Bisexual Ones Research Articles

Floral development in the androdioecious tree Tapiscia sinensis: Implications for the evolution to androdioecy

AbstractThe evolutionary pathway between hermaphroditism and dioecy (females and males in a single population) draws widespread interests, and androdioecy (bisexuals and males in a single population) is rarely achieved as an intermediate state between the two breeding systems. Flower bud differentiations in the pistils of hermaphrodites and the pistillodes of males in androdioecious Tapiscia sinensis Oliv. are investigated by routine paraffin section technology, light microscopy, and scanning electron microscopy. A phylogenetic approach is used to analyze the origin of androdioecy. In T. sinensis, hermaphroditic flowers (HF) and male flowers (MF) experienced a similar development pattern in early flower bud differentiation, including the initiation of tepals and stamens. However, the carpel differentiation of MF and HF proceed in different patterns. In HF, the central zone bulges out and produces a ring meristem on which two to three carpel primordia emerge, which eventually developed into a normal pistil with a stigma, a style, and an ovary. However, in most MF, vestigial pistils are stem‐like (type I), and very few have an empty ovary (type II) or a sterile ovule (type III). Moreover, the evolution of sexual systems within the Huerteales indicates that hermaphroditism is the primitive character of T. sinensis. Tapiscia sinensis shows different degrees of reduction between male flowers and bisexual ones in the evolution to dioecy. Functional androdioecy originated from a hermaphroditic ancestor in T. sinensis and, as an intermediate sexual system, involves evolution from hermaphrodites to dioecy.

Genetic Diversity in Populations of Silver Crucian Carp Carassius auratus gibelio (Cyprinidae, Cypriniformes), Depending on the Type of Reproduction and Reservoir Size

This paper presents data on the polymorphism of inter simple sequence repeats of DNA in the silver crucian carp Carassius auratus gibelio in water bodies in the southern part of Western Siberia. The share of polymorphic ISSR-PCR bands in silver crucian carp populations from different lakes varied from 40 to 70%, and Nei’s gene diversity index varied from 0.16 to 0.25. The genetic diversity indices were lower in the populations that were largely represented by females than in bisexual ones. The highest levels of genetic polymorphism were revealed in populations with diploid–triploid complexes. The gene diversity index of the silver crucian carp population is positively correlated with the reservoir size (r = 0.90, p = 0.015; Rs = 0.74, p = 0.036).

SEX EXPRESSION, BREEDING SYSTEM AND POLLINATORS OF Piper caldense (PIPERACEAE) IN THE BRAZILIAN ATLANTIC FOREST

Las especies neotropicales de Piper presentan flores bisexuales, condición considerada basal al interior de este género pantropical. Sin embargo, fueron observadas especies neotropicales con flores unisexuales (estaminadas), además de las bisexuales. La dicogamia es común en el género y se encuentra asociada a la autocompatibilidad o incompatibilidad, al igual que la entomofilia. Fue analizada una población natural de Piper caldense en un área de bosque Atlántico (municipio de Viçosa, Minas Gerais, sureste de Brasil). Las observaciones preliminares indicaron que esta especie produce dos tipos florales, para lo cual fue analizada la sexualidad de las flores en 50 espigas a través de estudios morfológicos, anatómicos y análisis con microscopia electrónica de barrido. La longevidad y dinámica de exposición de las papilas estigmáticas y la secuencia de liberación de los granos de polen en los cuatro estambres fueron observados para verificar el grado de dicogamia. El sistema reproductivo se evaluó mediante el test de autopolinización espontánea y polinización abierta. Los visitantes florales fueron identificados y se registró su frecuencia de visita. Piper caldense presenta flores bisexuales y estaminadas, cada tipo floral se encuentra en espigas separadas. Estas espigas se encuentran en la misma planta, lo que indica que es andromonoica; adicionalmente, fueron observadas plantas que solo presentaban espigas con flores estaminadas, lo que se constituye en una combinación sexual inédita para el género. La exposición gradual y secuencial de las papilas estigmáticas asociada con la liberación asincrónica de los granos de polen (un estambre por día) indica una protoginia incompleta. Los test de polinización mostraron que la especie es autoincompatible. Las abejas sociales, principalmente Apis mellifera y Melipona spp., fueron los polinizadores principales. Este estudio refuerza la necesidad de asociar los analisis morfológicos con la funcionalidad de las estructuras florales, además indica los cambios futuros en estudios que abordan características reproductivas asociadas a la filogenia de las especies de Piper.

