Premeiotic endoreplication is essential for obligate parthenogenesis in geckos.

Obligate parthenogenesis evolved in reptiles convergently several times, mainly through interspecific hybridization. The obligate parthenogenetic complexes typically include both diploid and triploid lineages. Offspring of parthenogenetic hybrids are genetic copies of their mother; however, the cellular mechanism enabling the production of unreduced cells is largely unknown. Here, we show that oocytes go through meiosis in three widespread, or even strongly invasive, obligate parthenogenetic complexes of geckos, namely in diploid and triploid Lepidodactylus lugubris, and triploid Hemiphyllodactylus typus and Heteronotia binoei. In all four lineages, the majority of oocytes enter the pachytene at the original ploidy level, but their chromosomes cannot pair properly and instead form univalents, bivalents and multivalents. Unreduced eggs with clonally inherited genomes are formed from germ cells that had undergone premeiotic endoreplication, in which appropriate segregation is ensured by the formation of bivalents made from copies of identical chromosomes. We conclude that the induction of premeiotic endoreplication in reptiles was independently co-opted at least four times as an essential component of parthenogenetic reproduction and that this mechanism enables the emergence of fertile polyploid lineages within parthenogenetic complexes.

Transcriptomic basis of sex loss in the pea aphid.

BACKGROUND: Transitions from sexual to asexual reproduction are common in eukaryotes, but the underlying mechanisms remain poorly known. The pea aphid-Acyrthosiphon pisum-exhibits reproductive polymorphism, with cyclical parthenogenetic and obligate parthenogenetic lineages, offering an opportunity to decipher the genetic basis of sex loss. Previous work on this species identified a single 840 kb region controlling reproductive polymorphism and carrying 32 genes. With the aim of identifying the gene(s) responsible for sex loss and the resulting consequences on the genetic programs controlling sexual or asexual embryogenesis, we compared the transcriptomic response to photoperiod shortening-the main sex-inducing cue-of a sexual and an obligate asexual lineage of the pea aphid, focusing on heads (where the photoperiodic cue is detected) and embryos (the final target of the cue). RESULTS: Our analyses revealed that four genes (one expressed in the head, and three in the embryos) of the region responded differently to photoperiod in the two lineages. We also found that the downstream genetic programs expressed during embryonic development of a future sexual female encompass ∼1600 genes, among which miRNAs, piRNAs and histone modification pathways are overrepresented. These genes mainly co-localize in two genomic regions enriched in transposable elements (TEs). CONCLUSIONS: Our results suggest that the causal polymorphism(s) in the 840 kb region somehow impair downstream epigenetic and post-transcriptional regulations in obligate asexual lineages, thereby sustaining asexual reproduction.

The Nuances of Intimacy: Asexual Perspectives and Experiences with Dating and Relationships.

Asexuality studies are an emerging field in North America and Europe which lack large-scale, qualitative studies. Much existing research focuses on defining and categorizing asexuality, with researchers calling for more focus on the romantic and sexual relationships of asexual people. Drawing from an online survey with 349 participants, this paper describes the perceptions and experiences that asexual people have with dating and relationships. Participants answered 16 open-ended and 9 close-ended questions. After rounds of coding, three themes were selected for examination. These were dating, romantic and/or sexual relationships, and platonic relationships. These results showcase the challenges asexuals face with dating while also demonstrating how asexual people actively dismantle understandings of romantic, sexual, and platonic relationships through their own experiences and perspectives. Overall, this study provides greater legitimacy to the fluidity of asexuality and asexual relationships.

A Comparison of Mate Preferences in Asexual and Allosexual Adults.

Asexuality is a sexual orientation characterized by a lack of sexual attraction. Sexual attraction is likely associated with preferences for certain characteristics in romantic partners, such as physical attractiveness. Preferred partner characteristics can be influenced by an individual's sexual orientation, gender, and age. Allosexual (N = 239; male = 48, female = 181, other = 4; Age M = 20.48 years) and asexual participants (N = 149; male = 36, female = 88, other = 23; Age M = 25.54 years) recruited from a pool of psychology students and through online asexual communities were presented with a survey in which a total of 388 participants rated 13 characteristics according to how desirable they were in a potential long-term romantic partner. Characteristics that are related to physical attractiveness were predicted to be rated lower by asexual participants than by allosexual participants. Asexual participants rated the desire to have children as being less desirable in a romantic partner than allosexual participants did. However, preferences for other traits, such as exciting personality, creative and artistic, and religious, were dependent on interactions of gender and attraction to men or women. Because asexual individuals report generally lower levels of sexual attraction, it will be important for future research to consider romantic attraction as a more nuanced measure than sexual orientation alone when considering sex differences in asexual and allosexual populations.

