Occurrence Of Gene Flow Research Articles

Comparative Phylogeography of Birds Across the Tocantins–Araguaia Interfluve Reveals a New Biogeographic Suture in the Amazon Far East

Few phylogeographic studies have focused on understanding the role of the Tocantins–Araguaia Interfluve (TAI) in the diversification of Amazonian biodiversity. Herein we evaluate the phylogeographic relationships of 14 avian lineages present in the TAI and its two neighboring Amazonian Areas of Endemism: the Xingu (XAE) and Belém (BAE). Four alternative scenarios coupling degree of genetic differentiation and area relationships were tested: (1) populations distributed in TAI, BAE, and XAE are not genetically differentiated from each other (assumed as the null hypothesis); (2) populations from TAI are more closely related to those from BAE; (3) populations from TAI are more closely related to those from XAE; and (4) TAI populations represent independent or endemic lineages not present in either the BAE or XAE. Molecular analyses considered Bayesian Inference methods and Bayesian Information Criterion (BIC) evolutionary models, haplotype sharing and genetic differentiation estimates. We found three distinct phylogeographic patterns: (i) four lineages presented no population structure across XAE, TAI and BAE; (ii) six lineages were represented in the TAI with distinct phylogroups replacing each other between XAE and BAE, but with varying degrees of contact and evidence of gene-flow within the TAI; and (iii) for four lineages, the Tocantins River acted as a barrier isolating BAE phylogroups from those inhabiting both TAI and XAE. These different patterns demonstrate a heterogeneous response to the barrier effects posed by both the Tocantins and Araguaia rivers on the local fauna. Historical geomorphological and hydromorphological factors, such as the presence and absence of paleochannels and anastomosed channel stretches and variations in sedimentation rates support a dynamic history for the Araguaia-Tocantins floodplains, likely accounting for the observed heterogeneity in species’ specific responses. Finally, the scenario of phylogeographic breaks and population subdivision recovered herein along the Tocantins and Araguaia rivers, associated with the existence of contact zones and the occurrence of gene flow, define the TAI as hitherto unknown biogeographic suture zone, localized in southeasternmost Amazonia.

Large-scale geography survey provides insights into the colonization history of a major aphid pest on its cultivated apple host in Europe, North America and North Africa

With frequent host shifts involving the colonization of new hosts across large geographical ranges, crop pests are good models for examining the mechanisms of rapid colonization. The microbial partners of pest insects may be involved or affected by colonization, which has been little studied so far. We investigated the demographic history of the rosy apple aphid, Dysaphis plantaginea, a major pest of the cultivated apple (Malus domestica) in Europe, North Africa and North America, as well as the diversity of its endosymbiotic bacterial community. We genotyped a comprehensive sample of 714 colonies from Europe, Morocco and the US using mitochondrial (CytB and CO1), bacterial (16s rRNA and TrnpB), and 30 microsatellite markers. We detected five populations spread across the US, Morocco, Western and Eastern Europe, and Spain. Populations showed weak genetic differentiation and high genetic diversity, except the Moroccan and the North American that are likely the result of recent colonization events. Coalescent-based inferences releaved high levels of gene flow among populations during the colonization, but did not allow determining the sequence of colonization of Europe, America and Morroco by D. plantaginea, likely because of the weak genetic differentiation and the occurrence of gene flow among populations. Finally, we found that D. plantaginea rarely hosts any other endosymbiotic bacteria than its obligate nutritional symbiont Buchnera aphidicola. This suggests that secondary endosymbionts did not play any role in the rapid spread of the rosy apple aphid. These findings have fundamental importance for understanding pest colonization processes and implications for sustainable pest control programs.

Morphological and genetic diversity of Senecio vulgaris L. (Asteraceae) in Iran

Senecio vulgaris L., an annual herb belonging to the Asteraceae, is widely distributed in different regions of the world. There is no information on the intraspecific variations of the morphological and molecular features of this species. In the present investigation, we studied the morphological and genetic diversity of 81 accessions of S. vulgaris collected from 10 geographical populations. Eleven inter simple sequence repeat (ISSR) primers were used for the examination of genetic variations among the populations. Analysis of molecular variance (AMOVA) and GST analyses revealed significant differences among the investigated populations. A significant correlation between genetic distance and geographical distance was revealed by the Mantel test. However, reticulation analysis indicated the occurrence of gene flow among most of the populations studied. Principal component analysis (PCA) plot showed that the number of capitula, length of the cauline leaf and plant height were the most variable morphological characters. Principal coordinates analysis (PCoA) plot revealed two groups of populations, according to molecular and morphological data. The results suggested the existence of possible intraspecific taxonomic ranks within this species.

