Abstract
Fungus-farming ants of the genus Mycetophylax exhibit intra and interspecific chromosome variability, which makes them suitable for testing hypotheses about possible chromosomal rearrangements that endure lineage diversification. We combined cytogenetic and molecular data from Mycetophylax populations from coastal environments to trace the evolutionary history of the clade in light of chromosomal changes under a historical and geographic context. Our cytogenetic analyses revealed chromosomal differences within and among species. M. morschi exhibited three distinct karyotypes and considerable variability in the localization of 45S rDNA clusters. The molecular phylogeny was congruent with our cytogenetic findings. Biogeographical and divergence time dating analyses estimated that the most recent common ancestor of Mycetophylax would have originated at about 30 Ma in an area including the Amazon and Southern Grasslands, and several dispersion and vicariance events may have occurred before the colonization of the Brazilian Atlantic coast. Diversification of the psammophilous Mycetophylax first took place in the Middle Miocene (ca. 18–10 Ma) in the South Atlantic coast, while “M. morschi” lineages diversified during the Pliocene-Pleistocene transition (ca. 3–2 Ma) through founder-event dispersal for the Northern coastal regions. Psammophilous Mycetophylax diversification fits into the major global climatic events that have had a direct impact on the changes in sea level as well as deep ecological impact throughout South America. We assume therefore that putative chromosomal rearrangements correlated with increased ecological stress during the past climatic transitions could have intensified and/or accompanied the divergence of the psammophilous Mycetophylax. We further reiterate that “M. morschi” comprises a complex of at least three well-defined lineages, and we emphasize the role of this integrative approach for the identification and delimitation of evolutionary lineages.
Highlights
Ants (Hymenoptera: Formicidae) exhibit astonishing ecological success that has been attributed to their social organization as well as the ability to associate with other organisms, e.g., fungi[1,2]
Under a molecular cytogenetic approach, such as Fluorescence in situ Hybridization (FISH) chromosome mapping, useful diagnostic characters for morphologically conservative species may be provided as variations in the number and/ or position of ribosomal DNA clusters or chromosomal rearrangements (CRs) indications given by changes in chromosome number
The detailed cytogenetic analysis with Mycetophylax populations revealed the presence of intra- and inter-specific karyotype variations related to the number of diploid chromosomes (2n), the karyotypic formula (KF), and the fundamental number (FN)
Summary
Ants (Hymenoptera: Formicidae) exhibit astonishing ecological success that has been attributed to their social organization as well as the ability to associate with other organisms, e.g., fungi[1,2]. Mycetophylax was formerly composed of three endemic species of coastal sand dune environments, known as Restinga[18,19]: M. conformis Mayr, 1884; M. morschi Emery, 1888; and M. simplex Emery, 1888 (see Fig. 1 for details of occurrence areas). Differences in both the number and structure of their chromosomes were found, including intraspecific variation within M. morschi, showing populations with two distinct karyotypes (2n = 26 and 2n = 30). We hypothesized that Mycetophylax populations may have diversified through chromosomal changes triggered by the climatic events that have continuously affected their habitat
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