Evidence Of Sexual Reproduction Research Articles

RIBOSOMAL RNA GENE DIVERSITY, EFFECTIVE POPULATION SIZE, AND EVOLUTIONARY LONGEVITY IN ASEXUAL GLOMEROMYCOTA

Arbuscular mycorrhizal fungi (phylum Glomeromycota) are among the oldest and most successful symbionts of land plants. With no evidence of sexual reproduction, their evolutionary success is inconsistent with the prediction that asexual taxa are vulnerable to extinction due to accumulation of deleterious mutations. To explore why Glomeromycota defy this prediction, we studied ribosomal RNA (rRNA) gene evolution in the Claroideoglomus lineage and estimated effective population size, N(e) , in C. etunicatum. We found that rRNA genes of these fungi exhibit unusual and complex patterns of molecular evolution. In C. etunicatum, these patterns can be collectively explained by an unexpectedly large N(e) combined with imperfect genome-wide and population-level rRNA gene repeat homogenization. The mutations accumulated in rRNA gene sequences indicate that natural selection is effective at purging deleterious mutations in the Claroideoglomus lineage, which is also consistent with the large N(e) of C. etunicatum. We propose that in the near absence of recombination, asexual reproduction involving massively multinucleate spores typical for Glomeromycota is responsible for the improved efficacy of selection relative to drift. We postulate that large effective population sizes contribute to the evolutionary longevity of Glomeromycota.

Evidence for an Invasive Aphid “Superclone”: Extremely Low Genetic Diversity in Oleander Aphid (Aphis nerii) Populations in the Southern United States

BackgroundThe importance of genetic diversity in successful biological invasions is unclear. In animals, but not necessarily plants, increased genetic diversity is generally associated with successful colonization and establishment of novel habitats. The Oleander aphid, Aphis nerii, though native to the Mediterranean region, is an invasive pest species throughout much of the world. Feeding primarily on Oleander (Nerium oleander) and Milkweed (Asclepias spp.) under natural conditions, these plants are unlikely to support aphid populations year round in the southern US. The objective of this study was to describe the genetic variation within and among US populations of A. nerii, during extinction/recolonization events, to better understand the population ecology of this invasive species.Methodology/Principal FindingsWe used five microsatellite markers to assess genetic diversity over a two year period within and among three aphid populations separated by small (100 km) and large (3,700 km) geographic distances on two host plant species. Here we provide evidence for A. nerii “superclones”. Genotypic variation was absent in all populations (i.e., each population consisted of a single multilocus genotype (MLG) or “clone”) and the genetic composition of only one population completely changed across years. There was no evidence of sexual reproduction or host races on different plant species.Conclusions/Significance Aphis nerii is a well established invasive species despite having extremely low genetic diversity. As this aphid appears to be obligatorily asexual, it may share more similarities with clonally reproducing invasive plants, than with other animals. Patterns of temporal and geographic genetic variation, viewed in the context of its population dynamics, have important implications for the management of invasive pests and the evolutionary biology of asexual species.

Evidence of sexual reproduction in the hermatypic corals Pocillopora damicornis, Porites panamensis, and Pavona gigantea in Banderas Bay, Mexican Pacific

The reproductive capacity of coral communities in the Mexican Pacific is still poorly documented. One of the most abundant coral communities in this region is found in Banderas Bay, yet the reproductive patterns of the coral species have not been analyzed. In order to document the annual reproductive cycle of the three most common species of corals in the bay, samples of Pocillopora damicornis, Porites panamensis, and Pavona gigantea were collected monthly from Redonda Island from December 2001 to November 2002. Colony fragments were processed by histological techniques and analyzed under a microscope. The three species showed the presence of gametes, which was associated with an increase in sea surface temperature. Gametogenesis was first observed in P. damicornis, classified as hermaphrodite. In P. panamensis, reproductive cells were observed in May 2002, and embryos and planulae in September 2002; this species was classified as gonochoric, showing internal fertilization and a distinct reproductive behavior compared with that reported for other areas of the eastern tropical Pacific. In P. gigantea, gametogenesis started later and occurred over a short period of time; this species was classified as gonochoric and no mature gametes were evident. All three species showed reproductive potential during the summer, confirming the reproductive capacity documented for these species in adjoining areas of the Mexican Pacific. The intensity and duration of the reproductive cycle in Banderas Bay are likely regulated by periodic events like El Niño and microscale climate oscillations that modulate temperature and light patterns in the area.

