Nota preliminar sôbre a variação em orquídeas brasileiras

Preliminary studies on brazilian orchid species show that the existing material offers the possibility for studying the following general questions: a) In spite of the rule about the relative proportion between numbers of individuals per species and number of species per unit area in tropical and in temperate zones, the orchid genera seem to follow more closely the rule of temperate zone species, and this in spite of the fact that the family is undoubtedly of tropical origin. b) The large amont of paralell variation existing between different genera recquires a detailed explanation, and extensive introgressive hybridization is mentioned as one possibility. c) The existence of natural sympatric hybrids, both inter-generic and interspecific, and the simultaneous existence of the species in the pure form, show that mechanismes of reproductive isolation must exist, though of an incomplete nature.

Ocorrência de domácias em espécies e híbridos da Família Vitaceae

The paper deals with the ocurrence of domatia in species and hybrids of Vitaceae family. The author found domaãtia in 95 of 157 hybrids studied. The domatia are always in the axils of the first and second ribs, and occasionaly also in ribs of others orders. The domatia found were of the types: "en touffe de poils", "en pertuis" and "en pochette", types according to the Chevalier's Classification (1941). It was found a varation of the type "en pertuis", the hole being not circular but narrow and long. One of the hybrids have domatia of two types: "en touffe de pois" and "en pertuis". Many of the domatia have mites in its interior.

Gonadal hybrid dysgenesis in Drosophila sturtevanti (Diptera, Drosophilidae)

The occurrence of hybrid dysgenesis was investigated in Drosophila sturtevanti Duda, 1927 using diagnostic crosses similar to those used for induction of dysgenics traits in D. melanogaster. Reciprocal test crosses were made, at 27° C, between an old laboratory strain of D. sturtevanti (COL, from Colombia), assumed to be an M'-like strain, and eight freshly collected strains from several natural populations. The gonadal dysgenesis indices were under 10% in most of crosses, except in hybrids of COL with I27, a strain from Minas Gerais (Brazil), in which the index values were moderate in both directions of crosses (25.71 and 12.87). The smallest productivity was also observed in hybrids of females COL mated to I27 males. No causal relationship between the observed gonadal dysgenesis and mobilization of P element or another transposable element could be effectively established.

Observations on two biological races of Schistosoma mansoni

A comparative study of the BH strain of Schistosoma mansoni from Belo Horizonte, Minas Gerais state, infective to Biomphalaria glabrata from the same locality, and the SJ strain from São José dos Campos, São Paulo state, infective to B. tenagophila from the latter locality, showed the following differences: 1. Length of adult worms and size of eggs significantly larger in the BH strain. 2. Higher infection rates in the B. glabrata-BH strain association than in the B. tenagophila-SJ strain association, following exposure of each snail to 1 or 10 miracidia. 3.Longer prepatent period (from penetration of miracidium to first shedding of cercariae) in the B. tenagophila-SJ strain association. 4. Infection of both Biomphalaria species when exposed to hybrid miracidia from crosses between the two strains, at lower levels than those resulting from exposure of each snail species to miracidia of the pure sympatric strain. (Both Biomphalaria populations are practically refractory to infection with the allopatric strain). These results are interpreted as pointing to a better host-parasite adjustment in the B. glabrata-BH strain association than in the B. tenagophila-SJ association. The interfertility between the two strains, which produced viable hybrids infective to both Biomphalaria species, supports the conclusion that the observed differences are merely intraspecific, and that the two strains may be considered distinct biological races of Schistosoma mansoni.

Secondary contact zones and hybridizations: the case of the lesser white-toothed shrew (Crocidura suaveolens group, Soricidae)

In the present study, we analyzed 58 samples of the lesser white-toothed shrew group (Crocidura suaveolens) from eastern Europe and Turkey, where, according to previous publications, three different mitochondrial and nuclear lineages are present. We sequenced 799 bp of the nuclear BRCA1 gene and 400 bp of the mitochondrial cytochrome b gene to: (1) determine a potential contact zone between the lineages; (2) detect hybridizations and introgressions between them; and (3) comment on the level of reproductive isolation of the different lineages. We revealed two zones of hybridization in Turkey, of which the first occurred west of the Bosphorus Straits (three hybrids) and the second in Anatolia (twelve hybrids). In the latter, the nuclear markers revealed a large zone of hybridization, of approximately 600 km. It also revealed that hybrids of first, second, and later generations are present within the populations, and therefore that the reproductive isolation between the different lineages is weak.

