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PubMed2025

Strong but diffuse genetic divergence underlies differentiation in an incipient species of marine stickleback.

Understanding how lineages proceed along the "speciation continuum" and how species boundaries are maintained over time remain central questions in evolutionary biology. Populations early in the speciation process can give us detailed insight into the reproductive barriers that first initiate speciation. In this study, we explore the nature of genomic divergence between two sympatric marine stickleback ecotypes from Atlantic Canada, "whites" and "commons". Males of each ecotype exhibit distinct nuptial colorations, nesting habits, and parental care strategies. Using population genomic analyses of SNPs and copy number variants (CNVs; deletions and duplications) we show that whites and commons consistently form distinct populations. We uncover genomic differentiation in the white ecotype characteristic of an incipient species, showing extremely low genome-wide differentiation (FST) and very recent divergence (~1 kya). Demographic analysis detected very low levels of ongoing gene flow between populations. Our results and prior genomic studies suggest that reproductive isolation is being maintained between ecotypes despite recent evidence that hybridization in nature does occur. Contrary to other systems, we found many small, but dispersed regions of high differentiation throughout the genome rather than explicitly within chromosomal inversions or the sex chromosomes. On chromosomes VII and XVI, we identified CNVs overlapping genes enriched for olfaction, which may play a role in differences in reproductive strategies between ecotypes. Ultimately, our results demonstrate that genome-wide rather than localized differences can underlie the early stages of divergence, and that this pattern is corroborated by both SNPs and CNVs.

Copy Number Variation↗
PubMed2001

Sexually antagonistic coevolution of a postmating-prezygotic reproductive character in desert Drosophila.

Rapid divergence in postmating-prezygotic characters suggests that selection may be responsible for generating reproductive barriers between closely related species. Theoretical models indicate that this rapid divergence could be generated by a series of male adaptations and female counteradaptations by means of sexual selection or conflict, but empirical tests of particular mechanisms are generally lacking. Moreover, although a male--female genotypic interaction in mediating sperm competition attests to an active role of females, molecular or morphological evidence of the female's participation in the coevolutionary process is critically needed. Here we show that postmating-prezygotic variation among populations of cactophilic desert Drosophila reflects divergent coevolutionary trajectories between the sexes. We explicitly test the female's role in intersexual interactions by quantifying differences in a specific postmating-prezygotic reproductive character, the insemination reaction mass, in two species, Drosophila mojavensis and Drosophila arizonae. A series of interpopulation crosses confirmed that population divergence was propelled by male--female interactions, a prerequisite if the selective forces derive from sexual conflicts. An association between the reaction mass and remating and oviposition behavior argues that divergence has been propelled by sexually antagonistic coevolution, and potentially has important implications for speciation.

Animals↗
PubMed2004

Novel inter-series hybrids in Solanum, section Petota.

Sexual hybrids between distantly related Solanum species can undergo endosperm failure, a post-zygotic barrier in inter-species hybridizations. This barrier is explained by the endosperm balance number (EBN) hypothesis, which states that parents must have corresponding EBNs for viable seed formation. Tests for inter-crossability were made involving the Mexican species Solanum pinnatisectum Dunal. (series Pinnatisecta, ApiApi, 1EBN), autotetraploids of this species, Solanum verrucosum Schlechtd. (series Tuberosa, AA, 2EBN), haploids (2x, 2EBN) of the South American S. tuberosum L. (series Tuberosa, A1A1A2A2, 4EBN), and F2 haploid-species hybrids with South American species (AA, 2EBN) S. berthaultii Hawkes, S. sparsipilum (Bitter.) Juz. and Bukasov and S. chacoense Bitter. The development of hybrid endosperms was investigated for these combinations by confocal microscopy with regard to cell-division timing and tissue collapse. Novel sexual diploid (AApi) and triploid (AApiApi) inter-series hybrids were generated from S. verrucosum x S. pinnatisectum crosses by using post-pollination applications of auxin. F1 embryos were rescued in vitro. The hybrid status of recovered plants was verified by microsatellite marker analysis, and the ploidy was determined by chromosome counting. The application of phytohormones in inter-ploidy S. pinnatisectum x S. tuberosum crosses, however, did not delay endosperm collapse, and embryos were not formed. Other diploid, 1EBN species tested in remote hybridizations with Group Tuberosum were S. cardiophyllum Lindl., S. trifidum Correll, and S. tarnii Hawkes and Hjert., series Pinnatisecta, and S. bulbocastanum Dunal., series Bulbocastana. Based on the analysis of post-zygotic reproductive barriers among isolated species of section Petota, we propose strategies to overcome such incompatibilities.

