High levels of genetic variation in Indian field and house mice

Genetic variation in the Indian pygmy field miceMus booduga and theMus terricolor complex and in the house mouseMus musculus tytleri was analysed electro phoretically at 20 enzymatic and nonenzymatic protein loci. The results show an unusually high genetic variation in the field mice in terms of per cent polymorphism (P = 75 to 90 at 0-95 level), observed heterozygosity (Ho = 0.215[ ± 0.213] to 0.314 [±0.236]) and average number of alleles(A = 2.0[± 0.858] to 2.38 [±0.868]). Very high values of P,Ho andA were also observed for the house mouse. Genetic distance (D) determined by using Nei’s (1978) formula in theM. terricolor complex ranged from the lowest,D = 0.082, betweenM. terricolor I and II to the highest,D = 0.155, betweenM. terricolor II and III. Genetic distance betweenM. booduga and theM. terricolor complex was 0-259 and that between the house mouseM. m. tytleri and theM. booduga-terricolor lineage was 0.285. TheseD values corroborate that the pygmy field and house mice are closely allied.     

Chromosomal and molecular divergence in the Indian pygmy field mice Mus booduga-terricolor lineage of the subgenus Mus

Mus booduga and Mus terricolor both have 2n=40. Unlike M. booduga, with all acrocentric chromosomes, M. terricolor invariably has large submetacentric X and acrocentric Y due to an increase of heterochromatin. In contrast to the conservative karyotype of the co-existing sibling species booduga, three chromosome types of terricolor are found in different populations and their divergent karyotypes have autosomal heterochromatin variations established in the homozygous condition. The average genetic distance determined from electrophoretic study of 20 protein loci ranges from lowest (D=0.106) between chromosome types I & II to highest (D=0.185) between types II & III. In terricolor, booduga and M. m. tytleri high mean values of variations per locus (range A=1.604 to 1.928) and heterozygosity per individual per locus (range H=0.180 to 0.336) have been observed. Sequence divergence of 0.39 to 1.2%, calculated from restriction profiles of mtDNA, shows that the terricolor chromosome types have diverged recently. Hybridizations between type I females and type III males gave a preponderance of males in the F1 with varying degrees of sterility. The terricolor complex is an interesting system for critical probing for the role of heterochromatin in the process of speciation. MtDNA, protein loci and AT-rich musculus-related major and minor satellite DNA data indicate that progenitors of the booduga-terricolor lineage might have evolved simultaneously with the caroli-cookii-cervicolor lineage in the evolution of the subgenus Mus.     

Allozyme variation in relation to morphology and taxonomy inMedicago sect.Spirocarpos subsect.Intertextae (Fabaceae)

Medicago intertexta andM. ciliaris have been controversially recognized as separate species. The only reliable diagnostic character, gland-tipped trichomes on the fruits inM. ciliaris, is controlled by presence of a single dominant allele, and such one-character taxonomies are debatable. Contributing to the difficulty,M. muricoleptis andM. granadensis, the other two species ofMedicago sectionSpirocarpos subsectionIntertextae, are sometimes confusingly similar toM. intertexta or to each other. Allozyme differences provided 95% verification of the suitability of the gland-tipped trichome character for separatingM. intertexta andM. ciliaris, thus corroborating their recognition as separate taxa. Several measures of allozyme variation indicated thatM. intertexta is more polymorphic than its sister species. Heterozygosity was also highest inM. intertexta, suggestive of a higher outcrossing rate, which is also consistent with larger floral size. Heterozygosity ofM. intertexta was concentrated in Sicily and nearby countries. Taxonomic difficulties in identifying SicilianM. intertexta are well known, and may be the result of interspecific hybridization and introgression.Medicago muricoleptis differed from the above two species in the frequency of several alleles, whileM. granadensis possessed numerous unique alleles consistent with its complete absence of genetic exchange with the other three substantially interfertile species.     

Isoenzyme variation in the wild relatives ofVicia faba (Fabaceae)

Electrophoretic analysis of five enzyme systems, LAP, PGI, SKDH, SOD and 6-PGDH, among 102Vicia accessions representingV. bithynica and seven species of theV. narbonensis complex, namelyV. eristalioides, V. kalakhensis, V. johannis, V. galilaea, V. serratifolia, V. narbonensis andV. hyaeniscyamus, has been performed. The recorded variation was tentatively assigned to 41 allelic genes at eight loci; intraspecific variation was observed in all species except forV. eristalioides. The results obtained were compared with the corresponding data reported earlier forV. faba. Hierarchical grouping of the investigated taxa, includingV. faba, was based onNei's genetic identities calculated from the allozyme frequency data.Vicia faba andV. bithynica were shown to be most distantly related to one another and to the remaining species investigated.Vicia serratifolia appeared to be a peripheral member of theV. narbonensis complex. The results are discussed with reference to genetic diversity and taxonomic relationships of the species under study.     

