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Background The red claw crayfish ( Cherax quadricarinatus ) is a commercially and ecologically significant species that displays a unique intersex model with an ovotestis gonad and was identified to have functional testes and a vestigial ovary, which was inhibited by insulin-like androgenic gland hormone ( IAG ), but the underlying molecular mechanisms are still unclear. Results In this study, the structure and transcriptomic profiles of ovotestis and female and male gonad was analysis and compared, 406 differentially expressed genes were identified, among which membrane-anchored AG-specific factor ( MAG ) exhibited significantly greater expression in ovotestis gonads than in male or female gonads. The localization of MAG in type I or II cells of androgenic gland revealed its potential function of IAG hormone synthesis. Furthermore, the analyses of gene regulation relationship revealed that IAG positively regulates MAG expression, while MAG negatively regulates vitellogenin gene ( VTG ) expression. Conclusions Our research suggesting MAG participates in the IAG regulated ovarian suppression in the intersex red claw crayfish, which provides important information on the regulatory mechanism of the ovarian dysplasia in the ovotestis of intersex red claw crayfish. These results will enhance the knowledge of IAG -related pathways in the female reproductive axis, as well as the mechanisms of sexual differentiation in crustaceans.

In bean beetles ( Callosobruchus maculatus ), population density affects larval development. Under high density, individuals develop into a dispersal morph, with larger wings and smaller gonads, while under low density we observe the flightless morph with smaller wings and larger gonads. Past research has shown that the effect of density on wing size is stronger in males than in females, and we hypothesized that this difference is caused by a sex-specific trade-off between immunocompetence and reproduction. We predicted that females reared under high larval density would have an overall stronger immune response compared to those reared in low densities, and to males in general. We tested this hypothesis by rearing males and females under different density treatments and measuring wing size, gonad size, and immune response through phenoloxidase and lytic activity. Females reared under the high-density treatment displayed stronger immune responses, and a trade-off between immunity and gonad size. This provides evidence for a sex-specific, density-specific trade-off between immunocompetence and reproduction.