Deepening Sexual Desire and Erotic Fantasies Research in the ACE Spectrum: Comparing the Experiences of Asexual, Demisexual, Gray-Asexual, and Questioning People.

Over the past 30 years, an increasing number of people have identified within the asexual (ACE) spectrum recognizing an absence/low/situational sexual attraction to individuals of any gender. The current study aims to deepen the knowledge of sexual desire, erotic fantasies, and related emotions within the ACE spectrum. A total of 1072 Italian volunteers were recruited to take part to the present study via social media. Data were collected from October 2021 to January 2022 using the Sexual Desire and Erotic Fantasies questionnaire and the Sexual Desire Inventory-2. Participants were divided into four groups: asexual, demisexual, gray-asexual, and questioning. Focusing on sexual desire, asexual people reported significantly lower scores than the other groups in all the dimensions except for "negative feelings to sexual desire," while demisexual participants showed the higher scores in all the domains except for "negative feelings to sexual desire." The questioning group reported the highest scores in the "negative feelings toward sexual desire" compared to the asexual and demisexual ones. The asexual group reported significantly lower scores than the other groups in fantasies frequency, fantasies importance, negative emotions, and sharing and experiencing. The demisexual group showed higher frequency of romantic fantasies than the asexual and gray-asexual ones. The results showed some specific patterns of desire and fantasies among the asexual, gray-asexual, demisexual, and questioning groups. These data may provide relevant material to clinicians working with asexual patients who need greater awareness about the diversity and heterogeneity of the sexual experience within the ACE spectrum.

Enhanced heterozygosity from male meiotic chromosome chains is superseded by hybrid female asexuality in termites.

Although males are a ubiquitous feature of animals, they have been lost repeatedly in diverse lineages. The tendency for obligate asexuality to evolve is thought to be reduced in animals whose males play a critical role beyond the contribution of gametes, for example, via care of offspring or provision of nuptial gifts. To our knowledge, the evolution of obligate asexuality in such species is unknown. In some species that undergo frequent inbreeding, males are hypothesized to play a key role in maintaining genetic heterozygosity through the possession of neo-sex chromosomes, although empirical evidence for this is lacking. Because inbreeding is a key feature of the life cycle of termites, we investigated the potential role of males in promoting heterozygosity within populations through karyotyping and genome-wide single-nucleotide polymorphism analyses of the drywood termite Glyptotermes nakajimai We showed that males possess up to 15 out of 17 of their chromosomes as sex-linked (sex and neo-sex) chromosomes and that they maintain significantly higher levels of heterozygosity than do females. Furthermore, we showed that two obligately asexual lineages of this species-representing the only known all-female termite populations-arose independently via intraspecific hybridization between sexual lineages with differing diploid chromosome numbers. Importantly, these asexual females have markedly higher heterozygosity than their conspecific males and appear to have replaced the sexual lineages in some populations. Our results indicate that asexuality has enabled females to supplant a key role of males.

Haplotype divergence supports long-term asexuality in the oribatid mite Oppiella nova.

Sex strongly impacts genome evolution via recombination and segregation. In the absence of these processes, haplotypes within lineages of diploid organisms are predicted to accumulate mutations independently of each other and diverge over time. This so-called "Meselson effect" is regarded as a strong indicator of the long-term evolution under obligate asexuality. Here, we present genomic and transcriptomic data of three populations of the asexual oribatid mite species Oppiella nova and its sexual relative Oppiella subpectinata We document strikingly different patterns of haplotype divergence between the two species, strongly supporting Meselson effect-like evolution and long-term asexuality in O. nova: I) variation within individuals exceeds variation between populations in O. nova but vice versa in O. subpectinata; II) two O. nova sublineages feature a high proportion of lineage-specific heterozygous single-nucleotide polymorphisms (SNPs), indicating that haplotypes continued to diverge after lineage separation; III) the deepest split in gene trees generally separates the two haplotypes in O. nova, but populations in O. subpectinata; and IV) the topologies of the two haplotype trees match each other. Our findings provide positive evidence for the absence of canonical sex over evolutionary time in O. nova and suggest that asexual oribatid mites can escape the dead-end fate usually associated with asexual lineages.

