Transmission rate variation among three B chromosome variants in the fish Prochilodus lineatus (Characiformes, Prochilodontidae)

Abstract

Cytogenetic studies were developed in Prochilodus lineatus (Valenciennes 1836), describing an interesting system of small supernumerary chromosomes. The purpose of this work is to study the frequency and morphology of B chromosomes in individuals from the parental line and the inheritance patterns of these elements in individuals obtained from controlled crosses in the species P. lineatus. The transmission rate of B chromosomes revealed a k B =0.388 for the acrocentric type, a kB=0.507 for the metacentric type and a k B =0.526 for the submetacentric type. The obtained results raise hypothesis that B-acrocentric chromosomes are involved in an extinction process in this species, while the metacentric and submetacentric supernumerary elements comprises a neutral mechanism and follows a Mendelian transmission rate.

Transmission Behavior of B Chromosomes in <b><i>Prochilodus lineatus </i></b>(Characiformes, Prochilodontidae)

“…Cytogenetic analyses of 136 specimens of P. lineatus revealed a consistent diploid number of 54 meta-and submetacentric chromosomes in addition to the presence of up to 7 B chromosomes in somatic cells, as has been previously described Bertollo 1983, 1990;Penitente et al, 2013].…”

“…The metacentric chromosomes have a mean value of k B = 0.587, while the acrocentric and submetacentric variants have a k B = 0.333 and k B = 0.385, respectively ( [Penitente et al, 2013]. The comparison of these data sets with those from our current study using χ 2 test by means of contingency tests reveals a significant change in the variant frequencies in less than 10 years (χ 2 = 21.844, p = 0.00001; table 4 ) with an increased frequency of the metacentric B chromosome and, consequently, a reduction in frequency of the other chromosome types.…”

“…Likewise, in the wasp Trypoxylon albitarse , the fre- [Araújo et al 2002]. Furthermore, between 2004and 2007, Penitente et al [2013 analyzed the transmission and inheritance pattern of the B chromosome variants in P. lineatus through controlled crosses and found a lower k B for the acrocentric type chromosome (k B = 0.388), which is lower than the Mendelian rate (k B = 0.500), but the metacentric and submetacentric types have a neutral transmission pattern (k B = 0.507 and k B = 0.526, respectively). These authors proposed that the acrocentric B chromosomes are undergoing an extinction process due to the low transmission pattern and could disappear unless new mutations occur that ensure their permanence in the population.…”

“…However, despite our results showing different k B values from the Mendelian rate, when we applied the Z-test there were no significant differences, which may be related to the low number of progeny analyzed in each cross. Apart from the k B values, the frequency in the natural population is another variable that indicates a change, with the acrocentric and submetacentric variants experiencing a reduction in recent years, whereas the metacentric chromosomes are increasing in the last years ( [Penitente et al, 2013[Penitente et al, ] and 2011[Penitente et al, -2012 showed a significant difference regarding the frequency of morphotypes in the natural population (χ 2 = 21.844, p = 0.00001). Therefore, the variation in the frequency of different types of B chromosomes in the natural population is our most reliable variable complementing the k B values obtained in the crossings.…”

B chromosome dynamics in Prochilodus costatus (Teleostei, Characiformes) and comparisons with supernumerary chromosome system in other Prochilodus species

“…However, prominent intra- and interspecific differences have been reported regarding the frequency and occurrence of B chromosomes. To date, supernumerary elements were reported in five species: Prochilodus lineatus (Valenciennes, 1836), Prochilodus brevis Steindachner, 1874, Prochilodus nigricans Agassiz, 1829, Prochilodus mariae Eigenmann, 1922, and Prochilodus argenteus Agassiz, 1829 (Pauls and Bertollo 1983, 1990, Venere et al 1999, Oliveira et al 2003, Penitente et al 2015); however, information regarding the origin, molecular content, and populational dynamics of these B chromosomes are restricted to P. lineatus (Maistro et al 2000, Jesus et al 2003, Artoni et al 2006, Voltolin et al 2010, 2013a, Penitente et al 2013). …”