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PubMed1976

Robertsonian metacentrics in the mouse.

A survey is given on the occurrence, the geographic origin and the arm composition of 27 Robertsonian fusion metacentric chromosomes of wild populations of the mouse. Their study is of twofold interest: a) it is possible to introduce these naturally occuring metacentrics in laboratory strains for experimental use. At present, altogether 34 metacentric chromosomes of different composition are available including 7 cases of metacentrics known form laboratory strains of the mouse. b) With the search for metacentrics in the mouse and with their identification insights are permitted in the role of Robertsonian changes in the course of mammalian evolution--Several separate populations of the mouse with different sets of multiple (up to 9) metacentrics have been found in Switzerland and Italy. Some of the individual metacentrics may occur in different populations. The participation of an acrocentric autosome in the formation of metacentrics seem to be at random, but the sex chromosomes are never included in a metacentric.--Homology of the arms involved in metacentrics is conserved, so that in meiosis of interpopulation hybrids is due to mechanisms of segregational imbalance and subsequent prenatal elimination of fetal offspring, but it follows also the pattern of male limited hybrid sterility.--From an evolutionary view point, karyotype rearrangements of Robertsonian type may initiate reproductive isolation, which prepares the ground for further genetic diversification and, as in the case of the mouse, of incipient speciation.

Animals↗
PubMed1993

Mismatch recognition in chromosomal interactions and speciation.

Homologous chromosomes interact during meiosis by means of proteins involved in recombination and in the recognition and repair of mismatched base pairs. Recombination proteins bring homologous chromosomes or chromosomal regions together by facilitating the search for DNA homology and by catalyzing strand exchange between homologous molecules or regions. Mismatch recognition and repair proteins act as editors of recombination and appear to disrupt those DNA associations that contain mismatched base pairs. Thus, it may be that, as chromosomes diverge in their primary sequence and become increasingly polymorphic, recombinational interactions leading to chromosome pairing and recombination tend to be inhibited. Decreasing homologous interactions within and between chromosomes will clearly contribute to maintaining the integrity of individual chromosomes and may ultimately lead, as a result of sterile meioses, to the reproductive isolation of closely related species.

Biological Evolution↗
PubMed1978

Evidence for the presence of two sympatric species of mice (genus Mus L.) in southern France based on biochemical genetics.

Populations of mice established outdoors as well as indoors have been investigated at 24 loci using starch gel electrophoresis. Two reproductively isolated groups are recognized, one of which is referable to a house mouse subspecies, Mus musculus brevirostris, and the other to a different species. Mus spretus, contrary to the view of Schwarz and Schwarz that only one species of Mus is present in the Mediterranean Basin. The genetic distance between these two groups is larger than between any pair of investigated subspecies of M. musculus. M. m. brevirostris is biochemically almost indistinguishable from M. m. domesticus. On the other hand, M. spretus exhibits several allelic variants unknown or at most very infrequent in M. musculus, as for instance at the lactate dehydrogenase B-chain locus.

Animals↗
PubMed1990

Genetic polymorphism of urine deoxyribonuclease I isomerases of subterranean mole rats, Spalax ehrenbergi superspecies, in Israel: ecogeographical patterns and correlates.

Genetic polymorphism of urine deoxyribonuclease I (DNase I) of mole rats was analyzed by isoelectric focusing in a thin-layer polyacrylamide gel (IEF-PAGE). One hundred and three subterranean mole rats, comprising 13 populations belonging to the four chromosomal species (2n = 52, 54, 58, 60) of the actively speciating Spalax ehrenbergi superspecies in Israel, were tested. The following results were indicated. (i) Spalax DNase I consisted of 6-12 major isozymes. (ii) Four phenotypes (numbers in parentheses) were 1 (92), 1-2 (5), 1-3 (4), and 2 (1). The decreasing order of genetic diversity, He, in the four species was 0.37, 0.13, 0.10, and 0.0 for 2n = 58, 52, 54, and 60, respectively. (iii) Spearman rank correlations and multiple regression analyses indicated associations of allele frequencies and genetic diversity with climatic and vegetation factors. We concluded that (a) climatic selection, either directly or indirectly through plant (i.e., food resources) diversity, plays an important role in DNase genetic differentiation and (b) no gene flow and introgression occur between the recent derivative of speciation (2n = 60) and its ancestor (2n = 58), suggesting the operation of reproductive isolation between both species despite natural hybridization.

