The material ancestry and approximate age of parthenogenetic species of Caucasian rock lizards (Lacerta: Lacertidae)

Restriction enzymes were used to assay variation among mitochondrial DNAs from parthenogenetic and sexual species of Lacerta. This permitted identification of the sexual species that acted as the maternal parent of the various hybrid-parthenogenetic lineages. Lacerta mixta was the maternal parent for both L. dahli and L. armeniaca, L. valentini was the maternal parent for L. uzzelli, and L. raddei was the maternal parent of L. rostombekovi. The maternal ancestry of L. unisexualis is not as clear. The sample of L. nairensis was very similar to one from a population of L. raddei and either species could be the maternal parent of L. unisexualis. The parthenogenetic species all had very low nucleotide diversity in absolute terms and in comparison to their sexual relatives. The close similarity between mtDNAs from the parthenogenetic species and their respective sexual maternal ancestor species provides strong evidence for the recent origin of the parthenogens. The low diversity of the parthenogens indicates that few females were involved in their origins; the maternal parents of L. dahli and L. armeniaca could have come from a single population. The patterns of mtDNA variation in Lacerta are very similar to those in Cnemidophorus and Heteronotia, establishing recent and geographically restricted origins as a general feature of parthenogenetic lizards.     

Phylogeography of the fire-bellied toads Bombina: independent Pleistocene histories inferred from mitochondrial genomes

The fire-bellied toads Bombina bombina and Bombina variegata, interbreed in a long, narrow zone maintained by a balance between selection and dispersal. Hybridization takes place between local, genetically differentiated groups. To quantify divergence between these groups and reconstruct their history and demography, we analysed nucleotide variation at the mitochondrial cytochrome b gene (1096 bp) in 364 individuals from 156 sites representing the entire range of both species. Three distinct clades with high sequence divergence (K2P = 8-11%) were distinguished. One clade grouped B. bombina haplotypes; the two other clades grouped B. variegata haplotypes. One B. variegata clade included only Carpathian individuals; the other represented B. variegata from the southwestern parts of its distribution: Southern and Western Europe (Balkano-Western lineage), Apennines, and the Rhodope Mountains. Differentiation between the Carpathian and Balkano-Western lineages, K2P approximately 8%, approached interspecific divergence. Deep divergence among European Bombina lineages suggests their preglacial origin, and implies long and largely independent evolutionary histories of the species. Multiple glacial refugia were identified in the lowlands adjoining the Black Sea, in the Carpathians, in the Balkans, and in the Apennines. The results of the nested clade and demographic analyses suggest drastic reductions of population sizes during the last glacial period, and significant demographic growth related to postglacial colonization. Inferred history, supported by fossil evidence, demonstrates that Bombina ranges underwent repeated contractions and expansions. Geographical concordance between morphology, allozymes, and mtDNA shows that previous episodes of interspecific hybridization have left no detectable mtDNA introgression. Either the admixed populations went extinct, or selection against hybrids hindered mtDNA gene flow in ancient hybrid zones.     

GYNOGENETIC REPRODUCTION IN HYBRID MOLE SALAMANDERS (GENUS AMBYSTOMA)

Ambystoma platineum, a unisexual clonal triploid taxon of mole salamander, originated by hybridization between the Mendelian species A. jeffersonianum and A. laterale. Studies of lampbrush chromosomes indicated that A. platineum reproduces gynogenetically, that is, sperm from a sexual host species is required to activate egg development but makes no genetic contribution to the developing embryo. Nevertheless, electrophoretic diversity in populations of some hybrid Ambystoma suggested continual in situ recreation of unisexual hybrids and bidirectional gene exchange between the parental species and the hybrids. A. platineum usually lives with, and is sexually dependent on, one of its parental species, A. jeffersonianum. In central Indiana, however, A. platineum populations have shifted their host dependency to A. texanum. Such A. texanum-dependent populations of A. platineum provide an almost ideal system for studying reproductive mode in A. platineum, because both replacement of a jeffersonianum or laterale genome of A. platineum by a texanum genome, and movement of genes from A. platineum to the host species, A. texanum, would be readily detected by electrophoretic markers. Our samples of A. texanum provided no evidence for the transfer of jeffersonianum or laterale genes into A. texanum. Similarly, among 32 A. platineum sampled from six localities in east-central Illinois and central Indiana, we find no texanum alleles, and thus no evidence for genome replacement. The one diploid hybrid individual contained only a jeffersonianum and a laterale genome; because of the absence of either parental species from these populations, this hybrid could only have come from a diploid ovum produced by A. platineum. Both morphometric and electrophoretic results for the two tetraploid individuals indicate that they resulted from fertilization of triploid oocytes of A. platineum by sperm of A. texanum. Because genome replacement in A. texanum-dependent populations of A. platineum is irreversible, the persistence of A. platineum in A. texanum-dependent populations demonstrates conclusively that the major mode of reproduction in A. platineum populations is clonal: A. platineum produces mainly triploid eggs that develop gynogenetically.     