Background Blotched snakehead ( Channa maculata ) displays significant sexual dimorphism, with males exhibiting faster growth rates and larger body sizes compared to females. The cultivation of the all-male population of snakeheads holds substantial economic and ecological value. Nonetheless, the intricate processes governing the development of bipotential gonads into either testis or ovary in C. maculata remain inadequately elucidated. Therefore, it is necessary to determine the critical time window of sex differentiation in C. maculata , providing a theoretical basis for sex control in production practices. Methods The body length and weight of male and female C. maculata were measured at different developmental stages to reveal when sexual dimorphism in growth initially appears. Histological observations and spatiotemporal comparative transcriptome analyses were performed on ovaries and testes across various developmental stages to determine the crucial time windows for sex differentiation in each sex and the sex-related genes. Additionally, qPCR and MG2C were utilized to validate and locate sex-related genes, and levels of E 2 and T were quantified to understand sex steroid synthesis. Results Sexual dimorphism in growth became evident starting from 90 dpf. Histological observations revealed that morphological sex differentiation in females and males occurred between 20 and 25 dpf or earlier and 30–35 dpf or earlier, respectively, corresponding to the appearance of the ovarian cavity or efferent duct anlage. Transcriptome analyses revealed divergent gene expression patterns in testes and ovaries after 30 dpf. The periods of 40–60 dpf and 60–90 dpf marked the initiation of molecular sex differentiation in females and males, respectively. Male-biased genes ( Sox11a , Dmrt1 , Amh , Amhr2 , Gsdf , Ar , Cyp17a2 ) likely play crucial roles in male sex differentiation and spermatogenesis, while female-biased genes ( Foxl2 , Cyp19a1a , Bmp15 , Figla , Er ) could be pivotal in ovarian differentiation and development. Numerous biological pathways linked to sex differentiation and gametogenesis were also identified. Additionally, E 2 and T exhibited sexual dimorphism during sex differentiation and gonadal development. Based on these results, it is hypothesized that in C. maculata , the potential male sex differentiation pathway, Sox11a – Dmrt1 – Sox9b , activates downstream sex-related genes ( Amh , Amhr2 , Gsdf , Ar , Cyp17a2 ) for testicular development, while the antagonistic pathway, Foxl2/Cyp19a1a , activates downstream sex-related genes ( Bmp15 , Figla , Er ) for ovarian development. Conclusions This study provides a comprehensive overview of gonadal dynamic changes during sex differentiation and gametogenesis in C. maculata , establishing a scientific foundation for sex control in this species. Plain language summary Blotched snakehead ( Channa maculata ) exhibits significant sexual dimorphism, as males display faster growth rates and larger body sizes compared to females. The cultivation of the all-male population of snakeheads holds substantial economic and ecological value. However, the mechanisms underlying sex determination and differentiation in C. maculata remain insufficiently elucidated. In this study, sexual dimorphism in growth became evident starting from 90 dpf through the measurement of body length and weight of male and female C. maculata at different developmental stages. Histological observations indicated that morphological sex differentiation in females and males occurred at 20–25 dpf or earlier and 30–35 dpf or earlier, respectively, corresponding to the appearance of the ovarian cavity or efferent duct anlage. Transcriptome analyses revealed divergent gene expression patterns in male and female gonads after 30 dpf, suggesting that the period preceding 30 dpf might be the critical time window for sex control in C. maculata. The periods of 40–60 dpf and 60–90 dpf marked the initiation of molecular sex differentiation in females and males, respectively. Male-biased genes ( Sox11a , Dmrt1 , Amh , Amhr2 , Gsdf , Ar , Cyp17a2 ) likely play crucial roles in testicular differentiation and spermatogenesis, while female-biased genes ( Foxl2 , Cyp19a1a , Bmp15 , Figla , Er ) could be pivotal in ovarian differentiation and oogenesis. Additionally, numerous biological pathways linked to sex differentiation and gametogenesis were identified. Moreover, sexual dimorphism was observed in the levels of E 2 and T during gonadal differentiation and development. Based on these findings, it is hypothesized that in C. maculata , the potential male sex differentiation pathway, Sox11a – Dmrt1 – Sox9b , activates downstream sex-related genes ( Amh , Amhr2 , Gsdf , Ar , Cyp17a2 ) for testicular development, while the antagonistic pathway, Foxl2/Cyp19a1a , activates downstream sex-related genes ( Bmp15 , Figla , Er ) for ovarian development. This study provides a comprehensive overview of gonadal dynamic changes during sex differentiation and gametogenesis in C. maculata , thereby establishing a scientific foundation for sex control in this species. Highlights Sexual dimorphism in growth became apparent starting from 90 dpf. The morphological differentiation of ovary and testis occurred at 20–25 dpf or earlier and 30–35 dpf or earlier, respectively, and the period preceding 30 dpf may be the critical time for sex control in C. maculata. Male-biased genes ( Sox11a , Dmrt1 , Amh , Amhr2 , Gsdf , Ar , Cyp17a2 ) likely play crucial roles in testicular differentiation and spermatogenesis, whereas female-biased genes ( Foxl2 , Cyp19a1a , Bmp15 , Figla , Er ) could be pivotal in ovarian differentiation and oogenesis. The fate of undifferentiated primordial gonads in C. maculata may be determined by the antagonistic action of the Sox11a – Dmrt1 – Sox9b and Foxl2/Cyp19a1a pathways .

The peppermint shrimp Lysmata vittata (Caridea: Hippolytidae) is a marine caridean shrimp popular in marine aquarium trade. The species is known to display the sexual system of protandric simultaneous hermaphrodite. In this study, based on captive bred specimens, the complete ontogenetic gonad development of L. vittata was studied both morphologically and histologically, from newly settled juveniles until they reached euhermaphrodite phase. It was found that in all specimens examined (carapace length: 1.8-8.5 mm), including the newly settled juveniles, possessed ovotestes, which comprised of an anterior ovarian and a posterior testicular part. Based on both morphological (e.g., size, color and shape) and histological features (e.g., oogenesis and spermatogenesis), four gonadal development stages were defined and described for L. vittata. From Stage I to III, the testicular part of the gonad became gradually mature but the ovarian part was still immature, which is defined as the male phase. At the male phase, cincinulli (5-8 hooks) presented at the tips of the appendix interna on the first pair of pleopods while appendices masculinae (AM), in a form of a stick structure with spines, presented at the inner edge of the appendix interna (AI) on the second pair of pleopods. At Stage IV, both the testicular part and the ovarian part were mature and hence is defined as euhermaphrodite phase. At the euhermaphrodite phase, most individuals lacked cincinulli and appendices masculinae on the first and second pair of pleopods respectively. This is the first time that complete ontogenetic gonadal and external sexual character development have been described and staged for a species from the genus Lysmata from newly settled juveniles to euhermaphrodite phase.

