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bioRxiv2023

Cold tolerance and diapause within across trophic levels: endoparasitic wasps and their fly host have similar phenotypes

Low temperatures associated with winter can limit the survival of organisms, especially ectotherms whose body temperature is similar to their environment. Important adaptations for overwintering such as cold hardiness and diapause have been well-explored in many insect taxa. However, there is a gap in understanding how overwintering may vary among groups of species that interact closely, such as multiple parasitoid species that attack the same host insect. Our study investigated cold tolerance and diapause phenotypes in three endoparasitoid wasps of the apple maggot fly Rhagoletis pomonella (Diptera: Tephritidae): Utetes canaliculatus, Diachasma alloeum, and Diachasmimorpha mellea (Hymenoptera: Braconidae). Using a combination of respirometry and eclosion tracking, we detected diapause phenotypes in all three wasp species, remarkably similar to the fly host. Weak diapause was rare (< 5%) in all three wasp species, and while most D. mellea (93%) entered prolonged diapause under warm conditions, the majority of U. canaliculatus (92%) and D. alloeum (72%) averted diapause (non-diapause). There was limited interspecific variation in acute cold tolerance among the three wasp species: wasps and flies had similarly high survival (>87%) following exposure to extreme low temperatures (- 20{degrees}C) as long as their body fluids did not freeze. The wasp species showed little interspecific variation in survival following prolonged exposure to mild chilling of 8 or more weeks at 4{degrees}C. This study shows remarkable conservation of cold tolerance and diapause phenotypes within and across trophic levels. The interaction between diapause phenotype and cold hardiness in these parasitoids is an interesting direction for future research. Graphical Abstract and Highlights O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=133 SRC="FIGDIR/small/522725v1_ufig1.gif" ALT="Figure 1"> View larger version (23K): org.highwire.dtl.DTLVardef@826a3aorg.highwire.dtl.DTLVardef@c3963org.highwire.dtl.DTLVardef@8baa33org.highwire.dtl.DTLVardef@1530d03_HPS_FORMAT_FIGEXP M_FIG C_FIG O_LIThe apple maggot fly and its parasitoids exhibit the same three diapause phenotypes C_LIO_LIEach parasitoid wasp species exhibits different proportions of these phenotypes C_LIO_LIUtetes canaliculatus and Diachasma alloeum are freeze-avoidant, like their host fly C_LIO_LIThese wasps and flies survive to similarly extreme low temperatures (c. -20{degrees}C) C_LIO_LIEach wasp species survives prolonged exposure to mild chilling (4{degrees}C) similarly well C_LI

physiology↗

bioRxiv2022

Transcriptomic and functional genetic evidence for distinct ecophysiological responses across complex life cycle stages

Organisms with complex life cycles demonstrate a remarkable ability to change their phenotypes across development, presumably as an evolutionary adaptation to developmentally variable environments. Developmental variation in environmentally sensitive performance, and thermal sensitivity in particular, has been well documented in holometabolous insects. For example, thermal performance in adults and juvenile stages exhibit little genetic correlation (genetic decoupling) and can evolve independently, resulting in divergent thermal responses. Yet, we understand very little about how this genetic decoupling occurs. We tested the hypothesis that genetic decoupling of thermal physiology is driven by fundamental differences in physiology between life stages, despite a potentially conserved Cellular Stress Response. We used RNAseq to compare transcript expression in response to a cold stressor in Drosophila melanogaster larvae and adults and used RNAi (RNA interference) to test whether knocking down nine target genes differentially affected larval and adult cold tolerance. Transcriptomic responses of whole larvae and adults during and following exposure to -5{degrees}C were largely unique both in identity of responding transcripts and in temporal dynamics. Further, we found no relationship between stage-specificity and tissue-specificity of transcripts, suggesting that the differences are not simply driven by differences in tissue composition across development. In addition, RNAi of target genes resulted in largely stage-specific and sometimes sex-specific effects on cold tolerance. The combined evidence suggests that thermal physiology is largely stage-specific at the level of gene expression, and thus natural selection may be acting on different loci during the independent thermal adaptation of different life stages. Summary StatementRNAseq and gene knockout via transgenic RNAi lines suggest that physiological responses to low temperatures are largely distinct across life stages of the fly Drosophila melanogaster.

evolutionary biology↗