Simultaneous Hermaphrodites Research Articles

Hermaphroditism in fish: incidence, distribution and associations with abiotic environmental factors

The distribution of hermaphroditism in fishes has traditionally been mainly explained by its dependence on biotic factors. However, correlates with major abiotic factors have not been investigated on a quantitative basis and at a global scale. Here, we determined the incidence of hermaphroditism in fish at the family and species level, tested the hypothesis that evolutionary relationships account for the poor presence of hermaphroditism in freshwater species, and tested the association of sexual systems with latitude, habitat type and depth. Functional hermaphroditism is reported in 8 orders, 34 families and 370 species of fishes, all teleosts. Sequential hermaphroditism predominates over simultaneous hermaphroditism at a ratio ~ 5:1 and protogyny (female-to-male sex change) predominates ~ 6:1 over protandry (male-to-female). We found 12 hermaphroditic species that can live in freshwater. However, seven of these species are from four primarily marine families while there are only five species from two mostly freshwater families. Protogynous and bi-directional sex changers have a tighter association with reef-associated tropical and subtropical habitats when compared to protandrous species, which tend to be more plastic in terms of distribution requirements. Finally, simultaneous hermaphrodite species live both in the deep sea and shallow waters in similar proportions. This study can be the basis for further research in specific groups for different purposes, including ecological and evolutionary issues as well as conservation and management of exploited species. Understanding the environmental correlates can help to forecast changes in the distribution or phenology of hermaphrodites in a global change scenario.

SNP-based parentage analyses over two successive generations demonstrates the feasibility of efficient production of inbred lines in the Pacific oyster (Crassostrea gigas) by self-fertilization of simultaneous hermaphrodites despite severe inbreeding depression

The Pacific oyster, Crassostrea gigas, is a species in which true male and true female well as hermaphrodite individuals have been reported. Among the latter, most are sequential, with one or more sex changes throughout their live, while a few (<2%) are simultaneous hermaphrodites (SH) which may self-fertilize. Sex determinism and its functional bases remain unclear is this species. In this study, one SH oyster was found among a mature broodstock and used to produce a progeny by self-fertilization. Several thousand offspring were obtained for this family (SF1) but only 73 SF1 oysters survived following an episode of mass mortality at the spat stage. Six of them were conditioned for reproduction and three were found to be SH, and one produced a limited but viable progeny by self-fertilization (SF2). Oysters were sampled and genotyped with 226 SNP markers, confirming that the SF1 and the SF2 oysters were produced by self-fertilization over two successive generations. To our knowledge, it is the second study reporting the feasibility of production on an inbred line of Pacific oysters by self-fertilization using a simultaneous hermaphrodite as primary genitor, and the first study to generate two successive generations of selfing. Observed mean inbreeding coefficient of SF2 oysters produced by selfing for two generations was 0.61, ranging from 0.46 to 0.80. This coefficient was lower than the expected theoretical value (0.8125), suggesting that the most homozygous offspring died at early stages due to inbreeding depression. Our study demonstrates that inbred lines of Pacific oysters can be produced by self-fertilization but may exhibit higher heterozygosity than theoretically expected due to better survival of the most heterozygous offspring.

Epigenetic mechanisms in sex determination and in the evolutionary transitions between sexual systems.

The hypothesis that epigenetic mechanisms of gene expression regulation have two main roles in vertebrate sex is presented. First, and within a given generation, by contributing to the acquisition and maintenance of (i) the male or female function once during the lifetime in individuals of gonochoristic species; and (ii) the male and female function in the same individual, either at the same time in simultaneous hermaphrodites, or first as one sex and then as the other in sequential hermaphrodites. Second, if environmental conditions change, epigenetic mechanisms may have also a role across generations, by providing the necessary phenotypic plasticity to facilitate the transition: (i) from one sexual system to another, or (ii) from one sex-determining mechanism to another. Furthermore, if the environmental change lasts enough time, epimutations could facilitate assimilation into genetic changes that stabilize the new sexual system or sex-determining mechanism. Examples supporting these assertions are presented, caveats or difficulties and knowledge gaps identified, and possible ways to test this hypothesis suggested.This article is part of the theme issue ‘Challenging the paradigm in sex chromosome evolution: empirical and theoretical insights with a focus on vertebrates (Part I)’.

