Sexual Species Research Articles

Establishment of Apomixis in Diploid F2 Hybrids and Inheritance of Apospory From F1 to F2 Hybrids of the Ranunculus auricomus Complex.

Hybridization and polyploidization play important roles in plant evolution but it is still not fully clarified how these evolutionary forces contribute to the establishment of apomicts. Apomixis, the asexual reproduction via seed formation, comprises several essential alterations in development compared to the sexual pathway. Furthermore, most natural apomicts were found to be polyploids and/or hybrids. The Ranunculus auricomus complex comprises diploid sexual and polyploid apomictic species and represents an excellent model system to gain knowledge on origin and evolution of apomixis in natural plant populations. In this study, the second generation of synthetically produced homoploid (2x) and heteroploid (3x) hybrids derived from sexual R. auricomus species was analyzed for aposporous initial cell formation by DIC microscopy. Complete manifestation of apomixis was determined by measuring single mature seeds by flow cytometric seed screen. Microscopic analysis of the female gametophyte formation indicated spontaneous occurrence of aposporous initial cells and several developmental irregularities. The frequency of apospory was found to depend on dosage effects since a significant increase in apospory was observed, when both F1 parents, rather than just one, were aposporous. Other than in the F1 generation, diploid Ranunculus F2 hybrids formed BIII seeds and fully apomictic seeds. The results indicate that hybridization rather than polyploidization seems to be the functional activator of apomictic reproduction in the synthetic Ranunculus hybrids. In turn, at least two hybrid generations are required to establish apomictic seed formation.

New diploid species in the Ranunculus auricomus complex (Ranunculaceae) from W and SE Europe

The Euro-Siberian complex of Ranunculus auricomus (Ranunculaceae) consists of about 800 mainly apomictic and polyploid taxa. So far, only four sexual species have been described (R. carpaticola Soo, R. cassubicifolius W. Koch, R. notabilis Horandl & Gutermann and R. marsicus Guss. & Ten.). With the exception of R. marsicus and rare autotetraploids of R. cassubicifolius, sexuality seems to be linked to diploidy. Using flow cytometric ploidy estimation, flow cytometric seed screen and pollen quality, six new diploid sexual species have been revealed in C France, C and SE Slovenia and Croatia: Ranunculus austroslovenicus Dunkel, R. calapius Dunkel, R. cebennensis Dunkel, R. mediocompositus Dunkel, R. peracris Dunkel and R. subcarniolicus Dunkel. Here, they are described and depicted in detail. Sexual reproduction has been verified for R. austroslovenicus, R. cebennensis, R. subcarniolicus and also for the previously described R. envalirensis Grau and R. flabellifolius Heuff. ex Rchb.Citation: Dunkel F. G., Gregor T. & Paule J. 2018: New diploid species in the Ranunculus auricomus complex (Ranunculaceae) from W and SE Europe. – Willdenowia 48: 227–257. doi: https://doi.org/10.3372/wi.48.48205Version of record first published online on 24 August 2018 ahead of inclusion in August 2018 issue.

Genome-specific histories of divergence and introgression between an allopolyploid unisexual salamander lineage and two ancestral sexual species.

Quantifying introgression between sexual species and polyploid lineages traditionally thought to be asexual is an important step in understanding what drives the longevity of putatively asexual groups. Here, we capitalize on three recent innovations-ultraconserved element (UCE) sequencing, bioinformatic techniques for identifying genome-specific variation in polyploids, and model-based methods for evaluating historical gene flow-to measure the extent and tempo of introgression over the evolutionary history of an allopolyploid lineage of all-female salamanders and two ancestral sexual species. Our analyses support a scenario in which the genomes sampled in unisexual salamanders last shared a common ancestor with genomes in their parental species ∼3.4 million years ago, followed by a period of divergence between homologous genomes. Recently, secondary introgression has occurred at different times with each sexual species during the last 500,000 years. Sustained introgression of sexual genomes into the unisexual lineage is the defining characteristic of their reproductive mode, but this study provides the first evidence that unisexual genomes have undergone long periods of divergence without introgression. Unlike other sperm-dependent taxa in which introgression is rare, the alternating periods of divergence and introgression between unisexual salamanders and their sexual relatives could explain why these salamanders are among the oldest described unisexual animals.

