- Karyotype of a male marsh deer. 

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... and white hairs inside the conspicuously large ears, as well as the insides of the legs (Azara 1809; de Miranda Ribeiro 1919). The legs of adult Blastocerus are black up to the radius or tibia. The pelage of the young fawn is unspotted. Azara (1801) reported albino marsh deer. The marsh deer has 66 chromosomes, with FN = 74, (figure 3). The first two pairs are metacentric with AR=1,36 and 1,14. The third pair is submetacentric (AR = 1.16). The autosomes are acrocentric. The chromosome X is the largest and metacentric, with AR = 1.16 and the Y is the smallest chromosome and submetacentric. The C banding marks all the acrocentric chromosomes with large centromeric blocks. The chromosome number 1 is not marked and chromosomes 2 and 3 are weakly marked by C bands. The X chromosome generally shows two telomeric markings and the Y is C band negative. The Nucleolus Organizer Regions (NOR) is located in the telomere of chromosomes 4 and 5. The chromosome 4 showed polymorphism with this banding, it may be absent in one of these chromosomes, for some animals. Although some cytogenetic data may suggest similarity between Odocoileus and Blastocerus, the morphological differences between these two Genera are indisputable (Duarte and Giannoni 1995). In relation to the genetic structure, Oliveira et al. (2005) studied 17 loci, based on the protein variability of the marsh deer red blood cells. They found that 35,29% of the loci studied were polymorphic and the average number of alleles per locus was 2.34 ± 0.96. For all the 17 loci an average of 1.47 alleles per locus and a heterozygosity rate of 6.3 ± 3.5% was estimated. In the same study the authors estimated a gene flow equivalent to 4.8 animals per generation, between three areas along the Paraná river basin. The analysis of Dloop mt DNA genetic variation performed in 127 marsh deer from 4 areas (Brazil, Bolivia and Argentina) distributed throughout the Río de la Plata basin found a low variation of only 17 haplotypes (Marquez et al. 2006). Phylogeny and distribution of control region haplotypes suggested that populations close to the Pantanal area in central Brazil underwent a rapid population expansion and that this occurred approximately 28,000-25,000 years BP. The marsh deer historically occurred in a vast region in central South America covering most of the lowland areas located east from the Andes, from the southern headwaters of the Amazon basin to the delta of the Paraná river. Yet the distribution was not homogeneous and did not include the semi-arid northeastern Brazilian region the semi-arid Chaco region of Paraguay, Bolivia and Argentina, and the mountainous, forested region of the Brazilian Atlantic coast. In a few places the species reached the Brazilian and Uruguayan coasts. Marsh deer once occurred in all major river floodplains of southern Brazil, such as the large southern tributaries of the Amazon basin (Araguaia-Tocantins), the Paraguay-Paraná basin, the Araguaia-Tocantins basin, the São Francisco river basin and the Uruguay river basin. The species also was found in the smaller wetlands scattered in the central Brazilian plateau. In Uruguay, marsh deer were found in the departments of Rocha and Treinta y Tres, in the wetlands of the Bañados del Este, and in the west of the country along the Uruguay river. It was also common in northern Uruguay, near to the Brazilian border. In Peru the species was known in the Pampas del Heath, department of Madre de Dios (Hofmann et al. 1976; Tomas et al. 1997). In Bolívia, the geographic distribution of the marsh deer was supposed to include Mamoré River and its tributaries and eastern area of the Santa Cruz Department, along the Brazilian border and near to the Peru (actual location of the Madidi National Park). In Paraguay, the species occupied almost every suitable habitat along the Pilcomayo, Paraguay and Paraná rivers. Marsh deer also occurred in northern Argentina, along the Pilcomayo river, the lower Bermejo river (Chaco Province), and along the Paraná river (Chaco, Missiones, Corrientes, Santa Fé, Entre Rios and Buenos Aires), the region of the Iberá floodplain, and also in the Uruguay river (Tomas et al. 1997). Although the broad geographic range of the marsh deer has not changed much, habitat loss has caused fragmentation of its historical area of distribution (Pinder and Grosse 1991). Even though local extinctions occurred, mostly in smaller scattered wetlands, the species still occurs in major river floodplain systems (figure 4). The reser voirs of hydroelectric power plants have caused considerable