Reproductive cycle and embryonic development of the ornamental shrimp Lysmata ankeri

In this study, the maturation of the ovarian portion of the ovotestes, the viability of mating, and the embryonic development were investigated for Lysmata ankeri, an ornamental species widely exploited by marine aquariums that presents protandric simultaneous hermaphroditism. Two types of pairs were formed: hermaphrodite × hermaphrodite (HH, n = 7 pairs) and male shrimp × hermaphrodite (MH, n = 7 pairs). The maturation time of the ovaries averaged 11.7 ± 0.18 days and it was classified into three stages: depleted ovary (DOg), developing ovary (DOb) and developed ovary (DOr), with each one showing different colors: gray (Pantone: Cool gray 1C), brown (Pantone: 465C) and red-orange (Pantone: 4011C), respectively. The incubation of the eggs coincided with the maturation of the ovaries. Embryonic development was classified into 11 periods. There was greater mating success between HH pairs than MH pairs. In the MH pairs, the male was cannibalized by the hermaphrodite when molting most of the time. L. ankeri showed continuous reproduction with the production of viable larvae with a low yolk reserve.

Reproduction and early life stages of the poecilosclerid sponge Crella incrustans

AbstractDespite their important ecological roles in marine ecosystems, reproduction and early life stages of the majority of marine sponges remain undescribed. Here we characterize the mode of reproduction and the early life stages of an abundant sponge in temperate Pacific waters, Crella incrustans. Through histology, we characterized the production of gametes and the sequential steps of larval ontogeny. Using in vivo observations, we described larval release, settlement, and metamorphosis. Specimens of C. incrustans presented spermatocytes, oocytes, and several developmental stages in the sponge mesohyl during the Australasian summer (from January to March 2020), demonstrating this sponge to be a simultaneous hermaphrodite with internal fertilization, asynchronous development, and brooded embryos. As in other viviparous demosponges, mature embryos were released during the Australasian summer as free‐swimming non‐tufted parenchymella larvae. Under laboratory conditions, 94.3% of larvae settled within 2 days and metamorphosed into functional settlers within a week. Gametogenesis, embryonic development, larval characteristics, settlement, and metamorphosis of C. incrustans are consistent with the reproductive features common to the majority of poecilosclerid sponges. Overall, our study provides important information on the early life stages of this temperate model species for future ecophysiological experiments.

RNAi Reveals Role of Insulin-Like Androgenic Gland Hormone 2 (IAG2) in Sexual Differentiation and Growth in Hermaphrodite Shrimp

Insulin-like androgenic gland hormone (IAG) is the most widely known hormone that regulates sexual differentiation in crustaceans. Previously, a transcriptome study described two transcripts of IAGs (Lvit-IAG1 and Lvit-IAG2) in the peppermint shrimp Lysmata vittata, a species characterized by a rare reproductive system of protandric simultaneous hermaphroditism (PSH). Herein, we explored the function of Lvit-IAG2 via RNA interference (RNAi) experiments, and then compared the functional differences between the two IAGs. We demonstrated that Lvit-IAG2 positively regulated the expression of crustacean hyperglycemic hormone (Lvit-CHH) in eyestalk ganglion but exhibited no significant effect on the expression of gonad-inhibiting hormone (Lvit-GIHs) and crustacean female sex hormone (Lvit-CFSHs). Besides, Lvit-IAG2 gene knockdown caused degeneration in appendices masculinae (AM) and suppressed germ cells at the secondary spermatocyte stage. Moreover, silencing the Lvit-IAG2 gene impeded ovarian development, including smaller previtellogenic oocytes, and lower expression of vitellogenin (Lvit-Vg) gene in hepatopancreas and vitellogenin receptor (Lvit-VgR) gene in the ovarian region. Notably, silencing the Lvit-IAG2 gene impeded individual growth of the species. Collectively, findings from this study demonstrate that Lvit-IAG2 and Lvit-IAG1 coordinatively function to modulate sexual differentiation in L. vittata; meanwhile, Lvit-IAG2 stimulates the growth of the PSH species.