Flow cytometric seed screen data are consistent with models of chromosome inheritance in asymmetrically compensating allopolyploids

Angiosperms have evolved a mechanism of double fertilization, which results in the production of a separate embryo (new individual) and endosperm (nutritive tissue). The flow cytometric seed screen (FCSS) was developed to infer plant reproduction modes based on endosperm-to-embryo DNA content ratio (Pind ). A ratio of 1.5 indicates sexual reproduction, whereas higher values of ≥2.0 are consistent with apomixis. Although FCSS has been successfully applied to the study of sexual and asexual plants, the limits of FCSS and particularly its potential for determination of reproduction modes in hemisexual plants have not been explored. Here, we evaluated the application of FCSS to the study of reproduction modes in two asymmetrically compensating allopolyploids (ACAs), Onosma arenaria and Rosa canina. These two species are characterized by the presence of asexually inherited univalent-forming and sexually inherited bivalent-forming chromosome sets. They both use asymmetric meiosis, which eliminates univalent-forming chromosome sets from the male gamete and retains them in the female gamete. Different chromosomal behavior in male and female meiosis in these plants is reflected in different theoretically derived Pind values, which deviate from a sexual 1.5 value. Here, we determined Pind FCSS-based values in seeds of ACAs, and compared the results to sexual species. As expected, we determined that the mean Pind is 1.51, 1.52, and 1.52 in the sexual plants, that is, Capsella bursa-pastoris, Crataegus monogyna, and O. pseudoarenaria, respectively. In the ACAs, different mean Pind values were determined for O. arenaria (1.61) and R. canina (1.82). These values are consistent with the theoretical Pind values determined based on models of chromosome inheritance. This study highlights the precision of flow cytometry in determining DNA content and it's utility in screening reproduction modes. Additionally, it advocates for more in-depth investigations into rapid screening of accessions where the Pind ratio has deviated from the 1.5 value typical of sexual species, which may indicate meiotic irregularities.

The repeated emergence of asexuality, the hidden genomes and the role of parthenogenetic rare males in the brine shrimp Artemia

The backbone of this endeavour consists of three major components as they appear in the title. My intention is to summarise, as explicitly as possible, both existing and novel data on the occurrence of parthenogenetic rare males assessing their role in conveying sets of genetic information between asexual strains and sexual Artemia species to and fro. Additionally, an assemblage of strong indications and evidence is quoted aiming to unravel possible scenarios of the repeated emergence of asexuality in the brine shrimp and its significance in evolutionary processes involved in speciation.

Differences in the reliance on cuticular hydrocarbons as sexual signaling and species discrimination cues in parasitoid wasps

BackgroundCuticular hydrocarbons (CHC) have been documented to play crucial roles as species- and sex-specific cues in the chemical communication systems of a wide variety of insects. However, whether they are sufficient by themselves as the sole cue triggering sexual behavior as well as preference of con- over heterospecific mating partners is rarely assessed. We conducted behavioral assays in three representative species of parasitoid wasps (Hymenoptera: Pteromalidae) to determine their reliance on CHC as species-specific sexual signaling cues.ResultsWe found a surprising degree of either unspecific or insufficient sexual signaling when CHC are singled out as recognition cues. Most strikingly, the cosmopolitan species Nasonia vitripennis, expected to experience enhanced selection pressure to discriminate against other co-occurring parasitoids, did not discriminate against CHC of a partially sympatric species from another genus, Trichomalopsis sarcophagae. Focusing on the latter species, in turn, it became apparent that CHC are even insufficient as the sole cue triggering conspecific sexual behavior, hinting at the requirement of additional, synergistic sexual cues particularly important in this species. Finally, in the phylogenetically and chemically most divergent species Muscidifurax uniraptor, we intriguingly found both CHC-based sexual signaling as well as species discrimination behavior intact although this species is naturally parthenogenetic with sexual reproduction only occurring under laboratory conditions.ConclusionsOur findings implicate a discrepancy in the reliance on and specificity of CHC as sexual cues in our tested parasitioid wasps. CHC profiles were not sufficient for unambiguous discrimination and preference behavior, as demonstrated by clear cross-attraction between some of our tested wasp genera. Moreover, we could show that only in T. sarcophagae, additional behavioral cues need to be present for triggering natural mating behavior, hinting at an interesting shift in signaling hierarchy in this particular species. This demonstrates the importance of integrating multiple, potentially complementary signaling modalities in future studies for a better understanding of their individual contributions to natural sexual communication behavior.

