@article {KNZ001334, title = {Comparative genome scan detects host-related divergent selection in the grasshopper Hesperotettix viridis}, journal = {Molecular Ecology}, volume = {19}, year = {2010}, pages = {4012 -4028}, abstract = {

In this study, we used a comparative genome scan to examine patterns of population differentiation with respect to host plant use in Hesperotettix viridis, a Nearctic oligophagous grasshopper locally specialized on various Asteraceae including Solidago, Gutierrezia, and Ericameria. We identified amplified fragment length polymorphism (AFLP) loci with significantly elevated FST (outlier loci) in multiple different-host and same-host comparisons of populations while controlling for geographic distance. By comparing the number and identities of outlier loci in different-host vs. same-host comparisons, we found evidence of host plant-related divergent selection for some population comparisons (Solidago- vs. Gutierrezia-feeders), while other comparisons (Ericameria- vs. Gutierrezia-feeders) failed to demonstrate a strong role for host association in population differentiation. In comparisons of Solidago- vs. Gutierrezia-feeding populations, a relatively high number of outlier loci observed repeatedly in different-host comparisons (35\% of all outliers and 2.7\% of all 625 AFLP loci) indicated a significant role for host-related selection in contributing to overall genomic differentiation in this grasshopper. Mitochondrial DNA sequence data revealed a star-shaped phylogeny with no host- or geography-related structure, low nucleotide diversity, and high haplotype diversity, suggesting a recent population expansion. mtDNA data do not suggest a long period of isolation in separate glacial refugia but are instead more compatible with a single glacial refugium and more recent divergence in host use. Our study adds to research documenting heterogeneity in differentiation across the genome as a consequence of divergent natural selection, a phenomenon that may occur as part of the process of ecological speciation.

}, keywords = {LTER-KNZ}, doi = {10.1111/j.1365-294X.2010.04792.x}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-294X.2010.04792.x}, author = {Apple, J.L. and Grace, T. and Anthony Joern and Amand, P. and Wisely, S.M.} } @article {KNZ001335, title = {Divergent host plant adaptation drives the evolution of reproductive isolation in the grasshopper Hesperotettix viridis (Orthoptera: Acrididae)}, journal = {Biological Journal of the Linnaean Society}, volume = {100}, year = {2010}, pages = {866 -878}, abstract = {

Early stages of lineage divergence in insect herbivores are often related to shifts in host plant use and divergence in mating capabilities, which may lead to sexual isolation of populations of herbivorous insects. We examined host preferences, degree of differentiation in mate choice, and divergence in cuticular morphology using near-infrared spectroscopy in the grasshopper Hesperotettix viridis aiming to understand lineage divergence. In Kansas (USA), H. viridis is an oligophagous species feeding on Gutierrezia and Solidago host species. To identify incipient mechanisms of lineage divergence and isolation, we compared host choice, mate choice, and phenotypic divergence among natural grasshopper populations in zones of contact with populations encountering only one of the host species. A significant host-based preference from the two host groups was detected in host-paired feeding preference studies. No-choice mate selection experiments revealed a preference for individuals collected from the same host species independent of geographic location, and little mating was observed between individuals collected from different host species. Female mate choice tests between males from the two host species resulted in 100\% fidelity with respect to host use. Significant differentiation in colour and cuticular composition of individuals from different host plants was observed, which correlated positively with host choice and mate choice. No evidence for reinforcement in the zone of contact was detected, suggesting that divergent selection for host plant use promotes sexual isolation in this species.

