Sexual Reproduction Research Articles

Investigating Vesicle-Mediated Regulation of Pollen Tube Growth through BFA Inhibition and AS-ODN Targeting of TfRABA4D in Torenia fournieri

Abstract In flowering plants, pollen tube growth is essential for delivering immotile sperm cells during double fertilization, directly influencing seed yield. This process relies on vesicle-mediated trafficking to drive tip growth and maintain fertility. However, investigating pollen tube growth is challenging in non-model plants due to the lack of transgenic tools. Here, we established a method to transiently inhibit vesicle activity in pollen tubes of the wishbone flower (Torenia fournieri), a classic plant for sexual reproduction studies, using brefeldin A (BFA) and antisense oligodeoxynucleotides (AS-ODNs) targeting key genes. BFA broadly disrupted vesicle gradient homeostasis in T. fournieri pollen tubes, leading to widespread changes in cell wall deposition, ROS distribution, and pollen tube morphology. To assess the role of specific genes, we designed AS-ODNs against TfANX, the sole ANXUR homolog in T. fournieri, which successfully penetrated cell membranes and suppressed TfANX expression. This inhibition impaired pollen tube tip growth, causing pollen tube leakage at the shank region and, in some cases, multiple leakages. Similarly, AS-ODN targeting TfRABA4D, a pollen-specific vesicle regulator, induced a bulging phenotype and disrupted pectin deposition and reduced ROS distribution, mirroring BFA effects. These findings elucidate vesicle-mediated regulation in pollen tube tip growth and introduce an accessible method for genetic manipulation in reproductive research of non-model plants.

Reproductive and persistence strategy of the liverwort Arnellia fennica after the last glaciation in the area of disjunction in Central Europe (Polish Tatra Mountains, carpathians)

The liverwort Arnellia fennica has a circumarctic distribution with disjunct and scarce localities in the Alps, Carpathians, and Pyrenees. Within the Carpathians, it is only known from the Tatra Mountains (in Poland), where so far only four occurrences have been documented in the forest belt of the limestone part of the Western Tatras. The species is considered a tertiary relict, which owes its survival during the last glaciation period to low-lying locations in areas not covered by ice. Previously, it has been demonstrated that this plant does not produce gemmae in the Tatra Mountains, nor does it reproduce sexually, hence it has not spread in this massif despite the high availability of potential habitats. These studies address the following questions: (1) why A. fennica, an arctic-alpine species, has only been found at low elevations in the Tatra Mountains so far, (2) what were the possibilities of its survival during the glaciation period as verified based on the latest paleoglaciological map, (3) how this species persists in the Tatras and why it remains a rare plant. As a result, nine additional new occurrences were found, bringing the total to 13 throughout the massif. Some of the sites were found in the high mountain area. For the first time, the production of gemmae in the Tatra population of A. fennica was observed and documented, along with the presence of male specimens of this dioecious species. Genetic studies have shown that individuals from all three groups of sites are genetically homogeneous, indicating a lack of sexual reproduction. The only way of dispersal for A. fennica in the Tatras is through propagule production. The uniqueness and specificity of these structures have been described, which differ significantly from the common model known in liverworts. The rarity of the species in the Tatra massif is attributed to the inefficient mode of vegetative reproduction and the absence of sexual reproduction. Paleoglaciological analysis of all montane sites (historical and new) of A. fennica showed that half were located in areas covered by glaciers. The hypothesis of this liverwort’s survival during the glaciation period, at lower elevations, should be rejected. In light of the new data obtained, montane localities should be considered as secondary, which could have arisen after the glacier retreated only from high-mountain populations producing propagules transported downhill.