Quantitative variation of “Mus musculus-like” constitutive heterochromatin and satellite DNA-sequences in the genus Mus

The extent of conservation of constitutive heterochromatin in three species of Mus viz. M. musculus, M. booduga and M. dunni, with shared cytological properties and homologous DNA sequences has been studied. The cytological properties were investigated by doing fluorescence staining and condensation inhibition of their chromosomes with Hoechst 33258. Both the parameters indicate the occurrence of a reduced quantum of M. musculus like heterochromatin at specific sites in the other two genomes. In situ hybridization of the nick translated ³H-labelled M. musculus satellite DNA with M. booduga and M. dunni chromosomes, also corroborates our Hoechst 33258 findings and comparable variation in the amount and site of occurrence of sequences homologous to M. musculus satellite DNA in these species are noticed. The study thus provides a good example of a gradual quantitative variation of a particular type of heterochromatin and in turn of the repetitive DNA constituting it in different related species. Further since the heterochromatin in M. booduga and M. dunni is expected to contain different repetitive DNA sequences in addition to those homologous to M. musculus satellite DNA, it is proposed that a change in the balance between two or more repetitive sequences in heterochromatin may be more crucial in its evolutionary consequences rather than a mere increase or decrease of a homogeneous repetitive sequence.     

Mitochondrial DNA restriction maps ofMus booduga,Mus terricolor andMus musculus tytleri

Restriction maps of milochondrial DNA of the Indian pygmy field miceMus booduga andM. terricolor, and the house mouseM. musculus tytleri were determined with seven six-cutter restriction enzymes. The restriction map of the mitochondrial DNA of the laboratory mouseM. m. domesticus was used as a reference. Pairwise comparison was made of the mitochondrial DNAs for the presence or absence of the restriction sites, and per cent sequence divergence was calculated. The results show that the sequence divergence betweenbooduga andterricolor is 8-7% while thedomesticus-tytleri andbooduga-terricolor groups are divergent by 16-3%. The mtDNA sequence divergences we have obtained suggest that thebooduga-terricolor lineage might not have diverged before the Southeast Asiancervicolor-cookii-caroli lineage during evolution of these lineages of the subgenusMus as inferred by others earlier. On the other hand, it seems likely that these lineages evolved in parallel.     

Genetic Heterogeneity in the Indian Mus musculus

This study deals with the characterization of 10populations of M. musculus from differentgeographical locations in India. The genetics of Indianwild mice has been completely obscure and this is thefirst report on allozyme variations in the naturalpopulation. We have used a set of 24 biochemical geneticmarkers to measure levels of diversity within and amongpopulations. The allelic frequency data indicate extreme genetic variability, which is furtherenhanced by the presence of novel alleles. Overall thespecies shows a high level of heterogenity. The highlypolymorphic central populations of M. musculus cannot be assigned to any one particularsubspecies. The allelic profiles, however, indicate agradual differentiation toward the castaneus andbatcrianus subspecies lineages.     

Fructose bisphosphatase isozymes of the mouse. I. Inheritance

Electrophoretically detectable polymorphisms of fructose bisphosphatase (EC 3.1.3.11) have been found in the mouse. One polymorphism, found among inbred strains of Mus musculus and feral animals, affects the isozymes found in the muscle and in most other tissues examined but is not expressed in kidney, liver, or testis. These tissues have other electrophoretically distinct isozymes which are monomorphic in Mus musculus but are present as a different electromorph in the sympatric species Mus spretus. Breeding data have established that the genetic control of the muscle enzyme is expressed by an autosomal structural locus Fbp-1 which is distinct from that expressing the liver, kidney, and testis enzyme, Fbp-2. The organ-specific expression of the two loci suggests possible functional differences between the two products.This work was supported by the Medical Research Council.     

Genetic analysis of protein variations in Mus musculus using two-dimensional electrophoresis

We have investigated the variation of proteins from crude homogenates of mouse kidneys in several strains of Mus musculus by means of two-dimensional electrophoresis. In this study, we have used the strains C57BL/6J, DBA/2J, CD-1, M. m. castaneus, and M. m. molossinus, as well as offspring from crosses among these strains. Out of the 100 loci screened, we have found nine loci showing interstrain differences. We have been able to identify three proteins as Id-1, Car-2, and Sep-1. The remaining variants are probably new loci in the mouse. Most of the variants (seven) can be mapped to a chromosome. We have found also that differences in the protein pattern as seen on two-dimensional gels are small among subspecies of Mus musculus.     

A triose-phosphate isomerase polymorphism in the Atlantic salmonSalmo salar L.

