Abstract
It is thought that two evolutionary mechanisms gave rise to chromosomal variation in bees: the first one points to polyploidy as the main cause of chromosomal evolution, while the second, Minimum Interaction Theory (MIT), is more frequently used to explain chromosomal changes in Meliponini and suggests that centric fission is responsible for variations in karyotype. However, differences in chromosome number between Meliponini and its sister taxa and in the karyotype patterns of the Melipona genus cannot be explained by MIT, suggesting that other events were involved in chromosomal evolution. Thus, we assembled cytogenetical and molecular information to reconstruct an ancestral chromosome number for Meliponini and its sister group, Bombini, and propose a hypothesis to explain the evolutionary pathways underpinning chromosomal changes in Meliponini. We hypothesize that the common ancestor shared by the Meliponini and Bombini tribes possessed a chromosome number of n = 18. The karyotype with n = 17 chromosomes was maintained in Meliponini, and variations of haploid numbers possibly originated through additional Robertsonian fissions and fusions. Thus, the low chromosome number would not be an ancestral condition, as predicted by MIT. We then conclude that Robertsonian fission and fusions are unlikely to be the cause of chromosomal rearrangements that originated the current karyotypes in Meliponini.
Highlights
Meliponini, Bombini, Apini, and Euglossini tribes comprise those bees known as "corbiculate", and their evolutionary history has been studied through morphological, phylogenetic, and cytogenetic analyses [1,2,3,4,5,6,7,8,9,10]
In Bombini species, on the other hand, the haploid number varied from n = 12 to n = 20 chromosomes, with n = 18 predominating (Table 1)
The concatenated dataset resulted in 3,263 aligned base pairs and the phylogenetic tree obtained from Bayesian inference analysis recovered the phylogeny proposed by Rasmussen and Cameron [7] (S1 Fig)
Summary
Meliponini, Bombini, Apini, and Euglossini tribes comprise those bees known as "corbiculate", and their evolutionary history has been studied through morphological, phylogenetic, and cytogenetic analyses [1,2,3,4,5,6,7,8,9,10]. 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.
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