Animals↗
PubMed1995

Mating behaviour in mixed infections of Schistosoma haematobium and S. mattheei.

In mixed infections of Schistosoma haematobium and S. mattheei, homospecific and heterospecific pairs are formed, with a preponderance of homospecific pairs indicating the existence of a mate preference system. S. haematobium apparently exhibits a greater specific mate recognition system than does S. mattheei. In sequential infections when mice are exposed to S. mattheei 4 weeks after infection with S. haematobium, S. haematobium males are better at pairing with S. mattheei females than are S. mattheei males. Hence, genetic exchanges between S. haematobium and S. mattheei giving rise to viable hybrids poses the problem of the genetic identity of these species of schistosomes. The most important reproductive isolating mechanisms are definitive host specificity, S. haematobium being primarily a parasite of man, whereas S. mattheei is a parasite of domestic stock and wild ungulates, and the preference for homospecific pairings in simultaneous infections. In contrast, when S. haematobium is the older infection, S. haematobium males are better than S. mattheei males at pairing with females of either species. Hybridisation is the likely outcome of such interactions. The lack of viability of S. mattheei male X S. haematobium female indicates genetic differences between the two species. Occurrences of natural hybridisation between S. haematobium and S. mattheei may lead to a change in the response of the parasite to chemotherapeutic treatment.

Animals↗
PubMed1989

Applying the species concept to plant viruses.

Plant virologists who maintain that the concept of species cannot be applied to viruses argue their case in terms of an obsolete concept of biological species defined by gene pools and reproductive isolation and applicable only to sexually reproducing organisms. In fact, various species concepts have been used by biologists and some of them are applicable to asexual organisms. The rationale for applying the species concept in virology is that viruses are biological entities and not chemicals: they possess genes, replicate, specialize, evolve and occupy specific ecological niches. The following definition is proposed: a virus species is a polythetic class of viruses constituting a replicating lineage and occupying a particular ecological niche. Such a definition of the species category does not and cannot provide a list of diagnostic properties for recognizing members of a particular virus species. It should also be stressed that a single property such as an arbitrary level of genome homology or the extent of serological relationship always fails to establish membership in a polythetic class. A binomial system of nomenclature is advocated in which the vernacular English name of the plant virus is adopted as the species name and the group name is assimilated to the level of genus. Adoption of this system would ensure that a universal classification system based on the classical categories of species, genus, and family becomes possible for all viruses.

Phylogeny↗
PubMed1978

[Hybridization between Mus musculus L. and Mus spretus Lataste under laboratory conditions (author's transl)].

2 species of mice Mus musculus brevirostris and Mus spretus are sympatric in Southern France and reproductively isolated. However, under laboratory conditions, they breed and give fully viable F 1 hybrids. This indicates that premating isolating mechanisms probably occur in nature and have yet to be investigated. Moreover, it now enables us to introduce new genetical markers in laboratory strains.

Animals↗
PubMed1976

Assortative mating between chromosome forms of the mole rat, Spalax ehrenbergi.

Females of two parapatric chromosomal forms (2n = 52 and 2n =58) of the fossorial mole rat, Spalax ehrenbergi, in Israel, were tested for mate selection between two alternative, a homo- and a heterochromosomal, males. Estrous females significantly preferred the male of their own chromosomal form, on the basis of several behavioural criteria. The evolutionary significance of the positive assortative mating found, lies presumably in reinforcing reproductive isolation between the chromosome forms, thereby contributing to finalize speciation.

Animals↗
PubMed1991

Sequences homologous to Tc(s) transposable elements of Caenorhabditis elegans are widely distributed in the phylum nematoda.

To have a better understanding of the evolutionary history of mobile elements within the nematodes, we examined the distribution and the conservation of homologues to transposable elements from Caenorhabditis elegans (Tc1, Tc2, Tc3, Tc4, Tc5, and FB1) in 19 nematode species belonging to the class Secernentea. Our results show that Tc1 elements display a distribution restricted to the family Rhabditidae with poor conservation. The Tc2 and FB1 homologous elements have the same patchy distribution within the Rhabditidae. They were only found in Caenorhabditis and in Teratorhabditis. The Tc3 element is widely distributed among nematode species. Tc3 homologous elements are present in the majority of the Rhabditidae but also in two genera within the family Panagrolaimidae, and in Bursaphelenchus, which belongs to the order Aphelenchida. Tc4 and Tc5 homologues show the most limited distribution of all tested elements, being strictly limited to C. elegans. These data indicate that in some cases, the distribution of transposable elements in the nematode cannot be explained by strict vertical transmission. The distribution of Tc3, Tc4, and Tc5 suggests that horizontal transmission may have occurred between reproductively isolated species during their evolutionary history.

