Timing Of Sexual Reproduction Research Articles

Abiotic and biotic factors controlling sexual reproduction in populations of Pseudo-nitzschia pungens (Bacillariophyceae)

Pseudo-nitzschia pungens is a widely distributed marine pennate diatom. Hybrid zones, regions in which two different genotypes may interbreed, are important areas for speciation and ecology, and have been reported across the globe for this species. However, sexual reproduction between differing clades in the natural environment is yet to be observed and is difficult to predict. Here we carried out experiments using two mono-clonal cultures of P. pungens from different genotypes to measure the frequency and timing of sexual reproduction across varying biotic (growth phases and cell activity potential) and abiotic conditions (nutrients, light, turbulence). We found the mating rates and number of zygotes gradually decreased from exponential to late stationary growth phases. The maximum zygote abundance observed was 1,390 cells mL−1 and the maximum mating rate was 7.1%, both which occurred during the exponential growth phase. Conversely, only 9 cells mL−1 and a maximum mating rate of 0.1% was observed during the late stationary phase. We also found the higher the relative potential cell activity (rPCA) in parent cells, as determined by the concentration of chlorophyll a per cell and the ratio of colony formation during parent cultivations, revealed higher mating rates. Furthermore, sexual events were reduced under nutrient enrichment conditions, and mating pairs and zygotes were not formed under aphotic (dark) or shaking culture conditions (150 rpm). In order to understand the sexual reproduction of Pseudo-nitzschia in the natural environment, our results highlight that it is most likely the combination of both biotic (growth phase, Chl. a content) and abiotic factors (nutrients, light, turbulence) that will determine the successful union of intraspecific populations of P. pungens in any given region.

Intra-Meadow Variation in Seagrass Flowering Phenology Across Depths

Variation in the timing of sexual reproduction, as well as differences in the relative investment in asexual vs sexual reproduction, commonly occurs among populations. Less is known about such variation within populations, yet small-scale differences in phenology and reproductive investment have the potential to limit gene flow and consequently the adaptive capacity of populations. We examined within-site variation in sexual reproduction in seagrasses, marine angiosperms that can reproduce asexually via clonal propagation or sexually via flowering, and that form the foundation of critical marine ecosystems globally. Many factors, including light availability, temperature, nutrient availability, and genetic identity, influence the rate and timing of seagrass flower development, yet little is known about how phenology varies across common environmental gradients within individual seagrass meadows. Here, we investigate how the density, morphology, and phenology of eelgrass (Zostera marina) differs across depths within multiple sites in New England. Despite variation in the proportion of reproductive vs vegetative shoots across sites, reproductive investment did not differ across depths within sites. However, a comparison of developmental stages of flowering shoots revealed delays in flower development for deep plants compared with shallow plants for all sites, demonstrating a consistent offset in reproductive phenology across depths. Our results suggest that differences in the timing of flowering may limit gene flow across seagrass meadows, with the potential for repeated genetic divergence in eelgrass populations spanning a depth gradient.

Auxin-Mediated Sterility Induction System for Longevity and Mating Studies in Caenorhabditis elegans.

The ability to control both the means and timing of sexual reproduction provides a powerful tool to understand not only fertilization but also life history trade-offs resulting from sexual reproduction. However, precisely controlling fertilization has proved a major challenge across model systems. An ideal sterility induction system should be external, non-toxic, and reversible. Using the auxin-inducible degradation system targeting the spe-44 gene within the nematode Caenorhabditis elegans, we designed a means of externally inducing spermatogenesis arrest. We show that exposure to auxin during larval development induces both hermaphrodite self-sterility and male sterility. Moreover, male sterility can be reversed upon cessation of auxin exposure. The sterility induction system developed here has multiple applications in the fields of spermatogenesis and mating systems evolution. Importantly, this system is also a highly applicable tool for aging studies. In particular, we show that auxin-induced self-sterility is comparable to the commonly used chemically-induced FUdR sterility, while offering multiple benefits, including being less labor intensive, being non-toxic, and avoiding compound interactions with other experimental treatments.