Breeding↗
PubMed2026

Digest: Chromosomal architecture of behavioral isolation in marine isopods.

How do reproductive barriers persist when diverging species come back into contact? Ribardière et al. (2026) investigated this question in 2 marine isopods, Jaera albifrons and Jaera praehirsuta, whose males court females using divergent specialized setae. By combining population genomics and controlled crosses, the authors show that genomic regions resisting interspecific gene flow are concentrated on sex chromosomes and rearranged chromosomes-regions of low recombination that harbor the genetic bases of divergent male courtship traits.

Animals↗
PubMed2005

Late blight resistance linkages in a novel cross of the wild potato species Solanum paucissectum (series Piurana).

The cultivated potato, Solanum tuberosum, is affected by a variety of diseases with late blight, caused by Phytophthora infestans, being the most severe. Wild potato species have proven to be a continuing source of resistance, sometimes of an extreme type, to this disease. The present study constructs the first late blight linkage map of a member of series Piurana, S. paucissectum, a tuber-bearing relative of potato, using probes for conserved sequences from potato and tomato. Eight probes mapped to unexpected linkage groups, but syntenic differences with prior maps of potato were not supported by any blocks of rearranged chromosome segments. All 12 linkage groups were resolved and significant associations with late blight resistance were found on chromosomes 10, 11 and 12. A major quantitative trait locus (QTL) on chromosome 11 accounts for more than 25% of the phenotypic variance measured in a field trial. Crossing of S. paucissectum with cultivated potato resulted in very few seeds indicating partial reproductive barriers. Differential reactions of accessions of this potential donor species with simple and complex isolates of P. infestans suggest that it carries major resistance genes that are not those previously described from the Mexican species, S. demissum. However, the additivity of the QTL effects argues for the quantitative nature of resistance in this cross.

Analysis of Variance↗
PubMed1995

Genetic aspects of artificial fertilization.

Artificial fertilization protocols were developed to circumvent natural reproduction barriers. Genetically determined barriers were commonly estimated at approximately 30%. This review presents an overview of possible genetic barriers and divides them into four different groups for discussion of their specific aspects. Obviously, genetically determined sterility factors are mostly associated with the phenotype of severe idiopathic male sterility. Before the development of ICSI, the treatment of this patient group showed only a low rate of success. Now many scientists are afraid that ICSI will not only increase this rate of success significantly, but will also increase the rate of genetically determined diseases, including sterility, to ICSI offspring.

Chromosome Aberrations↗
PubMed2025

Admixture Mapping Reveals Evidence for Multiple Mitonuclear Incompatibilities in Swordtail Fish Hybrids.

How barriers to gene flow arise between closely related species is one of the oldest questions in evolutionary biology. Classic models in evolutionary biology predict that negative epistatic interactions between variants in the genomes of diverged lineages, known as hybrid incompatibilities, will reduce viability or fertility in hybrids. The genetic architecture of these interactions and the evolutionary paths through which they arise have profound implications for the efficacy of hybrid incompatibilities as barriers to gene flow between species. While these questions have been studied using theoretical approaches for several decades, only recently has it become possible to genetically map larger numbers of hybrid incompatibilities. Here, we use admixture mapping in natural hybrid populations of swordtail fish (Xiphophorus) to identify hybrid incompatibilities involving genetic interactions between the mitochondrial and nuclear genomes. We find that at least nine regions of the genome are involved in mitonuclear incompatibilities. These incompatibilities involve interactions between the nuclear genome and the X. malinche mitochondria, the X. birchmanni mitochondria, or both. Moreover, they vary in the strength of selection they experience and the degree to which they limit gene flow in natural hybrid populations. Our results build a deeper understanding of the complex architecture of selection against incompatibilities in naturally hybridising species and highlight an important role of mitonuclear interactions in the evolution of reproductive barriers between closely related species.