Abstract Aspects of the reproductive biology of Donax striatus were studied from individuals collected from Gado Bravo Beach in the municipality of Tibau do Norte, state of Rio Grande do Norte, Brazil. Donax striatus is a dioic species without external (on the shell) or internal (gonads) macroscopic dimorphism. Thus, a microscopic examination of the reproductive cells is necessary. For the characterization of the gonadal development stages and determination of the size at first sexual maturity (L50), 30 specimens were selected monthly between February 2021 and January 2022 and submitted to histological processing. The condition index (CI) of each individual was estimated and monthly variations were statistically assessed. The size at first maturity (L50) was estimated to be 14.2 mm in shell length. To foster conservation of the species, catches of individuals larger than 14.2 mm is recommended. The lowest condition indices were found in the dry season, with a greater occurrence of organisms in the elimination stage and exhibiting gonad tissue reorganization. Higher indices were found in the rainy season, with the presence of mature individuals. The continuous nature of gametogenesis in Donax stritatus reflects the influence of rainfall in the region. Males and females have peak gamete elimination with pauses during the year, but with the presence of maturing and eliminating individuals throughout the year. As shellfish gathering targeting Donax striatus is excessive on Gado Bravo Beach in the state of Rio Grande do Norte, it is hoped that the results of the present study can contribute to the establishment of management measures for the activity and conservation strategies for the species. Resumo Aspectos da biologia reprodutiva de Donax striatus foram estudados. Os indivíduos foram coletados mensalmente de fevereiro de 2021 a janeiro de 2022 na praia Gado Bravo, no município de Tibau do Norte, estado do Rio Grande do Norte, Brasil. Donax striatus é uma espécie dióica sem dimorfismo macroscópico externo (na concha) ou interno (gônadas). Assim, é necessário um exame microscópico das células reprodutivas. Para a caracterização dos estágios de desenvolvimento gonadal e determinação do tamanho na primeira maturidade sexual (L50), 30 espécimes foram selecionados mensalmente entre fevereiro de 2021 e janeiro de 2022 e submetidos ao processamento histológico. O índice de Condição (IC) de cada indivíduo foi estimado e as variações mensais foram estatisticamente avaliadas. O tamanho de primeira maturação (L50) foi estimado em 14,2 mm de comprimento de concha. Para promover a conservação da espécie, recomenda-se a captura de indivíduos maiores que 14,2 mm. Os menores índices de condição foram encontrados na estação seca, com maior ocorrência de organismos em fase de eliminação e exibindo reorganização do tecido gonadal. Índices maiores foram encontrados no período chuvoso, com presença de indivíduos maduros. A natureza contínua da gametogênese em Donax stritatus reflete a influência das chuvas na região. Machos e fêmeas apresentam pico de eliminação de gametas com pausas durante o ano, mas com presença de indivíduos em maturação e eliminação ao longo do ano. Como a mariscagem visando Donax striatus é excessiva na Praia de Gado Bravo, no estado do Rio Grande do Norte, espera-se que os resultados do presente estudo possam contribuir para o estabelecimento de medidas de manejo da atividade e estratégias de conservação da espécie.

Germ cell-deficient fish usually develop as phenotypic males. Thus, the presence of germ cells is generally considered to be essential for female gonadal differentiation or the maintenance of ovarian structure. However, little is known of the role of germ cells in the determination of the sexual fate of gonadal somatic cells. We have established an inducible germ cell deficiency system in the loach (Misgurnus anguillicaudatus, Cypriniformes: Cobitidae), a small freshwater fish, using knockdown of the dead end gene with a morpholino antisense oligonucleotide. Interestingly, loach lacking germ cells could develop as either phenotypic males or females, as characterized morphologically by the presence or absence of bony plates in the pectoral fins, respectively. The phenotypic males and females had testicular and ovarian structures, respectively, but lacked germ cells. Gene expression patterns in these male and female germ cell-deficient gonads were essentially the same as those in gonads of normal fish. Our observations indicate that sexually dimorphic gonads can develop in germ cell-deficient loach. In contrast to the situation in other model fish species, the gonadal somatic cells in phenotypic females autonomously differentiated into ovarian tissues and also played a role in the maintenance of gonadal structure. On the basis of our observations, we propose two possible models to explain the role of germ cells in sex determination in fish.

Breaking left-right symmetry in Bilateria embryos is a major event in body plan organization that leads to polarized adult morphology, directional organ looping, and heart and brain function. However, the molecular nature of the determinant(s) responsible for the invariant orientation of the left-right axis (situs choice) remains largely unknown. Mutations producing a complete reversal of left-right asymmetry (situs inversus) are instrumental for identifying mechanisms controlling handedness, yet only one such mutation has been found in mice (inversin) and snails. Here we identify the conserved type ID unconventional myosin 31DF gene (Myo31DF) as a unique situs inversus locus in Drosophila. Myo31DF mutations reverse the dextral looping of genitalia, a prominent left-right marker in adult flies. Genetic mosaic analysis pinpoints the A8 segment of the genital disc as a left-right organizer and reveals an anterior-posterior compartmentalization of Myo31DF function that directs dextral development and represses a sinistral default state. As expected of a determinant, Myo31DF has a trigger-like function and is expressed symmetrically in the organizer, and its symmetrical overexpression does not impair left-right asymmetry. Thus Myo31DF is a dextral gene with actin-based motor activity controlling situs choice. Like mouse inversin, Myo31DF interacts and colocalizes with β-catenin, suggesting that situs inversus genes can direct left-right development through the adherens junction.

