The tench Tinca tinca (Linnaeus, 1758) is a valued table fish native to Europe and Asia, but which is now widely distributed in many temperate freshwater regions of the world as the result of human-mediated translocations. Spatial genetic analysis applied to sequence data from four unlinked loci (introns of three nuclear genes and mitochondrial DNA) defined two groups of populations that were little structured geographically but were significantly differentiated from each other, and it identified locations of major genetic breaks, which were concordant across genes and were driven by distributions of two major phylogroups. This pattern most reasonably reflects isolation in two principal glacial refugia and subsequent range expansions, with the Eastern and Western phylogroups remaining largely allopatric throughout the tench range. However, this phylogeographic variation was also present in European cultured breeds and some populations at the western edge of the native range contained the Eastern phylogroup. Thus, natural processes have played an important role in structuring tench populations, but human-aided dispersal have also contributed significantly, with the admixed genetic composition of cultured breeds most likely contributing to the introgression. I have then designed novel PCR-RFLP assays...

The aim of this thesis was to evaluate the genetic diversity of mtDNA of populations in Central Europe and to assess its relation to geographic distances and/or linguistic affiliation of individual populations. For this purpose, HVS-1 mtDNA segments of 194 individuals of 6 Slovak populations were sequenced. Basic parameters of genetic diversity were estimated for obtained sequences, and compared with similar data published by other authors (4 798 sequences of HVS-1 mtDNA segment of 42 population units in Central Europe in total). Intra-population analysis revealed a high level of gene and nucleotide diversity of studied populations, with values clearly decreasing from north to south. While the Slovak populations were bearing the highest rates of genetic diversity, the lowest values were detected in the Croatian populations. The results of ΦST distances point to a certain similarity of the Slavic population (Slovakia, Czech Republic, Poland, Slovenia, Serbia, Bosnia and Herzegovina), Germanic (Germany, Austria, Switzerland) as well as some groups from Hungary and Romania. As the most distant appeared especially the population of Croatia, which differed from almost all populations included in the study. AMOVA showed that the geographic division of population explains the layout of genetic variation...

Le plateado ou dorado - Brachyplatystoma rousseauxii (Pimelodidae, Siluriformes) est un grand poisson-chat Amazonien d’intérêt commercial, qui présente un des cycles de vie les plus surprenants et énigmatiques, avec la plus grande migration connue en eaux douces, entre l’estuaire de l'Amazone et les têtes de fleuves en Amazonie occidentale. Le but de ce travail était de déterminer, au niveau moléculaire, la position phylogénétique du plateado dans la famille Pimelodidae ainsi que sa structure génétique dans le Haut Madera (Villa Bella–VB, Cachuella Esperanza–CE, Puerto Maldonado–PM, Rurrenabaque–RU, Puerto Villarroel–PV) et ouest de l'Amazonie (Iquitos–IQ) bassins (Bolivie et Pérou). Les relations phylogénétiques ont été définies par une analyse du maximum de vraisemblance (ML) des séquences nucléotidiques de deux gènes mitochondriaux (Région de Contrôle–RC, ~ 900 pb, 32 taxons; Cytochrome Oxydase 1-CO1, ~ 650 pb, 61 taxons), et d’un gène nucléaire (F-reticulon4–RTN4, ~ 1700 pb, 38 taxons). La structure génétique des populations a été évaluée par le polymorphisme de longueur de neuf microsatellites (284 inds) et par les variations de séquence de la RC (461 inds + 45 en provenance du Brésil, disponibles dans GenBank). Les variations de fréquences des microsatellites ont été utilisées pour identifier les unités panmictiques (clusters) les plus probables dans l'ensemble des données, à travers une approche bayésienne (BAPS), après avoir démontré une déviation significative à l'équilibre de Hardy-Weinberg (HWE) quand l’ensemble des données étaient analysé comme faisant partie d’une seule unité.L’analyse phylogénétique concaténée (ML) a montré que la famille Pimelodidae était un groupe monophylétique. Les résultats les plus notables de la phylogénie sont la monophylie peu soutenue (77%) de la tribu Brachyplatystomatini et la non-monophylie des Brachyplatystoma. Seul le sous-genre Malacobagrus (B. rousseauxii + (B. filamentosum + B. capapretum)), défini morphologiquement, s’est avéré monophylétique. Ces