ГЕНЕТИЧЕСКОЕ РАЗНООБРАЗИЕ ПОПУЛЯЦИЙ СЕРЕБРЯНОГО КАРАСЯ CARASSIUS AURATUS GIBELIO (CYPRINIDAE, CYPRINIFORMES) В ЗАВИСИМОСТИ ОТ ТИПА РАЗМНОЖЕНИЯ И РАЗМЕРА ВОДОЁМА

The paper presents data on the polymorphism of the interior simple sequence repeats of DNA in the silver crucian carp Carassius auratus gibelio from waterbodies in the Western Siberia. The proportion of the polymorphic ISSR-PCR bands in the silver crucian carp populations from different lakes varied from 40 to 70%, the rate of Nei’s gene diversity being 0.16 - 0.25. Genetic diversity indicators were lower in the populations primarily presented by females, as compared with bisexual ones. The highest levels of genetic polymorphism were revealed in the populations of diploid-triploid complexes. The gene diversity level of the silver crucian carp population positively correlates with the reservoir’s size (r = +0.90, p = 0.015; Rs = 0.74, p = 0.036).

Multiple lines of evidence on the genetic relatedness of the parthenogenetic and bisexual Haemaphysalis longicornis (Acari: Ixodidae)

As an obligate hematophagous ectoparasite, the hard tick Haemaphysalis longicornis exhibits two reproductive strategies, bisexual reproduction, and obligate parthenogenesis, which have attracted a widespread attention. However, the speciation of parthenogenetic population remained ambiguous due to its similarity in morphology but the remarkable differences in cytogenetics as compared with those of the bisexual ones. In the present study, we explored several new lines of genetic evidence to resolve this controversial issue. The number of the chromosomes in two lineages was checked by classical methods and their total DNA levels were determined utilizing flowcytometry. In addition, the sequences of 12S rDNA, 16S rDNA, cytochrome c oxidase I and II (COI, COII) and internal transcribed spacer-2 (ITS-2) genes were used to assess their phylogenetic relationship. We observed that the chromosome ploidy of bisexual and parthenogenetic H. longicornis collected by our laboratory was diploid and triploid, respectively. Flowcytometry analysis indicated a ratio close to 2:3 in the DNA contents of bisexual to parthenogenetic H. longicornis. Although the chromosome ploidy is different, their gene sequences are extremely similar. Analogous to the intra-species genetic difference of other invertebrates, sequence differences of all loci examined are below 2%. Phylogenetic trees constructed from 12S rDNA, 16S rDNA, COI, and ITS-2 genes revealed that they were all in the same monophyletic clade instead of splitting independently into evolutional branches. Moreover, according to 4× Rule, the K/θ ratio of two reproductive populations calculated based on COI was much smaller than four, strongly supporting that they belong to the same species. Therefore, we conclude that the evolutionary process just disturbs the chromosome ploidy and the sexual determination of parthenogenetic population and that it would be better to consider parthenogenetic H. longicornis as a metapopulation rather than a cryptic species.

Sexual phenotype of Capparis herbacea (Capparaceae)

Floral morphology coupled with the morphometry of androecium revealed that Capparis herbacea Willd. has an andromonoecious sexual system, producing both male and perfect flowers on the same plant. Functionally male flowers develop more stamens with larger anthers than bisexual ones (63.6 ± 0.6 and 4.1 ± 0.01 mm; 58.1 ± 0.7 and 3.6 ± 0.02 mm, respectively). The ratio of male to perfect flowers ranges from 0.5 to 2.6 during the flowering season. The development of dense trichomes on the adaxial surface of the cavity made by variegated connate petals is presumably adaptive and serves to protect nectary exudate from evaporation in a hot and dry environment. Air temperatures below 30 °C and successful cross pollination—rather than light and relative humidity—limit florescence time and duration. No preference for flower morphs was observed during pollinator visitations. These data confirm the pollen donation hypothesis regarding the role of male flowers in andromonoecious plants. It is a primary benefit of effective pollination in Capparis herbacea, a species with a short blooming period. Results also indicate that Capparis herbacea is the second member of the section Capparis L., after Capparis spinosa L., in which the coexistence of male and hermaphrodite flowers on the same plant has been reported.

