Search Results (8)

The naviculoid genus Luticola exhibits a high degree of morphological convergence, complicating species delimitation when based solely on traditional morphometrics. Here, we describe Luticola edaphica sp. nov., a new species isolated from the forest soils of Mount Sestra (Primorsky Territory, Russian Far East) using an integrative taxonomic approach (phylogenetic, morphological, ultrastructural, and life cycle data). Molecular phylogenetic analysis, based on the chloroplast rbcL gene, placed the new strain within the Luticola clade, showing the closest affinity to L. tenera. However, L. edaphica is distinguished from similar Luticola species by a unique combination of morphological traits (structure of the valvocopula, maximal valve length and width, position and number of striae in 10 µm, central area, and distal raphe ends). A comprehensive study of its life cycle revealed that L. edaphica is homothallic and capable of both cis- and trans-anisogamy, with the latter being reported for the genus for the first time. Full article

Diatoms inhabit different aquatic and non-aquatic environments, including soils. The naviculoid genus Luticola is widespread in various habitats and accounts for 264 species that are only based on morphological and morphometric characteristics. These parameters can greatly vary during the life cycle, making the species very similar to each other and complicating their unambiguous identification. During a study on soil algal diversity in the Russian Far East (Jewish Autonomous Region), we isolated a strain of naviculoid diatom and examined it using an integrative approach (phylogenetic, morphological, ultrastructural data, and life cycle). Phylogenetic analyses, based on chloroplast rbcL gene data, showed affinity of the new strain with the genus Luticola. Our alga shares morphological features typical of the genus members but differs from them by having valves with a larger width and hook-shaped external proximal raphe ends deflected to the side opposite the stigma. It was revealed that the strain reproduces via two types of sexual reproduction—isogamy and cis-anisogamy. Based on these phenotypic traits, we described the new isolate as Luticola tenera sp. nov. Full article

The diatom Nitzschia acidoclinata is a widespread eurybiontic alga. There is little information on its life cycle properties and cardinal points. To fill this gap, we analyzed six N. acidoclinata clones from a range of habitats in Asiatic Russia regarding their genetic diversity, morphology, morphometry, geography, and ecology. A comparison of 15 N. acidoclinata rbcL sequences sampled across its relatively wide distribution area and contrasting habitats revealed no distinct genotypes in the species. We demonstrated that the valve morphology, their length, and the sexual activity of the investigated clones varied depending on the phase of their life cycle. In this species, abrupt size reduction was observed. It was revealed that N. acidoclinata reproduced by pedogamy, and its auxosporulation was season-dependent and observed in spring and autumn only. The mating activity in our clones was detected only when the cell size was reduced to 9–22 µm in length. The available data on sexual reproduction in the genus Nitzschia suggest that neither clades nor subclades comprise pedogamous or anisogamous taxa at the same time. However, isogamy could occur in the same clade with either pedogamy or anisogamy. These data provide a fundamental basis for the development of N. acidoclinata mass cultivation and long-term maintenance in culture technologies. Full article

Recently, it was pointed out that classic models for the evolution of anisogamy do not take into account the possibility of parthenogenetic reproduction, even though sex is facultative in many relevant taxa (e.g., algae) that harbour both anisogamous and isogamous species. Here, we complement this recent analysis with an approach where we assume that the relationship between progeny size and its survival may differ between parthenogenetically and sexually produced progeny, favouring either the former or the latter. We show that previous findings that parthenogenesis can stabilise isogamy relative to the obligate sex case, extend to our scenarios. We additionally investigate two different ways for one mating type to take over the entire population. First, parthenogenesis can lead to biased sex ratios that are sufficiently extreme that one type can displace the other, leading to de facto asexuality for the remaining type that now lacks partners to fuse with. This process involves positive feedback: microgametes, being numerous, lack opportunities for syngamy, and should they proliferate parthenogenetically, the next generation makes this asexual route even more prominent for microgametes. Second, we consider mutations to strict asexuality in producers of micro- or macrogametes, and show that the prospects of asexual invasion depend strongly on the mating type in which the mutation arises. Perhaps most interestingly, we also find scenarios in which parthenogens have an intrinsic survival advantage yet facultatively sexual isogamous populations are robust to the invasion of asexuals, despite us assuming no genetic benefits of recombination. Here, equal contribution from both mating types to zygotes that are sufficiently well provisioned can outweigh the additional costs associated with syngamy. Full article