Evidence for cryptic sex in parthenogenetic stick insects of the genus Timema.

Obligately parthenogenetic species are expected to be short lived since the lack of sex and recombination should translate into a slower adaptation rate and increased accumulation of deleterious alleles. Some, however, are thought to have been reproducing without males for millions of years. It is not clear how these old parthenogens can escape the predicted long-term costs of parthenogenesis, but an obvious explanation is cryptic sex. In this study, we screen for signatures of cryptic sex in eight populations of four parthenogenetic species of Timema stick insects, some estimated to be older than 1 Myr. Low genotype diversity, homozygosity of individuals and high linkage disequilibrium (LD) unaffected by marker distances support exclusively parthenogenetic reproduction in six populations. However, in two populations (namely, of the species Timema douglasi and T. monikensis) we find strong evidence for cryptic sex, most likely mediated by rare males. These populations had comparatively high genotype diversities, lower LD, and a clear LD decay with genetic distance. Rare sex in species that are otherwise largely parthenogenetic could help explain the unusual success of parthenogenesis in the Timema genus and raises the question whether episodes of rare sex are in fact the simplest explanation for the persistence of many old parthenogens in nature.

Phylotranscriptomics interrogation uncovers a complex evolutionary history for the planarian genus Dugesia (Platyhelminthes, Tricladida) in the Western Mediterranean.

The Mediterranean is one of the most biodiverse areas of the Paleartic region. Here, basing on large data sets of single copy orthologs obtained from transcriptomic data, we investigated the evolutionary history of the genus Dugesia in the Western Mediterranean area. The results corroborated that the complex paleogeological history of the region was an important driver of diversification for the genus, speciating as microplates and islands were forming. These processes led to the differentiation of three main biogeographic clades: Iberia-Apennines-Alps, Corsica-Sardinia, and Iberia-Africa. The internal relationships of these major clades were analysed with several representative samples per species. The use of large data sets regarding the number of loci and samples, as well as state-of-the-art phylogenomic inference methods allowed us to answer different unresolved questions about the evolution of particular groups, such as the diversification path of D. subtentaculata in the Iberian Peninsula and its colonization of Africa. Additionally, our results support the differentiation of D. benazzii in two lineages which could represent two species. Finally, we analysed here for the first time a comprehensive number of samples from several asexual Iberian populations whose assignment at the species level has been an enigma through the years. The phylogenies obtained with different inference methods showed a branching topology of asexual individuals at the base of sexual clades. We hypothesize that this unexpected topology is related to long-term asexuality. This work represents the first phylotranscriptomic analysis of Tricladida, laying the first stone of the genomic era in phylogenetic studies on this taxonomic group.

Beliefs About the Inevitability of Sexual Attraction Predict Stereotypes About Asexuality.

Similar to other sexual minorities, asexual individuals often face prejudice and stereotyping. However, the source of these attitudes and beliefs is not well understood. We hypothesized that asexual stereotypes stem from the belief that sexual attraction is an inevitable part of human development. This attraction inevitability assumption can lead to the deduction that people who identify as asexual do so because they are going through a transitory stage or excusing socially avoidant tendencies. To test this stereotype deduction account, we examined whether specific asexual stereotypes (immaturity and non-sociality) were associated with adherence to the attraction inevitability assumption. Heterosexual participants (N = 322; 201 women, 114 men; mean age 34.6 yrs.) from the UK and the US read vignettes describing a target character that was either asexual or heterosexual. People who assumed that attraction is inevitable were more likely to evaluate asexual targets (but not heterosexual targets) as immature and non-social. The impact of the sexual inevitability assumption was present even when social dominance orientation, an attitude closely related to negativity toward all sexual minorities, was accounted for. Participants who adhered to the attraction inevitability assumption also showed a reduced inclination to befriend asexual individuals. These findings suggest that generalized negativity toward sexual minorities does not fully explain stereotypes and prejudice against asexual people. Instead, the current study highlights how perceived deviation from the shared understanding of sexuality uniquely contributes to anti-asexual bias.

