Migration direction in a songbird explained by two loci

Abstract

Migratory routes and remote wintering quarters in birds are often species and even population specific. It has been known for decades that songbirds mainly migrate solitarily, and that the migration direction is genetically controlled. Yet, the underlying genetic mechanisms remain unknown. To investigate the genetic basis of migration direction, we track genotyped willow warblers Phylloscopus trochilus from a migratory divide in Sweden, where South-West migrating, and South-East migrating subspecies form a hybrid swarm. We find evidence that migration direction follows a dominant inheritance pattern with epistatic interaction between two loci explaining 74% of variation. Consequently, most hybrids migrate similarly to one of the parental subspecies, and therefore do not suffer from the cost of following an inferior, intermediate route. This has significant implications for understanding the selection processes that maintain narrow migratory divides.

Gauge-and-compass migration: inherited magnetic headings and signposts can adapt to changing geomagnetic landscapes

“…3). Such a scenario could lead to effective reproductive isolation through hybrid mortality (39,79), or alternatively development of dominance inheritance patterns between competing alleles (38), in contrast to the co-dominance (averaging) of traits modelled here. Naturally, the actual routes taken by leucoroha wheatears and their robustness to geomagnetic shifts could be modulated by other factors not explicitly considered, such as capacity for migratory endurance flight (51,80), reliability of selected winds (19,81) and avoidance of hazards associated with the longer detour (e.g., diminishing seasonal resources, exposure to predation (20)).…”

“…Regarding robustness to temporal variability, it is important to consider whether plasticity in inheritance of orientation cues (11,36,37) can track temporal geomagnetic shifts at a population level. In order to assess this, since migratory headings will vary geographically (16,37,38), and are typically inherited as averages (11,39, but see 38), it is important to account for trans-generational changes (mixing) in orientation (11,37). For example, natal dispersal will create population-level variation among individual migratory headings (40,41).…”

Autumn migration tracks of Helopsaltes grasshopper‐warblers from Northeast Asia support recent taxonomic assignments

“…In this study, we investigate the migration strategy of the “Magadan grasshopper‐warblers” and compare their nonbreeding spatiotemporal distribution to what is known of the winter distribution of Pallas's and Middendorff's Grasshopper‐warblers. The spatiotemporal migration program is heritable and genetically controlled, so hybrids descending from parents with different migratory orientations might be expected to show “intermediate” or “hybrid” migration patterns (Delmore & Irwin, 2014 ; Sokolovskis et al, 2023 ). In general, differences in migratory directions are important to separate otherwise closely related taxa, as different routes can, for example, imply differences in arrival at the breeding grounds that can support speciation processes (Irwin & Irwin, 2005 ).…”

“…In this study, we investigate the migration strategy of the "Magadan grasshopper-warblers" and compare their nonbreeding spatiotemporal distribution to what is known of the winter distribution of Pallas's and Middendorff's Grasshopper-warblers. The spatiotemporal migration program is heritable and genetically controlled, so hybrids descending from parents with different migratory orientations might be expected to show "intermediate" or "hybrid" migration patterns (Delmore & Irwin, 2014;Sokolovskis et al, 2023).…”

A gradual migratory divide determines not only the direction of migration but also migration strategy of a social migrant bird

“…Implication of a precipitous divide is obviously stronger in comparison to a gradual divide, as the birds from different sides of the divide are able to intermingle in the overlapping zone of the flyways on a gradual divide. Despite the possible implications of the structure of the divide, only a few recent studies have tracked individuals breeding both on a divide and at different distances from it [8,9]. Thus, in many cases, the structure of the divide has usually remained unknown (e.g.…”