Refining the genetic structure and relationships of European cattle breeds through meta-analysis of worldwide genomic SNP data, focusing on Italian cattle

The availability of genotyping assays has allowed the detailed evaluation of cattle genetic diversity worldwide. However, these comprehensive studies did not include some local European populations, including autochthonous Italian cattle. In this study, we assembled a large-scale, genome-wide dataset of single nucleotide polymorphisms scored in 3,283 individuals from 205 cattle populations worldwide to assess genome-wide autozygosity and understand better the genetic relationships among these populations. We prioritized European cattle, with a special focus on Italian breeds. Moderate differences in estimates of molecular inbreeding calculated from runs of homozygosity (FROH) were observed among domesticated bovid populations from different geographic areas, except for Bali cattle. Our findings indicated that some Italian breeds show the highest estimates of levels of molecular inbreeding among the cattle populations assessed in this study. Patterns of genetic differentiation, shared ancestry, and phylogenetic analysis all suggested the occurrence of gene flow, particularly among populations originating from the same geographical area. For European cattle, we observed a distribution along three main directions, reflecting the known history and formation of the analyzed breeds. The Italian breeds are split into two main groups, based on their historical origin and degree of conservation of ancestral genomic components. The results pinpointed that also Sicilian breeds, much alike Podolian derived-breeds, in the past experienced a similar non-European influence, with African and indicine introgression.

Taming the Red Bastards: Hybridisation and species delimitation in the Rhodanthemum arundanum-group (Compositae, Anthemideae)

Delineating species boundaries in a group of recently diverged lineages is challenging due to minor morphological differences, low genetic differentiation and the occurrence of gene flow among taxa. Here, we employ traditional Sanger sequencing and restriction-site associated DNA (RAD) sequencing, to investigate species delimitation in the close-knit Moroccan daisy group around Rhodanthemum arundanum B.H.Wilcox & al. that diverged recently during the Quaternary. After evaluation of genotyping errors and parameter optimisation in the course of de-novo assembly of RADseq reads in Ipyrad, we assess hybridisation patterns in the study group based on different data assemblies and methods (Neighbor-Net networks, FastStructure and ABBA-BABA tests). RADseq data and Sanger sequences are subsequently used for delimitation of species, using both, multi-species coalescent methods (Stacey and Snapp) and a novel approach based on consensus k-means clustering. In addition to the unveiling of two novel subspecies in the R. arundanum-group, our study provides insights into the performance of different species delimitation methods in the presence of hybridisation and varying quantities of data.

Structure and genetic variability of golden mussel (Limnoperna fortunei) populations from Brazilian reservoirs.

The golden mussel, Limnoperna fortunei a highly invasive species in Brazil, has generated productive, economical, and biological impacts. To evaluate genetic structure and variability of L. fortunei populations present in fish farms in the reservoirs of Canoas I (CANFF), Rosana (ROSFF), and Capivara (CAPFF) (Paranapanema River, Paraná, Brazil), eight microsatellite loci were amplified. Five of those eight loci resulted in 38 alleles. The observed heterozygosity (Ho) was lower than the expected heterozygosity (He) in all populations, with a deviation from the Hardy–Weinberg equilibrium (HWE). The average value for the inbreeding coefficient (Fis) was positive and significative for all populations. There was higher genetic variability within populations than among them. The fixation index (Fst) showed a small genetic variability among these populations. The occurrence of gene flow was identified in all populations, along with the lack of a recent bottleneck effect. The clustering analysis yielded K = 2, with genetic similarity between the three populations. The results demonstrate low genetic structure and suggest a founding population with greater genetic variability (ROSFF). Our data point to the possible dispersal of L. fortunei aided by anthropic factors in the upstream direction. It was concluded that the three populations presented a unique genetic pool for Paranapanema River, with occurrence of gene flow.