Sexual Development of the Hermaphroditic Scallop Argopecten irradians Revealed by Morphological, Endocrine and Molecular Analysis.

Simultaneous or functional hermaphrodites possessing both ovary and testis at the same time are good materials for studying sexual development. However, previous research on sex determination and differentiation was mainly conducted in gonochoristic species and studies on simultaneous hermaphrodites are still limited. In this study, we conducted a combined morphological, endocrine and molecular study on the gonadal development of a hermaphroditic scallop Argopecten irradians aged 2–10 month old. Morphological analysis showed that sex differentiation occurred at 6 months of age. By examining the dynamic changes of progesterone, testosterone and estradiol, we found testosterone and estradiol were significantly different between the ovaries and testes almost throughout the whole process, suggesting the two hormones may be involved in scallop sex differentiation. In addition, we identified two critical sex-related genes FoxL2 and Dmrt1L, and investigated their spatiotemporal expression patterns. Results showed that FoxL2 and Dmrt1L were female- and male-biased, respectively, and mainly localized in the germ cells and follicular cells, indicating their feasibility as molecular markers for early identification of sex. Further analysis on the changes of FoxL2 and Dmrt1L expression in juveniles showed that significant sexual dimorphic expression of FoxL2 occurred at 2 months of age, earlier than that of Dmrt1L. Moreover, FoxL2 expression was significantly correlated with estradiol/testosterone ratio (E2/T). All these results indicated that molecular sex differentiation occurs earlier than morphological sex differentiation, and FoxL2 may be a key driver that functions through regulating sex steroid hormones in the scallop. This study will deepen our understanding of the molecular mechanism underlying sex differentiation and development in spiralians.

Insulin-like androgenic gland hormone 1 (IAG1) regulates sexual differentiation in a hermaphrodite shrimp through feedback to neuroendocrine factors

Insulin-like androgenic gland hormone (IAG) is regarded as a key sexual differentiation regulator in gonochoristic crustaceans. However, until now the knowledge concerning its functions in hermaphroditic crustaceans is scanty. Herein, we investigated the function of IAG (Lvit-IAG1) in peppermint shrimp Lysmata vittata, a species that possesses protandric simultaneous hermaphroditism (PSH) reproductive system, which is rare among crustaceans. Lvit-IAG1 was exclusively expressed in the androgenic gland. The qRT-PCR demonstrated that its mRNA expression level was relatively high at the functional male phase but decreased sharply in the subsequent euhermaphrodite phase. Both the short-term and long-term silencing experiments showed that Lvit-IAG1 negatively regulated both the gonad-inhibiting hormone (Lvit-GIH) and crustacean female sex hormone (Lvit-CFSH) expressions in the eyestalk ganglion. Besides, Lvit-IAG1 gene knockdown induced a retarded development of the appendices masculinae (AM) and male gonopores while suppressing the germ cells at the primary spermatocyte stage. Also, Lvit-IAG1 gene silencing hindered ovarian development. This in turn led to small vitellogenic oocytes and decreased expression of vitellogenin and vitellogenin receptor genes in hepatopancreas and ovarian region, respectively. Generally, this study’s findings imply that Lvit-IAG1 modulated the male sexual differentiation in PSH species L. vittata, and exhibited negative feedback on Lvit-GIH and Lvit-CFSH genes expression in the species’ eyestalk ganglion.

Comparative transcriptome analysis of three gonadal development stages reveals potential genes involved in gametogenesis of the fluted giant clam (Tridacna squamosa)