Recognition of Rubrointrusa membranacea gen. et comb. nov., Rhodonematella subimmersa gen. et comb. nov. (with a reinterpretation of the life history) and the Meiodiscaceae fam. nov. within the Palmariales (Rhodophyta)

Clayden S.L. and Saunders G.W. 2010. Recognition of Rubrointrusa membranacea gen. et comb. nov., Rhodonematella subimmersa gen. et comb. nov. (with a reinterpretation of the life history) and the Meiodiscaceae fam. nov. within the Palmariales (Rhodophyta). Phycologia 49: 283–300. DOI: 10.2216/09-43.1Two members currently classified in the florideophyte Colaconematales, Colaconema membranaceum and C. subimmersum, display life history and morphological/anatomical characteristics suggestive of some Palmariales, prompting the current investigation. We observed a direct life history by regenerative tetrasporangia for C. membranaceum as previously reported and provide the first evidence of sexual reproduction in C. subimmersum from the Pacific northeast, corroborating reports from Japan. However, the life history pattern in C. subimmersum is reinterpreted as intermediate between that typical of the Palmariaceae and Rhodophysemataceae. We addressed the phylogenetic affinities of these two species by sequencing large-subunit ribosomal DNA and the ‘DNA barcode’ (5′ region of the cytochrome oxidase subunit I gene), which was also used to assess species diversity. In phylogenetic analyses both C. membranaceum and C. subimmersum were unequivocally supported as members of the Palmariales. Colaconema membranaceum displayed a weak affinity for species of Meiodiscus but is distinct in its endozoic basal system, and we propose Rubrointrusa gen. nov., typified by Rubrointrusa membranacea (Magnus) comb. nov. Colaconema subimmersum, consistently grouped with species of Rhodophysema but is divergent from these species in habit, life history, and molecular signature, so that we propose a new monotypic genus Rhodonematella, typified by Rhodonematella subimmersa (Setchell & N.L. Gardner) comb. nov. Rhodonematella, is provisionally placed in the Rhodophysemataceae. We concomitantly examined the phylogenetic affinities of Halosacciocolax kjellmanii and Meiodiscus spp., both tentatively included in the Rhodophysemataceae. Halosacciocolax kjellmanii is retained in the Rhodophysemataceae and transferred to Rhodophysema, Rhodophysema kjellmanii (S. Lund) comb. nov., based on our molecular results and new anatomical observations. Conversely, Meiodiscus species resolved independently of other palmarialean families, and we propose the Meiodiscaceae fam. nov. to accommodate them, as well as Rubrointrusa. Meiodiscus concrescens is restricted to populations from the northeast Pacific; whereas, so-called Atlantic M. concrescens is conspecific with M. spetsbergensis.

Multinucleate Spores Contribute to Evolutionary Longevity of Asexual Glomeromycota

Arbuscular mycorrhizal fungi (Glomeromycota) are the dominant symbionts of land plants and one of the oldest multicellular lineages that exist without evidence of sexual reproduction. The mechanisms that protect these organisms from extinction due to accumulation of deleterious mutations in the absence of sexual recombination are unclear. Glomeromycota reproduce by spores containing hundreds of nuclei, which represents a departure from the typical eukaryotic developmental pattern, where a multicellular organism is re-created from a uninucleate propagule. To understand whether the multinucleate spore makeup may have contributed to the evolutionary success of Glomeromycota, we examined the dynamics of spore nuclei in Glomus etunicatum using live three-dimensional imaging and mathematical models. We show that the spores are populated by an influx of a stream of nuclei from the surrounding mycelium rather than by divisions of a single founder nucleus. We present evidence that mechanisms of selection are likely to operate at the level of individual nuclei. On the basis of mathematical analyses of the effects that these nuclear dynamics have on the population mutation load, we postulate that the developmental patterns of sporogenesis have adaptive significance for moderating the accumulation of deleterious mutations and may have contributed to the evolutionary longevity of Glomeromycota.

