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The surfperches (Embiotocidae) are comprised of 24 species, all but one species is marine and they range from central Baja California to Alaska (not including the Aleutian Islands) and Japan [...]

Enigmatic macrofossils of late Ediacaran age (580-541 million years ago) provide the oldest known record of diverse complex organisms on Earth, lying between the microbially dominated ecosystems of the Proterozoic [...]

With more than 460 described species (4), bdelloid rotifers (Fig. 1) represent the highest metazoan taxonomic rank in which males, hermaphrodites and meiosis are unknown. Such persistence and diversification ofan [...], Loss of sexual reproduction is considered an evolutionary dead end for metazoans, but bdelloid rotifers challenge this view as they appear to have persisted asexually for millions of years (1). Neither male sex organs nor meiosis have ever been observed in these microscopic animals: oocytes are formed through mitotic divisions, with no reduction of chromosome number and no indication of chromosome pairing (2). However, current evidence does not exclude that they may engage in sex on rare, cryptic occasions. Here we report the genome of a bdelloid rotifer, Adineta vaga (Davis, 1873) (3), and show that its structure is incompatible with conventional meiosis. At gene scale, the genome of A. vaga is tetraploid and comprises both anciently duplicated segments and less divergent allelic regions. However, in contrast to sexual species, the allelic regions are rearranged and sometimes even found on the same chromosome. Such structure does not allow meiotic pairing; instead, we find abundant evidence of gene conversion, which may limit the accumulation of deleterious mutations in the absence of meiosis. Gene families involved in resistance to oxidation, carbohydrate metabolism and defence against transposons are significantly expanded, which may explain why transposable elements cover only 3% of the assembled sequence. Furthermore, 8% of the genes are likely to be of non-metazoan origin and were probably acquired horizontally. This apparent convergence between bdelloids and prokaryotes sheds new light on the evolutionary significance of sex.

Introduction Endemic species with restricted geographic distributions have become a central concern of biologists faced with the problem of preserving rare species endangered by habitat destruction and fragmentation (Ge et [...], This is the first report on chromosome numbers and the reproductive behaviour in Stenodrepanum Harms, a rare endemic and monotypic legume genus from the arid and salty areas of central-western Argentina. Sixty individuals belonging to two populations from two salty areas ('salinas') were surveyed and included mostly triploid (2n = 3x = 36) and only two diploid (2n = 2x = 24) plants. Meiosis in diploids is regular, with bivalent pairing and uniform and viable pollen. In contrast, meiosis in triploids is characterized by high trivalent pairing, with irregularly shaped pollen and variation in cytoplasm content and stainability, which is in agreement with an unbalanced segregation occurring in anaphases I and II. However, different triploid plants/individuals showed various degrees of pollen fertility, which may be attributed to particular genotypes. Research on reproductive biology events indicates sexual cross-pollinated reproduction enhanced by protogyny in both cytotypes. All plants produced seeds, but seedlings were only recovered from diploid plants pollinated with triploids, and even those eventually perished. Chromosome counts in these seedlings revealed aneuploid chromosome numbers owing to the combination of unbalanced gametes. Key words: Stenodrepanum, triploids, diploids, endemic, Fabaceae, Argentina. Les auteurs presentent ici la premiere caracterisation du nombre chromosomique et du comportement reproductif au sein du Stenodrepanum Harms, un genre rare et monotypique au sein des legumineuses qui est originaire dans les regions arides et salees du Centre-Ouest de l'Argentine. Soixante individus appartenant a deux populations provenant de deux regions salines (<< salinas >>) ont ete etudies et comprenaient une majorite d'individus triploides (2n = 3x = 36) et seulement deux diploides (2n = 2x = 24). La meiose chez les diploides est normale, avec la formation de bivalents et de pollen uniforme et viable. Par contre, la meiose chez les triploides se caracterise par une grande frequence de trivalents et des grains de pollen de forme irreguliere qui presentent de la variation pour le contenu cytoplasmique et la coloration, des caracteristiques qui concordent avec une segregation irreguliere au cours des anaphases I et II. Cependant, differents plants/individus triploides presentaient differents degres de fecondite du pollen, ce qui pourrait etre la consequence de differents genotypes particuliers. Une investigation de la biologie reproductive indique une allofecondation sexuelle favorisee par la protogynie chez les deux cytotypes. Toutes les plantes ont produit des graines, mais des plantules n'ont ete obtenues que chez les diploides fecondes par des triploides, mais meme ces individus sont eventuellement morts. Des decomptes chromosomiques chez ces plantules ont indique une aneuploidie due a la combinaison de gametes debalances. Mots-cles : Stenodrepanum, triploides, diploides, endemique, fabacees, Argentine. [Traduit par la Redaction]

BACKGROUND: A single in utero exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on gestation day 15 decreased epididymal sperm count in adult rats and thus was used to establish a tolerable daily intake [...]

