Many animals use photoperiod cues to synchronize reproduction with environmental conditions and thereby improve their reproductive success. The circadian clock, which creates endogenous behavioral and physiological rhythms typically entrained to photoperiod, is well characterized at the molecular level. Recent work provided evidence for an association between Clock poly-Q length polymorphism and latitude and, within a population, an association with the date of laying and the length of the incubation period. Despite relatively high overall breeding synchrony, the timing of clutch initiation has a large impact on the fitness of swallows in the genus Tachycineta. We compared length polymorphism in the Clock poly-Q region among five populations from five different Tachycineta species that breed across a hemisphere-wide latitudinal gradient (Fig. 1). Clock poly-Q variation was not associated with latitude; however, there was an association between Clock poly-Q allele diversity and the degree of clutch size decline within breeding seasons. We did not find evidence for an association between Clock poly-Q variation and date of clutch initiation in for any of the five Tachycineta species, nor did we found a relationship between incubation duration and Clock genotype. Thus, there is no general association between latitude, breeding phenology, and Clock polymorphism in this clade of closely related birds.
Bibliographical noteFunding Information:
Funded by the Cornell Lab of Ornithology and National Science Foundation grants DEB-0814277 to IJL and DEB-0717021, IOS-0744753, and OISE-0730180 to DWW.
We thank the many people who served the “Golondrinas de las Americas” project for assistance in collecting Tachycineta genetic samples and breeding data. For laboratory assistance we thank A. Talaba and L. Stenzler. We thank M. Carling, M. Liedvogel, B. Kempenaers and two anonymous reviewers for comments and suggestions. This research was supported by the Cornell Lab of Ornithology and National Science Foundation grants DEB-0814277 to IJL and DEB-0717021, IOS-0744753, and OISE-0730180 to DWW.
© 2011 The Authors. Ecology and Evolution published by Blackwell Publishing Ltd.
- Time of breeding
- Tree swallow