An intraspecific origin of B chromosomes in Tetragonisca fiebrigi (Apidae: Meliponini) inferred from cytogenetic and nuclear genome size data

Tetragonisca angustula and Tetragonisca fiebrigi are two stingless bees' species commonly known as "jataí". Cytogenetic data indicates the presence of B chromosomes in T. fiebrigi and absence in T. angustula, constituting a cytotaxonomic character. The present study aimed to investigate karyotypic and genome size differences between T. angustula and T. fiebrigi, focusing on the possible correlation between number of B chromosomes and DNA content variation. 10 colonies of T. angustula and 16 colonies of T. fiebrigi were sampled from different geographical locations. Conventional cytogenetic analyses were performed, and 1 C DNA content was measured by flow cytometry. Both species showed 2n = 34 and similar karyotype, with biarmed chromosomes composed of one euchromatic and one heterochromatic arm. B chromosomes were found only in T. fiebrigi individuals, varying from 1B to 7B in females and from 0B to 5B in males. The mean 1 C value from 45 T. angustula individuals was 1 C = 0.95 ± 0.079 pg, and the mean 1 C value from 53 T. fiebrigi individuals was 1 C = 0.93 ± 0.048 pg. The ANOVA indicated no statistical difference in 1 C value between T. angustula and T. fiebrigi. The fact that there is no increase in T. fiebrigi genome size points to the direction of an intraspecific origin of the B chromosomes in this species.