Sexual behaviour of the genus Equisetum, subgenus Hippochaete

When grown for long periods in axenic single spore cultures, gametophytes of the four European species of subgenus Hippochaete are initially male or female. Females invariably produce antheridia as they get older, but archegonium formation by males is a much rarer event and was only observed in E. hyemale and E. scirpoides. Male gametophytes are smaller, grow more slowly than the females and in E. hyemale and E. variegatum are often short-lived. The proportions of male and bisexual individuals are relatively constant within each species but vary between species. Likewise species differ in the rate at which females later produce antheridia. Gametophytes grow in three ways: activity of antheridial meristems which are totally committed to the formation of male tissues, activity of cushion meristems which may produce archegonia for an indefinite period or switch to antheridium formation, and proliferation from lamellae. Either archegonia or antheridia may arise on the adventitious branches resulting from lamellar proliferation, but the type of sex organ produced is strongly influenced by the culture medium, the sex and age of the parent tissue and the particular species in question. Only by this means are archegonia formed on initially male individuals. The sexual behaviour of the subgenus Hippochaete is compared in some detail with that of the subgenus Equisetum and several subgeneric characteristics are outlined.     

Comparative morphology of the gametophytes of Equisetum subgenus Hippochaete and the sexual behaviour of E. ramosissimum subsp. debile, (Roxb.) Hauke, E. hyemale var. affine (Engelm.) A.A., and E. laevigatum A. Br.

Gametophytes of Equisetum , subgenus Hippochaete , species E. hyemale, E. ramosissimum, E. laevigatum, E. variegatum and E. scirpoides are morphologically distinct. Lamellae from female branches and the archegonial neck cells provide a range of diagnostic features but antheridia are uniform throughout this subgenus, unlike the subgenus Equisetum , in which antheridial morphology is the most reliable criterion for specific identification of gametophytes. The classification of Equisetum into two subgenera based on sporophytic features is supported by gametophyte morphology: column lamellae and sunken antheridia with two opercular cells occur in Hippochaete whereas plate lamellae and projecting antheridia prevail in subgenus Equisetum. The absence of well-marked discontinuities in gametophyte morphology in Hippochaete reinforces cytologica! and hybridization data indicating that the taxa are more closely interrelated man in the subgenus Equisetum. No differences in gametophyte morphology were detected at the intraspecific level. Neither gametophyte morphology nor sexuality provide any definitive data to support me theory that Hippochaete contains the most primitive extant horsetails.
Sexuality in E. ramosissimum subsp. debile, E. hyemale var. affine and E. laevigatum is far more labile than in other taxa of Equisetum. Both male and female secondary gametophytes may be derived from initially male or female individuals as a result of lamellar proliferation.     

Sexual behaviour of the genus Equisetum, subgenus Equisetum

Gametophytes of five species of Equisetum that were studied in axenic single spore cultures are initially male or female, and the first antheridia appear on the males before the first arche-gonia on the females. The males never produce archegonia, but the females all produce antheridia later in progressively increasing numbers. The proportions of male and bisexual gametophytes are relatively constant within each species but vary greatly between species. Likewise between species there is great variation in the rate at which females later produce antheridia. Male gametophytes are smaller and grow more slowly than females, but individuals of both sexes live for the same length of time. After prolonged culture, growth rates fall to very low levels and there is necrosis of the older parts of the gametophytes; but sex organs are still produced. Initially female gametophytes have much sexually uncommitted tissue, whereas males are composed almost entirely of antheridial branches. The absence of archegonium formation on males may well be related to this lack of sexually undifferentiated tissue and the fact that the growth of the males is intimately connected with antheridium production.     

Comparative morphology of the gametophytes of the genus Equisetum, subgenus Equisetum

When grown under a variety of axenic conditions gametophytes of E. arvense, E. telmateia, E. sylvaticum, E. palustre , and E. fluviatile are all morphologically distinct. Lamellae from archegonial branches provide several diagnostic features but lamellae associated with antheridia are much less distinct. The archegonia of all five species have two neck canal cells and three tiers of neck cells and are of limited use taxonomically. Although antheridium development is basically similar in all species, during the metamorphosis of the spermatocytes specific differences arise in the shape of the cavity, degree of emergence and the number of opercular cells. A taxonomy of the gametophytes based on antheridium morphology corresponds very closely to the classification of the subgenus Equisetum into three sections based on the coning behaviour of the sporophytes.     

