Circatidal gene expression in the mangrove cricket Apteronemobius asahinai

Aya Satoh,Yohey Terai

doi:10.1038/s41598-019-40197-2

Aya Satoh, Yohey Terai

Open Access

https://doi.org/10.1038/s41598-019-40197-2

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Abstract

The mangrove cricket Apteronemobius asahinai is endemic to mangrove forest floors. It shows circatidal rhythmicity, with a 12.6-h period of locomotor activity under constant conditions. Its free-running activity also has a circadian component; i.e. it is more active during the subjective night than during the day. In this study, we investigated rhythmic gene expression under constant darkness by RNA sequencing to identify genes controlled by the biological clock. Samples collected every 3 h for 48 h were analysed (one cricket per time-point). We identified 284 significant circatidal cycling transcripts (period length 12–15 h). Almost half of them were annotated with known genes in the NCBI nr database, including enzymes related to metabolic processes and molecular chaperones. There were less transcripts with circadian rhythmicity than with circatidal rhythmicity, and the expression of core circadian clock genes did not show significant rhythmicity. This may reflect the nature of the mangrove cricket or may be due to the paucity of the sampling repeats: only two periods for circadian cycle with no replications. We evaluated for the first time the rhythmic transcriptome of an insect that shows circatidal rhythmic activity; our findings will contribute to future studies of circatidal clock genes.

Highlights

Diverse biological phenomena, such as eclosion[1], stridulation activity[2] and flight activity[3], occur at specific times of day
The present study revealed the first rhythmic transcriptome of an insect with a circatidal activity rhythm: we identified a few hundreds of significant circatidal cycling transcripts, which are expected to be underlain by the biological clock
The expression of genes encoding enzymes related to metabolic processes, such as peroxiredoxin 1, showed circatidal rhythmicity

Summary

Introduction

Diverse biological phenomena, such as eclosion[1], stridulation activity[2] and flight activity[3], occur at specific times of day. Mangrove forests are influenced by tidal flooding and ebbing, and the activity rhythm of the mangrove cricket is defined by the tidal cycle Under constant conditions, it shows a clear circatidal rhythm in its locomotor activity, with a period of approximately 12.6 h22,23. Recent studies have demonstrated that the circadian, but not the circatidal, component of locomotor activity under constant darkness (DD) is disrupted by silencing of the expression of circadian clock genes, period or Clock, by RNAi24,25 This finding indicates that the molecular components of the circatidal clock differ from those of the circadian clock in the mangrove cricket. Sample collection for evaluation of the rhythmic expression of clock genes and CCGs must be performed under constant conditions

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