Revisiting the female germline cell development

The formation of the female germline is the fundamental process in most flowering plants’ sexual reproduction. In Arabidopsis, only one somatic cell obtains the female germline fate, and this process is regulated by different pathways. Megaspore mother cell (MMC) is the first female germline, and understanding MMC development is essential for comprehending the complex mechanisms of plant reproduction processes. Recently, more advanced technologies such as whole-mount single-molecule fluorescence in situ hybridization (smFISH), laser-assisted microdissection (LCM), chromatin immunoprecipitation/sequencing, and CRISPR gene editing have provided opportunities to reveal the mechanism of female germline development at different stages. Single-cell transcriptome/spatial transcriptomics analysis helps to investigate complex cellular systems at the single-cell level, reflecting the biological complexity of different cell types. In this review, we highlight recent progress that facilitates the development of the female germline to explore the roles of crucial gene regulatory networks, epigenetic pathways, cell-cycle regulators, and phytohormones in this process. This review discusses three key phases in female germline development and provides the possibility of distinct pathways restricting germline development in the future.

Empowering Regional Conservation: Genetic Diversity Assessments as a Tool for Eelgrass Management.

To halt the loss of biodiversity, collaboration among scientists, managers and decision-makers is vital. Although biodiversity loss is a global problem, management actions influencing diversity are often on a local to regional scale. Our study is an example of a regional conservation genomic assessment developed in collaboration between scientists and managers. We used 2bRAD sequencing to assess 18 eelgrass (Zostera marina) meadows in northwestern Sweden, an area that has experienced large losses of eelgrass since the 1980s. Genetic diversity was comparable to other assessed meadows in the Atlantic, but an order of magnitude lower than eelgrass in the Pacific. All but one meadow showed high rates of sexual reproduction. Almost all meadows were divergent but grouped into five genetic clusters. Four of the clusters correspond to geographic regions that can be used to define management units. Meadows in areas with a high decline in eelgrass between the 1980s and 2020s are more inbred than meadows in areas with an increase in eelgrass. Overall, our results indicate that striving to protect a number of large eelgrass meadows within each genetic cluster is important for maintaining the genetic diversity and connectivity of eelgrass in northwestern Sweden and is likely beneficial for the wider ecosystem. We estimate current indicators and essential biodiversity variables and discuss their challenges in marine facultative clonal species. We showcase how regional-scale conservation genomic assessments can serve as a foundation for protection and restoration of a priority species.

A positive feedback loop between germ cells and gonads induces and maintains sexual reproduction in a cnidarian.

The fertile gonad includes cells of two distinct developmental origins: the somatic mesoderm and the germ line. How somatic and germ cells interact to develop and maintain fertility is not well understood. Here, using grafting experiments and transgenic reporter animals, we find that a specific part of the gonad-the germinal zone-acts as a sexual organizer to induce and maintain de novo germ cells and somatic gonads in the cnidarian Hydractinia symbiolongicarpus. Germ cells express a member of the transforming growth factor-β family, Gonadless (Gls), that induces gonad morphogenesis. Loss of Gls resulted in animals lacking gonads but having nonproliferative germ cells. We propose that primary germ cells drive gonad development though Gls secretion. The germinal zone in the newly formed gonad provides positive feedback to induce secondary germ cells by activating Tfap2 in resident pluripotent stem cells. The contribution of germ cell signaling to the patterning of somatic gonadal tissue may be a general animal feature.

Close cooperation between Semi1 and Semi2 proteins is essential for pronuclear positioning in Tetrahymena thermophila.

During sexual reproduction in the ciliate Tetrahymena thermophila, meiosis occurs in the germline micronucleus, resulting in the formation of four haploid micronuclei. Of these, only one is selected to evade autophagy, and subsequently migrates to the membrane junction with the partner cell for reciprocal pronuclear exchange. We previously demonstrated that the transmembrane protein Semi1 is essential for this nuclear migration. Semi1 is specifically expressed in mating cells and localizes to the periphery of the selected nucleus. Loss of Semi1 disrupts nuclear attachment to the junction, leading to infertility. However, the mechanism by which Semi1 positions the nucleus at the junction remains unclear. Here, we report that the Semi1-interacting protein, Semi2, is also necessary for proper nuclear positioning. Deletion of Semi2 results in the same nuclear mislocalization phenotype and infertility observed in Semi1 mutant cells. Semi2 colocalizes with Semi1, but in the absence of Semi1, Semi2 fails to exhibit perinuclear localization. The selected nucleus anchors to microtubules prior to migration, a process dependent on both Semi1 and Semi2. We propose a model in which Semi1 recruits Semi2 to the selected nucleus, facilitating the interaction between the nucleus and microtubules required for proper nuclear positioning at the membrane junction.