Positively Negative Evidence for Asexuality

No evidence of sexual reproduction has been detected in many eukaryotes, but this "negative evidence" of obligatory asexuality is still met with widespread skepticism. This is partly because obligatory asexual reproduction is deleterious in the long run and partly because it is logically possible that there are undetected sexual individuals. I point out that this skepticism stems from failure to think statistically, and the absence of sexual individuals in a sufficiently large sample can be very convincing evidence of obligatory asexuality. A survey of rotifer workers showed that approximately 458 515 bdelloid rotifers have been examined without finding any males or hermaphrodites; applying the Poisson distribution to these data shows that the upper 95% confidence interval of the number of sexual individuals is less than 8.1 x 10(-6). In darwinulid ostracods, a smaller sample puts the estimate at less than 1.75 x 10(-4) sexual individuals. If there were undetected sexual individuals at these low levels, the frequency of outcrossing must be even lower; so that sex will be ineffective and easily lost. Furthermore, recently published evidence shows that these ancient asexuals are not "scandalous" but merely the tail end of the age distribution of asexual lineages.

Host‐associated differentiation and evidence for sexual reproduction in Iranian populations of the cotton aphid, Aphis gossypii

AbstractPhytophagous insects with wide host ranges often exhibit host‐associated genetic structure. We used microsatellite analysis to assess the population structure of the cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae), a serious pest on many economically important crops worldwide. We sampled aphids from five host plant species in Iran and detected strong population subdivision, with an overall multilocus FST of 0.191. The matrix of pairwise FST values indicated that differentiation between populations collected from different hosts was significantly stronger than between populations from the same hosts. Host‐associated differentiation was further supported by Bayesian clustering analyses, which grouped all samples from cotton together with aubergine, and all samples from cucumber together with pumpkin and hibiscus. This adds to the growing body of evidence that many seemingly generalist aphids are in fact an assemblage of host‐specialized lineages. Although we detected a clear genetic signature of clonal reproduction, the genotypic diversity of A. gossypii in Iran is much higher than in other parts of the world. Particularly samples from cotton exhibited a surprisingly high genotypic diversity, suggesting that many lineages on this host are cyclical parthenogens that engage in regular bouts of sexual reproduction.

A massive and simultaneous sex event of two Pseudo-nitzschia species

Abstract Sex is an obligatory event in the life cycle of many diatoms, being the means of restoration of maximum cell size that counteracts the progressive miniaturization induced by asexual divisions. Nonetheless, sexual stages and evidence for sexual reproduction in diatoms have rarely been directly reported from the marine environment. On September 20, 2006, different stages of the sexual cycle of two species, Pseudo-nitzschia cf. delicatissima and P. cf. calliantha, were detected in surface waters of the Gulf of Naples, at the Long Term Ecological Research Station MareChiara. The sampling date corresponded with a seasonal peak of abundance of the two species, which reached maximum concentrations of 9.1×106 and 7.0×105 cells L−1, respectively. Gametangia, auxospores of different size, and initial cells within and outside the perizonium were observed. Up to 9.2% of P. cf. delicatissima and 14.3% of P. cf. calliantha cells were undergoing sexual reproduction. The sexual event was mainly concentrated in surface waters and no sexual stages were observed a week before or after the date. The low percentage of sexual stages and the short duration of such events are probably the reasons for the scarcity of sexual stage observations in nature.