résultats suggèrent que le genre Brachyplatystoma pourrait contenir Platynematichthys ou pourrait être limité au sous-genre Malacobagrus.L'analyse des microsatellites sur l'ensemble des échantillons (ouest Amazone + haut Madera) a montré un écart significatif á la panmixia, ainsi que sur l'ensemble des échantillons du haut Madera. A la lumière de ces résultats, l’approche bayésienne a été développée, montrant qu'au moins trois clusters (1, 2, 3) sont présents dans les bassins du haut Madera et de l'ouest de l'Amazone, avec des répartitions qui se chevauchent partiellement. En parallèle á l'identification des clusters, il a été mis en évidence une différence significative au sein de B. rousseauxii entre l’ouest de l'Amazonie et le haut Madera bassin.L'analyse généalogique (ML) des séquences de la RC a montré une topologie en peigne, sans groupe d'haplotypes montrant une histoire commune. En revanche, l'analyse des fréquences haplotypiques a révélé l’existence de 4 haplogroupes, liés à la géographie. Un haplogroupe a été identifié le long de l'axe principal de l’Amazonas-Solimões (Belem-Brésil et Iquitos-Pérou) et 3 autres dans le haut Madera (VB; CE+MD; RU+PV), organisés selon une tendance aval - amont. Ainsi, nous observons d’un coté 3 populations (clusters) avec une distribution géographique partiellement chevauchante, et de l’autre quatre haplogroupes positionnés selon une logique géographique. Le scenario le plus probable implique un comportement de homing des individus du cluster 1 (homing à l’échelle des grands sous-bassins), qui préfèrent ou tendent à retourner dans le sous-bassin du Madera. Les 3 populations coexisteraient alors dans le haut Madera en se reproduisant à des périodes (phénologie) ou à des endroits différents (ségrégation spatiale). Enfin, les résultats sont discutés à la lumière des résultats précédemment publiés dans le bassin de l'Amazone et des menaces qui pèsent sur l'espèce dans le bassin du Madera. / The Plateado or Dorado - Brachyplatystoma rousseauxii (Pimelodidae, Siluriformes) is a commercial migratory catfish species with one of the most surprising and enigmatic life histories in the Amazon basin, involving the largest migration known for a freshwater species, between the estuary and the head waters in the Andean piedmont. The aim of the present work was to determine the molecular phylogenetic position of the Plateado in the Pimelodidae family and its population genetic structure in the Upper Madera (Villa Bella – VB, Cachuella Esperanza – CE, Puerto Maldonado – PM, Rurrenabaque – RU, Puerto Villarroel - PV) and Western Amazon (Iquitos - IQ) basins (Bolivia and Peru). The phylogenetic relationships were defined through a Maximum Likelihood (ML) analysis of nucleotide sequences of two mitochondrial (Control Region – CR, ~ 900 pb, 32 taxa; Cytochrome Oxidase 1 – CO1, ~ 650 bp, 61 taxa), and a nuclear fragment (F-reticulon4 - RTN4, ~1700 bp, 38 taxa). The population genetic structure was evaluated through the length polymorphism of nine microsatellites (284 inds) and CR sequence variations (461 inds + 45 from Brazil available in GenBank). Microsatellites frequencies variations were used to identify through a Bayesian approach (BAPS) the most probable panmictic units (clusters) in the whole data, after previous demonstration of a deviation to Hardy-Weinberg Equilibrium (HWE). The ML phylogenetic concatenated analysis showed the Pimelodidae family as a monophyletic group, with the genera Phractocephalus and Leiarius as basal lineages. The most notable results in the phylogeny were the not well-supported monophyly (77%) of the tribe Brachyplatystomatini and the non-monophyly of Brachyplatystoma. Only the morfologically defined subgenus Malacobagrus (B. rousseauxii + (B. filamentosum + B. capapretum)) was recovered as monophyletic. These results suggest that Brachyplatystoma could contain Platynematichthys or be restricted to the subgenus Malacobagrus, and the other species be related to distinct (earliest) genera, in agreement with another study carried out in parallel with other markers.Microsatellite analysis of the whole data (Western Amazon + Upper Madera) showed a significant departure of the HWE expectations, as well as the analysis of the whole data from the Upper Madera region. In the light of these results, the Bayesian approach has been implemented, showing that at least three clusters (1, 2, 3) are present in the Upper Madera and Western Amazon basins with partial overlapping distribution.To the margin of the cluster identification, it was evident the significant difference between Western Amazon (Iquitos region) and the Upper Madera