<p>Abstract</p><p>In Oneida Lake, New York, USA, three species of amphipods are present: Hyalella azteca is native, Gammarus fasciatus is invasive and was first observed sometime before 1940 and Echinogammarus ischnus was introduced in 2001 in shallow water. The purpose of this study was to investigate the spatial and temporal abundance of amphipods in Oneida Lake. In the Great Lakes, the invasive E. ischnus has outcompeted G. fasciatus and this was also expected to be occur in Oneida Lake. Quantitative field sampling of transects that extended from the shore to deeper water (3.8 m) at six sites around Oneida Lake showed that the abundance of all amphipod species had a positive correlation to the abundance of zebra mussels (Dreissena polymorpha). Echinogammarus ischnus were observed at low densities (mean, 18 no./m2) in shallow water (<0.6 m) areas with cobbles covered with zebra mussels, whereas just a few individuals were found in deep water. At all depths, G. fasciatus were found at high densities (mean 950 no./m2), and H. azteca were present at low densities (mean 77 no./m2). The main factor limiting E. ischnus and its coexistence with G. fasciatus is the lack of favourable habitat i.e. too few cobble areas and too much Cladophora spp. and other macrophyte species growing in the lake. In addition, exposure of shallow water habitats every fall and winter as a consequence of water level manipulations produces unfavorable habitat for E. ischnus.</p> / <p>Sammanfattning</p><p>I sjön Oneida Lake, New York, USA, finns tre arter av märlkräftor (Amphipoda): Hyalella azteca är naturligt förekommande i sjön, Gammarus fasciatus hittades för första gången någon gång före år 1940 och Echinogammarus ischnus hittades för första gången 2001 på grunt vatten. Syftet med studien var att undersöka märlkräftornas utbredning och abundans över tid i Oneida Lake. I de Stora sjöarna (the Great Lakes) i Nordamerika har den invaderande E. ischnus konkurrerat ut G. fasciatus och samma sak förväntades att finna i Oneida Lake. I fält togs kvantitativa stickprover i transekter från strandlinjen och ut till djupt vatten (3,8 m), dessa visade att samtliga märlkräftsarter hade en positiv abundans korrelation med zebra musslor (Dreissena polymorpha). E. ischnus hittades i låga densiteter (medel 18 st/m2) på stenar täckta med zebra musslor på grunt vatten (<0,6 m) och endast ett fåtal individer hittades på djupt vatten. I Oneida Lake på alla djup hittades G. fasciatus i höga densiteter (medel 950 st/m2) medan H. azteca endast fanns i låga densiteter (medel 77 st/m2). Största anledningen till E. ischnus begränsning till samexistens med G. fasciatus är avsaknaden av gynnade habitat i sjön, det vill säga för få områden med stenar, samt att det växer för mycket alger (Cladophora spp.) och andra växter i sjön vilket missgynnar E. ischnus. Även vattennivåreglering under höst och vinter är ogynnsam för E. ischnus, då habitat på grunt vatten blir exponerande.</p>

Abstract In Oneida Lake, New York, USA, three species of amphipods are present: Hyalella azteca is native, Gammarus fasciatus is invasive and was first observed sometime before 1940 and Echinogammarus ischnus was introduced in 2001 in shallow water. The purpose of this study was to investigate the spatial and temporal abundance of amphipods in Oneida Lake. In the Great Lakes, the invasive E. ischnus has outcompeted G. fasciatus and this was also expected to be occur in Oneida Lake. Quantitative field sampling of transects that extended from the shore to deeper water (3.8 m) at six sites around Oneida Lake showed that the abundance of all amphipod species had a positive correlation to the abundance of zebra mussels (Dreissena polymorpha). Echinogammarus ischnus were observed at low densities (mean, 18 no./m2) in shallow water (&lt;0.6 m) areas with cobbles covered with zebra mussels, whereas just a few individuals were found in deep water. At all depths, G. fasciatus were found at high densities (mean 950 no./m2), and H. azteca were present at low densities (mean 77 no./m2). The main factor limiting E. ischnus and its coexistence with G. fasciatus is the lack of favourable habitat i.e. too few cobble areas and too much Cladophora spp. and other macrophyte species growing in the lake. In addition, exposure of shallow water habitats every fall and winter as a consequence of water level manipulations produces unfavorable habitat for E. ischnus. / Sammanfattning I sjön Oneida Lake, New York, USA, finns tre arter av märlkräftor (Amphipoda): Hyalella azteca är naturligt förekommande i sjön, Gammarus fasciatus hittades för första gången någon gång före år 1940 och Echinogammarus ischnus hittades för första gången 2001 på grunt vatten. Syftet med studien var att undersöka märlkräftornas utbredning och abundans