Animals↗
PubMed1991

The malignant primate?

Speciation and carcinogenesis result from genomic instability at the gametic or at the somatic levels. After an infinity of trials they occur, by chromosome rearrangements, in single individuals or in single cells and evolve by similar chromosomal or clonal evolutions. Loss of heterozygosity for the first event is essential in both processes: in evolution, a chromosomal rearrangement, a pericentric inversion or a Robertsonian fusion, must become homozygous to ensure a reproductive barrier for a new species; Knudson's two-event sequence is a similar situation in cancer. Position effect is equally important: we have shown overexpression of the SOD1 gene in the orangutan phylum probably by an intrachromosomal rearrangement; the t(9;22) in CML acts by typical position effect. Parental imprinting underlies the evolution of genome function and the unset of certain cancers. Evolution and malignancy are interweaved by viruses and oncogenes since the dawn of life. Cancer uses its intelligence to expand and to destroy the other tissues, using subtle metabolic pathways and a variety of tricks to metastasize other cells. It always wins but saws the branch on which it sits. Mankind also grows exponentially, killing thousands of other species, poisoning the oceans and soft waters, polluting the atmosphere, all for his egoistic needs. Man also travels and metastasizes other Earths. He modifies his genome or that of other species, and develops new technologies for his reproduction. He can destroy the planet in an eyeblink. To be or not to be the malignant primate, that will be the dilemma for the 21st Century.

Animals↗
PubMed2006

The genetic basis of intrinsic and extrinsic post-zygotic reproductive isolation jointly promoting speciation in the lake whitefish species complex (Coregonus clupeaformis).

Understanding the genetic architecture of reproductive barriers and the evolutionary forces that drove their divergence represents a considerable challenge towards understanding speciation. The objective of this study was to determine the genetic basis of intrinsic and extrinsic post-zygotic isolation in diverging populations of dwarf and normal lake whitefish with allopatric glacial origins. We found that the rate of embryonic mortality was 5.3-6.5 times higher in dwarf-normal hybrid backcrosses during development than in F1 dwarf and normal crosses. When comparing embryos that died during development against larvae that successfully hatched, patterns of Mendelian segregation at 101 loci whose linkage is known identified 13 loci distributed over seven linkage groups that exhibited significant shifts in segregation ratios leading to significant segregation distortion at these loci in the surviving progeny. Controlled crosses and quantitative trait loci analysis revealed a significant genetic basis for developmental time until emergence, a trait critical to fish larval survival in nature. Hatching backcross progeny exhibited asynchronous emergence and transgressive segregation, suggesting that extrinsic post-zygotic isolation may select against hybridization in specific environmental contexts. Evidence of a genetic basis for increased embryonic mortality followed by asynchronous emergence indicated that intrinsic and extrinsic mechanisms are not mutually exclusive in the formation and maintenance of reproductive isolation, but may be jointly promoting population divergence and ultimately speciation.

Animals↗
PubMed2006

Gametic isolation in guppies (Poecilia reticulata).

Post-mating reproductive isolating mechanisms may be among the earliest reproductive barriers to emerge among incipient species. Trinidadian guppy, Poecilia reticulata, populations in the Caroni and Oropouche drainages in Northern Trinidad exhibit marked genetic divergence and provide an ideal system in which to search for these barriers. We inseminated virgin females with equal amounts of sperm from two males, a 'native' male from the female's own population and a 'foreign' male from the other drainage. Artificial insemination ensured that mating order and mate choice did not affect the outcome. Paternities were assigned to the resulting broods using microsatellite markers. As predicted, sperm from native males had precedence over foreign sperm. Moreover, this effect was symmetrical for both drainages. In contrast, we detected no native sperm precedence in controls, in which females received sperm from the same and another population within the same drainage. Our results show that gametic isolation can arise between geographically proximate, though genetically divergent, populations of a single species and highlight the potential role of this process in speciation.

