Journal of Comparative Physiology A

, Volume 195, Issue 4, pp 385–391 | Cite as

Evolution of photoperiodic time measurement is independent of the circadian clock in the pitcher-plant mosquito, Wyeomyia smithii

  • Kevin J. Emerson
  • Sabrina J. Dake
  • William E. Bradshaw
  • Christina M. Holzapfel
Original Paper


For over 70 years, researchers have debated whether the ability to use day length as a cue for the timing of seasonal events (photoperiodism) is related to the endogenous circadian clock that regulates the timing of daily events. Models of photoperiodism include two components: (1) a photoperiodic timer that measures the length of the day, and (2) a photoperiodic counter that elicits the downstream photoperiodic response after a threshold number of days has been counted. Herein, we show that there is no geographical pattern of genetic association between the expression of the circadian clock and the photoperiodic timer or counter. We conclude that the photoperiodic timer and counter have evolved independently of the circadian clock in the pitcher-plant mosquito Wyeomyia smithii and hence, the evolutionary modification of photoperiodism throughout the range of W. smithii has not been causally mediated by a corresponding evolution of the circadian clock.


Geographic variation Biological clocks Seasonality Diapause Photoperiodism 



Response to Nanda–Hamner protocols


Number of hours of light (L) and dark (D) in a given environmental cycle


Total numbers of hours in a given environmental cycle (T = L + D)


Development time


Akiake’s Information Criterion


Log-likelihood of a given model



We thank A. Letaw for discussion, A. Letaw and two anonymous reviewers for their comments on previous versions of this paper, and B. Kolaczkowski for valuable discussions on likelihood methods. All work presented here complied with the “Principles of animal care,” publication No. 86-23 of the National Institute of Health, and also with current laws of the United States, where these experiment were performed. This work was made possible by generous support from the National Science Foundation through grants DEB-0412573, IOB-0445710 and IOB-0520799 (REU supplement for SJD) to WEB, and the National Science Foundation and National Institutes of Health through training grants DGE-0504727 and 5-T32-GMO7413 to KJE.

Appendix: Glossary of terms highlighted in the text


A trait is adaptive if it is genetically determined and the possession of that trait improves fitness. We do not use adaptive or adaptation to mean phenotypically plastic, accommodative or acclimative responses of individuals to the environment

Akiake’s information criterion (AIC)

A measure of the goodness of fit of a model to a given set of data. AIC estimates the information lost by using the model rather than the data itself and, hence, lower values of AIC indicate better support of a given model.


One half of the difference between the maximum and minimum magnitude of a rhythm or oscillation. If the amplitude is zero, then there is no rhythm.

Critical photoperiod

The length of day that induces or maintains 50% diapause and stimulates 50% development in a sample cohort. Critical photoperiod is an overt expression of the photoperiodic timer.

Depth of diapause

Herein, the number of long-days required to terminate diapause in 50% of a sample cohort (Bradshaw and Lounibos 1977; Emerson et al. 2008b). Depth of diapause is an overt expression of the photoperiodic counter. Depth of diapause is also referred to as the intensity of diapause (Danks 1987, p. 17);

NH response

Response to Nanda–Hamner experiments in which organisms are exposed to a fixed day length and, in separate experiments with separate animals, varying night length. The phenotypic response may be either rhythmic or non-rhythmic (linear).


Peak-to-peak or valley-to-valley interval of a rhythm or oscillation. If there is no significant period of oscillation, then there is no rhythm.


The influence of a locus on more than one trait. Pleiotropic effects can be assessed either by molecular genetic techniques showing the effect of a single gene on more than one phenotype, or by quantitative genetic techniques showing a correlated response to selection in the absence of linkage disequilibrium (Roff 1997).


Total period of light plus dark = L + D of an L:D = light:dark cycle.


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Copyright information

© Springer-Verlag 2009

Authors and Affiliations

  • Kevin J. Emerson
    • 1
  • Sabrina J. Dake
    • 1
  • William E. Bradshaw
    • 1
  • Christina M. Holzapfel
    • 1
  1. 1.Center for Ecology and Evolutionary BiologyUniversity of OregonEugeneUSA

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