Sexual selection predicts species richness across the animal kingdom

Our improving knowledge of the animal tree of life consistently demonstrates that some taxa diversify more rapidly than others, but what contributes to this variation remains poorly understood. An influential hypothesis proposes that selection arising from competition for mating partners plays a key role in promoting speciation. However, empirical evidence showing a link between proxies of this sexual selection and species richness is equivocal. Here, we collected standardized metrics of sexual selection for a broad range of animal taxa, and found that taxonomic families characterized by stronger sexual selection on males show relatively higher species richness. Thus, our data support the hypothesis that sexual selection elevates species richness. This could occur either by promoting speciation and/or by protecting species against extinction.

Papiliotrema plantarum sp. nov., a novel tremellaceous sexual yeast species.

During a survey of the yeast community associated with the phylloplane of corn in Thailand, a basidiomycetous yeast strain belonging to the genus Papiliotrema was isolated. Analyses of the D1/D2 domains of the 26S (LSU) rRNA gene and complete ITS region supported the recognition of a novel species, for which the name Papiliotrema plantarum sp. nov. is proposed (type strain DMKU-CP801T=CBS 15220T=PYCC 7257T). Another strain of P. plantarum sp. nov., isolated in French Guiana, was found to be sexually compatible with the Thai isolate and mycelium with clamp connections, basidia and basidiospores were observed in culture. The basidial morphology of P. plantarum combined features previously observed for Papiliotrema bandonii and Papiliotrema fuscus, which represent the only sexual species hitherto known in the genus, i.e. transversely septate basidia, with sexual structures of the Tremella type.

Plasticity of Meiotic Recombination Rates in Response to Temperature in Arabidopsis.

Meiotic recombination shuffles genetic information from sexual species into gametes to create novel combinations in offspring. Thus, recombination is an important factor in inheritance, adaptation, and responses to selection. However, recombination is not a static parameter; meiotic recombination rate is sensitive to variation in the environment, especially temperature. That recombination rates change in response to both increases and decreases in temperature was reported in Drosophila a century ago, and since then in several other species. But it is still unclear what the underlying mechanism is, and whether low- and high-temperature effects are mechanistically equivalent. Here, we show that, as in Drosophila, both high and low temperatures increase meiotic crossovers in Arabidopsis thaliana We show that, from a nadir at 18°, both lower and higher temperatures increase recombination through additional class I (interfering) crossovers. However, the increase in crossovers at high and low temperatures appears to be mechanistically at least somewhat distinct, as they differ in their association with the DNA repair protein MLH1. We also find that, in contrast to what has been reported in barley, synaptonemal complex length is negatively correlated with temperature; thus, an increase in chromosome axis length may account for increased crossovers at low temperature in A. thaliana, but cannot explain the increased crossovers observed at high temperature. The plasticity of recombination has important implications for evolution and breeding, and also for the interpretation of observations of recombination rate variation among natural populations.

Assembly of the Boechera retrofracta Genome and Evolutionary Analysis of Apomixis-Associated Genes.