Introduction Reproductive physiology in crustaceans is highly controlled and regulated by the nervous and endocrine systems (Engelmann, 1994). Endocrine control of female reproduction is governed by a variety of hormonal [...], In this study we have investigated the role of 17β-estradiol and progesterone in the reproduction of the crayfish Cherax albidus by using vitellogenin (VTG) as a biomarker. Early-vitellogenic (EV), full-vitellogenic (FV), and non-vitellogenic (NV) females of Cherax albidus were treated with 17β-estradiol, progesterone, or both for 4 weeks. Levels of VTG mRNA in the hepatopancreas were detected by RT-PCR. The PCR product was sequenced and showed 97% homology with Cherax quadricarinatus VTG. 17β-estradiol was more effective than progesterone and 17β-estradiol plus progesterone in increasing the vitellogenin transcript in the hepatopancreas of EV and FV females. On the contrary, progesterone was more effective than 17β-estradiol and 17β-estradiol plus progesterone in increasing the vitellogenin concentration in the hemolymph of EV and FV females. Hepatopancreas histology and fatty acid composition of females injected with hormones showed major modifications. No effects were registered in NV females. In conclusion, 17β-estradiol and progesterone influence VTG synthesis, although our data indicate that they act through different pathways and are not effective until the proper hormonal environment is established, as demonstrated by their inefficacy in NV females.

The unsolved problem of the evolution of sexual reproduction has been almost exclusively in the domain of population genetics. This suggests that new approaches may be fruitful; here I develop [...]

Author(s): Lewis G. Spurgin, Tracey ChapmanAuthor Affiliations:Darwin's finches choose parent lookalikes as mates New species form when groups of individuals in a population become reproductively isolated and can no longer [...], A preference for mating with similar individuals can have a key role in speciation. Research on Darwin's finches suggests that individuals might use the likeness of their parents as a guide for choosing mates. Sexual imprinting drives mating choices in Darwin's finches.

Introduction Recent studies on reproduction of colonial, scleractinian corals have revealed that polyps in small colonies produce no eggs or few eggs, and that in large, fecund colonies polyps at [...], The factors that influence egg production in the massive coral Goniastrea aspera were examined in colonies of various sizes collected before the first spawning of the year. Particular attention was given to polyp size, measured in three dimensions as volume. Although a polyp in a colony containing as few as 13 polyps produced eggs, colonies with fewer than 60 polyps had fewer eggs per unit volume of polyp. The relationship between colony size and colony fecundity suggested that 60 polyps is the minimum size at which a colony can achieve active maturity. Polyp volume of small colonies before maturation was also smaller than that of the larger colonies, suggesting that colony size, as well as polyp size, is crucial for sexual maturity. The position of a polyp in the colony (and thus its mode of budding) also affects its maturity (and thus its egg production). Marginal polyps (those on the edge of the colony) usually exhibited extratentacular budding, and the resulting polyps were initially immature. Consequently, egg production by such polyps is a function of their age, calculated from the time of their formation by extratentacular budding. In contrast, non-marginal polyps always exhibited intratentacular budding. Moreover, in the non-marginal areas of large colonies (>84 polyps), the polyps produced by intratentacular budding were always mature. In all colonies, marginal polyps were smaller in volume and had a lower number of eggs for each unit of volume than did non-marginal ones. This suggests that polyps play different roles according to their position in a colony: marginal polyps contribute to defense and expansion of the area of attachment, whereas the role of non-marginal polyps is reproductive. The fecundity of mature colonies increased linearly with colony size, and large colony size cannot be attained without expansion of the attachment area.

Fire ant females have many and varied reproductive options The fire ants are a group of about twenty New World species belonging to the genus and subgenus Solenopsis (Trager 1991). [...]

