Abstract
Avian research has begun to reveal associations between candidate genes and migratory behaviors of captive birds, yet few studies utilize genotypic, morphometric, and phenological data from wild individuals. Previous studies have identified an association between ADCYAP1 polymorphism and autumn migratory behavior (restlessness, or zugunruhe), but little is known about the relationship between ADCYAP1 and spring migratory behavior. The timing of spring migration and arrival to the breeding ground are phenological traits which could be particularly favorable for establishing territories and acquiring mates, thus important to fitness and reproductive success. Here, we investigated how individual genotypic ADCYAP1 variation and phenotypic variation (wing length and shape) of blackcaps (Sylvia atricapilla) affect spring arrival date across nine natural populations in Europe. We hypothesized that longer alleles should be associated with earlier spring arrival dates and expected the effect on arrival date to be stronger for males as they arrive earlier. However, we found that longer wings were associated with earlier spring arrival to the breeding grounds for females, but not for males. Another female-specific effect indicated an interaction between ADCYAP1 allele size and wing pointedness on the response of spring arrival: greater allele size had a positive effect on spring arrival date for females with rounder wings, while a negative effect was apparent for females with more pointed wings. Also, female heterozygotes with pointed wing tips arrived significantly earlier than both homozygotes with pointed wings and heterozygotes with round wings. Stable isotope ratios (δ 2 H) of a subset of blackcaps captured in Freiburg in 2011 allowed us also to assign individuals to their main overwintering areas in northwest (NW) and southwest (SW) Europe. NW males arrived significantly earlier to the Freiburg breeding site than both SW males and females in 2011. NW females had more pointed wing tips compared to SW females, but no difference in ADCYAP1 allele size was found between the different migration routes.
Highlights
Humans are fascinated by the seasonal migration of millions of animals around the globe
The ADCYAP1 gene is a member of the secretinglucagon growth hormone-releasing hormone (GHRH) / vasoactive intestinal peptide (VIP) superfamily of peptides
No differences in ADCYAP1 allele size were found between western and eastern migrants (Wilcoxon rank sum tests: p > 0.05 with Set 5; see Fig 1 and [27] for categorization of orientations), while western migrants arrived to breeding grounds earlier than eastern migrants
Summary
Humans are fascinated by the seasonal migration of millions of animals around the globe. Environmental stimuli, day length and photoperiod, influence migratory behavior by acting as time keepers or ‘zeitgeber’ to synchronize the endogenous, physiological rhythms of migratory animals which oscillate in daily and seasonal patterns [3]. Male blackcaps typically arrive earlier to the breeding grounds than females and NW-migrating males tend to precede both SW-males and SW-females [10], being able to establish territories first. While migratory behaviors such as onset/intensity of migration and orientation are seemingly complex traits, many appear to have simple inheritance patterns. Offspring of parents with different migratory orientations were found to have orientations intermediate to their parents [11]
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