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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↗

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↗

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↗

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↗

PubMed1991

Genetic evidence for three species within Pseudoterranova decipiens (Nematoda, Ascaridida, Ascaridoidea) in the North Atlantic and Norwegian and Barents Seas.

Genetic variation of 1017 specimens of codworm, Pseudoterranova decipiens, collected from fish and seals at 23 sampling locations in the North Atlantic and Norwegian and Barents Seas, was analysed on the basis of 16 enzyme loci. Three reproductively isolated species, provisionally designated P. decipiens A, B and C, were detected, showing distinct alleles at the following loci: Mdh-1, 6Pgdh, Np, Pgm, Est-2 (between species A and B); Mdh-3, 6Pgdh, Np, Sod-1, Adk, Pgm, Est-2, Mpi (between A and C); Mdh-1, Mdh-3, Sod-1, Adk, Pgm, Est-2, Mpi (between B and C). One F1 hybrid was observed between P. decipiens A and B, but this apparently does not lead to any gene exchange between the two species, which do not show any evidence of introgression. No hybrids or introgressed individuals were observed between P. decipiens C and either A or B. Genetic distances among conspecific populations were low (average Nei's D 0.001-0.005), even though they were collected thousands of kilometres apart, indicating high levels of gene flow within each of the three species. The values of Nei's index D were 0.44 between P. decipiens A and B, 0.57 between B and C, and 0.79 between A and C. Estimated evolutionary divergence times, using Nei's formula, range from 2 to 4 million years. Differences between P. decipiens A, B and C were also found with respect to genetic variability, morphology, geographical distribution and hosts. Mean heterozygosity values of 0.08, 0.05 and 0.02 were obtained for P. decipiens A, B and C, respectively. Preliminary morphological examination of adult males, previously identified by multilocus electrophoresis, revealed differences in the relative size and pattern of caudal papillae. P. decipiens B is widespread in the study area, whereas P. decipiens A was found only in the North-East Atlantic and Norwegian Sea. In this area P. decipiens A is most common in the grey seal, Halichoerus grypus, while the common seal, Phoca vitulina, is the main host for P. decipiens B. In Canadian Atlantic waters, where P. decipiens A is apparently absent, P. decipiens B infects both grey and common seals; a few specimens were also found in the hooded seal, Cystophora cristata. The only definitive host so far identified for P. decipiens C is the bearded seal, Erignathus barbatus; P. decipiens C appears to be widespread, occurring in both the North-West Atlantic and Barents Sea.

Animals↗

PubMed1992

Sexual pheromones in lipids and other fractions from urine of the male mole rat, Spalax ehrenbergi.

Spalax ehrenbergi mole rats are blind, solitary, territorial, aggressive, subterranean rodents with a yearly breeding season that peaks in December and January. We confirm here an earlier report that estrous females are attracted to substances present in the urine of homospecific as compared to heterospecific adult males. We have also found that nonestrous female mole rats show avoidance behavior to the same homospecific urine. Our objective was to ascertain the nature of the pheromone(s) and gain insight as to its possible role in reproductive isolation and speciation. An active principle, detected in either two- or three-choice behavior tests, was found to be extractable from urine by methylene chloride (CH2Cl2) and mainly found in the neutral lipid fraction. Total lipids were chromatographed by thin layer chromatography on silica gel G60 plates. Most of the activity was found in a zone bounded by Rfs 0.2 and 0.7. Cholesterol, other sterols, and ethyl esters of fatty acids chromatographed in this zone as determined by standards and staining. Ethyl esters of fatty acids were also detected in this fraction by GC/MS analysis. Although a large amount of activity was found in lipids, it only accounted for about 1% of that found in urine. Some activity may have been destroyed or lost during the extraction procedure and some may remain in a lipid insoluble form. Preliminary tests of lipid extracts of various portions of the male urogenital tract revealed pheromonal activity present, particularly in tissues associated with testes, epididymis, prostate, and bladder.

Animals↗

PubMed1985

Further analysis of intraspecific variation in Trypanosoma brucei using restriction site polymorphisms in the maxi-circle of kinetoplast DNA.

We have compared the maxi-circle kinetoplast DNA of 21 Trypanosoma brucei sp. stocks by analysis of restriction sites for nine restriction endonucleases. The analysis shows most of these stocks to have a maxi-circle sequence similar to that of 11 previously analysed stocks, with a difference of less than 3% between any two stocks. However, seven stocks stand out from the rest with at least two sites lost or gained for six of the nine restriction enzymes used. These seven distinctive stocks fall into two groups with some shared and some unique polymorphisms. One group had already been designated the kiboko group on the basis of isoenzyme patterns, but the relationship between nuclear markers and maxi-circle type is less clear-cut for the other group, designated sindo. Both groups seem to be in a wild animal-tsetse fly transmission cycle, with occasional infections in domestic stock, and may be reproductively isolated from the main T. brucei sp. population. The existence of the kiboko and sindo sub-groups shows that the maxi-circle is not shielded from evolutionary change. The lack of difference observed between the maxi-circles of the majority of T. brucei sp. stocks, including the gambiense and rhodesiense variants, must therefore reflect their close homology. Two geographical trends occur in T. brucei as a whole: (a) a trend in maxi-circle size, with increasing length of the variable region from West to East Africa, and (b) a greater frequency of certain restriction enzyme polymorphisms in East African stocks as compared to West African stocks.

