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PubMed1995

Concordant evolutionary patterns among Indo-West Pacific butterflyfishes.

Genetic differences within a 495 base pair section of the mitochondrial cytochrome b gene reveal a striking concordance among species in two monophyletic groups of Indo-west Pacific butterflyfishes. In both species groups, an approximately 2.0% genetic break clearly partitions individuals between the Indian Ocean and Pacific Ocean. However, levels of intra-Pacific mtDNA variation are low, on average less than 1.0%, and fail to cluster by species boundaries defined by colour pattern. Individuals from different species, separated by thousands of kilometers, often possess identical cytochrome b sequences, whereas conspecifics from the same reefs can show up to 1.5% difference. The discrepancy between the mtDNA gene tree and species boundaries may reflect retained ancestral variation or may be the result of hybridization. The strong temporal and phylogenetic concordance between these two independent species groups suggests that genetic differentiation was influenced by common environmental factors. Low levels of within- and between-species genetic differences imply a recent divergence time and suggest a link between speciation within each group and Pleistocene climatic fluctuations. These results paint a turbulent picture of the recent evolutionary history of the Indo-West Pacific.

Animals↗
PubMed2006

Genetics of host plant use and life history in the comma butterfly across Europe: varying modes of inheritance as a potential reproductive barrier.

Comma butterflies (Nymphalidae: Polygonia c-album L.) from one Belgian site and three Spanish sites were crossed with butterflies from a Swedish population in order to investigate inheritance of female host plant choice, egg mass and larval growth rate. We found three different modes of inheritance for the three investigated traits. In line with earlier results from crosses between Swedish and English populations, the results regarding female oviposition preference (choice between Urtica dioica and Salix caprea) showed X-linked inheritance to be of importance for the variation between Sweden and the other sites. Egg mass and growth rate did not show any sex-linked inheritance. Egg mass differences between populations seem to be controlled mainly by additive autosomal genes, as hybrids showed intermediate values. The growth rates of both hybrid types following reciprocal crossings were similar to each other but consistently higher than for the two source populations, suggesting a nonadditive mode of inheritance which is not sex-linked. The different modes of inheritance for host plant preference vs. important life history traits are likely to result in hybrids with unfit combinations of traits. This type of potential reproductive barrier based on multiple ecologically important traits deserves more attention, as it should be a common situation for instance in the early stages of population divergence in host plant usage, facilitating ecological speciation.

Animals↗
PubMed1985

Mitochondrial DNA variation in Drosophila pseudoobscura and related species in Pacific northwest populations.

We have analysed mitochondrial DNA (mtDNA) from Pacific Northwest populations of Drosophila pseudoobscura, D. persimilis, and D. miranda using six restriction enzymes. We find that HpaII restriction sites are hypervariable compared to the other enzymes used. This hypervariability allows construction of a maximum parsimony map linking each mtDNA genotype. Small insertions, possibly tandem duplications, appear to have arisen concomitantly with, or subsequent to, speciation events, perhaps within the A + T rich region. Convergence of mtDNA genotypes is also evident. Unlike findings for other populations of these species, we find little evidence of mitochondrial introgression between D. pseudoobscura and D. persimilis, despite their ability to produce fertile hybrid females.

Animals↗
PubMed1984

Quantitative DNA variation and chromosome homology.

In many genera, of both plants and animals, divergence and speciation is often accompanied by massive changes in the amount of nuclear DNA. These changes, in turn, result from amplification or repetition of base sequences within the chromosomal DNA. The chromosomes of different species are consequently of different size and structure. Observations in hybrids between species differing in nuclear DNA amount show that, despite large differences in DNA content, homoeologous chromosomes pair effectively at pachytene and form chiasmata. Only when the DNA differences are very large, of the order of 60% or more, is pairing at pachytene and chiasma formation impaired. The conclusion is that large scale chromosome structural change due to the repetition of DNA base sequences has surprisingly little effect upon the homology of chromosomes, i.e. their ability to pair effectively and form chiasmata at meiosis. Similar repetitive sequences are frequently distributed widely among non-homologous chromosomes within complements. The question then arises as to what prevents chiasma formation between the non-homologous chromosomes which have in common DNA segments of similar sequences? Evidence is presented which indicates that prevention is under the control of the genotype. The control is effected in one of two ways, either by the suppression of pairing at zygotene or pachytene or by suppression of chiasma formation subsequent to pairing.