BackgroundGonad development and differentiation is an essential function for all sexually reproducing species, and many aspects of these developmental processes are highly conserved among the metazoa. However, the mechanisms underlying gonad development and gametogenesis remain unclear in Tridacna squamosa, a large-size bivalve of great ecological value. They are protandrous simultaneous hermaphrodites, with the male gonad maturing first, eventually followed by the female gonads. In this study, nine gonad libraries representing resting, male and hermaphrodite stages in T. squamosa were performed to identify the molecular mechanisms.ResultsSixteen thousand four hundred ninety-one unigenes were annotated in the NCBI non-redundant protein database. Among the annotated unigenes, 5091 and 7328 unigenes were assigned to Gene Ontology categories and the Kyoto Encyclopedia of Genes and Genomes (KEGG) Pathway database, respectively. A total of 4763 differentially expressed genes (DEGs) were identified by comparing male to resting gonads, consisting of 3499 which were comparatively upregulated in males and 1264 which were downregulated in males. Six hundred-ninteen DEGs between male and hermaphroditic gonads were identified, with 518 DEGs more strongly expressed in hermaphrodites and 101 more strongly expressed in males. GO (Gene Ontology) and KEGG pathway analyses revealed that various biological functions and processes, including functions related to the endocrine system, oocyte meiosis, carbon metabolism, and the cell cycle, were involved in regulating gonadal development and gametogenesis in T. squamosa. Testis-specific serine/threonine kinases 1 (TSSK1), TSSK4, TSSK5, Doublesex- and mab-3-related transcription factor 1 (DMRT1), SOX, Sperm surface protein 17 (SP17) and other genes were involved in male gonadal development in Tridacna squamosal. Both spermatogenesis- (TSSK4, spermatogenesis-associated protein 17, spermatogenesis-associated protein 8, sperm motility kinase X, SP17) and oogenesis-related genes (zona pellucida protein, Forkhead Box L2, Vitellogenin, Vitellogenin receptor, 5-hydroxytryptamine, 5-hydroxytryptamine receptor) were simultaneously highly expressed in the hermaphroditic gonad to maintain the hermaphroditism of T. squamosa.ConclusionAll these results from our study will facilitate better understanding of the molecular mechanisms underlying giant clam gonad development and gametogenesis, which can provided a base on obtaining excellent gametes during the seed production process for giant clams.

Fshr: a fish sex-determining locus shows variable incomplete penetrance across flathead grey mullet populations.

SummaryWhole-genome sequencing data were produced from a single flathead grey mullet female and assembled into a draft genome sequence, whereas publicly available sequence data were used to obtain a male draft sequence. Two pools, each consisting of 60 unrelated individuals, respectively, of male and female fish were analyzed using Pool-Sequencing. Mapping and analysis of Pool-Seq data against the draft genome(s) revealed >30 loci potentially associated with sex, the most promising locus of which, encoding the follicle-stimulating hormone receptor (fshr) and harboring two missense variants, was genotyped on 245 fish from four Mediterranean populations. Genotype data showed that fshr represents a previously unknown sex-determining locus, although the incomplete association pattern between fshr genotype and sex-phenotype, the variability of such pattern across different populations, and the presence of other candidate loci reveal that a greater complexity underlies sex determination in the flathead grey mullet.

Sclerozoan and fouling sabellid worms (Annelida: Sabellidae) from Mexico with the establishment of two new species.

BackgroundThe sabellid genera Anamobaea Krøyer, 1856 and Notaulax Tauber, 1879 are two of the most attractive polychaete worms in coral reefs. Anamobaea is represented by two Caribbean species and Notaulax with 24 species from around the world, six of them previously known to tropical America. During examination of fouling biota and sclerozoans from Mexico, Anamobaea orstedii Krøyer, 1856 was found in coral reefs from the southern Gulf of Mexico and three species of Notaulax were identified to the Mexican Pacific, two of them being new species to science.New informationAnamobaea orstedii Krøyer, 1856 is first reported as sclerozoan of dead coral from the southern Gulf of Mexico. An amendment to the generic diagnosis of Anamobaea is provided, based on the presence of a higher number of skeletal cells than previously recorded; height, shape and exposition of the anterior peristomial ring; the non-fusion of dorsal collar margins to faecal groove; shape of collar chaetiger and abdominal chaetae and distribution and shape of radiolar ocelli. Notaulax californica (Treadwell, 1906) is reported as fouling in buoys and docks from the Gulf of California. Two new species of Notaulax are described: the former was found in hull and dock fouling from La Paz (Gulf of California) and the second one as sclerozoan of oysters from a dock fouling in Acapulco (south Mexican Pacific). In addition, reproductive features are described for the first time for A. orstedii which is a simultaneous hermaphrodite with female and males gametes found within the same segments of abdominal region. Oocytes develop synchronously and sperm morphology (spherical nucleus and rounded acrosome, four spherical mitochondria and a long free flagellum) suggest an adaptation to broadcast spawning and external fertilisation. Species of Notaulax here examined were gonochoric, with gametes distributed in abdominal segments.