Introduction Tidal and semilunar rhythms of reproductive activity have been reported in many intertidal and estuarine organisms (e.g., see Korringa, 1947; Hauenschild, 1960; DeCoursey, 1983: Pearse, 1990). Marine midges of [...], The emergence of an intertial midge was investigated at a site on the coast of the Inland Sea of Japan. The population emerging at this site was drawn from a single species of the genus Clunio, probably C. tsushimensis. Emergence was not synchronized with the day-night cycle, but with the tidal cycle. Moreover, the pattern of synchrony changed with season. A bimodal phase appeared in midwinter; but the pattern of synchrony shifted gradually, during January and February, from morning low tides to afternoon low tides, and a unimodal phase appeared in March. This pattern - i.e., synchrony with afternoon low tides - lasted until early October. In mid-October, the synchrony shifted to the morning low tides. Only a brief bimodal phase appeared in autumn. The phase modality was clearly correlated with the height of tides; i.e., when the low waters in a day were very different in height, emergence was synchronized only with the lower one (April to December). During January and February, the higher low tide, as well as the lower low tide, recedes considerably. The exposure of the larval habitat at the higher low tide may stimulate emergence, resulting in bimodal phases in midwinter. But the unimodal pattern in March cannot be accounted for by a simple synchrony with lower low tide, or with exposure of the larval habitat to the air; the day-night cycle not only would be one of the zeitgebers of the tidal rhythm in every season, but also must participate in the expression of the unimodal phase in spring. Furthermore, the number of midges that emerged each day fluctuated with a semilunar cycle with the season. The phase of this rhythm would be shifted by water temperature.

A framework for the inclusion of population-quality variables as central features of herbivore population-dynamics models Historically, population quality, although recognized as an important issue, has been omitted from models of [...]

Author(s): Dorothy Bishop Author Affiliations: Rein in the four horsemen of irreproducibility More than four decades into my scientific career, I find myself an outlier among academics of similar age [...], Dorothy Bishop describes how threats to reproducibility, recognized but unaddressed for decades, might finally be brought under control. Dorothy Bishop describes how threats to reproducibility, recognized but unaddressed for decades, might finally be brought under control.

Progress in the biomedical and clinical sciences has relied heavily on experimental animal research. However, the impact of other comparative disciplines such as evolutionary biology, and in particular its subdisciplines [...]

Endoenous Reproductive Rhythms in a Tropical Bird IN MANY TROPICAL ANIMALS, REPRODUCTION and other seasonal events are organized on the basis of an annual rhythm. This is true even in [...]

Knowledge of the sperm-specific protein that is required for the attachment of sperm to eggs during fertilization in mammals has led to the identification of the protein's receptor on the [...]

Why have some organisms evolved the capacity for sexual reproduction, whereas others make do with reproducing asexually? Since the time of Weismann (1), most biologists have been taught that sex [...]

Like mating in other organisms, attraction between the opposite sexes in plants is important for reproduction. Chance brings pollen grains (the male gametophytes) to the surface of the pistil (the [...]

Ecological speciation occurs when organisms exposed to divergent selective regimes evolve reproductive isolation as a by-product of adaptation (1-3). Mechanisms contributing to ecological speciation include mate choice based on traits [...], Colonization of new environments should promote rapid speciation as a byproduct of adaptation to divergent selective regimes. Although this process of ecological speciation is known to have occurred over millennia or centuries, nothing is known about how quickly reproductive isolation actually evolves when new environments are first colonized. Using DNA microsatellites, population-specific natural tags, and phenotypic variation, we tested for reproductive isolation between two adjacent salmon populations of a common ancestry that colonized divergent reproductive environments (a river and a lake beach). We found evidence for the evolution of reproductive isolation after fewer than 13 generations.

The part that natural selection plays in the origin of species has long been debated. It is easy to see that if two populations are kept separate--by mountains or ocean, [...]

Primates OUR GENETIC RELATIONSHIP TO APES AND MONKEYS, THE consequence of our relatively recent common evolutionary ancestry, underlies the similar structural organizational development, and functioning of humans and primates. The [...]

When dividing to produce mammalian sex cells, cells coordinate how DNA breaks occur. The cell-division process that forms these sex cells, which contain one set of chromosomes instead of the [...]

Women's health and noncommunicable diseases are both generating increasing interest within the international community. Over the past two years major action platforms have been launched in these areas, including the [...]

In what direction is the field of reproductive biology moving? Do funding priorities match hot research areas? In this special focus, we try to find out. In 2002, Nature Medicine [...]

The mountain gorilla is one of our closest living relatives, surviving in the wild as a population of perhaps no more than a few hundred individuals. Despite the gorillas' extreme [...]

A female mouse can ovulate a fresh batch of eggs about every 4 to 6 days. To learn more about the genes that sustain egg production and orchestrate other ovarian [...]

Yeast use partially overlapping kinase modules to specify discrete cellular responses. For example, the upstream kinases in the mitogen-activated protein kinase (MAPK) cascade, Stel 1 and Ste7, are both activated [...]

When a sperm joins with an egg, development is begun by a signal encoded in oscillations in the concentration of intracellular-free calcium ([[[Ca.sup.2+]].sub.i]) in the cytoplasm of the egg. PreciseLy [...]

Monoclonal Antibody to a Human Germ Cell Membrane Glycoprotein That Inhibits Fertilization Immunization of male or female animals of different species with homogenates of mature sperm, testis, or their extracts [...]