över tid i Oneida Lake. I de Stora sjöarna (the Great Lakes) i Nordamerika har den invaderande E. ischnus konkurrerat ut G. fasciatus och samma sak förväntades att finna i Oneida Lake. I fält togs kvantitativa stickprover i transekter från strandlinjen och ut till djupt vatten (3,8 m), dessa visade att samtliga märlkräftsarter hade en positiv abundans korrelation med zebra musslor (Dreissena polymorpha). E. ischnus hittades i låga densiteter (medel 18 st/m2) på stenar täckta med zebra musslor på grunt vatten (&lt;0,6 m) och endast ett fåtal individer hittades på djupt vatten. I Oneida Lake på alla djup hittades G. fasciatus i höga densiteter (medel 950 st/m2) medan H. azteca endast fanns i låga densiteter (medel 77 st/m2). Största anledningen till E. ischnus begränsning till samexistens med G. fasciatus är avsaknaden av gynnade habitat i sjön, det vill säga för få områden med stenar, samt att det växer för mycket alger (Cladophora spp.) och andra växter i sjön vilket missgynnar E. ischnus. Även vattennivåreglering under höst och vinter är ogynnsam för E. ischnus, då habitat på grunt vatten blir exponerande.

Freshwater ecosystems worldwide are being altered by multiple stressors. One of the most important stressors is biological invasion---the introduction of exotic species, which can contribute to the loss of native species. The effects of an introduced species are correlated with its abundance and typically vary across ecosystems, suggesting that its impact on native species is mediated by its environment, i.e. the physical habitat and the recipient community. However, there are few studies that explore the effects of environment on the interactions between exotic and native species. My thesis examines the influence of physical habitat variables and community interactions on the relative abundance of exotic and native freshwater crustaceans in the St. Lawrence River. / The Eurasian amphipod Echinogammarus ischnus invaded the Great Lakes-St. Lawrence River system in the mid-1990s and has replaced the native North American Gammarus fasciatus as the dominant amphipod in littoral areas throughout Lake Erie and Lake Ontario.

Whole document restricted until 2010, see Access Instructions file below for details of how to access the print copy. / Blind Mexican cave fish (Astyanax fasciatus) lack a functioning visual system, and are known to use self-generated water motion to sense their surroundings; an ability termed hydrodynamic imaging. Nearby objects distort the flow field created by the motion of the fish. These flow distortions are sensed by the mechanosensory lateral line. Little is known about the fluid mechanics involved in hydrodynamic imaging, or how the behaviour of the fish might influence their ability to sense the world around them. Automated image analysis was used to study the effects of swimming kinematics on the ability of the fish to sense their surroundings when introduced into a novel environment. The fish reacted to avoid head-on collisions with a wall at a remarkably short mean distance of 4.0 ± 0.2 mm. The ability of the fish to react, was dependent on whether they were beating their tail as they approached the wall. When following surfaces, such as a wall, the fish changed their swimming kinematics significantly and used both tactile and hydrodynamic information. Measuring the tendency of the fish to follow a tightening curve showed the fish to be moderately thigmotactic. The flow fields around freely swimming fish were experimentally measured using Particle Image Velocimetry (PIV). A new algorithm was developed to calculate the pressure field around the fish based on the velocity field measured using PIV. The algorithm was validated against analytical and computational fluid dynamic (CFD) solutions. The flow fields around gliding fish and the stimuli to the lateral line of the fish were calculated using CFD models, validated against the experimental PIV data. The flow fields changed in characteristic ways as the fish approached a wall head-on or swam parallel to a wall. At 0.10 body lengths from a wall, the stimulus to the lateral line was estimated to be sufficient for the fish to be able to detect the wall, but this decreased rapidly with increasing distance from the wall. The CFD models suggested that the velocity of the fish does not affect the distance at which they detect an object. Hydrodynamic imaging is a short range sensory ability and blind cave fish require their sensitive lateral line and fast reactions in order to be able to use it to sense the world around them and avoid collisions. The information gained about the fluid mechanics of hydrodynamic imaging, and the flow measurement and modelling techniques developed here will be useful for further study of this remarkable ability.