Loss of gill rakers and teeth in adult specimens of barracudina Arctozenus risso (Aulopiformes: Paralepididae) from the western North Atlantic.

Two unusual adult specimens of the barracudina Arctozenus risso were caught in midwater trawls off the Flemish Cap in April 2016. These specimens displayed atypical traits including lack of teeth and gill rakers and fragile jaw bones; a combination of morphological examination and mtDNA sequencing confirmed species identification. Both specimens exhibited ripening ovaries and testes, confirming simultaneous hermaphroditism. These fish represent the first records of late-stage loss of features in the genus Arctozenus and may indicate a relationship to spawning in larger specimens.

A unique reproductive strategy in the mushroom coral Fungia fungites

The vast majority of scleractinian corals are either simultaneous hermaphrodites or gonochoric. Exceptions to these are rare. Nevertheless, species belonging to the family Fungiidae are known to exhibit a wide variety of reproductive strategies. We examined the reproductive ecology of the mushroom coral Fungia fungites in Okinawa. Our study was conducted as part of a long-term, wide-ranging project (2009–2010 and 2013–2017) which explored the unique reproductive strategies of several species belonging to the family Fungiidae. Here we report the co-occurrence of males, females, and hermaphrodite individuals in a long-term monitored population of the reproductively atypical brooder coral F. fungites within the family Fungiidae. F. fungites status as a single-polyped solitary coral, was used to perform manipulative experiments to determine the degree of dependence of an individual coral on its conspecific neighbors for reproduction, and examined whether a constant sperm supply is obligatory for the continuous production of planulae. Isolated females of F. fungites exhibited a distinctive reproductive strategy, expressed in continuously releasing planulae also in the absence of males. Observations conducted on a daily basis for 2.5 months (throughout the reproductive season of 2015) revealed that some of these individuals released planulae continuously, often between tens and hundreds every day. In an effort to explain this phenomenon, three hypotheses are discussed: (1) Self-fertilization; (2) Asexual production of planulae (i.e., parthenogenetic larvae); and (3) Extended storage of sperm. Finally, we emphasize the importance of continuous and long-term monitoring of studies of coral reproduction; through further genetic studies of coral populations representing a broad range of species and their larval origin.

How do whale barnacles live on their hosts? Functional morphology and mating-group sizes of Coronula diadema (Linnaeus, 1767) and Conchoderma auritum (Linnaeus, 1767) (Cirripedia: Thoracicalcarea)

Abstract Whale-associated barnacles are intriguing in terms of their planktonic food sources, mating habits, and mechanisms of host attachment. We present observations of the whale-associated barnacles Coronula diadema (Linnaeus, 1767) and Conchoderma auritum (Linnaeus, 1767) obtained from dead humpback whales (Megaptera novaeangliae (Borowski, 1781)) collected in Korea. Shell bases of Coronula diadema are inflected and sharp-edged with hollow coring tubes at the periphery. The coring tubes are filled with whale skin, supporting the model that shell accretion into the whale skin is achieved by basal constriction to achieve strong attachment. Conchoderma auritum attaches to the shell surfaces of Coronula and has a pair of tubular ear-shaped structures on the capitulum. Both species have short and thick-segmented cirri that allow feeding in strong currents. The distal ends of the cirri in both species are often equipped with sharp, large claw-like setae, which are likely used to capture large zooplankton for food. Coronula diadema and Conchoderma auritum are simultaneous hermaphrodites. Coronula diadema can mate up to nine surrounding individuals. Conchoderma auritum lives in clumps and mating group size can up to 26 individuals.