An experimental study of the reproductive biology and hybridization in the European and North American species of Equisetum

Sporophytc production was investigated in the eleven North American and European species of Equisetum by means of fertilization experiments on both intact and subcultured gametophytes. Comparison of intra- and inter-gametophytic selfing with intergametophytic crossing failed to reveal any evidence of recessive sporophytic lethals, leaky lethals or deleterious recessive genes. Fertilization in Equisetum depends solely on the availability of ripe archegonia. Despite the absence of detectable genetic load in Equisetum , intergametophytic mating is ensured by gametophyte dioecism in the wild. All populations tested were freely interfcrtile indicating a high degree oi genetic con-specihcity, even between North America and Europe. Low sporophyte frequencies in European E. scirpoides are attributed to defective spermatozoids. Polyembryony occurs. Cessation in gametophyte development is mediated by allelopathic compounds liberated from the young sporophytes.
Reciprocal crosses resulted in the synthesis of 12 hybrids (six in subgenus Equisetum and six in subgenus Hippochaete plus abortive zygotes in the cross E. ramosissimum female x E. scirpoides male), 11 of which had previously been reported in nature. No intersubgeneric hybrids were produced, indicating that both subgenera are natural groups only distantly related to one another. The putative wild combinations E. pratense x E. atvense and E. variegatum x E. scirpoides were not synthesized, but a new hybrid from the allopatric E. ramosissimum and E. laevigatum arose. Reciprocal crosses within the subgenus Hippochaete usually yielded equal frequencies of hybrids, but in the subgenus Equisetum the majority of successful crosses were unidirectional. All taxa oi Hippochaete are linked by hybrids whereas in subgenus Equisetum, E. pratense and E. sylvatkum form an isolated pair, Hybridization studies, and evidence from gametophyte morphology support the traditional sectional classification of Equisetum.     

AN ELECTROPHORETIC INVESTIGATION OF INTRAGAMETOPHYTIC SELFING IN EQUISETUM ARVENSE

Because homosporous pteridophytes (Psilotophyta, Arthrophyta, most Microphyllophyta and Pteridophyta) produce bisexual gametophytes, it was maintained that high levels of inbreeding would characterize these plants. Electrophoretic evidence was used to estimate the frequency of intragametophytic selfing in Equisetum arvense (Arthrophyta). A total of 669 samples from 17 populations was examined from western North America. Although some populations exhibited as many as seven or eight genotypes, 10 populations were each characterized by only a single genotype; eight of these populations were heterozygous for one or more loci. For most populations, estimates of intragametophytic self-fertilization are 0.000, indicating that virtually all matings involve different gametophytes. Genetic data corroborate predictions based on earlier field and laboratory investigations of Equisetum gametophytes. These detailed studies demonstrated that in many species, including E. arvense, gametophytes are initially either male or female; only later and in the absence of fertilization do some gametophytes become bisexual. Our findings join a growing electrophoretic data base which demonstrates that homosporous pteridophytes are not highly inbreeding as previously suggested.     

Karyology and sex determination in Aglaothamnion oosumiense Itono (Ceramiaceae,Rhodophyta)

A cytogenetic investigation on male and female reproductive cells of Aglaothamnion oosumiense Itono indicates that the sexuality of this species might be determined by a sex chromosome. Chromosome counts in female and male gametophytes gave 37 and 36, respectively. Sex ratio of gametophytes was 1:1. Both male-derived and female-derived bisexual plants were observed. Bisexual plants were different in gross morphology and position of carpogonial branches from normal unisexual gametophytes. The chromosome number of female-derived bisexual plants was N=37 and male-derived bisexual plants was N=36. Some male plants developed parasporangia in addition. The paraspore germlings showed the same chromosome number as the male plants. The fertilized carpogonium and gonimoblast cells had 2N = ca. 70 chromosomes.     

Direct production of sporophytic plants from spores of Equisetum arvense

Spores of Equisetum arvense were cultured in Murashige and Skoog liquid medium with or without cytokinin. Without cytokinin, spores germinated 2–3 days after sowing and developed into normal young gametophytes. These gametophytes were composed of well-vacuolated cells. On the other hand, germinated spores in the medium with cytokinin formed globular cell masses that were composed of small and dense cells. These cell masses developed into sporophytic plants after further culture. This revised version was published online in June 2006 with corrections to the Cover Date.     