Collection of new diversity of wild and cultivated bananas (Musa spp.) in the Autonomous Region of Bougainville, Papua New Guinea

Bananas (Musa spp.), including dessert and cooking types, are of major importance in the tropics. Due to extremely high levels of sterility, the diversity of cultivated bananas is fixed over long periods of time to the existing genotypes. This pattern puts banana-based agrosystems at risk. Therefore, assessing the extent of wild and cultivated banana diversity, conserving it and making it available for further use is a priority. We report here the collection of new wild and cultivated banana germplasm in the Autonomous Region of Bougainville, Papua New Guinea. In total, 61 accessions were collected and their names and uses were recorded when possible. Classification was also provided based on the observations made in the field. Three wild specimens were collected. Among the 58 cultivated accessions, we noted that eight were used as ornamental plants, seven were edible varieties of the Fe’i type and two were natural tetraploids from the Musa section. The ploidy was then checked by flow cytometry and the accessions were genotyped with a set of 19 SSR markers. The genotyping results were merged to the dataset from Christelová et al. (Biodivers Conserv 26:801–824, 2017). This joint analysis helped refine or confirm the classification of the collected accessions. It also allowed to identify 10 private alleles and 35 genotypes or Genotype Groups that were not present in the wider dataset. Finally, it shed light on the diversification processes at work in the region, such as the capture of mutations by farmers and the likely occurrence of geneflow within the cultivated genepool.

Floristic and ecological attributes of a Seasonal Semideciduous Atlantic Forest in a key area for conservation of the Zona da Mata region of Minas Gerais State, Brazil

ABSTRACT We evaluated the floristic and ecological attributes of a seasonal semideciduous forest remnant (SSF) (500-1,050 m) located in a key area for biodiversity conservation. The importance of the fragment to the ecosystem conservation was revealed by its species richness (253), diversity (Shannon index = 4.6; Simpson's complementary index = 0.98) and evenness (Pielou index = 0.83), which are considered high values for a SSF. Zoochory occurred in 77% of the species, indicating the existence of important biotic interactions that ensure the occurrence of gene flow. We recorded 14 endangered species, among which two are rare (Trigynaea oblongifolia and Trattinnickia ferruginea) and two are indicators of mature forests (Trattinnickia ferruginea and Virola bicuhyba). We confirmed the importance of key areas for biodiversity conservation and of the Atlantic SSF located at the 0-1,000 m altitudinal range. These areas deserve attention from conservationists due to the high species richness and high number of endemic and endangered species.

Gene flow between vicariant tree species: insights into savanna-forest evolutionary relationships

Studying the genetic structure of vicariant species (i.e., closely related species that occupy ecologically distinct yet adjacent habitats) can shed light on the evolution and divergence of species with different ecological requirements. A previous phylogeographic study identified chloroplast DNA haplotype sharing between two vicariant tree species, one from forest (Hymenaea courbaril) and one from savanna (H. stigonocarpa) habitats. These species co-occur in the Brazilian Cerrado, a biome that encompasses forest patches and riverine forests within a savanna matrix. In order to investigate the evolutionary processes involved in the genetic divergence of these trees, we used nuclear microsatellite markers, statistical methods including approximate Bayesian computation (ABC), and leaf morphology to analyze neighboring and distant populations. Bayesian analysis revealed admixture between the species. ABC analysis supported the scenarios with the occurrence of gene flow between species during the Last Glacial Maximum or from the Holocene to the present, when compared to alternative scenarios of no gene flow or constant gene flow since divergence. However, putative hybrids did not exhibit intermediate leaflet morphology, which could be related to distinct selective pressures maintaining species integrity even in the face of gene flow. Our results suggest that despite morphological differences between savanna and forest species, interspecific barriers to gene flow might not be fully developed between vicariant tree species and that interspecific hybridization in trees from Cerrado biome may be an underdiagnosed process.

Genetic diversity analyses of tropical goats from some countries of Middle East

The genetic structure of 10 goat breeds from four countries of the Middle East and Horn of Africa was investigated at 17 microsatellite loci. The average allele number and richness were 9.65 and 5.78, respectively. The mean expected heterozygosity per population was 0.703, 0.715, 0.719, 0.699, 0.749, 0.719, 0.731, 0.721, 0.719, and 0.730 for Somali from Somalia, Tohami, Bishi, Jabali, Ardi, and Saudi Damascus from Saudi Arabia, Black Bedouin, Sahrawi, and Jordanian Damascus from Jordan, and Syrian Damascus from Syria. The low level of genetic differentiation across large topographic features was expressed by pairwise difference coefficient (FST = 0.001-0.135). The goats were assigned to four genetic pools, indicating the occurrence of gene flow within a potential genetic exchange network. The genetic exchange possibly occurred in the past when the ancient trade routes - Incense and Pilgrimage Routes - were active in these countries. Despite the distances far by thousands of kilometers or separated by the boundaries, Saudi goats kept a reasonable level of admixture, indicating common ancestry. These results are in agreement with a known history of the goat populations in regards to geographical location and evolutionary time of past common ancestors. Further study is recommended considering goats from other Middle East countries.

