Estimation of Nuclear Genome Size of Three Species of Camponotus (Mayr, 1861) (Hymenoptera: Formicidae: Formicinae) and Their Cytogenetic Relationship

Abstract

The chromosome variability among ant species is remarkable, and the processes generating such variation are still under discussion since polyploidy has been observed in some distinct taxa. The chromosome number of species belonging to the Camponotus, subgenera Myrmothrix and Myrmobrachys, are highly different, whereas, the first subgenus has double the number of chromosomes of the second. In order to test the hypothesis of chromosome number doubling through polyploidy, the genome sizes of Camponotus (Myrmothrix) rufipes, Camponotus (Myrmothrix) renggeri and Camponotus (Myrmobrachys) crassus were estimated by flow cytometry. The chromosome number of specimens from the nests studied was also defined. No significant variation was noted in the genome size among them. The mean haploid genome size value (1C) of workers for the three species was 286.16 Mpb (0.29 pg). The polyploidy hypothesis can be ruled out as an evolutionary step linking the karyotype variations among the three studied species since the genome size of C. crassus with 2n = 20 chromosomes was the same as that of C. rufipes and C. renggeri with 2n = 40. The lack of variation in the amount of DNA between the related species C. rufipes and C. renggeri also demonstrate that flow cytometry is not an adequate approach to distinguish them. Our results highlight the importance of combining distinct methods, DNA quantification, and cytogenetics from the same colony. Understanding the path of chromosome evolution of three species with distinct degrees of relatedness should provide further information in enriching our knowledge about the Minimum Interaction Theory.

Cytogenetic studies on populations of Camponotus rufipes (Fabricius, 1775) and Camponotus renggeri Emery, 1894 (Formicidae: Formicinae)

“…An alternative explanation could be that it is due to the centromere drive [57]. This karyotype pattern is completely different from that observed in the ant Camponotus ( Myrmobrachys ) crassus Mayr, 1862 (2n = 20) characterized by lower chromosome numbers, all of them metacentric [25, 27]. This demonstrates the rich chromosome diversity and the distinct array of evolutionary chromosome paths existing inside the Camponotus genus.…”

“…Only 4% of the valid Camponotus species have any kind of cytogenetic information available [ 21 ] and only recently C . renggeri has been described by cytogenetic means [ 25 ] through chromosome morphology and number. On the other hand, its presupposed sister species, C .…”

Robertsonian rearrangements in Neotropical Meliponini karyotype evolution (Hymenoptera: Apidae: Meliponini)

“…Genome size variations are usually credited to noncoding DNA, such as repetitive sequences and mobile elements, commonly present in the heterochromatin portion of the chromosomes (Moura et al ., 2019; Blommaert, 2020). Considering the phylogeny of the tribe (Rasmussen and Cameron, 2010) and that the heterochromatin content influences the nuclear genome size (Tavares et al ., 2010; Aguiar et al ., 2016; Moura et al ., 2019), we suggest that the heterochromatin was independently amplified in a few Meliponini genera (Fig. 6), as well documented in the genus Melipona ( Michmelia and Melikerria subgenera), and additionally in Tetragonisca , Geotrigona and Trigona .…”

“…Comparative studies with social stingless bee species have shown that variations in the nuclear genome size do not always correlate with changes in chromosome number, eg, Trigona pallens and Melipona fasciculata have close 1C values, 0.81 pg and 0.82 pg, respectively, and very different chromosome numbers, 2 n = 34 and 2 n = 18, respectively (Lopes et al ., 2009; Tavares et al ., 2012). On the order hand, the species' heterochromatin content has been correlated with nuclear genome size differences (Tavares et al ., 2010; Aguiar et al ., 2016; Moura et al ., 2019).…”