Divergence of Threespine Stickleback That Differ in Nuptial Coloration

Recent research has led to a much better understanding of the evolutionary processes that mold and structure variation within and among populations. How populations diverge at the genome-wide level and how polymorphism is maintained within a species, however, remains unclear. We address these questions with two freshwater color morphs, red and black, of the threespine stickleback fish (Gasterosteus aculeatus) from the northwest United States, in which a shift from red to black nuptial coloration occurred in several locations following glacial retreat. We measured phenotypic variation in a suite of traits and used next generation sequencing to characterize within-species and among-morph genetic variation between the two morphs. We found substantial phenotypic and genetic divergence between color morphs, and patterns observed in a third, mixed morph that are likely due to hybridization between anadromous and freshwater stickleback. This work highlights the central role of natural and sexual selection in the evolution of divergence in nature

Geographic variation in phenotypic divergence between two hybridizing field cricket species

Patterns of morphological divergence across species' ranges can provide insight into local adaptation and speciation. In this study, we compared phenotypic divergence among 4,221 crickets from 337 populations of two closely related species of field cricket, Gryllus firmus and G. pennsylvanicus, and their hybrids. We found that these species differ across their geographic range in key morphological traits, such as body size and ovipositor length, and we directly compared phenotype with genotype for a subset of crickets to demonstrate nuclear genetic introgression, phenotypic intermediacy of hybrids, and essentially unidirectional mitochondrial introgression. We discuss how these morphological traits relate to life history differences between the two species. Our comparisons across geographic areas support prior research suggesting that cryptic variation within G. firmus may represent different species. Our study highlights how variable morphology can be across wide-ranging species and the importance of studying reproductive barriers in more than one or two transects of a hybrid zone

Supplementary material 1 from: Byerly AR, Jenck C, Goetz ARB, Weissman DB, Gray DA, Ross CL, Maroja LS, Larson EL (2023) Geographic variation in phenotypic divergence between two hybridizing field cricket species. Journal of Orthoptera Research 32(2): 189-200. https://doi.org/10.3897/jor.32.90713

Supplementary material 1 from: Byerly AR, Jenck C, Goetz ARB, Weissman DB, Gray DA, Ross CL, Maroja LS, Larson EL (2023) Geographic variation in phenotypic divergence between two hybridizing field cricket species. Journal of Orthoptera Research 32(2): 189-200. https://doi.org/10.3897/jor.32.9071