Reproductive biology and larval development of the scleractinian corals Favites colemani and F. abdita (Faviidae) in northwestern Philippines

The timing of sexual reproduction was investigated in Favites colemani and F. abdita in Bolinao, Pangasinan, northwestern Philippines. Bimonthly to weekly rapid sampling and histological analyses were conducted in permanently marked colonies for the period of 12 months from February 2014 to January 2015. The study showed both F. colemani and F. abdita are hermaphroditic broadcasting species with an annual gametogenic cycle. Both species spawned in days between full moon and last quarter of May. Maximal gamete release occurred 1–2 days before the last quarter between 20:30 and 22:30 h. Spawning events coincided with the highest mean seawater temperature and low tidal stands, suggesting lunar cycle and temperature variations may serve as potential proximate cues that could affect the timing and synchronize reproduction of these two faviid species. Larval development up to settlement in the two species was also described herein.

The dynamics of sexual phase in the marine diatom Pseudo-nitzschia multistriata (Bacillariophyceae).

Sexual reproduction represents a fundamental phase in the life cycle of diatoms, linked to both the production of genotypic diversity and the formation of large-sized initial cells. Only cells below a certain size threshold can be sexualized, but various environmental factors can modulate the success of sexual reproduction. We investigated the role of cell density and physiological conditions of parental strains in affecting the success and timing of sexual reproduction in the marine heterothallic diatom Pseudo-nitzschia multistriata. We also studied the dynamics of the sexual phase in still conditions allowing cell sedimentation and in gently mixed conditions that keep cells in suspension. Our results showed that successful sexual reproduction can only be achieved when crossing parental strains in the exponential growth phase. Evidence was provided for the fact that sexual reproduction is a density-dependent event and requires a threshold cell concentration to start, although this might vary considerably amongst strains. Moreover, the onset of the sexual phase was coupled to a marked reduction in growth of the vegetative parental cells. The crosses carried out in physically mixed conditions produced a significantly reduced number of sexual stages as compared to crosses in still conditions, showing that mixing impairs sexualization. The results of our experiments suggest that the signaling that triggers the sexual phase is favored when cells can accumulate, reducing the distance between them and facilitating contacts and/or the perception of chemical cues. Information on the progression of the sexual phase in laboratory conditions help understanding the conditions at which sex occurs in the natural environment.

Temperature modulation of photoperiodism and the timing of late-season changes in life history for an aphid, Acyrthosiphon pisum

AbstractWhere winters are severe, aphids reproduce parthenogenetically and viviparously in summer, switch to sexual reproduction in late summer, and produce winter-hardy eggs by the end of the season. The role of day length and temperature in initiating seasonal changes from parthenogenetic to sexual reproduction by pea aphids, Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae), are described and the selection pressures that affect the timing of this transition are investigated. Over four seasons, a pea aphid clone was sampled from field cages through late summer in southern Manitoba, Canada, and reared in the laboratory to determine the phenotypes of progeny produced as the season progressed. The timing of transitions from one phenotype to another under natural day length and temperature, and the critical day lengths that caused the transitions, coincided with expectations from laboratory studies of photoperiodic responses. Males and mating females appeared later when the weather in August was warm than when it was cool. The timing of seasonal changes was adapted to minimize the physiological time to the end of the season, which maximized the number of asexual summer generations. Ambient temperature modulated the response to day length and fine-tuned the timing of sexual reproduction to adapt for annual variation in autumn weather.

Timing of sexual reproduction in chydorid cladocerans (Anomopoda, Chydoridae) from nine lakes in southern Finland