Diversity and genetic structure of cassava landraces and their wild relatives (Manihotspp.) in Colombia revealed by simple sequence repeats

Understanding the genetic composition and population structure of plant species at a molecular level is essential for the development of adequate strategies aimed at enhancing the conservation and use of their genetic resources. In addition, such knowledge can help to plan ahead for a scenario under which wild and cultivated species come into contact with their genetically modified (GM) counterpart(s). Using ten simple sequence repeat markers, we genotyped 409 samples pertaining to the species in theManihotgenus known to occur in Colombia, i.e. cassava (Manihot esculenta)and its wild relativesManihot brachyloba,Manihot carthaginensisandManihot tristis. High genetic variation was observed in all the species (HE= 0.212–0.603), with cassava showing highest diversity. Most of the genetic variation was found within species populations. Our results suggest that outcrossing events among populations occur much more frequently inM. tristisandM. esculenta, and particularly so in the latter, where the exchange of varieties among local farmers plays a key role in maintaining and introducing new genetic diversity. The occurrence of gene flow within and among populations ofManihotspecies in Colombia becomes relevant in a biosafety context, where gene flow from GM cassava, if introduced to the country, might have detrimental effects on the structure and dynamics of populations of wild species. The baseline information on the genetic diversity and structure of the four Colombian species that we have presented here provides a first and indispensable step towards the development of targeted interventions necessary to preserve their genetic resources.

The population genetic structure and diversification ofAristolochia delavayi(Aristolochiaceae), an endangered species of the dry hot valleys of the Jinsha River, southwestern China

Aristolochia delavayi Franch. is an endangered species of the dry hot valleys of the Jinsha River, southwestern China. The genetic diversity and structure of the species and the occurrence of gene flow were investigated with eight inter-simple sequence repeat (ISSR) markers and four plastid loci (matK, trnL-trnT, rps4-trnT, and trnC-rpoB). The analysis of ISSR markers indicated that the genetic diversity of the species is relatively high (PPB = 84.71%). Similarly, a high gene diversity of HT= 0.833 was found based on the four plastid loci. It is possible that this species previously maintained a large effective population size and that the current relict distribution of the species is a result of large-scale fragmentation and habitat destruction. The origin of the species at approximately 3.407 million years ago and the ensuing intraspecific divergence are generally consistent with the history of two major glaciations in this region. Conservation measures are urgently needed to increase the genetic diversity and population size of this species through both in- and ex-situ action.

Genetic diversity and morphological variation of the common chaffinch Fringilla coelebs in the Azores

We present new insights into the genetic diversity and phylogeography of the common chaffinch Fringilla coelebs from the Azores, based on sequences of mitochondrial and nuclear genes from 44 individuals and an outgroup/comparison of 44 birds from Madeira, the Canary Islands and the Continental Western Palearctic. To understand the level of concordance between the genetic data and morphometric variability we analysed eight morphometric characters from 413 adult living birds from all the Azores islands and compared the population genetic distances with quantitative morphometric traits. Our results indicate the occurrence of gene flow among the common chaffinch populations in the archipelago revealing the lack of current genetic structure within it and the existence of two co‐occurring lineages. Results also indicate the existence of morphometric differences among islands that could be due to ecological features instead of island isolation. This study also confirms the genetic distance among the common chaffinch populations within Macaronesia and between these archipelagos and the Continental Western Palearctic.