Alternative reproductive tactics are characterized by the occurrence of discrete alternative morphs that differ in behavioural, morphological and physiological traits within the same sex. Although much effort has been made to describe the behaviour, morphology and physiology of such alternative morphs, less effort has been invested investigating how much overlap there is in the characteristics of such morphs in natural populations. We studied random population samples of the invasive Round Goby Neogobius melanostomus from five different localities in the river Rhine system in the Netherlands. We found two morphologically and physiologically distinct male morphs which likely represent alternative reproductive tactics. Almost all mature males under 9.35 cm total length had a gonadosomatic index > 3%, suggestive of a sneaker tactic, while nearly all males above 9.35 cm has a gonadosomatic index of < 3%, suggestive of a parental tactic. Cheek size and eye diameter alone were sufficient to distinguish the two morphs. Gonads had a different relationship with size in the two morphs, indicating separate growth trajectories. The gonad mass of sneaker morphs would be ca. 7.5 times as high as the gonad mass of parental morphs of the same total length after extrapolation. Few (9%) intermediates were found, suggesting that the expression of alternative reproductive tactics is determined before the first breeding season. This contrasts with studies on other goby species, which show evidence of plastic tactics that can be affected by social circumstances. We conclude that it is possible to distinguish two alternative male morphs in the Dutch Round Goby population using morphological measurements alone. Although behavioural observations are needed to provide conclusive evidence, the difference in GSI between these morphs indicates that these morphs reflect alternative reproductive tactics.

Fish are amongst vertebrates the group with the highest diversity of known sex-determining genes. Particularly, the genus Oryzias is a suitable taxon to understand how different sex determination genetic networks evolved in closely related species. Two closely related species, O. latipes and O. curvinotus, do not only share the same XX/XY sex chromosome system, but also the same male sex-determining gene, dmrt1bY . We performed whole mRNA transcriptomes and morphology analyses of the gonads of hybrids resulting from reciprocal crosses between O. latipes and O. curvinotus . XY male hybrids, presenting meiotic arrest and no production of sperm were sterile, and about 30% of the XY hybrids underwent male-to-female sex reversal. Both XX and XY hybrid females exhibited reduced fertility and developed ovotestis while aging. Transcriptome data showed that male-related genes are upregulated in the XX and XY female hybrids. The transcriptomes of both types of female and of the male gonads are characterized by upregulation of meiosis and germ cell differentiation genes. Differences in the parental species in the downstream pathways of sexual development could explain sex reversal, sterility, and the development of intersex gonads in the hybrids. We hypothesize that male-to-female sex reversal may be connected to a different development time between species at which dmrt1bY expression starts. Our results provide molecular clues for the proximate mechanisms of hybrid incompatibility and Haldane’s rule.

During meiosis I, ring-shaped cohesin complexes play important roles in aiding the proper segregation of homologous chromosomes. RAD21L is a meiosis-specific vertebrate cohesin that is required for spermatogenesis in mice but is dispensable for oogenesis in young animals. The role of this cohesin in other vertebrate models has not been explored. Here, we tested if the zebrafish homolog Rad21l1 is required for meiotic chromosome dynamics during spermatogenesis and oogenesis. We found that Rad21l1 localizes to unsynapsed chromosome axes. It is also found between the axes of the mature tripartite synaptonemal complex (SC) in both sexes. We knocked out rad21l1 and found that nearly all rad21l1 -/- mutants develop as fertile males, suggesting that the mutation causes a defect in juvenile oogenesis, since insufficient oocyte production triggers female to male sex reversal in zebrafish. Sex reversal was partially suppressed by mutation of the checkpoint gene tp53 , suggesting that the rad21l1 mutation activates Tp53-mediated apoptosis or arrest in females. This response, however, is not linked to a defect in repairing Spo11-induced double-strand breaks since deletion of spo11 does not suppress the sex reversal phenotype. Compared to tp53 single mutant controls, rad21l1 -/- tp53 -/- double mutant females produce poor quality eggs that often die or develop into malformed embryos. Overall, these results indicate that the absence of rad21l1 -/- females is due to a checkpoint-mediated response and highlight a role for a meiotic-specific cohesin subunit in oogenesis but not spermatogenesis.