Project description:Bilateral animals are featured by an extremely compact mitochondrial (mt) genome with 37 genes on a single circular chromosome. To date, the complete mt genome has only been determined for four species of Liposcelis, a genus with economic importance, including L. entomophila, L. decolor, L. bostrychophila, and L. paeta. They belong to A, B, or D group of Liposcelis, respectively. Unlike most bilateral animals, L. bostrychophila, L. entomophila and L. paeta have a bitipartite mt genome with genes on two chromosomes. However, the mt genome of L. decolor has the typical mt chromosome of bilateral animals. Here, we sequenced the mt genome of L. sculptilis, and identified 35 genes, which were on a single chromosome. The mt genome fragmentation is not shared by the D group of Liposcelis and the single chromosome of L. sculptilis differed from those of booklice known in gene content and gene arrangement. We inferred that different evolutionary patterns and rate existed in Liposcelis. Further, we reconstructed the evolutionary history of 21 psocodean taxa with phylogenetic analyses, which suggested that Liposcelididae and Phthiraptera have evolved 134 Ma and the sucking lice diversified in the Late Cretaceous.
Project description:Booklice in the genus Liposcelis are pests of stored grain products. They pose a considerable economic threat to global food security and safety. To date, the complete mitochondrial genome has only been determined for a single booklouse species Liposcelis bostrychophila. Unlike most bilateral animals, which have their 37 mt genes on one circular chromosome, ?15 kb in size, the mt genome of L. bostrychophila has two circular chromosomes, 8 and 8.5 kb in size. Here, we report the mt genome of another booklouse, Liposcelis decolor. The mt genome of L. decolor has the typical mt chromosome of bilateral animals, 14,405 bp long with 37 genes (13 PCGs, 22 tRNAs and 2 rRNAs). However, the arrangement of these genes in L. decolor differs substantially from that observed in L. bostrychophila and other insects. With the exception of atp8-atp6, L. decolor differs from L. bostrychophila in the arrangement of all of the other 35 genes. The variation in the mt genome organization and mt gene arrangement between the two Liposcelis species is unprecedented for closely related animals in the same genus. Furthermore, our results indicate that the two-chromosome mt genome organization observed in L. bostrychophila likely evolved recently after L. bostrychophila and L. decolor split from their most recent common ancestor.
Project description:How sex is determined in insects is diverse and dynamic, and includes male heterogamety, female heterogamety, and haplodiploidy. In many insect lineages, sex determination is either completely unknown or poorly studied. We studied sex determination in Psocodea-a species-rich order of insects that includes parasitic lice, barklice, and booklice. We focus on a recently discovered species of Liposcelis booklice (Psocodea: Troctomorpha), which are among the closest free-living relatives of parasitic lice. Using genetic, genomic, and immunohistochemical approaches, we show that this group exhibits paternal genome elimination (PGE), an unusual mode of sex determination that involves genomic imprinting. Controlled crosses, following a genetic marker over multiple generations, demonstrated that males only transmit to offspring genes they inherited from their mother. Immunofluorescence microscopy revealed densely packed chromocenters associated with H3K9me3-a conserved marker for heterochromatin-in males, but not in females, suggesting silencing of chromosomes in males. Genome assembly and comparison of read coverage in male and female libraries showed no evidence for differentiated sex chromosomes. We also found that females produce more sons early in life, consistent with facultative sex allocation. It is likely that PGE is widespread in Psocodea, including human lice. This order represents a promising model for studying this enigmatic mode of sex determination.
Project description:Many species of Rickettsia are well-known mammalian pathogens transmitted by blood-feeding arthropods. However, molecular surveys are continually uncovering novel Rickettsia species, often in unexpected hosts, including many arthropods that do not feed on blood. This study reports a systematic molecular characterization of a Rickettsia infecting the psocid Liposcelis bostrychophila (Psocoptera: Liposcelidae), a common and cosmopolitan household pest. Surprisingly, the psocid Rickettsia is shown to be Rickettsia felis, a human pathogen transmitted by fleas that causes serious morbidity and occasional mortality. The plasmid from the psocid R. felis was sequenced and was found to be virtually identical to the one in R. felis from fleas. As Liposcelis insects are often intimately associated with humans and other vertebrates, it is speculated that they acquired R. felis from fleas. Whether the R. felis in psocids causes disease in vertebrates is not known and warrants further study.