Julio E. Pérez

The Biology of Invasions: The Genetic Adaptation Paradox

One of the most relevant topics in the biology of invasion concerns the genetic changes that occur subsequent to a species invasion, an issue of particular focus among conservation biologists. Colonizing a novel environment presents a genetic challenge to invading species because such species surely have not experienced the selective pressures presented by the environment. Here we ask, by what mechanisms and processes do alien species genetically naïve to their new environment, become successful invaders? We attempt to resolve this paradox by considering the interplay between an invader’s ability to modify its new environment, and genetic modifications imposed by the new environment. We postulate that epigenetic adaptations, and adaptive mutations are likely play a role in enhancing invasion success.

Cytogenetic characterization of hybrids offspring between Colossoma macropomum (Cuvier, 1818) and Piaractus brachypomus (Cuvier, 1817) from Caicara del Orinoco, Venezuela

Abstract Conventional karyotype and nucleolar organizer regions (NORs) of C. macropomum x P. brachypomus hybrids and parental species are reported. A modal diploid number of 54 chromosomes and a fundamental number (NF) of 108 were found for C. macropomum, P. brachypomus and their hybrids. P. brachypomus shows a pair of silver stained chromosomes, while cells with three and four Ag-NOR bearing chromosomes were observed in C. macropomum. The hybrids consistently presented cells with a single metacentric Ag-NOR bearing chromosome and cells with three Ag-NOR bearing chromosomes. The FISH technique was employed to localize 18S rDNA in the chromosomes of the parentals and the hybrids. In P. brachypomus the FITC signals appeared in the SM pair as when stained with silver salts. In C. macropomum the signals were evidenced in six chromosomes. In the hybrids, as expected, the FITC dots were observed in four chromosomes. All the techniques employed in the present work represent good tools to identify the parentals and distinguish them of the hybrids.

Cytogenetic characterization of Rhomboplites aurorubens and Ocyurus chrysurus, two monotypic genera of Lutjaninae from Cubagua Island, Venezuela, with a review of the cytogenetics of Lutjanidae (Teleostei: Perciformes)

Lutjanidae, commonly known as snappers, includes 105 species, grouped in four subfamilies. In spite of the high number of species and of its worldwide distribution, the family has been little investigated and the phylogenetic relationships among some of its genera and species are still cause for debate. Only a small number of the species has been cytogenetically analysed. This study reports the first description of the karyotype of Rhomboplites aurorubens as well as data concerning the distribution of the constitutive heterochromatin and the location of the 18S rRNA and the 5S rRNA genes. Specimens of Ocyurus chrysurus from Venezuela were also investigated for the same cytogenetic features. Both species have a 48 uniarmed karyotype, but R. aurorubens has a single subtelocentric chromosome pair, the smallest of the chromosome complement, among the other acrocentric chromosomes. The C-positive heterochromatin is limited to the pericentromeric regions of all chromosomes. Both species show a single chromosome pair bearing the Nucleolus Organizer Regions, but NORs are differently located, in a terminal position on the short arms of the smallest chromosomes in R. aurorubens and in a paracentromeric position in a chromosome pair of large size in O. chrysurus. In O. chrysurus, the 5S rDNA gene cluster is located on a medium-sized chromosome pair, whereas in R. aurorubens it is syntenic with the 18S rDNA gene cluster on chromosome pair number 24. The obtained cytogenetic data, along with previous cytogenetic, morphological and molecular data for the family, reinforce the proposal to synonymize genus Ocyurus with Lutjanus. A review of Lutjanidae cytogenetics is also included.

Cytogenetic studies in three species of Lutjanus (Perciformes: Lutjanidae: Lutjaninae) from the Isla Margarita, Venezuela

