Mechanisms of chromosomal evolution and its possible relation to natural history characteristics in Ancistrus catfishes (Siluriformes: Loricariidae)

Abstract

Ancistrus is the most speciose genus of the tribe Ancistrini, with 58 valid species and many yet to be described. Cytogenetic studies were conducted on five apparently undescribed species from the Amazon basin, which showed different diploid numbers: Ancistrus sp. Purus (2n = 34); Ancistrus sp. Macoari (2n = 46); Ancistrus sp. Dimona (2n = 52); Ancistrus sp. Vermelho (2n = 42) and Ancistrus sp. Trombetas (2n = 38). All species possessed only one pair of NOR-carrying chromosomes, but with extensive variation in both the location on the chromosome as well as in the position of the ribosomal sites on the karyotype. The karyotypic evolution of Ancistrus species seems to be based on chromosomal rearrangements, with a tendency to a reduction of the diploid number. Two new instances of XX/XY sex chromosomes for Ancistrus species, based on the heteromorphism in the male karyotype, were also recorded. The large karyotypic diversity among Ancistrus species may be related to biological and behavioural characteristics of these fish that include microhabitat preferences, territoriality and specialized reproductive tactics. These characteristics may lead to a fast rate of fixation of chromosomal mutations and eventually speciation across the basin.

Population divergence and peculiar karyoevolutionary trends in the loricariid fish Hypostomus aff. unae from northeastern Brazil

“…In general, loricariids exhibit a strong correlation between high numbers of meta/ submetacentric chromosomes and low diploid number (i.e., the higher the 2n, the higher the frequency of subtelo/acrocentric chromosomes). For instance, a karyotype formula of 32m/ sm+2st is reported for Ancistrus sp Purus (2n = 34) (Oliveira et al, 2009b) while Upsilodus sp (2n = 96) presents 16m+8sm+72a (Kavalco et al, 2005). This pattern indicates that centric fissions have played a major role in the karyotypic evolution of this family (Artoni and Bertollo, 2001) and can be inferred to explain the derived karyotype observed in H. aff.…”

“…Instead, the subfamily Hypostominae is characterized by a remarkable diversity of karyotypic forms, with 2n ranging from 34 (Oliveira et al, 2009b) to 84 (Cereali et al, 2008). In general, loricariids exhibit a strong correlation between high numbers of meta/ submetacentric chromosomes and low diploid number (i.e., the higher the 2n, the higher the frequency of subtelo/acrocentric chromosomes).…”

“…A remarkable karyotypic variation has been identified within Loricariidae, with diploid numbers ranging from 2n = 34 in Ancistrus sp (Oliveira et al, 2009b) to 2n = 96 in Upsilodus sp (Kavalco et al, 2005) and quite distinct karyotype formulae. Such diversity suggests that centric fissions and pericentric inversions have played a major role in the karyoevolutionary divergence of this family (Artoni and Bertollo, 2001).…”

Cytogenetic description of Ancistrus abilhoai (Siluriformes: Loricariidae) from Iguaçu River basin, southern Brazil

“…The presence of diploid numbers less than 52 suggests the predominance of Robertsonian chromosomal rearrangements (centric fusion) in the karyotypic evolution of this genus (Alves et al, 2003), although rearrangements such as pericentric inversions and translocations have also had an effect on the chromosomal evolution of this group. These rearrangements could explain the existence of many karyotypes with higher numbers of acrocentric chromosomes (de Oliveira et al, 2009, Mariotto et al, 2011.…”

“…Due to the high cytogenetic diversity found in Ancistrus whether in the Amazon basin (de Oliveira et al, 2009) or in the Paraguay basin (Mariotto et al, 2011), some degree of variability could be present in two allopatric populations of Ancistrus in the high heterogeneous Iguaçu River basin. However, no differences were observed among the individuals from the two sites analyzed in this study.…”