Base Sequence↗
PubMed2006

Reproductive isolation between two closely related hummingbird-pollinated neotropical gingers.

Empirical estimates of the relative importance of different barriers to gene flow between recently diverged species are important for understanding processes of speciation. I investigated the factors contributing to reproductive isolation between Costus pulverulentus and C. scaber (Costaceae), two closely related hummingbird-pollinated understory Neotropical herbs. I studied broad-scale geographic isolation, microhabitat isolation, flowering phenology, overlap in pollinator assemblages, floral constancy by pollinators, mechanical floral isolation, pollen-pistil interactions, seed set in interspecific crosses, and postzygotic isolation (hybrid seed germination, greenhouse survival to flowering, and pollen fertility). Aside from substantial geographic isolation, I found evidence for several factors contributing to reproductive isolation in the sympatric portion of their geographic ranges, but the identity and relative strength of these factors varied depending on the direction of potential gene flow. For C. pulverulentus as the maternal parent, mechanical floral isolation was the most important factor, acting as a complete block to interspecific pollen deposition. For C. scaber as the maternal parent, microhabitat isolation, pollinator assemblage, mechanical floral isolation, and postpollination pollen-pistil incompatibility were important. Overall, prezygotic barriers were found to be strong, resulting in 100% reproductive isolation for C. pulverulentus as the maternal parent and 99.0% reproductive isolation for C. scaber as the maternal parent. Some postzygotic isolation also was identified in the F1 generation, increasing total isolation for C. scaber to 99.4%. The results suggest that ecological factors, including habitat use and plant-pollinator interactions, contributed to speciation in this system and evolved before extensive intrinsic postzygotic isolation.

Animals↗
PubMed2006

Linkage of butterfly mate preference and wing color preference cue at the genomic location of wingless.

Sexual isolation is a critical form of reproductive isolation in the early stages of animal speciation, yet little is known about the genetic basis of divergent mate preferences and preference cues in young species. Heliconius butterflies, well known for their diversity of wing color patterns, mate assortatively as a result of divergence in male preference for wing patterns. Here we show that the specific cue used by Heliconius cydno and Heliconius pachinus males to recognize conspecific females is the color of patches on the wings. In addition, male mate preference segregates with forewing color in hybrids, indicating a genetic association between the loci responsible for preference and preference cue. Quantitative trait locus mapping places a preference locus coincident with the locus that determines forewing color, which itself is perfectly linked to the wing patterning candidate gene, wingless. Furthermore, yellow-colored males of the polymorphic race H. cydno alithea prefer to court yellow females, indicating that wing color and color preference are controlled by loci that are located in an inversion or are pleiotropic effects of a single locus. Tight genetic associations between preference and preference cue, although rare, make divergence and speciation particularly likely because the effects of natural and sexual selection on one trait are transferred to the other, leading to the coordinated evolution of mate recognition. This effect of linkage on divergence is especially important in Heliconius because differentiation of wing color patterns in the genus has been driven and maintained by natural selection for Müllerian mimicry.

Animals↗
PubMed1999

Localization of human midisatellite and macrosatellite DNA sequences on chromosomes 1 and X in the great apes.