Animals↗
PubMed1989

Mitochondrial DNA evolution in the Drosophila nasuta subgroup of species.

The Drosophila nasuta group consists of about 12 closely related species distributed throughout the Indo-Pacific region. They are of great interest because of their evolutionary idiosyncrasies including little morphological differentiation, the ability to intercross in the laboratory often producing fertile offspring, and substantial chromosomal evolution. Studies of metric traits, reproductive isolation, and chromosomal and enzyme polymorphisms have failed to resolve the phylogeny of the species. We report the results of a survey of the mitochondrial DNA (mtDNA) restriction patterns of the species. The phylogeny obtained is consistent with other available information and suggests that D. albomicans may represent the ancestral lineage of the group. The amount of polymorphism in local populations (pi = 1.0% per site) is within the typical range observed in other animals, including Drosophila. The degree of differentiation between species is, however, low: the origin of the group is tentatively dated about 6-8 million years ago. This study confirms the usefulness of mtDNA restriction patterns for ascertaining the phylogeny of closely related species.

Animals↗
PubMed1996

Fanconi anaemia in Italy: high prevalence of complementation group A in two geographic clusters.

Cell fusion studies using lymphoblastoid cell lines from Fanconi anaemia (FA) patients have identified five complementation groups (FA-A to FA-E) among European FA patients. In Italy, of the 45 FA families referred to the Italian Registry of Fanconi Anaemia (RIAF), 15 took part in a project for the identification of complementation groups. Since three immortalized lymphoblast lines were resistant to a cross-linking agent, we analysed only 12 patients by complementation analysis and found that 11 belong to complementation group A. Four and seven families came from two geographic clusters in the Veneto and Campania regions, respectively, which are thought to consist of aggregates of related families in reproductive isolation. The clinical characteristics of the patients showed both intra- and interfamilial heterogeneity, although overall the disease had a relatively mild course. Since the populations in both Veneto and Campania are likely to represent genetic isolates, our finding predicts linkage disequilibrium for markers flanking the FAA gene. DNAs from these FA families may thus be utilized for positional cloning of this gene through haplotype disequilibrium mapping.

Cell Fusion↗
PubMed2006

Lyriform slit sense organs on the pedipalps and spinnerets of spiders.

Lyriform slits sense organs (LSSO) are a precise assembly of stress detecting cuticular slit sensilla found on the appendages of arachnids. While these structures on the legs of the wandering spider Cupennius salei are well studied in terms of morphology, function and contribution to behaviour, their distribution on pedipalps and spinnerets of spiders is not well explored. A study was therefore carried out to observe the distribution of LSSO on pedipalps and spinnerets of some spider species. Haplogyne spiders belonging to family Pholcidae have a simple complement of LSSOs represented by one or two LSSOs on their femur. The entelegyne spiders possess a complex assembly of LSSOs on the distal segments of their pedipalps. Various types of LSSOs are found on the pedipalps indicating a capacity for analysis of complex cuticular stress. It is suggested that the complexity of LSSOs on pedipalps of entel-egyne spiders relates to courtship and spermatophore transfer and may help in reproductive isolation. Lack of LSSOs on the distal segments of pedipalps leads us to infer that unlike legs, pedipalps are less likely to receive vibratory input through their distal segments. Spinnerets have a relatively simple complement of LSSOs. One LSSO is found only on anterior spinnerets and it is a common feature observed among spiders, irrespective of the variations in web building behaviour. The orb-weaving araneid Argiope pulchella, however, has two LSSOs on the anterior spinneret. As non-web builders and orb weavers do not differ markedly in terms of LSSOs on the spinnerets and LSSOs are simple in nature (type A), it is likely that spinning and weaving are not largely regulated by sensory input from LSSOs on the spinnerets.

Animals↗
PubMed2003

Gene flow among different taxonomic units: evidence from nuclear and cytoplasmic markers in Cedrus plantation forests.