Coexistence of Hermaphrodites and Males in Androgenetic Clam Corbicula fluminea Müller in Shirakawa River, Kyoto, Japan

Sex, maturity, and the incidence of males in a population of hermaphroditic Corbicula fluminea Muller from Shirakawa River, Kyoto, Japan, are reported. Two shell color types (yellow and green) of this species are recognized. High frequencies of females (63.3% yellow and 58.5% green) are represented among individuals in this population. Histological examination of gonads and measurements of shell length suggest this species first matures as a female before commencing spermatogenesis (i.e., it is a protogynous simultaneous hermaphrodite). Low frequencies of males (mostly less than 5%), the testes of which are filled with spermatozoa, are reported; no histological evidence for any change from males to hermaphrodites, or hermaphrodites to males, is found. Requirements for maintaining males, and for their successful reproduction in self-compatible hermaphrodite populations, are proposed as follows: (1) the protogynous nature of the hermaphrodite, (2) low self-fertilization rates of hermaphrodites, (3) more spermatozoa and greater survival of males than hermaphrodites, and (4) high population densities, ensuring males and hermaphrodites are in close proximity.

Functional morphology of the sperm-containing chambers of the sea slug Okenia polycerelloides in the context of sexual selection.

Sea slugs are interesting models to study post-copulatory sexual selection in simultaneous hermaphrodites due to the enormous variation of their reproductive systems. However, the knowledge of the functional morphology of their reproductive system is limited to few species, and it is rarely discussed in the context of sexual selection theory. In this study, we investigated the functional morphology of the sperm-containing chambers (i.e., ampulla, seminal receptacle, and bursa copulatrix) of the reproductive system of Okenia polycerelloides (Ortea & Bouchet, 1983), based on light, confocal, and electron microscopy. Although the morphology of the ampulla is similar to other species, indicating that it is a site for autosperm storage, we found some sperm facing the ampullar epithelium, a feature commonly regarded as characteristic of the seminal receptacle of sea slugs. The seminal receptacle of O. polycerelloides showed secretory activity and contained sperm with distribution and orientation suggestive of stratification of allosperm from distinct mating events, a feature that would affect sperm competition. The bursa copulatrix had epithelial cells with secretory and absorptive characteristics, and contained degraded sperm and yolk granules within its lumen. Comparative analyses of the contents of each organ demonstrated that sperm digestion occurs in the bursa copulatrix and affects sperm heads first, changing their morphology from slender and curved to shorter and ellipsoid before complete lysis. Although digestion and absorption of surplus sperm are currently the main hypothesized functions for the bursa copulatrix, its role in cryptic female choice should not be ruled out. The close structural connection between the seminal receptacle and bursa copulatrix, as well as their muscular walls, would enable control over the fate of the sperm received in each mating event, that is, storage or digestion.

Disentangling female postmating responses induced by semen transfer components in a simultaneous hermaphrodite

Optimizing reproductive success is an essential part of evolution for both sexes. Females can optimize mating by avoiding superfluous mating advances and insemination, since both take time away from other activities and may incur costs related to sperm receipt. While many separate-sexed organisms are known to exhibit mate avoidance, much less is known about this for simultaneous hermaphrodites. We addressed this here, using a simultaneously hermaphroditic species that can choose to mate in either of the two sex roles during each mating interaction. Recently, avoidance behaviours in response to natural matings were observed in the hermaphroditic pond snail Lymnaea stagnalis, potentially deterring insemination. To disentangle whether such behaviours are mediated by the mechanical act of mating or the receipt of accessory gland proteins and/or sperm, we intravaginally injected individuals with control or test fluids. Our results show that the avoidance behaviours, crawl-out and biting, were more frequently expressed when individuals were inseminated with accessory gland proteins and/or sperm. These behavioural components of the recipient increased time in courtship prior to insemination, which is concordant with the hypothesis that the partner tries to discourage the potential sperm donor from inseminating. Understanding the mechanism underlying the effects that molluscan accessory gland proteins induce contributes to our understanding of the molecular basis of the recipient's (behavioural) responses as well as how such biochemical postcopulatory strategies evolve.

Impairment of reproductive capabilities in three subsequent generations of asymmetric hybrids between Eisenia andrei and E. fetida from French, Hungarian and Polish laboratory colonies.