Whole document restricted until 2010, see Access Instructions file below for details of how to access the print copy. / Blind Mexican cave fish (Astyanax fasciatus) lack a functioning visual system, and are known to use self-generated water motion to sense their surroundings; an ability termed hydrodynamic imaging. Nearby objects distort the flow field created by the motion of the fish. These flow distortions are sensed by the mechanosensory lateral line. Little is known about the fluid mechanics involved in hydrodynamic imaging, or how the behaviour of the fish might influence their ability to sense the world around them. Automated image analysis was used to study the effects of swimming kinematics on the ability of the fish to sense their surroundings when introduced into a novel environment. The fish reacted to avoid head-on collisions with a wall at a remarkably short mean distance of 4.0 ± 0.2 mm. The ability of the fish to react, was dependent on whether they were beating their tail as they approached the wall. When following surfaces, such as a wall, the fish changed their swimming kinematics significantly and used both tactile and hydrodynamic information. Measuring the tendency of the fish to follow a tightening curve showed the fish to be moderately thigmotactic. The flow fields around freely swimming fish were experimentally measured using Particle Image Velocimetry (PIV). A new algorithm was developed to calculate the pressure field around the fish based on the velocity field measured using PIV. The algorithm was validated against analytical and computational fluid dynamic (CFD) solutions. The flow fields around gliding fish and the stimuli to the lateral line of the fish were calculated using CFD models, validated against the experimental PIV data. The flow fields changed in characteristic ways as the fish approached a wall head-on or swam parallel to a wall. At 0.10 body lengths from a wall, the stimulus to the lateral line was estimated to be sufficient for the fish to be able to detect the wall, but this decreased rapidly with increasing distance from the wall. The CFD models suggested that the velocity of the fish does not affect the distance at which they detect an object. Hydrodynamic imaging is a short range sensory ability and blind cave fish require their sensitive lateral line and fast reactions in order to be able to use it to sense the world around them and avoid collisions. The information gained about the fluid mechanics of hydrodynamic imaging, and the flow measurement and modelling techniques developed here will be useful for further study of this remarkable ability.

Whole document restricted until 2010, see Access Instructions file below for details of how to access the print copy. / Blind Mexican cave fish (Astyanax fasciatus) lack a functioning visual system, and are known to use self-generated water motion to sense their surroundings; an ability termed hydrodynamic imaging. Nearby objects distort the flow field created by the motion of the fish. These flow distortions are sensed by the mechanosensory lateral line. Little is known about the fluid mechanics involved in hydrodynamic imaging, or how the behaviour of the fish might influence their ability to sense the world around them. Automated image analysis was used to study the effects of swimming kinematics on the ability of the fish to sense their surroundings when introduced into a novel environment. The fish reacted to avoid head-on collisions with a wall at a remarkably short mean distance of 4.0 ± 0.2 mm. The ability of the fish to react, was dependent on whether they were beating their tail as they approached the wall. When following surfaces, such as a wall, the fish changed their swimming kinematics significantly and used both tactile and hydrodynamic information. Measuring the tendency of the fish to follow a tightening curve showed the fish to be moderately thigmotactic. The flow fields around freely swimming fish were experimentally measured using Particle Image Velocimetry (PIV). A new algorithm was developed to calculate the pressure field around the fish based on the velocity field measured using PIV. The algorithm was validated against analytical and computational fluid dynamic (CFD) solutions. The flow fields around gliding fish and the stimuli to the lateral line of the fish were calculated using CFD models, validated against the experimental PIV data. The flow fields changed in characteristic ways as the fish approached a wall head-on or swam parallel to a wall. At 0.10 body lengths from a wall, the stimulus to the lateral line was estimated to be sufficient for the fish to be able to detect the wall, but this decreased rapidly with increasing distance from the wall. The CFD models suggested that the velocity of the fish does not affect the distance at which they detect an object. Hydrodynamic imaging is a short range sensory ability and blind cave fish require their sensitive lateral line and fast reactions in order to be able to use it to sense the world around them and avoid collisions. The information gained about the fluid mechanics of hydrodynamic imaging, and the flow measurement and modelling techniques developed here will be useful for further study of this remarkable ability.