Animals↗
PubMed2001

Reproductive processes in two oak (Quercus) contact zones with different levels of hybridization.

Patterns of reproductive isolation between two sympatric species of oaks, Quercus gambelii and Q. grisea, that exhibit strong ecological differentiation were examined. A full diallel cross using four trees of each species (i.e. all possible pollinations among eight trees) was performed. This design was repeated at two sites that represent different outcomes of sympatry: (1) a xeric mountain ridge where many hybrids are established (HZ); and (2) a mesic valley bottom where virtually no hybrids are established (MOCYN). By measuring fruit survival at several developmental stages, both the timing and strength of reproductive barriers within and between sites, species, cross types, and pollen dosage levels were examined. In three of four cases, heterospecific fruit set was significantly reduced compared to conspecific fruit set. This reduction occurred after the time of fertilization, but before the onset of embryo growth. Increasing the dose of pollen from an average of 9-194 grains/stigma did not affect this result. Thus, early postfertilization processes play a strong role in species fidelity in these oaks. Quercus gambelii experienced a five-fold decrease in conspecific fruit set at HZ relative to MOCYN. In contrast, heterospecific fruit set of Q. gambelii was the same at both sites. Poor Q. gambelii pollen performance is implicated as playing the major role in this result. One Q. gambelii individual at HZ was highly fecund, and had higher heterospecific than conspecific fruit set; slight introgression in this tree was detected uisng RAPD markers. The Environmental Emasculation Hypothesis that posits that environmental stress can increase the probability of hybrid formation by reducing the competitive ability of male gametes of one species is proposed.

Crosses, Genetic↗
PubMed2000

The S receptor kinase determines self-incompatibility in Brassica stigma.

The self-incompatibility possessed by Brassica is an intraspecific reproductive barrier by which the stigma rejects self-pollen but accepts non-self-pollen for fertilization. The molecular/biochemical bases of recognition and rejection have been intensively studied. Self-incompatibility in Brassica is sporophytically controlled by the polymorphic S locus. Two tightly linked polymorphic genes at the S locus, S receptor kinase gene (SRK) and S locus glycoprotein gene (SLG), are specifically expressed in the papillar cells of the stigma, and analyses of self-compatible lines of Brassica have suggested that together they control stigma function in self-incompatibility interactions. Here we show, by transforming self-incompatible plants of Brassica rapa with an SRK28 and an SLG28 transgene separately, that expression of SRK28 alone, but not SLG28 alone, conferred the ability to reject self (S28)-pollen on the transgenic plants. We also show that the ability of SRK28 to reject S28 pollen was enhanced by SLG28. We conclude that SRK alone determines S haplotype specificity of the stigma, and that SLG acts to promote a full manifestation of the self-incompatibility response.

Brassica↗
PubMed2006

Natural hybrids in Atlantic eels (Anguilla anguilla, A. rostrata): evidence for successful reproduction and fluctuating abundance in space and time.

The outcome of natural hybridization is highly variable and depends on the nonexclusive effects of both pre- and post-mating reproductive barriers. The objective of this study was to address three specific questions regarding the dynamics of hybridization between the American and European eels (Anguilla rostrata and Anguilla anguilla). Using 373 AFLP loci, 1127 eels were genotyped, representing different life stages from both continents, as well as multiple Icelandic locations. We first evaluated the extent of hybridization and tested for the occurrence of hybrids beyond the first generation. Second, we tested whether hybrids were randomly distributed across continents and among Icelandic sampling sites. Third, we tested for a difference in the proportion of hybrids between glass eel and yellow eel stages in Iceland. Our results provided evidence for (i) an overall hybrid proportion of 15.5% in Iceland, with values ranging from 6.7% to 100% depending on life stages and locations; (ii) the existence of hybrids beyond the first generation; (iii) a nonrandom geographic distribution of hybrids in the North Atlantic; and (iv) a higher proportion of first and later generation hybrids in yellow eels compared to glass eels, as well as a significant latitudinal gradient in the proportion of hybrids in Icelandic freshwater. We propose that the combined effect of both differential survival of hybrids and variation in hybridization rate through time best explain these patterns. We discuss the possibility that climate change, which is impacting many environmental features in the North Atlantic, may have a determinant effect on the outcome of natural hybridization in Atlantic eels.