basin.The genealogical analysis (ML) of the CR sequences showed a generalized comb-like topology without group of haplotypes with common ancestry. On the other hand, CR frequency analysis showed the conformation of four haplogroups associated to geography. One haplogroup was identified along the main axis of the Amazonas-Solimões, from Belem (Brazil) to Iquitos (Peru), and three other haplogroups were observed in the Upper Madera basin (VB; CE+PM; RU+PV), positioned in a downstream - upstream pattern.Hence, we observed on the one hand three genetic populations (clusters), distributed in partially overlapping geographical areas, and on the other hand four haplogroups, positioned according to a geographical pattern. The most probable scenario involves a homing behavior of individuals from cluster 1 (homing at the scale of large watersheds), which prefer or tend to return to the Madera basin, with the three populations coexisting within the upper Madera because they reproduce at different moments (phenology) or different places (spatial segregation). Finally, the results are discussed in the light of previous results in the Amazon basin and the threats to the species in the Madera basin (p.e. fragmentation by dams, overfishing, climate variability, among other).

The praying mantis (Mantis religiosa) is the only representative of the order Mantodea in central Europe. Within Czech Republic, this species is distributed mostly on xerothermic localities in southern Moravia. However, M. religiosa has been spreading more to the north not only in Czech Republic, but also in other Europian countries recently. The aim of this study was to reconstruct phylogeography based on genetic markers. It seems that studied species was distributed at least in three lineages in Europe, which could be connected with glacial refugias. First lineage was spread to the north probably from Pyrenean peninsula, second lineage from Crimea peninsula and third lineage from Balkan area. Nine microsatellite loci were tested and will be used for consequent sctudy of phylogeography and distribution of M. religiosa within Europe. Keywords: Mantis religiosa, mtDNA, microsatellite, expansion, phylogeography, phylogeny.

Master of Science / Division of Biology / Samantha M. Wisely / Range-wide estimates of shorebird (Aves: Charadriiformes) populations suggest sharp declines in population sizes across a range of species. Efforts to accurately assess the conservation status of wild populations are becoming increasingly vital to species management. One shorebird of conservation concern, the Buff-breasted Sandpiper (Tryngites subruficollis), is a New World migrant which winters in southeastern South America and breeds in the arctic. To establish an updated conservation status for Buff-breasted Sandpipers, we conducted a molecular survey of wild populations on spatial and temporal scales. We analyzed patterns of global population structure, demographic trends, and phylogeography using nine polymorphic microsatellites and two mitochondrial DNA (mtDNA) markers, cytochrome b and the control region, among 477 individuals across their distributional range. To empirically assess the impact of population declines on genetic diversity, we also surveyed segments of the same two mtDNA markers from 220 museum specimens collected across a 135-year period. Contemporary microsatellite and mtDNA analyses revealed that Buff-breasted Sandpipers are admixed on a global scale, with effective population size estimates ranging from 2,657 to 16,400 birds and no signal of a recent genetic bottleneck. Contemporary mtDNA analyses suggested a pattern of haplotype diversity consistent with a historic radiation from a single refugium which we estimated to have occurred between 8,000−45,000 years before present. Using five measures of mtDNA diversity (haplotype and nucleotide diversity, trend analyses of haplotype richness, Watterson’s estimate of theta, and phi-statistics), as well as a Bayesian Skyline reconstruction of demographic trends in effective population size (N[subscript]e[subscript]f), we concluded that substantial mtDNA diversity and N[subscript]e[subscript]f had not been lost as a result of the population declines in this species. While genetic diversity did not appear to have been lost due to population losses, management efforts must focus on preventing future losses in order for wild populations to remain viable. Our results suggested that the global population of Buff-breasted Sandpipers should be treated as a single, panmictic conservation unit and that successful management must focus on preventing further declines and habitat fragmentation.