Atlantic salmon,Salmo salar L., from four European locations show allelic variation at one of three triose-phosphate isomerase (TPI) loci (TPI-3*) when separated on horizontal starch gel electrophoresis, using either eye or liver extracts. Two common alleles (*100 and*103) and one rare allele (*97) segregate atTPI-3* with unambiguous typing being possible by observing the interlocus heterodimers. Family studies demonstrate thatTPI-3* 100 and*103 are of autosomal location and are inherited in a Mendelian fashion.TPI-3* variation can also be typed in adipose fin tissue, allowing nondestructive tissue sampling. Three loci are also active in brown trout,Salmo trutta, with two individuals being homozygous forTPI-3*, as are a small number ofS. salar from eastern Canada. The presence of this additional variable allozyme locus inS. salar is important, since genetic studies in that species have been limited by the low level of allozyme variability detectable.     

Tail length variation inMacaca fascicularis andM. mulatta

Based on collectors' measurements of 1,040 specimens, variation of relative tail length [RTL = (tail length/head and body length) × 100] has been studied inMacaca fascicularis andM. mulatta, two closely related species that replace one another in tropical Asia and subtropical Asia, respectively. RTL usually is greater than 90 inM. fascicularis and usually is less than 60 inM. mulatta; intermediate values occur in only 3.5% of specimens studied. Within each species, RTL is approximately equal in females and males. From infancy to adulthood, RTL tends to decline in both species. InM. fascicularis, RTL generally decreases with increasing latitude; inM. mulatta, RTL is approximately constant latitudinally. Where the geographic ranges of these two species meet at ca. 15°N in the Indochinese Peninsula, a few specimens have been collected in which RTL and dorsal pelage color are intermediate between those inM. fascicularis andM. mulatta. The observed pattern of variation suggests that the ranges ofM. fascicularis andM. mulatta formerly were separated by a zoogeographic barrier — perhaps during a Pleistocene glacial interval. After disappearance of the postulated barrier, the ranges of these two species apparently became contiguous and limited hybridization has occurred.     

Bioinformatics Analysis of Lactoferrin Gene for Several Species

Much attention has been focused on the study of lactoferrin due to its function in antibacterial, antiviral, antifungal, anti-inflammatory, anti-oxidant, and immunomodulatory activities. A total of 60 lactoferrin (LF) gene sequences with the complete coding regions (CDS) and corresponding amino acids belonging to 11 species were analyzed, and the differentiation within and among the species was also studied. The results showed that most of the species have the stop codon TAA, with the variation of TGA for Mus musculus. The length of the LF gene with the complete CDS varies greatly, from 2,055 to 2,190 bp, due to deletion, insertion, and stop codon mutation resulting in elongation. Observed genetic diversity was higher among species than within species, and Sus scrofa had more polymorphisms than any other species. Novel amino acid variation sites were detected within several species (8 in Homo sapiens, 6 in Mus musculus, 6 in Capra hircus, 10 in Bos taurus, and 20 in Sus scrofa), which might be used to illustrate the functional variation. Differentiation of the LF gene was obvious among species, and the clustering result was consistent with the taxonomy in the National Center for Biotechnology Information.     

Patterns of genetic differentiation in two annual bromegrasses,Bromus lanceolatus andB. hordeaceus (Poaceae)

Infraspecific genetic differentiation was analysed in two tetraploid annual bromegrasses,Bromus lanceolatus (from N Africa) andB. hordeaceus (from N Africa and France). Genetic analysis of populations was based on allozyme polymorphisms at 17 loci. Different fixed heterozygous phenotypes were scored in both species, according to their allopolyploid origin. In N Africa, more variation occurred among populations ofB. lanceolatus than ofB. hordeaceus. The variation was not randomly distributed among populations of both species. InB. lanceolatus, differentiation was correlated with climatic variables rather than with geographic distance between populations. Higher correlation of genetic differentiation with geographic distance occurred inB. hordeaceus, particularly at large geographic scale, between French and N African populations. Within each region, the populations appeared weakly genetically differentiated, even when belonging to different subspecies.     

Gene variation and gene flow inOrchis morio (Orchidaceae) from Italy

Data are presented on genetic variation at 27 enzyme loci of the Green-Winged orchid,Orchis morio, in 18 population samples from Italy. The existence in Italy of two subspecies, i.e. subspp.morio andpicta, is not supported by allozyme data. No genetic heterogeneity was found betweenmorio-like andpicta-like samples and specimens. Moreover, morphological transition between the two forms was observed in different Italian populations. The parameters of genetic variability estimated forO. morio populations are consistent with those found among monocotyledon plants, and among those outcrossing, animal-pollinated and with wind-dispersed seeds. Genetic diversity of ItalianO. morio is mostly within populations. Correspondingly, low values of interpopulational genetic distance were found. This appears to be due to high levels of gene flow, which were estimated with different methods. The lack ofO. longicornu from Italian samples, as well as of any hybrid withO. morio (F₁, backcrossed or recombinant individuals) is demonstrated on the basis of genetic data. It is concluded that recurrent reports ofO. longicornu from Italy are due to confusion withO. morio or with otherOrchis species.     