Parental effects provide an opportunity for coral resilience following major bleaching events.

Identifying processes that promote coral reef recovery and resilience is crucial as ocean warming becomes more frequent and severe. Sexual reproduction is essential for the replenishment of coral populations and maintenance of genetic diversity; however, the ability for corals to reproduce may be impaired by marine heatwaves that cause coral bleaching. In 2014 and 2015, the Hawaiian Islands experienced coral bleaching with differential bleaching susceptibility in the species Montipora capitata, a dominant reef-building coral in the region. We tested the hypothesis that coral bleaching resistance enhances reproductive capacity and offspring performance by examining the reproductive biology of colonies that bleached and recovered (B) and colonies that did not bleach (NB) in 2015 in the subsequent spawning seasons. The proportion of colonies that spawned was higher in 2016 than in 2017. Regardless of parental bleaching history, we found eggs with higher abnormality and bundles with fewer eggs in 2016 than 2017. While reproductive output was similar between B and NB colonies in 2016, survivorship of offspring that year were significantly influenced by the parental bleaching history (egg donor × sperm donor: B × B, B × NB, NB × B, and NB × NB). Offspring produced by NB egg donors had the highest survivorship, while offspring from previously bleached colonies had the lowest survivorship, highlighting the negative effects of bleaching on parental investment and offspring performance. While sexual reproduction continues in M. capitata post-bleaching, gametes are differentially impacted by recovery time following a bleaching event and by parental bleaching resistance. Our results demonstrate the importance of identifying bleaching resistant individuals during and after heating events. This study further highlights the significance of maternal effects through potential egg provisioning for offspring survivorship and provides a baseline for human-assisted intervention (i.e., selective breeding) to mitigate the effects of climate change on coral reefs.

The smallest Zosterophyllum plant from the Lower Devonian of South China and the divergent life-history strategies in zosterophyllopsids.

Plants have evolved different life-history strategies to overcome limited amounts of available resources; however, when and how divergent strategies of sexual reproduction evolved in early land plants are not well understood. As one of the notable and vital components of early terrestrial vegetation, the Zosterophyllopsida and its type genus Zosterophyllum reached maximum species diversity during the Pragian (Early Devonian; ca 410.8-407.6 million years ago). Here we describe a new species, Zosterophyllum baoyangense sp. nov., based on well-preserved specimens from the Pragian-aged Mangshan Group of Duyun, Guizhou Province, China. The new plant is characterized by its small size, K-shaped branching and tiny spikes with 5-10 sporangia. This plant is most likely r-selected, completing its whole lifespan in a short time, and such a strategy contributes to reproduction in a suitable window time. In contrast, most other species of Zosterophyllum and the zosterophyllopsids on a broader scale are larger in body size and have greater investments in fertile tissues, reflected in the size and total number of sporangia. We argue that the zosterophyllopsids probably benefited from the divergence of various life-history strategies and thus constituted a major part of the Early Devonian floras.

Genome Sequencing Providing Molecular Evidence of Tetrapolar Mating System and Heterothallic Life Cycle for Edible and Medicinal Mushroom Polyporus umbellatus Fr.

