Genome Size Evaluations in Cockroaches: New Entries

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).

Morphologic and molecular data help adopting the insect-pathogenic nephridiophagids (Nephridiophagidae) among the early diverging fungal lineages, close to the Chytridiomycota

Nephridiophagids are poorly known unicellular eukaryotes, previously of uncertain systematic position, that parasitize the Malpighian tubules of insects. Their life cycle includes merogony with multinucleate plasmodia and sporogony leading to small, uninucleate spores. We examined the phylogenetic affiliations of three species of Nephridiophaga, including one new species, Nephridiophaga maderae, from the Madeira cockroach (Leucophaea maderae). In addition to the specific host, the new species differs from those already known by the size of the spores and by the number of spores within the sporogenic plasmodium. The inferred phylogenetic analyses strongly support a placement of the nephridiophagids in the fungal kingdom near its root and with a close, but unresolved, relationship to the chytids (Chytridiomycota). We found evidence for the nephridiophagidean speciation as being strongly coupled to host speciation.

Light Affects the Branching Pattern of Peptidergic Circadian Pacemaker Neurons in the Brain of the Cockroach Leucophaea maderae

Pigment-dispersing factor–immunoreactive neurons anterior to the accessory medulla (aPDFMes) in the optic lobes of insects are circadian pacemaker neurons in cockroaches and fruit flies. The authors examined whether any of the aPDFMes of the cockroach Leucophaea maderae are sensitive to changes in period and photoperiod of light/dark (LD) cycles as a prerequisite to adapt to changes in external rhythms. Cockroaches were raised in LD cycles of 11:11, 13:13, 12:12, 6:18, or 18:6 h, and the brains of the adults were examined with immunocytochemistry employing antisera against PDF and orcokinin. Indeed, in 11:11 LD cycles, only the number of medium-sized aPDFMes specifically decreased, while it increased in 13:13. In addition, 18:6 LD cycles increased the number of large- and medium-sized aPDFMes, as well as the posterior pPDFMes, while 6:18 LD cycles only decreased the number of medium-sized aPDFMes. Furthermore, PDF-immunoreactive fibers in the anterior optic commissure and orcokinin-immunoreactive fibers in both the anterior and posterior optic commissures were affected by different lengths of light cycles. Thus, apparently different groups of the PDFMes, most of all the medium-sized aPDFMes, which colocalize orcokinin, respond to changes in period and photoperiod and could possibly allow for the adjustment to different photoperiods.