In the present study, three species of Lutjaninae, Lutjanus analis, L. griseus and L. synagris, were analyzed by conventional Giemsa staining, C-banding and silver staining, to reveal active Nucleolus Organizer Regions (NORs). Fluorescent in situ hybridization (FISH) was also applied to establish the number and location of the ribosomal gene clusters (18S and 5S rRNA genes). Counts of diploid metaphasic cells revealed a diploid modal chromosome complement composed of 48 acrocentric chromosomes in both L. analis and L. griseus. Two cytotypes were observed in L. synagris: cytotype I, with 2n=48 acrocentric chromosomes, found in 19 specimens, and cytotype II, with 46 acrocentric chromosomes and one large metacentric, found in two specimens. The large metacentric, which possibly originated from a Robertsonian rearrangement, was not found to be sexrelated. In the three species, constitutive heterochromatin is located in the centromeres of all chromosomes. NORs were detected on the short arms of a single chromosome pair, number 24 in L. analis and number 6 in both cytotypes of L. synagris. In L. griseus, a polymorphism of the NORs number was detected, by both Ag-staining and FISH, as females show a maximum of three NORs, and males a maximum of six NORs. In all species, minor ribosomal genes were found located on a single chromosome pair. The obtained data, along with those previously reported for other five Lutjanidae species, show that a general chromosome homogeneity occurs within the family, but that derived karyotypes based on Robertsonian rearrangements as well as multiple and variable NORs sites can also be found. No presente estudo tres especies de Lutjaninae, Lutjanus analis, L. griseus e L. synagris foram analisadas atraves da coloracao convencional com Giemsa, banda C e coloracao com nitrato de prata para identificar as Regioes Organizadoras de Nucleolo (NORs) ativas. Hibridacao fluorescente in situ (FISH) foi tambem aplicada para estabelecimento do numero e localizacao dos agrupamentos de genes ribossomicos (18S e 5S rRNA). A contagem de celulas metafasicas revelou um numero diploide modal de 48 cromossomos acrocentricos em L. analis e L. griseus. Dois citotipos foram observados em L. synagris: citotipo I com 2n=48 cromossomos acrocentricos, encontrado em 19 especimes, e citotipo II com 46 cromossomos acrocentricos e um grande metacentrico, encontrado em dois especimes. O grande metacentrico, que possivelmente se originou por um rearranjo Robertsoniano, nao esta relacionado com o sexo. Nas tres especies a heterocromatina constitutiva esta localizada nas regioes centromericas de todos os cromossomos. NORs foram detectadas no braco curto de um unico par cromossomico, numero 24 em L. analis e numero 6 em ambos os citotipos de L. synagris. Em L. griseus, um polimorfismo de numero de NORs foi observado, apos coloracao com prata e por FISH, as femeas apresentaram um maximo de tres NORs e os machos um maximo de seis NORs. Em todas as especies os genes ribossomicos 5S foram encontrados em um unico par cromossomico. Os dados obtidos, somados aos demais previamente publicados para cinco outras especies de Lutjanidae, mostram que na familia ha uma homogeneidade cromossomica, porem tambem sao encontrados cariotipos derivados, originados por rearranjos Robertsonianos, assim como pela ocorrencia de sitios multiplos e variados de NORs.

Aquaculture: part of the problem, not a solution.

Sir — Stem-cell research, including the use of human embryonic stem cells, has important implications for medical practice in the future, and the relief of suffering in many serious and intractable diseases. The European Commission’s European Group on Ethics in Science and New Technologies (EGE) has recently issued an opinion on the ethical aspects of human stem-cell research. As one of the two rapporteurs of this opinion, I was disappointed by your report “European panel rejects creation of human embryos for research” (Nature 408, 277; 2000) Human embryonic stem cells, which can give rise to many different cell types and tissues, are derived from early embryos in vitro. Your report makes little attempt to distinguish between (1) embryos donated for research by patients undergoing in vitro fertilization (IVF) treatment (‘spare embryos’); (2) embryos made for research by fertilizing donated oocytes in vitro (‘research embryos’) and (3) embryos made for research by transfer of somatic nuclei to donated oocytes (‘nucleartransfer embryos’). The first category, spare embryos, covers all the human embryonic stem-cell lines at present being studied in the United States and Australia. The EGE concludes that in those countries (including the United Kingdom) where human embryo research is allowed, it is hard to see any specific argument that would prohibit extending the scope of such research in order to develop new treatments to cure severe diseases. Further, the group sees no argument for excluding funding of such research from the European Union’s Framework programme. Thus it takes the view that, in Europe, the derivation of stem cells from IVF embryos should be not only publicly controlled but also publicly funded — unlike the situation in the United States, where state funding is not permitted to be used for this research. The second category, research embryos, is deemed ethically unacceptable when spare embryos, including tens of thousands of frozen embryos in Europe which may become available for donation, represent a ready alternative source. The headline on your report is misleading, since the present EGE opinion deals only with stem-cell research, and does not consider the possible use of research embryos for projects that cannot by their nature be carried out on spare embryos. For the third category, nuclear-transfer embryos, the group concludes that making such embryos would be premature at present, in view of the extensive research still to be done on embryonic stem cells derived from spare human embryos, as well as on fetal and adult stem cells. It is this third conclusion that apparently has led you to refer to a “dramatic twist” to the debate. Nature has an excellent reputation for clarity of presentation of scientific and social issues. It is unfortunate that in this instance, when Parliament is about to give its considered opinion on whether to extend the purposes of human embryo research in the United Kingdom in order to develop new treatments for severe diseases, an article has appeared that engenders confusion rather than clarity. Anne McLaren The Wellcome/CRC Institute, Tennis Court Road, Cambridge CB2 1QR, UK