Closely related to the model plant Arabidopsis thaliana, the genus Boechera is known to contain both sexual and apomictic species or accessions. Boechera retrofracta is a diploid sexually reproducing species and is thought to be an ancestral parent species of apomictic species. Here we report the de novo assembly of the B. retrofracta genome using short Illumina and Roche reads from 1 paired-end and 3 mate pair libraries. The distribution of 23-mers from the paired end library has indicated a low level of heterozygosity and the presence of detectable duplications and triplications. The genome size was estimated to be equal 227 Mb. N50 of the assembled scaffolds was 2.3 Mb. Using a hybrid approach that combines homology-based and de novo methods 27,048 protein-coding genes were predicted. Also repeats, transfer RNA (tRNA) and ribosomal RNA (rRNA) genes were annotated. Finally, genes of B. retrofracta and 6 other Brassicaceae species were used for phylogenetic tree reconstruction. In addition, we explored the histidine exonuclease APOLLO locus, related to apomixis in Boechera, and proposed model of its evolution through the series of duplications. An assembled genome of B. retrofracta will help in the challenging assembly of the highly heterozygous genomes of hybrid apomictic species.

Sexes and species as rival units of niche saturation during community assembly

AbstractAimCommunity assembly is traditionally assumed to result from speciation and colonization mediated by available niche space. This paradigm is expanded by the theory that niche space can also be saturated by intersexual adaptive divergence (ecological sexual dimorphism) when interspecific competition is relaxed. This theory (here termed ‘niche‐packing equivalence’) predicts that the evolution of ecological sexual dimorphism constrains the ecological opportunity that would otherwise lead to ecological speciation or colonization, and that saturation of niches by different species constrains divergent selection for divergence between the sexes. Therefore, sexes and species are equivalent, yet antagonistic units of niche occupation. We present the most comprehensive test of the niche‐packing equivalence theory at ecological time‐scales (assemblage level) to date.LocationSouth AmericaMajor taxa studiedLiolaemuslizards.MethodsWe identified 23Liolaemusassemblages varying in species richness and sexual size dimorphism (SSD), distributed across a wide environmental range. We used mixed effects models, permutation tests and Markov Chain Monte Carlo (MCMC) regressions to quantify the relationship between SSD and species richness. We then partitioned the body size niche dimension between the sexes and amongst species, and tested for non‐overlapping body size distributions. We regressed SSD and species richness of each assemblage against environmental predictors, using multi‐model inference and structural equation modelling.ResultsSexual dimorphism declines with increasing species richness, and a strong signal of tension between the two remains following phylogenetic control. This pattern is accompanied by evidence of constraints on body‐size partitioning amongst species and between the sexes: the two units of niche saturation tend not to overlap. However, across assemblages, species richness and SSD correlate with different environmental variables, suggesting that their tension is context‐specific.Main conclusionsOur evidence supports the prediction that sexual dimorphism and species richness are alternative outcomes of adaptive radiation. However, this antagonism is mediated by a suite of environmental predictors that influence dimorphism and species richness differentially.

Clonal polymorphism and high heterozygosity in the celibate genome of the Amazon molly

The extreme rarity of asexual vertebrates in nature is generally explained by genomic decay due to absence of meiotic recombination, thus leading to extinction of such lineages. We explore features of a vertebrate asexual genome, the Amazon molly, Poecilia formosa, and find few signs of genetic degeneration but unique genetic variability and ongoing evolution. We uncovered a substantial clonal polymorphism and, as a conserved feature from its interspecific hybrid origin, a 10-fold higher heterozygosity than in the sexual parental species. These characteristics seem to be a principal reason for the unpredicted fitness of this asexual vertebrate. Our data suggest that asexual vertebrate lineages are scarce not because they are at a disadvantage, but because the genomic combinations required to bypass meiosis and to make up a functioning hybrid genome are rarely met in nature.

Histological evidence that diploid hybrids of Cobitis taenia and C. elongatoides (Teleostei, Cobitidae) develop into fertile females and sterile males