Animals↗

PubMed1987

Kinetoplast DNA of Trypanosoma evansi.

We show here that the kinetoplast DNA (kDNA) networks from six Trypanosoma evansi strains differ from those of T. brucei by their lack of maxi-circles and absence of mini-circle sequence heterogeneity. The lack of maxi-circles is sufficient to account for the inability of T. evansi to multiply in tsetse flies, since this requires functional mitochondria containing maxi-circle gene products. Judged by restriction enzyme analysis, five of the six T. evansi strains contain mini-circles that differ less than 4% in sequence. This type A mini-circle is found in strains from East Africa, West Africa and South America. Another strain from East Africa contains a very different mini-circle (type B), which shows about the same degree of hybridization to type A mini-circles as to a mini-circle from T. brucei. We propose that the pronounced sequence heterogeneity of the mini-circles of T. brucei has arisen by recombination of strains that had diverged for long periods of time in reproductive isolation. We further propose that the homogeneous mini-circles of T. evansi (and T. equiperdum) reflect the inability of species to mate. This proposal implies that mini-circle heterogeneity indicates (infrequent) genetic exchange and that all kinetoplastid flagellates with heterogeneous mini-circles exchange DNA.

Animals↗

PubMed1992

Periodicity and diversity in ant mating flights.

1. Flight hours and seasons are alike within species, but differ among species and among genera. 2. Laboratory studies indicate internal circadian control of the phase relation to the light-dark cycle, with field evidence for modification by temperature (or other environmental variables). 3. In at least two species there is abrupt loss of obvious rhythm after mating, suggesting some special function before loss, e.g. to facilitate cross-breeding within species or reproductive isolation between species.

Animals↗

PubMed1989

Effects of the chitin synthesis inhibitor diflubenzuron on development of Ascaris suum and Haemonchus contortus.

The potential of the chitin synthesis inhibitor diflubenzuron (DFB) to alter the development of the parasitic nematodes (Ascaris suum and Haemonchus contortus was investigated. DFB given orally (10 mg kg-1 per day for 30 days) to sheep inoculated with H. contortus infective larvae did not prevent the establishment of adults or affect fecal egg output. However, there was a significant (greater than 90%) decrease in the number of infective larvae recovered from fecal cultures derived from lambs harboring H. contortus adults that were treated with DFB. DFB did not affect egg hatching. Oral administration (10 mg kg-1 per day for 20 days) of DFB to swine harboring adult A. suum adults had no effect on the adult worm burden or on egg morphology, but eggs removed from worms obtained from DFB-treated swine contained less chitin than eggs removed from untreated control swine. DFB also inhibited chitin synthesis in vitro in the isolated reproductive tract of A. suum adults. These results indicate that DFB at high doses can inhibit the subsequent development of H. contortus larvae in the feces. Since H. contortus larvae lack chitin, DFB may act on these larvae by a mechanism independent of a direct effect on chitin synthesis.

Animals↗

PubMed1978

Esterase and malate dehydrogenase isozyme polymorphisms in 15 Artemia populations.

1. Starch gel electrophoresis of adult brine shrimps from 15 populations revealed little intrapopulation polymorphism in NAD-dependent malate dehydrogenase (MDH) isozymes or in the two fastest esterases (demonstrated with alpha-naphthyl propionate as substrate). 2. Interpopulation differences could be summarized as three different electrophoresis band patterns for the five- to seven-banded MDH isozymes and another three patterns for the two fastest esterases. 3. These differences in electrophoresis patterns divide the 15 Artemia populations into four categories (each containing one to seven populations) which may be distinguished by isozyme content and which are congruent with categories established by the criterion of reproductive isolation in an earlier study.

Animals↗

PubMed1983

Comparative progesterone concentrations in two Peromyscus species.

1. Plasma progesterone concentrations were measured by radioimmunoassay in the oldfield mouse (Peromyscus polionotus) and the deermouse (P. maniculatus) at estrus and at 5-day intervals during pregnancy. 2. P. polionotus had significantly higher progesterone levels, both at estrus and during gestation. 3. The level was markedly less in female P. polionotus bearing interspecific (P. polionotus x P. maniculatus) hybrid conceptuses than in those with conspecific conceptuses. 4. It is postulated that the reduced progesterone level in females bearing hybrid fetuses may be responsible for reproductive failure which regularly occurs when this cross is attempted. 5. An endocrine difference of this magnitude could represent an incipient reproductive isolating mechanism.

Animals↗

PubMed1983

Isozymic differentiation of two sibling species of Squatina (chondrichthyes) in South Brazil.

Two sympatric morphotypes of the nominal species Squatina argentina from South Brazil are compared by the frequencies of 25 isozymes distributed over 14 presumptive loci. The Nei's Genetic Identity index obtained in a comparison of the populations is of 0.71. The loci EST-2 and EST-4 are fixed at different isozymes for each population, indicating a reproductive isolation between them. The most significant morphological and meristical differences between the morphotypes are the presence or absence of dorsal spines and the dental formula. The agreement between these characteristics and the genetical data indicates that the two morphotypes belong to different species.

Animals↗