Reproductive biology and population dynamics of wild gametophytes ofEquisetum

This is d study of the reproductive biology of wild gametophytes of Equisetum arvense L., E. fluviatile L., and E. palustre L., which form extensive populations during the summer months on previously inundated bare mud along the margins of reservoirs and lakes in Northern England and Wales. The garnetophytes have all the characteristics of pioneer species: they rapidly attain sexual maturity and are adversely affected by competition. Early in the summer mixtures of male and female gametophytes are produced. The former are smaller and their frequency (which is always less) diminishes throughout the season as a result of bryophytic competition. The rarity of bisexual, initially female, gametophytes, in wild populations is related to the absence of metabolite accumulation which mediates this change in rulture. Significantly different sex ratios between populations and species underlines the labile nature of the sex-determining mechanism in Equisetum. The high frequency of females bearing sporophytes indicates that intergarnetophytic fertilization is highly effective in nature. Absence of any correlation between the incidence of fertilized females and the proportions of males, in conjunction with a consideration of the male gamete dispersal distance, suggests that sporophyte formation is restricted by the availability of ripe archegonia. Sexual reproduction in Equisetum is probably limited by the narrow range of conditions under which gametophytes can become established rather than availability of water for fertilization. The majority of females, which bear one sporophyte, are smaller than unfertilized or polyembryonic females. Their small size results from nutrient demands and allelopathic compounds from the sporophytes which also probably prevent the establishment of gametophytes within mature stands of the parent species. Correlations between female diameters and frequencies of males suggest that gametophytes are more likely to produce archegonia under favourable conditions. The natural reproductive biology of Equisetum is in accord with predictions based on an understanding of the mechanism of sex determination in axenic culture. Several striking parallels between sexuality in Equisetum and dioecious angiosperms are revealed. The absence of winter flooding at two of the gametophyte sites led to the establishment of mature rtands of Equisetum, which produced cones after 3–4 years; two hybrids, E. fluviatile×E. arvense and E. fluviatile×E. palustre, were detected.     

Density affects gametophyte growth and sexual expression of Osmunda cinnamomea (Osmundaceae: Pteridophyta)

BACKGROUND AND AIMS: To understand how gametophyte densities affect the sexual expression and sizes of Osmunda cinnamomea and to provide information on the density of growth needed to favour successful reproduction, fresh spores were sown at various densities and subsequent gametophyte growth was studied. METHODS: Spores were sown and cultured in the laboratory. Subsequent gameophytes at different population densities were sampled and their sexual expression and sizes were recorded. KEY RESULTS: One-year-old multispore cultures of the fern O. cinnamomea demonstrated that population density affected gametophyte growth and sexual expression. As density increased, gametophytes became significantly smaller and more slender. Female and asexual gametophytes dominated in populations of low and high densities, respectively. At intermediate population densities, hermaphroditic and male gametophytes were dominant. Female gametophytes were larger than gametophytes of all other types. Hermaphroditic gametophytes were larger than male gametophytes, which were larger than asexual gametophytes. Large gametophytes were wide-cordate, whereas smaller ones tended to be narrow-spathulate. CONCLUSIONS: Gametophyte size of O. cinnamomea is negatively related to the population density, which significantly affects gametophytes' sexual expression. The presence of unisexual and bisexual gametophytes at intermediate densities indicates that both intergametophytic and intragametophytic selfing may occur.     

A Method for the Rapid Growth in Culture of Gametophytes of Equisetum arvense with Antheridia

Rapid growth in culture of Equisetum arvense gametophytes wasobtained using Murashige-Skoog's medium plus 3% (w/v) sucroseand continuous illumination. In darkness, growth was reducedand chlorophyll synthesis markedly inhibited. Antheridia formedon the top margin of gametophytes in light and darkness butarchegonia were not observed in either case. ¹Present address: Interdisciplinary Research Institute of EnvironmentalSciences, Higashi-yanagi-cho, Nishi-iru, Shichihon-matsu, Itsutsuji-dori,Kamigyo-ku, Kyoto, 602 Japan. (Received June 5, 1989; Accepted September 12, 1989)     

Sporophyte formation in experimentally-induced unisexual female and bisexual gametophytes ofLygodium japonicum

Unisexual female and male and bisexual gametophytes were experimentally induced inLygodium japonicum. A single bisexual gametophyte was isolated in a dish and a female gametophyte was paired with a male one to allow intragametophytic selfing and intergametophytic mating, respectively. About 30% of the females formed sporophytes but no bisexual gametophytes formed them.     

