Isolation leads to greater clonality and reduced seed production in a temperate seagrass.

<p>Understanding the evolutionary forces that shape populations in the marine environment is critical for predicting population dynamics and dispersal patterns for marine organisms. For organisms with complex reproductive strategies, this remains a challenge. Sponges fulfil many functional roles and are important components of benthic environments in tropical, temperate and polar oceans. They have evolved diverse reproductive strategies, reproducing both sexually and asexually, and thus provide an opportunity to investigate complicated evolutionary questions. This PhD thesis examines sexual and asexual reproduction in two common golf-ball sponges in central New Zealand (Tethya bergquistae and T. burtoni), with particular focus on how the environment influences these modes of reproduction, and further, how they shape species delineations and connectivity patterns. New Zealand waters are projected to experience increases in temperature and decreases in nutrients over the next century, and therefore these species may be experience changes in basic organismal processes like reproduction due to climate change, requiring adaptation to local environments. Therefore, this work has important implications when considering how reproductive phenology, genetic diversity and population structure of marine populations may change with shifts in climate. In my first data chapter, I highlight the difficulty in delineating sponge species by investigating the evolutionary relationship of Tethya spp. in central New Zealand using both morphological and molecular methods. Phylogenetic reconstructions based on two mitochondrial markers (rnl, COI-ext) and one nuclear marker (18S) revealed three genetic clades, with one clade representing T. bergquistae and two clades belonging to what was a priori thought to be a single species, T. burtoni. Morphological analysis based on spicule characteristics allowed T. bergquistae to be distinguished from T. burtoni, but revealed no apparent differences between the T. burtoni clades. These results indicate hidden genetic diversity within T. burtoni, which likely represents a group consisting of incipient species that have undergone speciation but have yet to express clear morphological differences. This chapter supports the notion that cryptic speciation in sponges may go undetected and diversity underestimated when using only morphology-based taxonomy, a result which has implications for conservation and management of marine systems. In my second data chapter, I characterize the reproductive biology for both species of Tethya in relation to potential environmental drivers, including sea surface temperature, chlorophyll-a concentration and rainfall. Using histological methods for sponges collected monthly over two years, Tethya spp. were found to be gonochoristic and oviparous sexual reproducers, with one annual reproductive event occurring in the austral summer from January to March. Differences in oocyte density and reproductive output between both species and sites highlighted both species-specific adaptive responses and environmental influences on reproduction. Temperature and rainfall were found to be correlated with instances of sexual reproduction, and the summer reproductive event occurred each year following the spring bloom of chlorophyll-a. These findings indicate that seasonal fluctuations in the environment may be important for triggering gametogenesis for these species. With shifts in temperature, productivity, and timing of seasons projected for New Zealand, there is a potential for reproductive phenology to become mismatched with the surrounding environment under future climate change scenarios, which has consequences for the frequency, duration and overall output of sexual reproduction for these sponges. My third data chapter characterizes asexual reproduction in both species of Tethya, exploring relationships between reproductive traits and potential environmental drivers that may influence asexual budding events. Two sponge populations, one for each species of Tethya, were monitored over two years by both monthly sampling and periodic in situ observations. Data revealed that budding occurred continuously throughout the year, but had a cyclic pattern where instances of budding and densities of buds were higher during the austral spring and summer. Asexual reproduction coincided with sexual reproduction, and some individuals were found to simultaneously reproduce using both modes. Instances of asexual reproduction were positively associated with temperature and rainfall, but distinct differences between species were difficult to identify. As temperature proved important, an experiment looking at bud production in relation to thermal stress was conducted, where sponges were subjected to stable temperatures treatments of 17°C (control), 19°C and 21°C. No instances of budding were observed under any temperature treatment, and high mortality occurred in the 21°C treatment. These results suggest that temperature changes (i.e., heterogeneous environments) may be more important than temperature alone in driving asexual reproduction, and further, indicate thermal stress will result in increased sponge mortality. Correlations to potential environmental drivers indicate that future shifts in climate may affect instances of asexual reproduction and thus sponge abundance, which has the potential to alter the genetic structure and overall diversity of these populations. In the final data chapter, I developed novel microsatellite markers for Tethya burtoni to characterize the genetic connectivity patterns among four populations in central New Zealand, with particular interest in the roles that sexual and asexual reproduction play in connectivity. I sampled three sites within 10 km of each other in the Wellington Region (WR), and another site on an island (Kapiti Island) approximately 50 km north of the WR. At one of the WR sample sites, I monitored a T. burtoni population over two years to examine the dispersal range of asexually reproduced buds and the ability of clones to sexually reproduce. The WR and Kapiti Island populations were strongly genetically differentiated, but within the WR region, two populations were genetically similar, indicative of high connectivity. For the monitored population, asexual bud dispersal was restricted to no greater than 1 m and clonal individuals had reduced sexual reproductive ability. Asexual reproduction did not appear to play an important role in interpopulation connectivity nor gene flow, as buds had low dispersal ability and rarely reproduced. Population structure and connectivity for T. burtoni appear to be largely driven by sexual reproduction, and asexual reproduction instead aids genotype survivorship and population maintenance. These findings highlight that different reproductive modes can differentially contribute to population dynamics in sessile marine organisms, suggesting that predictions about future population viability under changing environments may be difficult to make. In summary, this PhD thesis uses a combination of genetic, histological, field-based and experimental methods to examine species boundaries, reproduction and connectivity for Tethya spp. on rocky reefs of New Zealand. The sympatric nature, complex reproductive ecology and connectivity patterns observed likely shape the complex evolutionary processes occurring in these sponges, including introgressive hybridization and cryptic species. Individuals that showed evidence of possible introgressive events occurred mainly in populations with more restricted gene flow, while the presence of both cryptic species were more prevalent in well connected populations. Such a trend allows for discussion of under what circumstances both of these processes occur. Furthermore, environmental correlates to both sexual and asexual reproduction indicate that both of these modes of reproduction have the potential to be altered with future changes in the environment. As both modes were found to play different roles in gene flow within and between populations, future shifts in climate are also expected to alter population structure and connectivity for these sponges. Such shifts in gene flow will also likely result in changes to species boundaries and thus the overall diversity of this genus. Many other sessile, benthic marine organisms present reproductive traits and behaviours similar to those of Tethya spp., and therefore these results can aid in the interpretation of results for other marine taxa. Overall, this thesis describes the population dynamics of Tethya spp., which are abundant and ecologically important on New Zealand reefs, and provides insight on how temperate sponge populations may fare with climate change, which has important implications for management and conservation efforts.</p>

