Contrasting Patterns of Genetic Differentiation among Blackcaps (Sylvia atricapilla) with Divergent Migratory Orientations in Europe

Abstract

Migratory divides are thought to facilitate behavioral, ecological, and genetic divergence among populations with different migratory routes. However, it is currently contentious how much genetic divergence is needed to maintain distinct migratory behavior across migratory divides. Here we investigate patterns of neutral genetic differentiation among Blackcap (Sylvia atricapilla) populations with different migratory strategies across Europe. We compare the level of genetic divergence of populations migrating to southwestern (SW) or southeastern (SE) wintering areas with birds wintering in the British Isles following a recently established northwesterly (NW) migration route. The migratory divide between SW and SE wintering areas can be interpreted as a result of a re-colonization process after the last glaciation. Thus we predicted greater levels of genetic differentiation among the SW/SE populations. However, a lack of genetic differentiation was found between SW and SE populations, suggesting that interbreeding likely occurs among Blackcaps with different migratory orientations across a large area; therefore the SW/SE migratory divide can be seen as diffuse, broad band and is, at best, a weak isolating barrier. Conversely, weak, albeit significant genetic differentiation was evident between NW and SW migrants breeding sympatrically in southern Germany, suggesting a stronger isolating mechanism may be acting in this population. Populations located within/near the SW/SE contact zone were the least genetically divergent from NW migrants, confirming NW migrants likely originated from within the contact zone. Significant isolation-by-distance was found among eastern Blackcap populations (i.e. SE migrants), but not among western populations (i.e. NW and SW migrants), revealing different patterns of genetic divergence among Blackcap populations in Europe. We discuss possible explanations for the genetic structure of European Blackcaps and how gene flow influences the persistence of divergent migratory behaviors.

Acoustic but no genetic divergence in migratory and sedentary populations of blackcaps,Sylvia atricapilla

“…It has been suggested that migratory behaviour not only shapes population genetic structure across migratory flow patterns, but also at an individual level as a result of microhabitat choice . However, consistent with our results, previous genetic studies failed to show a clear genetic structure for blackcap populations (Mettler et al, 2013), which may be because the use of neutral genetic markers is not sufficient to detect the finescale genetic structure of populations (Reed & Frankham, 2001). This also strongly suggests that the genetic divergence is recent and that gene flow between populations can persist (P erez-Tris et al, 2004).…”

“…A total of 17 microsatellite markers developed for the blackcap were used (Segelbacher et al, 2008;Mettler et al, 2013). F-primers were fluorescently labelled using the commercially available dyes, FAM, VIC, NED, and PET.…”

Serial founder effects and genetic differentiation during worldwide range expansion of monarch butterflies

“…Results here also indicate that different migration strategies, such as the use of different overwintering sites or the presence of non-migratory behaviour, can be maintained between populations despite high levels of gene flow [38], as also seen in the admixed populations of migratory and sedentary groups of broad-tailed hummingbirds in North America [59]. A similar lack of neutral genetic differentiation has been observed in other highly mobile, migrating species, such as hoverflies with different overwintering strategies in France [60] and blackcaps with different migratory behaviours and destinations in Europe [61].…”

Genomic analysis of a migratory divide reveals candidate genes for migration and implicates selective sweeps in generating islands of differentiation

“…; Mettler et al . ). Combined with over a decade of work on reproductive isolation between these subspecies groups (e.g., Ruegg & Smith ; Ruegg et al .…”