Reduced meiotic fitness in hybrids with heterozygosity for heterochromatin in the speciating<Emphasis Type="Italic">Mus terricolor</Emphasis> complex

Mus terricolor I, II and III are the three chromosomal species which differ in stable autosomal short-arm heterochromatin variations established in homozygous condition. Analysis of meiosis in the laboratory-generated F₁ male hybrids from crosses (both ways) betweenM. terricolor I and II and betweenM. terricolor I and III shows high frequencies of pairing abnormalities at pachytene. The backcross (N3 generation) male hybrids betweenM. terricolor I and II have meiotic abnormalities as in the F₁male hybrids, though to a lesser extent. They show difference in pairing abnormalities in the different karyotypic forms; the backcross hybrids heterozygous for the heterochromatic short arms have more anomalies compared to the homokaryotypic hybrids. This suggests a negative influence of the heterochromatin heterozygosity in meiotic pairing. The results indicate a role for heterochromatin variations in the development of a reproductive barrier in the speciatingM. terricolor complex.     

A new species of fossil Mus (Rodentia, Muridae) from the Indian Himalaya: Evolutionary and phylogenetic implications

A new species of fossil Mus (Rodentia, Mammalia) is reported from the Late Pleistocene fluvio-lacustrine deposits of the Kumaun sector of Indian Himalaya. The fossiliferous horizon, medium-coarse grained sand lenses embedded in the massive carbonaceous mud, is exposed at locality Dulam and is Late Pleistocene (ca. 30 ka) in age. A new species, Mus dulamensis n. sp., is proposed. Characterized by strongly distorted and moderately elongated M¹ (about 170% of M² length) with prominent conules in front of the t₂, higher magnitude of stephanodonty (between the t₁ and t₄ and between the t₃ and t₆), moderately reduced M³ (about 56% of M² length) and stronger connection between the cusps, this species is distinct from all other species of the genus and is included in the “booduga group”. I suggest that M. dulamensis n. sp. is comparatively more derived than M. auctor, M. flynni, M. jacobsi and Mus sp. and it may have given rise to M. booduga or M. dunni. It is further suggested that presently living M. booduga and M. dunni are more specialized than Mus dulamensis n. sp.     

Speciation inVirgilia (Fabaceae): Allopatric divergence followed by introgression?

Levels of variation revealed by starch gel-electrophoresis were compared with morphological and chemical variation within and among the species and subspecies ofVirgilia:V. oroboides subsp.oroboides, V. oroboides subsp.ferruginea andV. divaricata. The data sets exhibited concordance in that all point to a very close relationship between the taxa. Differences are mostly quantitative and an overlapping east-west gradient of character variation is indicated. Analysis of morphological and chemical characters showed thatV. oroboides subsp.ferruginea andV. divaricata are relatively distinct, whereas allozyme analysis indicated a high degree of genetic similarity among populations of these two taxa. The observed pattern of variation suggests relatively recent speciation with subsequent introgressive hybridisation resulting in a geographical and ecological gradient.     

Diazepam phase shifts the circadian clock of the field mouseMus booduga

Single 2h administration of diazepam (benzodiazepine) in 3.5% ethanol solution was found to evoke advance and delay phase shifts in the locomotor activity rhythm in the field mouseMus booduga. Through such pulsed administration of diazepam at various phases of circadian rhythm a phase response curve could be constructed. Phase advance occurred during early subjective day (CT 2) and phase delays were observed in the remaining phases. The shape of the diazepam phase response curve is similar to the general shape of the phase response curves generated by intraperitoneal injections of other benzodiazepines in hamsters. The phase shifting action of diazepam may be explained by its agonistic action on the neurotransmitter gamma-aminobutyric acid.     

Genetic structure,allozyme-habitat associations and reproductive fitness in Gypsophila fastigiata (Caryophyllaceae)

Relationships between allozyme differentiation, habitat variation and individual reproductive success were examined in local populations of a perennial herb, Gypsophila fastigiata, on the Baltic island of Öland (Sweden). Relatively little (c. 2%) of the total allozyme diversity in this largely outcrossing species is explained by differentiation between sites tens of kilometres apart. The low level of geographic differentiation suggests that gene flow between sites is, or has recently been, extensive. Yet the component of allozyme diversity due to differentiation between plots (only tens of meters apart) within sites is 3 times larger than the between-site component of diversity. Allozyme variation, especially at the Pgi-2 locus, is significantly associated with habitat variation within sites. Different allele x habitat combinations for the Pgi-2 locus are associated with differences in individual reproductive fitness. Differential selection in different local habitats may thus contribute to the fine-scale structuring of genetic diversity within sites.