INTRODUCTION Cladocerans (Crustacea) have two strategies of reproduction. During most of their active period, which occurs in the ice-free season in northern temperate and subarctic climates, they reproduce asexually (parthenogenetically). Sexual reproduction, or gamogenesis, usually begins towards the end of the active period and leads to hatching of males and gamogenetic females, which results in fertilized resting eggs. Resting eggs are very tolerant of extreme environmental conditions, such as freezing and drying, and ensure the survival of cladoceran populations during the winter, from which new asexually reproducing females hatch in spring. Much of the research on cladoceran sexual reproduction has focused on the genus Daphnia (e.g. Stross & Hill, 1965, 1968; Kleiven et al., 1992; Pijanowska & Stolpe, 1996; Slusarczyk, 1995, 2001), while the patterns of sexual reproduction in the family Chydoridae (chydorids) have not been widely examined. It is generally known that sexual reproduction in chydorids also occurs in autumn in central and northern Europe (e.g. Poulsen, 1940; Maemets, 1961; Flossner, 1964; Green, 1966; Frey, 1982; Koksvik, 1995), probably triggered by declining temperatures and shortening photoperiods (Shan, 1974; Frey, 1982). Nevertheless, the mechanisms that induce gamogenetic reproduction in chydorids have not yet been entirely clarified. Frey (1982) generalized the life cycles of chydorids as predominantly monocyclic with autumnal gamogenetic periods, with some species having variable and insignificant earlier periods of gamogenesis. Berg (1929) and Flossner (1964) stated that some chydorid communities on the European mainland also have sexual individuals present during the summer months; i.e. they are dicyclic. Some chydorid species are dicyclic as far north as in Denmark (Raen, 1995) and Estonia (Maemets, 1961). There is also one record of summer gamogenesis from southern Finland. Jarnefelt (1956) recorded gamogenetic females ofAlonella excisa (Fischer) from Lake Tuusulanjarvi in early June during a single year. The aim of the present study was to examine the patterns of sexual reproduction in chydorids from several lakes in southern Finland. Our focus was on the timing of sexual reproduction among chydorid populations, i.e. does summer gamogenesis occur in most species and are induction and incidence of autumnal gamogenesis synchronous among populations? Nine lakes in southern Finland were monitored weekly for living chydorids and their sexual reproduction during the open-water season of 2005. Most of the lakes chosen for the study differed in their physical, chemical, and ecological conditions, but were situated in the same climate region. SITES The nine study lakes are located in southern Finland, near Helsinki (Fig. 1). The limnological variables of the lakes measured during three seasons are presented in Table 1. The mean annual air temperature in the area is approximately 4.5 [degrees]C, the mean July air temperature 17[degrees]C, and the mean January air temperature -6[degrees]C (Helminen, 1987). The open-water season lasts about 7 months, from early May to late November (Kuusisto, 1986), depending on yearly variation in spring and autumn temperatures. Lakes Hauklampi (60[degrees] 18' N, 24[degrees]36' E, 76.7 m above sea level, area 2.7 ha), Iso Majaslampi (60[degrees]19' N, 24[degrees]36' E, 92.7 m a.s.l., area 6.3 ha), and Pieni Majaslampi (60[degrees]19.3' N, 24[degrees]35.7' E, 97.3 m a.s.l., area about 1 ha) are located close to one another. They are acidic and oligotrophic lakes whose catchments are small and characterized by patches of mire, bedrock outcrops, and pine (Pines) forests. The shores are inhabited by sedges and Sphagnum mosses, and the aquatic macrophyte zone consists only of European white waterlily (Nymphaea alba). The lakes were severely acidified during the 1980s as a result of acid deposition, but experienced a recovery process during the 1990s. …

Timing of Sexual Reproduction and Reproductive Success in the High‐Mountain Plant Saxifraga bryoides L.

SAXIFRAGA BRYOIDES L. is one of the plant species reaching the upper limits of distribution for flowering plants in the European Alps. Because of its abundance in the subnival and nival zones, we expected S. BRYOIDES to reproduce efficiently in the highly stochastic climate at higher altitudes. Investigations were carried out at two subnival sites (2650 m and 2880 m a.s.l.) in the Austrian Alps. We studied flowering phenology, dynamics of seed development, and reproductive success in the climatically different years from 2001 - 2004. For a nival plant species, S. BRYOIDES showed a particularly long prefloration period (6 - 9 weeks). From onset of anthesis until seed maturity took an individual flower another 6 - 7 weeks and all individuals at a site 9 - 10 weeks. The length of the prefloration period and seed histogenesis was temperature-dependent, whereas seed maturation seemed to be endogenously controlled. Only in the exceptionally long and warm growing season of 2003 did all fruits mature at a site. In the other years, the onset of winter conditions halted development in many fruits before maturity. The seed/ovule ratio of mature fruits was around 0.7 in all years. The relative reproductive success (RRS) ranged from zero to 0.7, depending on the site and year. In conclusion, S. BRYOIDES needs an unexpectedly long time to undergo reproductive development. Though fruit maturation is uncertain, the high S/O ratio of single intact fruits results in at least a small seed crop in most years. This seems to be sufficient to assure the spread and maintenance of S. BRYOIDES at higher altitudes. As a seed-risk strategist (Molau,1993), S. BRYOIDES would clearly benefit from a prolonged growing season, which might occur more often if climate warming continues.

