The genetics of migratory traits: moving towards studying regulatory mechanisms of gene expression

Submitted by Michi on 19 June 2024.

Iberian chiffchaff (P. ibericus) during geolocator attachment in the present field season in Spain (Spring 2024; Photo by Violeta Caballero-Lopez).

Text by Violeta Cabalerro-Lopez

For nearly 40 years, it has been well established that in many bird species migratory routes are greatly shaped by genetic factors. This genetic influence is strongest in birds that are presumed to migrate individually for the first time, without any proof of learning, or guidance by conspecifics. However, despite the improvement of sequencing and tracking technologies, no study has been able to link any sequence-based mechanism to this complex “migratory syndrome”. Our recent mini-review, mostly inspired by our own results, intends to bring into attention that this is very likely due to one main reason: there is not necessarily a common genetic sequence that determines bird migration routes across species. We propose that, instead, these birds have likely evolved a diverse set of non-coding mechanisms (regulatory, epigenetic, and structural variation) which can be very labile and vary across species and time.

                                       Process of geolocator attachment to a willow warbler in Sweden (Spring 2018; Photo by Kristaps Sokolovskis).

Research in our group is focused on comparative analyses between different migratory phenotypes in Phylloscopus species, such as the willow warbler (P. trochilus) and several chiffchaff species and subspecies (P. collybita and P. ibericus). Willow warblers are strict long-distance migrants, whose different subspecies follow different directions to wintering grounds in sub-Saharan and southern Africa. Common chiffchaff subspecies also follow parallel directions to willow warblers, although they display a wider variety of distances (short to long, cross-Saharan flights). Our work is mainly centred in tracking the birds with loggers (light and/or pressure) and conducting genomic analyses, mainly using resequence data. This way, we can find correlations between genomic regions and different traits that compose the migratory syndrome. Our group has so far deployed > 550 loggers in Europe (Sweden, Lithuania, Poland and Spain) in the past 6 years. The phenotype-genotype associations we observe, indicate that rather than specific sequences in the genome, migratory direction seems to be influenced by regulatory processes. This is, to our knowledge, the strongest association between migratory direction and a genetic mechanism to date. Furthermore, genetic architecture seems to differ, to a certain degree, across these two sister species. These findings, together with the lack of a common genetic basis behind migratory traits in the literature, inspired the present review. This has important implications on the current direction of research, and we discuss the increasing shift towards exploring gene-expression and regulatory mechanisms across migratory phenotypes, rather than the traditional, sequence-based comparative approaches. We also propose a thought-provoking model in which environment - genome interaction can regulate migratory syndrome components such as direction.

                                                                          Process of extraction from the mist-net in Poland (spring 2022; Photo by Kristaps Sokolovskis).

                                        Mist-net setup in the Alavese mountains in Basque Country, Spain (spring 2024; Photo by Violeta Caballero-Lopez).

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