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1. Distinct Adult Eclosion Traits of Sibling Species Rhagoletis pomonella and Rhagoletis zephyria (Diptera: Tephritidae) Under Laboratory Conditions

   https://doi.org/10.1093/ee/nvaa148  

   Yee, Wee L; Goughnour, Robert B; Feder, Jeffrey L (November 2020, Environmental Entomology)

   Schilder, Rudolf (Ed.)

   Abstract Closely related phytophagous insects that specialize on different host plants may have divergent responses to environmental factors. Rhagoletis pomonella (Walsh) and Rhagoletis zephyria Snow (Diptera: Tephritidae) are sibling, sympatric fly species found in western North America that attack and mate on plants of Rosaceae (~60 taxa) and Caprifoliaceae (three taxa), respectively, likely contributing to partial reproductive isolation. Rhagoletis zephyria evolved from R. pomonella and is native to western North America, whereas R. pomonella was introduced there. Given that key features of the flies’ ecology, breeding compatibility, and evolution differ, we predicted that adult eclosion patterns of the two flies from Washington State, USA are also distinct. When puparia were chilled, eclosion of apple- and black hawthorn-origin R. pomonella was significantly more dispersed, with less pronounced peaks, than of snowberry-origin R. zephyria within sympatric and nonsympatric site comparisons. Percentages of chilled puparia that produced adults were ≥67% for both species. However, when puparia were not chilled, from 13.5 to 21.9% of apple-origin R. pomonella versus only 1.2% to 1.9% of R. zephyria eclosed. The distinct differences in eclosion traits of R. pomonella and R. zephyria could be due to greater genetic variation in R. pomonella, associated with its use of a wider range of host plants than R. zephyria. 

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2. Phylogeography of Walnut-Infesting Rhagoletis suavis (Diptera: Tephritidae) Flies

   https://doi.org/10.1093/isd/ixy002  

   Glover, Mary M; Egan, Scott P; Hood, Glen R; Rull, Juan; Aluja, Martin; Feder, Jeffrey L (February 2018, Insect Systematics and Diversity)
3. Rapid brain development and reduced neuromodulator titres correlate with host shifts in Rhagoletis pomonella

   https://doi.org/10.1098/rsos.220962  

   Kharva, Hinal; Feder, Jeffrey L.; Hahn, Daniel A.; Olsson, Shannon B. (September 2022, Royal Society Open Science)

   Host shifts are considered a key generator of insect biodiversity. For insects, adaptation to new host plants often requires changes in larval/pupal development and adult behavioural preference toward new hosts. Neurochemicals play key roles in both development and behaviour and therefore provide a potential source for such synchronization. Here, we correlated life-history timing, brain development and corresponding levels of 14 neurochemicals in Rhagoletis pomonella (Diptera: Tephritidae), a species undergoing ecological speciation through an ongoing host shift from hawthorn to apple fruit. These races exhibit differences in pupal diapause timing as well as adult behavioural preference with respect to their hosts. This difference in behavioural preference is coupled with differences in neurophysiological response to host volatiles. We found that apple race pupae exhibited adult brain morphogenesis three weeks faster after an identical simulated winter than the hawthorn race, which correlated with significantly lower titres of several neurochemicals. In some cases, particularly biogenic amines, differences in titres were reflected in the mature adult stage, when host preference is exhibited. In summary, life-history timing, neurochemical titre and brain development can be coupled in this speciating system, providing new hypotheses for the origins of new species through host shifts. 

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4. A reversal in sensory processing accompanies ongoing ecological divergence and speciation in Rhagoletis pomonella

   https://doi.org/10.1098/rspb.2021.0192  

   Tait, Cheyenne; Kharva, Hinal; Schubert, Marco; Kritsch, Daniel; Sombke, Andy; Rybak, Jürgen; Feder, Jeffrey L.; Olsson, Shannon B. (March 2021, Proceedings of the Royal Society B: Biological Sciences)

   null (Ed.)

   Changes in behaviour often drive rapid adaptive evolution and speciation. However, the mechanistic basis for behavioural shifts is largely unknown. The tephritid fruit fly Rhagoletis pomonella is an example of ecological specialization and speciation in action via a recent host plant shift from hawthorn to apple. These flies primarily use specific odours to locate fruit, and because they mate only on or near host fruit, changes in odour preference for apples versus hawthorns translate directly to prezygotic reproductive isolation, initiating speciation. Using a variety of techniques, we found a reversal between apple and hawthorn flies in the sensory processing of key odours associated with host fruit preference at the first olfactory synapse, linking changes in the antennal lobe of the brain with ongoing ecological divergence. Indeed, changes to specific neural pathways of any sensory modality may be a broad mechanism for changes in animal behaviour, catalysing the genesis of new biodiversity. 

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5. Sensory specificity and speciation: a potential neuronal pathway for host fruit odour discrimination in Rhagoletis pomonella

   https://doi.org/10.1098/rspb.2016.2101  

   Tait, Cheyenne; Batra, Srishti; Ramaswamy, Sree Subha; Feder, Jeffrey L.; Olsson, Shannon B. (December 2016, Proceedings of the Royal Society B: Biological Sciences)