Lack of directed V alpha 14-J alpha 281 rearrangements in NK1+ T cells.

NK1.1+ T cells are an unusual subset of TCR alpha beta cells distinguished by their highly restricted V beta repertoire and predominant usage of an invariant V alpha 14-J alpha 281 chain. To assess whether a directed rearrangement mechanism could be responsible for this invariant alpha chain, we have analyzed V alpha 14 rearrangements by polymerase chain reaction and Southern blot in a panel of cloned T-T hybrids derived from thymic NK1.1+ T cells. As expected a high proportion (17/20) of the hybrids had rearranged V alpha 14 to J alpha 281. However, V alpha 14-J alpha 281 rearrangements always occurred on only one chromosome and were accompanied by other V alpha-J alpha rearrangements (not involving V alpha 14) on the homologous chromosome. These data argue that rigorous ligand selection rather than directed rearrangement is responsible for the high frequency of V alpha 14-J alpha 281 rearrangements in NK1.1+ T cells.

Repeated unidirectional introgression towards Populus balsamifera in contact zones of exotic and native poplars.

As the evolutionary significance of hybridization is largely dictated by its extent beyond the first generation, we broadly surveyed patterns of introgression across a sympatric zone of two native poplars (Populus balsamifera, Populus deltoides) in Quebec, Canada within which European exotic Populus nigra and its hybrids have been extensively planted since the 1800s. Single nucleotide polymorphisms (SNPs) that appeared fixed within each species were characterized by DNA-sequencing pools of pure individuals. Thirty-five of these diagnostic SNPs were employed in a high-throughput assay that genotyped 635 trees of different age classes, sampled from 15 sites with various degrees of anthropogenic disturbance. The degree of admixture within sampled trees was then assessed through Bayesian clustering of genotypes. Hybrids were present in seven of the populations, with 2.4% of all sampled trees showing spontaneous admixture. Sites with hybrids were significantly more disturbed than pure stands, while hybrids comprised both immature juveniles and trees of reproductive age. All three possible F1s were detected. Advanced-generation hybrids were consistently biased towards P. balsamifera regardless of whether hybridization had occurred with P. deltoides or P. nigra. Gene exchange between P. deltoides and P. nigra was not detected beyond the F1 generation; however, detection of a trihybrid demonstrates that even this apparent reproductive isolation does not necessarily result in an evolutionary dead end. Collectively, results demonstrate the natural fertility of hybrid poplars and suggest that introduced genes could potentially affect the genetic integrity of native trees, similar to that arising from introgression between natives.

Monophyletic origin of multiple clonal lineages in an asexual fish (Poecilia formosa).

Despite the advantage of avoiding the costs of sexual reproduction, asexual vertebrates are very rare and often considered evolutionarily disadvantaged when compared to sexual species. Asexual species, however, may have advantages when colonizing (new) habitats or competing with sexual counterparts. They are also evolutionary older than expected, leaving the question whether asexual vertebrates are not only rare because of their 'inferior' mode of reproduction but also because of other reasons. A paradigmatic model system is the unisexual Amazon molly, Poecilia formosa, that arose by hybridization of the Atlantic molly, Poecilia mexicana, as the maternal ancestor, and the sailfin molly, Poecilia latipinna, as the paternal ancestor. Our extensive crossing experiments failed to resynthesize asexually reproducing (gynogenetic) hybrids confirming results of previous studies. However, by producing diploid eggs, female F(1) -hybrids showed apparent preadaptation to gynogenesis. In a range-wide analysis of mitochondrial sequences, we examined the origin of P. formosa. Our analyses point to very few or even a single origin(s) of its lineage, which is estimated to be approximately 120,000 years old. A monophyletic origin was supported from nuclear microsatellite data. Furthermore, a considerable degree of genetic variation, apparent by high levels of clonal microsatellite diversity, was found. Our molecular phylogenetic evidence and the failure to resynthesize the gynogenetic P. formosa together with the old age of the species indicate that some unisexual vertebrates might be rare not because they suffer the long-term consequences of clonal reproduction but because they are only very rarely formed as a result of complex genetic preconditions necessary to produce viable and fertile clonal genomes and phenotypes ('rare formation hypothesis').

