group (NPA group). The symbiotic microorganism diversity of the PA group significantly decreased than NPA group, while the relative abundance of chemoautotrophic symbiotic bacteria that provide the host with organic carbon compounds significantly increased in PA. Interestingly, RNA-seq revealed that G. haimaensis hosts responded to B. pettiboneaei parasitism through significant upregulation of protein and lipid anabolism related genes, and that this parasitism may enhance host mussel nutrient anabolism but inhibit the host’s ability to absorb nutrients, thus potentially helping the parasite obtain nutrients from the host. In an integrated analysis of the interactions between changes in the microbiota and host gene dysregulation, we found an agreement between the microbiota and transcriptomic responses to B. pettiboneaei parasitism. Together, our findings provide new insights into the effects of parasite scale worms on changes in symbiotic bacteria and gene expression in deep sea mussel hosts. We explored the potential role of host-microorganism interactions between scale worms and deep sea mussels, and revealed the mechanisms through which scale worm parasitism affects hosts in deep sea chemosynthetic ecosystem.

Changes in the height of minute tubercles on the skin of Korean bitterling embryos (Acheilognathus signifer) and embryo movement in the host mussels

Bitterlings are freshwater fish that have developed morphological adaptations to improve the survival of their embryos in host mussels. The most well-known adaptation is the development of minute tubercles, which develop in the early embryonic stage when the embryos have poor swimming ability, and disappear when the embryos reach the free-swimming stage and leave the host mussels. In this study, the embryonic developmental stages of Acheilognathus signifer were analysed to elucidate the relationship between the changes in the height of the minute tubercles and their movement. The height changes in the minute tubercles in the embryos can be divided into five stages, i.e., formation, growth, peak, reduction and disappearance. The authors found that the embryos lived in the gill demibranch of the host mussel until day 6 after hatching. The movement of embryos to the suprabranchial cavity in the gill demibranch was firstly observed on day 7. At this point, the embryos showed a heartbeat and movement. From day 13, the minute tubercles had almost disappeared, and the hatchlings started swimming outside the host mussels from day 16. These observations highlight the different adaptations of minute tubercles among bitterling groups without wing-like projections.

Estimation of non-nucleated pearl quality traits from donor and host mussel-derived genetic parameters in the golden strain of Hyriopsis cumingii

Hyriopsis cumingii is the most important freshwater mussel for pearl production in China and its pearl color is polymorphic. In order to establish a selective breeding program, the genetic parameters of growth and inner shell color traits of golden H. cumingii were evaluated in our lab. Due to the long culture time for pearl production, very little is known about the genetic parameters of commercially important pearl traits. In this study, the genetic parameters of donor-derived and host-derived pearl quality traits were estimated and the genetic contribution from donor and host interaction to pearl quality traits was analyzed. In addition, the correlation of pearl traits with growth traits, inner shell color and luster of donor and host mussels was examined. Microsatellite-based DNA parentage analyses were used to assign mussels to families and populations of origin. A total of 653 individual mussels could be clearly assigned to eight paternal half-sib and 39 full-sib families. Five pearl traits that constitute the major determinants of pearl value (color, luster, size, weight and roundness) were recorded at harvest. Pearl weight and size were significantly correlated with growth traits of the host mussel, while pearl color and luster were significantly correlated with the inner shell color and luster of the donor mussel. Our results indicated that the b⁎ value may be a representative parameter for the evaluation of pearl color in the golden strain in Hyriopsis cumingii. Donor-derived heritability estimates for pearl luster (h2 = 0.37) and color b⁎ values (h2 = 0.47) were high, while heritability estimates for pearl weight (h2 = 0.16), size (h2 = 0.18) and roundness (h2 = 0.07) were low to moderate. By contrast, host-derived heritability estimates for pearl luster and color were low to moderate, while heritability estimates for pearl weight (h2= 0.28), size (h2= 0.24) and roundness (h2 = 0.16) were moderate. The genetic contribution of the donor and host (D × H) interaction on pearl color and pearl luster were low, while the genetic contribution of the D × H interaction on pearl size, weight and roundness were moderate to high. This study revealed the possibility of promoting different selective breeding programs for improving host and donor mussels. Selecting mussels with excellent luster, golden color and higher growth traits as the donors and mussels with excellent growth traits as the hosts may cultivate bigger and brighter golden pearls.