Understanding worldwide declines in reptiles due to factors such as habitat loss and emerging infectious disease has become an increasingly important focus in conservation biology. Here, I use novel approaches from the field of landscape genetics to combine spatial genetic data with landscape data at both regional and local spatial scales to explore natural and anthropogenic landscape features that shape population structure and gene flow in a federally threatened reptile, Gopherus polyphemus. I also utilize approaches from the field of spatial epidemiology to examine the extent to which environmental variables can be used to predict the seroprevalence of an associated pathogen Mycoplasma agassizzi in gopher tortoise populations. Using mitochondrial data, I find evidence of a historical barrier to gene flow that appears to coincide with the Apalachicola River. I also discover low genetic diversity and evidence of population bottlenecks in the western portion of the range. My evaluation at the regional scale shows that dispersal is limited by geographic distance, areas of low elevation and major roads ways. A finescale study reveals no evidence of spatial genetic structure within a 14 x 35 km area. However, soil type is significantly correlated with pairwise genetic distances between individuals, suggesting that this variable influences fine-scale population structure in the gopher tortoise. In addition to soil, high density canopy cover is an important factor impeding gene flow at the local level for females, while land cover type explains some of the genetic variance between males. Finally, temperature and precipitation appear to be important predictors of the seroprevalence of the pathogen Mycoplasma agassizii in gopher tortoises. The probability of an individual testing seropositive for exposure to this disease increased with high temperature and low precipitation values. The methods presented in this dissertation evaluate novel approaches for assessing the influence of environmental variables on population structure, dispersal and disease occurrence and could be applied in future studies of other threatened and endangered taxa.

<p>Ovom tezom je obuhvaćena analiza genetičke strukture i filogeografskog položaja vuka (<em>Canis lupus L. </em>1758) na teritoriji Bosne i Hercegovine, na uzorku od ukupno 79 jedinki. Analize su sprovedene primjenom (i) 18 mikrosatelitskih lokusa nDNK pomoću kojih su detektovani: nivo genetičke varijabilnosti, populaciona struktura, prolazak populacije kroz genetičko usko grlo, te ukr&scaron;tanje u srodstvu, i (ii) kontrolnog&nbsp; regiona&nbsp; (CR)&nbsp; regiona&nbsp; mtDNK&nbsp; pomoću&nbsp; kojih&nbsp; su sprovedene filogeografske analize.&nbsp; U&nbsp; radu&nbsp; je&nbsp; uočeno&nbsp; je&nbsp; grupisanje&nbsp; jedinki&nbsp; vuka&nbsp; Bosne&nbsp; i Hercegovine&nbsp; u&nbsp; dva&nbsp; genetička&nbsp; klastera&nbsp; &scaron;to,&nbsp; s&nbsp; obzirom&nbsp; na&nbsp; slabu&nbsp; statističku&nbsp; podržanost, najvjerovatnije&nbsp; ukazuje&nbsp; na&nbsp; prisustvo&nbsp; strukture&nbsp; na&nbsp; većem&nbsp; nivou.&nbsp; Prethodno&nbsp; navedeno&nbsp; je detektovano analizama populacione strukture dijela dinarsko - balkanske populacije vuka,gdje je uočena distribucija vukova Bosne i Hercegovine i Srbije u odvojene genetičke klastere. Statistički značajni signali prolaska populacije vuka Bosne i Hercegovine kroz genetičko usko grlo u skorijoj pro&scaron;losti nisu detektovani. Sekvence kontrolnog regiona mtDNK vuka pokazale su se dovoljno informativnim za detekciju jedinstvenih haplotipova vuka Bosne i Hercegovine, za&nbsp; koje&nbsp; je&nbsp; uočena&nbsp; distribucija&nbsp; u&nbsp; dvije,&nbsp; prethodno&nbsp; u&nbsp; literaturi, detektovane haplogrupe bez jasnog alopatrijskog obrasca. Pored toga, analizama sekvenci dijela kontrolnog regiona mtDNK&nbsp; uzorka&nbsp; vuka&nbsp; Evrope,&nbsp; uočeno&nbsp; je da se demografska ekspanzija haplogrupe 2 desila mnogo ranije u pro&scaron;losti u odnosu na period ekspanzije haplogrupe 1, koji se poklapa sa periodom razdvajanja navedenih haplogrupa, prije oko 13000 godina, &scaron;to ukazuje da je posljednji glacijalni maksimum imao uticaja u oblikovanju strukture genetičkih linija vuka u pro&scaron;losti. Rezultati dobijeni u ovom istraživanju su veoma informativni u cilju uspostavljanja pravilnog menadžmenta vrste i kreiranja plana za&scaron;tite vuka na nivou Bosne i Hercegovine, odnosno, na nivou dinarsko - balkanske populacije vuka iz koje se vr&scaron;e rekolonizacije jedinki u susjedne populacije.