Clock gene polymorphism and scheduling of migration: a geolocator study of the barn swallow Hirundo rustica.

Gaia Bazzi,Manuela Caprioli,Chiara Scandolara,Luca Gianfranceschi,Andrea Romano,Diego Rubolini,Maria Romano,Emanuele Gatti,Roberto Ambrosini,Felix Liechti,Alessandra Costanzo,Nicola Saino,Stefano Podofillini

doi:10.1038/srep12443

Abstract

Circannual rhythms often rely on endogenous seasonal photoperiodic timers involving ‘clock’ genes, and Clock gene polymorphism has been associated to variation in phenology in some bird species. In the long-distance migratory barn swallow Hirundo rustica, individuals bearing the rare Clock allele with the largest number of C-terminal polyglutamine repeats found in this species (Q8) show a delayed reproduction and moult later. We explored the association between Clock polymorphism and migration scheduling, as gauged by light-level geolocators, in two barn swallow populations (Switzerland; Po Plain, Italy). Genetic polymorphism was low: 91% of the 64 individuals tracked year-round were Q7/Q7 homozygotes. We compared the phenology of the rare genotypes with the phenotypic distribution of Q7/Q7 homozygotes within each population. In Switzerland, compared to Q7/Q7, two Q6/Q7 males departed earlier from the wintering grounds and arrived earlier to their colony in spring, while a single Q7/Q8 female was delayed for both phenophases. On the other hand, in the Po Plain, three Q6/Q7 individuals had a similar phenology compared to Q7/Q7. The Swiss data are suggestive for a role of genetic polymorphism at a candidate phenological gene in shaping migration traits, and support the idea that Clock polymorphism underlies phenological variation in birds.

Highlights

Latitudinal increase in the number of Poly-Q repeats across populations has been suggested to reflect adaptation to local regimes of circannual photoperiodic variation[14,16,19]
Though the evidence for an association between Circadian Locomotor Output Cycles Kaput (Clock) polymorphism and timing of seasonal events at the population level is scant, two recent studies conducted on a long-distance migratory bird, the barn swallow Hirundo rustica, have shown that a very rare Clock genotype, the heterozygous Q7/Q8 (c.a. 1.5% of the population), which contains the largest Poly-Q stretch observed in this species (Q8), has a delayed timing compared to the most frequent (94%) Q7/Q7 genotype[17,20]
These findings are consistent with the idea that larger Poly-Q stretches are associated with a delayed phenology[15,17,20,21], and suggest that the Q7/Q8 genotype shows a delayed annual routine

Summary

Introduction

Latitudinal increase in the number of Poly-Q repeats across populations has been suggested to reflect adaptation to local regimes of circannual photoperiodic variation[14,16,19]. We exploit data retrieved from 64 individual barn swallows tracked along the entire annual migration cycle using miniaturized light-level geolocators[22] to explore the association between Clock genotype polymorphism and scheduling of migration events in two barn swallow populations breeding in Southern Switzerland (Magadino) and Northern Italy (Po Plain).

Results

Conclusion