Colonization ability of two invasive weevils with different reproductive modes

The flightless weevils Naupactus leucoloma and Naupactu xanthographus (Coleoptera: Curculionidae: Naupactini), which are native to and partially co-distributed in South America, apparently have asexual and bisexual reproductive modes, respectively. We used two different molecular markers to elucidate the effects of these reproductive modes on the colonization ability and genetic variability of both species. First, we investigated the occurrence of clonal reproduction in the putative parthenogenetic species (i.e. significant bias in sex ratio) and second, whether parthenogenesis was associated with higher colonization ability and low levels of genetic variability in marginal environments compared with those of the bisexual species. We assessed the central and marginal areas of distribution of these species with ecological niche modeling that includes environmental variables and with landscape interpolation of molecular variability. Our results support the idea that parthenogenetic species are more successful than bisexual ones in colonizing new environments. N. leucoloma is most probably apomictic, and would have recently experienced significant population growth concomitant with an important geographic range expansion to distant areas with moderately suitable environmental conditions. On the other hand, the populations of the bisexual species, N. xanthographus, seem to have maintained fairly constant sizes, expanding its geographic distribution to locations close to the proposed ancestral area.

Studies on the Formation of Microspores and Development of Male Gametophyte in Acer yanjuechi (Aceraceae)

Acer yanjuechi is on the extremely endangered situation. This paper studied the formation of microspores and development of male gametophyte in Acer yanjuechi by using paraffin method to find the cause. The results are as follows: there are two kinds of flowers in Acer yanjuechi, bisexual flower and male flower. The stamens of male flowers could dehisce, but bisexual ones could not. Four pollen sacs make up one anther. The anther wall is of ground form. The endothercium develops fibular thickenings, and the tapetum is of the glandular type. The cytokinesis of the microspore mother cells in meiosis is of the simultaneous type. The microspore tetrads is of tetrahedral, and pollen grains are two-celled when mature. In the whole development of anthers, pollen abortions appear constantly and make pollens shriveled and embolic. The reasons are following: the callose dissolve ahead of time, nucleus microspore adhere to each other, anthers become vacuolating, and so on, which maybe one of the causes of being in danger of Acer yanjuechi. Pollen viability was detected initially, ranging from 36.98% to 60.54%, and the average is 45.97%. This article laid the foundation of anatomical data about Acer yanjuechi in the formation of microspores and development of male gametophyte.

Reproductive phenology of bryophytes in tropical rain forests: the sexes never sleep

Events of the sexual reproductive cycle of 11 bryophyte species (mosses and liverworts with monoicous and dioicous sexual conditions) were described for two different sites (montane and sea level) of a Brazilian tropical rain forest, during a 15 month-period. The sex expression of many species was continuous over the whole period, irrespective of the seasons and the forest sites. The specific sexual conditions of dioicous species did not change, but synoicous species had strategies to increase the chances of out-crossing, bearing unisexual branches in addition to bisexual ones. The pattern of gametangia and sporophyte development was different among the species, but the same between the sites. There was a seasonal effect on the maturation of gametangia and sporophytes. Male gametangia were mostly mature by the end of the dry season. Fertilization occurred during the wettest months and sporophytes developed during the dry season, dispersal of spores mostly towards the end of the dry season. Female gametangia were receptive over the whole period, with many mature gametangia before the start of the rainy season. Male gametangia, in contrast to female, took longer to develop and aborted in high numbers. Bryophytes in tropical rain forests are favored by wet weather and mild temperatures. Similar reproductive phenological patterns were found in different habitats with minor variations.

Carex secalina (Cyperaceae), a species critically endangered in Europe: from propagule germination to propagule production

The size and reproduction ability of the three field populations of <em>Carex secalina</em> Willd. ex Wahlenb. have been assessed. In the parallel garden study selected traits from the life history of the species have been studied, such as age at first reproduction, fertility, the size of seeds, their germination ability and size of seedlings. The populations of <em>C. secalina</em> discovered in Poland in 2000 are characterised by small abundance and small area. All individuals from the three populations in the garden produced generative shoots in the third year of life. Statistically significant differences between the populations were found in the production of shoots with unisexual spikes and bisexual ones, the latter had not been reported in the hitherto literature on the species. The seeds started germinating after a 6-months rest. The first seedlings were observed in the first decade of May. The largest seedlings were noted in the population producing the smallest seeds. The results contribute to explaining the renewal of the populations of this species in the field.