Hemoglobin heterogeneity in Venezuelan fishes

Abstract 1. 1. Hemoglobins from 125 species of tropical marine and freshwater fishes were analyzed electrophoretically. 2. 2. The mean number of hemoglobins per branchial-respiring species was 3.6, whereas aero-branchial respiring species of the Order Batrachoidiformes had a mean of 6.4. 3. 3. Hemoglobin polymorphism was observed in 9% of the species. 4. 4. The incidence of species with single hemoglobins was 11%, the highest reported from comparable studies on fish. 5. 5. The results are discussed with respect to the hypothesis that hemoglobin heterogeneity is adaptive for unstable environments.

The evolution of multiple haemoglobins in fishes

Introduction The Bohr and Root effects in teleost haemoglobins Evolution of protein polymorphism The selectionist hypothesis and haemoglobin multiplicity Functional heterogeneity of haemoglobin components in fishes Haemoglobin multiplicity and environment Haemoglobin multiplicity and levels of activity Changes in haemoglobin multiplicity due to temperature variation The neutralist hypothesis and amino acid substitution Constancy of evolutionary rate Functional constraints of evolutionary rate DNA sequence data Concluding remarks and summary Acknowledgements References page 304 305 306

Hemoglobin polymorphism in the toadfish Thalassophryne maculosa Gunther

Abstract A hemoglobin polymorphism characterized by three phenotypes is described in the toadfish, Thalassophryne maculosa Gunther. The genetic basis of the polymorphism seems to be rather simple: two alleles in one locus determine three phenotypes with different physiological properties; i.e. oxygen affinity of both blood and stripped hemolysates, root effect, and heme-heme interactions. Gene frequencies varied rather drastically in one of the four populations studied in eastern Venezuela. Although temperature variations may explain polymorphisms in some cases, it appears that environmental heterogeneity, in general, is a more feasible explanation.

Cytogenetic characterization of the silverside fish Odontesthes regia (Humboldt, 1833) (Teleostei: Atheriniformes: Atherinopsidae) from Iquique, Chile

Este trabajo describe el cariotipo de Odonthestes regia, por medio de tincion Giemsa, bandeo C, para revelar la distribucion de la heterocromatina constitutiva, y por medio de tincion con nitrato de plata e hibridacion fluorescente in situ (FISH), para localizar genes ribosomales (rADN). El recuento modal cromosomico diploide en la especie fue de 2n = 48. El cariotipo esta compuesto por un par submetacentrico (par 1), 16 pares subtelocentricos (pares 2 al 17) y 7 pares acrocentricos (pares 18 al 24). Con excepcion del par 1, no fue posible clasificar con exactitud a los cromosomas homologos, ya que las diferencias en el tamano fueron muy pequenas entre pares adyacentes. La distribucion de la heterocromatina por bandeo C permitio aparear a la mayoria de los cromosomas de la serie subtelocentrica. La tincion con plata de preparaciones metafasicas permitio la identificacion de las regiones organizadoras del nucleolo (Ag-RON) en el par 1. Los experimentos FISH mostraron que las secuencias ADNr 18S estaban localizadas, como era de esperar, en el mismo par cromosomico identificado como los portadores de Ag-RON.