Understanding Attraction, Behavior, and Identity in the Asexual Community.

Models of sexuality have evolved substantially in the past several decades through the inclusion of new aspects which were previously overlooked. Components such as romantic attraction and behavior have also traditionally been included in models of sexuality. However, romantic and sexual orientations do not coincide for all individuals. A population for which this is true and one that has developed a robust language for discussing romantic orientation is the asexual community. The current study aimed to explore romantic and sexual orientation through patterns found within the factors of attraction, behavior, and identity in the asexual community. The current sample composed of individuals who identified as asexual (N = 306, Mage = 27.1) was 61% female, 13% non-binary, and 10% self-described or used multiple labels. Within this sample, aspects of sexual and romantic orientations and experiences were measured, including fluidity, the quantity and type of self-identified labels, desire for romance or sex, and the role of contextual influences on these experiences. These aspects were used as the primary characteristics to construct participant profiles, both complete profiles and factor specific (attraction, behavior, identity). t-distributed stochastic neighbor embedding (tSNE) was used to find patterns of similarity between individual participant profiles. Overall, it appeared that attraction was the factor most closely associated with overall experiences; however, substantial variability existed between participants. These findings provide a mechanism for better understanding of some nuances of romantic and sexual orientation and may be a useful first step toward future inquiry and hypothesis generation.

Population Genomic Analyses Suggest a Hybrid Origin, Cryptic Sexuality, and Decay of Genes Regulating Seed Development for the Putatively Strictly Asexual Kingdonia uniflora (Circaeasteraceae, Ranunculales).

Asexual lineages are perceived to be short-lived on evolutionary timescales. Hence, reports for exceptional cases of putative 'ancient asexuals' usually raise questions about the persistence of such species. So far, there have been few studies to solve the mystery in plants. The monotypic Kingdonia dating to the early Eocene, contains only K. uniflora that has no known definitive evidence for sexual reproduction nor records for having congeneric sexual species, raising the possibility that the species has persisted under strict asexuality for a long period of time. Here, we analyze whole genome polymorphism and divergence in K. uniflora. Our results show that K. uniflora is characterized by high allelic heterozygosity and elevated πN/πS ratio, in line with theoretical expectations under asexual evolution. Allele frequency spectrum analysis reveals the origin of asexuality in K. uniflora occurred prior to lineage differentiation of the species. Although divergence within K. uniflora individuals exceeds that between populations, the topologies of the two haplotype trees, however, fail to match each other, indicating long-term asexuality is unlikely to account for the high allele divergence and K. uniflora may have a recent hybrid origin. Phi-test shows a statistical probability of recombination for the conflicting phylogenetic signals revealed by the split network, suggesting K. uniflora engages in undetected sexual reproduction. Detection of elevated genetic differentiation and premature stop codons (in some populations) in genes regulating seed development indicates mutational degradation of sexuality-specific genes in K. uniflora. This study unfolds the origin and persistence mechanism of a plant lineage that has been known to reproduce asexually and presents the genomic consequences of lack of sexuality.

Beyond sexual deviance: Elevating the expansive intimacies of Chicana lesbian life in Chicana Lesbians: The Girls Our Mothers Warned Us About.

In this article, I expand popular readings of Chicana lesbianism focused on sexuality by tending more deeply to the affective terrains of love and kinship represented in the 1991 anthology Chicana Lesbians: The Girls Our Mothers Warned Us About edited by Carla Trujillo. Countering the (il)logics of white supremacy and Chicano nationalism which reduce Chicana lesbians to symbols of sexual deviance, I argue that Chicana Lesbians embodies an expansive matrix of intimacies that reconstruct the Chicana lesbian figure from a one-dimensional symbol of sexual deviance to a multi-faceted figure who redefines what it means to love one's people and culture beyond colonial paradigms that privilege heterosexuality. Drawing upon theories of decolonial love and queer asexuality, I examine the expansive inner lives and intimacies of Chicana lesbians to construct a more thorough portrait of how we love and relate to each other. While many studies foreground the sexual lives and politics of Chicana lesbians as subversive to the heteronormative status quo, I elevate the equally powerful forces of love and kinship in our struggle to transform the legacies of colonialism and Chicano nationalism.