Cyclically parthenogenetic zooplankters like rotifers are important tools for assessing toxicity in aquatic environments Sexual reproduction is an essential component of rotifer life cycles, but current toxicity tests utilize only asexual reproduction We compared the effects of four toxicants on asexual and sexual reproduction of the rotifer Brachionus calyciflorus Toxicants had a differential effect on sexual and asexual reproduction, with sexual reproduction consistently the most sensitive Concentrations of 0 2 μg/ml PCP (sodium pentachlorophenate) had no effect on the asexual reproductive rate, but significantly reduced sexual reproduction Likewise, chlorpyrifos concentrations of 0 3 μg/ml had no significant effect on asexual reproduction, but sexual reproduction was significantly reduced There was no difference in NOECs, LOECs, and chronic values for asexual and sexual reproduction for cadmium and naphthol tests However, comparison of toxicant effect levels revealed that sexual reproduction was more strongly reduced at each toxicant concentration The four toxicants tested inhibited sexual reproduction 2 to 68 times more than asexual reproduction at the lowest observed effect concentrations Toxicants inhibited sexual reproduction in its initial step sexual female production Because sexual reproduction is more sensitive, toxicity tests based exclusively on asexual reproduction may not be protective of rotifer life cycles

Late Quaternary Fossils of Poa fendleriana (Muttongrass): Holocene Expansions of Apomicts