Polyporus umbellatus is a species whose sclerotia have been extensively employed in traditional Chinese medicine, which has diuretic, antitumor, anticancer, and immune system enhancement properties. However, prolonged asexual reproduction has resulted in significant homogenization and degeneration of seed sclerotia. In contrast, sexual reproduction has emerged as an effective strategy to address these challenges, with a distinct mating system serving as the foundation for the implementation of sexual breeding. This study presents the first sequencing and assembly of the genome of P. umbellatus, thereby providing an opportunity to investigate the mating system at the genomic level. Based on the annotated mating-type loci within the genome, monokaryotic offspring exhibiting different mating-types were identified. Through the integration of traditional mating tests, the tetrapolar mating system of P. umbellatus was distinctly elucidated. The resequencing of monokaryotic strains with four different mating-types, along with comparative analyses of mating-type loci, revealed the HD1 and HD2 (HD, homeodomain) genes determined the mating A types, and the PR4, PR5, and PR6 (PR, pheromone receptor) genes determined the mating B types. Meanwhile, this study offers a successful case study in the molecular investigation of mating systems. Additionally, the number of sterigma and basidiospores on each basidium was examined using scanning electron microscopy, while the nuclei of basidiospores and basidia at various developmental stages were analyzed through DAPI staining. This research clarifies the heterothallic life cycle of P. umbellatus. The findings of this study are expected to facilitate advancements in genetic research, breeding development, strain improvement, and the industry of P. umbellatus.

Effects of Biological Factors and Temperature Elevation on Stigmatic Receptivity and Pollen Tube Growth in Diploid and Hexaploid Plum Genotypes [Prunus salicina and Prunus insititia

ABSTRACTPremise of the study. Biological factors and environmental stresses are predominant elements affecting the progamic phase of sexual plant reproduction. Thus, new knowledge is needed to select and develop cultivars adapted to these changes. This work was conducted to evaluate the pollen growth dynamics and the stigmatic receptivity at normal and elevated temperatures, in 12 Tunisian plum genotypes selected based on six different biological factors. Methods. The pistils were hand‐pollinated using their own pollen, and then the dynamics of pollen tube growth and stigma receptivity of Tunisian plum genotypes were surveyed under ambient temperature and under 35 °C. Key results. Results showed that the differences in flower size, geographical origin and drought tolerance did neither affect pollen growth dynamics nor stigma receptivity. However, the polyploidization enlarged the stigmatic receptivity but does not affect the pollen dynamics. Flowering time and wild plantation fasten the pollen growth and enlarge the stigmatic receptivity. We assume that, in particular case, the flowering plants seem to opt for an enlarged stigmatic receptivity and a rapid pollen growth as reproductive strategies to ‘hold on for dear life’. Experiments conducted at 35 °C showed that the temperature elevation accelerates pollen growth dynamics, while it shortens the stigmatic receptivity period. In particular, two accessions: the wild plum ‘Sauvage’ and the late flowering ‘Tasstour Hamra Tardive’ showed faster pollen growth and enlarged stigmatic receptivity, compared to other accessions. Conclusion. The main relevant conclusion of this work resides in the identification of the best adapted Tunisian genotypes that could be selected as pollen sources to extend the pollination period. Especially, accessions presenting a tolerance to high‐temperature deserve serious attention.

Proteomic and phosphoproteomic analyses reveal that TORC1 is reactivated by pheromone signaling during sexual reproduction in fission yeast.

Starvation, which is associated with inactivation of the growth-promoting TOR complex 1 (TORC1), is a strong environmental signal for cell differentiation. In the fission yeast Schizosaccharomyces pombe, nitrogen starvation has distinct physiological consequences depending on the presence of mating partners. In their absence, cells enter quiescence, and TORC1 inactivation prolongs their life. In presence of compatible mates, TORC1 inactivation is essential for sexual differentiation. Gametes engage in paracrine pheromone signaling, grow towards each other, fuse to form the diploid zygote, and form resistant, haploid spore progenies. To understand the signaling changes in the proteome and phospho-proteome during sexual reproduction, we developed cell synchronization strategies and present (phospho-)proteomic data sets that dissect pheromone from starvation signals over the sexual differentiation and cell-cell fusion processes. Unexpectedly, these data sets reveal phosphorylation of ribosomal protein S6 during sexual development, which we establish requires TORC1 activity. We demonstrate that TORC1 is re-activated by pheromone signaling, in a manner that does not require autophagy. Mutants with low TORC1 re-activation exhibit compromised mating and poorly viable spores. Thus, while inactivated to initiate the mating process, TORC1 is reactivated by pheromone signaling in starved cells to support sexual reproduction.