</p> / <p>In this thesis, the genetic structure and phylogeography of the wolf (Canis L. 1758) in the territory of Bosnia and Hercegovina were analysed, from a total sample of 79 individuals. Analyses were conducted by applying (i) 18 microsatellite loci of nuclear DNA, by which we estimated: the level of genetic&nbsp; variability, population structure, kinship, bottleneck and inbreeding, and (ii) control region of mtDNA by which we analysed phylogeography. Two genetic clusters were observed for the wolf population&nbsp; from Bosnia and Hercegovina, although with statistically low support, which may point to structuring at the higher level. Indeed, after analysing the population structure at the higher, Dinaric - Balkan level, the distribution of wolves&nbsp; from Bosnia and Hercegovina and&nbsp; Serbia was observed as falling into two distinct genetic clusters. Statistically significant signs of the recent bottleneck were not observed in the wolf&nbsp; population from Bosnia and Hercegovina. Analyses of control region mtDNA were conducted with the aim of detecting haplotypes in the Bosnia and Hercegovina population, as well as in the European&nbsp; samples. Distribution of&nbsp; haplotypes into two haplogroups, described in previous literature, was&nbsp; observed, without a clear alopatric phylogeny pattern. Furthermore, the analyses of the same&nbsp; molecular marker showed that demographic expansion of haplogroup 2 occurred significantly earlier when compared to the demographic explosion of haplogroup 1 . Results from this study are extremely&nbsp; important for the creation of a management plan for wolves from Bosnia and Hercegovina, and at the higher Dinaric - Balkan level.</p>

O gênero Pagurus é um táxon heterogêneo de ermitões, com ampla distribuição mundial, descrito há mais de duzentos anos. A sistemática do grupo é complexa com uma longa história de rearranjos taxonômicos. A classificação conta com a inclusão de numerosas novas espécies e separação de algumas inicialmente contidas no táxon estabelecendo-se novos gêneros. Devido à extensa distribuição das espécies que compõem o táxon, foi necessário restringir o objetivo deste estudo. Assim foi avaliado o status taxonômico das espécies que ocorrem nas costas Pacífica e Atlântica da América do Sul, por meio da combinação de análises morfológicas e moleculares das espécies, utilizando dois marcadores genéticos (16S rDNA e Histona 3). As análises taxonômicas mostraram uma alta variabilidade morfológica nas 22 espécies examinadas. As espécies se encaixam perfeitamente em quatro dos onze grupos preestabelecidos dentro de Pagurus. Além disso, foram fornecidos os caracteres morfológicos que definem um desses grupos. Adicionalmente foi incluída uma chave para ajudar na identificação de todas as espécies. As análises independentes dos dados moleculares mostraram resultados contrastantes. O gene mitocondrial foi mais variável e portanto mais informativo, proporcionando uma hipótese mais clara das relações internas entre os membros de Pagurus. Assim, as topologias moleculares resultantes, concordaram em vários aspectos com o reportado nos dados morfológicos das espécies. De modo que, as semelhanças morfológicas foram refletidas na formação dos nós internos. Assim, as análises do gene 16S e H3 mostraram-se concordante com a morfologia, refletindo-se na formação de alguns dos grupos previamente propostos. Como ponto importante, ressalta-se a separação das espécies que compõe o grupo provenzanoi como um táxon diferenciado dentro de Pagurus. Ao mesmo tempo, as análises com o gene H3 mostraram a espécie Propagurus gaudichaudii inserida dentro de Pagurus, questionando a validade taxonômica de Propagurus. Como só foi incluída uma das cinco espécies do gênero, é claramente necessário a inclusão de outras espécies contidas neste táxon, bem como alguns outros genes uma revisão das espécies contidas neste táxon, junto com análises de outros genes, a fim de resolver definitivamente o status taxonômico de Propagurus. / The genus Pagurus is a heterogeneous taxon of hermit crabs, with worldwide distribution which was described more than two hundred years ago. Systematics of the group is complex and with a long history of taxonomic rearrangements. Thus current classification accounts for inclusion of many new species and splitting-off of some of the original species in order to