Abstract
Among insect taxa, ants exhibit one of the most variable chromosome numbers ranging from n = 1 to n = 60. This high karyotype diversity is suggested to be correlated to ants diversification. The karyotype evolution of ants is usually understood in terms of Robertsonian rearrangements towards an increase in chromosome numbers. The ant genus Mycetophylax is a small monogynous basal Attini ant (Formicidae: Myrmicinae), endemic to sand dunes along the Brazilian coastlines. A recent taxonomic revision validates three species, Mycetophylax morschi, M. conformis and M. simplex. In this paper, we cytogenetically characterized all species that belongs to the genus and analyzed the karyotypic evolution of Mycetophylax in the context of a molecular phylogeny and ancestral character state reconstruction. M. morschi showed a polymorphic number of chromosomes, with colonies showing 2n = 26 and 2n = 30 chromosomes. M. conformis presented a diploid chromosome number of 30 chromosomes, while M. simplex showed 36 chromosomes. The probabilistic models suggest that the ancestral haploid chromosome number of Mycetophylax was 17 (Likelihood framework) or 18 (Bayesian framework). The analysis also suggested that fusions were responsible for the evolutionary reduction in chromosome numbers of M. conformis and M. morschi karyotypes whereas fission may determines the M. simplex karyotype. These results obtained show the importance of fusions in chromosome changes towards a chromosome number reduction in Formicidae and how a phylogenetic background can be used to reconstruct hypotheses about chromosomes evolution.
Highlights
Chromosomes are the units of inheritance contained in the nuclei of eukaryotic cells
The chromosome evolution in ants generally tends towards an increase in chromosome number in order to reduce the risk of deleterious rearrangements [5]
To describe an evolutionary scenario for chromosome evolution inferred by ChromEvol to Mycetophylax, we focused on the haploid chromosome numbers estimated in the Bayesian method, since this method provides posterior probabilities (PP) as a statistical parameter
Summary
Chromosomes are the units of inheritance contained in the nuclei of eukaryotic cells. A large number of ant species have been studied cytogenetically and they exhibit an enormous diversity of chromosome number, varying from n = 1 to n = 60 (reviewed in [2]) This marked variation aroused attention over 35 years ago [3], such that several evolutionary mechanisms and the manner in which this diversity has evolved have been proposed. Among the evolutionary mechanism proposed, rearrangements involving Robertsonian fissions stands out (see [4,5]) in the so–called ‘‘minimum interaction theory’’ According to this theory, the chromosome evolution in ants generally tends towards an increase in chromosome number in order to reduce the risk of deleterious rearrangements [5]. It has been thought that the typical trend in chromosome increase probably respects certain limits [2]
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