In Europe, two bisexual fish species, Cobitis taenia (TT) and Cobitis elongatoides (EE), hybridized, producing diploid and polyploid clonal lineages. This study compared, for the first time, embryonic development, hatching success, sex ratio, body size and as well as reproductive ability based on the gonad histology of F1 reciprocal diploid hybrids (TE, ET) of both species. Hybrid F1 progeny showed the same proper pattern of embryonic and larval development. Among TE and ET offspring, slightly more females and males, respectively, occurred, but sex parity among 18-month-old hybrids was observed. Two- and three-year-old F1 hybrid females were mature, possessing all stages of oogenesis in their ovaries. Females (TE) back-crossed with C. taenia males had properly developing progeny. In testes of two- and three-year-old F1 hybrids, only early stages of spermatogenesis and pyknotic cells indicating the degeneration process were observed, but they exhibited an external feature (lamina circularis) of maturation. The results were confirmed by the structure of gonads that two sexual species, C. taenia and C. elongatoides, hybridize, producing F1 progeny of sterile males and fertile females. Hybrid females may participate in subsequent steps of speciation via hybridization and polyploidy or, on the contrary, represent an element of new species isolation.

Sharing the burden: A neutral approach to socioecological theory.

The socioecological model (SEM) is a popular collection of controversial models purporting to explain mating systems in terms of ecological and social parameters. Despite its guise of objectivity, several of its hypotheses assume Victorian gender stereotypes of active, competing males heedlessly sowing their seeds, and cautious, passive females, imprisoned by greater costs of reproduction and their consequent resourceߚdependence. We enter this debate by taking a previously neglected explanatory approach borrowed from species theory. According to the Recognition Concept of sexual species, the unit of reproductive success/fitness is irreducible to fewer than two integrated subparts (minimally a male and a female). Phyletic changes in mating systems logically effect changes in fertilization systems, leading to reproductive isolation. We take our primary assumption of the average equivalence of female and male contributions to successful reproduction from the writings of the natural philosopher, Antoinette Blackwell. We revisit the SEM with its contradictions and extrapolations, and develop a genderߚneutral alternative hypothesis termed SpecificߚMate Contact (SMC), centered on two fundamental mating strategies: sexual animals may behave as synchronous mateߚattractors or asynchronous mateߚseekers, generating four possible mating system combinations (monogamy: two attractors; promiscuity: two seekers; polygyny: male attractor and female seeker; polyandry: female attractor and male seeker). Our approach predicts all known primate mating systems using a neutral (nonߚsexist) principle. The approach is also neutral in the sense that it does not invoke either competition or cooperation: fertilization success is considered a posteriori and males and females are coߚadapted to this end rather than cognitively cooperative.

The gonadal transcriptome of the unisexual Amazon molly Poecilia formosa in comparison to its sexual ancestors, Poecilia mexicana and Poecilia latipinna

BackgroundThe unisexual Amazon molly (Poecilia formosa) originated from a hybridization between two sexual species, the sailfin molly (Poecilia latipinna) and the Atlantic molly (Poecilia mexicana). The Amazon molly reproduces clonally via sperm-dependent parthenogenesis (gynogenesis), in which the sperm of closely related species triggers embryogenesis of the apomictic oocytes, but typically does not contribute genetic material to the next generation. We compare for the first time the gonadal transcriptome of the Amazon molly to those of both ancestral species, P. mexicana and P. latipinna.ResultsWe sequenced the gonadal transcriptomes of the P. formosa and its parental species P. mexicana and P. latipinna using Illumina RNA-sequencing techniques (paired-end, 100 bp). De novo assembly of about 50 million raw read pairs for each species was performed using Trinity, yielding 106,922 transcripts for P. formosa, 115,175 for P. latipinna, and 133,025 for P. mexicana after eliminating contaminations. On the basis of sequence similarity comparisons to other teleost species and the UniProt databases, functional annotation, and differential expression analysis, we demonstrate the similarity of the transcriptomes among the three species. More than 40% of the transcripts for each species were functionally annotated and about 70% were assigned to orthologous genes of a closely related species. Differential expression analysis between the sexual and unisexual species uncovered 2035 up-regulated and 564 down-regulated genes in P. formosa. This was exemplary validated for six genes by qRT-PCR.ConclusionsWe identified more than 130 genes related to meiosis and reproduction within the apomictically reproducing P. formosa. Overall expression of these genes seems to be down-regulated in the P. formosa transcriptome compared to both ancestral species (i.e., 106 genes down-regulated, 29 up-regulated). A further 35 meiosis and reproduction related genes were not found in the P. formosa transcriptome, but were only expressed in the sexual species. Our data support the hypothesis of general down-regulation of meiosis-related genes in the apomictic Amazon molly. Furthermore, the obtained dataset and identified gene catalog will serve as a resource for future research on the molecular mechanisms behind the reproductive mode of this unisexual species.