Evidence for sexual reproduction and zoospore formation in Botryosphaerella sudetica UTEX 2629, previously assigned to the genus Botryococcus (Chlorophyceae, Chlorophyta)

Evidence for sexual reproduction and zoospore formation in Botryosphaerella sudetica UTEX 2629, previously assigned to the genus Botryococcus (Chlorophyceae, Chlorophyta)

Genetic diversity and clonal vs. sexual reproduction in Fallopia spp. (Polygonaceae)

Although fundamental to the study of invasion mechanisms, the relationship between mode of reproduction and plant invasion is not well understood. Fallopia japonica (Japanese knotweed), a highly aggressive invasive plant in both Europe and North America, serves as a model species for examining this relationship. In Britain, F. japonica var. japonica is a single female clone reproducing solely through vegetative growth or obligate hybridization with other Fallopia spp. In the U.S., however, there is more evidence for sexual reproduction. Here, simple sequence repeat (SSR) markers were developed, and three Massachusetts populations were sampled at regular intervals. The amount of sexual and clonal reproduction in each population was determined based on within-population genetic diversity. Clonal growth was apparent, but the populations together contained 26 genotypes and had evidence of sexual reproduction. One genotype that was present in all populations matched the single aggressive British clone of F. japonica var. japonica. Also, a potentially diagnostic marker for the F. sachalinensis genome provided evidence of inter- and intraspecific sexual reproduction and introgression. These differences observed in U.S. populations compared to European populations have significant implications for management of Fallopia spp. in the U.S. and underscore the importance of regional studies of invasive species.

New insights into the cryptic diversity of the North Atlantic–Mediterranean ‘ Porphyra leucosticta ’ complex: P. olivii sp. nov. and P. rosengurttii (Bangiales, Rhodophyta)

The existence of cryptic diversity in the ‘Porphyra leucosticta' complex of the North Atlantic and Mediterranean was confirmed from a wide variety of recent and over 100-year-old herbarium specimens using plastid and nuclear molecular data in combination with karyological, morphological and ecological observations. The results revealed the presence of a new species, P. olivii sp. nov., within the P. leucosticta complex. Possible evidence for sexual reproduction was observed in a culture of P. olivii from the holotype site, Gulf of Thessaloniki in Greece, where n = 2 chromosomes in male gametes and neutral spores, and 2n = 4 in zygotospores. Archeospores and neutral spores also formed in culture providing evidence for possible asexual reproduction. The results also revealed the presence of P. rosengurttii, originally described from the north-western Atlantic, in both the north-eastern Atlantic and the Mediterranean, and enabled new morphological and ecological information to be obtained for this species. The rbcL sequences for P. olivii, including from an 1889 specimen of ‘Porphyra leucosticta’, differed by one transition between the north-western Atlantic and Mediterranean. The ITS1 of the holotype of P. olivii differed by a single bp transition from another specimen from the same location. The ITS1 of specimens from the northwestern Atlantic were identical but differed by 3-4 bp substitutions from the specimens from the Mediterranean. Partial rDNA SSU sequences were identical. In P. rosengurttii, rbcL sequences, including from specimens dated 1890 and 1906, differed by a single transition between both regions, the ITS1 had 92–100% similarity and partial rDNA SSU sequences were identical. Our study indicates that molecular, morphological and ecological evidence from a wide variety of samples (recent and old) and locations should be investigated before a new species is erected. The molecular comparison with old herbarium specimens also revealed that P. olivii and P. rosengurttii are not recent invaders to the Mediterranean but have been present for at least 100 years.

Zygospores as evidence of sexual reproduction in the genus Orphella

The presence of zygospores in the genus Orphella is newly described. We found zygospores in three species of the genus, O. catalaunica, O. coronata and O. helicospora, which are all the species of the genus known from the Iberian territory. Zygospores are associated with a heterothallic conjugating sexual process in O. coronata, whereas in O. catalaunica and O. helicospora, they form homothallically. In all instances, zygospores are consistently associated with an organized pattern of sterile cells, forming structures comparable to those present with asexual trichospores. We compare the ontogeny of Orphella zygospores with that found in the harpellid Genistellospora homothallica and discuss the possible close relationship of Orphella with Kickxellales (Zygomycetes). We report O. coronata in Spain for the first time, replacing all previous records of O. haysii. Results are supported with line drawings and photographs.

