Chromosome polymorphism in the Brazilian dwarf brocket deer, Mazama nana (Mammalia, Cervidae)

Abstract

The Brazilian dwarf brocket deer (Mazama nana) is the smallest deer species in Brazil and is considered threatened due to the reduction and alteration of its habitat, the Atlantic Rainforest. Moreover, previous work suggested the presence of intraspecific chromosome polymorphisms which may contribute to further population instability because of the reduced fertility arising from the deleterious effects of chromosome rearrangements during meiosis. We used G- and C-banding, and nucleolus organizer regions localization by silver-nitrate staining (Ag-NOR) to investigate the causes of this variation. Mazama nana exhibited eight different karyotypes (2n = 36 through 39 and FN = 58) resulting from centric fusions and from inter and intraindividual variation in the number of B chromosomes (one to six). Most of the animals were heterozygous for a single fusion, suggesting one or several of the following: a) genetic instability in a species that has not reached its optimal karyotypic evolutionary state yet; b) negative selective pressure acting on accumulated rearrangements; and c) probable positive selection pressure for heterozygous individuals which maintains the polymorphism in the population (in contrast with the negative selection for many rearrangements within a single individual)

Características reprodutivas de veado-bororó-do-sul ou veado-mão-curta (Mazama nana)

“…Este elevado desvio padrão pode ter sido provocado por alguns fatores. O primeiro fator a ser conside- Abril & Duarte (2008) influenciarem no padrão seminal, pois algumas destas alterações cromossômicas podem levar a mortalidade de células germinativas. A média de células espermáticas anormais (40,90%) é considerada alta, sendo predominante os defeitos de cauda (25,95% das células totais), caracterizando uma baixa qualidade seminal nestes animais.…”

“…Estas variações foram atribuídas a prováveis translocações Robertsonianas, fixadas por um alto grau de endogamia. Porém ainda não é possível saber qual a influência deste elevado polimorfismo nestas populações, devido ao reduzido número de indivíduos estudados (Abril & Duarte, 2008).…”

Elucidating the Evolution of the Red Brocket Deer <i>Mazama americana</i> Complex (Artiodactyla; Cervidae)

“…3.0%), E (acrocentric chromosomes with RL 1 3.0%) and B (microchromosomes or extranumerary chromosomes with RL 1 1.0%). B chromosomes were not considered in calculating the diploid and fundamental numbers because there was intraindividual variation [Abril and Duarte, 2008]. …”

“…Among the neotropical deer, in addition to the M. americana species , there are reports of B chromosomes in M. nana (1 to 6 chromosomes) [Abril and Duarte, 2008], M. bororo (4 to 5 chromosomes) [Duarte and Jorge, 2003], M. gouazoubira (0 to 3 chromosomes) and M. nemorivaga (2 to 8 chromosomes) [Duarte, 1998]. The be- havior of these chromosomes was variable under different banding techniques [Abril and Duarte 2008] reflecting their instability and the different origin possibilities [Camacho et al, 2000;Palestis et al, 2004].…”

“…The be- havior of these chromosomes was variable under different banding techniques [Abril and Duarte 2008] reflecting their instability and the different origin possibilities [Camacho et al, 2000;Palestis et al, 2004]. Camacho [2005] explained that small Bs exhibit a tendency to be mitotically unstable, and thus may vary in number from cell to cell within the same individual.…”