Transcriptome profiling of foxtail millet (Setaria italica) pollen and anther

Pollen development and germination play a crucial role in the sexual reproduction of plants. This study analysis of transcriptional dynamics of foxtail millet pollen with other tissues and organs (ovule, glume, seedling and root) through RNA-sequencing revealed that a total of 940 genes were up-regulated in foxtail millet pollen. Based on this, we analyzed the genes involved in pollen tube growth of receptor kinases and small peptides, calcium signaling, small G proteins, vesicle transport, cytoskeleton, cell wall correlation, and transcription factors that are up-regulated in pollen. At the same time, we compared the gene expression of foxtail millet pollen and mature anthers, and found that a large number of transcription factors were specific expressed in mature anthers. In addition, we verified the accuracy of the transcriptome data using RT-qPCR. Finally, employed the antisense Oligonucleotide (as-ODN) system found that inhibiting SiPME67 expression would cause abnormal growth of pollen tube subapical. In summary, we preliminarily analyzed the genes that were up-regulated in foxtail millet pollen, which provided a reference for understanding the male sterility mechanism of foxtail millet in the future and theoretical basis for creating new male sterility lines.

Development of female and male reproductive structures in <I>Borodinia macrophylla</I> (Brassicaceae)

For the first time, cytoembryological study of the female and male reproductive structures development in the East Siberian endemic, Borodinia macrophylla (Turcz.) O.E. Schulz (order Capparales, family Brassicaceae, tribe Boechereae), is presented. The general plan of the reproductive structures development occurs similarly to the studied species of Boechera. The anther contains 4 microsporangia with four layers, namely epidermis, endothecium, middle layer, and tapetum at the beginning of development; as the anther matures, the wall becomes two-layered. The anther tapetum is unevenly 2-layered, microsporocytes develop simultaneously; most pollen grains in mature anthers are bicellular. The ovule is ortho-campylotropous, bitegmic, medionucellate. The embryo sac is 7-celled, 8-nucleate, formed according to the monosporic Polygonum type. The polar nuclei of the central cell in the mature embryo sac do not fuse. Female gametophytes developed in all the ovules studied. In B. macrophylla, only a sexual mode of reproduction was observed; no apomictic development was detected.

Cell‐Tailored Multi‐Chamber Cd5(PO4)3Cl/CdO Mesocrystals Hetero‐Superstructure Toward Promoting Charge Transfer for Enhanced Photocatalytic H2 Evolution

AbstractElaborate mesocrystal superstructures assembled by nanocrystals enable the photocatalysts to effectively transfer photo‐generated charges over long‐distance. Especially, the hetero superstructure can facilely adjust the bandgaps to promote the separation of electron–hole pairs and enhance photocatalytic activity. Herein, a unique bio‐derived mesocrystal superstructures with multi‐chamber network is developed tactfully using the yeast cells with multi‐ascopore as templates obtained by sexual reproduction way. Specifically, the natural phosphorus and oxygen species derived from the yeast are tactfully exploited during the synthetic process of Cd5(PO4)3Cl/CdO hetero‐superstructure. The transient surface photovoltage and the time‐resolved transient photoluminescence (PL) result indicate that the well‐defined orientation of the mesocrystal contributes to enhancing photogenerated carriers transfer efficiency and reducing the recombination of electron–hole pairs. The hetero‐superstructures exhibit an excellent solar H2 releasing activity (18.71 mmol·g−1·h−1) and a high quantum yield of 28.27% at wavelength of 380 nm. The design of hetero‐superstructure with multi‐chamber by means of the inner interlaced network and microelements of the organisms introduces a new clue to construct functional materials with hierarchical structures for solar fuel conversion.

