The Queensland fruit fly,Bactrocera tryoni, is a major pest of Australian horticulture which has expanded its range in association with the spread of horticulture over the last ~ 150 years. Its distribution in northern Australia overlaps that of another fruit fly pest to which some authors accord full species status,Bactrocera aquilonis. We have used reduced representation genome-wide sequencing to genotype 359 individuals taken from 35 populations from across the current range of the two taxa, plus a further 73 individuals from six of those populations collected 15–22 years earlier. We find significant population differentiation along an east–west transect across northern Australia which likely reflects limited but bidirectional gene flow between the two taxa. The southward expansion ofB. tryonihas led to relatively little genetic differentiation, and most of it is associated with a move into previously marginal inland habitats. Two disjunct populations elsewhere in Australia and three on Melanesian islands are each clearly differentiated from all others, with data strongly supporting establishment from relatively few founders and significant isolation subsequently. Resequencing of historical samples from one of the disjunct Australian populations shows that its genetic profile has changed little over a 15-year period, while the Melanesian data suggest a succession of‘island hopping’events with progressive reductions in genetic diversity. We discuss our results in relation to the control ofB. tryoniand as a model for understanding the genetics of invasion and hybridisation processes.

Background: The highly polyphagous Queensland fruit fly (Bactrocera tryoniFroggatt) expanded its range substantially during the twentieth century and is now the most economically important insect pest of Australian horticulture, prompting intensive efforts to develop a Sterile Insect Technique (SIT) control program. Using a “common garden” approach, we have screened for natural genetic variation in key environmental fitness traits among populations from across the geographic range of this species and monitored changes in those traits induced during domestication.Results: Significant variation was detected between the populations for heat, desiccation and starvation resistance and wing length (as a measure of body size). Desiccation resistance was correlated with both starvation resistance and wing length. Bioassay data for three resampled populations indicate that much of the variation in desiccation resistance reflects persistent, inherited differences among the populations. No latitudinal cline was detected for any of the traits and only weak correlations were found with climatic variables for heat resistance and wing length. All three stress resistance phenotypes and wing length changed significantly in certain populations with ongoing domestication but there was also a strong population by domestication interaction effect for each trait.Conclusions: Ecotypic variation in heat, starvation and desiccation resistance was detected in Australian Qfly populations, and these stress resistances diminished rapidly during domestication. Our results indicate a need to select source populations for SIT strains which have relatively high climatic stress resistance and to minimise loss of that resistance during domestication.

Background: Borrelia are important disease-causing tick- and louse-borne spirochaetes than can infect a wide variety of vertebrates, including humans and reptiles. Reptile-associated (REP) Borrelia, once considered a peculiarity, are now recognised as a distinct and important evolutionary lineage, and are increasingly being discovered worldwide in association with novel hosts. Numerous novel Borrelia spp. associated with monitor lizards (Varanus spp.) have been recently identified throughout the Indo-Pacific region; however, there is a lack of genomic data on these Borrelia. Methods: We used metagenomic techniques to sequence almost complete genomes of novel Borrelia spp. from Varanus varius and Varanus giganteus from Australia, and used long- and short-read technologies to sequence the complete genomes of two strains of a novel Borrelia sp. previously isolated from ticks infesting Varanus salvator from Indonesia. We investigated intra- and interspecies genomic diversity, including plasmid diversity and relatedness, among Varanus-associated Borrelia and other available REP Borrelia and, based on 712 whole genome orthologues, produced the most complete phylogenetic analysis, to the best of our knowledge, of REP Borrelia to date. Results: The genomic architecture of Varanus-associated Borrelia spp. is similar to that of Borrelia spp. that cause relapsing fever (RF), and includes a highly conserved megaplasmid and numerous smaller linear and circular plasmids that lack structural consistency between species. Analysis of PF32 and PF57/62 plasmid partitioning genes indicated that REP Borrelia plasmids fall into at least six distinct plasmid families, some of which are related to previously defined Borrelia plasmid families, whereas the others appear to be unique. REP Borrelia contain immunogenic variable major proteins that are homologous to those found in Borrelia spp. that cause RF, although they are limited in copy number and variability and have low sequence identities to RF variable major proteins. Phylogenetic analyses based on single marker genes and 712 single copy orthologs also definitively demonstrated the monophyly of REP Borrelia as a unique lineage. Conclusions: In this work we present four new genomes from three novel Borrelia, and thus double the number of REP Borrelia genomes publicly available. The genomic characterisation of these Borrelia clearly demonstrates their distinctiveness as species, and we propose the names Borrelia salvatorii, ‘Candidatus Borrelia undatumii’, and ‘Candidatus Borrelia rubricentralis’ for them. Graphical

Australia and Southeast Asia are hotspots of global diversity in the fruit-fly genus Bactrocera. Although a great diversity of species has been long recognised, evolutionary relationships are poorly understood, largely because previous sequencing techniques have provided insufficient historical signal for phylogenetic reconstruction. Poorly understood biogeographic history in Bactrocera has prevented a deeper understanding of migratory patterns in this economically important pest group. Using representatives from Australia and Malaysia, we tested the utility of a genome-reduction approach that generates thousands of single-nucleotide polymorphisms for phylogenetic reconstructions. This approach has high utility for species identification because of the ease of sample addition over time, and the species-level specificity able to be achieved with the markers. These data have provided a strongly supported phylogenetic tree congruent with topologies generated using more intensive sequencing approaches. In addition, our results do not support taxonomic assignments to species complex for a number of species, such as B. endiandrae in the dorsalis complex, yet find a close relationship between B. pallida and the dorsalis species. Our data have further validated non-monophyletic evolution of male response to primary attractants. We also showed at least two diversification events between Australia and Southeast Asia, indicating trans-regional dispersal in important pest species.

Fusarium oxysporum f. sp. vasinfectum (Fov) is a devastating cotton pathogen. Australian Fov strains are distinguished by their ability to infect plants without nematode interaction and are genetically distinct from global Fov, classified into two vegetative compatibility groups (VCG-01111 and VCG-01112). Here, we present chromosome-level genome assemblies of a historical isolate for each Australian Fov VCG. The end-to-end gapless genome assemblies demonstrate high contiguity and completeness, with 97.7% BUSCO completeness for both isolates. Phylogenetic analysis indicates that the Australian Fov lineages diverged from other known Fov genomes over 3.6 million years ago, while VCG-01111 and VCG-01112 separated approximately 1.1 million years ago. Comparative genomics analysis identified four accessory chromosomes unique to the Australian isolates. Functional annotations revealed 14,495 and 15,342 genes in VCG-01111 and VCG-01112, respectively, with accessory chromosomes containing significantly fewer genes than core chromosomes. Ortholog analysis uncovered unique gene clusters enriched in key metabolic pathways, pathogenicity, and cell division processes. Additionally, we identified several novel lineage-specific peptides unique to each Australian isolate. This comprehensive genomic characterization provides the first insights into the unique evolutionary history of Australian Fov, distinguishing them from global Fov races. Our findings lay the foundation for understanding the genetic factors underlying their exceptional virulence, which makes Australian Fov among the most aggressive cotton pathogens worldwide.