Whole document restricted until 2010, see Access Instructions file below for details of how to access the print copy. / Blind Mexican cave fish (Astyanax fasciatus) lack a functioning visual system, and are known to use self-generated water motion to sense their surroundings; an ability termed hydrodynamic imaging. Nearby objects distort the flow field created by the motion of the fish. These flow distortions are sensed by the mechanosensory lateral line. Little is known about the fluid mechanics involved in hydrodynamic imaging, or how the behaviour of the fish might influence their ability to sense the world around them. Automated image analysis was used to study the effects of swimming kinematics on the ability of the fish to sense their surroundings when introduced into a novel environment. The fish reacted to avoid head-on collisions with a wall at a remarkably short mean distance of 4.0 ± 0.2 mm. The ability of the fish to react, was dependent on whether they were beating their tail as they approached the wall. When following surfaces, such as a wall, the fish changed their swimming kinematics significantly and used both tactile and hydrodynamic information. Measuring the tendency of the fish to follow a tightening curve showed the fish to be moderately thigmotactic. The flow fields around freely swimming fish were experimentally measured using Particle Image Velocimetry (PIV). A new algorithm was developed to calculate the pressure field around the fish based on the velocity field measured using PIV. The algorithm was validated against analytical and computational fluid dynamic (CFD) solutions. The flow fields around gliding fish and the stimuli to the lateral line of the fish were calculated using CFD models, validated against the experimental PIV data. The flow fields changed in characteristic ways as the fish approached a wall head-on or swam parallel to a wall. At 0.10 body lengths from a wall, the stimulus to the lateral line was estimated to be sufficient for the fish to be able to detect the wall, but this decreased rapidly with increasing distance from the wall. The CFD models suggested that the velocity of the fish does not affect the distance at which they detect an object. Hydrodynamic imaging is a short range sensory ability and blind cave fish require their sensitive lateral line and fast reactions in order to be able to use it to sense the world around them and avoid collisions. The information gained about the fluid mechanics of hydrodynamic imaging, and the flow measurement and modelling techniques developed here will be useful for further study of this remarkable ability.

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Submitted by Jorge Silva (jorgelmsilva@ufrrj.br) on 2018-03-27T18:34:33Z No. of bitstreams: 1 2013 - Fl?via Guerra Vieira de Menezes.pdf: 5858835 bytes, checksum: 4d6199e1cbd8ddce6884aa2b408fe0e5 (MD5) / Made available in DSpace on 2018-03-27T18:34:33Z (GMT). No. of bitstreams: 1 2013 - Fl?via Guerra Vieira de Menezes.pdf: 5858835 bytes, checksum: 4d6199e1cbd8ddce6884aa2b408fe0e5 (MD5) Previous issue date: 2013-02-22 / CNPq / This study aimed to identify the species that compose the endoparasite fauna of Astyanax fasciatus (Cuvier, 1819) from the upper S?o Francisco river to downstream of the dam of Tr?s Marias, Minas Gerais, Brazil, as well as record the parasitic parameters (prevalence, severity and abundance) and sites of infection for each helminths species A. fasciatus. Besides providing morphological and morphometric data of helminths species, the study also sought to identify possible correlations between