The mechanism of speciation has remained largely unresolved, and hominoid evolutionary history based on chromosome rearrangements has been continuously challenged. The recent availability of the human-derived chromosome 1-specific midisatellite (D1Z2) and chromosome X-specific macrosatellite (DXZ4) DNA sequence probes has prompted us to hybridize the aforementioned to the members of the hominoid clade (chimpanzee, gorilla, and orangutan), using the fluorescence in-situ hybridization technique. Inconsistencies in the hybridization pattern for the D1Z2 DNA probe in the great ape species suggests that changes in this sequence have apparently taken place during the evolutionary process. No hybridization signal was observed in the orangutan chromosome 1, suggesting that a homologous D1Z2 DNA sequence may not be present in its genome, or that the sequence may be altered, rendering itself undetectable by human-derived DNA probes. Homology in the hybridization patterns for the DXZ4 probe in all three ape species illustrates that the sequence is apparently conserved. Such hybridization data provide some level of phylogenetic information on the recent ancestry of higher primates.

Animals↗
PubMed2005

Phylogenomic study of the subfamily Caprinae by cross-species chromosome painting with Chinese muntjac paints.

Chromosomal homologies have been established between the Chinese muntjac (Muntiacus reevesi, MRE, 2n = 46) and five ovine species: wild goat (Capra aegagrus, CAE, 2n = 60), argali (Ovis ammon, OAM, 2n = 56), snow sheep (Ovis nivicola, ONI, 2n = 52), red goral (Naemorhedus cranbrooki, NCR, 2n = 56) and Sumatra serow (Capricornis sumatraensis, CSU, 2n = 48) by chromosome painting with a set of chromosome-specific probes of the Chinese muntjac. In total, twenty-two Chinese muntjac autosomal painting probes detected thirty-five homologous segments in the genome of each species. The chromosome X probe hybridized to the whole X chromosomes of all ovine species while the chromosome Y probe gave no signal. Our results demonstrate that almost all homologous segments defined by comparative painting show a high degree of conservation in G-banding patterns and that each speciation event is accompanied by specific chromosomal rearrangements. The combined analysis of our results and previous cytogenetic and molecular systematic results enables us to map the chromosomal rearrangements onto a phylogenetic tree, thus providing new insights into the karyotypic evolution of these species.

Animals↗
PubMed1991

Low diversity of t haplotypes in the eastern form of the house mouse, Mus musculus L.

In previous studies, 13 different recessive embryonic lethal genes have been associated with t haplotypes in the wild mice of the species Mus domesticus. In this communication we have analyzed five populations of Mus musculus for the presence and identity of t haplotypes. The populations occupy geographically distant regions in the Soviet Union: Altai Mountains, western and eastern Siberia, Azerbaijan and Turkmenistan. No t haplotypes were found in mice from eastern Siberia. In the remaining four populations, t haplotypes occurred with frequencies ranging from 0.07 to 0.21. All the t haplotypes extracted from these populations and analyzed by the genetic complementation test were shown to carry the same lethal gene tcl-w73. In one population (that of western Siberia), another lethal gene (tcl-w5) was found to be present on the same chromosome as tcl-w73. This situation is in striking contrast to that found in the populations of the western form of the house mouse, M. domesticus. In the latter species, tcl-w73 has not been found at all and the different populations are characterized by the presence of several different lethal genes. The low diversity of t haplotypes in M. musculus is consistent with lower genetic variability of other traits and indicates a different origin and speciation mode compared to M. domesticus. Serological typing for H-2 antigenic determinants suggests that most, if not all, of the newly described t haplotypes might have arisen by recombination of tw73 from M. musculus with t haplotypes from M. domesticus either in the hybrid zone between the two species or in regions where the two species mixed accidentally.

Animals↗
PubMed2001

Retrieval of four adaptive lineages in duiker antelope: evidence from mitochondrial DNA sequences and fluorescence in situ hybridization.