Genetic structure of the ornamental tetra fish species Piabucus melanostomus Holmberg, 1891 (CHARACIDAE, IGUANODECTINAE) in the Brazilian Pantanal wetlands inferred by mitochondrial DNA sequences

The subfamily Iguanodectinae comprises a group of small Neotropical fishes composed by two genera and 11 nominal species widely distributed in the Atlantic drainages of South America. Piabucus is the only genus of Iguanodectinae found in the Paraguay River basin, especially in the Pantanal of Mato Grosso State, where it is represented by Piabucus melanostomus. Given the wide distribution and the low dispersion capacity of this species, due the ecological constraints, it is possible that many interesting genetic features could be found in different populations. In this way, the aim of his work was to perform the phylogeographic pattern of P. melanostomus populations using mitochondrial DNA sequences. A total of 13 individuals from three rivers belonging the Mato Grosso wetland were sampled. The ATP sintetase (subunits 6 and 8) gene was completely sequenced, the mean of nucleotide base composition in the sequences was 31.2% (T), 30.2% (C), 26.9% (A) and 11.9% (G), with no gene saturation. The population analysis in the TCS program generated a network with six haplotypes (A to F), where the ancestral haplotype (A) has a frequency of 25% and is composed by individuals from Cuiabá and Paraguay Rivers. The phylogenetic analysis showed the occurrence of two mtDNA lineages (1 and 2), the distance observed between the two lineages was 0.6%. The phylogenetic and phylogeographic results as well as the negative values of Fst for some populations, indicate a possible occurrence of gene flow among the analyzed populations. These results highlights the importance of flood pulse existent on wetland as a vehicle that permits a temporary connection among isolated population maintaining the species genetic variability.

Fluxo gênico recíproco entre cultivares de soja convencional e geneticamente modificada

O objetivo deste trabalho foi determinar o fluxo gênico recíproco entre duas cultivares de soja, uma tolerante e outra sensível ao glifosato, além de aplicar estimadores para determinar a taxa de fecundação cruzada na população e o número de sementes híbridas na progênie. O experimento compôs-se de quatro blocos com 40 fileiras de soja, com 20 fileiras de cada cultivar (CD217 e CD219RR). No estádio R8, cinco fileiras, distantes 0, 5, 1, 2, 4 e 8 m da cultivar adjacente, foram colhidas, trilhadas e analisadas quanto à ocorrência de fluxo gênico. Como características marcadoras, foram utilizadas as cores da flor, hipocótilo e pubescência, e a tolerância ao glifosato. As cultivares contrastam quanto às características analisadas, cada uma condicionada por um gene com dois alelos, em interação de dominância completa. Na progênie da cultivar tolerante, a maior taxa de híbridos encontrada foi 0, 27% e, na progênie da cultivar sensível, identificou-se 0, 83%; pela hipótese do efeito diluição, as taxas de hibridação natural populacional seriam 0, 104 e 0, 388%, respectivamente. O fluxo gênico recíproco entre as cultivares CD217 e CD219RR não é o mesmo em ambas as direções. Os estimadores propostos são úteis para determinar a taxa de híbridos em amostras de sementes.

Population delimitation across contrasting evolutionary clines in deer mice (Peromyscus maniculatus).

Despite current interest in population genetics, a concrete definition of a “population” remains elusive. Multiple ecologically and evolutionarily based definitions of population are in current use, which focus, respectively, on demographic and genetic interactions. Accurate population delimitation is crucial for not only evolutionary and ecological population biology, but also for conservation of threatened populations. Along the Pacific Coast of North America, two contrasting patterns of geographic variation in deer mice (Peromyscus maniculatus) converge within the state of Oregon. Populations of these mice diverge morphologically across an east–west axis, and they diverge in mitochondrial DNA haplotypes across a north–south axis. In this study, we investigate these geographically contrasting patterns of differentiation in the context of ecological and evolutionary definitions (paradigms) of populations. We investigate these patterns using a new and geographically expansive sample that integrates data on morphology, mitochondrial DNA, and nuclear DNA. We found no evidence of nuclear genetic differentiation between the morphologically and mitochondrially distinct populations, thus indicating the occurrence of gene flow across Oregon. Under the evolutionary paradigm, Oregon populations can be considered a single population, whereas morphological and mitochondrial differentiations do not indicate distinct populations. In contrast, under the ecological paradigm morphological differentiation indicates distinct populations based on the low likelihood of demographic interactions between geographically distant individuals. The two sympatric but mitochondrially distinct haplogroups form a single population under the ecological paradigm. Hence, we find that the difference between evolutionary and ecological paradigms is the time-scale of interest, and we believe that the more chronologically inclusive evolutionary paradigm may be preferable except in cases where only a single generation is of interest.

