![]() This low value constrains species evolutionary adaptation, and our study adds to warnings that such populations may be threatened, e.g. ![]() Although male spring arrival date was significantly repeatable (R = 0.24 ± 0.08 SE), most was attributable to permanent environmental effects, while the additive genetic variance and heritability were very low (h2 = 0.03 ± 0.17 SE). This negative result was confirmed by direct observations of males arriving in spring to the breeding site over four consecutive years. We found that none of the four studied candidate genes (CLOCK, NPAS2, ADCYAP1 and CREB1) had any consistent effect on the timing of six annual cycle stages of geolocator-tracked individuals. Here, we combined both approaches to study the timing of migration in a long-distance migrant, the collared flycatcher (Ficedula albicollis). The genetic regulation of annual cycles can be studied either via candidate genes or through the decomposition of phenotypic variance by quantitative genetics. Plant and animal populations can adapt to prolonged environmental changes if they have sufficient genetic variation in important phenological traits. In contrast, the influence of Clk on annual-cycle timing at higher latitudes might be mediated by its interactions with genes involved in (circadian) photoperiodic pathways. Our data suggest that at low latitudes with constant photoperiod, Clk genotype might orchestrate a range of consistent, individual chronotypes. Specifically, equatorial African stonechats showed delayed timing with longer repeat length for all annual-cycle stages. Repeat length and annual-cycle timing was linked in a population-specific way. Gene diversity was lowest in resident African and Canary Island populations and increased with latitude, independently of migration distance. Including 950 individuals from nine populations with diverse migratory strategies. Here we combine field data with a common-garden set up to study associations of Clk with latitude, migration and annual-cycle timing within the stonechat species complex with trans-equatorial distribution range. However, findings are inconsistent, difficult to disentangle from environmental responses, and biased towards high latitudes. Clk genotype varies in some species with latitude, seasonal timing and migration. The core circadian clock gene Clk has been implicated in annual timing and shows highly conserved sequence homology across vertebrates except for one variable region of poly Glutamine repeats. Timing is essential for survival and reproduction of organisms across the tree of life. thalassina from Mono Lake, California, Photographers: B: Valentina Ferretti A, C-E: David Winkler. meyeni from Puerto Varas, Chile, and E) T. leucorrhoa from Chascomús, Argentina, C) T. ![]() Photos of Tachycineta swallows that were used in this study: A) T. Thus, there is no general association between latitude, breeding phenology, and Clock polymorphism in this clade of closely related birds. 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. 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 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. Despite relatively high overall breeding synchrony, the timing of clutch initiation has a large impact on the fitness of swallows in the genus Tachycineta. 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. The circadian clock, which creates endogenous behavioral and physiological rhythms typically entrained to photoperiod, is well characterized at the molecular level. Many animals use photoperiod cues to synchronize reproduction with environmental conditions and thereby improve their reproductive success.
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