Polytene chromosomes of monogenic and amphogenic Chrysomya species (Calliphoridae, Diptera): analysis of banding patterns and in situ hybridization with Drosophila sex determining gene sequences

Why put all your eggs in one basket? Evolutionary perspectives on the origins of monogenic reproduction

Sexual reproduction is ubiquitous in eukaryotes, but the mechanisms by which sex is determined are diverse and undergo rapid turnovers in short evolutionary timescales. Usually, an embryo's sex is fated at the moment of fertilisation, but in rare instances it is the maternal genotype that determines the offspring's sex. These systems are often characterised by mothers producing single-sex broods, a phenomenon known as monogeny. Monogenic reproduction is well documented in Hymenoptera (ants, bees and wasps), where it is associated with a eusocial lifestyle. However, it is also known to occur in three families in Diptera (true flies): Sciaridae, Cecidomyiidae and Calliphoridae. Here we review current knowledge of monogenic reproduction in these dipteran clades. We discuss how this strange reproductive strategy might evolve, and we consider the potential contributions of inbreeding, sex ratio distorters, and polygenic control of the sex ratio. Finally, we provide suggestions on future work to elucidate the origins of this unusual reproductive strategy. We propose that studying these systems will contribute to our understanding of the evolution and turnover of sex determination systems.

Chrysomya pinguis (Walker) (Diptera: Calliphoridae), blow fly of forensic importance: A review of bionomics and forensic entomology appraisal

Role of blow flies as the entomological evidence used in forensic investigations has risen dramatically worldwide. As the diverse habitats of Thailand suitably endowed with biodiversity of insects, blow flies of forensic importance need investigation in their bionomics, which are further applied in forensic investigations. Chrysomya pinguis (Walker, 1858) (Diptera: Calliphoridae) make up one of the most common blow fly species found associated with the human corpses and/or death scenes in several countries of the Asia continent. Given the major species as forensically important, this review is performed by the need for gathering information of C. pinguis from literature search in the future application in the regions where this species exists. This review deals with morphology, current knowledge on bionomics and forensic entomology involvement. Important morphological characteristics of egg, larva, puparium and adult were highlighted with illustration and/or micrographs. Search pertaining to molecular analysis used for fly identification and developmental rate of larvae were included. Furthermore, we outline potential issues and challenges of C. pinguis research that necessitate forensic applications in the future.

Molecular phylogeny of the blowfly genus Chrysomya

Chrysomya Robineau-Desvoidy (Diptera: Calliphoridae) is a genus of blowfly commonly observed in tropical and subtropical countries of the Old World. Species in this genus are vectors of bacteria, protozoans and helminths, cause myiasis, are predators of other carrion insects, and are important forensic indicators. Hypotheses concerning the evolution of sex determination, larval anatomy and genome size in Chrysomya have been difficult to evaluate because a robust phylogeny of the genus was lacking. Similarly, the monophyly of subgenera was uncertain. The phylogeny of Chrysomya spp. was reconstructed based on 2386 bp of combined mitochondrial cytochrome oxidase subunit I (COI) and nuclear carbamoylphosphate synthetase (CPS) genes. Maximum parsimony (MP), maximum likelihood (ML) and Bayesian analysis (BA) differed only slightly in the resulting tree topology. Chrysomya was monophyletic. Monogenic reproduction is almost certainly derived rather than, as has been suggested, primitive within the genus, and tuberculate larvae probably evolved twice. Genome size is more likely to have decreased over evolutionary time rather than, as has been suggested, increased within the genus, but its correlation with developmental time was not observed. The subgenera Microcalliphora, Eucompsomyia and Achoetandrus were recovered as monophyletic.

Karyotypes, constitutive heterochromatin, and genomic DNA values in the blowfly genera Chrysomya, Lucilia, and Protophormia (Diptera: Calliphoridae)

The karyotypes and C-banding patterns of Chrysomya species C. marginalis, C. phaonis, C. pinguis, C. saffranea, C. megacephala (New Guinean strain), Lucilia sericata, and Protophormia terraenovae are described. All species are amphogenic and have similar chromosome complements (2n = 12), including an XY-XX sex-chromosome pair varying in size and morphology between species. Additionally, the C-banding pattern of the monogenic species Chrysomya albiceps is presented. The DNA contents of these and of further species Chrysomya rufifacies, Chrysomya varipes, and Chrysomya putoria were assessed on mitotic metaphases by Feulgen cytophotometry. The average 2C DNA value of the male genomes ranged from 1.04 pg in C. varipes to 2.31 pg in C. pinguis. The DNA content of metaphase X chromosomes varied from 0.013 pg (= 1.23% of the total genome) in C. varipes to 0.277 pg (12.20%) in L. sericata; that of Y chromosomes ranged from 0.003 pg (0.27%) in C. varipes to 0.104 pg (5.59%) in L. sericata. In most species, the corresponding 5 large chromosome pairs showed similar relative DNA contents. The data suggest that the interspecific DNA differences in most species are mainly due to quantitative variation of (repetitive) sequences lying outside the centromeric heterochromatin blocks of the large chromosomes. The results are also discussed with regard to phylogenetic relationships of some species.