Comparative cytogenetics in three Melipona species (Hymenoptera: Apidae) with two divergent heterochromatic patterns

Abstract

The genus Melipona is subdivided into four subgenera based on morphological characteristics, and two groups based on cytogenetic patterns. The cytogenetic information on this genus is still scarce, therefore, the goal of this study was to characterize Melipona paraensis, Melipona puncticollis, and Melipona seminigra pernigra using the following techniques: C-banding, DAPI/CMA3 fluorochromes, and FISH with an 18S rDNA probe. Melipona paraensis (2n=18) and M. seminigra pernigra (2n=22) were classified as high heterochromatin content species (Group II). Their euchromatin is restricted to the ends of the chromosomes and is CMA3 +; the 18S rDNA probe marked chromosome pair number 4. Melipona puncticollis (2n=18) is a low heterochromatin content species (Group I) with chromosome pair number 1 marked with CMA3 and 18S rDNA. Low heterochromatin content is a putative ancestral karyotype in this genus and high content is not a monophyletic trait (Melikerria presents species with both patterns). Differences concerning the karyotypic characteristics can be observed among Melipona species, revealing cytogenetic rearrangements that occurred during the evolution of this genus. Studies in other species will allow us to better understand the processes that shaped the chromatin evolution in Melipona.

Different Levels of Chromatin Condensation in <b><i>Partamona chapadicola</i></b> and <b><i>Partamona nhambiquara</i></b> (Hymenoptera, Apidae)

“…Considering that heterochromatin in Meliponini arose at different times [Cunha et al, 2018;Piccoli et al, 2018;Pereira, 2018] and that chromatin with intermediate staining was observed only in species with centromeric heterochromatin, this "new class" of chromatin can indicate the beginning of the process of heterochromatinization in these species, and will result in the formation of completely heterochromatic arms as seen in high frequency in the Meliponini. Therefore, the verification of the existence of a new class of chromatin with intermediate staining intensity, between that of the euchromatin and heterochromatin, demonstrates a possible path of how karyotype evolution has taken place in the tribe Meliponini.…”

“…One possible explanation for the intermediate staining is that these are regions of heterochromatin formation that is involved in more than just the stabilization of the telomeric region, as proposed in Imai et al [1988]. Recent studies have shown that heterochromatin emerged at different times during the evolution of Meliponini species, indicating that its formation is a continuous and recurrent process [Cunha et al, 2018;Piccoli et al, 2018]. Recent developments in the field of cytogenetics include new techniques for studying chromosomes and new software for analyzing images, both leading to the investigation of chromosome banding patterns with improved depth and reliability.…”

The evolution of haploid chromosome numbers in Meliponini

“…On the other hand, in different taxa such as ants, fish, mammals, and frogs, fissions are also important events in chromosome rearrangement throughout evolutionary time [21], [72–74]. In Meliponini, an example of chromosome fission was observed in Melipona seminigra (Friese, 1903), which has n = 11 chromosomes [12], [45]. According to our findings, this chromosome number observed today likely originated by fission events from an ancestor with n = 9.…”

“…Cytogenetic analyses, in particular, are an important tool for understanding the macro-scale genomic organization of different any species. These analyses comprise descriptions of chromosome number [11], [2], [9], heterochromatin distribution patterns [12], characterization of AT and CG rich regions [13], [12], localization of 18S ribosomal genes [14], [12], mapping of repetitive DNA sequences [15], and inferences of karyotype evolution [10–11].…”

Chromosomal mapping of repetitive DNA in Melipona seminigra merrillae Cockerell, 1919 (Hymenoptera, Apidae, Meliponini)

“…The species Melipona quinquefasciata Lepeletier, 1836 and M. rufiventris Lepeletier, 1836 which have B chromosomes ( Rocha et al 2007 ; Lopes et al 2008 ), while M. seminigra merrillae Cockerell, 1919, M. seminigra pernigra Moure & Kerr, 1950 and M. seminigra abunensis Cockerell, 1912 have 2n = 22 and n = 11 chromosomes ( Francini et al 2011 ; Andrade-Souza et al 2018 ; Cunha et al 2018 ). Melipona has a unique distribution pattern of constitutive heterochromatin ( CH ), which differentiates it from other Meliponini ( Hoshiba and Imai 1993 ; Rocha et al 2003 ; Cunha et al 2018 ). Based on the distribution pattern/quantity of CH , species in the genus can be divided into two groups: Group I – composed of species with a low amount of CH , present only in pericentromeric regions, and Group II – composed of species with a high amount of CH , present along almost the entire length of each chromosome ( Rocha and Pompolo 1998 ; Rocha et al 2002 ; Lopes et al 2011 ).…”