Representativeness of wild bluegrass accessions from Russia and neighboring countries in the VIR collection

N.I. Vavilov All-Russian Institute of Plant Genetic Resources (VIR) maintains a living bluegrass seed collection, which includes cultivars bred in Russia and abroad and wild specimens gathered by collecting missions of the institute in Russia, the Soviet Union and foreign countries. There are also specimens of various bluegrass species and cultivars obtained from botanical gardens of Russia and other countries.The core of the collection is composed of accessions of Kentucky bluegrass, an economically significant species, a valuable pasture and lawn plant. Wild Poa pratensis from Russia and neighboring countries is represented in the VIR catalogue by 825 seed accessions. The natural gene pool of Kentucky bluegrass is distinguished by significant polymorphism, genetically determined by a mixed system of sexual and asexual reproduction, polyploidy and aneuploidy of this species. The genetic diversity of Kentucky bluegrass, coupled with its geographical diversity, is the reason for ensuring wide representation of wild specimens of this species the in collection for the purposes of ex situ conservation. The VIR Kentucky bluegrass collection has been analyzed by gap analysis for representativeness of this species collected within the Russian Federation; the main stages of collecting activities were outlined, and regions for further expeditionary surveys identified. The diversity of wild bluegrass species collected in Russia and neighboring countries was assessed at 21 species.

Ecophysiology of extremophilic diatom alga <i>Nitzschia</i> cf. <i>thermaloides</i> from mud volcanoes of Crimea

The diatom alga Nitzschia cf. thermaloides can be found in large numbers in puddles and lakes in the places where mud volcanoes function in the area of the Bulganak mud volcano field (eastern Crimea). Environmental conditions in such reservoirs are extreme: salinity is from 18 to ≥70‰, insolation is extremely high, and ultraviolet radiation is very strong. The growth rate and the intensity of sexual reproduction of N. cf. thermaloides at different salinity and illumination levels have been studied in laboratory conditions. We have determined the limits of halotolerance and the optima of salinity and illumination for growth and sexual reproduction of the alga, capable of vegetative reproduction in an environment with salinity from 0 to 220‰. The range for sexual reproduction is narrower, from 6 to 54‰. The salinity of 22–25‰ and illumination of about 1.5 klx are optimal for both vegetative and sexual reproduction of N. cf. thermaloides.

Ecological diversification in sexual and asexual lineages

The presence or absence of sex can have a strong influence on the processes whereby species arise. Yet, the mechanistic underpinnings of this influence are poorly understood. To gain insights into the mechanisms whereby the reproductive mode may influence ecological diversification, we investigate how natural selection, genetic mixing, and the reproductive mode interact and how this interaction affects the evolutionary dynamics of diversifying lineages. To do so, we analyze models of ecological diversification for sexual and asexual lineages, in which diversification is driven by intraspecific resource competition. We find that the reproductive mode strongly influences the diversification rate and, thus, the ensuing diversity of a lineage. Our results reveal that ecologically-based selection is stronger in asexual lineages because asexual organisms have a higher reproductive potential than sexual ones. This promotes faster diversification in asexual lineages. However, a small amount of genetic mixing accelerates the trait expansion process in sexual lineages, overturning the effect of ecologically-based selection alone and enabling a faster niche occupancy than asexual lineages. As a consequence, sexual lineages can occupy more ecological niches, eventually resulting in higher diversity. This suggests that sexual reproduction may be widespread among species because it increases the rate of diversification.

Essential genes encoded by the mating-type locus of the human fungal pathogen Cryptococcus neoformans.