Prospects for the Survival of the Navajo Language: A Reconsideration

What is the role of schools in the loss of indigenous languages? A study 25 years ago of prospects for the survival of Navajo placed most of the blame for the spread of English on increasing access to schools. Reconsidering that evidence and recent developments, the central role of the introduction of Western schooling is seen still to be highly relevant. But other factors have worked through the school, the major effect of which has been the ideological acceptance of English. Vernacular literacy, traditional or introduced religion, and political structure all have failed to establish a counterforce. Economic changes also led to new living patterns that, together with improved communication, broke down isolation and supported the threat to the survival of language. This study confirms the importance of seeing language and education in the full social, cultural, religious, and political context recognized by educational anthropology.     

Evolutionary history of the hybridogenetic hybrid frog Rana esculenta as deduced from mtDNA analyses [published erratum appears in Mol Biol Evol 1986 Sep;3(5):463]

mtDNA of the hybridogenetic hybrid frog Rana esculenta from Switzerland, Austria, and Poland was compared to mtDNA of the parental species R. ridibunda and R. lessonae using electrophoretic analysis of restriction enzyme fragments. Two mtDNA phenotypes, with 3.4% sequence divergence, are present in R. lessonae: type C is found in Poland, and type D is found in Switzerland. Rana ridibunda from Poland has either of two mtDNA phenotypes: type A is the typical ridibunda mtDNA, and type B is a lessonae mitochondrial genome, introgressed into R. ridibunda, that differs from type C mtDNA of R. lessonae by only 0.3%. Each of the three lessonae genomes differs from A, the typical ridibunda mtDNA, by approximately 8%. All four types of mtDNA (A and B of R. ridibunda, C and D of R. lessonae) are found in R. esculenta. Of 62 R. esculenta from Poland, 58 had type C, three had type A, and one had type B mtDNA. All nine R. esculenta from Switzerland had type D mtDNA. All three R. esculenta from Austria, from a population in which males of R. esculenta are rare, had ridibunda mtDNA, two having type B and one having type A. Both field observations and studies of mating preference indicate that the primary hybridizations that produce R. esculenta are between R. ridibunda females and R. lessonae males; thereafter, R. esculenta lineages are usually maintained by matings of R. esculenta females with R. lessonae males. The presence of ridibunda mtDNA in the three R. esculenta sampled from Austria, its occasional presence in R. esculenta populations in Poland, and its absence from R. esculenta in Switzerland support both the direction of the original hybridization and the rarity of formation of new R. esculenta lineages. The preponderance of R. esculenta individuals with lessonae mtDNA in our samples from central Europe suggests that most lineages have gone through at least one mating between an R. lessonae female and an R. esculenta male. This reveals a greater reproductive role for R. esculenta males than their partial sterility and infrequent matings would suggest.      

