Molecular basis of photoperiodic diapause in the Asian tiger mosquito, Aedes albopictus

Abstract

My dissertation examines the molecular basis of photoperiodic diapause in the Asian tiger mosquito, Aedes albopictus, using high-throughput DNA sequencing technologies. Photoperiodic diapause is a developmental arrest in response to the seasonal change in photoperiod. Diapause enables the insects to synchronize growth and reproduction with favorable conditions, and developmental arrest with harsh conditions, such as winter in the temperate zone. Previous studies from our laboratory have established extensive global transcriptional profiles of diapause in Ae. albopictus at the diapause preparation and the actual developmental arrest stages. My dissertation research has elucidated global transcriptional dynamics during the diapause induction phase that initiates the diapause program. I discovered that essential components of the circadian clock governing daily rhythmic gene expression are implicated in photoperiodic time measurement. Also, energy metabolism and offspring provisioning were discovered to be crucial physiological processes during diapause induction.

I also compared and evaluated four common approaches to transcriptome assembly, using the extensive transcriptomic resources for Ae. albopictus and its recently published genome assembly. I recommended general guidelines for transcriptome assembly, especially for non-model organisms. These guidelines will help to establish consistent methodological standards for the research community conducting high-throughput sequencing studies, a rapidly expanding field of research.

In another study, I took advantage of a natural evolutionary experiment that has occurred between tropical and temperate populations of Ae. albopictus. Tropical populations do not undergo photoperiodic diapause whereas the temperate populations do. Therefore, crossing genetic backgrounds from distinct geographic regions of the same species allowed me to examine the genetic basis of photoperiodic diapause. I utilized a bulked segregant analysis coupled with RNA sequencing (RNA-Seq) to identify genomic regions associated with diapause. Using a novel approach to leverage the unique expression information provided by RNA-Seq, combined with traditional single nucleotide polymorphism discovery, I identified candidate genomic regions and candidate genes likely involved in regulating diapause. Overall, this research helps to fill in important gaps in our understanding of the molecular basis of diapause and provides candidate genes for further functional interrogations.