Eisenia andrei (Ea) and E. fetida (Ef) lumbricid earthworms are simultaneous hermaphrodites potentially capable of self-fertilization and hybridization. We have shown previously that reproductive isolation in these species is incomplete in Ea and Ef earthworms of French provenance, as viable offspring appeared in inter-specific pairs. Fertile asymmetric hybrids developed from Ea-derived ova fertilized by Ef-derived spermatozoa, as well as Ea or Ef specimens derived after self-fertilization (resulting from admixture of endogenously produced spermatozoa with sperm from a partner), but never Ef-hybrids from Ef-ova fertilized by Ea-spermatozoa. The latter appeared only in backcrosses of Ea-hybrids with the Ef. Here we show that these phenomena are not unique for French Ea/Ef earthworms, but are shared by earthworms from French, Hungarian, and Polish laboratory cultures. Semi-quantitative studies on fertility of Ea-derived hybrids revealed gradually decreasing numbers of offspring in three successive generations, more rapid in backcrosses with Ef than with Ea, and the absence of progeny in pairs of hybrids, despite the presence of cocoons in almost all pairs. Based on species specific mitochondrial and nuclear DNA sequences, we provide the first examples of two unique sterile hybrids with mitonuclear mismatch and potential mitonuclear incompatibility among offspring of one of the hybrid+Ef pairs. Earthworms from the investigated populations did not reproduce when kept from hatching in isolation or with representatives of Dendrobaena veneta but started reproducing upon recognition of a related partner, such as Ea, Ef or their hybrids. The existence of Ea or Ef specimens among offspring of hybrid+Ea/Ef pairs might be explained either by partner-induced self-fertilization of Ea/Ef or hybrid-derived ova, or by cross-fertilization of Ea/Ef /hybrid ova by partner-derived spermatozoa; the latter might contribute to interspecific gene introgression.

Semimytilus algosus: first known hermaphroditic mussel with doubly uniparental inheritance of mitochondrial DNA

Doubly uniparental inheritance (DUI) of mitochondrial DNA is a rare phenomenon occurring in some freshwater and marine bivalves and is usually characterized by the mitochondrial heteroplasmy of male individuals. Previous research on freshwater Unionida mussels showed that hermaphroditic species do not have DUI even if their closest gonochoristic counterparts do. No records showing DUI in a hermaphrodite have ever been reported. Here we show for the first time that the hermaphroditic mussel Semimytilus algosus (Mytilida), very likely has DUI, based on the complete sequences of both mitochondrial DNAs and the distribution of mtDNA types between male and female gonads. The two mitogenomes show considerable divergence (34.7%). The presumably paternal M type mitogenome dominated the male gonads of most studied mussels, while remaining at very low or undetectable levels in the female gonads of the same individuals. If indeed DUI can function in the context of simultaneous hermaphroditism, a change of paradigm regarding its involvement in sex determination is needed. It is apparently associated with gonadal differentiation rather than with sex determination in bivalves.

Roles of gonad-inhibiting hormone in the protandric simultaneous hermaphrodite peppermint shrimp†.

To date, the molecular mechanisms of the unique gonadal development mode known as protandric simultaneous hermaphroditism (PSH) are unclear in crustaceans. In this study, cDNA of a gonad-inhibiting hormone (Lv-GIH1) was isolated from the PSH peppermint shrimp Lysmata vittata, and its expression was exclusively found in the eyestalk ganglion. Real-time quantitative polymerase chain reaction (qRT-PCR) revealed that the expression of Lv-GIH1 increased during gonadal development of the functional male stages but decreased significantly at subsequent simultaneous hermaphroditism stage. Further in vitro experiment showed that recombinant GIH1 protein (rGIH1) effectively inhibited Vg expression in the cultured hepatopancreas tissues while the short-term injection of GIH1-dsRNA resulted in reduced expression of Lv-GIH1 and upregulated expression of Vg in the hepatopancreas. Moreover, long-term rGIH1 injection led to significantly reduced expression of Lv-Vg, Lv-VgR, and Lv-CFSH1, subdued growth of oocytes, and feathery setae as a secondary sexual characteristic in females. Interestingly, while germ cells in testicular part were suppressed by rGIH1 injection, the expression of Lv-IAGs showed no significant difference; and long-term GIH1-dsRNA injection results were contrary to those of rGIH1 injection. Taken together, the results of this study indicate that Lv-GIH1 is involved in gonadal development and might also participate in controlling secondary sexual characteristic development in L. vittata by inhibiting Lv-CFSH1 expression.