In order to assess the importance of sexual and asexual reproduction during the life history of Scirpus mariqueter , its reproductive and growth characters were concurrently examined along an elevational gradient (from low elevation to high elevation). The proportions of flowering shoot and inflorescence mass, seed : flower ratio and seed weight were used to quantify the investment in sexual reproduction. The proportions of current‐year shoot and rhizome mass were used to quantify the investment in asexual reproduction, and the proportion of corm mass was used for growth, respectively. It was found that vegetative propagation predominated at low elevation, whereas sexual reproduction predominated at high elevation; and that sexual reproduction increased with declining asexual reproduction along the gradient. The results suggest that asexual reproduction is relatively favored in the early life stage, whereas sexual reproduction is favored when the population becomes mature and aged, probably because of the functional differentiation between the two reproductive types. Sexual productive characters (i.e. the proportions of flowering shoot and inflorescence mass) were negatively correlated to both growth and asexual reproductive characters along the gradient, indicating there might exist some trade‐offs among growth, sexual and asexual reproduction during the life history. However, no obvious pattern was found between asexual reproductive characters and growth characters along the elevational gradient, possibly because of the varied relationships between them at different life stages. The variations in sexual and asexual reproduction in the species and the relationship between them are thought to be of great significance for local population growth, species persistence and evolution.

Seagrasses form a unique group of submerged marine angiosperms capable of both sexual and asexual reproduction. The amounts of sexual and asexual reproduction differ within some species relying on geographic location and environmental factors. Here, we studied the reproductive strategies of different geographic Zostera japonica populations, S1 and S2 at Swan Lake lagoon (SLL), and H1 and H2 at Huiquan Bay (HQB), in northern China. The duration of flowering at SLL was longer than at HQB, whereas flowering initiation at HQB occurred earlier than at SLL. In addition, the timing of seed maturation at HQB occurred earlier than at SLL. The allocation to sexual reproduction at SLL was greater than at HQB. The maximum potential seed production was greatest at S1 (22228.52 ± 8832.46 seeds ⋅ m–2), followed by S2 (21630.34 ± 9378.67 seeds ⋅ m–2), H2 (7459.60 ± 1779.33 seeds ⋅ m–2), and H1 (2821.05 ± 1280.57 seeds ⋅ m–2). The seasonal changes in total shoot density and biomass were small at HQB. There was a relatively large number of overwintering shoots at HQB because of the higher average temperature during winter. The allocation to sexual reproduction was lower than at SLL, and no seedlings were observed at HQB during our study. Thus, the population of Z. japonica at HQB was maintained by asexual reproduction. Compared with HQB, the biomass of overwintering shoots at SLL was less than 30 g dry weight ⋅ m–2. The Z. japonica at SLL relied on asexual and sexual reproduction to maintain the population. The results show the necessity of understanding local reproductive strategies before starting restoration and management projects. The study provides fundamental information and guidance for the conservation and restoration of seagrass beds.

Sexual reproduction is a mysterious phenomenon. Most animals and plants invest in sexual reproduction, even though it is more costly than asexual reproduction. Theoretical studies suggest that occasional or conditional use of sexual reproduction, involving facultative switching between sexual and asexual reproduction, is the optimal reproductive strategy. However, obligate sexual reproduction is common in nature. Recent studies suggest that the evolution of facultative sexual reproduction is prevented by males that coerce females into sexual fertilization; thus, sexual reproduction has the potential to enforce costs on a given species. Here, the effect of sex on biodiversity is explored by evaluating the reproductive costs arising from sex. Sex provides atypical selection pressure that favors traits that increase fertilization success, even at the expense of population growth rates, that is, sexual selection. The strength of sexual selection depends on the density of a given species. Sexual selection often causes strong negative effects on the population growth rates of species that occur at high density. Conversely, a species that reduces its density is released from this negative effect, and so increases its growth rate. Thus, this negative density‐dependent effect on population growth that arises from sexual selection could be used to rescue endangered species from extinction, prevent the overgrowth of common species and promote the coexistence of competitive species. Recent publications on sexual reproduction provide several predictions related to the evolution of reproductive strategies, which is an important step toward integrating evolutionary dynamics, demographic dynamics and community dynamics.