Hybridization and introgression are important natural evolutionary processes that can be successfully investigated using molecular markers and open- and controlled-pollinated progeny. In this study, we collected open-pollinated seeds from Cedrus atlantica, Cedrus libani and C. libani x C. atlantica hybrids from three French-plantation forests. We also used pollen from C. libani and Cedrus brevifolia to pollinate C. atlantica trees. The progeny were analyzed using three different types of molecular markers: RAPDs, AFLPs and cpSSRs. Chloroplast DNA was found to be paternally inherited in Cedrus from the progeny of controlled-crosses. Heteroplasmy, although possible, could not be undoubtedly detected. There was no indication of strong reproductive isolating barriers among the three Mediterranean Cedrus taxa. Gene flow between C. atlantica and C. libani accounted for 67 to 81% of viable open-pollinated seedlings in two plantation forests. We propose that Mediterranean Cedrus taxa should be considered as units of a single collective species comprising two regional groups, North Africa and the Middle East. We recommend the use of cpSSRs for monitoring gene flow between taxa in plantation forests, especially in areas where garden specimens of one species are planted in the vicinity of selected seed-stands and gene-conservation reserves of another species.

Cedrus↗
PubMed2003

Comparative genetic linkage maps of Eucalyptus grandis, Eucalyptus globulus and their F1 hybrid based on a double pseudo-backcross mapping approach.

Comparative genetic mapping in interspecific pedigrees presents a powerful approach to study genetic differentiation, genome evolution and reproductive isolation in diverging species. We used this approach for genetic analysis of an F(1) hybrid of two Eucalyptus tree species, Eucalyptus grandis (W. Hill ex Maiden.) and Eucalyptus globulus (Labill.). This wide interspecific cross is characterized by hybrid inviability and hybrid abnormality. Approximately 20% of loci in the genome of the F(1) hybrid are expected to be hemizygous due to a difference in genome size between E. grandis (640 Mbp) and E. globulus (530 Mbp). We investigated the extent of colinearity between the two genomes and the distribution of hemizygous loci in the F(1) hybrid using high-throughput, semi-automated AFLP marker analysis. Two pseudo-backcross families (backcrosses of an F(1) individual to non-parental individuals of the parental species) were each genotyped with more than 800 AFLP markers. This allowed construction of de novo comparative genetic linkage maps of the F(1) hybrid and the two backcross parents. All shared AFLP marker loci in the three single-tree parental maps were found to be colinear and little evidence was found for gross chromosomal rearrangements. Our results suggest that hemizygous AFLP loci are dispersed throughout the E. grandis chromosomes of the F(1) hybrid.

Chromosome Mapping↗
PubMed2004

Genetic divergence in the cacophony IVS6 intron among five Brazilian populations of Lutzomyia longipalpis.

Genes involved in the reproductive isolation are particularly useful as molecular markers in speciation studies. Lutzomyia longipalpis (Diptera: Psychodidae: Phlebotominae), a putative species complex, is a vector of visceral leishmaniasis in Latin America. We isolated from this species a fragment homologous to cacophony, a Drosophila gene that encodes features of the lovesong, an acoustic signal that is important in the sexual isolation of closely related species and known to vary considerably among L. longipalpis putative siblings species. Using an intron of the sandfly cacophony as a marker, we analyzed the molecular variation and sequence divergence among five populations of L. longipalpis from Brazil, three allopatric (Jacobina, Lapinha and Natal) and two putative sympatric sibling species from the locality of Sobral. A high level of polymorphism was found and analysis of the data indicates that very little gene flow is occurring among the populations of Jacobina, Lapinha, and Natal. A high level of differentiation was also observed between the two putative sympatric species of Sobral, one of which seems to be the same sibling species found in Natal, while the other is somewhat more related to Jacobina and Lapinha. However, the amount of estimated gene flow among the Sobral siblings is about seven times higher than the previously estimated for period, another lovesong gene, perhaps indicating that introgression might be affecting cacophony more than period. The results suggest that L. longipalpis is not a single species in Brazil, but it is yet not clear whether the different populations studied deserve species status rather than representing an incipient speciation process.

Analysis of Variance↗
PubMed2026

Genomic and Structural Analysis of Gamete Recognition Proteins in a Broadcast Spawning Echinoderm Mesocentrotus franciscanus.