Independent molecular markers (mitochondrial DNA sequences from two genes and fluorescence in situ hybridization with satellite DNA sequences as hybridization probes) were employed to investigate phylogenetic relationships among duiker antelope. When analyzed singly or taken together, the molecular and cytogenetic data allowed for the delimitation of four adaptive groups: the conservative dwarfs which are basal, a savanna specialist which groups apart from the forest duikers, the giant duikers, and the red duikers. Within the latter, a further subdivision comprising an east African and a west African red duiker clade is evident. The placement of the endangered zebra duiker and Aders' duiker remains problematic. Several of the nomenclatural divisions in current use are questioned by our results. These include the recognition of Philantomba as genus name for the blue and Maxwell's duiker and that Harvey's duiker be relegated to a subspecies of the Natal red duiker. We place our results in a biogeographic context and argue that duiker speciation has been driven predominantly by habitat fragmentation which probably led to the disruption of gene flow between geographic populations.

Animals↗
PubMed2006

Evolution of Mycobacterium ulcerans and other mycolactone-producing mycobacteria from a common Mycobacterium marinum progenitor.

It had been assumed that production of the cytotoxic polyketide mycolactone was strictly associated with Mycobacterium ulcerans, the causative agent of Buruli ulcer. However, a recent study has uncovered a broader distribution of mycolactone-producing mycobacteria (MPM) that includes mycobacteria cultured from diseased fish and frogs in the United States and from diseased fish in the Red and Mediterranean Seas. All of these mycobacteria contain versions of the M. ulcerans pMUM plasmid, produce mycolactones, and show a high degree of genetic relatedness to both M. ulcerans and Mycobacterium marinum. Here, we show by multiple genetic methods, including multilocus sequence analysis and DNA-DNA hybridization, that all MPM have evolved from a common M. marinum progenitor to form a genetically cohesive group among a more diverse assemblage of M. marinum strains. Like M. ulcerans, the fish and frog MPM show multiple copies of the insertion sequence IS2404. Comparisons of pMUM and chromosomal gene sequences demonstrate that plasmid acquisition and the subsequent ability to produce mycolactone were probably the key drivers of speciation. Ongoing evolution among MPM has since produced at least two genetically distinct ecotypes that can be broadly divided into those typically causing disease in ectotherms (but also having a high zoonotic potential) and those causing disease in endotherms, such as humans.

Bacterial Toxins↗
PubMed2002

The fate of duplicated major histocompatibility complex class Ia genes in a dodecaploid amphibian, Xenopus ruwenzoriensis.

The dodecaploid anuran amphibian Xenopus ruwenzoriensis represents the only polyploid species of Xenopus in which the full silencing of the extra copies of the major histocompatibility complex (MHC) has not occurred. Xenopus ruwenzoriensis is a recent polyploid that has evolved within one of the two tetraploid groups of Xenopus through allopolyploidization. Family studies of its MHC haplotype suggested a polysomic inheritance of the MHC class I and II genes. Four class Ia bands can be detected per individual in Southern blot analysis and, similarly, four different cDNA sequences are expressed per individual. The Xenopus class Ia sequences we analyzed belong to only one of the old class I lineages and show a homogenization of their alpha3 domain sequences. This homogenization occurred after speciation within the Xenopus ruwenzoriensis species, either due to gene conversion or inter-alleles/loci recombination.A re-evaluation of the polymorphism of class Ia in Xenopus, by looking at the rate of non-synonymous versus synonymous substitutions, suggests that Xenopus MHC class Ia genes are not under strong overdominant selection. This is a rare situation among vertebrates. The observed polymorphism is most likely due to the interlocus genetic exchanges related to the peculiar mode of speciation of the genus.

Alleles↗
PubMed2005

Contrasting patterns of polymorphism and divergence on the Z chromosome and autosomes in two Ficedula flycatcher species.