Breaking the rules: discovery of sexual deception in Caladenia abbreviata (Orchidaceae), a species with brightly coloured flowers and a non-insectiform labellum

Caladenia is exceptional among orchid genera in that it contains both species pollinated by sexual deception and species pollinated by food-foraging insects. Whereas pollination strategies have been elucidated in some species complexes, others groups have received limited attention, hampering our ability to understand the evolution of the exceptional diversity of species and floral traits in Caladenia. Here, we conducted the first detailed pollination study of a member of the Caladenia filamentosa complex. On the basis of the brightly coloured and scented flowers exhibited by many species, it has been assumed that most members of the group are food-deceptive. However, we show that Caladenia abbreviata Hopper & A.P.Br. is pollinated by an undescribed species of Rhytidothynnus thynnine wasp via sexual deception. Floral dissections showed that the terminal glands on the sepals and petals are the primary source of the sexual attractant, supporting observations from intact flowers that pollinators frequently copulate with these floral parts. Interestingly, contact with the reproductive structures of the plant was not associated with attempted copulation. Our findings highlighted that sexual deception can evolve in lineages without dull-coloured flowers and insectiform labellum structures. Given that the orchid is apparently dependent on a single pollinator species, efforts to conserve this rare species will be dependent on the availability of the pollinator in suitable orchid habitat.

The Straight Mind in Corinth: Queer Readings across 1 Corinthians 11:2–16 by Gillian Townsley

Reviewed by: The Straight Mind in Corinth: Queer Readings across 1 Corinthians 11:2–16 by Gillian Townsley Deryn Guest gillian townsley, The Straight Mind in Corinth: Queer Readings across 1 Corinthians 11:2–16 (SBLSS 88; Atlanta: SBL Press, 2017). Pp xiii + 351. Paper $43.95. This is a welcome addition to studies of this notorious passage. Townsley spends some time pondering whether she is equipped to write a queer reading when she does not own a non-normative sexual or gender identity, but her work demonstrates well how it can be done. In chap. 1, T. reviews current research, noting how it is hostage to a heteronormative blind spot. She exposes how historical-critical approaches have produced vast swaths of scholarship, with each contributor holding out the “key” for unlocking the meaning of this passage yet failing the reader who wants to know how to negotiate or discern between the multiple keys on offer. In this regard, 1 Cor 11:2–16 is a rather queer text, stubbornly impervious to attempts to solve it and perhaps inherently queer since Paul is disconcerted by behaviors he considers questionable and yet responds in a way that is itself strange and puzzling. T. recognizes that an ancient text like 1 Corinthians requires commentators who avoid making anachronistic assumptions concerning sex and gender. In the first century, acts were significant, not notions of individuals belonging to a sexual species or having a sexual orientation. She is right about this, but in my view, while social constructionism holds sway, we should not be blinkered to the way in which humans may have recognized like-mindedness in past societies. It is at least possible that the Corinthian men, who are the focus of her study, were not only individual gender outlaws by practice but part of a wider community of gender nonconformists who were recognizable as a “kind” of “men.” The chapter functions as a helpful opening gambit for the book as a whole and includes a useful discussion of the reception of queer biblical studies, noting the more limited resources that relate specifically to the NT, which will be helpful for students newly engaging with the field. In chap. 2, T. problematizes lack of critical examination when it comes to the men at Corinth and demonstrates how an understanding of first-century codes of masculinity is vital to such a study. There is also a critique of how contemporary readings use this passage to sanction heteronormative gender behavior. T. uses the debate between Jerome Murphy-O’Connor and Richard Oster to demonstrate the pull of ideology and political/religious interests (see Richard Oster, “When Men Wore Veils to Worship: The Historical Context of 1 Corinthians 11.4,” NTS 34 [1988] 481–505; Jerome Murphy-O’Connor, “Sex and Logic in 1 Corinthians 11:2–16,” CBQ 42 [1980] 482–500; idem, “1 Corinthians 11:2–16 Once Again,” CBQ 50 [1988] 265–74). What interests T. is how “scholars have determined that this text can (or ought to) be read as dealing with the actual behavior of women, but only hypothetically with regard to the men” (p. 57). The problem is “the refusal of the majority of scholars even to acknowledge the presence of men in this passage,” which has the effect of making the Corinthian men “invisible and trouble free” (p. 62) rather than seeing them as just as gendered as the women. Readings that suggest the presence of “homosexual” men in the Corinthian church are noted for relying on repeated claims that lack justification. As C. K. Barrett (A Commentary on the First Epistle to the Corinthians [2nd ed.; BNTC; London: Black, 1971]), Murphy-O’Connor (see above), and Robin Scroggs (“Paul and the Eschatological Woman,” JAAR 40 [1972] 283–303) are the ones most cited, T. reviews their interpretations in detail. The chapter concludes that effeminacy is the primary disturbing notion and that Paul is attempting to reinstate clear gender boundaries. [End Page 540] In chap. 3, T. clarifies how the theory of Monique Wittig can be used to “lesbianize” the problematic Corinthian men. Wittig’s theory is important for T.’s book. Indeed, T.’s title plays on Wittig...