Distribution and diversity of aquatic protists: an evolutionary and ecological perspective

Assessment of the distribution and diversity of free-living protists is currently hampered by a limited taxonomic resolution of major phyla and by neglecting the significance of spatial and temporal scaling for speciation. There is a tremendous physiological and ecological diversity that is hidden at the morphological level and not apparent at the level of conserved genes. A conceptual framework linking the various levels of diversity is lacking. Neutral genetic markers are useful indicators of population structure and gene flow between populations, but do not explain adaptation to local habitat conditions. The correspondence between protein-coding genes, ecophysiological performance, and fitness needs to be explored under natural conditions. The area and the associated typical temporal dimension of active cells (their ‘home range’) are much smaller, respectively shorter, than the area and time period potentially covered during passive dispersal of protist resting stages. The assumptions that dispersal rates are generally high in free-living protists and that extinction of local populations is, therefore, infinitesimally small wait rigorous testing. Gene flow may be uncoupled largely from dispersal, because local adaptation and numerical effects of residents may strongly reduce or even prevent successful invasion (immigration). The significance of clonal selection depends on the as yet unknown frequency and timing of sexual reproduction, and on the stability of the environment. The extent of local adaptation and the fitness-related ecophysiological divergence are critical for the speciation process and, hence, for defining protist species.

Phenology and phylogenetic positioning of the Hawaiian endemic freshwater alga, Batrachospermum spermatiophorum (Rhodophyta, Batrachospermales)

SUMMARY The only known population of Batrachospermum spermatiophorum Vis et Sheath, located in a small stream on east Maui, Hawaii, was sampled from November 2001 to October 2002 to investigate its phenology. Additionally, the taxonomic status of the alga was examined. Phylogenetic analyses of the large subunit of the ribulose-1,5-bisphosphate carboxylase/oxygenase (rbcL) gene for B. spermatiophorum confirm its placement within the Section Contorta of the genus Batrachospermum. Comparisons with rbcL gene sequences for all other available Batrachospermum species, including 10 other members of the Section Contorta, illustrate that B. spermatiophorum is distinct in its rbcL nucleotide sequence and should be maintained as a separate species. The phenology of B. spermatiophorum differed from most studies of Batrachospermum reproduction in that the gametophytes were present year round, and no macroscopic chantran-sia stages were identified at any point during the present study. Maximum plant length was highest in the late fall and early winter months, while gametangial production peaked in February and March. Carposporophyte abundance rose sharply in July and August, and the percentage of carposporophytes producing carpospores was highest in late summer and early fall months. Although significant correlations were determined among stream conditions and among phenological characteristics, only pH was associated with several of the reproductive characters, which is unusual for studies of Batrachospermum phenology. Timing of sexual reproduction for all macroalgal community members in the stream site was not coordinated, with some reproducing year round and others more sporadically. The year-round presence of Batrachospermum gametophytes may be a result of a combination of smaller seasonal changes in cues such as day length and water temperature in the tropical environment than occur in temperate locations, and lack of extreme conditions that might inhibit the persistence of the gametophyte.

SEXUAL REPRODUCTION IN THE PENNATE DIATOMS PSEUDO‐NITZSCHIA MULTISERIES AND P. PSEUDODELICATISSIMA (BACILLARIOPHYCEAE)

Clones of the domoic‐acid‐producing pennate diatom Pseudo‐nitzschia multiseries (Hasle) Hasle and of the potentially toxic P. pseudodelicatissima (Hasle) Hasle normally decrease in cell size in culture until they eventually die without undergoing sexual reproduction to regain the largest cell size. However, we induced sexual reproduction by mixing individual exponentially growing clonal cultures of the appropriate minimal cell size under the same conditions that are normal for vegetative growth. We observed pairing of parent cells (gametangiogamy); production of four morphologically isogamous, nonflagellated gametes per gametangial pair; rearrangement of the gametes and their fusion to form zygotes, revealing physiological anisogamy; enlargement of auxospores; and formation of long initial cells. Our observations of allogamous reproduction are consistent with those reported for other dioecious pennate diatoms. Clones of P. pseudodelicatissima from the Black Sea and from the CCMP culture collection failed to auxosporulate when mixed together, although they are the same species according to scanning electron microscopy. The range in apical length of P. multiseries was broader than that reported in the literature for field samples, necessitating a modification of the species description. Knowledge of the pattern and timing of sexual reproduction in Pseudo‐nitzschia spp. may provide insights into their bloom dynamics.