Do ocean currents shape patterns of penguin hybridization?

Summary

Asymmetrical hybridization and gene flow can result from biotic factors, such as demographic shifts, behavioral differences, or genetic incompatibilities, as well as abiotic factors, such as prevailing winds or oceans currents. Although birds generally circumvent these abiotic influences due to their high mobility, penguins may represent an exception, as ocean currents can constrain their dispersal. In this study, I investigated whether ocean currents indeed lead to asymmetrical hybridization patterns in penguins. I compiled an overview of known penguin hybrids and examined whether these hybridization events aligned with the prevailing ocean currents. Most instances of penguin hybridization were linked to numerical imbalances at the breeding colonies—often involving vagrant individuals—suggesting that limited mate choice is the primary driver of hybridization between penguin species. Assessing the role of ocean currents in these events was challenging due to uncertainties about the origin of vagrant individuals or cases where the hybridizing species shared the same breeding location. Nevertheless, ocean currents do appear to play an important role in penguin hybridization dynamics. In four instances, I was able to infer the most probable origin of vagrant individuals, showing that hybridization patterns were generally consistent with the prevailing ocean currents. Overall, hybridization in penguins is thus shaped by a combination of abiotic (ocean currents) and biotic factors (numerical imbalances at breeding colonies).