白背叶(大戟科)性系统和传粉生物学研究

为探讨野桐属(Mallotus)雌雄异株的进化和传粉机制,对白背叶(Mallotus apelta)野生居群的性系统和传粉生物学进行了研究。结果表明,所调查的白背叶居群均由雌性(F)、雄性(M)和少数两性(B)个体组成,平均性比为1：0.66：0.18(F：M：B);3种性别植株的基径大小差异不显著;雌株与两性植株的单花胚珠数、单果结籽数和自然结实率无显著差异;雄株与两性植株的花粉萌发率、花粉组织化学和花粉微形态特征也无显著差异,但雄株的单花花粉量是两性植株的1.26~1.63倍,且差异显著;雌株的异交结实率为96.67%,两性植株的异交结实率为76.00%,两者差异显著,说明居群内雌株的潜在种子生产力明显高于两性植株;野外观察到雄株和两性植株上的雄花具有访花者而雌株没有;雌株经套网处理后结实率超过30%而套袋处理不结实。这些表明白背叶具典型的亚雌雄异株性系统,雌株和雄株的适合度均高于两性植株;雌株以风媒传粉结实,两性植株可能兼有风媒和虫媒传粉特征。     

Genetic diversity,sexual condition,and microhabitat preference determine mating patterns in Sphagnum (Sphagnaceae) peat‐mosses

In bryophytes, the possibility of intragametophytic selfing creates complex mating patterns that are not possible in seed plants, although relatively little is known about patterns of inbreeding in natural populations. In the peat‐moss genus Sphagnum, taxa are generally bisexual (gametophytes produce both sperm and egg) or unisexual (gametes produced by separate male and female plants). We sampled populations of 14 species, aiming to assess inbreeding variation and inbreeding depression in sporophytes, and to evaluate correlations between sexual expression, mating systems, and microhabitat preferences. We sampled maternal gametophytes and their attached sporophytes at 12–19 microsatellite loci. Bisexual species exhibited higher levels of inbreeding than unisexual species but did generally engage in some outcrossing. Inbreeding depression did not appear to be common in either unisexual or bisexual species. Genetic diversity was higher in populations of unisexual species compared to populations of bisexual species. We found a significant association between species microhabitat preference and population genetic diversity: species preferring hummocks (high above water table) had populations with lower diversity than species inhabiting hollows (at the water table). We also found a significant interaction between sexual condition, microhabitat preference, and inbreeding coefficients, suggesting a vital role for species ecology in determining mating patterns in Sphagnum populations. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 115 , 96–113.     

REGENERATION AND SEXUAL DIFFERENTIATION OF GRIFFITHSIA JAPONICA (CERAMIACEAE,RHODOPHYTA) THROUGH SOMATIC CELL FUSION1

Hybrid cells were obtained from somatic cell fusion among male, female, and tetrasporangial plants in Griffithsia japonica Okamura by a wound-healing process. Isolated fusion cells regenerated new mature plants with mixed reproductive structures. The plants regenerated from hybrid cells between male and female plants developed into 1) spermatangiate, 2) carpogonial, 3) bisexual with spermatangia and carpogonial branches, 4) mixed-phase with spermatangia and tetrasporangia, or 5) bisexual/mixed-phase plants with spermatangia, carpogonial branches, and tetrasporangia. About 70% of the plants regenerated from hybrid cells between male and female plants produced tetrasporangia that were always formed with spermatangia on a single cell. Some of those tetrasporangia released tetraspores, six of which gave rise to mature plants. The plants regenerated from hybrid cells between male and tetrasporangial plants developed into spermatangiate, tetrasporangiate, or mixed-phase plants with spermatangia and tetrasporangia. The plants regenerated from hybrid cells between female and tetrasporangial plants developed into carpogonial, tetrasporangiate, or mixed-phase plants with carpogonial branches and tetrasporangia. All types of reproductive structures we re functional.     