habitat loss for marsh deer (Tomas 1996; Weber and Gonzalez 2003; Piovezan 2004), but the intense agricultural use of floodplains and poaching are also important threats (Tiepolo et al. 2004). In Argentina, the most important areas for marsh deer are located in the province of Corrientes and in the Delta of the Paraná river, near Buenos Aires. Isolated populations are found in the wet regions of Chaco, and northeastern Argentina (D’alessio et al. 2001). In the Iberá wetland (12,000 km 2 ) the marsh deer population may reach 1,100 to 2,000 individuals (Beccaceci 1994; Parera 2002, respectively). Smaller populations are found in the Esteros of Santa Lucía, Batel, Riachuelo, Miriñay and Aguapey. The delta of the Paraná river shelters the southernmost marsh deer population, which is also the second largest population of this species in Argentina (Varela 2003). The main populations of the delta occur at San Fernando and Campana departments (Buenos Aires province) and in the Ibicuy islands (Entre Rios province). Marquez et al. (2006) suggest that the population of the delta of the Paraná river should be considered distinct from the Iberá population, in Argentina, and also from the Pantanal and Paraná river basin populations in Brazil. The existence of a population of marsh deer that inhabits the marshes of the Paraná river, in the department of San Fernando, southeastern Chaco province, is well known. There are also several isolated populations in eastern Formosa province, departments of Laishi, Formosa and Pirané, and probably in the Pilcomayo and Bermejo rivers. In Bolivia the main marsh deer populations are found in the seasonally flooded savannas in the east and northeast of the country, from the Pantanal (Otuquis and San Matias) to the region of Los Llanos de Moxos, including the floodplains of the Beni, Mamoré and Iténez (or Guaporé) rivers. Rios-Uzeda (2008) estimated marsh deer density in the Northern portion of the La Paz state (0.24 deer/km 2 ), along Mamoré River (0.12 deer/km 2 ) and along the Iténez river floodplain (0.15 deer/km 2 ), the standard error of both estimative was SE=0.003 deer/ km 2 . The species also occurs in the complex of lagoons of Rogagua and Rogaguado, the marshes of the Maniquí river, and in the floodplains of Ixiamas and pampas del Heath (Sarmiento and Barrera 1998; Rumiz 2002; Cuellar and Noss 2003; Gómez and Rios-Uzeda 2004). One aerial survey conducted in Bolivia estimated the marsh deer population in the Pampas del Heath, north of the Madidi National Park (Gómez and Rios-Uzeda 2004). The authors estimated a population of 689 ± 549 (SD) marsh deer, with a mean density of 0.84 ind./km 2 (range: 0-4 ind./km 2 ). Some small isolated marsh deer populations occur along the Paraguay and Paraná rivers, in Paraguay (Tomas et al. 1997). There is no available data on these populations, but the occurrence of the species is confirmed in the floodplains of the rivers Paraguai (Pantanal Rio Negro Ramsar site), Paraná (Refúgio Biológico Mbaracayú) and Pilcomayo (Tinfunque National park), as well as in the region of Ñeembucú (Refugio de vida Silvestre Yabebyry) and the complex of lagoons in the Ypoá National Park. In Peru, marsh deer are found in the Peruvian portion of the Pampas del Heath, department of Madre de Dios, near the boundaries of the National Park of Madidi, in Bolívia (Hofman et al. 1976; Tomas et al. 1997; Montanbault 2002). In Brazil, the largest known population of the species is found in the Pantanal wetland (140,000 km 2 ), formed by the upper Paraguay river and its tributaries. Estimates of marsh deer population size in this large floodplain have been produced since 1976, when Schaller and Vasconcelos (1978) reported 7,000 individuals. More recently, in 1991 and 1992, large scale surveys estimated the marsh deer population in the Pantanal to be 44,000 ± 7,700 individuals (Mourão et al. 2000). The differences between the two estimates does not indicate an increase in the population size, but only a response to different methodological approaches. More intensive surveys covering smaller ranges have been conducted in the Pantanal, revealing densities from 0.38 ± 0.36 (SE) deer/km 2 to 0.57 ± 0.23 (SE) deer/km 2 in the dry season (Tomas et al. 2001; Tomas et al. 2004, repectively) and 0.40 ± 0.14 deer/km 2 during the flooding season (Tomas et al. 2001). Several surveys of marsh deer were conducted independently by different researchers in the floodplains inundated by the reservoir of the Sergio Motta Power plant, in the Paraná river. Mourão and Campos (1995) estimated a density of 0.51 ± 0.10 (SE) deer/km 2 and a population size of 650 ± 127 deer in 1,280km 2 of ...