Genome-wide SNPs resolve phylogenetic relationships in the North American spruce budworm (Choristoneura fumiferana) species complex.

High throughput sequencing technologies have revolutionized the potential to reconcile incongruence between gene and species trees, and numerous approaches have been developed to take advantage of these advances. Genotyping-by-sequencing is becoming a regular tool for gathering phylogenetic data, yet comprehensive evaluations of phylogenetic methods using these data are sparse. Here we use multiple phylogenetic and population genetic methods for genotyping-by-sequencing data to assess species relationships in a group of forest insect pests, the spruce budworm (Choristoneura fumiferana) species complex. With few exceptions, all methods agree on the same relationships, most notably placing C. pinus as basal to the remainder of the group, rather than C. fumiferana as previously suggested. We found strong support for the monophyly of C. pinus, C. fumiferana, and C. retiniana, but more ambiguous relationships and signatures of introgression in a clade of western lineages, including C. carnana, C. lambertiana, C. occidentalis occidentalis, C. occidentalis biennis, and C. orae. This represents the most taxonomically comprehensive genomic treatment of the spruce budworm species group, which is further supported by the broad agreement among multiple methodologies.

Comparison of bacterial 16S rRNA variable regions for microbiome surveys of ticks.

Ticks vector diverse pathogenic bacteria that are important to identify in public health and veterinary contexts. Technological advances in high throughput sequencing have given an unprecedented opportunity to comprehensively characterize bacterial associates of ticks, but recent studies have used different 16S rRNA variable regions and sequence read lengths with little consideration of whether they reveal the same bacterial diversity. We compare the effectiveness of bacterial surveys using three library preparations across nine 16S variable regions and a set of 12 tick specimens (Acari: Ixodidae). We identify the bacterial assemblages present in extractions from wild-collected Ixodes scapularis from two regions of Canada, and provide the first microbiome survey for Ixodes angustus. Four bacterial families accounted for most diversity, with Rickettsiaceae being replaced as most common by Enterobacteriaceae or Pseudomonadaceae in some I. scapularis, and Francisellaceae being most abundant in I. angustus. The commercially available Ion 16S kit, based on 6 amplicons representing 16S regions V2, V3, V4, V67, V8 and V9, gave the most comprehensive estimates of bacterial families, with the Ion V4 amplicon generally giving the highest estimated diversity. Sequencing of the V4 amplicon by the MR DNA commercial service also provided cost effective assays of tick microbiomes that were within the range of results from the Ion 16S kit. Subtraction of the number of reads found in an extraction control sample lowered estimates of the number of bacterial families by approximately half. Our study shows that diversity patterns obtained from 16S microbiome surveys depend on the amplicon and protocol used, demonstrating that more than one marker region is needed to provide reliable inferences.

Hybrid dynamics in a species group of swallowtail butterflies.

Hybrid zones provide unique natural laboratories for studying mechanisms of evolution. But identification and classification of hybrid individuals (F1, F2, backcross, etc.) can be complicated by real population changes over time as well as by use of different marker types, both of which challenge documentation of hybrid dynamics. Here, we use multiple genetic markers (mitochondrial DNA, microsatellites and genomewide single nucleotide polymorphisms) to re-examine population structure in a hybrid zone between two species of swallowtail butterflies in western Canada, Papilio machaon and P. zelicaon. Our aim was to test whether their hybrid dynamics remain the same as found 30 years ago using morphology and allozymes, and we compared different genetic data sets as well as alternative hybrid identification and classification methods. Overall, we found high differentiation between the two parental species, corroborating previous research from the 1980s. We identified fewer hybrid individuals in the main zone of hybridization in recent years, but this finding depended on the genetic markers considered. Comparison of methods with simulated data sets generated from our data showed that single nucleotide polymorphisms were more powerful than microsatellites for both hybrid identification and classification. Moreover, substantial variation among comparisons underlined the value of multiple markers and methods for documenting evolutionarily dynamic systems.

Polygamy and an absence of fine-scale structure in Dendroctonus ponderosae (Hopk.) (Coleoptera: Curcilionidae) confirmed using molecular markers.

An understanding of mating systems and fine-scale spatial genetic structure is required to effectively manage forest pest species such as Dendroctonus ponderosae (mountain pine beetle). Here we used genome-wide single-nucleotide polymorphisms to assess the fine-scale genetic structure and mating system of D. ponderosae collected from a single stand in Alberta, Canada. Fine-scale spatial genetic structure was absent within the stand and the majority of genetic variation was best explained at the individual level. Relatedness estimates support previous reports of pre-emergence mating. Parentage assignment tests indicate that a polygamous mating system better explains the relationships among individuals within a gallery than the previously reported female monogamous/male polygynous system. Furthermore, there is some evidence to suggest that females may exploit the galleries of other females, at least under epidemic conditions. Our results suggest that current management models are likely to be effective across large geographic areas based on the absence of fine-scale genetic structure.