In geographic areas where pied and collared flycatchers (Ficedula hypoleuca and F. albicollis) breed in sympatry, hybridization occurs, leading to gene flow (introgression) between the two recently diverged species. Notably, while such introgression is observable at autosomal loci it is apparently absent at the Z chromosome, suggesting an important role for genes on the Z chromosome in creating reproductive isolation during speciation. To further understand the role of Z-linked loci in the formation of new species, we studied genetic variation of the two species from regions where they live in allopatry. We analyzed patterns of polymorphism and divergence in introns from 9 Z-linked and 23 autosomal genes in pied and collared flycatcher males. Average variation on the Z chromosome is greatly reduced compared to neutral expectations based on autosomal diversity in both species. We also observe significant heterogeneity between patterns of polymorphism and divergence at Z-linked loci and a relative absence of polymorphisms that are shared by the two species on the Z chromosome compared to the autosomes. We suggest that these observations may indicate the action of recurrent selective sweeps on the Z chromosome during the evolution of the two species, which may be caused by sexual selection acting on Z-linked genes. Alternatively, reduced variation on the Z chromosome could result from substantially higher levels of introgression at autosomal than at Z-linked loci or from a complex demographic history, such as a population bottleneck.

Animals↗
PubMed1998

Gene-based anchoring of the rat genetic linkage and cytogenetic maps: new regional localizations, orientation of the linkage groups, and insights into mammalian chromosome evolution.

In order to generate anchor points connecting the rat cytogenetic and genetic maps, the cytogenetic position of 62 rat markers (including 55 genes) already localized genetically was determined by fluorescence in situ hybridization. Whenever possible, markers located near one end of the linkage groups were included. These new localizations allowed us to unambiguously orient the 20 autosomal and the X chromosome linkage groups. The position of the centromere in the linkage map could also be determined in the case of several metacentric chromosomes. In addition, the regional localization of 15 other rat genes was determined. These new data bring useful information with respect to comparative mapping with the mouse and the human and to mammalian evolution. They illustrate, for instance, that groups of genes can remain syntenic during mammalian evolution while being subjected to intrachromosomal rearrangements in some lineages (synteny is conserved while gene order is not). This analysis also disclosed cases of synteny conservation in one the two rodent species and the human, while the synteny is split in the other rodent species: such configurations are likely examples of lineage-specific interchromosomal rearrangements associated with speciation.

Animals↗
PubMed2006

The chimpanzee-specific pericentric inversions that distinguish humans and chimpanzees have identical breakpoints in Pan troglodytes and Pan paniscus.

Seven of nine pericentric inversions that distinguish human (HSA) and chimpanzee karyotypes are chimpanzee-specific. In this study we investigated whether the two extant chimpanzee species, Pan troglodytes (common chimpanzee) and Pan paniscus (bonobo), share exactly the same pericentric inversions. The methods applied were FISH with breakpoint-spanning BAC/PAC clones and PCR analyses of the breakpoint junction sequences. Our findings for the homologues to HSA 4, 5, 9, 12, 16, and 17 confirm for the first time at the sequence level that these pericentric inversions have identical breakpoints in the common chimpanzee and the bonobo. Therefore, these inversions predate the separation of the two chimpanzee species 0.86-2 Mya. Further, the inversions distinguishing human and chimpanzee karyotypes may be regarded as early acquisitions, such that they are likely to have been present at the time of human/chimpanzee divergence. According to the chromosomal speciation theory the inversions themselves could have promoted human speciation.

Animals↗
PubMed2025

Integrated genomics and morphological approach reveals interspecific gene flow cases and decodes the origin of selected feathergrasses (Poaceae, Stipa).

Central Asia is a diversity hotspot of arid-adapted grasses from the genus Stipa, with approximately 100 taxa found in the region. Recent studies in the steppe areas of Kazakhstan revealed specimens displaying intermediate morphology, distinguishing them from other taxa that grow sympatrically. Using integrative taxonomy, we investigated whether these individuals resulted from natural speciation or hybridisation, and if so, we would like to know which species were involved in this process feathergrasses. Research conducted in steppes of central Kazakhstan (Kyzylorda region), revealed the existence of individuals morphologically intermediate between S. arabica and S. richteriana, suggesting that these are probably of hybrid origin. Morphology and SNP markers validated the specimens as F1 hybrid between the aforementioned species by cladding separately based on neighbor-joining phylogenetic tree. Moreover, genetic structure displayed a separate cluster and showed almost equal genetic admixture between S. arabica and S. richteriana. Additionally, fastStructure analysis detected two geographically separated cryptic genotypes within S. richteriana population and their involvement in the hybridisation resulted in occurrence of S. × heptapotamica, S. × czerepanovii and S. × korshinskyi which recently were suggested as hybrids. Based on these evidences, we described a new nothospecies S. × kyzylordensis, as F1 hybrid. Furthermore, morphologically, the nothospecies delimited with other hybrids in Kazakh steppe area, marking the first report of hybridisation between S. arabica and S. richteriana, along with molecular evidence for the origin of further species supposed to be hybrids. This finding is crucial to understanding species diversity and hybridisation process in morphologically and genetically distant Stipa species.

