Article

The diapause response of Rhagoletis pomonella to varying environmental conditions and its significance for geographic and host plant‐related adaptation

Wissenshaftskolleg zu Berlin, 19 Wallotstrasse, D14193 Berlin, Germany
Entomologia Experimentalis et Applicata (Impact Factor: 1.62). 06/2010; 136(1):31 - 44. DOI: 10.1111/j.1570-7458.2010.01003.x

ABSTRACT

The recent shift of Rhagoletis pomonella Walsh (Diptera: Tephritidae) from its ancestral host hawthorn to apple is a model for incipient sympatric speciation in action. Previous studies have shown that changes in the over-wintering pupal diapause are critical for differentially adapting R. pomonella flies to a difference in the fruiting times of apples vs. hawthorns, generating ecologically based reproductive isolation. Here, we exposed pupae of the hawthorn race to various combinations of pre- and over-wintering rearing conditions and analyzed their effects on eclosion time and genetics. We report certain unexpected results in regards to a combination of brief pre-winter and over-wintering periods indicative of gene*environment interactions requiring a reassessment of our current understanding of R. pomonella diapause. We present a hypothesis that involves physiological factors related to stored energy reserves in pupae that influences the depth and duration of Rhagoletis diapause. This ‘pupal energy reserve’ hypothesis can account for our findings and help clarify the role host plant-related life history adaptation plays in phytophage biodiversity.

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    • "Most diapausing B. minax individuals in the field end their diapause and enter a phase of “quiescence” due to the prolonged winter 20. The mechanisms governing diapause transitions diverge in univoltine tephritids that are characterized by varying diapause intensity in different ontogenetic trajectories 22, 27, 28. The diapause developmental transition controlling system manages harnessed nutrient reserves and schedules when diapause will end, as well as complete post-diapause challenges and metamorphosis 29. "
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    ABSTRACT: Bactrocera minax is a major citrus pest distributed in China, Bhutan and India. The long pupal diapause duration of this fly is a major bottleneck for artificial rearing and underlying mechanisms remain unknown. Genetic information on B. minax transcriptome and gene expression profiles are needed to understand its pupal diapause. High-throughput RNA-seq technology was used to characterize the B. minax transcriptome and to identify differentially expressed genes during pupal diapause development. A total number of 52,519,948 reads were generated and assembled into 47,217 unigenes. 26,843 unigenes matched to proteins in the NCBI database using the BLAST search. Four digital gene expression (DGE) libraries were constructed for pupae at early diapause, late diapause, post-diapause and diapause terminated developmental status. 4,355 unigenes showing the differences expressed across four libraries revealed major shifts in cellular functions of cell proliferation, protein processing and export, metabolism and stress response in pupal diapause. When diapause was terminated by 20-hydroxyecdysone (20E), many genes involved in ribosome and metabolism were differentially expressed which may mediate diapause transition. The gene sets involved in protein and energy metabolisms varied throughout early-, late- and post-diapause. A total of 15 genes were selected to verify the DGE results through quantitative real-time PCR (qRT-PCR); qRT-PCR expression levels strongly correlated with the DGE data. The results provided the extensive sequence resources available for B. minax and increased our knowledge on its pupal diapause development and they shed new light on the possible mechanisms involved in pupal diapause in this species.
    Full-text · Article · Sep 2014 · International journal of biological sciences
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    • "The process of HAD in phytophagous insects has been widely discussed, both in general [14] and in the context of a few well-studied model systems (e.g., apple maggot fly [25] [26], goldenrod ball-gall fly [27] [28]). Perhaps unsurprisingly, nearly all studies of HAD have emphasized insect responses to differences in plant traits between the alternative hosts, while downplaying variation in plant traits among individuals within each host. "
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    ABSTRACT: Ecological speciation via host shifting has contributed to the astonishing diversity of phytophagous insects. The importance for host shifting of trait differences between alternative host plants is well established, but much less is known about trait variation within hosts. I outline a conceptual model, the “gape-and-pinch” (GAP) model, of insect response to host-plant trait variation during host shifting and host-associated differentiation. I offer four hypotheses about insect use of plant trait variation on two alternative hosts, for insects at different stages of host-associated differentiation. Collectively, these hypotheses suggest that insect responses to plant trait variation can favour or oppose critical steps in herbivore diversification. I provide statistical tools for analysing herbivore trait-space use, demonstrate their application for four herbivores of the goldenrods Solidago altissima and S. gigantea , and discuss their broader potential to advance our understanding of diet breadth and ecological speciation in phytophagous insects.
    Full-text · Article · Feb 2012
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    • "The process of HAD in phytophagous insects has been widely discussed, both in general [14] and in the context of a few well-studied model systems (e.g., apple maggot fly [25] [26], goldenrod ball-gall fly [27] [28]). Perhaps unsurprisingly, nearly all studies of HAD have emphasized insect responses to differences in plant traits between the alternative hosts, while downplaying variation in plant traits among individuals within each host. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Ecological speciation via host shifting has contributed to the astonishing diversity of phytophagous insects. The importance for host shifting of trait differences between alternative host plants is well established, but much less is known about trait variation within hosts. I outline a conceptual model, the “gape-and-pinch” (GAP) model, of insect response to host-plant trait variation during host shifting and host-associated differentiation. I offer four hypotheses about insect use of plant trait variation on two alternative hosts, for insects at different stages of host-associated differentiation. Collectively, these hypotheses suggest that insect responses to plant trait variation can favour or oppose critical steps in herbivore diversification. I provide statistical tools for analysing herbivore trait-space use, demonstrate their application for four herbivores of the goldenrods Solidago altissima and S. gigantea, and discuss their broader potential to advance our understanding of diet breadth and ecological speciation in phytophagous insects.
    Full-text · Article · Jan 2012
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