Zygospores as evidence of sexual reproduction in the genus Orphella

The presence of zygospores in the genus Orphella is newly described. We found zygospores in three species of the genus, O. catalaunica, O. coronata and O. helicospora, which are all the species of the genus known from the Iberian territory. Zygospores are associated with a heterothallic conjugating sexual process in O. coronata, whereas in O. catalaunica and O. helicospora, they form homothallically. In all instances, zygospores are consistently associated with an organized pattern of sterile cells, forming structures comparable to those present with asexual trichospores. We compare the ontogeny of Orphella zygospores with that found in the harpellid Genistellospora homothallica and discuss the possible close relationship of Orphella with Kickxellales (Zygomycetes). We report O. coronata in Spain for the first time, replacing all previous records of O. haysii. Results are supported with line drawings and photographs.

Further evidence for sexual reproduction in Rhynchosporium secalis based on distribution and frequency of mating-type alleles

Rhynchosporium secalis, the causal agent of scald on barley, is thought to be exclusively asexual because no teleomorph has been found. Partial sequences of the HMG-box and α-domain of Rhynchosporium secalis isolates were identified and used to develop a PCR assay for the mating-type locus. PCR amplification of only one of these two domains was possible in each strain, suggesting that R. secalis has a MAT organization that is similar to other known heterothallic fungi. A multiplex PCR with primers amplifying either a MAT1-1- or MAT1-2-specific amplicon was used to determine the distribution of mating types in several R. secalis populations. In total, 1101 isolates from Australia, Switzerland, Ethiopia, Scandinavia, California, and South Africa were included in the analysis. Mating types occurred in equal frequencies for most of these populations, suggesting frequency-dependent selection consistent with sexual reproduction. In addition, both mating types were frequently found occupying the same lesion or leaf, providing opportunities for isolates of opposite mating type to interact and reproduce sexually. We propose that R. secalis should be considered a sexual pathogen, although the sexual cycle may occur infrequently in some populations.

Three Clonal Lineages of Phytophthora cinnamomi in Australia Revealed by Microsatellites

ABSTRACT The genetic structure of populations of Phytophthora cinnamomi, a pathogen of an enormous variety of woody plants, was investigated using microsatellites. Three intensively sampled disease sites in southwest Australia were analyzed along with a large culture collection of Austra-lian isolates and some isolates from elsewhere in the world. The mutation in the four microsatellite loci analyzed revealed spatial patterns at the disease sites that correlated with the age of the infestation. Only three clonal lineages were identified in Australian populations and these same clonal lineages were present in worldwide populations, where it is suggested that a limited number of clonal lineages have spread in most regions. No evidence for sexual reproduction between these clonal lineages in Australia has been found even though the pathogen has the opportunity. Instead, mitotic recombination is frequent within the clonal lineages. The implications of this are discussed.

Spawning patterns of scleractinian corals at the Solitary Islands-a high latitude coral community in eastern Australia

