Abstract
We present karyotypic characteristics and report on the occurrence of ZZ/ZW sex chromosomes in Ancistrus ranunculus (rio Xingu) and Ancistrus sp. "Piagaçu" (rio Purus), of the Brazilian Amazon. Ancistrus ranunculus has a modal number of 2n=48 chromosomes, a fundamental number (FN) of 82 for both sexes, and the karyotypic formula was 20m+8sm+6st+14a for males and 19m+9sm+6st+14a for females. Ancistrus sp. "Piagaçu" presented 2n=52 chromosomes, FN= 78 for males and FN= 79 for females. The karyotypic formula was 16m+8sm+2st+26a for males and 16m+9sm+2st+25a for females. The high number of acrocentric chromosomes in karyotype of Ancistrus sp. "Piagaçu" differs from the majority of Ancistrini genera studied so far, and may have resulted from pericentric inversions and translocations. The lower number of chromosomes in A. ranunculus indicates that centric fusions also occurred in the evolution of Ancistrus karyotypes. We conclude that karyotypic characteristics and the presence of sex chromosomes can constitute important cytotaxonomic markers to identify cryptic species of Ancistrus. However, sex chromosomes apparently arose independently within the genus and thus do not constitute a reliable character to analyze phylogenetic relations among Ancistrus species.
Highlights
Loricariidae is the largest family in the Siluriformes, with 683 valid species distributed across the entire Neotropical region (Isbrücker, 1980; Reis et al, 2003)
Voucher specimens were deposited in the fish collection at the Instituto Nacional de Pesquisa da Amazônia (INPA)
Ancistrus ranunculus has a modal number of 2n=48 chromosomes and a fundamental number of 82 for both sexes; the karyotypic formula was different for males (20m+8sm+6st+14a) and females (19m+9sm+6st+14a)
Summary
Loricariidae is the largest family in the Siluriformes, with 683 valid species distributed across the entire Neotropical region (Isbrücker, 1980; Reis et al, 2003). The family is currently divided into six subfamilies: Delturinae, Hypoptopomatinae, Hypostominae, Lithogeneinae, Loricariinae, and Neoplecostominae (Reis et al, 2006). Within the Hypostominae, the tribe Ancistrini has been the subject of few taxonomic studies and its position within the subfamily is controversial (Isbrücker, 1980; Howes, 1983; Schaefer, 1987; Montoya-Burgos et al, 1998). Ancistrini presently includes 217 valid species in 27 genera (Fish-Muller, 2003). Cytogenetic studies of this tribe, as well as of Loricariids overall, are scarce relative to the number of species involved. 23 species from seven genera (Ancistrus, Baryancistrus, Hemiancistrus, Megalancistrus, Panaque, Parancistrus, and Peckoltia) have been analyzed
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