parameters and parasitic total length, body weight and sex of the hosts still investigating ecological interactions of them based on the interpretation of possible cycles of biological endohelminth. A total of 74 specimens of A. fasciatus was collected in the upper S?o Francisco river to downstream of the dam of Tr?s Marias, Tr?s Marias municipality, state of Minas Gerais (18?12'32''S, 45?15'41''W), in the month of January 2011 and 2012. Fourteen species of parasites were found in A. fasciatus, being distributed in taxa Eucestoda (one specie), Nematoda (12 species) and Acanthocephala (one specie). They are: metacestodes, Contracaecum sp., Hysterothylacium sp., Goezia sp., Brevimulticaecum sp., Procamallanus (Spirocamallanus) saofranciscencis (Moreira Oliveira e Costa, 1994), Cystidicoloides sp., Spinitectus rodolphiheringi Vaz & Pereira, 1934, Rhabdochona sp., Spiroxys sp., Eustrongylides sp. and Neoechinorhynchus pimelodi Brazil-Sato & Pavanelli, 1998. The helminths fauna of A. fasciatus characterized mainly by larvae Contracaecum sp., Hysterothylacium sp., Spiroxys sp. and larvae and adults of P. saofranciscencis beyond metacestodes. It appears that this fish mainly acts as an intermediate host larvae of an unidentified species of cestode and nematode larvae, your diet has been the factor responsible for this. Astyanax fasciatus further assists in transmitting species such Rhabdochona sp. for carnivorous fish and also acts as a definitive host for P. saofranciscencis occupying so different trophic levels. / O presente estudo teve como objetivo identificar as esp?cies que comp?em a fauna endoparasit?ria de Astyanax fasciatus (Cuvier, 1819) do alto rio S?o Francisco ? jusante da barragem de Tr?s Marias, Minas Gerais, Brasil, bem como registrar os par?metros parasit?rios (preval?ncia, intensidade e abund?ncia) e os s?tios de infec??o de cada esp?cie de helminto de A. fasciatus. Al?m de prover os dados morfom?tricos e morfol?gicos das esp?cies de helmintos, o trabalho tamb?m procurou identificar poss?veis correla??es entre os par?metros parasit?rios e o comprimento total, o peso corporal e o sexo dos hospedeiros e investigar intera??es ecol?gicas dos mesmos baseando-se na interpreta??o de poss?veis ciclos biol?gicos dos endohelmintos. Um total de 74 esp?cimes de A. fasciatus foi coletado no alto rio S?o Francisco ? jusante da barragem de Tr?s Marias, munic?pio de Tr?s Marias, estado de Minas Gerais (18?12?32??S, 45?15?41??W), no m?s de janeiro de 2011 e 2012. Quatorze esp?cies de parasitos foram encontradas em A. fasciatus, sendo distribu?das nos t?xons Eucestoda (uma esp?cie), Nematoda (12 esp?cies) e Acanthocephala (uma esp?cie): metacest?ides, Contracaecum sp., Hysterothylacium sp., Goezia sp., Brevimulticaecum sp., Procamallanus (Spirocamallanus) saofranciscencis (Moreira, Oliveira e Costa, 1994), Cystidicoloides sp., Spinitectus rodolphiheringi Vaz & Pereira, 1934, Rhabdochona sp., Spiroxys sp., Eustrongylides sp. e Neoechinorhynchus pimelodi Brasil-Sato & Pavanelli, 1998. A fauna de helmintos de A. fasciatus caracterizou-se principalmente por larvas de Contracaecum sp., Hysterothylacium sp., Spiroxys sp. e larvas e adultos de P. saofranciscencis al?m dos metacest?ides. Verificou-se que A. fasciatus atua principalmente como hospedeiro intermedi?rio de larvas de uma esp?cie n?o identificada de cest?ide e de larvas de nemat?ides, tendo sido a sua dieta o fator respons?vel por isto; auxilia na transmiss?o de esp?cies como Rhabdochona sp. para peixes carn?voros e atua tamb?m como hospedeiro definitivo para P. saofranciscencis, ocupando assim, n?veis tr?ficos distintos.

