Diversidade cariotípica entre dez espécies do gênero Ancistrus (Siluriformes, Loricariidae) da Bacia Amazônica: estrutura e mecanismos de evolução cromossômica

Abstract

The tribe Ancistrini belongs to the subfamily Hypostominae (Siluriformes: Loricariidae). Phylogenetic studies of this group of fishes are few, leaving their systematics relatively unknown. Ancistrus, the type genus of the Ancistrini tribe, contains 53 valid species and at least six Amazonian species that have yet to be described. In order to explore mechanisms of chromosome evolution in the genus Ancistrus, we studied 10 species collected from locations across the Amazon basin. We found a large karyotypic diversity among the ten species, in both macrostructure (chromosome number and formula) and pattern of nucleolar organizer regions and constitutive heterochromatin. The diploid number varied between 34 and 52 chromosomes and the number of arms varied between 68 and 82. The RON varied in both chromosome location (terminal, interstitial, long arm, short arm) and karyotype position. Few chromosomes presented constitutive heterochromatin; when present, this heterochromatin was distributed in discrete blocks in the centromeric position, terminal or interstitial. The occurrence of low diploid numbers suggests the presence of centric fusions in the chromosomal evolution of this group. Besides documenting karyotypic diversity, we also studied the sex chromosome systems of seven of the 10 species. We found two cases of ZZ/ZW, three cases of XX/XY, and two multiple systems: XX/XY1Y2 and Z1Z1Z2Z2/Z1Z2W1W2. Fish of the genus Ancistrus exhibit low vagility, territoriality and parental care. These ethological characteristics may create a gene flow barrier among populations, allowing microallopatric speciation and resulting in the large karyotypic diversity found in these species.