Extensive chromosomal rearrangements and nuclear DNA content changes in the evolution of the armoured catfishes genus Corydoras (Pisces, Siluriformes, Callichthyidae)

Abstract

Karyotypes and nuclear DNA content were studied in 11 species of the genus Corydoras from rivers in South America: C. sp. from Caripi river 2n = 60, C. cf. simulatus 2n = 62, C. simulatus 2n = 62, C. reticulafus 2n = 74, C. sp. from Galheiro river 2n = 84, C. aff. punctatus from Negro river 2n = 102, C.Javeolus 2n = 58, C. arcuatus 2n = 46, C . trilineatus 2n =46, C. schwartzi 2n = 46, and C. metae 2n=92. Extensive chromosome diversity and differences in DNA content were detected among species. The high variability in chromosome counts was not exclusively related to chromosomal structural rearrangements, but also to large changes in DNA content. Species could be grouped using their shared cytogenetic characteristics, suggesting that within the genus Corydoras different groups of species followed distinct evolutionary trends. Chromosomal rearrangements in Corydoras are, apparently, more frequent that morphological modifications, so cytogenetic data may be very useful for species delimitation and for the understanding of interrelationships among species.

Cytogenetics of two sympatric Corydoras species (pisces, siluriformes, challichtyidae) of Southern Brazil

“…According to Oliveira et al (1992), Corydoras comprises five groups of species presenting similar karyotypic and DNA content. C. ehrhardti and C. paleatus belong to the same karyotypic group, which occurs in the southeastern coastal region of Brazil (Oliveira et al, 1993a).…”

“…The diploid chromosome number varies from 2n = 40 in C. natterei (Oliveira et al, 1990) to 2n = 134 in C. aeneus (Turner et al, 1992), while the nuclear DNA content varies from 1.04 0.09 pg in C. cf. simulatus to 8.75 1.50 pg in C. metae (Oliveira et al, 1992).…”

“…According to Oliveira et al (1992), this genus encompasses five natural groups of species that present karyotypic and DNA content similarities. Vicariance events such as those that occurred in the costal basin are mechanisms that help explain the high interspecific diversity in this group (Weitzman et al, 1988).…”

Nuclear DNA content determination in Characiformes fish (Teleostei, Ostariophysi) from the Neotropical region

“…The data obtained by Hinegardner and Rosen (1972) on 275 teleostei showed that there is a clear modal value of about 2.0 pg of DNA per diploid nucleus. However, differences greater than two times may be found among specimens of the same family or even of the same genus, as is the case of cyprinids of the genus Barbus (Ohno et al, 1967;Wolf et al, 1969) and species of the genus Corydoras (Hinegardner and Rosen 1972;Oliveira et al, 1992). Although some authors have suggested that this variation may be related to the number of genes in the organisms or to the complexity of their development (Kauffman, 1971cited by Cavalier-Smith, 1978, many agree that there is no significant correlation between the amount of nuclear DNA and organic or genetic complexity (Cavalier-Smith, 1978).…”

“…Studies of nuclear DNA content in living organisms in general and in fish in particular have been conducted using Feulgen-stained blood smears and microdensitometry analysis (Hinegardner and Rosen, 1972;Gold and Price, 1985;Majumdar and McAndrew, 1986;Gold and Amemiya, 1987;Oliveira et al, 1992Oliveira et al, , 1993aOliveira et al, and 1993bCarvalho et al, 1998), or blood cell samples in suspension, stained with base-specific fluorochromes and analyzed by flow cytometry (Thorgaard et al, 1982;Johnson et al, 1987;Tiersch and Chandler, 1989;Tiersch et al, 1989aTiersch et al, , 1989bTiersch et al, and 1990.…”