The Origin of Asexual Brine Shrimps.

AbstractDetermining how and how often asexual lineages emerge within sexual species is central to our understanding of sex-asex transitions and the long-term maintenance of sex. Asexuality can arise "by transmission" from an existing asexual lineage to a new one through different types of crosses. The occurrence of these crosses, cryptic sex, variations in ploidy, and recombination within asexuals greatly complicates the study of sex-asex transitions, as they preclude the use of standard phylogenetic methods and genetic distance metrics. In this study we show how to overcome these challenges by developing new approaches to investigate the origin of the various asexual lineages of the brine shrimp Artemia parthenogenetica. We use a large sample of asexuals, including all known polyploids, and their sexual relatives. We combine flow cytometry with mitochondrial and nuclear DNA data. We develop new genetic distance measures and methods to compare various scenarios describing the origin of the different lineages. We find that all diploid and polyploid A. parthenogenetica likely arose within the past 80,000 years through successive and nested hybridization events that involved backcrosses with different sexual species. All A. parthenogenetica have the same common ancestor and therefore likely carry the same asexuality gene(s) and reproduce by automixis. These findings radically change our view of sex-asex transitions in this group and show the importance of considering scenarios of asexuality by transmission. The methods developed are applicable to many other asexual taxa.

Reduced Mitochondrial Respiration in Hybrid Asexual Lizards.

AbstractThe scarcity of asexual reproduction in vertebrates alludes to an inherent cost. Several groups of asexual vertebrates exhibit lower endurance capacity (a trait predominantly sourced by mitochondrial respiration) compared with congeneric sexual species. Here we measure endurance capacity in five species of Aspidoscelis lizards and examine mitochondrial respiration between sexual and asexual species using mitochondrial respirometry. Our results show reduced endurance capacity, reduced mitochondrial respiration, and reduced phenotypic variability in asexual species compared with parental sexual species, along with a positive relationship between endurance capacity and mitochondrial respiration. Results of lower endurance capacity and lower mitochondrial respiration in asexual Aspidoscelis are consistent with hypotheses involving mitonuclear incompatibility.

Clonal gametogenesis is triggered by intrinsic stimuli in the hybrid's germ cells but is dependent on sex differentiation†.

Interspecific hybridization may trigger the transition from sexual reproduction to asexuality, but mechanistic reasons for such a change in a hybrid's reproduction are poorly understood. Gametogenesis of many asexual hybrids involves a stage of premeiotic endoreplication (PMER), when gonial cells duplicate chromosomes and subsequent meiotic divisions involve bivalents between identical copies, leading to production of clonal gametes. Here, we investigated the triggers of PMER and whether its induction is linked to intrinsic stimuli within a hybrid's gonial cells or whether it is regulated by the surrounding gonadal tissue. We investigated gametogenesis in the Cobitis taenia hybrid complex, which involves sexually reproducing species (Cobitis elongatoides and C. taenia) as well as their hybrids, where females reproduce clonally via PMER while males are sterile. We transplanted spermatogonial stem cells (SSCs) from C. elongatoides and triploid hybrid males into embryos of sexual species and of asexual hybrid females, respectively, and observed their development in an allospecific gonadal environment. Sexual SSCs underwent regular meiosis and produced normally reduced gametes when transplanted into clonal females. On the other hand, the hybrid's SSCs lead to sterility when transplanted into sexual males but maintained their ability to undergo asexual development (PMER) and production of clonal eggs, when transplanted into sexual females. This suggests that asexual gametogenesis is under complex control when somatic gonadal tissue indirectly affects the execution of asexual development by determining the sexual differentiation of stem cells and once such cells develop to female phenotypes, hybrid germ cells trigger the PMER from their intrinsic signals.

Are Autism Spectrum Disorder and Asexuality Connected?