Made available in DSpace on 2016-06-02T20:20:38Z (GMT). No. of bitstreams: 1 TeseRP.pdf: 4407176 bytes, checksum: f55e8130a1b9477505b02d9785dcefa3 (MD5) Previous issue date: 2005-03-10 / Universidade Federal de Sao Carlos / Astyanax fasciatus is characterized as a cytogenetically diverse species. Sympatric and syntopic occurrence of distinct cytotypes corroborates the hypothesis that A. fasciatus might represent a species complex sharing a common denomination. In this work, specimens from three collection sites along Mogi-Guaçu River, on Southeastern Brazil, were examined: (1) close to headwaters (Ouro Fino MG), (2) in the mean river portion (Cachoeira de Emas, Pirassununga SP, characterized by the presence of a dam) and (3) close to river mouth at Pardo river (Barrinha SP). Two karyotypes bearing perfectly paired chromosomes, named standard cytotypes, were identified; one of them with 2n=46 and another one with 2n=48 chromosomes. The cytotype 2n = 48 was found in all collection sites, whereas the cytotype 2n = 46 was restricted to Barrinha and Cachoeira de Emas. In this latter locality, the cytotype 2n=46 was predominant, but variant karyotypical forms were also reported, bearing 2n=45 and 47 chromosomes, besides a structural variant with 2n=46. A variant with 2n=47 chromosomes was also found in Ouro Fino. The Ag-NORs and 18S and 5S rDNA sites showed a conserved distribution among cytotypes, as well as the constitutive heterochromatin, preferentially located at terminal region on the long arms of submetacentric, subtelocentric and acrocentric chromosomes and terminal region on short arms of a submetacentric pair. This latter region showed to be GC-rich after chromomycin A3 staining and it corresponds to the location of a Nucleolar Organizer Region. Sites bearing the satellite DNA As51 were detected at terminal region on the long arms of several chromosomes, distributed over 4 submetacentric pairs, 3 subtelocentric pairs and one acrocentric pair in the standard cytotype 2n=46, and over 3 submetacentric pairs, 4 subtelocentric pairs and one acrocentric pair in the standard cytotype 2n=48. The variant karyotypical forms also presented other chromosomes bearing such satellite DNA, remarkably at a large metacentric chromosome bearing a terminal site on the long arms (found in two variant karyotypes), two subtelocentric pairs bearing additional interstitial site (found in one variant karyotype), and one submetacentric pair bearing a subterminal site on the long arms (found in one variant karyotype). Data based on RAPD (Random Amplified Polymorphic DNA) were poorly informative to analyze the reported diversity, indicating a high number of migrants per generation among cytotypes. On the other hand, data from ISSR (Inter-Simple Sequence Repeats) showed a low structuring, mainly between two standard cytotypes from Barrinha, where a Nm value of 0,4301 was observed, with a genetic identity of 0,6862 and genetic distance of 0,3765. The values of genetic distance (0,3219) and genetic identity (0,7248) between cytotypes with 2n=48 from Barrinha and Ouro Fino also evidenced a slight differentiation, indicating that the dam at Cachoeiras de Emas is probably a barrier to gene flow among populations located upstream and downstream the dam. The obtained results with molecular markers do not discard the possibility of inbreeding among the cytotypes of A. fasciatus, as a source of the diversity found. Hypothetically, the standard cytotype with 2n=48 might be the resident form at Mogi- Guaçu River, while the cytotype with 2n=46 would represent an invasive form, showing recent divergence. Although the variant karyotypes present a karyotypical structure similar to the cytotype with 2n=46, there are evidences that chromosomes typical from the cytotype with 2n=48 have been incorporated, suggesting that such variants may be derived from viable crossings among standard cytotypes, and/or their offsprings, which share some homologies, as demonstrated by chromosomal markers. The presence of a higher number of As-51 sites in some variants reinforces their inbreeding origin. The As-51 sites, which showed to be specific for some variant forms, might be originated by complementary chromosomal rearrangements, propitious to new locations of this satellite DNA on