Gamete recognition proteins are expressed on the surfaces of sperm and eggs, where they mediate interactions between gametes. The genetic basis for gamete recognition proteins, as well as their structure and interactions, have yet to be fully resolved. Using a new high-quality de novo genome assembly for the sea urchin Mesocentrotus franciscanus, we investigated the genomic structure, expression, and protein forms of several gamete recognition proteins: sperm bindin, egg receptor for sperm (HSP110), and egg bindin receptor (EBR1), as well as the receptor for egg jelly (REJ) and its paralogs. To inform future population genetic and evolutionary studies, we resolve the genomic structure of the large EBR1 protein, identifying fewer tandem CUB-TSP1 repeats in EBR1 compared to the initial characterization of this protein. As expected for an egg receptor for sperm, EBR1 is highly expressed in female reproductive tissues (eggs and female gonad), compared to other tissues. In contrast, HSP110 shows similar levels of expression across male and female reproductive tissues, as well as across non-reproductive tissues and development stages. HSP110 might be a pleiotropic gene that in part influences fertilization. Using protein structural modeling and functional domain predictions, we propose hypotheses about potential interactions among EBR1, bindin, and HSP110 proteins that may provide insight into sperm-egg interactions in sea urchins. Resolving the genomic structure of genes encoding gamete recognition proteins, in combination with functional annotations and protein structural modeling, enables deeper investigation into the consequences of variation in gamete recognition proteins and the evolution of reproductive isolation.

Mesocentrotus franciscanus↗
PubMed1999

Growth Rates of Marine Ciliates on Diverse Organisms Reveal Ecological Specializations within Morphospecies.

Abstract The growth rate of 31 stocks of Euplotes, a cosmopolitan, marine, unicellular protist, on six food species representing two different food types, microalgae and bacteria, has been determined. The 31 stocks represented nine reproductively isolated groups (biological species?) based on breeding relationships. Three morphospecies, E. vannus, E. crassus, and E. minuta, each with both autogamous and cross-breeding breeding groups, were included. The mean number of fissions completed in 5 days of a breeding group growing on one of the six food species varied from zero to 17.06. There is a strong interaction between morphospecies and food type. The largest morphospecies, E. vannus, translates the nutritional content of algae into growth better than it translates that of bacteria, while the reverse is true for E. minuta, the smallest morphospecies. Autogamous breeding groups grow more rapidly on algae than on bacteria when compared to cross-breeding groups in the same morphospecies. Two breeding groups cannot grow on Escherichia coli. ANOVA of fissions completed in 5 days revealed significant main effects and interactions between many hierarchical levels of stocks and food species. These significant interactions indicate that genetically determined ecologically important information is present at all taxonomic levels-morphospecies, breeding system, breeding group, and stock. As all these levels are biologically meaningful, measuring biodiversity in the E. vannus-crassus-minuta complex solely on morphospecies will inadequately represent the ecological diversity present in the organisms and their environment.

Journal Article↗
PubMed2004

Genetic analysis of X-linked hybrid sterility in the house mouse.

Hybrid sterility is a common postzygotic reproductive isolation mechanism that appears in the early stages of speciation of various organisms. Mus musculus musculus and Mus musculus domesticus represent two recently separated mouse subspecies particularly suitable for genetic studies of hybrid sterility. Here we show that the introgression of Chr X of M. m. musculus origin (PWD/Ph inbred strain, henceforth PWD) into the genetic background of the C57BL/6J (henceforth B6) inbred strain (predominantly of M. m. domesticus origin) causes male sterility. The X-linked hybrid sterility is associated with reduced testes weight, lower sperm count, and morphological abnormalities of sperm heads. The analysis of recombinant Chr Xs in sterile and fertile males as well as quantitative trait locus (QTL) analysis of several fertility parameters revealed an oligogenic nature of the X-linked hybrid sterility. The Hstx1 locus responsible for male sterility was mapped near DXMit119 in the central part of Chr X. To ensure full sterility, the PWD allele of Hstx1 has to be supported with the PWD allelic form of loci in at least one proximal and/or one distal region of Chr X. Mapping and cloning of Hstx1 and other genes responsible for sterility of B6-X PWD Y B6 males could help to elucidate the special role of Chr X in hybrid sterility and consequently in speciation.

Acrosome Reaction↗