SYNOPSIS. The class Rotifera includes species which reproduce solely by apomictic female parthenogenesis and species which alternate this “asexual” reproduction with ordinary sexual reproduction. The transition between asexual and sexual reproduction is controlled by the environment. Laboratory studies with the genus Asplanchna have shown that it is possible to identify specific molecules as inducers, which act on embryos in utero to modify their development and determine whether they will mature as sexually or asexually reproducing females. Moreover, an evolutionary rationale can be provided for the response to these particular environmental controlling agents, which are such that sexual reproduction will occur only when it will result in successful fertilization. Rotifers are opportunistic or colonising organisms, which implies selection for rapid reproduction. We suggest that this may account, at least in part, for the origin of both apomicitc parthenogenesis and certain features of the pattern of macromolecular syntheses during development. To account for the success of those rotifers which have lost sexual reproduction entirely, we note that accumulation of mutations during periods of exponential apomictic parthenogenetic reproduction, together with “mitotic” crossing-over, could theoretically produce sufficient genotypic diversity to provide evolutionary flexibility. This would eliminate a major advantage of sexual reproduction.

The roles of sexual and asexual reproduction in the origin and dissemination of strains causing fungal infectious disease outbreaks

Reproductive Ecology of Tetraphis pellucida. I. Population Density and Reproductive Mode

Genetic diversity among biological entities, including populations, species, and communities, serves as a fundamental source of information for understanding their structure and functioning. However, many ecological and evolutionary problems arise from limited and complex datasets, complicating traditional analytical approaches. In this context, our study applies a deep learning-based approach to address a crucial question in evolutionary biology: the balance between sexual and asexual reproduction. Sexual reproduction often disrupts advantageous gene combinations favored by selection, whereas asexual reproduction allows faster proliferation without the need for males, effectively maintaining beneficial genotypes. This research focuses on exploring the coexistence patterns of sexual and asexual reproduction within a single species. We developed a convolutional neural network model specifically designed to analyze the dynamics of populations exhibiting mixed reproductive strategies within changing environments. The model developed here allows one to estimate the ratio of population members who originate from sexual reproduction to the clonal organisms produced by parthenogenetic females. This model assumes the reproductive ratio remains constant over time in populations with dual reproductive strategies and stable population sizes. The approach proposed is suitable for neutral multiallelic marker traits such as microsatellite repeats. Our results demonstrate that the model estimates the ratio of reproductive modes with an accuracy as high as 0.99, effectively handling the complexities posed by small sample sizes. When the training dataset’s dimensionality aligns with the actual data, the model converges to the minimum error much faster, highlighting the significance of dataset design in predictive performance. This work contributes to the understanding of reproductive strategy dynamics in evolutionary biology, showcasing the potential of deep learning to enhance genetic data analysis. Our findings pave the way for future research examining the nuances of genetic diversity and reproductive modes in fluctuating ecological contexts, emphasizing the importance of advanced computational methods in evolutionary studies.

A major challenge for plants in a rapidly changing climate is to adapt to rising temperatures. Some plants adapt to temperature conditions by generating an epigenetic memory that can be transmitted both meiotically and mitotically. Such epigenetic memories may increase phenotypic variation to global warming and provide time for adaptation to occur through classical genetic selection. The goal of this study was to understand how warmer temperature conditions experienced during sexual and asexual reproduction affect the transcriptomes of different strawberry (Fragaria vesca) ecotypes. We let four European F. vesca ecotypes reproduce at two contrasting temperatures (18 and 28°C), either asexually through stolon formation for several generations, or sexually by seeds (achenes). We then analyzed the transcriptome of unfolding leaves, with emphasis on differential expression of genes belonging to the epigenetic machinery. For asexually reproduced plants we found a general transcriptomic response to temperature conditions but for sexually reproduced plants we found less significant responses. We predicted several splicing isoforms for important genes (e.g. a SOC1, LHY, and SVP homolog), and found significantly more differentially presented splicing event variants following asexual vs. sexual reproduction. This difference could be due to the stochastic character of recombination during meiosis or to differential creation or erasure of epigenetic marks during embryogenesis and seed development. Strikingly, very few differentially expressed genes were shared between ecotypes, perhaps because ecotypes differ greatly both genetically and epigenetically. Genes related to the epigenetic machinery were predominantly upregulated at 28°C during asexual reproduction but downregulated after sexual reproduction, indicating that temperature-induced change affects the epigenetic machinery differently during the two types of reproduction.