Host species of a sexual-parasite do not differentiate between clones of Amazon mollies

Species recognition is an important process prior to copulation that is thought to be continuous with mate and individual recognition. Amazon mollies—a sperm-parasitic fish—show recognition at the clonal level; here, we investigate if the sexual host species have the same capabilities. We show that both sexual hosts do not exhibit a detectable preference for different clonal females. This raises the possibility that clonal recognition evolved in the Amazon molly, not in its ancestors.

General environmental heterogeneity as the explanation of sexuality? Comparative study shows that ancient asexual taxa are associated with both biotically and abiotically homogeneous environments.

Ecological theories of sexual reproduction assume that sexuality is advantageous in certain conditions, for example, in biotically or abiotically more heterogeneous environments. Such theories thus could be tested by comparative studies. However, the published results of these studies are rather unconvincing. Here, we present the results of a new comparative study based exclusively on the ancient asexual clades. The association with biotically or abiotically homogeneous environments in these asexual clades was compared with the same association in their sister, or closely related, sexual clades. Using the conservative definition of ancient asexuals (i.e., age >1 million years), we found eight pairs of taxa of sexual and asexual species, six differing in the heterogeneity of their inhabited environment on the basis of available data. The difference between the environmental type associated with the sexual and asexual species was then compared in an exact binomial test. The results showed that the majority of ancient asexual clades tend to be associated with biotically, abiotically, or both biotically and abiotically more homogeneous environments than their sexual controls. In the exploratory part of the study, we found that the ancient asexuals often have durable resting stages, enabling life in subjectively homogeneous environments, live in the absence of intense biotic interactions, and are very often sedentary, inhabiting benthos, and soil. The consequences of these findings for the ecological theories of sexual reproduction are discussed.

Imitating the cost of males: A hypothesis for coexistence of all-female sperm-dependent species and their sexual host.

All‐female sperm‐dependent species are particular asexual organisms that must coexist with a closely related sexual host for reproduction. However, demographic advantages of asexual over sexual species that have to produce male individuals could lead both to extinction. The unresolved question of their coexistence still challenges and fascinates evolutionary biologists. As an alternative hypothesis, we propose those asexual organisms are afflicted by a demographic cost analogous to the production of males to prevent exclusion of the host. Previously proposed hypotheses stated that asexual individuals relied on a lower fecundity than sexual females to cope with demographic advantage. In contrast, we propose that both sexual and asexual species display the same number of offspring, but half of asexual individuals imitate the cost of sex by occupying ecological niches but producing no offspring. Simulations of population growth in closed systems under different demographic scenarios revealed that only the presence of nonreproductive individuals in asexual females can result in long‐term coexistence. This hypothesis is supported by the fact that half of the females in some sperm‐dependent organisms did not reproduce clonally.