No evidence for an association between Clock gene allelic variation and migration timing in a long-distance migratory shorebird (Limosa lapponica baueri)
The gene Clock is a key part of the Core Circadian Oscillator, and the length of the polyglutamine (poly-Q) repeat sequence in Clock (ClkpolyQcds) has been proposed to be associated with the timing of annual cycle events in birds. We tested whether variation in ClkpolyQcds corresponds to variation in migration timing in the bar-tailed godwit (Limosa lapponica baueri), a species in which individuals show strong annual consistency in their migration timing despite the New Zealand population migrating across a 5-week period. We describe allelic variation of the ClkpolyQcds in 135 godwits over-wintering in New Zealand (N.Z.) and investigate whether polymorphism in this region is associated with northward migration timing (chronophenotype) from N.Z. or (for 32 birds tracked by geolocator) after the primary stopover in Asia. Six Clock alleles were detected (Q7‒Q12) and there was substantial variation between individuals (heterozygosity of 0.79). There was no association between ClkpolyQcds polymorphism and migration timing from N.Z. The length of the shorter Clock allele was related to migration timing from Asia, though this relationship arose largely from just a few northern-breeding birds with longer alleles. Other studies show no consistent associations between ClkpolyQcds and migration timing in birds, although Clock may be associated with breeding latitude in some species (as an adaptation to photoperiodic regime). Apparent relationships with migration timing could reflect latitude-related variation in migration timing, rather than Clock directly affecting migration timing. On current evidence, ClkpolyQcds is not a strong candidate for driving migration timing in migratory birds generally.
KeywordsClock Polyglutamine Circannual Phenology Migration Bar-tailed godwit
We are grateful to the Royal Society of New Zealand for the Marsden Fund Grant (MAU1202) that supported this research and to the New Zealand Foundation for Science, Research and Technology for the Postdoctoral Fellowship that supported P.F.B. in the earlier Firth of Thames work (2004–06). We thank David Melville, Adrian Riegen, Rob Schuckard, Murray Potter, and Brett Gartrell for assistance during capture attempts, Peter Langlands, Ian Southey and Thomas Burns for resighting work, numerous volunteers who helped during captures, and Yvonne Verkuil for useful discussion and comments on drafts.
Author contribution statement
Fieldwork was done principally by PFB (bird capture efforts at all sites and monitoring in the Firth of Thames from 2004–06) and JRC (captures and departure monitoring at the Manawatu River estuary). APM was responsible for microsatellite data generation in the lab, subsequent analyses and writing the manuscript. AEF guided and supervised the laboratory work and AEF and PFB gave input to data analyses. All authors contributed to drafting of the manuscript.
This study was funded by the Royal Society of New Zealand for the Marsden Fund grant (MAU1202).
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