karyotypes. / Astyanax fasciatus caracteriza-se como uma espécie diversificada do ponto de vista citogenético. A ocorrência simpátrica e sintópica de diferentes citótipos corrobora a hipótese de que A. fasciatus possa representar um grupo de espécies, hoje englobadas em uma mesma denominação comum. Neste trabalho foram examinados exemplares provenientes de três pontos de coleta, ao longo do rio Mogi-Guaçu, no Sudeste do Brasil: (1) próximo à sua cabeceira (Ouro Fino MG), (2) no trecho médio do rio (Cachoeira de Emas, Pirassununga SP, caracterizado pela ocorrência de uma barragem) e (3) próximo à sua foz no rio Pardo (Barrinha SP). Foram detectados dois tipos de cariótipos com cromossomos perfeitamente pareáveis, denominados citótipos padrão, um com 2n=46 e outro com 2n=48 cromossomos. O citótipo 2n = 48 foi encontrado em todos os pontos de coleta, enquanto o citótipo 2n = 46 foi encontrado somente em Barrinha e Cachoeira de Emas. Nesta última localidade o citótipo 2n=46 foi predominante, mas ocorrendo também formas cariotípicas variantes com 2n=45 e 47 cromossomos, além de um variante estrutural 2n=46. Um variante 2n=47 cromossomos foi também encontrado em Ouro Fino. As Ag-RONs e os sítios de rDNA 18S e 5S mostraram uma distribuição conservada entre os citótipos, assim como heterocromatina constitutiva, localizada preferencialmente na região terminal do braço longo de cromossomos submetacêntricos, subtelocêntricos e acrocêntricos e na região terminal do braço curto de um par submetacêntrico. Esta última região mostrou-se também GC rica, após coloração com cromomicina A3, e corresponde à localização de uma região organizadora de nucléolo. Foram detectados sítios do DNA satélite As51 na região terminal do braço longo de vários cromossomos, distribuídos em 4 pares submetacêntricos, em 3 pares subtelocêntricos e em um par acrocêntrico no citótipo padrão 2n=46, e em 3 pares submetacêntricos, em 4 pares subtelocêntricos e em um par acrocêntrico no citótipo padrão 2n=48. As formas cariotípicas variantes apresentaram também outros cromossomos portadores desse DNA satélite, destacando-se um cromossomo metacêntrico grande com um sítio terminal no braço longo (em dois cariótipos variantes), dois pares subtelocêntricos com um sítio intersticial extra (em um dos cariótipos variantes), e um par submetacêntrico com um sítio subterminal no braço longo (em um dos cariótipos variantes). Dados de RAPD ( Random Amplified Polymorphic DNA ) mostraram-se pouco informativos quanto à análise da diversidade encontrada, indicando altos valores de migrantes por geração entre os citótipos. Dados de ISSR, Inter- Simple Sequence Repeats , por outro lado, mostraram uma pequena estruturação, principalmente entre os dois citótipos padrão provenientes de Barrinha, onde o Nm foi de 0,4301, com identidade genética de 0,6862 e distância genética de 0,3765. Os valores de distância genética (0,3219) e de identidade genética (0,7248) entre os citótipos 2n=48 de Barrinha e Ouro Fino também evidenciam uma certa diferenciação entre os mesmos, indicando que a barragem de Cachoeira de Emas provavelmente seja um obstáculo ao livre fluxo entre populações situadas à jusante e à montante da mesma. Os resultados gerais obtidos com os marcadores moleculares não descartam a possibilidade de intercruzamentos entre os citótipos de A. fasciatus, como fonte da diversidade encontrada. É levantada a hipótese que o citótipo padrão 2n=48 seja a forma residente do rio Mogi-Guaçu, sendo o citótipo 2n=46 uma forma invasora, com divergência recente. Embora os cariótipos variantes apresentem uma estrutura cariotípica mais similar ao citótipo 2n=46, há evidências de que cromossomos característicos do citótipo 2n=48 tenham sido neles incorporados, sugerindo que tais variantes sejam decorrentes de intercruzamentos viáveis entre os dois citótipos padrão e/ou seus descendentes, os quais ainda compartilham uma série de homologia, como evidenciado na análise dos marcadores cromossômicos. A presença de um maior número de sítios As-51 em alguns variantes reforça, de certa forma, a sua origem por intercruzamentos. Os sítios As-51, que se mostraram específicos para algumas formas variantes, poderiam ser decorrentes de rearranjos cromossômicos complementares, propiciando novas localizações desse DNA satélite nos cariótipos.