Fungal sexual reproduction is controlled by the mating-type (MAT) locus. In contrast to a majority of species in the phylum Basidiomycota that have tetrapolar mating-type systems, the opportunistic human pathogen Cryptococcus neoformans employs a bipolar mating-type system, with two mating types (a and α) determined by a single MAT locus that is unusually large (~120 kb) and contains more than 20 genes. While several MAT genes are associated with mating and sexual development, others control conserved cellular processes (e.g. cargo transport and protein synthesis), of which five (MYO2, PRT1, RPL22, RPL39, and RPO41) have been hypothesized to be essential. In this study, through genetic analysis involving sporulation of heterozygous diploid deletion mutants, as well as in some cases construction and analyses of conditional expression alleles of these genes, we confirmed that with the exception of MYO2, both alleles of the other four MAT genes are indeed essential for cell viability. We further showed that while MYO2 is not essential, its function is critical for infectious spore production, faithful cytokinesis, adaptation for growth at high temperature, and pathogenicity in vivo. Our results demonstrate the presence of essential genes in the MAT locus that are divergent between cells of opposite mating types. We discuss possible mechanisms to maintain functional alleles of these essential genes in a rapidly-evolving genomic region in the context of fungal sexual reproduction and mating-type evolution.

Selfing Shapes Fixation of a Mutant Allele Under Flux Equilibrium.

Sexual reproduction with alternative generations in a life cycle is an important feature in eukaryotic evolution. Partial selfing can regulate the efficacy of purging deleterious alleles in the gametophyte phase and the masking effect in heterozygotes in the sporophyte phase. Here, we develop a new theory to analyze how selfing shapes fixation of a mutant allele that is expressed in the gametophyte or the sporophyte phase only or in two phases. In an infinitely large population, we analyze a critical selfing rate beyond which the mutant allele tends to be fixed under equilibrium between irreversible mutation and selection effects. The critical selfing rate varies with genes expressed in alternative phases. In a finite population with partial self-fertilization, we apply Wright's method to calculate the fixation probability of the mutant allele under flux equilibrium among irreversible mutation, selection, and drift effects and compare it with the fixation probability derived from diffusion model under equilibrium between selection and drift effects. Selfing facilitates fixation of the deleterious allele expressed in the gametophyte phase only but impedes fixation of the deleterious allele expressed in the sporophyte phase only. Selfing facilitates or impedes fixation of the deleterious allele expressed in two phases, depending upon how phase variation in selection occurs in a life cycle. The overall results help to understand the adaptive strategy that sexual reproductive plant species evolve through the joint effects of partial selfing and alternative generations in a life cycle.

Eelgrass (Zostera marina) Recovery Affected by Disturbance Timing on Mechanically Harvested Oyster Culture Beds

Amid global seagrass declines and increasing human demands of coastal habitat, it is critical to mitigate the loss of seagrass habitat through understanding seagrass resilience following large-scale disturbance. Although seagrasses often respond to disturbance through increased sexual or asexual reproduction, past research on the cosmopolitan Zostera marina (eelgrass) is highly variable in terms of whether recovery occurs, and whether seeds or clonal growth is the primary contributor. In Willapa Bay, Washington state, we studied eelgrass recovery following large-scale disturbance on six adjacent oyster culture beds (~ 10,000 m2 in area) that were harvested using mechanical methods (i.e., dredging). We found that recovery potential and mode are heavily affected by the timing of disturbance. In the 200 and 400 days post-disturbance, beds disturbed during the early growing season (EGS; January–April) were estimated to have more than double the vegetative shoot density of beds disturbed during the late growing season (LGS; May–September). We also found a higher contribution of new shoots from seedlings following EGS relative to LGS disturbance, with up to 71% of shoots following EGS disturbance occurring from seedling origin. Consistent with eelgrass life history, spring seedling densities were positively affected by flowering shoot densities the previous summer. Clonal reproduction (i.e., branching) was negatively affected by a disturbance within the past 4 months, likely from physical damage, but also showed negative density dependence, meaning that higher branching rates were observed at lower shoot densities. Overall, this work emphasizes the importance of seedlings to seagrass recovery and demonstrates that Z. marina has higher recovery when disturbed (here by mechanical harvest of shellfish) during EGS versus LGS time periods. These findings provide straightforward guidelines for the management of anthropogenic disturbance on eelgrass beds to reduce permanent habitat loss and can also guide restoration efforts of eelgrass beds.