establish new genera. Because of the extensive distribution of the species that conform this taxon it was necessary to restrict the aim of this study. Thus I evaluated the taxonomic status of the species found in the Pacific and Atlantic coasts of South America using a combination of both morphologic and molecular analyses (16S rDNA and Histona 3). The taxonomic analysis showed high morphological variation among all the 21 examined species. The analyzed species seemed to perfectly fit four out of the eleven morphologically pre-established groups of Pagurus. Furthermore I provide morphological characters that define one of these groups. Additionally, I included a key to aid in the identification of all the target species. Independent analysis of the molecular data showed contrasting results. The mitochondrial gene was the most variable and thus the most informative, providing a clearer hypothesis of the internal relationships among members of Pagurus. Therefore, both 16S and H3 analyses were in general agreement with the morphology. Thus, the resultant molecularly based topologies reflected some of the groups previously proposed. It is important to point out that all the included species belonging to the provenzanoi group were clustered together separated from other clades within Pagurus. At the same time, the analysis with the gen H3 showed Propagurus gaudichaudii clustered within Pagurus, thus questioning the taxonomic validity of Propagurus. As I only included one of the five species of the genus, it is obviously necessary to include other the species contained in this taxon, as well as some other genes in order to definitely solve the taxonomic status of Propagurus.

Understanding the degree of connectivity among populations, forming migratory links and evaluating factors that influence reproductive fitness is fundamental for the successful management of migratory species of conservation concern. In this thesis I focus on a regionally important rookery of green turtles (Chelonia mydas) at Alagadi beach in northern Cyprus that has been intensively studied since 1992. I employ high resolution genetic markers with different modes of inheritance to reveal fine scale population structuring among four rookeries within a 200 km stretch of shoreline. The relative importance of four foraging areas and the annual contribution from each site to the breeding cohort are evaluated using the stable isotope ratios of the turtles calibrated by satellite telemetry. The stable isotope ratios of the turtles reveal that a previous undisclosed foraging site at Lake Bardawil in Egypt is critical for the population recovery of the Alagadi rookery. The temporal consistency of stable isotope ratios reaffirm that green turtles exhibit high fidelity to foraging sites allowing the evaluation of foraging area effects on reproductive traits to be evaluated over multiple seasons. I investigate the population sub-structuring of the Alagadi nesting aggregation grouped by the foraging area used. The absence of genetic structure supported the Learning Migration Goal Theory and provided evidence that the significant among site phenotypic variability in the body size of recruits, the length of interbreeding intervals and the date that the first nest of the season was made is a result of foraging areas effects. No significant among site phenotypic variability was found for the size or number of clutches laid. Among site variability in interbreeding intervals resulted in substantial variation in the reproductive potential of individuals due to assumed differences in resource availability and environmental factors. The multilocus genotypes generated for 243 nesting females were employed to reconstruct the first wild marine turtle pedigree using a full-likelihood sib-ship reconstruction approach. This revealed that the effective contribution to the next generation was unequal and allowed a minimum age to maturity to be estimated from parent – offspring assignations. However, sample size constraints prevented accurate estimates for the narrow-sense heritability of the five morphological and life-history traits from the quantitative genetic analysis. The multifaceted approach taken here to unravel the cryptic life-history of marine turtles emphasises the importance of long-term individual-based monitoring and the data generated can be employed to advise conservation strategy for this critically endangered regional management unit.