Triploidy in Equisetum subgenus Hippochaete (Equisetaceae, Pteridophyta)

BACKGROUND AND AIMS: The genus Equisetum is cytologically uniform, having a base chromosome number of x = 108. All previously known species and hybrids that have been counted represent diploids with a sporophytic chromosome number of 2n = 216. Biosystematic studies on Equisetum subgenus Hippochaete revealed evidence that triploids occur in nature. The objective of this study was to confirm that triploid plants exist in the natural environment. METHODS: Flow cytometry was used to establish nuclear DNA values and cytological investigations of meiosis were carried out to obtain information on chromosome number and pairing behaviour. KEY RESULTS: Triploidy exists in three morphologically different hybrid taxa. Two of these are morphologically intermediate between a primary diploid hybrid and a parent, while the third apparently combines genomes from all three Central European Hippochaete species. Nuclear 1C DNA values for the four European Hippochaete species range from 21.4-31.6 pg. For the hybrids, the 1C DNA values not only occupy the same range as the species, but their total DNA amounts agree closely with values predicted by adding the 1C DNA values of each parental genome. Chromosome counts confirm diploidy in the species E. hyemale and E. variegatum and in the hybrid E. xtrachyodon (= E. hyemale x E. variegatum). For the triploids (2n approximately 324), cytological information is presented for the first time. CONCLUSIONS: Triploid taxa may have originated by backcrossing or by crossing of a diploid hybrid with an unrelated diploid species. As tetraploid plants are unknown, these crossings probably involve diploid gametophytes that developed from unreduced diplospores. By repeated crossing events or backcrossing, reticulate evolution patterns arise that are similar to those known for a number of ferns and fern allies.     

GENETICS OF GRACILARIA TIKVAHIAE (RHODOPHYCEAE). X. STUDIES ON A BISEXUAL CLONE12

A male done of the red alga Gracilaria tikvahiae McLachlan spontaneously produced a bisexual frond which remained bisexual in subsequent subcultures. Both male and female components of bisexual fronds were functional; however, some unusual results were obtained in crosses. When bisexual fronds were crossed with a normal haploid male, the resulting carpospores all developed into diploid male gametophytes. When bisexual plants were self fertilized, all the carpospores yielded diploid bisexual gametophytes. Only when bisexual plants were crossed to normal haploid females, did carpospores develop into diploid tetrasporophytes as they normally do. The F₁ gametophyte generation obtained from these tetrasporophytes, however, included not only females and males but also bisexual plants, in a 2:1:1 ratio. These results are consistent with the interpretation that bisexual plants have a recessive mutation of a gene other than the primary sex determining locus, and that this mutation is expressed only in male plants. It is suggested that the altered gene may ordinarily have a regulatory function in the maintenance of the dioecious condition.     

Parthenogenesis in the brown alga Lessonia nigrescens (Laminariales,Phaeophyceae) from central Chile1*

Parthenogenesis, the development of female gametes without fertilization, is relatively common in brown algae, although limited quantitative information on the phenomenon is available. Its occurrence is reported for the first time in Lessonia nigrescens Bory, a member of the Laminariales and a key ecological component of the benthic algal communities along the Chilean coast. Isolated female gametophytes developed into parthenosporophytes throughout the year, with a maximum in spring to early summer. Isolated male gametophytes, on the other hand, never developed fronds. Parthenosporophytes obtained in the laboratory developed normally when cultivated under greenhouse conditions, and the resulting individuals were indistinguishable in size, shape, texture, and color from heterozygous sporophytes. Quantification of DNA of various tissues demonstrated that early during their development, parthenosporophytes duplicated their DNA content, displaying levels similar to heterozygous sporophytes and almost twice the level found in gametophytes. One out of 45 individuals from a field population yielded only female gametophytes, strongly suggesting that parthenogenesis does occur in wild stands of L. nigrescens.     

Morphological and histological features of the gonad structure in hermaphroditic walleye pollock <Emphasis Type="Italic">Theragra chalcogramma</Emphasis> (Gadidae)

Morphology of hermaphroditic gonads is studied in the individuals of walleye pollock Theragra chalcogramma collected in different regions of the seas of the North Pacific from 1987 to 2014. Based on the external morphological characteristics of sexual glands of 17 fishes, the most frequent types of the structure of bisexual gonads are described. Histological analysis shows the absence of differences in the composition and condition of oocytes in the left and right-paired ovaries, and the testes and ovaries of each individual are at the same maturity stage. In the ovigerous lamellae of ovaries in the areas adjacent to testes the zones of oocyte resorption are observed. These zones are located exclusively near the joining of the female and male parts of the gonads. The development of ovaries and testes of bisexual gonads is similar to that in the majority of normally maturing males and females collected during the same period. The occurrence of hermaphrodites is 0.0003–0.0016% from the total number of investigated exemplars.