Background: Plant reproduction ensures the survival and diversity of plant species. Plants use both sexual and asexual methods of reproduction, each offering distinct advantages. Sexual reproduction involves the combination of genetic material from two parent plants, leading to genetic diversity. Asexual reproduction, on the other hand, allows plants to reproduce without the fusion of gametes, producing genetically identical offspring. Methods: This study explored sexual and asexual reproduction methods across different plant species, analyzing their mechanisms through a review of literature and observational data from selected plant species. Data was collected from field and greenhouse experiments involving species like Arabidopsis thaliana for sexual reproduction and Bryophyllum for asexual reproduction. Pollination, fertilization, seed germination, and vegetative propagation were observed and analyzed using microscopic, genetic, and statistical tools. Results: Sexual reproduction was found to increase genetic variation, contributing to greater resilience in changing environments. Asexual reproduction provided faster population growth in stable conditions. Sexual reproduction was more common in flowering plants, while asexual reproduction was predominant in species with poor pollination opportunities or those in extreme environments. Conclusion: Sexual and asexual reproduction methods provide evolutionary advantages based on environmental factors and species-specific needs. The choice between the two strategies is influenced by the availability of resources, environmental conditions, and genetic diversity requirements. A combination of both methods is seen in some species, enabling adaptation and survival across diverse ecosystems.

Seagrasses are ecosystem engineers that offer important habitat for a large number of species and provide a range of ecosystem services. Many seagrass ecosystems are dominated by a single species, with research showing that genotypic diversity at fine spatial scales plays an important role in maintaining a range of ecosystem functions. However, for most seagrass species, information on fine-scale patterns of genetic variation in natural populations is lacking. In this study, we use a hierarchical sampling design to determine the levels of genetic and genotypic diversity at different spatial scales (centimeters, meters, kilometers) in the Australian seagrass Zostera muelleri. Our analysis shows that at fine spatial scales (<1 m), levels of genotypic diversity are relatively low (R(Plots) = 0.37 ± 0.06 SE), although there is some intermingling of genotypes. At the site (10’s m) and meadow location (km) scale, we found higher levels of genotypic diversity (R(sites) = 0.79 ± 0.04 SE; R(Locations) = 0.78 ± 0.04 SE). We found some sharing of genotypes between sites within meadows, but no sharing of genotypes between meadow locations. We also detected a high level of genetic structuring between meadow locations (FST = 0.278). Taken together, our results indicate that both sexual and asexual reproductions are important in maintaining meadows of Z. muelleri. The dominant mechanism of asexual reproduction appears to occur via localized rhizome extension, although the sharing of a limited number of genotypes over the scale of 10’s of meters could also result from the localized dispersal and recruitment of fragments. The large number of unique genotypes at the meadow scale indicates that sexual reproduction is important in maintaining these populations, while the high level of genetic structuring suggests little gene flow and connectivity between our study sites. These results imply that recovery from disturbances will occur through both sexual and asexual regeneration, but the limited connectivity at the landscape scale implies that recovery at meadow-scale losses is likely to be limited.

Reproduction is a fundamental biological process, with organisms reproducing sexually, asexually, and, in some cases, utilizing both modes of reproduction within the same population. Does the ability to reproduce through a combination of asexual and sexual modes offer an evolutionary advantage over relying on either mode alone? Here, we introduce an empirically driven theoretical model to examine the dynamics and interplay between sexual and asexual reproduction in stick insect populations. We analyse it using a novel phase transition approach and corroborate it using published experimental data. We find that the presence of males can either increase or decrease the overall population size. However, maintaining an optimal ratio of parthenogenetic to sexual reproduction is crucial for male resilience, effectively delaying male extinction. Conversely, extreme levels of parthenogenetic reproduction-whether too high or too low-can lead to male extinction, emphasizing the need for a balanced number of virgin females to ensure the persistence of males. Our model also explains male absence in Carausius morosus and persistence in Extatosoma tiaratum. Our findings provide valuable insights into the interplay of reproductive strategies and contribute to broader discussions on the transitions between sexual and asexual reproduction.

Does reproductive assurance explain the incidence of polyploidy in plants and animals?