Parker, Baker, and Smith provided the first robust theory explaining why anisogamy evolves in parallel in multicellular organisms. Anisogamy sets the stage for the emergence of separate sexes, and for another phenomenon with which Parker is associated: sperm competition. In outcrossing taxa with separate sexes, Fisher proposed that the sex ratio will tend towards unity in large, randomly mating populations due to a fitness advantage that accrues in individuals of the rarer sex. This creates a vast excess of sperm over that required to fertilize all available eggs, and intense competition as a result. However, small, inbred populations can experience selection for skewed sex ratios. This is widely appreciated in haplodiploid organisms, in which females can control the sex ratio behaviorally. In this review, we discuss recent research in nematodes that has characterized the mechanisms underlying highly skewed sex ratios in fully diploid systems. These include self-fertile hermaphroditism and the adaptive elimination of sperm competition factors, facultative parthenogenesis, non-Mendelian meiotic oddities involving the sex chromosomes, and environmental sex determination. By connecting sex ratio evolution and sperm biology in surprising ways, these phenomena link two “seminal” contributions of G. A. Parker. Full article

The evolution of anisogamy or gamete size dimorphism is a fundamental transition in evolutionary history, and it is the origin of the female and male sexes. Although mathematical models attempting to explain this transition have been published as early as 1932, the 1972 model of Parker, Baker, and Smith is considered to be the first explanation for the evolution of anisogamy that is consistent with modern evolutionary theory. The central idea of the model is ingenious in its simplicity: selection simultaneously favours large gametes for zygote provisioning, and small gametes for numerical competition, and under certain conditions the outcome is anisogamy. In this article, I derive novel analytical solutions to a 2002 game theoretical update of the 1972 anisogamy model, and use these solutions to examine its robustness to variation in its central assumptions. Combining new results with those from earlier papers, I find that the model is quite robust to variation in its central components. This kind of robustness is crucially important in a model for an early evolutionary transition where we may only have an approximate understanding of constraints that the different parts of the model must obey. Full article

This review documents the history of the two papers written half a century ago that relate to this special issue of Cells. The first, “Sperm competition and its evolutionary consequences in the insects” (Biological Reviews, 1970), stressed that sexual selection continues after ejaculation, resulting in many adaptations (e.g., postcopulatory guarding phases, copulatory plugs, seminal fluid components that modify female reproduction, and optimal ejaculation strategies), an aspect not considered by Darwin in his classic treatise of 1871. Sperm competition has subsequently been studied in many taxa, and post-copulatory sexual selection is now considered an important sequel to Darwinian pre-copulatory sexual selection. The second, “The origin and evolution of gamete dimorphism and the male-female phenomenon” (Journal of Theoretical Biology, 1972) showed how selection, based on gamete competition between individuals, can give rise to anisogamy in an isogamous broadcast spawning ancestor. This theory, which has subsequently been developed in various ways, is argued to form the most powerful explanation of why there are two sexes in most multicellular organisms. Together, the two papers have influenced our general understanding of the evolutionary differentiation of the two forms of gametic cells, and the divergence of sexual strategies between males and females under sexual selection. Full article

The fundamental underlying paradigm of sexual reproduction is the production of male and female gametes of sufficient genetic difference and quality that, following syngamy, they result in embryos with genomic potential to allow for future adaptive change and the ability to respond to selective pressure. The fusion of dissimilar gametes resulting in the formation of a normal and viable embryo is known as anisogamy, and is concomitant with precise structural, physiological, and molecular control of gamete function for species survival. However, along the reproductive life cycle of all organisms, both male and female gametes can be exposed to an array of “stressors” that may adversely affect the composition and biological integrity of their proteins, lipids and nucleic acids, that may consequently compromise their capacity to produce normal embryos. The aim of this review is to highlight gamete genome organization, differences in the chronology of gamete production between the male and female, the inherent DNA protective mechanisms in these reproductive cells, the aetiology of DNA damage in germ cells, and the remarkable DNA repair mechanisms, pre- and post-syngamy, that function to maintain genome integrity. Full article