A parthenogenetic, simplified adult in the life cycle of Pliciloricus pedicularis sp. n. (Loricifera) from the deep sea of the Angola Basin (Atlantic)

A new species, Pliciloricus pedicularis (Pliciloricidae, Loricifera), is described inhabiting fine-grained clayish sediments in the deep sea of the Angola Basin. This is the first report of a Pliciloricus-species with a simplified parthenogenetic adult in its life cycle. The simplified adult is a non-free-living stage differing morphologically considerably from the free-living bisexual adults. It has a sack-like body without an introvert but with a persisting neck region covered with hooks or spiny pads. The sack-like body contains mainly the mature ovary. Large eggs are released into a shelter formed by the exuvium of the last or seventh instar Higgins-larva. Both types of adults, the parthenogenetic as well as the bisexual ones, are surrounded during metamorphosis by two exuviae: a simple inner one as rest of the postlarval stage and an outer one belonging to the seventh instar Higgins-larva. The bisexual adult of the new species is characterized by type B spinoscalids in the fourth row basally equipped with a ventral row of minute denticles; long rigid trichoscalids basally with numerous strong cross walls; small cuticular bars directly above the well-defined edge of the lorica, and a lorica consisting of 44 primary plicae. Distinguishing features of the Higgins-larva of the new species are: very long toes, and clavoscalids with a dorsal row of spinules and an additional fourth segment. The most conspicuous feature of the Higgins-larva is the stem-like basal part of the anterior setae called pedicels. Especially the enlarged pedicels of the posterolateral setae enable the larva to be determined even when the introvert is retracted. The study revealed new information about embryology and development, which have never been observed in any Loricifera-species so far. The great abundance of the new species in samples from the Angola Basin allows the identification of most life history stages and developmental instars.

Genetic structure of bisexual and parthenogenetic populations of Artemia from Italian brackish–hypersaline waters

Eight populations of Artemia displaying different reproduction modalities (amphigonic vs. parthenogenetic) and ploidies (diploid vs. polyploid) have been collected from Italian salt-works or brackish coastal lagoons, and their genetic structure has been investigated using allozyme electrophoresis. The results obtained on genetic differentiation showed that the Tyrrhenian bisexual samples ( A. salina) are genetically homogeneous even between populations located in relatively faraway sites (Sardinia–Latium), having a moderate gene flow assisted by migratory waterfowl. The parthenogenetic samples ( A. parthenogenetica) are genetically well differentiated both from the bisexual ones and among them, even when characterised by the same ploidy. Each sample presents few genotypes (i.e. few or single clones have been found in each sampling site), well distinguished from all the others. Further results concern the levels of genetic variability recorded. The parthenogenetic populations have an extremely high level of heterozygosity, due to a remarkable number of loci showing fixed heterozygosity, up to 13 out of 18 analysed. The preliminary data presented here show that some strains of A. parthenogenetica have a number of biological features typical of species of hybrid origin: fixed heterozygosity at many loci, parthenogenetic reproduction and genome polyploidisation. While too preliminary to advance a new hypothesis on the origin of A. parthenogenetica, our data suggest that further studies need to be carried out aimed at the research of possible bisexual parental species of A. parthenogenetica suspected hybrid strains.

Influence of parthenogenetic reproduction on the genotypic constitution and evolutionary success of populations and species

The life cycle of Daphnia commonly includes parthenogenesis, sexual reproduction, and diapause. Although there are no genotypic transformations during diapause, it separates the 'clonal' and 'pseudopanmictic' states of the population. During parthenogenetic reproduction primarily polymorphic natural populations gradually degenerate into a mixture of a few clones. As resting eggs are usually produced sexually (= by means of sexual reproduction), after the diapause the vast diversity of individual genotypes normal for panmictic populations is observed. It is the competitive interactions between parthenogenetic clones which again eventually decrease the genotypic polymorphism. Forms in which the sexual process and diapause are rare (or species which are represented by parthenogenetic populations in one part of their area and by bisexual ones in another) demonstrate the most significant differences between clonal and panmictic populations. Parthenogenesis, apomixis and other kinds of reproduction without genetic recombination are widely spread in branchiopod crustaceans (Notostraca, Anostraca, 'Conchostraca', 'Cladocera') and in many other animals and plants. Moreover, reproduction without recombination plays an important role in evolution of faunas and floras. It is emphasized that non-recombinating races and species having high heterozygosity but a low level of genetic variation, enjoy short term advantages, but die out after change in the environment.

Genetic similarity and diversity of parthenogenetic and bisexual populations of the freshwater snail Melanoides tuberculata (Gastropoda: Prosobranchia)

Genetic variability and similarity were analysed in four parthenogenetic and five bisexual populations of the snail Melanoides tuberculata found in Israel. Electrophoretic studies of six enzymatic systems revealed 28 zones of activity. The average genetic identity between populations was low—0.725. A particularly low similarity (0.628) was obtained between parthenogenetic populations, compared to the average of 0.822 observed among the bisexual ones. The percentage of fixed electrophoretic bands in parthenogens was 53.9% compared to 12.5% observed in bisexual populations. The diversity of parthenogenetic populations was found to be lower than those of bisexual. The amount of electrophoretic diversity between populations of the parthenogenetic group was found to be 80%, whereas within the bisexual group the diversity between populations was only 42%.