Distribution and hybridization between Culex pipiens and Culex quinquefasciatus (Diptera: Culicidae) in Argentina

To better undesrtand the distribution of Culex pipiens and Cx. quinquefasciatus in Argentina, samples were collected from six localities situated in a North-South line from Castelli (Chaco Province) to Puerto Madryn (Chubut Province). Identification was based on the morphology of male genitalia. Only Cx. quinquefasciatus was found in Castelli and Esperanza, while in Rosario, 95.3% belonged to this species and 4.7% represented hybrid forms. Southern samples included only Cx. pipiens. With the purpose of verfying if Cx. pipiens and Cx. quinquefasciatus hybridize, different crosses between the two species were perfomed. All crosses produced viable egg rafts. Hatching ranged from 70 to 100%, except in one cross, female Cx. pipiens x male Cx. quinquefasciatus, where a high incompatibility was observed (11.1%hatch). The F1 hybrids obtained all crosses were fertile. The finding of hybrid forms in nature can be interpreted as evidence for subspecific status of Cx. pipiens and Cx. quinquefasciatus in Argentina.

Questioning the utility of RNA-DNA chimera in gene repair.

In principle, we should be glad that Eric Kmiec and his colleagues published in Science's STKE (1) a detailed experimental protocol of their gene repair method (2, 3). However, a careful reading of their contribution raises more doubts about the method. The research published in Science five years ago by Kmiec and his colleagues was said to demonstrate that chimeric RNA-DNA oligonucleotides could correct the mutation responsible for sickle cell anemia with 50% efficiency (4). Such a remarkable result prompted many laboratories to attempt to replicate the research or utilize the method on their own systems. However, if the method worked at all, which it rarely did, the achieved efficiency was usually lower by several orders of magnitude. Now, in the Science's STKE protocol, we are given crucial information about the method and why it is so important to utilize these expensive chimeric RNA-DNA constructs. In the introduction we are told that the RNA-DNA duplex is more stable than a DNA-DNA duplex and so extends the half-life of the complexes formed between the targeted DNA and the chimeric RNA-DNA oligonucleotides. This logical explanation, however, conflicts with the statement in the section entitled "Transfection with Oligonucleotides and Plasmid DNA" that Kmiec and colleagues have recently demonstrated that classical single-stranded DNA oligonucleotides with a few protective phosphothioate linkages have a "gene repair conversion frequency rivaling that of the RNA/DNA chimera". Indeed, the research cited for that result actually states that single-stranded DNA oligonucleotides are in fact several-fold more efficient (3.7-fold) than the RNA-DNA chimeric constructs (5). If that is the case, it raises the question of why Kmiec and colleagues emphasize the importance of the RNA in their original chimeric constructs. Their own new results show that modified single-stranded DNA oligonucleotides are more effective than the expensive RNA-DNA hybrids. Moreover, the current efficiency of the gene repair by RNA-DNA hybrids, according to Kmiec and colleagues in their recent paper is only 4×10-4 even after several hours of pre-selection permitting multiplification of bacterial cells with the corrected plasmid (5). This efficiency is much lower than the 50% value reported five years ago, but is assuredly much closer to the reality.

Possible hybridization of Brazilian planorbid snails and its importance in population dynamics

This study focuses on the possibility of experimental hybridization among host snail species for Schistosoma mansoni in Brazil, with morphological characterization of the hybrids found. By using albinism as a genetic marker, intraspecific crossbreedings were performed between two strains of each species involved, in addition to interspecific crossbreedings; the only viable crossbreeding was between pigmented Biomphalaria glabrata (Paulista, PE) and albino B. tenagophila (Joinville, SC), with the formation of F1 and F2 generations. All offspring in F1 displayed black eyes and a renal ridge on the mantle, while F2 displayed dissociated morphological traits. With regard to reproduction, F1 was more efficient than F2. The experiment's results suggest post-zygotic reproductive isolation.

Mechanisms of reproductive isolation between an ant species of hybrid origin and one of its parents.

