Abstract
BackgroundThe mosquito Wyeomyia smithii overwinters in a larval diapause that is initiated, maintained and terminated by day length (photoperiod). We use a forward genetic approach to investigate transcriptional events involved in the termination of diapause following exposure to long-days.Methods/Principal FindingsWe incorporate a novel approach that compares two populations that differentially respond to a single day length. We identify 30 transcripts associated with differential response to day length. Most genes with a previously annotated function are consistent with their playing a role in the termination of diapause, in downstream developmental events, or in the transition from potentially oxygen-poor to oxygen-rich environments. One gene emerges from three separate forward genetic screens as a leading candidate for a gene contributing to the photoperiodic timing mechanism itself (photoperiodic switch). We name this gene photoperiodic response gene 1 (ppdrg1). WsPpdrg1 is up-regulated under long-day response conditions, is located under a QTL for critical photoperiod and is associated with critical photoperiod after 25 generations of recombination from a cross between extreme phenotypes.ConclusionsThree independent forward genetic approaches identify WsPpdrg1 as a gene either involved in the photoperiodic switch mechanism or very tightly linked to a gene that is. We conclude that continued forward genetic approaches will be central to understanding not only the molecular basis of photoperiodism and diapause, but also the evolutionary potential of temperate and polar animal populations when confronted with rapid climate change.
Highlights
At temperate latitudes, no life cycle is complete without the means to exploit the favorable season, to avoid or mitigate the unfavorable season, and to switch from one life style to the other in a timely manner
Ten of the genes are orphan genes in W. smithii, having no significantly similar sequences found in D. melanogaster, Aedes aegypti, or Anopheles gambiae
Despite this widespread use of photoperiod, the genes involved in the switch mechanism itself remain elusive in natural populations
Summary
No life cycle is complete without the means to exploit the favorable season, to avoid or mitigate the unfavorable season, and to switch from one life style to the other in a timely manner. At temperate and polar latitudes, most arthropods use the length of day, or photoperiod, to initiate and, in some cases, maintain and terminate diapause [1,2,3,4,5]. The timing of the transition between active development and diapause at the appropriate time of year in seasonal environments is central to maintaining fitness in natural populations [6,7]. The day length used to switch between active development and diapause (critical photoperiod) in the late summer or fall increases with latitude and altitude and is closely correlated with the length of the local growing season [7,8,9]. The mosquito Wyeomyia smithii overwinters in a larval diapause that is initiated, maintained and terminated by day length (photoperiod). We use a forward genetic approach to investigate transcriptional events involved in the termination of diapause following exposure to long-days
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