Genetic polymorphism and evolution in parthenogenetic animals. II. Diploid and polyploid Solenobia triquetrella (Lepidoptera: Psychidae).

Genic polymorphism at sixteen enzyme loci of four different chromosomal races of Solenobia triquetrella (bisexual, two diploid parthenogenetic races and tetraploid parthenogentiic) has been studied by starch gel electrophoresis. Isolated small diploid bisexual populations have rather uniform allele frequencies at all loci which we have studied. Diploid and tetraploid parthenogenetic individuals of this species are in general as heterozygous as bisexual ones. All parthenogenetic local populations are different from each other in the Alps. These parthenogenetic genotypes cannot be derived from a common ancestor through single mutations but rather bear evidence for a polyphyletic origin of parthenogenesis in Solenobia triquetrella. In the marginal distribution areas of the species in northern Europe single genotypes are spread over far larger areas than in the mountain regions of central Europe. This may be due to the old origin of parthenogenesis and polyploidy in northern Europe. No new parthenogenetic and polyploid strains have lately arisen in the regions outside of the Alps.

Parthenogenesis in Psocids (Insecta: Psocoptera)

synopsis. Obligate thelytokous parthenogenesis and, more rarely, facultative thelytoky are known to occur in psocids. The former phenomenon is known in 28 species. The latter is known only in two species, both of which have obligatorily thelytokous forms as well as bisexual ones. Attempts to force thelytokous females to mate have been carried out for four nominal species. All have failed. Differences in color or color pattern between the bisexual and thelytokous forms of a nominal species have been observed in two instances. In Echmepteryx hageni this seems to involve divergence where the two forms occur sympatrically but on different habitats. Investigations of geographic distribution of bisexual and thelytokous forms of a nominal species show in several cases that the thelytokous forms are much more widespread than the bisexual ones. In eastern United States, bisexual forms tend to occur peripherally and in ecologically unusual areas. The areas of occurrence of bisexual populations may be relictual, and some of them may have been Pleistocene refugia. Most of these areas correspond to areas where eoniferous trees now form an important part of the forest. Parthenogenesis in psocids is for the most part obligatory thelytoky. Only two cases are known of facultative thelytoky, in which egg viability is reduced, or a stringent limitation exists in the number of successive parthenogenetic generations, or both. A few instances are known in

PROBLEMS OF ANTIPODAL DISTRIBUTION IN LOWER LAND PLANTS

SummaryThe geographical distribution of the more primitive Hepaticae (subclass Jungermanniae) exhibits the same patterns of endemism and disjunction, and highly specific and restricted ranges as found in many groups of vascular plants. The subantarctic region is shown to have an unduly high preponderance of primitive genera present (ca. 50% of all known unspecialized types), of which very many are strictly endemic there. Many of these groups are cold‐adapted types which seem to have exhibited only limited displacement northward as a result of late‐Tertiary and Pleistocene deterioration of the climate; others (Blepharostomataceae) have shown some striking dispersal to the cold regions at the opposite side of the globe, but the bulk of taxa remain Antipodal. Other families (Gymnomitriaceae, Scapaniaceae) that seem to lack tolerance for warm climates are today very preponderantly Arctic subarctic (and Alpinesubalpine), but the most primitive taxa are still strictly subantarctic, leading to the conclusion that these largely Holarctic families are originally Panantarctic. From the evidence given it is concluded that many but probably not all major groups of the Jungermanniae may have originated in this Panantarctica (Gondwanaland). The recent overwhelmingly “in phase” data corroborating the theory of continental drift, plus the relatively late times for separation of the Australian‐Tasmanian‐New Zealand area from Antarctica (ca. 40‐60 m.y. ago; perhaps somewhat earlier in the case of New Zealand) suggest much of the dispersal (of older, unisexual taxa) may have been overland during late Mesozoic and early Tertiary times. Ranges of some taxa on islands near or on the Mid‐Atlantic and Indian‐Ocean ridges, islands which vary from 1‐20 million years in age, clearly indicate some taxa (especially bisexual ones) may have wider powers of spore‐dispersal than sometimes assumed. Present evidence does not, often, allow us to distinguish between ancient “overland” dispersal, and more recent dispersal via spores.