Anguilla↗
PubMed2001

Chimeric creatures in Greek mythology and reflections in science.

"The Chimaera" in Homer's Iliad, "was of divine stock, not of men, in the forepart a lion, in the hinder a serpent, and in the midst a goat, ellipsis Bellerophon slew her, trusting in the signs of the gods." In Hesiod's Theogony it is emphasized that "Chimaera ellipsis had three heads, one of a grim-eyed lion, another of a goat, and another of a snakeellipsis". In addition to this interspecies animal chimera, human/animal chimeras are referred to in Greek mythology, preeminent among them the Centaurs and the Minotaur. The Centaurs, as horse/men, first appear in Geometric and early Archaic art, but in the literature not until early in the fifth century B.C. The bullheaded-man Minotaur, who is not certainly attested in the literary evidence until circa 500 B.C., first appears in art about 650 B.C. Attempts, in the fourth century B.C. and thereafter, to rationalize their mythical appearance were in vain; their chimeric nature retained its fascinating and archetypal form over the centuries. Early in the 1980s, experimental sheep/goat chimeras were produced removing the reproductive barrier between these two animal species. Late in the 1990s, legal, political, ethical, and moral fights loomed over a patent bid on human/animal chimeras. Chimeric technology is recently developed; however, the concept of chimerism has existed in literary and artistic form in ancient mythology. This is yet another example where art and literature precede scientific research and development.

Animals↗
PubMed1987

Chromosome phylogenies of man, great apes, and Old World monkeys.

The karyotypes of man and of the closely related Pongidae--chimpanzee, gorilla, and orangutan--differ by a small number of well known rearrangements, mainly pericentric inversions and one fusion which reduced the chromosome number from 48 in the Pongidae to 46 in man. Dutrillaux et al. (1973, 1975, 1979) reconstructed the chromosomal phylogeny of the entire primate order. More and more distantly related species were compared thus moving backward in evolution to the common ancestors of the Pongidae, of the Cercopithecoidae, the Catarrhini, the Platyrrhini, the Prosimians, and finally the common ancestor of all primates. Descending the pyramid it becomes possible to assign the rearrangements that occurred in each phylum, and the one that led to man in particular. The main conclusions are that this phylogeny is compatible with the occurrence during evolution of simple chromosome rearrangements--inversions, fusions, reciprocal translocation, acquisition or loss of heterochromatin--and that it is entirely consistent with the known primate phylogeny based on physical morphology and molecular evolution. If heterochromatin is not taken into account, man has in common with the other primates practically all of his chromosomal material as determined by chromosome banding. However, it is arranged differently, according to species, on account of chromosome rearrangements. This interpretation has been confirmed by comparative gene mapping, which established that the same chromosome segments, identified by banding, carry the same genes (Finaz et al., 1973; Human Gene Mapping 8, 1985). A remarkable observation made by Dutrillaux is that different primate phyla seem to have adopted different chromosome rearrangements in the course of evolution: inversions for the Pongidae, Robertsonian fusions for the lemurs, etc. This observation may raise many questions, among which is that of an organized evolution. Also, the breakpoints of chromosomal rearrangements observed during evolution, in human chromosomal diseases, and after ionizing irradiation do not seem to be distributed at random. Chromosomal rearrangements observed in evolution are known to be harmful in humans, leading to complete or partial sterility through abnormal offspring in the heterozygous state but not in the homozygous state. They then become a robust reproductive barrier capable of creating new species, far more powerful than gene mutations advocated by neo-Darwinism. The homozygous state may be achieved especially through inbreeding, which must have played a major role during primate evolution.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2003

Reduced meiotic fitness in hybrids with heterozygosity for heterochromatin in the speciating Mus terricolor 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) between M. terricolor I and II and between M. terricolor I and III shows high frequencies of pairing abnormalities at pachytene. The backcross (N3 generation) male hybrids between M. terricolor I and II have meiotic abnormalities as in the F1 male 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 speciating M. terricolor complex.

