Robertsonian rearrangements in Neotropical Meliponini karyotype evolution (Hymenoptera: Apidae: Meliponini)

Abstract

Genome changes, evidenced through karyotype or nuclear genome size data, can result in reproductive isolation, diversification and speciation. The aim of this study was to understand how changes in the karyotype such as chromosome number and nuclear genome size accompanied the evolution of neotropical stingless bees, and to discuss these data in a phylogenetic context focusing on the karyotype evolution of this clade. We sampled 38 species representing the three Neotropical Meliponini groups; 35 for karyotype analyses and 16 for 1C value measurement. The chromosome number varied from 2n = 16 to 2n = 34, with distinct karyotypic formulae and the presence of a few polymorphisms, such as B chromosomes in one species and arm size differences between homologous chromosomes in two species. The mean 1C value varied from 0.31 pg to 0.92 pg. We associated empirical data on chromosome number and mean 1C value to highlight the importance of Robertsonian fusion rearrangements, leading to a decrease in chromosome number during the Neotropical Meliponini evolution. These data also allowed us to infer the independent heterochromatin amplification in several genera. Although less frequent, Melipona species with 2n = 22 represent evidence of Robertsonian fissions. We also pointed out the importance of chromosomal rearrangements that did not alter chromosome number, such as inversions and heterochromatin amplification.

Paving the Way for Gene Silencing in Lepidoptera: Integrated Sequencing Data Unveil the Rnai Core Machinery of Leucoptera Coffeella.

“…Nuclear 2C value ganglia were dissected in commercial saline solution from adult males and females of L. coffeella of two populations (Viçosa MG and Barreiras BA), and of female Drosophila melanogaster (standard 2C = 0.36 pg for flow cytometry, https://www.genomesize.com/results.php?page=1). Nuclei were isolated from each ganglion (external standard) or simultaneously (internal standard) from crushing in 100 µL OTTO I [35] nuclear extraction buffer (0.1 M citric acid, 0.5 percent Tween 20, 2.0 mM dithiothreitol and 50 µg mL-1 RNAse, pH = 2.3), and the nuclei sus-pensions were incubated for 5 min [43,44]. One milliliter of OTTO I was added, and the suspensions were filtered through a 30 µm nylon filter into a 2.0 mL microtube and centrifuged at 100 xg for 5 min.…”

“…The nuclei suspensions were stained for 30 min in the dark with 500 µL OTTO II [35] staining buffer (0.4 µM Na2HPO4.2H2O, 75 µM propidium iodide and 50 µg mL-1 RNAse, pH = 7.8, [43,44]. We processed the nuclei suspensions in a BD Accuri™ C6 Flow Cytometer (Accuri, Belgium) equipped with a 488 nm laser source to promote emissions at FL2 (615 -670 nm) and FL3 (> 670 nm).…”