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 <i>Tetragonisca angustula</i> and <i>Tetragonisca fiebrigi</i> are widely distributed in Brazil<i>,</i> and both are commonly known as “jataí.” Our goal was to investigate the possible origin of the B chromosomes in <i>T. fiebrigi</i>, a cytotaxonomic trait that differentiates <i>T. fiebrigi</i> from <i>T. angustula</i>. We analyzed diploid chromosome number (2<i>n</i>), B chromosome incidence, patterns of constitutive heterochromatin, and in situ localization of different repetitive DNA probes in <i>T. angustula</i> and <i>T. fiebrigi</i>. Both species displayed 2<i>n</i> = 34, with similar karyotype structures. One to three B chromosomes were observed in <i>T. fiebrigi</i> only. Constitutive heterochromatin was distributed on one arm of all chromosomes in both species, and <i>T. fiebrigi</i> 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 ribosomal DNA (rDNA) probe marked 10 chromosomes in <i>T. angustula</i> and 6 A chromosomes in <i>T. fiebrigi</i> with an additional marking on 1B in individuals with 3B. The Tan-Bsp68I repetitive DNA probe marked the heterochromatic portion of all <i>T. fiebrigi</i> A and B chromosomes. This probe also marked the heterochromatic portion of all <i>T. angustula</i> chromosomes; therefore, both alternative hypotheses to the B chromosome origin are possible: (i) from the A chromosome complement of <i>T. fiebrigi</i> (intraspecific origin); or (ii) a by-product of genome reshuffling following the hybridization between <i>T. fiebrigi</i> and <i>T. angustula</i> (interspecific origin).