Genome Size Evaluations in Cockroaches: New Entries

Abstract Background: Ten years ago the main Genome Size (GS) database contained records for 830 insects; although this number has now nearly doubled, 1645 (Gregory 2011 vs Gregory 2021 databases), the paucity of records highlights both the difficulty of animal field trapping and the time-consuming laboratory techniques to evaluate them. Thus, new entries are necessary to reach a satisfactory GS panorama for cockroaches. Results: We report GS values for nine cockroaches (order Blattodea, families Blattidae, Blaberidae and Ectobiidae, ex Blattelidae,), three of which are original additions to the ten already present in the GS database: the death’s head roach (Blaberus craniifer), the Surinam cockroach (Pycnoscelus surinamensis) and the Madeira cockroach (Leucophaea maderae). Three of our values confirm the existing data for the German (Blattella germanica), the oriental (Blatta orientalis) and the giant Mexican (Blabera fusca) cockroaches. Regarding the GS of the American cockroach (Periplaneta americana) the GS database contains two contrasting values (2.72 vs 3.41 pg). We suggest that the 2.72 pg value is likely to be the correct GS as it strikingly similar to our sperm DNA content evaluation (2.80 ± 0.11 pg). Finally, we suggest halving the published GS of the Argentine cockroach Blaptica dubia and the spotted cockroach (the gray cockroach) Nauphoeta cinerea as our estimates come from the evaluation of the sperm DNA content. The data already reported in the literature are based on DNA contents of neural cells (likely polyploid) obtained by grinding entire heads of animals.Conclusions: Although the paucity of the GS data does not allow firm considerations on the possible evolutionary role played by the GS in diversifying cockroach species, we offer two speculative hypotheses that need to be validated by increasing the available GS records: (i) the occurrence of a correlation between increasing 2N chromosome number and GS within the order Blattodea; and (ii) the possible occurrence of a polyploidization phenomenon doubling a basic GS of 0.58 pg of some termite families (superfamily Blattoidea, epifamily Termitoidae) up to the maximum GS value of 3.24 for the Blaberidae family within the order Blattodea (super-order Dictyoptera).