}, keywords = {LTER-KNZ, allopatry, ecological speciation, feeding preference, genetic divergence, host-associated divergence, mate choice, Microsatellites, near-infrared spectroscopy, reproductive isolation, secondary contact zones, sexual isolation, sympatry}, doi = {10.1111/j.1095-8312.2010.01458.x}, url = {https://academic.oup.com/biolinnean/article/100/4/866/2450537}, author = {Grace, T. and Dowell, F. and Anthony Joern and Wisely, S.M. and Brown, S.J. and Maghirang, E.} } @article {KNZ001273, title = {Highly polymorphic microsatellites in the North American snakeweed grasshopper, Hesperotettix viridis}, journal = {Journal of Orthoptera Research}, volume = {18}, year = {2009}, pages = {19 -21}, abstract = {

Microsatellite markers are preferred for fine-scale population genetic studies requiring high resolution. The grasshopper Hesperotettix viridis (Thomas) is an oligophagous species that feeds on composites and often exhibits locally restricted diets. Divergence in host plant use in some localities is seen where co-occurring subpopulations select alternate plant species, as expected with the evolution of host shifts and associated lineage divergence. To characterize the host-associated divergence patterns among populations of H. viridis, we developed markers from two microsatellite-enriched genomic libraries. Here we report the characterization and optimization of seven polymorphic di- and tri-nucleotide microsatellite loci for this species. One hundred and six individuals from 5 populations were tested for polymorphism. The number of alleles varied from 4 to 38 in all the populations. Ho ranged from 0.339 to 0.790. Homozygote excess was observed across loci, perhaps due to inbreeding. This is the first report of microsatellite markers for the subfamily Melanoplinae.

}, keywords = {LTER-KNZ, Hesperotettix viridis, host-associated divergence, local adaptation, microsatellite markers, snakeweed grasshopper}, doi = {10.1665/034.018.0111}, url = {https://bioone.org/journals/Journal-of-Orthoptera-Research/volume-18/issue-1/034.018.0111/Highly-Polymorphic-Microsatellites-in-the-North-American-Snakeweed-Grasshopper-iHesperotettix/10.1665/034.018.0111.full}, author = {Grace, T. and Anthony Joern and Brown, S.J. and Apple, J.L. and Wisely, S.M.} } @phdthesis {KNZ001283, title = {Host associated genetic divergence and sexual isolation in the grasshopper Hesperotettix viridis (Orthoptera: Acrididae)}, volume = {PhD Dissertation}, year = {2009}, pages = {1 -127}, school = {Kansas State University}, type = {Ph.D. Thesis}, address = {Manhattan, KS}, abstract = {

Understanding evolutionary processes that structure genetic variation associated with lineage diversification and speciation is a central problem. Shifts in host plant use by insect herbivores and subsequent divergence in mating signals can lead to sexual isolation, especially when selection for specialization on different hosts restricts gene flow among populations. The grasshopper Hesperotettix viridis (Thomas) is an oligophagous grasshopper feeding on plants primarily in the host plant genera Gutierrezia and Solidago in Kansas. I used mitochondrial and microsatellite genetic markers to evaluate the diversification pattern and underlying evolutionary mechanisms of two putative host races of H. viridis. I also quantified host preferences, the degree of sexual isolation among putative host races and divergence in cuticular attributes to identify the nature and origins of initial barriers that isolated populations in the formative stages of divergence. mtDNA data revealed a star-shaped phylogeny, suggesting isolation in a single refugium ~110,000 years ago based on a molecular clock, followed by rapid population expansion. Microsatellite data reveal significant host-based genetic differentiation and structuring in H. viridis populations in Kansas, including a microsatellite locus under strong divergent selection. Neutral microsatellite loci did not reveal a differentiation pattern specific to host plant use. Significant host-based preferences by individuals that fed on two host plant groups were detected in host paired-feeding preference studies. No-choice mate selection experiments revealed preferences for individuals collected from the same host species independent of location with little mating observed between individuals from different host species. Significant differentiation in color and cuticular composition among different host plant races within the study area was also detected. Correlations between host choice, mate choice and phenotypic divergence were observed and this host associated divergence appears to have a genetic basis. Based on the results of this study, I conclude that divergent selection for host plant use underlies observed sexual isolation among populations in this species. Hesperotettix viridis populations in Kansas that fed on Solidago and Gutierrezia species represent two incipient host races, early stages of diversification that could lead to speciation in insect herbivores.

}, keywords = {LTER-KNZ, Hesperotettix viridis, Host Associated Divergence, Microsatellites, Population genetics, sexual isolation, Speciation}, url = {http://hdl.handle.net/2097/1541}, author = {Grace, T.} }