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 260:115-123 (2003) - doi:10.3354/meps260115 Spawning patterns of scleractinian corals at the Solitary Islands‹a high latitude coral community in eastern Australia J. R. Wilson1,2,*, P. L. Harrison1 1School of Environmental Science and Management, Southern Cross University, PO Box 157, Lismore, 2480 New South Wales, Australia 2Present address: Centre for Natural Resources, Department of Infrastructure, Planning and Natural Resources, PO Box 2185, Dangar, 2309 New South Wales, Australia *Email: jwilson@dipnr.nsw.gov.au ABSTRACT: The timing and synchrony of reproduction in scleractinian corals varies greatly among geographic locations, along latitudinal gradients, and among regions. On the east coast of Australia, there are extensive subtropical coral communities within the Solitary Islands Marine Park (30°S). From 1994 to 1996, the pattern of reproduction was studied in 27 species from 10 genera of broadcast spawning scleractinian corals. Spawning periods were determined directly from observations of 4 species that spawned in aquaria, and indirectly from repeated sampling of 236 tagged field colonies by noting the disappearance of mature gametes. Evidence of sexual reproduction was observed in 24 coral species, and gametes were released annually from December to April. Spawning periods were staggered among species and among colonies within some species. Spawning in massive species was generally more synchronous and predictable than for acroporid species. Massive coral species spawned from 8 to 12 nights after a full moon, whereas there was no obvious lunar periodicity of spawning among acroporid corals. This asynchronous pattern of reproduction contrasts with the highly synchronous spawning of more than 140 coral species during mass spawning periods on the Great Barrier Reef (GBR) in October to December each year. The delay in the timing of coral spawning at the Solitary Islands compared with the GBR coincides with the delayed rise in sea temperatures in the subtropics. In addition, the highly variable nature of sea temperatures at the Solitary Islands around the time of gamete maturation and spawning may account for the less synchronous pattern of reproduction in this high-latitude coral community. KEY WORDS: Coral · Spawning · Subtropical reef · Reproductive synchrony Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 260. Online publication date: September 30, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.

EVIDENCE FOR SEXUAL REPRODUCTION IN THE MARINE DINOFLAGELLATES, PYROCYSTIS NOCTILUCA AND PYROCYSTIS LUNULA (DINOPHYTA)

Evidence for sexual reproduction was observed in two oceanic dinoflagellate species, Pyrocystis noctiluca Murray ex Haeckel and Pyrocystis lunula (Schütt) Schütt. Observations suggest that cells underwent fertilization as opposed to cell division because of the following: first, fusing cells had a conspicuous pore (fusion pore) connecting the two gametes; dividing cells lacked this feature. In culture, about 0.1% of P. noctiluca cells had a fusion pore, which serves as a possible site for gamete recognition on the cell wall. Second, we document a temporal progression of plasmogamy and karyogamy. Fusion events in both species were observed at the beginning of the day, whereas division stages were most apparent at the end of the day.

Abstracts, The Canadian Phytopathological Society annual meeting, London, Ontario, 2001

Abstracts, The Canadian Phytopathological Society annual meeting, London, Ontario, 2001

Distribution, seasonal abundance and shoot size of the seagrass Halodule wrightii near its southern limit at Rio de Janeiro state, Brazil

A search for Halodule wrightii. Aschers. carried out along the most coast of Rio de Janeiro state revealed 21 populations. Populations were usually small, sparsely distributed and essentially monospecific. To quantify the intensity of seasonal variation within these southerly populations, samples were collected every 45 days at the site with most seagrass—Ilha do Japonês, Cabo Frio. Variation in biomass and density, and size distributions of short shoot lengths were measured. Short shoots made up between 21 and 44% of H. wrightii biomass. Seasonal changes in seagrass parameters (e.g. biomass from 12.1–37.3 g dry weight m -2, short shoot density from 2080–8482 m −2 and short shoot size from 28–106 mm), were strongly pronounced in the population between 1995 and 1997, although inter-annual variation in the measured parameters was also evident. The variation (coefficient of variation) of shoot size distributions also showed seasonal differences but differences in size skewness (skewness coefficient) were not found. No evidence of sexual reproduction was found. A comparison of the same variables in ten populations distributed along the coast of Rio de Janeiro state revealed substantial between site variation in shoot density, biomass distribution and short shoot size distributions. Biomass values for H. wrightii were relatively low. In the populations at Rio de Janeiro, rhizome biomass was positively correlated with root biomass, while shoot biomass was positively correlated with mean shoot length rather than shoot density.

Limia vittata as host species for the Amazon molly: no evidence for sexual reproduction

DNA fingerprinting demonstrated no sexual reproduction of the gynogenetic Amazon molly Poecilia formosa with Limia vittata as host species, in contrast with a single report that claims to have found sexual reproduction with such matings.