Development of ancient DNA techniques and its application in evolutionary study of domestic animals

Domestic animals have accompanied the origin and development of human civilization; therefore, the study of their domestication history is important. However, the occurrence of gene flow, or even replacement, among wild or domestic populations has complicated genetic studies tracing the initial domestication and dispersal of modern species. Fortunately, the investigation of DNA from archeological remains (ancient DNA) provides a unique opportunity to unravel these past events. In the present study, the progress of ancient DNA techniques is summarized, including retrieval and evaluation methods, technological innovations in methods of ancient DNA extraction, amplification, and sequencing. As well, the implications of ancient DNA technology for the evolutionary study of four major domestic animals (pig, horse, sheep, and dog) are reviewed. This review will facilitate the development of ancient DNA techniques and their further applications.

Genetic diversity in watermelon (Citrullus lanatus) landraces from Zimbabwe revealed by RAPD and SSR markers

Low polymorphism in cultivated watermelon has been reported in previous studies, based mainly on US Plant Introductions and watermelon cultivars, most of which were linked to breeding programmes associated with disease resistance. Since germplasm sampled in a putative centre of origin in southern Africa may harbour considerably higher variability, DNA marker-based diversity was estimated among 81 seedlings from eight accessions of watermelon collected in Zimbabwe; five accessions of cow-melons (Citrullus lanatus var. citroides) and three of sweet watermelons (C. lanatus var. lanatus). Two molecular marker methods were used, random amplified polymorphic DNA (RAPD) and simple sequence repeats (SSR) also known as microsatellite DNA. Ten RAPD primers produced 138 markers of which 122 were polymorphic. Nine SSR primer pairs detected a total of 43 alleles with an average of 4.8 alleles per locus. The polymorphic information content (PIC) ranged from 0.47 to 0.77 for the RAPD primers and from 0.39 to 0.97 for the SSR loci. Similarity matrices obtained with SSR and RAPD, respectively, were highly correlated but only RAPD was able to provide each sample with an individual-specific DNA profile. Dendrograms and multidimensional scaling (MDS) produced two major clusters; one with the five cow-melon accessions and the other with the three sweet watermelon accessions. One of the most variable cow-melon accessions took an intermediate position in the MDS analysis, indicating the occurrence of gene flow between the two subspecies. Analysis of molecular variation (AMOVA) attributed most of the variability to within-accessions, and contrary to previous reports, sweet watermelon accessions apparently contain diversity of the same magnitude as the cow-melons.

Genetic population structure and hybridization in two sibling species, Tomoplagia reticulata and Tomoplagia pallens (Diptera: Tephritidae)

Tomoplagia reticulata and T. pallens are sibling species that are specialists on Eremanthus glomerulatus. Besides adult terminalia, they show slight morphological differences and distinct geographic distributions. Once, however, they were found sympatrically. Using data from allozyme and mtDNA, we examined patterns of intra- and interspecific genetic structure, and investigated the possible occurrence of gene flow between them. Both species showed low diversity and high genetic structure, which can be linked to their high degree of specialization. Larval development occurs within flower heads, tissues that are available only during a short period of the year. Afterward, as they do not hibernate, they probably suffer a great reduction in population size, which leads to low genetic diversity. As monophagous insects, their population structure may correspond to the fragmented distribution of E. glomerulatus, which could isolate fly populations and increase inbreeding within them. One population exhibited a mixed genetic composition, compatible with one hybridization season when species were sympatric. This hybridization seems to be a rare event, due to T. pallens unusual range expansion.

Large extent of mitochondrial DNA transfer from Oreochromis aureus to O. niloticus in West Africa.

Introgressive hybridization has an important evolutionary significance in terms of gene diversity and speciation. Among the major groups of vertebrates, fish show a strong propensity to hybridize. In order to highlight the possible occurrence of gene flow between two tilapia species, Oreochromis niloticus and O. aureus, a comparison of allozyme and mitochondrial DNA (mtDNA) polymorphism was performed on sympatric and allopatric populations of these two species. Nuclear data were congruent with the morphological identification of O. niloticus and O. aureus populations. In opposition, the mtDNA analysis resulted in two strictly differentiated groups which did not follow the morphological and nuclear DNA classification. The first group consisted of East African O. niloticus populations and the second included all the O. aureus populations and the West African O. niloticus populations. Moreover, in some cases, the same sequences were detected in both species. These data strongly support a differential introgression of mtDNA from O. aureus to O. niloticus involving all the West African area. This work points out the risk of misinterpretation of mtDNA or nuclear DNA data when only one single class of marker is used.