Browsing by Author "Zhang, Linyi"

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    The Arthropod Associates of 155 North American Cynipid Oak Galls
    (Academia Sinica, 2022) Ward, Anna K.G.; Busbee, Robert W.; Chen, Rachel A.; Davis, Charles K.; Driscoe, Amanda L.; Egan, Scott P.; Goldberg, Bailey A.R.; Hood, Glen Ray; Jones, Dylan G.; Kranz, Adam J.; Meadely-Dunphy, Shannon A.; Milks, Alyson K.; Ott, James R.; Prior, Kirsten M.; Sheikh, Sofia I.; Shzu, Shih-An; Weinersmith, Kelly L.; Zhang, Linyi; Zhang, Y. Miles; Forbes, Andrew A.
    The identities of most arthropod associates of cynipid-induced oak galls in the western Palearctic are generally known. However, a comprehensive accounting of associates has been performed for only a small number of the galls induced by the estimated 700 species of cynipid gall wasps in the Nearctic. This gap in knowledge stymies many potential studies of diversity, coevolution, and community ecology, for which oak gall systems are otherwise ideal models. We report rearing records of insects and other arthropods from more than 527,306 individual galls representing 201 different oak gall types collected from 32 oak tree species in North America. Of the 201 gall types collected, 155 produced one or more arthropods. A total of 151,075 arthropods were found in association with these 155 gall types, and of these 61,044 (40.4%) were gall wasps while 90,031 (59.6%) were other arthropods. We identified all arthropods to superfamily, family, or, where possible, to genus. We provide raw numbers and summaries of collections, alongside notes on natural history, ecology, and previously published associations for each taxon. For eight common gall-associated genera (Synergus, Ceroptres, Euceroptres, Ormyrus, Torymus, Eurytoma, Sycophila, and Euderus), we also connect rearing records to gall wasp phylogeny, geography, and ecology - including host tree and gall location (host organ), and their co-occurrence with other insect genera. Though the diversity of gall wasps and the large size of these communities is such that many Nearctic oak gall-associated insects still remain undescribed, this large collection and identification effort should facilitate the testing of new and varied ecological and evolutionary hypotheses in Nearctic oak galls.
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    Borders on the Rise: The Unintended Evolutionary Consequences of Border Barriers on Natural Populations
    (2018) Egan, Scott P.; Comerford, Mattheau; Hood, Glen R.; Zhang, Linyi; Weinersmith, Kelly L.; James A. Baker III Institute for Public Policy
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    Divergent host use promotes reproductive isolation between populations of gall-forming insects
    (2020-12-07) Zhang, Linyi; Egan, Scott P
    Understanding the formation of new species, termed ‘speciation’, is one of the central issues in evolutionary biology. The role of divergent selection in initiating and promoting the speciation process, termed ‘ecological speciation’, and maintaining species differences has been under intense study in recent decades. Despite accumulating individual case studies documenting individual reproductive barriers evolving between populations due to divergent selection, a synthetic view of the ecological speciation process requires: (1.) identifying the source(s) of divergent selection, (2.) identifying the trait(s) under divergent selection, and (3.) estimating the strength of multiple reproductive barriers as a result of divergent selection. When these issues can be linked in a single system, one can take a holistic approach to understanding the evolution of species. Moreover, despite emerging research linking these micro-evolutionary processes to macro-evolutionary patterns, there are still outstanding questions regarding the role of divergent selection as a common mechanism generating biodiversity across taxonomic orders. This is a challenging question, as many other factors can vary together and obscure clear patterns. To answer this question, we need to combine both bottom up and top down approaches in a broad but controlled system where many taxa can be queried simultaneously. If this challenge can be met, we can improve our predictability of the evolutionary outcomes under divergent selection, particularly, whether populations under divergent selection can complete the speciation process, and we can test the repeatability of ecological speciation across different species and taxonomic groups at different stages in the speciation process to bridge the micro-level evolution to macro-level evolution of biodiversity. In this dissertation, we address the above challenges by, first, using a magnifiying glass approach to study how divergent host-use generates and promotes RI between populations of a host-specific gall-forming insect, Belonocnema treatae (Chapter 1, 2, 3), and, second, testing whether the same divergent host environments drive ecological and genetic divergence among host-associated populations repeatably across five additional species of gall-forming insects (Chapter 4, 5). Chapter 1 of this thesis examines two reproductive barriers that are the direct results of divergent selection: reduced immigrant viability and fecundity, the latter is a potentially important, but often overlooked reproductive barrier. We found asymmetric, but opposing reproductive barriers that combined together to reduce gene flow in both directions. In chapter 2, we also identified one important source of selection related to divergent host use: the plant immune response that affects survival. In Chapter 2, we found that intra-specific variation in host quality among individual trees within each divergent host species, rather the tree species per se, is the major driver of hybrid fitness. Hybrids vary widely in both the direction and strength of hybrid fitness relative to pure crosses across individual trees. Thus, potentially inhibiting the speciation process on some trees, while promoting reproductive isolation on others. In Chapter 3, we tested whether a critical process occurs in the evolution of strong RI in host-associated populations of B. treatae: adaptive coupling, defined as selection favors the arise of another reproductive barrier as a response towards an existing reproductive barrier. We detected signatures of asymmetric adaptive coupling: in the presence of the cost of migration- reduced immigrant fitness and hybrid viability, stronger habitat, and sexual isolation are found among sympatric populations in the direction where migration rate is higher. In Chapters 4, we expand the scope of this work to include many species of gall-forming insects (and their predators) distributed across the same two host plant environments to test general principles of speciation. We demonstrate that temporal isolation between host-associated populations is present in six gall-forming insects and three natural enemies associated with gall-forming insects, suggesting phenological differences between different host plant species cascades across multiple species at multiple trophic levels. In sum, by combining field survey, manipulation experiment and behavior observation, we found that both divergent selection and migration are critical in the evolution of RI. Our findings call for more studies on assessing factors that affect the progression of ecological speciation, such as the role of heterogeneity within each divergent environment in promoting or inhibiting RI, population demography and multiple traits under divergent selection. Only by knowing the conditions that promote or inhibit the speciation process, can we better predict the evolutionary outcomes under divergent selection.
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    Speciation in Nearctic oak gall wasps is frequently correlated with changes in host plant, host organ, or both
    (Wiley, 2022) Ward, Anna K. G.; Bagley, Robin K.; Egan, Scott P.; Hood, Glen Ray; Ott, James R.; Prior, Kirsten M.; Sheikh, Sofia I.; Weinersmith, Kelly L.; Zhang, Linyi; Zhang, Y. Miles; Forbes, Andrew A.
    Quantifying the frequency of shifts to new host plants within diverse clades of specialist herbivorous insects is critically important to understand whether and how host shifts contribute to the origin of species. Oak gall wasps (Hymenoptera: Cynipidae: Cynipini) comprise a tribe of ∼1000 species of phytophagous insects that induce gall formation on various organs of trees in the family Fagacae—primarily the oaks (genus Quercus; ∼435 sp.). The association of oak gall wasps with oaks is ancient (∼50 my), and most oak species are galled by one or more gall wasp species. Despite the diversity of both gall wasp species and their plant associations, previous phylogenetic work has not identified the strong signal of host plant shifting among oak gall wasps that has been found in other phytophagous insect systems. However, most emphasis has been on the Western Palearctic and not the Nearctic where both oaks and oak gall wasps are considerably more species rich. We collected 86 species of Nearctic oak gall wasps from most of the major clades of Nearctic oaks and sequenced >1000 Ultraconserved Elements (UCEs) and flanking sequences to infer wasp phylogenies. We assessed the relationships of Nearctic gall wasps to one another and, by leveraging previously published UCE data, to the Palearctic fauna. We then used phylogenies to infer historical patterns of shifts among host tree species and tree organs. Our results indicate that oak gall wasps have moved between the Palearctic and Nearctic at least four times, that some Palearctic wasp clades have their proximate origin in the Nearctic, and that gall wasps have shifted within and between oak tree sections, subsections, and organs considerably more often than previous data have suggested. Given that host shifts have been demonstrated to drive reproductive isolation between host-associated populations in other phytophagous insects, our analyses of Nearctic gall wasps suggest that host shifts are key drivers of speciation in this clade, especially in hotspots of oak diversity. Although formal assessment of this hypothesis requires further study, two putatively oligophagous gall wasp species in our dataset show signals of host-associated genetic differentiation unconfounded by geographic distance, suggestive of barriers to gene flow associated with the use of alternative host plants.