Animals↗
PubMed1998

Phylogeny and rapid northern and southern hemisphere speciation of goldfinches during the Miocene and Pliocene epochs.

Mitochondrial cytochrome b (cyt b) from 25 out of 31 extant goldfinches, siskins, greenfinches and redpolls (genus Carduelis) has been sequenced from living samples taken around the world, specimens have also been photographed. Phylogenetic analysis consistently gave the same groups of birds, and this grouping was generally related to geographical proximity. It has been supposed that Pleistocene glaciations played a crucial role in the origin of extant diversity and distribution of Northern Hemisphere vertebrates. Molecular comparison of most extant songbird species belonging to the genus Carduelis does not support this assertion. The fossil record of chicken and pheasant divergence time has been used to calibrate the molecular clock; cyt b DNA dendrograms suggest that speciation in Carduelinae birds occurred during the Miocene and Pliocene Epochs (9-2 million years ago) in both the Northern and Southern Hemispheres. Only about 4% average amount of nucleotide substitution per lineage is found between the most distant Carduelis species; this suggests a remarkably rapid radiation when compared with the radiation of other passerine songbird genera. In addition, a continuum of small songbird speciation may be found during the Miocene Epoch in parallel with speciation of other orders (i.e. Galliformes, chicken/pheasant). Pleistocene glaciations may have been important in subspeciation (i.e. Eastern European grey-headed goldfinches/Western European black-headed goldfinches) and also in ice-induced vicariance (isolation) (i.e. siskin in Western Europe vs. siskin in Far East Asia) around the world. European isolated Serinus citrinella (citril finch) is not a canary, but a true goldfinch. South American siskins have quickly radiated in the last 4 million years coinciding with the emergence of the Isthmus of Panama; probably, a North American siskin related to C. notata invaded a suitable and varied biotope (the South American island) for Carduelis birds. North American goldfinches may be renamed as siskins, because they have a distant genetic relationship with European goldfinches. Genus Acanthis could be dropped, and thus redpolls should be separated from twite and linnet, the latter (Europeans) probably being related to American goldfinches. Also, reproductive barriers are observed between closely related species and not between other more distant ones. Finally, a tentative classification for genus Carduelis species is suggested.

Animals↗
PubMed2002

Genetic basis of hybrid breakdown in a Japonica/Indica cross of rice, Oryza sativa L.

Reproductive barriers often arise in hybrid progeny between two varietal groups of Asian cultivated rice ( Oryza sativa L.), Japonica and Indica. Hybrid breakdown showing poor growth habit, and complete sterility was found in the backcrossed progeny derived from a cross between a Japonica variety, Asominori, and an Indica variety, IR24. We employed RFLP analysis in the segregating population to study the genetic basis underlying hybrid breakdown. It was found that the hybrid breakdown is caused by a set of two nuclear genes, which were symbolized as hwe1 and hwe2. The parental varieties, Asominori and IR24, carry hwe1(+) hwe1(+) hwe2hwe2 and hwe1hwe1hwe2(+) hwe2(+) genotypes, respectively, whereas the progenies that showed a weakness performance carry the double recessive genotype ( hwe1hwe1hwe2hwe2). Abnormality was not observed in the progenies that carry the other genotypes, indicating that a single dominant allele at either locus is necessary for normal growth. Based on linkage analysis with RFLP markers, the hwe1 locus was located between RFLP markers R1869 and S1437 on chromosome 12 and the hwe2 locus was located between R3192 and C1211 on chromosome 1. The genetic basis was reconfirmed using near-isogenic lines carrying the genes with reciprocal genetic backgrounds. The present study provides clear evidence, viewed by previous workers, that hybrid breakdown is attributed to complementary genes from both parents.

Journal Article↗