Transcriptional Regulation of Reproductive Diapause in the Convergent Lady Beetle, Hippodamia convergens

Abstract

Diapause is an alternate development program that synchronizes an insect's life cycle with seasonally abundant resources and ensures survival in unfavorable conditions. The physiological basis of diapause has been well characterized, but the molecular mechanisms regulating it are still being elucidated. Here, we present a de novo transcriptome and quantify transcript expression during diapause in the convergent lady beetle Hippodamia convergens. H. convergens is used as an augmentative biocontrol agent, and adult females undergo reproductive diapause that is regulated by photoperiod. We sampled females at three stages (early, mid, and late diapause) and compared transcript expression to non-diapausing individuals. Based on principle component analysis, the transcriptomes of diapausing beetles were distinct from non-diapausing beetles, and the three diapausing points tended to cluster together. However, there were still classes of transcripts that differed in expression across distinct phases of diapause. In general, transcripts involved in muscle function and flight were upregulated during diapause, likely to support dispersal flights that occur during diapause, while transcripts involved in ovarian development were downregulated. This information could be used to improve biological control by manipulating diapause. Additionally, our data contribute to a growing understanding of the genetic regulation of diapause across diverse insects.

Keywords: Coleoptera; RNA-Seq; biological control; reproductive diapause; transcriptomics.

Figure 1

Principle Component Analysis (PCA) score plots of samples. This PCA was used to determine the relationship between transcript expression profiles from various stages of diapause. One of the mid-diapause samples was removed from the dataset prior to this analysis due to technical problems with the sample, so there are only three replicates for this group. One LD sample clustered with the ND samples, and that female had already broken diapause and started ovipositing at the time of sample collection. Thus, this sample was removed from further analyses. ED = early diapause, LD = late diapause, MD = mid-diapause, ND = non-diapause.

Figure 2

MA plots showing the number of differentially expressed transcripts between each diapausing stage and non-diapause beetles. For each comparison ((a): ED vs. ND; (b): MD vs. ND; (c): LD vs. ND), transcripts with FDR < 0.05 are shown in blue. In each panel the total number of up- and downregulated transcripts are indicated. For the full lists of differentially expressed transcripts, see Table S1. ED = early diapause, MD = mid-diapause, LD = late diapause, ND = non-diapause.