Mapping Bombina mitochondrial genomes: the conundrum of Carpathian Bombina variegata (Anura: Discoglossidae)

Complete mitochondrial genomes (mtDNA) of five individuals representing two haplotypes of Bombina bombina and three of Bombina variegata were compared using restriction site maps. Phylogenetic analyses reveal three ancient mitochondrial lineages: (1) two very similar haplotypes A and B of B. bombina ; (2) almost identical haplotypes D and E of B. variegata ; and (3) haplotype C of B. variegata . Haplotype C is as different from haplotypes D/E as from A/B. These data are strikingly discordant with relationships based on morphology and allozymes. Haplotypes C and D/E represent a pre-Pleistocene mitochondrial divergence within B. variegata , nearly coincident with speciation between B. variegata and B. bombina . Geographical partitioning of the two divergent B. variegata mitochondrial lineages indicates repeated localization of the lineages in separate glacial refugia during the Pleistocene. That nuclear genes do not show a similar divergence, but rather indicate relatively free genetic exchange between populations with divergent mtDNAs, suggests that males dispersed much more widely than females during expansions from glacial refugia. Comparison of Bombina mtDNA maps with a restriction site map of Xenopus laevis mtDNA revealed 16 homologous sites; 12 of these may be nearly invariant across primitive anuran mtDNAs. Two distinct regions of heteroplasmy, representing two regions with variable numbers of sequence repeats [length variable (LV) regions], were characterized. Comparison with the Xenopus map places LV1, present in all five haplotypes, near the 5'-end of the control region, and LV2 present only in B. variegata , near the 3'-end. Although phylogenetic analyses did not group the two major B. variegata lineages together, presence of LV2 in both lineages supports placement of both within B. variegata .     

Widespread unidirectional transfer of mitochondrial DNA: a case in western Palaearctic water frogs

Interspecies transfer of mitochondrial (mt) DNA is a common phenomenon in plants, invertebrates and vertebrates, normally linked with hybridization of closely related species in zones of sympatry or parapatry. In central Europe, in an area north of 48 degrees N latitude and between 8 degrees and 22 degrees E longitude, western Palaearctic water frogs show massive unidirectional introgression of mtDNA: 33.7% of 407 Rana ridibunda possessed mtDNA specific for Rana lessonae. By contrast, no R. lessonae with R. ridibunda mtDNA was observed. That R. ridibunda with introgressed mitochondrial genomes were found exclusively within the range of the hybrid Rana esculenta and that most hybrids had lessonae mtDNA (90.4% of 335 individuals investigated) is evidence that R. esculenta serves as a vehicle for transfer of lessonae mtDNA into R. ridibunda. Such introgression has occurred several times independently. The abundance and wide distribution of individuals with introgressed mitochondrial genomes show that R. lessonae mt genomes work successfully in a R. ridibunda chromosomal background despite their high sequence divergence from R. ridibunda mtDNAs (14.2-15.2% in the ND2/ND3 genes). Greater effectiveness of enzymes encoded by R. lessonae mtDNA may be advantageous to individuals of R. ridibunda and probably R. esculenta in the northern parts of their ranges.     

Mitochondrial DNA variation in the hybridizing fire-bellied toads, Bombina bombina and B. variegata

Using five restriction enzymes, geographical variation of mitochondrial DNA (mtDNA) in Bombina bombina and B. variegata was studied in samples from 20 locations. Each restriction enzyme produced a species-specific fragment pattern. B. bombina haplotypes A and B were closely related to each other. In contrast, haplotypes A and B of B. variegata formed two distinct lineages. A very distinctive haplotype (C) was found in the Carpathian Mountains, whereas two other haplotypes, D and E (differing by a single AvaI site), were present in western Europe and the Balkans, respectively. Populations polymorphic for haplotypes D and E occurred in the central Balkans where the haplotypes could replace each other clinally. mtDNA sequence divergence between B. bombina and B. variegata was estimated as 6.0-8.1% and 4.7-5.2% between type C and types D/E of B. variegata. The latter divergence is contrary to allozyme and morphological data that place the western and Carpathian B. v. variegata together (Nei's D = 0.07) and separate them from the Balkan subspecies B. v. scabra (Nei's D = 0.18). Broad interspecific correlation among morphology, allozymes and mtDNA types in European fire-bellied toads argues that, despite continuous hybridization (interrupted perhaps during Pleistocene glacial maxima), little or no mtDNA introgression between the species has occurred outside the narrow hybrid zones that separate these parapatric species.