The establishment of new species by hybridization is difficult because it requires the development of reproductive isolation (RI) in sympatry to escape the homogenizing effects of gene flow from the parental species. Here we investigated the role of two pre- and two postzygotic mechanisms of RI in a system comprising two interdependent Pogonomyrmex harvester ant lineages (the H1 and H2 lineages) of hybrid origin and one of their parental species (P. rugosus). Similar to most other ants, P. rugosus is characterized by an environmental system of caste determination with female brood developing either into queens or workers depending on nongenetic factors. By contrast, there is a strong genetic component to caste determination in the H1 and H2 lineages because the developmental fate of female brood depends on the genetic origin of the parents, with interlineage eggs developing into workers and intralineage eggs developing into queens. The study of a mixed mating aggregation revealed strong differences in mating flight timing between P. rugosus and the two lineages as a first mechanism of RI. A second important prezygotic mechanism was assortative mating. Laboratory experiments also provided support for one of the two investigated mechanisms of postzygotic isolation. The majority of offspring produced from the few matings between P. rugosus and the lineages aborted at the egg stage. This hybrid inviability was under maternal influence, with hybrids produced by P. rugosus queens being always inviable whereas a small proportion of H2 lineage queens produced large numbers of adult hybrid offspring. Finally, we found no evidence that genetic caste determination acted as a second postzygotic mechanism reducing gene flow between P. rugosus and the H lineages. The few viable P. rugosus-H hybrids were not preferentially shunted into functionally sterile workers but developed into both workers and queens. Overall, these results reveal that the nearly complete (99.5%) RI between P. rugosus and the two hybrid lineages stems from the combination of two typical prezygotic mechanisms (mating time divergence and assortative mating) and one postzygotic mechanism (hybrid inviability).

Hybridisation and diversification in the adaptive radiation of clownfishes.

BackgroundThe importance of hybridisation during species diversification has long been debated among evolutionary biologists. It is increasingly recognised that hybridisation events occurred during the evolutionary history of numerous species, especially during the early stages of adaptive radiation. We study the effect of hybridisation on diversification in the clownfishes, a clade of coral reef fish that diversified through an adaptive radiation process. While two species of clownfish are likely to have been described from hybrid specimens, the occurrence and effect of hybridisation on the clade diversification is yet unknown.ResultsWe generate sequences of three mitochondrial genes to complete an existing dataset of nuclear sequences and document cytonuclear discordance at a node, which shows a drastic increase of diversification rate. Then, using a tree-based jack-knife method, we identify clownfish species likely stemming from hybridisation events. Finally, we use molecular cloning and identify the putative parental species of four clownfish specimens that display the morphological characteristics of hybrids.ConclusionsOur results show that consistently with the syngameon hypothesis, hybridisation events are linked with a burst of diversification in the clownfishes. Moreover, several recently diverged clownfish lineages likely originated through hybridisation, which indicates that diversification, catalysed by hybridisation events, may still be happening.

Estudi del sistema reptroductor de la guatlla (Coturnix coturnix) i de la hibridació amb la guatlla japonesa (Coturnix japonica) domèstica i híbrids

La guatlla (Coturnix coturnix) és actualment una espècie amb un estat de conservació desfavorable. Una amenaça per a la seva conservació és la hibridació que pot produir-se degut als alliberaments massius amb finalitats cinegètiques de la guatlla japonesa (Coturnix japonica) o híbrids provinents de granges de cria. Els objectius d’estudi són: a) Aprofundir en el sistema sexual de la guatlla, ja que el seu coneixement pot permetre entendre els mecanismes d’hibridació amb la guatlla japonesa o híbrids. b) Conèixer la taxa de supervivència i l’eficàcia biològica dels individus no nadius a àrees de reproducció de la guatlla. c) Buscar evidències directes d’hibridació en condicions naturals i caracteritzar-la. d) Determinar si existeix competència espermàtica interespecífica mitjançant experiments en captivitat. S’ha seguit el comportament en condicions naturals de parelles homospecífiques i heterospecífiques de mascles i femelles de guatlla i de guatlla japonesa o híbrids. S’ha analitzat la paternitat dels polls d’aquestes parelles i s’ha pogut conèixer quins aspectes del comportament (segons l’espècie) es relacionen amb l’eficàcia biològica dels adults. S’han analitzat el mateix tipus de dades obtingudes durant cinc temporades reproductives, en les que hi van participar només individus de guatlla. Així s’ha pogut comparar el comportament de l’espècie en presència i absència dels individus al•lòctons. Els resultats indiquen que existeixen dues estratègies sexuals entre els mascles de guatlla. L’estat físic del mascle en relació al dels altres mascles coetanis i el temps de permanència amb la femella determinen la seva taxa de paternitat. Existeix una fracció relativament petita però significativa de guatlla japonesa de granja que sobreviu en condicions naturals i s’hibrida amb la guatlla silvestre, predominantment de forma unidireccional, entre femella japonesa i mascle de guatlla. Aquestes femelles presenten un sistema d’aparellament majoritàriament monògam. Els anàlisis sobre els experiments de competència espermàtica s’estan realitzant a l’actualitat.