A espécie Bos indicus, particularmente a raça Nelore, é grande maioria no rebanho bovino da região acima do trópico no Brasil. Embora a habilidade desses animais em resistir às doenças parasitárias, condições climáticas e pastagens de baixa qualidade enalteçam a utilização em larga escala desta raça, estes animais não são considerados bons conversores de alimento e, conseqüentemente, precoces em comparação aos seus homólogos Bos taurus. Durante a formação das raças zebuínas brasileiras, houve uma participação das linhas maternas de Bos taurus, que pode ser demonstrada pela contribuição majoritária do genoma mitocondrial desta subespécie. Embora em escala muito menor, estima-se que exista também uma participação destas linhas maternas no genoma nuclear. O objetivo deste trabalho foi iniciar os estudos para estimar esta participação. Para os estudos foram utilizados 104 animais da raça Nelore e 8 animais de diferentes raças européias. Cinco regiões do DNA que produzem fragmentos microssatélites taurus/indicus específicos (HEL1, HEL9, ETH225, ILSTS005 e INRA063) foram amplificadas com a utilização de primers marcados com sondas fluorescentes. Os fragmentos foram submetidos à eletroforese em gel de poliacrilamida desnaturante 6% e visualizados após excitação com laser. No total foram encontrados 23 alelos para os microssatélites analisados o que representa uma média de 4,6±1,82 alelos por locus. Amplificou-se também uma região do DNA satélite 1711b que posteriormente foi digerida com a enzima de restrição Msp I. Verificou-se a existência de três possíveis genótipos entre os animais Nelore mtDNA Bos taurus e mtDNA Bos indicus. Os animais europeus analisados apresentaram sempre o mesmo padrão de restrição. A comparação dos componentes de variância do tamanho dos alelos intra e inter população usando os fragmentos microssatélites permitem a separação dos animais Bos taurus dos animais Nelore, mas não dos Nelore de origem materna distinta. No entanto, a freqüência de alelos indicus específicos nos microssatélites e de padrões de digestão do DNA satélite também indicus específicos sugerem uma participação da ordem de aproximadamente 6% do genoma taurus na população de gado Nelore. / Bos indicus specie, especially Nellore breed is responsible for the majority of Brazilian tropical herd. These animals are notably capable to endure parasite infection as well as hot weather and low quality feed. In one hand this qualities suggest the large scale application of this breed, but in other hand this same breed is well characterized as bad food converter and consequently far from having good precocity status compared with its Bos taurus homologues. It has been reported a matrilineal European participation in Zebu cattle since its introduction in American lands. This hybridization is confirmed by the majority contribution of Bos taurus mtDNA in these animals. Although in a much lower frequency, we hypothesize a Bos taurus cow participation in nuclei genome. The main aim of this work was to give the firsts steps towards the estimation of this participation. A total of 104 Nellore and 8 animals of different European breeds were used for DNA analysis. Five microsatellites fragments (HEL1, HEL9, ETH225, ILSTS005 e INRA063) were amplified applying primers with fluorescent dye. Amplified fragments were used in 6% polyacrilamide electrophoresis and visualized after laser excitation. Overall 23 alleles were detected averaging 4.6±1,82/locus. Variance components of microsatellites allele size comparisons allowed the formation of two clusters separating both subspecies. No significant variation was observed between Nellore with different maternal origins. A satellite 1711b DNA was also amplified and digested with the restriction enzyme Msp I. Three possible genotypes were identified in Nellore animals harboring B. taurus and B. indicus mtDNA. European originated animals always showed the same restriction pattern. Finally B. indicus specific microsatellite allele and satellite 1711b digestion patterns frequency allowed the estimation of 6% of B. taurus contribution in purebred Nellore. These results are discussed in terms of application in cattle genetic improvement.