Abstract
Understanding the genetic background of complex behavioral traits, showing multigenic control and extensive environmental effects, is a challenging task. Among such traits, migration is known to show a large additive genetic component. Yet, the identification of specific genes or gene regions explaining phenotypic variance in migratory behavior has received less attention. Migration ultimately depends on seasonal cycles, and polymorphism at phenological candidate genes may underlie variation in timing of migration or other aspects of migratory behavior. In this study of a Nearctic–Neotropical migratory songbird, the Wilson's warbler (Cardellina pusilla), we investigated the association between polymorphism at two phenological candidate genes, Clock and Adcyap1, and two aspects of the migratory phenotype, timing of spring migration through a stopover site and inferred latitude of the breeding destination. The breeding destination of migrating individuals was identified using feather deuterium ratio (δ 2H), which reliably reflects breeding latitude throughout the species' western breeding range. Ninety‐eight percent of the individuals were homozygous at Clock, and the rare heterozygotes did not deviate from homozygous migration phenology. Adcyap1 was highly polymorphic, and allele size was not significantly associated with migration date. However, Adcyap1 allele size significantly positively predicted the inferred breeding latitude of males but not of females. Moreover, we found a strong positive association between inferred breeding latitude and Adcyap1 allele size in long‐distance migrating birds from the northern sector of the breeding range (western Canada), while this was not the case in short‐distance migrating birds from the southern sector of the breeding range (coastal California). Our findings support previous evidence for a role of Adcyap1 in shaping the avian migratory phenotype, while highlighting that patterns of phenological candidate gene–phenotype associations may be complex, significantly varying between geographically distinct populations and even between the sexes.
Highlights
In many migratory organisms, individuals embark on their first migratory journey without any guidance from conspecifics concerning the timing and the direction of migration and the distance to be covered, and in most cases in the absence of any cue concerning the ecological conditions they subsequently face (Newton 2008)
We investigated whether variation at two phenological candidate genes (PCG), Clock and Adcyap1, affected the timing of spring migration and breeding destination, as inferred from feather d2H values
By taking advantage of feather d2H gradients throughout the breeding range of Wilson’s warbler in western North America, we discovered the evidence of a very strong latitudinal cline in Adcyap1 microsatellite polymorphism among the genetically homogeneous cluster of northern breeding birds, that were genetically differentiated at this PCG from southern breeding ones
Summary
Individuals embark on their first migratory journey without any guidance from conspecifics concerning the timing and the direction of migration and the distance to be covered, and in most cases in the absence of any cue concerning the ecological conditions they subsequently face (Newton 2008). A latitudinal cline in Clock allele size, with the frequency of longer alleles increasing along a south– north gradient, has been documented in some migratory bird and fish species (Johnsen et al 2007; O’Malley and Banks 2008; O’Malley et al 2010; Lemay and Russello 2014) and probably reflects local adaptation to different photoperiodic regimes (Kyriacou et al 2008) Such a latitudinal cline has not been detected in other studies (e.g., Dor et al 2012; O’Brien et al 2013)
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