Poaceae↗
PubMed2000

Multi-locus genetic evidence for rapid ecologically based speciation in Daphnia.

The process of speciation involves the divergence of two or more subpopulations of a parent species into independent evolutionary trajectories. To study this process in natural populations requires a detailed knowledge of the genetic and ecological characteristics of the parent species and an understanding of how its populations can lose evolutionary cohesion. The cosmopolitan and speciose genus Daphnia provides many of these features by existing in multiple freshwater habitat types, particularly permanent lakes and temporary ponds, each of which presents distinct ecological challenges. We assayed the genetic composition of 20 temporary pond populations of members of the Daphnia pulex species complex in north-western Oregon and compared them to published data on related lake and pond populations. We collected molecular genetic data from 13 allozyme loci, from six microsatellite loci, and from the control region of the mitochondrial DNA. By assaying over 400 individual Daphnia for these data, we were able to compile composite genotypes not only of individual Daphnia but of each pond population as a whole. In these ponds, we discovered two distinct genotypic constellations, one which bears resemblance to the lake-dwelling taxon D. pulicaria, and one which bears resemblance to the pond-dwelling taxon, D. pulex. Using published genetic data from these and other species as a frame of reference, we characterized 13 of these ponds as being 'pond-like', three as being 'lake-like', and four as being 'mixed'. Unlike studies performed elsewhere, however, these ponds do not exhibit high probabilities of interspecific hybridization. Over 95% of all individuals have either a lake-like or a pond-like genotype at all three genetic systems, suggesting the two forms do not represent hybridized vs. nonhybridized genotypes. Because both types can be found in the same ponds at the same time in gametic disequilibrium, we also discount the possibility that they are two extremes of a single species that is highly genetically subdivided. With these genetic data, and with supporting life-history and ecological data previously gathered on these pond populations, we conclude that the most likely description of this system is of a taxon caught in the act of speciating, with new pond-adapted populations periodically stemming from lake-adapted sources during river flooding events.

Alleles↗
PubMed2005

Molecular distinction between true centric fission and pericentric duplication-fission.

Centromere (centric) fission, also known as transverse or lateral centric misdivision, has been defined as the splitting of one functional centromere of a metacentric or submetacentric chromosome to produce two derivative centric chromosomes. It has been observed in a range of organisms and has been ascribed an important role in karyotype evolution; however, the underlying mechanisms remain unknown. We have investigated four cases of apparent centric fission in humans. Two cases show a missing chromosome 22 or 18 that is replaced by two centric ring products, a third case shows two chromosome-10-derived telocentric chromosomes, whereas a fourth case involves the formation of two chromosome-18-derived isochromosomes. In all four cases, results of gross cytogenetic and fluorescence in situ hybridisation analyses were consistent with a simple centric fission event. However, detailed molecular analyses provided evidence in support of centromere duplication as a predisposing mechanism for the observed chromosomal breakage in two of the cases. Results for the third case are consistent with direct centric fission not involving centromere pre-duplication as the likely mechanism. Insufficient material has precluded the further study of the fourth case. The data provide the first molecular evidence for centromere pre-duplication as a possible mechanism to explain the classically assumed simple "centric fission" events in clinical cytogenetics, karyotype evolution and speciation.

Fluorescent Antibody Technique↗