Aim A critical step towards uncovering generalizable patterns of phenotype-niche relationships is understanding how functional traits have evolved as species occupy new habitats. Ecomorphological traits impact how organisms function in their environment and are predictive of habitat use and niche. Studying ecomorphological variation in the context of strong environmental filtering can provide opportunities to understand the role of convergent evolution in forming trait-habitat use patterns. By integrating a molecular phylogeny, habitat use, and morphometrics, this study aimed to understand the role of ancestry and convergent evolution in ecomorphological trait evolution. Location Montane and alpine streambeds, talus, and snowfields in Holarctic mountain ranges (0-5000 m. above sea level). Time Period 1970-2021 Major Taxa Studied Seventy-nine species comprising three species complexes in the ground beetle genus Nebria (Carabidae: Nebriini). Methods Morphological measurements including pronotal ratio (widest point divided by the base), elytral length, elytral ratio (length divided by width), antennal scape length, and pronotal and elytral shape (Fourier decomposition) were used in this study, in conjunction with measurements of habitat use habitat where specimens were collected. Morphological variation was examined in relation to habitat use and phylogenetic relatedness, and morphological trait evolution was tested for convergence. Results Ecomorphological traits are evolving slower than expected under a null model of Brownian motion evolution. Nebria species cluster in multivariate morphospace according to relatedness, but habitat use and relatedness together are the best predictors of morphological variation. There is evidence for convergence in riparian species based on morphologicy alone, and additional evidence for morphological convergence in riparian and alpine species when phylogenetic distance is considered. Main Conclusions In species assemblages of Nebria, we found evidence of rapid diversification followed by a slow rate of ecomorphological evolution, with convergent evolution playing a significant role in shaping trait-habitat use patterns and niche acquisition.

For several decades, the Midwestern USA has been impacted by blacklegged tick (Ixodes scapularis) range expansion, which, as the main vector of the Lyme disease-causing bacterium Borrelia burgdorferi, is linked to a regional increase in Lyme disease incidence. Earlier studies of genetic differentiation of blacklegged ticks have not tested detailed hypotheses about range expansion in the Midwest, despite the importance of this topic to public health. We addressed this gap by investigating the origin and environmental factors that influenced blacklegged tick establishment and spread in the Midwestern region. By analyzing fine-scale spatial population genomic data, we find low genetic differentiation consistent with the known recent range expansion. However, within Wisconsin, blacklegged ticks have unique genetic ancestries that differ from other Midwestern regions, suggesting multiple origins. Our data provide evidence for blacklegged tick sources in northern Wisconsin contributing to the recent expansion. In addition, we find a distinctive mixture of ancestry along the Mississippi River in southwestern Wisconsin and in Indiana, which was previously not identified. The most recently invaded populations in Michigan exhibit sharp genetic divergence from Wisconsin and Indiana samples despite their proximity, warranting further examination of their genetic origin and expansion processes. Lastly, landscape factors contribute to significant reductions in gene flow, potentially limiting genetic exchange and disease transmission within Midwestern states. This new knowledge of blacklegged tick range expansion processes can improve vector surveillance, pest management, and public health related to tick-borne disease risks.

Structural variations (SVs) have been associated with genetic diversity and adaptation in diverse taxa. Despite these observations, it is not yet clear what their relative importance is for microevolution, especially with respect to known drivers of diversity, e.g., nucleotide substitutions, in rapidly adapting species. Here we examine the significance of SVs in pesticide resistance evolution of the agricultural super-pest, the Colorado potato beetle, Leptinotarsa decemlineata. By employing a trio-binning procedure, we develop near chromosomal reference genomes to characterize structural variation within this species. These updated assemblies represent >100-fold improvement of contiguity and include derived pest and ancestral non-pest individuals. We identify >200,000 SVs, which appear to be non-randomly distributed across the genome as they co-occur with transposable elements. SVs intersect exons for genes associated with insecticide resistance, development, and transcription, most notably cytochrome P450 (CYP) genes. To understand the role that SVs might play in adaptation, we incorporate an additional 66 genomes among pest and non-pest populations of North America into the SV graph. Single nucleotide polymorphisms (SNPs) and SVs have a similar proportion in coding and non-coding regions of the genome, but there is a deficit of SNPs in SVs, suggesting SVs may be under selection. Using multiple lines of evidence, we identify 28 positively selected genes that include 337 SVs and 442 outlier SNPs. Among these, there are four associated with insecticide resistance. Two of these genes (CYP4g15 and glycosyltransferase-13) are physically linked by a structural variant and have previously been shown to be co-induced during insecticide exposure.

The hyper-diverse order Coleoptera comprises a staggering ~25% of known species on Earth. Despite recent breakthroughs in next generation sequencing, there remains a limited representation of beetle diversity in assembled genomes. Most notably, the ground beetle family Carabidae, comprising more than 40,000 described species, has not been studied in a comparative genomics framework using whole genome data. Here we generate a high-quality genome assembly for Nebria riversi, to examine sources of novelty in the genome evolution of beetles, as well as genetic changes associated with specialization to high elevation alpine habitats. In particular, this genome resource provides a foundation for expanding comparative molecular research into mechanisms of insect cold adaptation. Comparison to other beetles shows a strong signature of genome compaction, with N. riversi possessing a relatively small genome (~147 Mb) compared to other beetles, with associated reductions in repeat element content and intron length. Small genome size is not, however, associated with fewer protein-coding genes, and an analysis of gene family diversity shows significant expansions of genes associated with cellular membranes and membrane transport, as well as protein phosphorylation and muscle filament structure. Finally, our genomic analyses show that these high elevation beetles have endosymbiotic Spiroplasma, with several metabolic pathways (e.g. propanoate biosynthesis) that might complement N. riversi, although its role as a beneficial symbiont or as a reproductive parasite remains equivocal.

The evolutionary histories of alpine species are often directly associated with responses to glaciation. Deep divergence among populations and complex patterns of genetic variation have been inferred as consequences of persistence within glacier boundaries (i.e. on nunataks), while shallow divergence and limited genetic variation is assumed to result from expansion from large refugia at the edge of ice shields (i.e. massifs de refuge). However, for some species, dependence on specific microhabitats could profoundly influence their spatial and demographic response to glaciation, and such a simple dichotomy may obscure the localization of actual refugia. In this study, we use the Nebria ingens complex (Coleoptera: Carabidae), a water-affiliated ground beetle lineage, to test how drainage basins are linked to their observed population structure. By analyzing mitochondrial COI gene sequences and genome-wide single nucleotide polymorphisms, we find that the major drainage systems of the Sierra Nevada Mountains in California best explain the population structure of the N. ingens complex. In addition, we find that an intermediate morphotype within the N. ingens complex is the product of historical hybridization of N. riversi and N. ingens in the San Joaquin basin during glaciation. This study highlights the importance of considering ecological preferences in how species respond to climate fluctuations and provides an explanation for discordances that are often observed in comparative phylogeographic studies.