Supernumerary B Chromosomes of <i>Tetragonisca fiebrigi</i> Share Repeat Content with Standard Chromosome Set of both <i>T. fiebrigi</i> and <i>Tetragonisca angustula</i> (Apidae: Meliponini)

Abstract

The stingless bees Tetragonisca angustula and T. fiebrigi are widely distributed in Brazil, and both are commonly known as “jataí”. Our goal was to investigate the possible origin of the B chromosomes in T. fiebrigi, a cytotaxonomic trait that differentiates T. fiebrigi from T. angustula. We analyzed diploid chromosome number, B chromosome incidence, patterns of constitutive heterochromatin, and in situ localization of different repetitive DNA probes in T. angustula and T. fiebrigi. Both species displayed 2n = 34, with similar karyotype structure. One to three B chromosomes were observed in T. fiebrigi only. Constitutive heterochromatin was distributed on one arm of all chromosomes in both species and T. fiebrigi B chromosomes were mainly heterochromatic with one euchromatic extremity. The (GA)15 and (CAA)10 microsatellite probes marked the euchromatic arms of all chromosomes in both species, without marking the B chromosomes. The 18S rDNA probe marked 10 chromosomes in T. angustula and six A chromosomes in T. fiebrigi, with an additional marking on 1B in individuals with 3B. The Tan-Bsp68I repetitive DNA probe marked the heterochromatic portion of all T. fiebrigi A and B chromosomes. This probe also marked the heterochromatic portion of all T. angustula chromosomes, therefore, both alternative hypotheses to the B chromosome origin are possible: (i) from the A chromosome complement of T. fiebrigi (intraspecific origin); or (ii) as by-products of genome reshuffling following the hybridization between T. fiebrigi and T. angustula (interspecific origin).