Chromosomal variation among populations of a fungus-farming ant: implications for karyotype evolution and potential restriction to gene flow

Abstract

BackgroundIntraspecific variation in chromosome structure may cause genetic incompatibilities and thus provides the first step in the formation of species. In ants, chromosome number varies tremendously from 2n = 2 to 2n = 120, and several studies have revealed considerable variation in karyotype within species. However, most previous studies were limited to the description of chromosome number and morphology, and more detailed karyomorphometric analyses may reveal additional, substantial variation. Here, we studied karyotype length, genome size, and phylogeography of five populations of the fungus-farming ant Trachymyrmex holmgreni in order to detect potential barriers to gene flow.ResultsChromosome number and morphology did not vary among the five populations, but karyotype length and genome size were significantly higher in the southernmost populations than in the northern populations of this ant. Individuals or colonies with different karyotype lengths were not observed. Karyotype length variation appears to result from variation in centromere length.ConclusionT. holmgreni shows considerable variation in karyotype length and might provide a second example of centromere drive in ants, similar to what has previously been observed in Solenopsis fire ants. Whether this variation leads to genetic incompatibilities between the different populations remains to be studied.Electronic supplementary materialThe online version of this article (10.1186/s12862-018-1247-5) contains supplementary material, which is available to authorized users.

Comparative FISH-mapping of TTAGG telomeric sequences to the chromosomes of leafcutter ants (Formicidae, Myrmicinae): is the insect canonical sequence conserved?

“…Establishment of the karyotype (the chromosome number and determination of their morphology) is very important for the knowledge of chromosomal variations and possible genetic barriers between phylogenetic groups (Cristiano et al 2017;Cardoso et al 2018b). It is necessary to go further in describing the chromosome number and morphology, as more detailed karyomorphometric analyses may reveal additional and substantial variations not observed previously, mainly when accompanied with genome size estimates (Cardoso et al 2018b). Tsutsui et al (2008) state that closely related species, belonging to the same genus, may have very similar genome sizes, corroborating the pattern revealed by our karyomorphometric analyses in the Acromyrmex species studied here.…”

“…striatus (Cristiano et al 2013). Such chromosomal features are essential for understanding chromosomal variants and the possible genetic barriers among phylogenetic groups (Cardoso et al 2018b). Ac.…”

Intraspecific variation in the karyotype length and genome size of fungus-farming ants (genus Mycetophylax), with remarks on procedures for the estimation of genome size in the Formicidae by flow cytometry

“…Here, we demonstrated once again that differences in karyotype length can represent the variation in the estimates of genome size in either the cytotypes or among populations. In a study of geographically distant populations of the fungus-farming ant Mycetomoellerius holmgreni Cardoso et al [16] suggested that the correlation between genome size and karyotype length is probably due to changes in the centromeric satellite DNA. They also hypothesized that the changes in the karyotypes of the study populations are molded by a process of centromere drive, which favors the evolution of the karyotype and acts as a potential barrier to gene flow.…”

“…A number of studies have shown that genome size varies considerably among species and even between closely-related taxa [49], although only a few studies have focused on, and quantified, the extent of the variation in genome size among populations [16,50]. Some ecological and physiological traits have been correlated with the size of the genome, e.g., metabolic rate, genome expression, and cell size [3], and all these traits have a direct effect on the fitness of the organism, and are thus subject to natural selection [51].…”

“…So far, only a few studies have investigated the chromosomal variation at the population level (e.g. [11,[16][17][18]), and even fewer have applied a karyomorphometrical approach [18][19][20]. Karyomorphometry is a technique that has been applied amply in cytogenetic studies of plants, and is often combined with estimates of genome size, i.e.…”