Asexuality is a lack of sexual attraction to any gender. There is some evidence to suggest that many self-identified asexuals have a formal diagnosis of autism spectrum disorder which is characterized by deficits in social interaction and communication, as well as by restricted and repetitive interests and behaviors. Additionally, the literature shows that asexuality and lack of sexual attraction or low sexual interest is overrepresented in people with autism spectrum disorder compared with neurotypical samples. Nevertheless, no studies have been conducted to investigate the relationship between autism and asexuality in depth. We conducted a systematic review of the literature to examine whether asexuality and autism spectrum disorder are connected. We conclude that asexuality and autism share various aspects, such as a possible role of prenatal factors, reference to romantic dimensions of sexual attraction and sexual orientation, and non-partner-oriented sexual desire, but future research should explore and clarify this link.

Concordance Between Romantic Orientations and Sexual Attitudes: Comparing Allosexual and Asexual Adults.

Sexual and romantic orientations are often considered one and the same, and attitudes about engaging in sexual behavior are assumed to be predominantly positive. The current study explored the concordance between sexual and romantic orientations among allosexual and asexual adults as well as the frequency with which they identify as having a sex-positive, sex-neutral, or sex-averse attitude. As expected, allosexual adults were largely sex-positive (82%) and almost all (89%) had a romantic orientation that matched their sexual orientation. In contrast, we found that only 37% of asexual adults had concordant sexual and romantic orientations and that most asexual adults self-identify as either sex-neutral (41%) or sex-averse (54%). Further, we used a semantic differential task to assess sexual intimacy attitudes and how they varied for adults based on sexual attitude. Asexual adults, regardless of sexual attitude, had less positive attitudes overall than allosexual adults. Interestingly, aromantic asexual adults did not have more negative attitudes about sexual intimacy than romantic asexual participants. Although asexual adults held less positive attitudes about sex than allosexual adults, there was considerable heterogeneity within our asexual sample. The current study provides further insight into the concordance between romantic and sexual orientation, and the associations among sexual and intimacy attitudes for both allosexual and asexual adults. These findings will have implications for future research on how asexual adults navigate romantic relationships.

Sexuality, Sexual Behavior, and Relationships of Asexual Individuals: Differences Between Aromantic and Romantic Orientation.

Asexuality is a complex construct with a considerable lack of research until recently. Building upon available findings, we examined the extent to which romantic orientation shapes individual and relationship experiences, and expectations of asexual individuals. Specifically, our research focused on the distinction between romantic asexual individuals, who experience romantic attraction, and aromantic asexual individuals, who do not experience romantic attraction. A cross-sectional study with members of different asexual online communities (N = 447, 55.02% women; Mage = 24.77 years, SD = 7.21) aimed at examining how both groups differ in their identification with the asexuality construct as measured by the Asexuality Identification Scale (Yule et al., 2017), individual perspectives on sexuality, sexual behavior and relationships, concerns about commitment and sexual performance in a relationship, and attachment style. Results showed that aromantic asexual individuals identified more with asexuality, reported a more avoidant attachment style, and were more concerned with relationship commitment. In contrast, romantic asexual individuals reported less sex aversion, more sexual experiences (both past and current), and more sexual partners in the past. These individuals also engaged in romantic relationships more frequently in the past, had a stronger desire to engage in a romantic relationship in future (either with or without sexual intimacy), and were more concerned with sexual performance. Overall, our findings contribute to the literature by highlighting the need to consider romantic orientation when examining asexuality and its interpersonal outcomes.

A Scoping Review of Empirical Asexuality Research in Social Science Literature.

Research on asexuality as a part of the experience of human sexuality has increased over the last two decades. However, there has not yet been a systematic review of the extant literature on asexuality. This paper aims to provide a systematic scoping review of literature on asexuality with articles published in 2004 through August 2021. After a systematic search procedure, 48 studies were included. A codebook was developed to extract broad information about the literature on asexuality, including sampling techniques, research participant sociodemographics, and conceptualization of asexuality. Results of the review indicate that the research is currently split between qualitative and quantitative methods. The literature primarily relied on convenience sampling within asexual online communities. The primary online community was Asexual Visibility and Education Network (AVEN), which may have contributed to the majority of participants being White, presumptively cisgender, women between the ages of 20-30. Analysis of the overall literature scope demonstrates no support for asexuality as a medical condition (i.e., a disorder requiring treatment) and instead supports the need to recognize asexuality as a complex identity and sexual orientation. Implications for research are discussed, such as the need for additional research on the topic of human sexuality that includes asexuality as a sexual orientation as well as the need for more intersectional research within the literature.