Seasonal gene expression kinetics between diapause phases in Drosophila virilis group species and overwintering differences between diapausing and non-diapausing females.

Tiina S Salminen,Maaria Kankare,Laura Vesala,Anneli Hoikkala,Mikko Merisalo,Asta Laiho

doi:10.1038/srep11197

Tiina S Salminen, Maaria Kankare + Show 4 more

Open Access

https://doi.org/10.1038/srep11197

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Abstract

Most northern insect species experience a period of developmental arrest, diapause, which enables them to survive over the winter and postpone reproduction until favorable conditions. We studied the timing of reproductive diapause and its long-term effects on the cold tolerance of Drosophila montana, D. littoralis and D. ezoana females in seasonally varying environmental conditions. At the same time we traced expression levels of 219 genes in D. montana using a custom-made microarray. We show that the seasonal switch to reproductive diapause occurs over a short time period, and that overwintering in reproductive diapause has long-lasting effects on cold tolerance. Some genes, such as Hsc70, Jon25Bi and period, were upregulated throughout the diapause, while others, including regucalcin, couch potato and Thor, were upregulated only at its specific phases. Some of the expression patterns induced during the sensitive stage, when the females either enter diapause or not, remained induced regardless of the later conditions. qPCR analyses confirmed the findings of the microarray analysis in D. montana and revealed similar gene expression changes in D. littoralis and D. ezoana. The present study helps to achieve a better understanding of the genetic regulation of diapause and of the plasticity of seasonal responses in general.

Highlights

Changing environmental conditions present various kinds of challenges for species living at high latitudes, setting requirements for the plasticity of life-history traits important to reproduction and survival
Seasonal timing of reproductive diapause was determined by checking the ovarian development stage of three weeks old D. montana, D. littoralis and D. ezoana females, which had been transferred into the climate chamber between July and August
We determined the onset of reproductive diapause in three northern sympatric D. virilis group species, showing that the seasonal time window for entering to diapause is almost identical between these sympatric species, indicating strong adaptation in the timing of reproductive diapause

Summary

Introduction

Changing environmental conditions present various kinds of challenges for species living at high latitudes, setting requirements for the plasticity of life-history traits important to reproduction and survival. In the present study we have traced the effects of seasonally changing conditions on the development (reproductive diapause vs sexual maturation) and cold tolerance of the females of three sympatric northern D. virilis group species (D. montana, D. littoralis and D. ezoana), and simultaneously studied their gene expression kinetics. Females of all these species enter diapause when the day length decreases below a critical point, and can remain in this state for up to nine months[12,13,14]. We aimed to find answers to the following questions: (i) when does the onset of diapause occur in an environment showing gradual changes both in day length and temperature, (ii) does the overwintering state of the females affect their fitness in terms of cold tolerance after the diapause has terminated, and (iii) how do the gene expression patterns of the studied set of 219 genes vary during the initiation, maintenance and termination phases of diapause in different seasonal environments

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